US20090143696A1 - Sensor unit and procedure for monitoring intracranial physiological properties - Google Patents

Abstract

An anchor for an implantable sensing device, a sensor unit formed by the anchor and sensing device, and a surgical procedure for implanting the sensor unit for monitoring a physiological parameter within a cavity of a living body, such as an intracranial physiological property. The anchor includes a shank portion and a head portion. The shank portion defines a distal end of the anchor and has a bore defining an opening at the distal end. The head portion defines a proximal end of the anchor and has a larger cross-sectional dimension than the shank portion. The sensor unit comprises the anchor and the sensing device placed and secured within the bore of the anchor so that a sensing element of the sensing device is exposed for sensing the physiological parameter within the cavity.

Description

CROSS REFERENCE TO RELATED APPLICATIONS
• This application claims the benefit of U.S. Provisional Application Nos. 61/004,508 filed Nov. 29, 2007, and 61/008,202 filed Dec. 19, 2007. The contents of these prior patent applications are incorporated herein by reference.
BACKGROUND OF THE INVENTION
• The present invention generally relates to implantable medical devices, monitoring systems and associated procedures. More particularly, this invention relates to a sensor unit comprising an anchor and an implantable medical sensing device, and to a procedure for implanting the sensing device for monitoring intracranial physiological properties.
• Wireless devices such as pressure sensors have been implanted and used to monitor heart, brain, bladder and ocular function. With this technology, capacitive pressure sensors are often used, by which changes in pressure cause a corresponding change in the capacitance of an implanted capacitor (tuning capacitor). The change in capacitance can be sensed, for example, by sensing a change in the resonant frequency of a tank or other circuit coupled to the implanted capacitor.
• Telemetric implantable sensors that have been proposed include batteryless pressure sensors developed by CardioMEMS, Inc., Remon Medical, and the assignee of the present invention, Integrated Sensing Systems, Inc. (ISSYS). For example, see commonly-assigned U.S. Pat. Nos. 6,926,670 and 6,968,734 to Rich et al., and N. Najafi and A. Ludomirsky, “Initial Animal Studies of a Wireless, Batteryless, MEMS Implant for Cardiovascular Applications,” Biomedical Microdevices, 6:1, p. 61-65 (2004). With such technologies, pressure changes are typically sensed with an implant equipped with a mechanical (tuning) capacitor having a fixed electrode and a moving electrode, for example, on a diaphragm that deflects in response to pressure changes. The implant is further equipped with an inductor in the form of a fixed coil that serves as an antenna for the implant, such that the implant is able to receive a radio frequency (RF) signal transmitted from outside the patient to power the circuit, and also transmit the resonant frequency as an output of the circuit that can be sensed by a reader outside the patient. The implant can be placed with a catheter, for example, directly within the heart chamber whose pressure is to be monitored, or in an intermediary structure, for example, the atrial or ventricular septum of the heart.
• Presently in the United States, roughly one million people are treated for head injuries each year, with over a quarter million of these being moderate or severe injuries. Traumatic brain injuries currently account for approximately 70,000 deaths each year in the United States, with an additional 80,000 patients having severe long-term disabilities. Monitoring intracranial pressure (ICP) to identify intracranial hypertension (ICH) is one of the most important steps in treatment of severe head injuries. The ability to accurately monitor and identify high ICP levels enables physicians to diagnose and treat the underlying causes and significantly reduce the morbidity and mortality rates of these patients.
• ICP is currently measured and recorded through a variety of systems, such as intraventricular catheters, subarachnoid bolts, and catheter tip strain gauges. However, each of these systems has significant drawbacks, including the need for repositioning and balancing, the occurrence of occlusions and blockages, and the risk of infection.
BRIEF SUMMARY OF THE INVENTION
• The present invention provides an anchor for an implantable sensing device, a sensor unit formed by the anchor and sensing device, and a surgical procedure for implanting the sensor unit for monitoring a physiological parameter within a cavity of a living body, such as an intracranial physiological property.
• The anchor includes a shank portion and a head portion. The shank portion defines a distal end of the anchor and has a bore defining an opening at the distal end. The head portion defines a proximal end of the anchor and has a larger cross-sectional dimension than the shank portion. The sensor unit is configured to position a sensing element for monitoring a physiological parameter within a cavity of a living body, and includes the anchor and a sensing device that comprises the sensing element and is configured to be placed and secured within the bore of the anchor.
• The surgical procedure generally entails assembling the sensor unit by placing the sensing device within the bore of the anchor so that the sensing element of the sensing device is exposed at the distal end of the anchor for sensing a physiological parameter. An incision is made in the scalp of a patient to expose a portion of the skull, a hole is made through the skull, and the sensor unit is placed in the hole such that the distal end of the sensor unit (as defined by the sensing device or the distal end of the anchor) is flush with or protrudes into the cranial cavity within the skull, while an oppositely-disposed proximal end of the sensor unit (as defined by the proximal end of the anchor) remains outside the skull. The anchor is secured to the skull so that the hole in the skull is occluded by the sensor unit. A readout device located outside the patient can be used to telemetrically communicate with the sensing device to obtain a reading of the physiological parameter sensed by the sensing element.
• The sensor unit and implantation procedure are intended to be particularly well suited for providing safe, fast, detailed, real-time, and continuous intracranial pressure measurements. Compared to existing systems used for ICP monitoring, particular advantages of the invention include a miniature wireless unit with an uncomplicated anchoring system and implantation/placement procedure that enables accurate placement of a sensing element at various depths in the cranial cavity. The invention also offers reduced infection risk and patient discomfort, increased patient mobility, and improved post-surgical patient care. Preferred embodiments of the sensor unit are very small, allowing the unit to be easily placed under the scalp with minimal discomfort to the patient.
• Other objects and advantages of this invention will be better appreciated from the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIGS. 1aand1bare block diagrams of wireless pressure monitoring systems that utilize resonant and passive sensing schemes, respectively, which can be utilized by the present invention.
• FIGS. 2aand2bare schematic representations of a wireless sensing device and a readout device suitable for use in wireless monitoring systems of this invention.
• FIG. 3 schematically represents internal components of processing circuitry suitable for use in the sensing device ofFIG. 2a.
• FIG. 4 represents a perspective view of a cylindrical self-contained sensing device of the type represented inFIG. 2a.
• FIG. 5 represents the sensing device ofFIG. 4 assembled with an anchor in accordance with a preferred embodiment of the invention.
• FIGS. 6 through 8 schematically represent sensor units equipped with alternative anchors implanted through a hole in the skull of a subject.
DETAILED DESCRIPTION OF THE INVENTION
• FIGS. 1athrough4 schematically illustrate monitoring systems and components thereof that implement one or more implantable sensing devices (10,30,60) adapted to be placed through a hole in the skull of a patent for monitoring one or more intracranial physiological parameters, a notable but nonlimiting example of which is intracranial pressure (ICP). Each monitoring system preferably makes use of a readout unit (20,50,80) adapted to wirelessly communicate with the sensing device. The sensing device is placed at a desired location within the skull with ananchor120, of which several embodiments are shown inFIGS. 5 through 8. Together, the sensing device and itsanchor120 define asensor unit150. Because the sensing device communicates wirelessly with a readout unit, thesensor unit150 lacks a wire, cable, tether, or other physical component that conducts the output of the sensing device to the readout unit or another processing or transmission device outside the body of a patent. As such, thesensor unit150 defines the only implanted portion of the monitoring system.
• FIGS. 1aand1brepresent two types of wireless pressure sensing schemes disclosed in U.S. Pat. Nos. 6,926,670 and 6,968,734 to Rich et al., and capable of use with the present invention. InFIG. 1a, animplant10 is shown as operating in combination with a non-implantedexternal reader unit20, between which a wireless telemetry link is established using a resonant scheme. Theimplant10 contains a packagedinductor coil12 and a pressure sensor in the form of amechanical capacitor14. Together, theinductor coil12 andcapacitor14 form an LC (inductor-capacitor) tank resonator circuit that has a specific resonant frequency, expressed as 1/(LC)^1/2, which can be detected from the impedance of the circuit. At the resonant frequency, the circuit presents a measurable change in magnetically-coupled impedance load to anexternal coil22 associated with thereader unit20. Because the resonant frequency is a function of the capacitance of thecapacitor14, the resonant frequency of the LC circuit changes in response to pressure changes that alter the capacitance of thecapacitor14. Based on thecoil12 being fixed and therefore having a fixed inductance value, thereader unit20 is able to determine the pressure sensed by theimplant10 by monitoring the resonant frequency of the circuit.
• FIG. 1bshows another wirelesspressure sensor implant30 operating in combination with a non-implantedexternal reader unit50. A wireless telemetry link is established between theimplant30 andreader unit50 using a passive, magnetically-coupled scheme, in which onboard circuitry of theimplant30 receives power from thereader unit50. In the absence of thereader unit50, theimplant30 lays passive and without any internal means to power itself. When a pressure reading is desired, thereader unit50 must be brought within range of theimplant30. Theimplant30 contains a packagedinductor coil32 and a pressure sensor in the form of amechanical capacitor34. Thereader unit50 has acoil52 by which an alternating electromagnetic field is transmitted to thecoil32 of theimplant30 to induce a voltage in theimplant30. When sufficient voltage has been induced in theimplant30, arectification circuit38 converts the alternating voltage on thecoil32 into a direct voltage that can be used byelectronics40 as a power supply for signal conversion and communication. At this point theimplant30 can be considered alert and ready for commands from thereader unit50. Theimplant30 may employ thecoil32 as an antenna for both reception and transmission, or it may utilize thecoil32 solely for receiving power from thereader unit50 and employ asecond coil42 for transmitting signals to thereader unit50.Signal transmission circuitry44 receives an encoded signal generated bysignal conditioning circuitry46 based on the output of thecapacitor34, and then generates an alternating electromagnetic field that is propagated to thereader unit50 with thecoil42. Theimplant30 is shown inFIG. 1bwithout a battery, and therefore its operation does not require occasional replacement or charging of a battery. Instead, the energy required to perform the sensing operation is entirely derived from thereader unit50. However, theimplant30 ofFIG. 1bcould be modified to use a battery or other power storage device to power theimplant30 when thereader unit50 is not sufficiently close to induce a voltage in theimplant30.
• While the resonant and passive schemes described in reference toFIGS. 1aand1bare within the scope of the invention,FIG. 2arepresents a morepreferred sensing device60 that translates a physiologic parameter into a frequency tone and modulates the impedance of an antenna with the frequency tone to communicate the physiologic parameter to an external readout unit80 (FIG. 2b).FIG. 2arepresents the wirelessimplantable sensing device60 as comprising atransducer62, electronic circuitry64 (e.g., an application-specific integrated circuit, or ASIC), and anantenna66. Theantenna66 is shown as comprising windings68 (e.g., copper wire) wrapped around a core70 (e.g., ferrite), though other antenna configurations and materials are foreseeable. Thetransducer62 is preferably a MEMS device, more particularly a micromachine fabricated by additive and subtractive processes performed on a substrate. The substrate can be rigid, flexible, or a combination of rigid and flexible materials. Notable examples of rigid substrate materials include glass, semiconductors, silicon, ceramics, carbides, metals, hard polymers, and TEFLON. Notable flexible substrate materials include various polymers such as parylene and silicone, or other biocompatible flexible materials. A particular but nonlimiting example of thetransducer62 is a MEMS capacitive pressure sensor for sensing pressure, such as intracranial pressure (ICP) of the cerebrospinal fluid, though other materials and any variety of sensing elements, e.g., capacitive, inductive, resistive, piezoelectric, etc., could be used. For example, thetransducer62 could be configured to sense temperature, flow, acceleration, vibration, pH, conductivity, dielectric constant, and chemical composition, including the composition and/or contents of cerebrospinal fluid. Thesensing device60 may be powered with a battery or other power storage device, but in preferred embodiments is powered entirely by thereadout unit80 schematically represented inFIG. 2b.
• In addition to powering thesensing device60, thereadout unit80 is represented as being configured to receive an output signal from thesensing device60, process the signal, and relay the processed signal as data in a useful form to a user. Thereadout unit80 is shown equipped withcircuitry82 that generates a high-frequency (e.g., 13.56 MHz), high-power signal for anantenna84 to create the magnetic field needed in communicate with thesensing device60. Thereadout unit80 containsadditional circuitry86 to receive and demodulate a backscattered signal from thesensing device60, which is then processed with aprocessing unit88 using calibration coefficients to quantify the physiological parameter of interest. Thereadout unit80 is further shown as equipped with auser interface90, by which the operation of thereadout unit80 can be controlled to allow data logging or other user control and data examination. Thereadout unit80 can be further configured for wireless or wired communication with a computer, telephone, or web-based system.
• FIG. 3 represents a block diagram showing particularly suitable components for theelectronic circuitry64 ofFIG. 2a. Thecircuitry64 includes anoscillator92, for example a relaxation oscillator, connected to aresistor93 and a MEMs mechanical capacitor94 as an example of thetransducer62 ofFIG. 2a. A preferred MEMS capacitor94 comprises a fixed electrode and a moving electrode on a diaphragm that deflects relative to the fixed electrode in response to pressure, such that the capacitor94 is able to serve as a pressure sensing element for thetransducer62. A nonlimiting example of a preferred MEMS capacitor94 has a pressure range of about −100 to about +300 mmHg, with an accuracy of about 1 mmHg. Alternatively, a variable resistor transducer could be used with a fixed capacitance, or an inductor could be substituted for the transducer or fixed circuit element. Based on the RC or other time constant (1/(LC)^1/2), theoscillator92 produces a frequency tone that directly relates to the capacitive value of the capacitor94 and, therefore, the physiologic parameter of interest.
• Thecircuitry64 is further shown as including amodulator96, with which the frequency tone of theoscillator92 is encoded on a carrier frequency, placed on theantenna66, and then transmitted to thereadout unit80. This is accomplished simply by opening and closing aswitch98 and adding acapacitance100 to the antenna matching circuit, resulting in an AM (amplitude modulation) LSK (load shift keying) type modulation. This transmission approach is similar to that used in RFID (radio frequency identification) communications, except RFID does not typically encode analog information but instead encodes a few digital bits either on an AM LSK or FSK (frequency shift keying) modulation.
• Because the preferred embodiment of thesensing device60 does not utilize wires to transmit data or power to the readout unit80 (or another remote device), nor contains an internal power source, thecircuitry64 further includes a regulator/rectifier102 to extract its operating power from electromagnetic (EM) energy generated by thereadout unit80 or another EM power source. The regulator/rectifier102 rectifies incoming power from theinductive antenna66 and conditions it for the other circuit components within thecircuitry64. Finally, amatching circuit104 is shown as comprising atrimmable capacitor bank106 to resonate theinductor antenna66, which is energized by the magnetic field and backscatters data as previously described.
• As an alternative to the embodiment ofFIG. 3, themodulator96 could use a 13.56 MHz (or other frequency) magnetic field as a clock reference to create a second carrier frequency, such as one that is one-quarter or another sub-multiple or multiple of the original frequency. The second carrier frequency can then be amplitude modulated (AM) using the oscillator frequency tone and transmitted to thereadout unit80 via thesame antenna66. In this embodiment, thereadout unit80 may or may not have a second antenna to receive the second carrier frequency-based AM signal.
• The communication scheme described above differs from resonate tank communication systems that use capacitive pressure transducer elements in conjunction with an inductor/antenna. In particular, thecircuitry64 allows the use of any frequency for the highpower readout unit80, which in preferred embodiments utilizes an industrial, scientific, medical (ISM) band frequency. In contrast, the frequencies and potentially large bandwidths required of resonate tank communication systems are subject to FCC emission limitations, likely requiring the use of extra shielding or potentially other measures taken in the facilities where thesensing device60 andreadout unit80 are to be used. Another feature of thecircuitry64 is the allowance of more combinations of oscillator elements to be used. Because resonator tank systems require an inductive element and a capacitive element in which at least one of the elements serves as a transducer, resonator tank systems do not lend themselves well to resistive-based or other based sensors. Finally, thecircuitry64 also allows for signal conditioning, such as transducer compensation, which allows for such items as removing temperature dependence or other non-idealities that may be inherent to thetransducer62. In the embodiment ofFIG. 3, a negative temperature coefficient of the MEMS capacitor94 can be compensated with simple circuitry relying on the positive temperature coefficient of resistor elements arranged in a trimmable bank of two resistor units with largely different temperature coefficients that can be selectively added in a trimming procedure in production to select the precise level to compensate the transducer variation.
• Restrictive levels of energy available to small implantable medical sensing devices and the desire to maximize data rates to capture more detailed physiological parameter response have typically been met with a robust type of analog communication that places information on the frequency rather than amplitude of the carrier. In U.S. Pat. No. 6,929,970 to Rich et al., a secondary carrier frequency is used for communication with an interrogator unit, resulting in a technique that consumes substantially more power in the implant and requires a second external antenna to receive the signal. The greater power consumption of the implant necessitates a tradeoff between smaller size and longer communication range. In contrast, the communication scheme described above in reference toFIGS. 2a,2band3 draws upon the RFID-type communications, such as those described in U.S. Pat. Nos. 7,015,826 and 6,622,567, whose contents are incorporated herein by reference. However instead of communicating digital data using a fixed rate clock, the present invention transmits analog information as the frequency of the clock to lower power consumption and enhance powering and communication range. In this way, much of thereadout unit80 can utilize hardware that is commercially available for RFID, except that a different demodulator is required. An early example of RFID can be found in U.S. Pat. No. 4,333,072.
• The transducer62 (e.g., mechanical capacitor94), the electronic circuitry64 (including chips, diodes, capacitors, etc., thereof), theantenna66 and any additional or optional components (e.g., additional transducers62) of the sensing device60 (or any alternative sensing device, such as thedevices10 and30 ofFIGS. 1aand1b) are preferably contained in a single hermetically-sealed housing.FIG. 4 depicts a preferred example as being acylindrical housing110, which is convenient for placing thesensing device60 within theanchor120 discussed in reference toFIGS. 5 through 8 below. Other exterior shapes for thehousing110 are also possible to the extent that the exterior shape permits assembly of thesensing device60 with theanchor120 as discussed below. The cylindrical-shapedhousing110 ofFIG. 4 includes a flatdistal face112, though other shapes are also possible, for example, a torpedo-shape in which theperipheral face114 of thehousing110 immediately adjacent thedistal face112 is tapered or conical (not shown). Thehousing110 can be formed of glass, for example, a borosilicate glass such as Pyrex Glass Brand No 7740 or another suitable material capable of forming a hermetically-sealed enclosure for the electrical components of thesensing device60. A biocompatible coating, such as a layer of a hydrogel, titanium, nitride, oxide, carbide, silicide, silicone, parylene and/or other polymers, can be deposited on thehousing110 to provide a non-thrombogenic exterior for the biologic environment in which thesensing device60 will be placed. As can be seen inFIG. 4, the inductive antenna66 (for example, comprising thecoil68 surrounding the core70 as represented inFIG. 2a) occupies most of the internal volume of thehousing110. The size of theantenna66 is governed by the need to couple to a magnetic field to enable telepowering with thereadout unit80 from outside the body, for example, a transmission distance of about ten centimeters or more. Thecircuitry64 is disposed between theantenna66 and thedistal face112 of thehousing110 that preferably carries thetransducer62. A nonlimiting example of an overall size for thehousing110 is about 3.7 mm in diameter and about 16.5 mm in length.
• A preferred aspect of the invention is to locate thetransducer62 at or near the distal end of thesensing device60, for example, the flatdistal face112 of thecylindrical housing110 or on theperipheral face114 of thehousing110 immediately adjacent thedistal face112. Thedistal face112 can be defined by a biocompatible semiconductor material, such as a heavily boron-doped single-crystalline silicon, in whose outer surface the transducer62 (for example, a pressure-sensitive diaphragm of the capacitor94) is formed. In this manner, only thedistal face112 of thehousing110 need be in contact with cerebrospinal fluid, whose pressure (or other physiological parameter) is to be monitored. In the case of monitoring intracranial pressures, this aspect of the invention can be used to minimize the protrusion of thesensing device60 into the cranial cavity. For example, thesensing device60 can be placed so that thetransducer62 presses against the dura mater (extradural), though it is also within the scope of the invention that thetransducer62 is placed beneath the dura (subdural) in the subarachnoid space or beneath the pia mater and extend into brain tissue.
• FIGS. 5 through 8 represent different embodiments of theanchor120 assembled with thesensing device60 to form thesensor unit150. InFIG. 5, thesensor unit150 is represented as a coaxial assembly of thesensing device60 andanchor120, with thedistal face112 of thesensing device60 exposed and the oppositely-disposed proximal end of thesensing device60 concealed within theanchor120. As represented inFIG. 6, thesensor unit150 can be anchored to theskull134, for example, by making an incision in thescalp142, drilling ahole136 in theskull134, and then inserting thesensor unit150 in thehole136 so that theanchor120 secures thesensing device60 to theskull134. The protrusion of thesensor unit150 and itssensing device60 relative to theskull134 can be determined by theanchor120. For example, the distal end of the unit150 (for example, as defined by thedistal face112 of thehousing110 or thedistal end128 of the anchor120) may be slightly recessed or flush with the interior surface of theskull134 so that thetransducer62 presses against thedura mater138, or may be placed beneath thedura mater138 into the subarachnoid space or into brain tissue. As such, the length of theshank portion122 can be varied depending on the desired location of thetransducer92. Furthermore, theshank portion122 could be configured as a catheter through which pressure is conducted to thesensing device60, which can then be located within theshank portion122 nearer thehead portion124 than thedistal end128 of theanchor120.
• Theanchor120 can be fabricated as a unitary component or as an assembly, and can be formed of various biocompatible materials, nonlimiting examples of which include NITINOL, TEFLON, polymers such as parylene, silicone and PEEK, metals, glass, and ceramics. Theanchor120 is represented inFIGS. 5 through 8 as having ashank portion122 and ahead portion124 that define, respectively, thedistal end128 and an oppositely-disposed proximal end of theanchor120. Thehead portion124 is represented as having a larger cross-sectional dimension than theshank portion122 to prevent theentire anchor120 from being placed within theskull hole136. The shank andhead portions122 and124 are represented as having coaxial tubular and disk shapes, respectively, though a round outer periphery is nota requirement for eitherportion122 and124. Theshank portion122 is further represented as having aninternal bore126 that defines an opening at thedistal end128 of theanchor120. Thesensing device60 is axially disposed within the anchor bore126 such that thedistal face112 carrying thetransducer62 is exposed outside theanchor120. Thedistal face112 of thesensing device60 is shown as protruding from theshank portion122, though it is also within the scope of the invention that thedistal face112 could be recessed within the anchor bore126. The anchor bore126 andsensing device housing110 are represented as having complementary shapes, providing a close fit that prevents biological material (for example, cerebrospinal fluid) from infiltrating thebore126. Thesensing device60 can be temporarily or permanently secured within thebore126, for example, with an interference fit or another mechanical securement device, or a biocompatible adhesive such as a cement, glue, epoxy, etc. While theantenna66 of thesensing device60 is shown enclosed with thehousing110 inFIG. 5, theantenna66 could be placed within thehead portion124 of theanchor120, or within a separate subassembly (not shown) placed remotely on the patient and electrically coupled to the remaining components of thesensing device60 via theanchor120.
• InFIG. 6, thesensor unit150 is represented as anchored to theskull134, with theshank portion122 of theanchor120 received in theskull hole136, and the distal end of the unit150 (as defined by thedistal face112 of the housing110) placed by theanchor120 beneath thedura mater138 in thesubarachnoid space140. Thehead portion124 of theanchor120 abuts the exterior surface of theskull134, and may be exposed through the scalp142 (as shown) or covered by thescalp142. Theanchor120 can be secured to theskull134 with an interference fit between theshank portion122 and theskull hole136, and/or with threads formed on the exterior of theshank portion122, or with a biocompatible cement, glue or epoxy, spring, etc., placed between theskull134 and theshank portion122.
• InFIG. 7, theshank portion122 is shown to have a smaller cross-section than theskull hole136, for example, as a result of thehole136 being formed for another medical procedure. Theanchor120 is secured to theskull134 with thehead portion124 assisted by anattachment element144, for example, a biocompatible cement, glue or epoxy, screws, nails, etc.
• InFIG. 8, thesensor unit150 is shown as further including aninsert146 between theshank portion122 and theskull134. Theinsert146 can have a tubular shape, can be secured to theanchor120 by an interference fit, and can provide for an interference fit with theskull hole136. Alternatively or in addition, theinsert146 can be or comprise a spring or threads capable of securing theshank portion122 to theskull134, optionally assisted by a biocompatible cement, glue or epoxy, nails, etc. A preferred aspect of the embodiment ofFIG. 8 is that theanchor120 is not permanently joined to theinsert146, which permits theinsert146 to remain secured to theskull134 while allowing thesensor unit150 and/or itssensing device60 and/oranchor120 to be replaced.
• In addition to the above-noted features, theanchor120 can be modified to provide other functional features useful to thesensing device60 orsensor unit150, for example, a device similar to an RFID tag can be added to theanchor120 to wirelessly transmit ID information concerning thesensing device60. The ID information may include an ID number, ID name, patient name/ID, calibration coefficients/information, range of operation, date of implantation, valid life of the device (operation life), etc. Theanchor120 may further include additional capabilities such as features for connection to a catheter, shunt, or other device (not shown) that may be useful when monitoring ICP or treating intracranial hypertension (ICH) and severe head injuries.
• In addition to thesensing device60,sensor unit150 andreader unit80 described above, the monitoring systems of this invention can be combined with other technologies to achieve additional functionalities. For example, thereader unit80 can be implemented to have a remote transmission capability, such as home monitoring that may employ telephone, wireless communication, or web-based delivery of information received from thesensor units150 by thereader unit80 to a physician or caregiver. In this manner, thereader unit80 can be adapted for remote monitoring of the patient, closed-loop drug delivery of medications to treat the patient, warning of changes in the physiological parameter (pressure), portable or ambulatory monitoring or diagnosis, monitoring of battery operation, data storage, reporting global positioning coordinates for emergency applications, and communication with other medical devices such as deep brain stimulation (DBS) devices, drug delivery systems, non-drug delivery systems, and wireless medical management systems. Furthermore, the placement of thesensor unit150 can be utilized as part of a variety of different medical procedures, including diagnosis, treatment intervention, tailoring of medications, disease management, identification of complications, and chronic disease management.
• While the invention has been described in terms of specific embodiments, it is apparent that other forms could be adopted by one skilled in the art. Therefore, the scope of the invention is to be limited only by the following claims.

Claims (39)

1. An sensor unit configured to position a sensing element for monitoring a physiological parameter within a cavity of a living body, the sensor unit having an anchor comprising:

a shank portion defining a distal end of the anchor and having a bore defining an opening at the distal end; and

a head portion defining a proximal end of the anchor and having a larger cross-sectional dimension than the shank portion.

2. The sensor unit according toclaim 1, wherein the shank portion comprises means for securing the anchor within a hole.

3. The sensor unit according toclaim 2, wherein the securing means is at least one biocompatible attachment device chosen from the group consisting of inserts, threads, nails, screws, springs, and adhesives.

4. The sensor unit according toclaim 2, wherein the anchor consists of the shank portion, the head portion, the bore, and the securing means.

5. The sensor unit according toclaim 1, further comprising a sensing device within the bore of the anchor, the sensing device comprising a sensing element exposed and adapted to sense the physiological parameter within the cavity.

6. The sensor unit according toclaim 5, wherein the sensing device is operable to telemetrically communicate a reading of the physiological parameter to a readout device that is not adapted to be implanted in the living body.

7. The sensor unit according toclaim 5, wherein the sensing device has a distal end and the sensing element is disposed at the distal end of the sensing device.

8. The sensor unit according toclaim 7, wherein the distal end of the sensing device protrudes from the bore of the anchor such that the sensing device defines a distal end of the sensor unit.

9. The sensor unit according toclaim 7, wherein the sensing device has an oppositely-disposed proximal end concealed within the anchor.

10. The sensor unit according toclaim 5, wherein the physiological parameter is pressure.

11. The sensor unit according toclaim 10, wherein the sensing element comprises a diaphragm responsive to pressure.

12. The sensor unit according toclaim 11, wherein the diaphragm is at a distal surface of the sensing device.

13. The sensor unit according toclaim 5, wherein the sensing element comprises a micromachined structure.

14. The sensor unit according toclaim 5, further comprising a telemetry antenna adapted for telemetrically communicating a reading of the physiological parameter sensed by the sensing element and optionally electromagnetically receiving power for the sensing device.

15. The sensor unit according toclaim 14, wherein the telemetry antenna is within the sensing device.

16. The sensor unit according toclaim 14, wherein the sensor unit is wirelessly coupled with the telemetry antenna to a readout device that is not adapted to be implanted in the living body.

17. The sensor unit according toclaim 16, wherein the sensor unit is wirelessly coupled to the readout device for telemetric communication therewith using a resonant scheme in which the sensing device telemetrically receives power from the readout device.

18. The sensor unit according toclaim 16, wherein the sensor unit is wirelessly coupled to the readout device for telemetric communication therewith using a passive scheme in which the sensing device telemetrically receives electromagnetic power from the readout device.

19. The sensor unit according toclaim 16, wherein the sensing device further comprises processing circuitry for processing electrical communications between the sensing element and the telemetry antenna.

20. The sensor unit according toclaim 19, wherein the processing circuitry causes the telemetry antenna to transmit an amplitude modulation transmission.

21. The sensor unit according toclaim 5, wherein the sensor unit consists of the sensing device, the anchor, and means for telemetrically communicating a reading of the physiological parameter to a readout device.

22. A surgical procedure comprising:

assembling a sensor unit by placing a sensing device within a bore of an anchor so that a sensing element of the sensing device is exposed at a distal end of the anchor, the sensing element being adapted to sense a physiological parameter;

making an incision in the scalp of a patient to expose a portion of the skull;

making a hole through the skull;

placing the sensor unit in the hole such that the distal end of the sensor unit is flush with or protrudes into the cranial cavity within the skull and an oppositely-disposed proximal end of the sensor unit is outside the skull;

securing the anchor to the skull such that the sensing device is secured to the skull by the anchor and the hole is occluded by the sensor unit; and then

telemetrically communicating with the sensing device to obtain a reading of the physiological parameter using a readout device located outside the patient.

23. The surgical procedure according toclaim 22, wherein the sensing device has a distal end, the sensing element is disposed at the distal end of the sensing device, and the distal end of the sensing device protrudes from the anchor such that the sensing device defines the distal end of the sensor unit.

24. The surgical procedure according toclaim 22, wherein the anchor comprises a shank portion at the distal end of the sensor unit and a head portion that defines the proximal end of the sensor unit, the shank portion is inserted into the hole during the placing step and occludes the hole as a result of the placing step, and the head portion is not inserted into the hole during the placing step but instead is external to the skull following the placing step.

25. The surgical procedure according toclaim 24, wherein the securing step comprises securing the shank portion of the anchor to the skull.

26. The surgical procedure according toclaim 25, wherein the shank portion of the anchor is secured within the hole in the skull by an interference fit therebetween.

27. The surgical procedure according toclaim 25, wherein the shank portion of the anchor is secured within the hole in the skull by an element chosen from the group consisting of inserts, threads, nails, screws, springs, and adhesives.

28. The surgical procedure according toclaim 24, wherein an interference fit does not exist between the shank portion of the anchor and the hole in the skull.

29. The surgical procedure according toclaim 24, wherein the securing step comprises securing the head portion of the anchor to the skull.

30. The surgical procedure according toclaim 29, wherein the head portion of the anchor is secured to the skull by an element chosen from the group consisting of nails, screws, springs, and adhesives.

31. The surgical procedure according toclaim 24, wherein the bore of the anchor is located within the shank portion of the anchor.

32. The surgical procedure according toclaim 22, wherein the physiological parameter is pressure.

33. The surgical procedure according toclaim 22, wherein the telemetric communicating step between the sensing device and the readout device is established using a resonant scheme in which the sensing device telemetrically receives power from the readout device.

34. The surgical procedure according toclaim 22, wherein the telemetric communicating step between the sensing device and the readout device is established using a passive scheme in which the sensing device telemetrically receives electromagnetic power from the readout device.

35. The surgical procedure according toclaim 22, further comprising processing electrical communications between the sensing element and a telemetry antenna of the sensor unit.

36. The surgical procedure according toclaim 35, wherein the telemetry antenna of the sensor unit transmits an amplitude modulation transmission to the readout device.

37. The surgical procedure according toclaim 22, wherein the surgical procedure is part of at least one of the following medical procedures: diagnosis, treatment intervention, tailoring of medications, disease management, identification of complications, and chronic disease management.

38. The surgical procedure according toclaim 22, wherein the readout device is used to perform at least one of the following: remote monitoring of the patient, closed-loop drug delivery of medications to treat the patient, warning of changes in the physiological parameter, portable or ambulatory monitoring or diagnosis, monitoring of battery operation, data storage, reporting global positioning coordinates for emergency applications, and communication with other medical devices.

39. The surgical procedure according toclaim 22, wherein the sensor unit consists of the sensing device, the anchor, and means for telemetrically communicating the reading of the physiological parameter to the readout device.

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