US20200146742A1 - Controlled neuromodulation systems and methods of use - Google Patents

Abstract

The present disclosure relates to devices, systems and methods for positioning a neuromodulation device at a treatment site and evaluating the effects of therapeutic energy delivery applied to tissue in a patient. Before, during and/or after therapeutic energy delivery, a system can monitor parameters or values relevant to efficacious neuromodulation by emitting and detecting diagnostic energy at the treatment site. Feedback provided to an operator is based on the monitored values and relates to a relative position of the treatment device at the treatment site, as well as assessment of the likelihood that a completed treatment was technically successful.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application is a continuation of U.S. patent application Ser. No. 14/212,234, titled “Controlled Neuromodulation Systems and Methods of Use,” filed on Mar. 14, 2014, which claims the benefit of and priority to U.S. Provisional Patent Application No. 61/801,091, titled “Controlled Neuromodulation Systems and Methods of Use,” filed Mar. 15, 2013, the entire contents of these applications are hereby incorporated by reference herein.
TECHNICAL FIELD
• The present technology relates generally to monitoring neuromodulation and associated systems and methods. In particular, several embodiments are directed to endovascular monitoring systems and associated systems and methods.
BACKGROUND
• The sympathetic nervous system (SNS) is a primarily involuntary bodily control system typically associated with stress responses. SNS fibers that innervate tissue are present in almost every organ system of the human body and can affect characteristics such as pupil diameter, gut motility, and urinary output. Such regulation can have adaptive utility in maintaining homeostasis or preparing the body for rapid response to environmental factors. Chronic activation of the SNS, however, is a common maladaptive response that can drive the progression of many disease states. Excessive activation of the renal SNS in particular has been identified experimentally and in humans as a likely contributor to the complex pathophysiology of hypertension, states of volume overload (such as heart failure), and progressive renal disease. For example, radiotracer dilution has demonstrated increased renal norepinephrine (“NE”) spillover rates in patients with essential hypertension.
• Cardio-renal sympathetic nerve hyperactivity can be particularly pronounced in patients with heart failure. For example, an exaggerated NE overflow from the heart and kidneys is often found in these patients. Heightened SNS activation commonly characterizes both chronic and end stage renal disease. In patients with end stage renal disease, NE plasma levels above the median have been demonstrated to be predictive of cardiovascular diseases and several causes of death. This is also true for patients suffering from diabetic or contrast nephropathy. Evidence suggests that sensory afferent signals originating from diseased kidneys are major contributors to initiating and sustaining elevated central sympathetic outflow.
• Sympathetic nerves innervating the kidneys terminate in the blood vessels, the juxtaglomerular apparatus, and the renal tubules. Stimulation of the renal sympathetic nerves can cause increased renin release, increased sodium (Na.sup.+) reabsorption, and a reduction of renal blood flow. These neural regulation components of renal function are considerably stimulated in disease states characterized by heightened sympathetic tone and likely contribute to increased blood pressure in hypertensive patients. The reduction of renal blood flow and glomerular filtration rate that result from renal sympathetic efferent stimulation are likely a cornerstone of the loss of renal function in cardio-renal syndrome (i.e., renal dysfunction as a progressive complication of chronic heart failure). Pharmacologic strategies to thwart the consequences of renal efferent sympathetic stimulation include centrally acting sympatholytic drugs, beta blockers (intended to reduce renin release), angiotensin converting enzyme inhibitors and receptor blockers (intended to block the action of angiotensin II and aldosterone activation consequent to renin release), and diuretics (intended to counter the renal sympathetic mediated sodium and water retention). These pharmacologic strategies, however, have significant limitations including limited efficacy, compliance issues, side effects, and others. Recently, intravascular devices that reduce sympathetic nerve activity by applying an energy field to a target site in the renal artery (e.g., via radiofrequency ablation) have been shown to reduce blood pressure in patients with treatment-resistant hypertension.
BRIEF DESCRIPTION OF THE DRAWINGS
• Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale. Instead, emphasis is placed on illustrating clearly the principles of the present disclosure. Furthermore, components can be shown as transparent in certain views for clarity of illustration only and not to indicate that the illustrated component is necessarily transparent.
• FIG. 1 is a partially-schematic perspective view illustrating a renal neuromodulation system including a treatment device configured in accordance with an embodiment of the present technology.
• FIG. 2A is a schematic cross-sectional end view illustrating emission of energy toward a vessel wall from the transducer ofFIG. 1 in accordance with an embodiment of the present technology.
• FIGS. 2B and 2C are schematic cross-sectional end views illustrating the reflected energy from the energy emission shown inFIG. 2A in accordance with an embodiment of the present technology.
• FIG. 3 is a partially cross-sectional anatomical front view illustrating advancing the treatment device shown inFIG. 1 along an intravascular path in accordance with an embodiment of the present technology.
• FIG. 4A is a graph depicting an energy delivery algorithm that may be used in conjunction with the system ofFIG. 1 in accordance with an embodiment of the technology.
• FIG. 4B is a graph depicting a synchronization algorithm that may be used in conjunction with the energy delivery algorithm ofFIG. 4A in accordance with an embodiment of the present technology.
• FIG. 5 is a block diagram illustrating stages of a method for operating the system shown inFIG. 1 in accordance with an embodiment of the present technology.
• FIG. 6A is a block diagram illustrating an algorithm for providing operator feedback regarding contact between the energy delivery element and the tissue in accordance with an embodiment of the present technology.
• FIGS. 6B-6E are schematic cross-sectional end views illustrating a wall proximity of the treatment assembly to a vessel wall in accordance with an embodiment of the present technology.
• FIG. 7A is a block diagram illustrating an algorithm for providing operator feedback regarding circumferential proximity in accordance with an embodiment of the present technology.
• FIG. 7B is a graph depicting a parameter of return energy sensed by the system ofFIG. 1 in accordance with an embodiment of the technology.
• FIG. 7C is a block diagram illustrating an algorithm for providing operator feedback regarding radial proximity in accordance with an embodiment of the present technology.
• FIGS. 7D-7F are schematic cross-sectional end views illustrating radial and/or circumferential proximities of the treatment assembly to a nerve in accordance with an embodiment of the present technology.
• FIGS. 8A-8C are graphs depicting a parameter of return energy sensed by the system ofFIG. 1 in accordance with an embodiment of the present technology.
• FIG. 9 is a block diagram illustrating stages during operation of the system shown inFIG. 1 in accordance with an embodiment of the present technology.
• FIG. 10A is a block diagram illustrating an algorithm for providing operator feedback regarding tissue temperature at a vessel wall in accordance with an embodiment of the present technology.
• FIG. 10B is a graph depicting a parameter of return energy sensed by the system ofFIG. 1 in accordance with an embodiment of the present technology.
• FIG. 11 is a conceptual diagram illustrating the sympathetic nervous system and how the brain communicates with the body via the sympathetic nervous system.
• FIG. 12 is an enlarged anatomical view illustrating nerves innervating a left kidney to form a renal plexus surrounding a left renal artery.
• FIGS. 13A and 13B are anatomical and conceptual views, respectively, illustrating a human body including a brain and kidneys and neural efferent and afferent communication between the brain and kidneys.
• FIGS. 14A and 14B are anatomic views illustrating, respectively, an arterial vasculature and a venous vasculature of a human.
DETAILED DESCRIPTION
• Specific details of several embodiments of the present technology are described herein with reference toFIGS. 1-13B. Although many of the embodiments are described herein with respect to devices, systems, and methods for modulation of renal nerves using electrode-based, transducer-based, element-based, cryotherapeutic, and chemical-based approaches, other applications and other treatment modalities in addition to those described herein are within the scope of the present technology. Additionally, other embodiments of the present technology can have different configurations, components, or procedures than those described herein. For example, other embodiments can include additional elements and features beyond those described herein, or other embodiments may not include several of the elements and features shown and described herein. For ease of reference, throughout this disclosure identical reference numbers are used to identify similar or analogous components or features, but the use of the same reference number does not imply that the parts should be construed to be identical. Indeed, in many examples described herein, the identically-numbered parts are distinct in structure and/or function. Generally, unless the context indicates otherwise, the terms “distal” and “proximal” within this disclosure reference a position relative to an operator or an operator's control device. For example, “proximal” can refer to a position closer to an operator or an operator's control device, and “distal” can refer to a position that is more distant from an operator or an operator's control device.
I. RENAL NEUROMODULATION
• Renal neuromodulation is the partial or complete incapacitation or other effective disruption of nerves innervating the kidneys (e.g., rendering neural fibers inert or inactive or otherwise completely or partially reduced in function). For example, renal neuromodulation can include inhibiting, reducing, and/or blocking neural communication along neural fibers (i.e., efferent and/or afferent nerve fibers) innervating the kidneys. Such incapacitation can be long-term (e.g., permanent or for periods of months, years, or decades) or short-term (e.g., for periods of minutes, hours, days, or weeks). Renal neuromodulation is expected to efficaciously treat several clinical conditions characterized by increased overall sympathetic activity, and, in particular, conditions associated with central sympathetic overstimulation such as hypertension, heart failure, acute myocardial infarction, metabolic syndrome, insulin resistance, diabetes, left ventricular hypertrophy, chronic and end stage renal disease, inappropriate fluid retention in heart failure, cardio-renal syndrome, osteoporosis, and sudden death, among others. The reduction of afferent neural signals typically contributes to the systemic reduction of sympathetic tone/drive, and renal neuromodulation is expected to be useful in treating several conditions associated with systemic sympathetic overactivity or hyperactivity. Renal neuromodulation can potentially benefit a variety of organs and bodily structures innervated by sympathetic nerves. For example, a reduction in central sympathetic drive may reduce insulin resistance that afflicts patients with metabolic syndrome and Type II diabetics.
• Thermal heating effects described herein can include both thermal ablation and non-ablative thermal alteration or damage (e.g., via sustained heating and/or resistive heating). Desired thermal heating effects may include raising the temperature of target neural fibers above a desired threshold temperature to achieve non-ablative thermal alteration, or above a higher threshold temperature to achieve ablative thermal alteration.
• Various techniques can be used to partially or completely incapacitate neural pathways, such as those innervating the kidneys. The purposeful application of energy (e.g., radiofrequency energy, mechanical energy, acoustic energy, electrical energy, thermal energy, light, etc.) to tissue and/or the purposeful removal of energy (e.g., thermal energy) from tissue can induce one or more desired thermal heating and/or cooling effects on localized regions of the tissue. The tissue, for example, can be tissue of the renal artery and adjacent regions of the renal plexus (RP), which lay intimately within or adjacent to the adventitia of the renal artery. For example, the purposeful application and/or removal of energy can be used to achieve therapeutically effective neuromodulation along all or a portion of the renal plexus (RP).
• In the era of evidence-based medicine, evaluating the efficacy of an ablation treatment, such as neuromodulation, can be important in gauging whether a treated patient may need additional neuromodulation treatment and/or alternative treatment. Neuromodulation efficacy is currently assessed by measuring and analyzing various physiological parameters (e.g., heart rate, blood pressure, etc.). However, statistically meaningful changes in such physiological parameters may not be observed until at least two weeks (and in most cases, months) after completion of the treatment. In the absence of real-time or at least relatively contemporaneous feedback, nerves that are under ablated, over ablated, or missed altogether may go undetected, rendering the treatment unsuccessful. As a result, an unsuccessful treatment may not be clinically addressed until weeks or months after the initial treatment. Even then, the treatment will be categorized as “successful” or “not successful” but the cause of the non-success will remain unknown. To address this need, the present technology provides several embodiments of devices, systems, and methods that facilitate relatively rapid analysis of neuromodulation efficacy by using return energy of diagnostic ultrasound and/or electromagnetic energy, such as optical energy, emissions to characterize neuromodulated nerve and tissue as well as provide positional feedback to facilitate positioning of the device.
II. SYSTEMS AND METHODS FOR NEUROMODULATION
• FIG. 1 is a partially-schematic diagram illustrating asystem100 configured in accordance with an embodiment of the present technology. Thesystem100 can include a treatment device102 (e.g., a catheter) operably coupled to a console106 via a connector108 (e.g., a cable). As shown inFIG. 1, thetreatment device102 can include anelongated shaft116 having aproximal portion120, ahandle assembly112 at a proximal region of theproximal portion120, and adistal portion118 extending distally relative to theproximal portion120. Theelongated shaft116 can be configured to locate thedistal portion118 intravascularly (e.g., within a renal artery) or within another suitable body lumen (e.g., within a ureter) at a treatment location. Thetreatment device102 can further include atreatment assembly114 carried by or affixed to thedistal portion118 of theelongated shaft116. Thetreatment assembly114 can include a neuromodulation element140 (shown schematically inFIG. 1) configured to deliver a therapeutic energy or compound to a nerve located at least proximate to a wall of a body lumen and one or more transducers142 (also shown schematically inFIG. 1) configured to emit diagnostic energy toward the tissue as well as detect a return energy of the emitted diagnostic energy.
• The console106 can be configured to control, monitor, supply, or otherwise support operation of thetreatment device102. For example, the console106 can include an energy generator configured to generate a selected form and magnitude of therapeutic, neuromodulation energy (e.g., radiofrequency energy (“RF”), pulsed energy, microwave energy, optical energy, ultrasound energy (e.g., high intensity focused ultrasound energy or non-focused ultrasound energy), direct heat energy or another suitable type of energy) for delivery to the target treatment site via theneuromodulation element140. In some embodiments, neuromodulation may be achieved by a chemical treatment including delivering one or more chemicals (e.g., guanethidine, ethanol, phenol, a neurotoxin (e.g., vincristine)), or another suitable agent selected to alter, damage, or disrupt nerves. In some embodiments, the console106 can store cooling fluid that can be transferred to the treatment device102 (via the connector108) for cryotherapeutic neuromodulation.
• The console106 can further be configured to generate a selected form and magnitude of diagnostic energy and/or a signal that causes thetransducer142 to produce diagnostic energy for emission and reflection and/or absorption at a treatment site. Suitable diagnostic energies include diagnostic ultrasound (e.g., acoustic) and electromagnetic radiation (e.g., optical energy). Diagnostic energy provided for emission/detection purposes differs from therapeutic ultrasound and/or electromagnetic energy used to cause neuromodulation. In some embodiments, the console106 can be configured to generate and transmit (via the connector108) the neuromodulation energy and a signal that causes thetransducer142 to produce diagnostic energy to thetreatment assembly114. For example, thesystem100 can include a synchronization algorithm (FIG. 4B) that facilitates simultaneous and/or coordinated delivery of at least two different energy modalities to the treatment device102 (e.g., RF and diagnostic ultrasound, therapeutic ultrasound and diagnostic ultrasound, etc.). In other embodiments, thesystem100 can include a neuromodulation console (not shown) and a separate diagnostic console (not shown). The neuromodulation console can be operably connected to theneuromodulation element140 and configured to generate neuromodulation energy. The diagnostic console (not shown) can be operably connected to thetransducer142 and configured to generate diagnostic energy.
• The console106 can be electrically coupled to thetreatment device102 via the connector108 (e.g., a cable). One or more supply wires (not shown) can pass along theelongated shaft116 or through a lumen in theelongated shaft116 to theneuromodulation element140 and/or thetransducer142 to transmit the required energy to theneuromodulation element140 and/or the signals to thetransducer142. A control mechanism, such as foot pedal136, may be connected (e.g., pneumatically connected or electrically connected) to the console106 to allow the operator to initiate, terminate and, optionally, adjust various operational characteristics of the console106, including, but not limited to, power delivery.
• The console106 can also be configured to deliver the neuromodulation energy via anautomated control algorithm132 and/or under the control of a clinician. In addition, one or morediagnostic algorithms134 may be executed on a processor (not shown) of thesystem100. Suchdiagnostic algorithms134 can provide feedback to the clinician, such as via an indicator126 (e.g., a display, a user interface, one or more LEDs, etc.) associated with the console106 and/orsystem100. For example, the console106 may include an optional user interface that can receive user input and/or provide information to the user and/or processing circuitry for monitoring one or more optional sensors (e.g., pressure, temperature, impedance, flow, chemical, ultrasound, electromagnetic, etc.) of thetreatment assembly114 and/ortreatment device102. The feedback from the diagnostic information may allow a clinician to better position the device at the treatment site and/or determine the effectiveness of the applied energy during the treatment and/or shortly thereafter (e.g., while the patient is still catheterized). Likewise, while the patient is still catheterized, a clinician may decide to repeat a treatment based on feedback from the diagnostic information. Accordingly, this feedback may be useful in helping the clinician increase the likelihood of success of the current or subsequent treatments. Further details regardingsuitable control algorithms132 anddiagnostic algorithms134 are described below with reference toFIGS. 4A-10.
• Thesystem100 can further include acontroller138 having, for example, memory (not shown), storage devices (e.g., disk drives), one or more output devices (e.g., a display), one or more input devices (e.g., a keyboard, a touchscreen, etc.) and processing circuitry (not shown). The output devices may be configured to communicate with the treatment device102 (e.g., via the connector108) to control power to theneuromodulation element140 and/ortransducer142. In some embodiments the output devices can further be configured to obtain signals from theneuromodulation element140, thetransducer142, and/or any associated sensors. Display devices may be configured to provide indications of power levels or sensor data, such as audio, visual or other indications, and/or the display devices may be configured to communicate the information to another device.
• In some embodiments, thecontroller138 can be part of the console106, as shown inFIG. 1. Additionally or alternatively, thecontroller138 can be personal computer(s), server computer(s), handheld or laptop device(s), multiprocessor system(s), microprocessor-based system(s), programmable consumer electronic(s), digital camera(s), network PC(s), minicomputer(s), mainframe computer(s), tablets, and/or any suitable computing environment. The memory and storage devices are computer-readable storage media that may be encoded with non-transitory, computer-executable instructions (e.g., the control algorithm(s), the feedback algorithm(s), etc.). In addition, the instructions, data structures, and message structures may be stored or transmitted via a data transmission medium, such as a signal on a communications link and may be encrypted. Various communications links may be used, such as the Internet, a local area network, a wide area network, a point-to-point dial-up connection, a cell phone network, Bluetooth, RFID, and other suitable communication channels. Thesystem100 may be described in the general context of computer-executable instructions, such as program modules, executed by one or more computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, and so on that perform particular tasks or implement particular abstract data types. Typically, the functionality of the program modules may be combined or distributed as desired in various embodiments.
• Theneuromodulation element140 of thetreatment assembly114 can be configured to modulate one or more renal nerves within tissue at or at least proximate to a wall of the renal vessel or lumen. Theneuromodulation element140 can include one or more energy delivery elements (e.g., electrodes) (not shown). For example, in some embodiments, theneuromodulation element140 can be a single energy delivery element located at adistal portion118 of thetreatment assembly114. In other embodiments, theneuromodulation element140 can include two or more energy delivery elements. The energy delivery elements can be separate band electrodes spaced apart from each other along a portion of the length of theshaft116. The electrodes can be adhesively bonded to a support structure at different positions along the length of theshaft116. In some embodiments, the energy delivery elements can be formed from a suitable electrically conductive material (e.g., a metal, such as gold, platinum, alloys of platinum and iridium, etc.). The number, arrangement, shape (e.g., spiral and/or coil electrodes) and/or composition of the energy delivery elements may vary. The individual energy delivery elements of theneuromodulation element140 can be electrically connected to thehandle assembly112 and/or the console106 by a conductor or bifilar wire extending through a lumen of theshaft116.
• In embodiments where theneuromodulation element140 includes multiple energy delivery elements, the energy delivery elements may deliver power independently (e.g., may be used in a monopolar fashion), either simultaneously, selectively, or sequentially, and/or may deliver power between any desired combination of the elements (e.g., may be used in a bipolar fashion). Furthermore, the clinician optionally may be permitted to choose which energy delivery element(s) are used for power delivery in order to form highly customized lesion(s) within the vessel (e.g., the renal artery) or other body lumens (e.g., the ureter), as desired. In some embodiments, thesystem100 may be configured to provide delivery of a monopolar electric field via theneuromodulation element140. In such embodiments, a neutral ordispersive electrode130 may be electrically connected to the console106 and attached to the exterior of the patient (as shown inFIG. 3).
• Thetransducer142 can include an emitter144 (FIG. 2A) configured to emit energy (e.g. ultrasound or electromagnetic energy) and/or a detector146 (FIGS. 2B and 2C) configured to detect a return energy of the emitted energy. In some embodiments, thetransducer142 can comprise an emitter144 or adetector146, but not both. In these and other embodiments, thetreatment assembly114 can include two or more transducers142 (e.g., one to emit and one to detect). Likewise, in many of the embodiments described herein, the transducer142 (e.g., ultrasound and/or optical) can be configured to produce an energy emission and detect return energy of its own energy emissions.
• FIGS. 2A-2C are schematic cross-sectional end views showing the operation of one embodiment of adiagnostic ultrasound transducer142 in accordance with an embodiment of the present technology. As shown, when activated manually by the clinician and/or automatically by thecontroller138, the emitter144 (of the transducer142) can emit a diagnostic energy emission E1 toward tissue at least proximate to a wall (W) of the vessel or lumen (e.g., the renal artery). Depending on the physiological and anatomical parameters of each patient, a single diagnostic ultrasound emission can produce return energy in the form of countless reflections, individually corresponding to a unique reflecting surface. For example, almost instantaneously (e.g., within approximately 30 .mu.s), the correspondingdetector146 of thetransducer142 can detect the return energy in the form of reflections or echoes of the first diagnostic ultrasound emission. As shown inFIG. 2B, an ultrasound reflection R1 can correspond to an interior surface (S) of the vessel wall (W). This is because an interior surface (S) of the vessel is often times the closest reflecting surface to the transducer142 (and thus has the shortest response time). As shown inFIG. 2C, the emission E1 can also produce another, subsequent reflection R2 that can correspond to a nerve (e.g., a renal nerve (RN)). The second reflection R2 can be detected temporally after the first reflection R1 since the nerve (RN) is spatially farther from thediagnostic ultrasound transducer142 than the interior surface (S) of the vessel wall (W).
• Additionally or alternatively, thetransducer142 can be an electromagnetic transducer (not shown). Theelectromagnetic transducer142 can emit electromagnetic energy (e.g., infrared, near infrared, visible, ultraviolet radiation, etc.) toward tissue at least proximate a wall of a renal vessel, or artery or another body lumen (e.g., the renal artery). Return energy, however, is measured by how much radiation is absorbed by the tissue and how much energy is reflected by the tissue back to thetransducer142 and/ordetector146. For example, at least a portion of the electromagnetic energy emitted by the emitter144 of theelectromagnetic transducer142 can be absorbed by the vessel wall. Thedetector146 then measures the return energy as the quantity of light not absorbed. As discussed in greater detail below, the return energy (e.g., ultrasound reflections and/or the amount of electromagnetic energy absorbed/not absorbed) may have varying parameters depending on type of tissue contacted by the emitted diagnostic energy. For example, neural tissue, smooth muscle tissue of the vessel wall, fat tissue, lymph node tissue, damaged tissue, and other local tissue individually exhibit different responses to diagnostic ultrasound and/or electromagnetic energy.
• After detecting the return energy, thedetector146 and/ortransducer142 then convert the reflected energy to a signal, and transmits that signal to the controller138 (FIG. 1). In some embodiments, the emitter144 anddetector146 are continuously emitting/detecting energy and sending signals to thecontroller138. Both the emitter144 and thedetector146 can be operably coupled to thecontroller138 within the console106 via theconnector108 or wirelessly such that the console106 may transmit a signal to the emitter144 and receive signals from thedetector146 that correspond to the detected reflection R1. As described in further detail herein, thecontroller138 and/or one or morediagnostic algorithms134 can use the raw reflected signal and/or statistics based on the raw reflected signal (collectively referred to as a “parameters of the return energy”) to provide positional and/or tissue characterization feedback to the clinician.
• Non-exhaustive examples of the one or more parameters of return energy thecontroller138 and/ordiagnostic algorithms134 may include an amplitude of the return energy, an average amplitude of the return energy, a minimum amplitude of the return energy, a maximum amplitude of the return energy, rate of change of amplitude, an amplitude at a predetermined or calculated time relative to a predetermined or calculated amplitude, a frequency of the return energy, an average frequency of the return energy, a minimum frequency of the return energy, a maximum frequency of the return energy, rate of change of frequency, a frequency at a predetermined or calculated time relative to a predetermined or calculated frequency, a change in time between the emission of energy and the detection of a return energy (referred to herein as a “detection time”), a detection time at a predetermined or calculated time relative to a predetermined or calculated detection time, change(s) in temperature over a specified time, a maximum temperature, a maximum average temperature, a minimum temperature, a temperature at a predetermined or calculated time relative to a predetermined or calculated temperature, an average temperature over a specified time, and other suitable measurements and/or derived statistics thereof.
III. DELIVERY METHODS
• Referring toFIG. 3, intravascular delivery of thetreatment assembly114 can include percutaneously inserting a guidewire (not shown) within the vasculature at an access site (e.g., femoral, brachial, radial, or axillary artery) and moving theshaft116 and thetreatment assembly114 in a delivery state (e.g., generally straight, low-profile, etc.) along the guidewire until at least a portion of thetreatment assembly114 reaches the treatment location. In some embodiments, theshaft116 and thetreatment assembly114 can include a guidewire lumen (not shown) configured to receive a guidewire in an over-the-wire or rapid exchange configuration. In some embodiments, thetreatment assembly114 may be delivered to a treatment site within a guide sheath (not shown) with or without using the guide wire. In other embodiments, theshaft116 may be steerable itself such that thetreatment assembly114 may be delivered to the treatment site without the aid of the guidewire and/or guide sheath. As illustrated, thehandle assembly112 of theshaft116 can be extracorporeally positioned and manipulated by the operator (e.g., via the actuator122) to advance theshaft116 through the sometimes tortuous intravascular path (P) and remotely manipulate thedistal portion118 of theshaft116. Computed tomography (CT), fluoroscopy, intravascular ultrasound (IVUS), optical coherence tomography (OCT), or other suitable guidance modalities, or combinations thereof, may be used to aid the clinician's manipulation. Further, in some embodiments, image guidance components (e.g., IVUS, OCT) may be incorporated into thetreatment device102 itself.
• Once thetreatment assembly114 is positioned at a treatment location, the guidewire can be at least partially introduced (e.g., inserted) into or removed (e.g., withdrawn) from thetreatment assembly114 to transform or otherwise move thetreatment assembly114 to a deployed state. In cases where a guide sheath is used, the guide sheath can be at least partially removed (e.g., withdrawn) to transform thetreatment assembly114 into the deployed state (e.g., expanded, bent, deflected, helical and/or spiral, balloon, zig-zag, star-shaped, Malecot, etc.). For example, at least a portion of thetreatment assembly114 can have a shape memory corresponding to a deployed state and the sheath and/or guidewire can prevent thetreatment assembly114 from deploying in response to the shape memory before reaching the treatment location. In some embodiments, thetreatment assembly114 can be converted (e.g., placed or transformed) between the delivery and deployed states via remote actuation, e.g., using an actuator122 (FIG. 1) of thehandle assembly112. Theactuator122 can include a knob, a pin, a lever, a button, a dial, or another suitable control component.
• In the deployed state, thetreatment assembly114 can be configured to contact an inner wall of the vessel (e.g., the renal artery) and to cause a fully-circumferential lesion without the need for repositioning. For example, thetreatment assembly114 can be configured to form a lesion or series of lesions (e.g., a helical/spiral lesion or a discontinuous lesion) that is fully-circumferential overall, but generally non-circumferential at longitudinal segments of the treatment location. This can facilitate precise and efficient treatment with a low possibility of vessel stenosis. In other embodiments, thetreatment assembly114 can be configured to form a partially-circumferential lesion or a fully-circumferential lesion at a single longitudinal segment of the treatment location. During treatment, thetreatment assembly114 can be configured to partially or fully occlude the vessel (e.g., the renal artery). Partial occlusion can be useful, for example, to reduce renal ischemia, and full occlusion can be useful, for example, to reduce interference (e.g., warming or cooling) caused by blood flow through the treatment location. In some embodiments, thetreatment assembly114 can be configured to cause therapeutically-effective neuromodulation (e.g., using ultrasound energy) without contacting a vessel wall.
• Examples of other suitable neuromodulation delivery configurations, deployment configurations and/or deployment mechanisms can be found in U.S. application Ser. No. 12/910,631, filed Oct. 22, 2010, entitled “APPARATUS, SYSTEMS, AND METHODS FOR ACHIEVING INTRAVASCULAR, THERMALLY-INDUCED RENAL NEUROMODULATION,” U.S. application Ser. No. 13/281,361, filed Oct. 25, 2011, entitled “CATHETER APPARATUSES HAVING MULTI-ELECTRODE ARRAYS FOR RENAL NEUROMODULATION AND ASSOCIATED SYSTEMS AND METHODS,” and U.S. Provisional Application No. 61/646,218, filed May 5, 2012, entitled “MULTI-ELECTRODE CATHETER ASSEMBLIES FOR RENAL NEUROMODULATION AND ASSOCIATED SYSTEMS AND METHODS,” which are incorporated herein by reference in their entireties.
IV. CONTROL OF APPLIED ENERGY
• A. Power Delivery
• As mentioned above, the console106 can be configured to deliver the neuromodulation energy (e.g., RF energy) via anautomated control algorithm132 and/or under the control of a clinician.FIG. 4A shows one embodiment of anautomated control algorithm132 that may be implemented by thecontroller138 coupled to the console106. As seen inFIG. 4A, when a clinician initiates treatment (e.g., via the foot pedal136 illustrated inFIG. 1), thecontrol algorithm132 can include instructions that cause the console106 to gradually adjust the power output to a first power level P.sub.1 (e.g., 5 watts) over a first time period t.sub.1 (e.g., 15 seconds). The power can increase generally linearly during the first time period. As a result, the console106 increases its power output at a generally constant rate of P.sub.1/t.sub.1. Alternatively, the power may increase non-linearly (e.g., exponential or parabolic) with a variable rate of increase. Once P.sub.1 and t.sub.1 are achieved, the algorithm may hold at P.sub.1 until a new time t.sub.2 for a predetermined period of time t.sub.2-t.sub.1 (e.g., 3 seconds). At t.sub.2 power is increased by a predetermined increment (e.g., 1 watt) to P.sub.2 over a predetermined period of time, t.sub.3-t.sub.2 (e.g., 1 second). This power ramp in predetermined increments of about 1 watt over predetermined periods of time may continue until a maximum power P.sub.MAX is achieved or some other condition is satisfied. In one embodiment, P.sub.MAX is 8 watts. In another embodiment P.sub.MAX is 6.5 watts. Optionally, the power may be maintained at the maximum power P.sub.MAX for a desired period of time or up to the desired total treatment time (e.g., up to about 120 seconds).
• Furthermore, thecontrol algorithm132 includes monitoring one or more of the temperature, time, impedance, power, flow velocity, volumetric flow rate, blood pressure, heart rate, parameters of return energy, or other operating parameters. The operating parameters may be monitored continuously or periodically. Thecontrol algorithm132 checks the monitored parameters against predetermined parameter profiles to determine whether the parameters individually or in combination fall within the ranges set by the predetermined parameter profiles. If the monitored parameters fall within the ranges set by the predetermined parameter profiles, then treatment may continue at the commanded power output. If monitored parameters fall outside the ranges set by the predetermined parameter profiles, thecontrol algorithm132 adjusts the commanded power output accordingly. For example, if a measured temperature threshold (e.g., 65.degree. C.) is achieved, then power delivery is kept constant until the total treatment time (e.g., 120 seconds) has expired. If a first temperature threshold (e.g., 70.degree. C.) is achieved or exceeded, then power is reduced in predetermined increments (e.g., 0.5 watts, 1.0 watts, etc.) until the measured temperature drops below the first temperature threshold. If a second temperature threshold (e.g., 85.degree. C.) is achieved or exceeded, thereby indicating an undesirable condition, then power delivery may be terminated. The system may be equipped with various audible and visual alarms to alert the operator of certain conditions.
• B. Synchronization of Sensing and Power Delivery
• At one or more timepoints during and/or after delivering the therapeutic energy, thetransducer142 can be activated to provide feedback as to the efficacy of the ongoing or completed therapeutic energy delivery. Thetransducer142 can be activated automatically by thecontroller138 or manually by the clinician. Thetransducer142 can emit energy and detect a return energy continuously, at set intervals, and/or at one or more discrete timepoints that are selected automatically or by the clinician. When RF energy is used to modulate the nerves, the console106 and/orcontroller138 can run a synchronizingalgorithm400 that avoids interference between the RF signals to the neuromodulation element140 (e.g., .gtoreq.100 KHz) and the signals to the transducer142 (e.g., 20-40 MHz). As shown inFIG. 4B, the energy transmission to the neuromodulation element140 (RF) and the timing of energy transmission to the transducer142 (DE) can be time-multiplexed by the synchronizingalgorithm400 such that RF energy (RF) and diagnostic energy (DE) are activated at different time periods. For example, the RF and DE duty cycles can be alternatingly activated (e.g., RF on/off, DE on/off, RF on/off, DE on/off, etc.). Thetransducer142 can accordingly emit energy from the assembly toward the tissue while modulating the renal nerve and/or intermittently between modulating the renal nerve. Furthermore, the time RF remains on (t.sub.R1) and the time DE remains on (t.sub.U1) can be the same (e.g., 25 .mu.x) or different. In these and other embodiments, a filter may be used on the raw signal of the return energy to remove RF interference. One, a few, or all of the above techniques may be utilized.
V. PRE-NEUROMODULATION EVALUATION
• With the treatments disclosed herein for delivering therapeutic energy to target tissue, it may be beneficial to evaluate a relative position of at least a portion of thetreatment assembly114 before delivering the therapeutic energy. Contact between the energy delivery element and the tissue, nerve alignment, and nerve proximity are all factors that can affect the efficacy of the neuromodulation. Accordingly, one ormore transducers142 carried by thetreatment assembly114 can be configured to emit energy towards the vessel wall and send information regarding a detected return energy of the emission to thecontroller138. As discussed in greater detail below, thecontroller138 can execute one or morediagnostic algorithms134 that can inform a clinician of a position of at least a portion of thetreatment assembly114 relative to a vessel wall and/or a nerve (e.g., a renal nerve).
• A. Feedback Related to Tissue Contact
• The quality and/or success of the purposeful application of energy depends at least in part on having good contact between the energy delivery element and the tissue at a desired target site. If the contact between the energy delivery element and the tissue is insufficient, the energy delivery is more likely to be therapeutically ineffective. For example, insufficient contact can cause under-ablation, over-ablation, inadequate lesion formation, premature high impedance shut-off, etc. Accordingly, it is often important to determine whether there is adequate tissue contact before delivering energy. Many clinicians currently use a combination of tactile feedback, imaging devices, and/or other qualitative measures to assess tissue contact, but these measures often do not accurately determine electrode-tissue contact. For example, intracardiac echocardiography provides a real-time image of the anatomy surrounding the distal portion of an ablation catheter, but it does not give an objective assessment of electrode-tissue contact, nor does it have sufficient contrast to visualize the formation of created lesions (e.g., 2D images of a 3D surface).
• FIG. 5 is a block diagram illustrating stages of a method for operation of thesystem100 in accordance with an embodiment of the present technology. The method can include positioning thetreatment assembly114 within or at least proximate to a renal vessel or other body lumen of a human (block500). The emitter144 can then be activated automatically by a control algorithm or manually activated by the operator to emit energy towards tissue at or at least proximate to a wall of the renal vessel or other body lumen (block502). A return energy of the emitted energy can be detected by a detector146 (block504) that communicates a signal to the controller.
• The method can continue by determining the proximity of thetreatment assembly114 to the vessel wall which can be determined based on the detected return energy (block506).FIG. 6A is a block diagram of one embodiment of adiagnostic algorithm600 configured in accordance with the present technology. Thediagnostic algorithm600 can determine a wall proximity of at least a portion of thetreatment assembly114 to the vessel wall based on one or more parameters of return energy (e.g., the raw reflected signal and/or statistics based on the raw reflected signal including detection time and signal amplitude). As shown in the schematic cross-sectional end views ofFIGS. 6B-6E, anenergy delivery element148 can deliver energy within a particular zone or region (referred to herein as a “neuromodulation zone (NZ)”). As shown, “wall proximity (WP)” refers to the distance between a particularenergy delivery element148 and the inner surface of the vessel wall (W) in the direction of energy delivery and/or within the neuromodulation zone (NZ). The wall proximity (WP) can be calculated as an actual distance (e.g., 7 microns) or a relative distance (e.g., not close enough contact, etc.). Accordingly, the wall proximity (WP) can be the distance between theenergy delivery element148 and wall (W) within the neuromodulation zone (NZ). When theenergy delivery element148 is in contact with the vessel wall (W), as shown inFIG. 6B, the wall proximity (WP) is very small. Likewise, the wall proximity (WP) is larger than that ofFIG. 6B when theenergy delivery element148 is spaced apart from the vessel wall (W), as shown inFIGS. 6C-6E.
• Determining the relative position of theenergy delivery element148 to the vessel wall (VW) based on the return energy detected by thetransducer142 is possible so long as thetransducer142 and the correspondingenergy delivery element148 are fixedly positioned on thetreatment assembly114 relative to each other. In other words, thediagnostic algorithms134 discussed herein can take into account the relative position of the transducer(s)142 andenergy delivery elements148 and normalize the resulting proximity determinations accordingly.
• Referring toFIGS. 6A-6E together, thediagnostic algorithm600 can determine a wall proximity (WP) of at least a portion of thetreatment assembly114 to the vessel wall (W) based on, inter alia, a parameter of return energy such as detection time (e.g., a change in time between the emission of energy and the detection of the return energy). As shown indecision block602, thealgorithm600 can compare the detection time to a baseline detection time. The baseline detection time can take into account the power delivery schedule, time, blood flow through the vessel, biological parameters of the individual patient and/or a particular subset of patients, and other suitable criteria. In embodiments having two ormore transducers142, thecontroller138 can execute thealgorithm600 simultaneously for all of thetransducers142, or at different time periods using multi-plexing for eachtransducer142 individually or groups oftransducers142. For example, a clinician may only desire to check the contact and/or wall proximity (WP) of one of the energy delivery elements in an array having a plurality of energy delivery elements. The clinician can selectively run thealgorithm600 on thetransducer142 corresponding to the energy delivery element in question. In some embodiments, thecontroller138 may automatically select which energy delivery element to test and automatically activate the transducer to determine the proximity of the energy delivery element(s) to the vessel wall (W). For example, thecontroller138 can select all of the energy delivery elements serially or certain subsets of the energy delivery elements to be tested. In some embodiments, the detection time can be indicated by the console106 (e.g., via the indicator126) and manually compared to a baseline detection time by the clinician.
• Depending on the result ofdecision block602, thecontroller138 can cause an indicator to notify the clinician whether to reposition the treatment assembly114 (block604) or begin energy delivery (block606). For example, if the detection time within a desired range, the contact between theenergy delivery element148 and the vessel wall (W) is sufficient for treatment (seeFIG. 6D-6F). The desired range can have a maximum detection time setting an upper limit, a minimum detection time setting a non-zero lower limit and a maximum detection time setting an upper limit, or a mid-point and an acceptable margin around the midpoint. In this case, thecontroller138 can cause the indicator to notify the clinician of sufficient tissue contact and to begin energy delivery. Notifications of sufficient electrode-tissue contact can include messages on the display126 of the console106 such as “Contact Achieved,” a green light, or similar notifications. Likewise, the console106 can indicate sufficient electrode-tissue contact through one or more lights on the console106 and/or handleassembly112 of thetreatment device102.
• If the detection time is not in the desired range, the controller can cause the indicator to display insufficient electrode-tissue contact and the clinician can reposition thetreatment assembly114. Indications of insufficient electrode-tissue contact can include messages on the display126 of the console106 such as “Insufficient Contact,” “Reposition Catheter,” a red light, or other notifications. If thetreatment assembly114 is repositioned, stages502-506 (FIG. 5) can be repeated to ensure sufficient electrode-tissue contact is achieved. The method can continue by delivering energy through theneuromodulation element140 of thetreatment assembly114 to modulate the nerves (block508).
• The detection time may be greater than the baseline detection time due to chronic instability of at least a portion of thetreatment assembly114 instead of inadequate positioning of thetreatment assembly114 orenergy delivery element148. In these and other embodiments, the controller may further include an algorithm configured to assess such chronic instabilities in conjunction with one or more of the control and/or diagnostic algorithms disclosed herein. Such suitable algorithms are disclosed in U.S. application Ser. No. 13/281,269, filed Oct. 25, 2011, entitled “DEVICES, SYSTEMS, AND METHODS FOR EVALUATION AND FEEDBACK OF NEUROMODULATION TREATMENT,” and U.S. application Ser. No. 13/844,618, entitled “DEVICES, SYSTEMS, AND METHODS FOR SPECIALIZATION OF NEUROMODULATION TREATMENT,” filed Mar. 15, 2013, are incorporated herein by reference in their entireties.
• B. Feedback Related to Positioning
• Several aspects of the present technology that are directed to determining the proximity of at least a portion of thetreatment assembly114 to the renal nerve (RN) can also be used to enhance the efficacy of treatment. For example, theneuromodulation element140 of thetreatment assembly114 can be more accurately aligned with renal nerve(s) (RN) such that the energy is more consistently delivered to the renal nerves (RN) instead of smooth muscle tissue of the vessel where there is little or no neural tissue. This may provide for more consistent ablation or other neuromodulation of the renal nerves (RN), reduce or otherwise modify the power delivery, and/or enhance control of other parameters of thecontrol algorithm132.
• Without being bound by theory, it is believed that the amplitude and frequency of the detected return energy can depend in part on the types of tissue through which the diagnostic energy propagates. For example, referring toFIG. 7B, since muscle tissue (e.g., the vessel wall) will reflect a greater portion of ultrasound energy than does nerve tissue, it is expected that detectedreturn energy710 corresponding to muscle tissue will generally have a greater amplitude than that of detected return energy corresponding to nerve tissue. In one embodiment, the difference in amplitude between the detectedreturn energy710 from the muscle and the detectedreturn energy708 from nerves is at least approximately 10 dB. Similarly, it is believed that the frequencies of the detected return energy of muscle tissue and nerve tissue are different. Signal characterization, for example, could be determined using empirical data from animal studies. For example, return energy data could be collected in known anatomical locations and the histology of the tissue could then be correlated to the return energy data to characterize signals according to the type of reflecting tissue.
• FIGS. 7D-7F are schematic, cross-sectional end views of a vessel showing various proximities of thetreatment assembly114 and/or one or moreenergy delivery elements148.FIG. 7C is a block diagram of one embodiment of adiagnostic algorithm720 configured in accordance with the present technology that can determine a radial proximity (RPN) of at least a portion of thetreatment assembly114 to a target nerve (e.g., renal nerve) based on one or more parameters of return energy such as the amplitude and frequency (and/or derivations thereof) of the detected return energy. As shown inFIGS. 7D and 7E, “radial proximity (RPN)” refers to the distance between a particularenergy delivery element148 and the renal nerve (RN) in the direction of energy delivery and/or within the neuromodulation zone (NZ) along a radian (R) relative to a central axis (A) of the blood vessel. The radial proximity (RPN) can be calculated as an actual distance (e.g., 7 microns) or a relative distance from theenergy delivery element148 to the renal nerve (RN) (e.g., the nerve (RN) is deep within the wall (W), the nerve (RN) is close to the interior surface of the wall (W), etc.). Depending on the thickness (T) of the vessel wall (W), position of the nerve (RN) within and/or on the adventitia, and others parameters, the radial proximity (RPN) can be relatively small (FIG. 7E), relatively large (FIG. 7D), or other gradations in between (block724). Thediagnostic algorithm700 can evaluate the amplitude and/or frequency of the detected return energy (block722) and cause, for example, thecontroller138 to adjust and/or modify the powerdelivery control algorithm132 to compensate for the radial proximity (RPN) of theenergy delivery element148 to the nerve (RN) (block726). For example, if thediagnostic algorithm700 evaluates the raw signal of the detected return energy and determines a renal nerve (RN) is radially closer than predicted (block724), thecontroller138 can decrease P.sub.MAX and/or t.sub.1, t.sub.2, t.sub.3, etc. of the power-control algorithm132. In some embodiments, the duty cycle, frequency, or other parameters of the power-control algorithm can be modified.
• In some embodiments, if the parameter of return energy (e.g., amplitude or frequency) is outside of a predetermined range, thecontroller138 can cause the indicator to indicate the radial proximity (RPN) and automatically adjust and/or modify the power-control algorithm132. The predetermined range can have a selected minimum or maximum threshold value that set a floor or ceiling, a minimum a non-zero lower limit and a maximum upper limit that set a floor and a ceiling, or a mid-point and an acceptable margin around the midpoint. In one embodiment, the indicator can provide a message that the nerve is closer than expected when the radial proximity (RPN) value is low or that the nerve is deeper than expected when the radial proximity (RPN) value is high. In some embodiments, the clinician can manually adjust the power-control algorithm. If the parameter of return energy is within a predetermined threshold, thecontroller138 can cause the indicator to indicate the radial proximity (RPN) is suitable (e.g., the nerve is within a desired distance and alignment with the energy delivery element148). At this point, the clinician can begin neuromodulation, or alternatively, the clinician can continue to check other relative positions of thetreatment assembly114.
• FIG. 7A is a block diagram of one embodiment of adiagnostic algorithm700 configured in accordance with the present technology that can determine a circumferential proximity (CPN) of at least a portion of thetreatment assembly114 to a target nerve (e.g., renal nerve) based on one or more parameters of return energy such as the amplitude and frequency (and/or derivations thereof) of the detected return energy.FIGS. 7D and 7F show examples of “circumferential proximity (CPN),” which refers to the distance along the circumference of the inner wall (S) of the blood vessel between the location of theenergy delivery element148 and a location at the inner wall (S) directly opposite a renal nerve (RN). For example, inFIG. 7F, theenergy delivery element148 has a circumferential position CP1 and the nerve (RN) has a circumferential position CP2. The circumferential proximity (CPN) can be the angle.alpha. between radians R1 and R2 passing through circumferential positions CP1 and CP2, or the distance along the circumference of the inner wall (W) of the vessel between circumferential positions CP1 and CP2. If evaluation of the amplitude and/or frequency shows the value of the circumferential proximity (CPN) is above a selected value (block702), theenergy delivery element148 and the nerve (RN) are not adequately aligned circumferentially (FIG. 7F). In such cases, at least a portion of thetreatment assembly114 can be repositioned to better align theenergy delivery element148 with the nerve (RN) (FIG. 7D) (block704).
• In some embodiments, if the parameter of return energy (e.g., amplitude or frequency) is outside of a predetermined range thecontroller138 can cause the indicator to indicate the circumferential proximity (CPN) and automatically adjust and/or modify thepower control algorithm132. The predetermined range can have a selected minimum or maximum threshold value that set a floor or ceiling, a minimum a non-zero lower limit and a maximum upper limit that set a floor and a ceiling, or a mid-point and an acceptable margin around the midpoint. In one embodiment, the indicator can provide a message that the energy delivery element(s)148 of thetreatment assembly114 are not adequately circumferentially aligned with the renal nerve when the circumferential proximity (CPN) value is high. The indicator can further instruct the clinician to reposition thetreatment assembly114. In some embodiments, thecontroller138 can automatically cause a motorized transducer to rotate the energy delivery element(s)148 so as to be in proper alignment. If the parameter of return energy is within a predetermined threshold, thecontroller138 can cause the indicator to indicate alignment. At this point, the clinician can begin neuromodulation, or alternatively, the clinician can continue to check other relative positions of thetreatment assembly114.
VI. EVALUATION DURING OR AFTER DELIVERING ENERGY FOR Neuromodulation
• A. Feedback Related to Tissue Characterization
• Similar to the disclosure with reference toFIGS. 7A-7E above, it is believed that the reflection or absorption of ultrasound, electromagnetic energy or other diagnostic energies from adequately neuromodulated (e.g., ablated) tissue are different than those of non-neuromodulated or under-neuromodulated tissue (e.g., non- or under-ablated). As a result, the parameters of the detected return energy, such as the amplitude, frequency and/or derivations of these parameters, can be used to indicate the extent of ablation or other alteration of the neural tissue. For example,FIG. 8A shows that the amplitude of the signal corresponding to the detected return energy before neuromodulation can be different (e.g., smaller) than the signal corresponding to the detected return energy after neuromodulation.FIGS. 8B and 8C show that the frequency of the signal corresponding to the detected return energy pre-neuromodulation can be different than the frequency of the signal corresponding to the detected return energy post-neuromodulation. For example, the pre-neuromodulation frequency is lower than the post-neuromodulation frequency inFIG. 8B, while the pre-neuromodulation frequency is higher than the post-neuromodulation frequency inFIG. 8C.
• Accordingly, disclosed herein are one or more diagnostic algorithms that can use the raw signal corresponding to the detected return energy to characterize tissue at or at least proximate to a wall of a vessel (e.g., a renal artery). The diagnostic algorithm can characterize tissue based on one or more parameters of return energy to provide meaningful, real-time or relatively contemporaneous feedback to the clinician regarding the efficacy of the ongoing and/or completed energy delivery while the patient is still catheterized.
• FIG. 9 is a block diagram illustrating stages of a method for operating thesystem100 in accordance with an embodiment of the present technology. Blocks1000-1008 are similar to the blocks500-508 described above with reference toFIG. 5, however blocks1000-1006 are performed before applying energy to the target area (e.g., pre-neuromodulation). During these pre-neuromodulation stages, the pre-neuromodulation parameters of return energy can be determined according to the methods and algorithms discussed above with reference toFIGS. 2-7E and stored in the memory of thecontroller138. While modulating the nerves via energy delivery (block1008) and/or after terminating energy delivery, thetransducer142 can emit energy and detect a return energy automatically by thecontroller138 or manually by the clinician (block1010). Thediagnostic algorithm1000 can determine one or more parameters of return energy during or after neuromodulation based on the detected return energy (block1012). Thediagnostic algorithm1000 can then compare and/or evaluate the post-neuromodulation parameters of return energy in view of the pre-neuromodulation parameters of return energy to characterize the tissue (block1014). Thecontroller138 can then cause the indicator to provide a characterization to the clinician and/or suggest a course of action, such as adjust the power-delivery control algorithm, terminate modulation, continue modulation, reposition, and other suitable choices.
• B. Feedback Related to Vessel Wall Temperature
• As mentioned above, it is believed that the reflected energy associated with a diagnostic ultrasound energy emission can vary depending on the properties of the reflecting surface (e.g., tissue). During a neuromodulation treatment, the temperature of the tissue at the vessel wall increases as energy is delivered to the tissue. This increase in temperature alters and/or affects the reflective properties of the tissue such as the ability of the tissue to conduct sound. For example, as the temperature of the tissue is increases, the speed of sound propagating through the tissue can increase. As a result, the time it takes to detect a reflection of emitted diagnostic ultrasound energy decreases as the temperature of the tissue increases. Accordingly, disclosed herein are one or more diagnostic algorithms that can use the raw signal corresponding to the detected reflection of a diagnostic ultrasound emission to determine the temperature of the vessel wall tissue (e.g. a renal artery) at a treatment site.
• For example,FIG. 10 is a block diagram of one embodiment of adiagnostic algorithm700 configured in accordance with the present technology that can determine the temperature of the tissue based on one or more parameters of return energy such as the detection time, amplitude, and/or frequency (and/or derivations thereof) of the detected return energy. As shown, thediagnostic algorithm1100 can determine a detection time of the return energy at two sequential time points (i.e., at a first time (block1102) and a second time (block1104)). Thediagnostic algorithm1100 can then determine a difference in the detection times (block1106) and repeat this process (blocks1102-1104) over a longer time interval. The longer time interval could correspond to a portion of a neuromodulation treatment or an entire neuromodulation treatment. Likewise, one or more longer time intervals can be evaluated for a given treatment or portion of a treatment. For example, as shown inFIG. 10B, at a time t=0, the amplitude has a first value. At time t=10 second, the amplitude can have a different value. The distance between these two peaks can be tracked over time and correlated to temperature of the tissue.
• Using the difference in detection time between one or more sets of sequential time points, thediagnostic algorithm1100 can determine a vessel wall temperature gradient in the direction of energy delivery (block1108). For example, the temperature gradient may show different temperature values as the depth of the wall increases radially. In some embodiments, thediagnostic algorithm1100 can correlate the detection time data to other parameters of return energy, such as amplitude and/or frequency, to enhance the accuracy and/or interpretation of the temperature gradient. Furthermore, the tissue temperature of the vessel wall at increasing radial depths can also inform a clinician of the degree of tissue damage and/or lesion depth. Current neuromodulation systems measure temperature through a temperature sensor (e.g., thermocouple, thermistor, etc.) positioned in or near the energy delivery element and thus are unable to gauge temperature across a vessel wall since. Such sensors are limited to temperature measurements at or near the interior surface of the vessel wall and can be inaccurate due to variations in blood flow and the degree of contact between the energy delivery element and the vessel wall.
VII. PERTINENT ANATOMY AND PHYSIOLOGY
• The following discussion provides further details regarding pertinent patient anatomy and physiology. This section is intended to supplement and expand upon the previous discussion regarding the relevant anatomy and physiology, and to provide additional context regarding the disclosed technology and the therapeutic benefits associated with renal denervation. For example, as mentioned previously, several properties of the renal vasculature may inform the design of treatment devices and associated methods for achieving renal neuromodulation via intravascular access, and impose specific design requirements for such devices. Specific design requirements may include accessing the renal artery, facilitating stable contact between the energy delivery elements of such devices and a luminal surface or wall of the renal artery, and/or effectively modulating the renal nerves with the neuromodulatory apparatus.
• A. The Sympathetic Nervous System
• The Sympathetic Nervous System (SNS) is a branch of the autonomic nervous system along with the enteric nervous system and parasympathetic nervous system. It is always active at a basal level (called sympathetic tone) and becomes more active during times of stress. Like other parts of the nervous system, the sympathetic nervous system operates through a series of interconnected neurons. Sympathetic neurons are frequently considered part of the peripheral nervous system (PNS), although many lie within the central nervous system (CNS). Sympathetic neurons of the spinal cord (which is part of the CNS) communicate with peripheral sympathetic neurons via a series of sympathetic ganglia. Within the ganglia, spinal cord sympathetic neurons join peripheral sympathetic neurons through synapses. Spinal cord sympathetic neurons are therefore called presynaptic (or preganglionic) neurons, while peripheral sympathetic neurons are called postsynaptic (or postganglionic) neurons.
• At synapses within the sympathetic ganglia, preganglionic sympathetic neurons release acetylcholine, a chemical messenger that binds and activates nicotinic acetylcholine receptors on postganglionic neurons. In response to this stimulus, postganglionic neurons principally release noradrenaline (norepinephrine). Prolonged activation may elicit the release of adrenaline from the adrenal medulla.
• Once released, norepinephrine and epinephrine bind adrenergic receptors on peripheral tissues. Binding to adrenergic receptors causes a neuronal and hormonal response. The physiologic manifestations include pupil dilation, increased heart rate, occasional vomiting, and increased blood pressure. Increased sweating is also seen due to binding of cholinergic receptors of the sweat glands.
• The sympathetic nervous system is responsible for up- and down-regulating many homeostatic mechanisms in living organisms. Fibers from the SNS innervate tissues in almost every organ system, providing at least some regulatory function to things as diverse as pupil diameter, gut motility, and urinary output. This response is also known as sympatho-adrenal response of the body, as the preganglionic sympathetic fibers that end in the adrenal medulla (but also all other sympathetic fibers) secrete acetylcholine, which activates the secretion of adrenaline (epinephrine) and to a lesser extent noradrenaline (norepinephrine). Therefore, this response that acts primarily on the cardiovascular system is mediated directly via impulses transmitted through the sympathetic nervous system and indirectly via catecholamines secreted from the adrenal medulla.
• Science typically looks at the SNS as an automatic regulation system, that is, one that operates without the intervention of conscious thought. Some evolutionary theorists suggest that the sympathetic nervous system operated in early organisms to maintain survival as the sympathetic nervous system is responsible for priming the body for action. One example of this priming is in the moments before waking, in which sympathetic outflow spontaneously increases in preparation for action.
• 1. The Sympathetic Chain
• As shown inFIG. 11, the SNS provides a network of nerves that allows the brain to communicate with the body. Sympathetic nerves originate inside the vertebral column, toward the middle of the spinal cord in the intermediolateral cell column (or lateral horn), beginning at the first thoracic segment of the spinal cord and are thought to extend to the second or third lumbar segments. Because its cells begin in the thoracic and lumbar regions of the spinal cord, the SNS is said to have a thoracolumbar outflow. Axons of these nerves leave the spinal cord through the anterior rootlet/root. They pass near the spinal (sensory) ganglion, where they enter the anterior rami of the spinal nerves. However, unlike somatic innervation, they quickly separate out through white rami connectors which connect to either the paravertebral (which lie near the vertebral column) or prevertebral (which lie near the aortic bifurcation) ganglia extending alongside the spinal column.
• In order to reach the target organs and glands, the axons should travel long distances in the body, and, to accomplish this, many axons relay their message to a second cell through synaptic transmission. The ends of the axons link across a space, the synapse, to the dendrites of the second cell. The first cell (the presynaptic cell) sends a neurotransmitter across the synaptic cleft where it activates the second cell (the postsynaptic cell). The message is then carried to the final destination.
• In the SNS and other components of the peripheral nervous system, these synapses are made at sites called ganglia. The cell that sends its fiber is called a preganglionic cell, while the cell whose fiber leaves the ganglion is called a postganglionic cell. As mentioned previously, the preganglionic cells of the SNS are located between the first thoracic (T1) segment and third lumbar (L3) segments of the spinal cord. Postganglionic cells have their cell bodies in the ganglia and send their axons to target organs or glands.
• The ganglia include not just the sympathetic trunks but also the cervical ganglia (superior, middle and inferior), which sends sympathetic nerve fibers to the head and thorax organs, and the celiac and mesenteric ganglia (which send sympathetic fibers to the gut).
• 2. Innervation of the Kidneys
• As shown inFIG. 12, the kidney is innervated by the renal plexus (RP), which is intimately associated with the renal artery. The renal plexus (RP) is an autonomic plexus that surrounds the renal artery and is embedded within the adventitia of the renal artery. The renal plexus (RP) extends along the renal artery until it arrives at the substance of the kidney. Fibers contributing to the renal plexus (RP) arise from the celiac ganglion, the superior mesenteric ganglion, the aorticorenal ganglion and the aortic plexus. The renal plexus (RP), also referred to as the renal nerve, is predominantly comprised of sympathetic components. Accordingly, the renal plexus (RP) includes renal nerves and therefore modulating the renal plexus is one way to modulate a renal nerve. There is no (or at least very minimal) parasympathetic innervation of the kidney.
• Preganglionic neuronal cell bodies are located in the intermediolateral cell column of the spinal cord. Preganglionic axons pass through the paravertebral ganglia (they do not synapse) to become the lesser splanchnic nerve, the least splanchnic nerve, first lumbar splanchnic nerve, second lumbar splanchnic nerve, and travel to the celiac ganglion, the superior mesenteric ganglion, and the aorticorenal ganglion. Postganglionic neuronal cell bodies exit the celiac ganglion, the superior mesenteric ganglion, and the aorticorenal ganglion to the renal plexus (RP) and are distributed to the renal vasculature.
• 3. Renal Sympathetic Neural Activity
• Messages travel through the SNS in a bidirectional flow. Efferent messages may trigger changes in different parts of the body simultaneously. For example, the sympathetic nervous system may accelerate heart rate; widen bronchial passages; decrease motility (movement) of the large intestine; constrict blood vessels; increase peristalsis in the esophagus; cause pupil dilation, piloerection (goose bumps) and perspiration (sweating); and raise blood pressure. Afferent messages carry signals from various organs and sensory receptors in the body to other organs and, particularly, the brain.
• Hypertension, heart failure and chronic kidney disease are a few of many disease states that result from chronic activation of the SNS, especially the renal sympathetic nervous system. Chronic activation of the SNS is a maladaptive response that drives the progression of these disease states. Pharmaceutical management of the renin-angiotensin-aldosterone system (RAAS) has been a longstanding, but somewhat ineffective, approach for reducing over-activity of the SNS.
• As mentioned above, the renal sympathetic nervous system has been identified as a major contributor to the complex pathophysiology of hypertension, states of volume overload (such as heart failure), and progressive renal disease, both experimentally and in humans. Studies employing radiotracer dilution methodology to measure overflow of norepinephrine from the kidneys to plasma revealed increased renal norepinephrine (NE) spillover rates in patients with essential hypertension, particularly so in young hypertensive subjects, which in concert with increased NE spillover from the heart, is consistent with the hemodynamic profile typically seen in early hypertension and characterized by an increased heart rate, cardiac output, and renovascular resistance. It is now known that essential hypertension is commonly neurogenic, often accompanied by pronounced sympathetic nervous system overactivity.
• Activation of cardiorenal sympathetic nerve activity is even more pronounced in heart failure, as demonstrated by an exaggerated increase of NE overflow from the heart and the kidneys to plasma in this patient group. In line with this notion is the recent demonstration of a strong negative predictive value of renal sympathetic activation on all-cause mortality and heart transplantation in patients with congestive heart failure, which is independent of overall sympathetic activity, glomerular filtration rate, and left ventricular ejection fraction. These findings support the notion that treatment regimens that are designed to reduce renal sympathetic stimulation have the potential to improve survival in patients with heart failure.
• Both chronic and end stage renal disease are characterized by heightened sympathetic nervous activation. In patients with end stage renal disease, plasma levels of norepinephrine above the median have been demonstrated to be predictive for both all-cause death and death from cardiovascular disease. This is also true for patients suffering from diabetic or contrast nephropathy. There is compelling evidence suggesting that sensory afferent signals originating from the diseased kidneys are major contributors to initiating and sustaining elevated central sympathetic outflow in this patient group; this facilitates the occurrence of the well-known adverse consequences of chronic sympathetic over activity, such as hypertension, left ventricular hypertrophy, ventricular arrhythmias, sudden cardiac death, insulin resistance, diabetes, and metabolic syndrome.
• (i) Renal Sympathetic Efferent Activity
• Sympathetic nerves to the kidneys terminate in the blood vessels, the juxtaglomerular apparatus and the renal tubules. Stimulation of the renal sympathetic nerves causes increased renin release, increased sodium (Na+) reabsorption, and a reduction of renal blood flow. These components of the neural regulation of renal function are considerably stimulated in disease states characterized by heightened sympathetic tone and clearly contribute to the rise in blood pressure in hypertensive patients. The reduction of renal blood flow and glomerular filtration rate as a result of renal sympathetic efferent stimulation is likely a cornerstone of the loss of renal function in cardio-renal syndrome, which is renal dysfunction as a progressive complication of chronic heart failure, with a clinical course that typically fluctuates with the patient's clinical status and treatment. Pharmacologic strategies to thwart the consequences of renal efferent sympathetic stimulation include centrally acting sympatholytic drugs, beta blockers (intended to reduce renin release), angiotensin converting enzyme inhibitors and receptor blockers (intended to block the action of angiotensin II and aldosterone activation consequent to renin release) and diuretics (intended to counter the renal sympathetic mediated sodium and water retention). However, the current pharmacologic strategies have significant limitations including limited efficacy, compliance issues, side effects and others.
• (ii) Renal Sensory Afferent Nerve Activity
• The kidneys communicate with integral structures in the central nervous system via renal sensory afferent nerves. Several forms of “renal injury” may induce activation of sensory afferent signals. For example, renal ischemia, reduction in stroke volume or renal blood flow, or an abundance of adenosine enzyme may trigger activation of afferent neural communication. As shown inFIGS. 13A and 13B, this afferent communication might be from the kidney to the brain or might be from one kidney to the other kidney (via the central nervous system). These afferent signals are centrally integrated and may result in increased sympathetic outflow. This sympathetic drive is directed towards the kidneys, thereby activating the RAAS and inducing increased renin secretion, sodium retention, volume retention and vasoconstriction. Central sympathetic over activity also impacts other organs and bodily structures innervated by sympathetic nerves such as the heart and the peripheral vasculature, resulting in the described adverse effects of sympathetic activation, several aspects of which also contribute to the rise in blood pressure.
• The physiology therefore suggests that (i) modulation of tissue with efferent sympathetic nerves will reduce inappropriate renin release, salt retention, and reduction of renal blood flow, and that (ii) modulation of tissue with afferent sensory nerves will reduce the systemic contribution to hypertension and other disease states associated with increased central sympathetic tone through its direct effect on the posterior hypothalamus as well as the contralateral kidney. In addition to the central hypotensive effects of afferent renal denervation, a desirable reduction of central sympathetic outflow to various other sympathetically innervated organs such as the heart and the vasculature is anticipated.
• B. Additional Clinical Benefits of Renal Denervation
• As provided above, renal denervation is likely to be valuable in the treatment of several clinical conditions characterized by increased overall and particularly renal sympathetic activity such as hypertension, metabolic syndrome, insulin resistance, diabetes, left ventricular hypertrophy, chronic end stage renal disease, inappropriate fluid retention in heart failure, cardio-renal syndrome, and sudden death. Since the reduction of afferent neural signals contributes to the systemic reduction of sympathetic tone/drive, renal denervation might also be useful in treating other conditions associated with systemic sympathetic hyperactivity. Accordingly, renal denervation may also benefit other organs and bodily structures innervated by sympathetic nerves, including those identified inFIG. 11. For example, as previously discussed, a reduction in central sympathetic drive may reduce the insulin resistance that afflicts people with metabolic syndrome and Type II diabetics. Additionally, patients with osteoporosis are also sympathetically activated and might also benefit from the down regulation of sympathetic drive that accompanies renal denervation.
• C. Achieving Intravascular Access to the Renal Artery
• In accordance with the present technology, neuromodulation of a left and/or right renal plexus (RP), which is intimately associated with a left and/or right renal artery, may be achieved through intravascular access. AsFIG. 14A shows, blood moved by contractions of the heart is conveyed from the left ventricle of the heart by the aorta. The aorta descends through the thorax and branches into the left and right renal arteries. Below the renal arteries, the aorta bifurcates at the left and right iliac arteries. The left and right iliac arteries descend, respectively, through the left and right legs and join the left and right femoral arteries.
• AsFIG. 14B shows, the blood collects in veins and returns to the heart, through the femoral veins into the iliac veins and into the inferior vena cava. The inferior vena cava branches into the left and right renal veins. Above the renal veins, the inferior vena cava ascends to convey blood into the right atrium of the heart. From the right atrium, the blood is pumped through the right ventricle into the lungs, where it is oxygenated. From the lungs, the oxygenated blood is conveyed into the left atrium. From the left atrium, the oxygenated blood is conveyed by the left ventricle back to the aorta.
• As will be described in greater detail later, the femoral artery may be accessed and cannulated at the base of the femoral triangle just inferior to the midpoint of the inguinal ligament. A catheter may be inserted percutaneously into the femoral artery through this access site, passed through the iliac artery and aorta, and placed into either the left or right renal artery. This comprises an intravascular path that offers minimally invasive access to a respective renal artery and/or other renal blood vessels.
• The wrist, upper arm, and shoulder region provide other locations for introduction of catheters into the arterial system. For example, catheterization of either the radial, brachial, or axillary artery may be utilized in select cases. Catheters introduced via these access points may be passed through the subclavian artery on the left side (or via the subclavian and brachiocephalic arteries on the right side), through the aortic arch, down the descending aorta and into the renal arteries using standard angiographic technique.
• D. Properties and Characteristics of the Renal Vasculature
• Since neuromodulation of a left and/or right renal plexus (RP) may be achieved in accordance with the present technology through intravascular access, properties and characteristics of the renal vasculature may impose constraints upon and/or inform the design of apparatus, systems, and methods for achieving such renal neuromodulation. Some of these properties and characteristics may vary across the patient population and/or within a specific patient across time, as well as in response to disease states, such as hypertension, chronic kidney disease, vascular disease, end-stage renal disease, insulin resistance, diabetes, metabolic syndrome, etc. These properties and characteristics, as explained herein, may have bearing on the efficacy of the procedure and the specific design of the intravascular device. Properties of interest may include, for example, material/mechanical, spatial, fluid dynamic/hemodynamic and/or thermodynamic properties.
• As discussed previously, a catheter may be advanced percutaneously into either the left or right renal artery via a minimally invasive intravascular path. However, minimally invasive renal arterial access may be challenging, for example, because as compared to some other arteries that are routinely accessed using catheters, the renal arteries are often extremely tortuous, may be of relatively small diameter, and/or may be of relatively short length. Furthermore, renal arterial atherosclerosis is common in many patients, particularly those with cardiovascular disease. Renal arterial anatomy also may vary significantly from patient to patient, which further complicates minimally invasive access. Significant inter-patient variation may be seen, for example, in relative tortuosity, diameter, length, and/or atherosclerotic plaque burden, as well as in the take-off angle at which a renal artery branches from the aorta. Apparatus, systems and methods for achieving renal neuromodulation via intravascular access should account for these and other aspects of renal arterial anatomy and its variation across the patient population when minimally invasively accessing a renal artery.
• In addition to complicating renal arterial access, specifics of the renal anatomy also complicate establishment of stable contact between neuromodulatory apparatus and a luminal surface or wall of a renal artery. When the neuromodulatory apparatus includes an energy delivery element, such as an electrode, consistent positioning and appropriate contact force applied by the energy delivery element to the vessel wall are important for predictability. However, navigation is impeded by the tight space within a renal artery, as well as tortuosity of the artery. Furthermore, establishing consistent contact is complicated by patient movement, respiration, and/or the cardiac cycle because these factors may cause significant movement of the renal artery relative to the aorta, and the cardiac cycle may transiently distend the renal artery (i.e., cause the wall of the artery to pulse).
• Even after accessing a renal artery and facilitating stable contact between neuromodulatory apparatus and a luminal surface of the artery, nerves in and around the adventia of the artery should be safely modulated via the neuromodulatory apparatus. Effectively applying thermal treatment from within a renal artery is non-trivial given the potential clinical complications associated with such treatment. For example, the intima and media of the renal artery are highly vulnerable to thermal injury. As discussed in greater detail below, the intima-media thickness separating the vessel lumen from its adventitia means that target renal nerves may be multiple millimeters distant from the luminal surface of the artery. Sufficient energy should be delivered to or heat removed from the target renal nerves to modulate the target renal nerves without excessively cooling or heating the vessel wall to the extent that the wall is frozen, desiccated, or otherwise potentially affected to an undesirable extent. A potential clinical complication associated with excessive heating is thrombus formation from coagulating blood flowing through the artery. Given that this thrombus may cause a kidney infarct, thereby causing irreversible damage to the kidney, thermal treatment from within the renal artery should be applied carefully. Accordingly, the complex fluid mechanics and thermodynamic conditions present in the renal artery during treatment, particularly those that may impact heat transfer dynamics at the treatment site, may be important in applying energy (e.g., heating thermal energy) and/or removing heat from the tissue (e.g., cooling thermal conditions) from within the renal artery.
• The neuromodulatory apparatus should also be configured to allow for adjustable positioning and repositioning of the energy delivery element within the renal artery since location of treatment may also impact clinical efficacy. For example, it may be tempting to apply a full circumferential treatment from within the renal artery given that the renal nerves may be spaced circumferentially around a renal artery. In some situations, full-circle lesions likely resulting from a continuous circumferential treatment may be potentially related to renal artery stenosis. Therefore, the formation of more complex lesions along a longitudinal dimension of the renal artery via the mesh structures described herein and/or repositioning of the neuromodulatory apparatus to multiple treatment locations may be desirable. It should be noted, however, that a benefit of creating a circumferential ablation may outweigh the potential of renal artery stenosis or the risk may be mitigated with certain embodiments or in certain patients and creating a circumferential ablation could be a goal. Additionally, variable positioning and repositioning of the neuromodulatory apparatus may prove to be useful in circumstances where the renal artery is particularly tortuous or where there are proximal branch vessels off the renal artery main vessel, making treatment in certain locations challenging. Manipulation of a device in a renal artery should also consider mechanical injury imposed by the device on the renal artery. Motion of a device in an artery, for example by inserting, manipulating, negotiating bends and so forth, may contribute to dissection, perforation, denuding intima, or disrupting the interior elastic lamina.
• Blood flow through a renal artery may be temporarily occluded for a short time with minimal or no complications. However, occlusion for a significant amount of time should be avoided to prevent injury to the kidney such as ischemia. It could be beneficial to avoid occlusion all together or, if occlusion is beneficial to the embodiment, to limit the duration of occlusion, for example to 2-5 minutes.
• Based on the above described challenges of (1) renal artery intervention, (2) consistent and stable placement of the treatment element against the vessel wall, (3) effective application of treatment across the vessel wall, (4) positioning and potentially repositioning the treatment apparatus to allow for multiple treatment locations, and (5) avoiding or limiting duration of blood flow occlusion, various independent and dependent properties of the renal vasculature that may be of interest include, for example, (a) vessel diameter, vessel length, intima-media thickness, coefficient of friction, and tortuosity; (b) distensibility, stiffness and modulus of elasticity of the vessel wall; (c) peak systolic, end-diastolic blood flow velocity, as well as the mean systolic-diastolic peak blood flow velocity, and mean/max volumetric blood flow rate; (d) specific heat capacity of blood and/or of the vessel wall, thermal conductivity of blood and/or of the vessel wall, and/or thermal convectivity of blood flow past a vessel wall treatment site and/or radiative heat transfer; (e) renal artery motion relative to the aorta induced by respiration, patient movement, and/or blood flow pulsatility; and (f) the take-off angle of a renal artery relative to the aorta. These properties will be discussed in greater detail with respect to the renal arteries. However, dependent on the apparatus, systems and methods utilized to achieve renal neuromodulation, such properties of the renal arteries, also may guide and/or constrain design characteristics.
• As noted above, an apparatus positioned within a renal artery should conform to the geometry of the artery. Renal artery vessel diameter, D.sub.RA, typically is in a range of about 2-10 mm, with most of the patient population having a D.sub.RA of about 4 mm to about 8 mm and an average of about 6 mm. Renal artery vessel length, L.sub.RA, between its ostium at the aorta/renal artery juncture and its distal branchings, generally is in a range of about 5-70 mm, and a significant portion of the patient population is in a range of about 20-50 mm. Since the target renal plexus is embedded within the adventitia of the renal artery, the composite Intima-Media Thickness, IMT, (i.e., the radial outward distance from the artery's luminal surface to the adventitia containing target neural structures) also is notable and generally is in a range of about 0.5-2.5 mm, with an average of about 1.5 mm. Although a certain depth of treatment is important to reach the target neural fibers, the treatment should not be too deep (e.g., >5 mm from inner wall of the renal artery) to avoid non-target tissue and anatomical structures such as the renal vein.
• An additional property of the renal artery that may be of interest is the degree of renal motion relative to the aorta, induced by respiration and/or blood flow pulsatility. A patient's kidney, which located at the distal end of the renal artery, may move as much as 4″ cranially with respiratory excursion. This may impart significant motion to the renal artery connecting the aorta and the kidney, thereby requiring from the neuromodulatory apparatus a unique balance of stiffness and flexibility to maintain contact between the thermal treatment element and the vessel wall during cycles of respiration. Furthermore, the take-off angle between the renal artery and the aorta may vary significantly between patients, and also may vary dynamically within a patient, e.g., due to kidney motion. The take-off angle generally may be in a range of about 30.degree.-135.degree.
IX. CONCLUSION
• The above detailed descriptions of embodiments of the technology are not intended to be exhaustive or to limit the technology to the precise form disclosed above. Although specific embodiments of, and examples for, the technology are described above for illustrative purposes, various equivalent modifications are possible within the scope of the technology, as those skilled in the relevant art will recognize. For example, while steps are presented in a given order, alternative embodiments may perform steps in a different order. The various embodiments described herein may also be combined to provide further embodiments.
• From the foregoing, it will be appreciated that specific embodiments of the technology have been described herein for purposes of illustration, but well-known structures and functions have not been shown or described in detail to avoid unnecessarily obscuring the description of the embodiments of the technology. Where the context permits, singular or plural terms may also include the plural or singular term, respectively.
• Certain aspects of the present technology may take the form of computer-executable instructions, including routines executed by a controller or other data processor. In some embodiments, a controller or other data processor is specifically programmed, configured, and/or constructed to perform one or more of these computer-executable instructions. Furthermore, some aspects of the present technology may take the form of data (e.g., non-transitory data) stored or distributed on computer-readable media, including magnetic or optically readable and/or removable computer discs as well as media distributed electronically over networks. Accordingly, data structures and transmissions of data particular to aspects of the present technology are encompassed within the scope of the present technology. The present technology also encompasses methods of both programming computer-readable media to perform particular steps and executing the steps.
• Moreover, unless the word “or” is expressly limited to mean only a single item exclusive from the other items in reference to a list of two or more items, then the use of “or” in such a list is to be interpreted as including (a) any single item in the list, (b) all of the items in the list, or (c) any combination of the items in the list. Additionally, the term “comprising” is used throughout to mean including at least the recited feature(s) such that any greater number of the same feature and/or additional types of other features are not precluded. It will also be appreciated that specific embodiments have been described herein for purposes of illustration, but that various modifications may be made without deviating from the technology. Further, while advantages associated with certain embodiments of the technology have been described in the context of those embodiments, other embodiments may also exhibit such advantages, and not all embodiments need necessarily exhibit such advantages to fall within the scope of the technology. Accordingly, the disclosure and associated technology can encompass other embodiments not expressly shown or described herein.

Claims (20)

I/We claim:

1. A system, comprising:

an elongated shaft including a distal portion and being configured to locate the distal portion within or at least proximate to a lumen of a human;

a treatment assembly coupled to the elongated shaft and including:

a neuromodulation element configured to deliver a therapeutic energy, and

one or more transducers configured to emit diagnostic energy toward tissue of the lumen and detect a return energy associated with the diagnostic energy;

an indicator configured to notify a user of a position of the treatment assembly; and

a controller operably coupled to the one or more transducers and being configured to:

determine whether the treatment assembly is within a relative distance of a wall of the lumen, and

cause the indicator to notify the user to reposition the treatment assembly or to begin energy delivery based on the relative distance.

2. The system ofclaim 1, wherein the one or more transducers include an emitter that emits the diagnostic energy and a detector that detects the return energy associated with the diagnostic energy.

3. The system ofclaim 2, wherein the controller is configured to:

determine a detection time that is based on a difference in time between when the diagnostic energy is emitted and the return energy is detected; and

compare the detection time to a baseline detection time.

4. The system ofclaim 3, wherein the controller is configured to determine whether the treatment assembly is within the relative distance of the wall of the lumen based on the comparison.

5. The system ofclaim 3, wherein to cause the indicator to notify the user to reposition the treatment assembly or to begin energy delivery based on the relative distance the controller is configured to:

cause the indicator to notify the user that there is sufficient contact with the wall of the lumen and to begin energy delivery when the detection time is within a pre-determined range; and

cause the indicator to notify the user there is insufficient contact with the wall of the lumen and to reposition the treatment assembly when the detection time is not within the pre-determine range.

6. The system ofclaim 1, wherein the emitted diagnostic energy is ultrasound energy.

7. The system ofclaim 1, wherein the controller is configured to determine whether the treatment assembly is within the relative distance of the wall of the lumen based on one or more parameters of the detected return energy.

8. The system ofclaim 7, wherein the one or more parameters of the detected return energy includes a detection time or a signal amplitude of the detected return energy.

9. A system, comprising:

an elongated shaft including a distal portion and being configured to locate the distal portion within or at least proximate to a lumen of a human;

a treatment assembly coupled to the elongated shaft and including:

a neuromodulation element configured to deliver a therapeutic energy,

an emitter configured to emit diagnostic energy toward tissue of the lumen, and

a detector configured to detect a return energy associated with the diagnostic energy;

an indicator that is configured to notify a user of a position of the treatment assembly; and

a controller operably coupled to the emitter and the detector and being configured to:

determine a wall proximity of a portion of the treatment assembly to a wall of the lumen, and

cause the indicator to notify a user to reposition the treatment assembly or to begin energy delivery based on the wall proximity.

10. The system ofclaim 9, wherein the controller is configured to determine the wall proximity of the portion of the treatment assembly to the wall of the lumen based on one or more parameters of the detected return energy that includes at least one of a detection time or an amplitude.

11. The system ofclaim 9, wherein the controller is configured to:

determine a detection time that is based on a difference in time between when the diagnostic energy is emitted and when the return energy is detected; and

compare the detection time to a baseline detection time.

12. The system ofclaim 11, wherein the controller is configured to determine the wall proximity of the portion of the treatment assembly to the wall of the lumen based on the comparison.

13. The system ofclaim 9, wherein the emitted diagnostic energy is ultrasound energy.

14. The system ofclaim 9, wherein the neuromodulation element includes an array having a plurality of ablation electrodes and the indicator includes a user interface.

15. A system, comprising:

an elongated shaft including a distal portion and being configured to locate the distal portion within or at least proximate to tissue of a vessel of a human;

a treatment assembly carried by the distal portion of the elongated shaft and including:

a neuromodulation element configured to modulate nerves associated with sympathetic neural function,

an emitter configured to produce a first diagnostic emission toward the tissue and a second diagnostic emission toward the tissue, and

a detector configured to detect a parameter of return energy of the emitted energy;

an indicator; and

a controller operably connected to the emitter, the detector and the indicator and being configured to:

detect a first parameter of the return energy associated with the first diagnostic emission,

detect a second parameter of the return energy associated with the second diagnostic emission,

determine a status of the modulation of the nerves associated with sympathetic neural function based on the first parameter and the second parameter, and

cause the indicator to indicate a status of the modulation of the nerves.

16. The system ofclaim 15, wherein the first parameter of the return energy includes at least one of a first detection time of return energy, a first amplitude, or a first frequency and the second parameter includes at least one of a second detection time of return energy, a second amplitude, or a second frequency.

17. The system ofclaim 16, wherein the controller is configured to:

determine a tissue characteristic based on a difference between the first parameter of the returned energy and the second parameter of the returned energy.

18. The system ofclaim 17, wherein the tissue characteristic is at least one of a depth of a lesion, a temperature of the tissue or a degree of tissue damage.

19. The system ofclaim 17, wherein the first energy emission and the second energy emission includes an emission of ultrasound energy or electromagnetic energy.

20. The system of claim ofclaim 15, wherein the controller is configured to use the first parameter of the return energy to determine a relative position of at least a portion of the treatment assembly including an absolute radial distance between the portion of the treatment assembly and the vessel.

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