US20130006235A1 - Energy delivery algorithm for medical devices - Google Patents

Abstract

A method for controlling an electrosurgical waveform includes the initial steps of activating an electrosurgical generator and increasing power during a first sample window and determining a direction of change in a first average impedance during the first sample window. The method also includes the steps of performing a first adjustment of power in response to the direction of change in the first average impedance during a subsequent sample window and determining a direction of change in a subsequent average impedance during the subsequent sample window in response to the first adjustment of power. The method also includes performing a subsequent adjustment of power in response to the direction of change in the subsequent average impedance, wherein the subsequent adjustment of power is reverse to that of the first adjustment of power when the direction of change in the first and subsequent average impedances is the same.

Description

CROSS-REFERENCE TO RELATED APPLICATION
• The present application is a continuation of U.S. patent application Ser. No. 12/351,980 entitled “ENERGY DELIVERY ALGORITHM FOR MEDICAL DEVICES BASED ON MAINTAINING A FIXED POSITION ON A TISSUE ELECTRICAL CONDUCTIVITY V. TEMPERATURE CURVE” by Podhajsky et al. filed on Jan. 12, 2009, the entire disclosure of which is incorporated by reference herein.
BACKGROUND
• 1. Technical Field
• The present disclosure relates to electrosurgical apparatuses, systems and methods. More particularly, the present disclosure is directed to an algorithm that controls the application of energy to tissue.
• 2. Background of Related Art
• Electrosurgical generators are employed by surgeons in conjunction with an electrosurgical instrument to cut, coagulate, desiccate and/or seal patient tissue. High frequency electrical energy, e.g., radio frequency (RF) energy, is produced by the electrosurgical generator and applied to the tissue by the electrosurgical tool. Both monopolar and bipolar configurations are commonly used during electrosurgical procedures.
• Electrosurgical techniques and instruments can be used to coagulate small diameter blood vessels or to seal large diameter vessels or tissue, e.g., soft tissue structures, such as lung, brain and intestine. A surgeon can either cauterize, coagulate/desiccate and/or simply reduce or slow bleeding, by controlling the intensity, frequency and duration of the electrosurgical energy applied between the electrodes and through the tissue. In order to achieve one of these desired surgical effects without causing unwanted charring of tissue at the surgical site or causing collateral damage to adjacent tissue, e.g., thermal spread, it is necessary to control the output from the electrosurgical generator, e.g., power, waveform, voltage, current, pulse rate, etc.
• It is known that measuring the electrical impedance and change thereof across the tissue at the surgical site provides a good indication of the state of desiccation or drying of the tissue, e.g., as the tissue dries or loses moisture, the impedance across the tissue rises. This observation has been utilized in some electrosurgical generators to regulate the electrosurgical power based on a measurement of tissue impedance. For example, commonly-owned U.S. Pat. No. 6,210,403 relates to a system and method for automatically measuring the tissue impedance and altering the output of the electrosurgical generator based on the measured impedance across the tissue.
• It has been determined that the particular waveform of electrosurgical energy can be tailored to enhance a desired surgical effect, e.g., cutting, coagulation, sealing, blend, etc. For example, the “cutting” mode typically entails generating an uninterrupted sinusoidal waveform in the frequency range of 100 kHz to 4 MHz with a crest factor in the range of 1.4 to 2.0. The “blend” mode typically entails generating an uninterrupted cut waveform with a duty cycle in the range of 25% to 75% and a crest factor in the range of 2.0 to 5.0. The “coagulate” mode typically entails generating an uninterrupted waveform with a duty cycle of approximately 10% or less and a crest factor in the range of 5.0 to 12.0. In order to effectively and consistently seal vessels or tissue, a pulse-like waveform is preferred. Energy may be supplied in a continuous fashion to seal vessels in tissue if the energy input/output is responsive to tissue hydration/volume through feedback control. Delivery of the electrosurgical energy in pulses allows the tissue to cool down and also allows some moisture to return to the tissue between pulses which are both known to enhance the sealing process.
SUMMARY
• The present disclosure relates to a method for controlling an electrosurgical waveform generated by an electrosurgical generator. The method includes the initial steps of activating an electrosurgical generator to produce an electrosurgical waveform and increasing power of the electrosurgical waveform during a first sample window. The method also includes the steps of determining a direction of change in a first average impedance during the first sample window in response to the increase in power of the electrosurgical waveform and performing a first adjustment of power of the electrosurgical waveform in response to the direction of change in the first average impedance during a subsequent sample window. The method also includes the steps of determining a direction of change in a subsequent average impedance during the subsequent sample window in response to the first adjustment of power and performing a subsequent adjustment of power of the electrosurgical waveform in response to the direction of change in the subsequent average impedance, wherein the subsequent adjustment of power is reverse (i.e., adjusted in the opposite direction) to that of the first adjustment of power when the direction of change in the first and subsequent average impedances is the same.
• According to another embodiment of the present disclosure, a method for controlling an electrosurgical waveform generated by an electrosurgical generator includes the initial steps of activating an electrosurgical generator to produce an electrosurgical waveform and increasing power of the electrosurgical waveform during a first sample window of a normal priority task. The method also includes the steps of determining a direction of change in a first average impedance during the first sample window of the normal priority task in response to the increase in power of the electrosurgical waveform and performing a first adjustment of power of the electrosurgical waveform in response to the direction of change in the first average impedance during a subsequent sample window of the normal priority task. The method also includes the steps of determining a direction of change in a subsequent average impedance during the subsequent sample window of the normal priority task in response to the first adjustment of power and performing a subsequent adjustment of power of the electrosurgical waveform in response to the direction of change in the subsequent average impedance, wherein the subsequent adjustment of power is reverse (i.e., adjusted in the opposite direction) to that of the first adjustment of power when the direction of change in the first and subsequent average impedances is the same.
• According to another embodiment of the present disclosure, a control system for use with an electrosurgical generator adapted to generate an electrosurgical waveform for application to tissue includes a controller configured to adjust power of an electrosurgical waveform generated by an electrosurgical generator. The controller increases power of the electrosurgical waveform during a first sample window. A sensor module is configured to continually sense tissue impedance resulting from the application of the electrosurgical waveform to the tissue and generate at least one signal relating to the application of the electrosurgical waveform to the tissue. At least one loop control module is in operative communication with the controller for receiving the at least one signal from the sensor module to determine a direction of change in a first average impedance during the first sample window in response to the increase in power of the electrosurgical waveform made by the controller. The controller performs a first adjustment of power of the electrosurgical waveform in response to the direction of change in the first average impedance during a subsequent sample window. The at least one loop control module is further configured to determine a direction of change in a subsequent average impedance during the subsequent sample window in response to the first adjustment of power made by the controller. The controller is further configured to perform a subsequent adjustment of power of the electrosurgical waveform in response to the direction of change in the subsequent average impedance, wherein the subsequent adjustment of power is reverse (i.e., adjusted in the opposite direction) to that of the first adjustment of power when the direction of change in the first and subsequent average impedances is the same.
BRIEF DESCRIPTION OF THE DRAWINGS
• Various embodiments of the present disclosure are described herein with reference to the drawings wherein:
• FIG. 1 is a schematic block diagram of a monopolar electrosurgical system according to the present disclosure;
• FIG. 2 is a schematic block diagram of a generator control system according to one embodiment of the present disclosure;
• FIG. 3 illustrates a relationship between a tissue conductivity vs. temperature curve and a tissue impedance vs. temperature curve for tissue undergoing treatment;
• FIG. 4A is a schematic block diagram of a control algorithm according to embodiments of the present disclosure;
• FIG. 4B is a schematic block diagram of a control algorithm according to an embodiment of the present disclosure;
• FIG. 5 is a schematic block diagram of a dual loop control system for use with the generator ofFIG. 2;
• FIG. 6A is a schematic block diagram of a normal priority task algorithm according to embodiments of the present disclosure;
• FIG. 6B is a schematic block diagram of a high priority task algorithm according to embodiments of the present disclosure;
• FIG. 6C is a schematic block diagram of a low priority task algorithm according to embodiments of the present disclosure;
• FIG. 7A is a schematic block diagram of a software system for use with the generator ofFIG. 2;
• FIG. 7B is a schematic block diagram of a normal priority task algorithm for use with the software system ofFIG. 7A;
• FIG. 7C is a schematic block diagram of a high priority task algorithm for use with the software system ofFIG. 7A;
• FIG. 7D is a schematic block diagram of a normal priority task algorithm for use with the software system ofFIG. 7A; and
• FIG. 8 is a schematic block diagram of a user interface for use with the generator and software system according to embodiments of the present disclosure.
DETAILED DESCRIPTION
• Particular embodiments of the present disclosure will be described hereinbelow with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail to avoid obscuring the present disclosure in unnecessary detail. Those skilled in the art will understand that the present disclosure may be adapted for use with either an endoscopic instrument or an open instrument.
• A generator according to the present disclosure can perform monopolar and bipolar electrosurgical procedures, including tissue ablation procedures. The generator may include a plurality of outputs for interfacing with various electrosurgical instruments (e.g., a monopolar active electrode, return electrode, bipolar electrosurgical forceps, footswitch, etc.). Further, the generator includes electronic circuitry configured for generating radio frequency power specifically suited for various electrosurgical modes (e.g., cutting, blending, division, etc.) and procedures (e.g., monopolar, bipolar, vessel sealing).
• FIG. 1 is a schematic illustration of a monopolar electrosurgical system according to one embodiment of the present disclosure. The system includes a monopolar electrosurgical instrument2 including one or more active electrodes3, which can be electrosurgical cutting probes, ablation electrode(s), etc. Electrosurgical RF energy is supplied to the instrument2 by agenerator20 via asupply line4, which is connected to an active terminal30 (FIG. 2) of thegenerator20, allowing the instrument2 to coagulate, ablate and/or otherwise treat tissue. The energy is returned to thegenerator20 through areturn electrode6 via areturn line8 at a return terminal32 (FIG. 2) of thegenerator20. Theactive terminal30 and thereturn terminal32 are connectors configured to interface with plugs (not explicitly shown) of the instrument2 and thereturn electrode6, which are disposed at the ends of thesupply line4 and thereturn line8, respectively.
• The system may include a plurality ofreturn electrodes6 that are arranged to minimize the chances of tissue damage by maximizing the overall contact area with the patient P. In addition, thegenerator20 and thereturn electrode6 may be configured for monitoring so-called “tissue-to-patient” contact to insure that sufficient contact exists therebetween to further minimize chances of tissue damage.
• Not explicitly shown inFIG. 1, thegenerator20 includes suitable input controls (e.g., buttons, activators, switches, touch screen, etc.) for controlling thegenerator20, as well as one or more display screens for providing the surgeon with variety of output information (e.g., intensity settings, treatment complete indicators, etc.). The controls allow the surgeon to adjust power of the RF energy, waveform, and other parameters to achieve the desired waveform suitable for a particular task (e.g., tissue ablation). Further, the instrument2 may include a plurality of input controls which may be redundant with certain input controls of thegenerator20. Placing the input controls at the instrument2 allows for easier and faster modification of RF energy parameters during the surgical procedure without requiring interaction with thegenerator20.
• FIG. 2 shows a schematic block diagram of thegenerator20 having acontroller24, apower supply27, anRF output stage28, and asensor module22. Thepower supply27 may provide DC power to theRF output stage28 which then converts the DC power into RF energy and delivers the RF energy to the instrument2. Thecontroller24 includes amicroprocessor25 having amemory26 which may be volatile type memory (e.g., RAM) and/or non-volatile type memory (e.g., flash media, disk media, etc.). Themicroprocessor25 includes an output port connected to thepower supply27 and/orRF output stage28 which allows themicroprocessor25 to control the output of thegenerator20 according to either open and/or closed control loop schemes.
• A closed loop control scheme generally includes a feedback control loop wherein thesensor module22 provides feedback to the controller24 (i.e., information obtained from one or more sensing mechanisms for sensing various tissue parameters such as tissue impedance, tissue temperature, output current and/or voltage, etc.). Thecontroller24 then signals thepower supply27 and/orRF output stage28 which then adjusts the DC and/or RF power supply, respectively. Thecontroller24 also receives input signals from the input controls of thegenerator20 and/or instrument2. Thecontroller24 utilizes the input signals to adjust the power output of thegenerator20 and/or instructs thegenerator20 to perform other control functions.
• Themicroprocessor25 is capable of executing software instructions for processing data received by thesensor module22, and for outputting control signals to thegenerator20, accordingly. The software instructions, which are executable by thecontroller24, are stored in thememory26 of thecontroller24.
• Thecontroller24 may include analog and/or logic circuitry for processing the sensed values and determining the control signals that are sent to thegenerator20, rather than, or in combination with, themicroprocessor25.
• Thesensor module22 may include a plurality of sensors (not explicitly shown) strategically located for sensing various properties or conditions, e.g., tissue impedance, voltage at the tissue site, current at the tissue site, etc. The sensors are provided with leads (or wireless) for transmitting information to thecontroller24. Thesensor module22 may include control circuitry which receives information from multiple sensors, and provides the information and the source of the information (e.g., the particular sensor providing the information) to thecontroller24.
• More particularly, thesensor module22 may include a real-time voltage sensing system (not explicitly shown) and a real-time current sensing system (not explicitly shown) for sensing real-time values related to applied voltage and current at the surgical site. Additionally, an RMS voltage sensing system (not explicitly shown) and an RMS current sensing system (not explicitly shown) may be included for sensing and deriving RMS values for applied voltage and current at the surgical site.
• The measured or sensed values are further processed, either by circuitry and/or a processor (not explicitly shown) in thesensor module22 and/or by thecontroller24, to determine changes in sensed values and tissue impedance. Tissue impedance and changes therein may be determined by measuring the voltage and/or current across the tissue and then calculating changes thereof over time. The measured and calculated values may be then compared with known or desired voltage and current values associated with various tissue types, procedures, instruments, etc. This may be used to drive electrosurgical output to achieve desired impedance and/or change in impedance values. As the surgical procedure proceeds, tissue impedance fluctuates in response to adjustments in generator output as well as removal and restoration of liquids (e.g., steam bubbles) from the tissue at the surgical site. Thecontroller24 monitors the tissue impedance and changes in tissue impedance and regulates the output of thegenerator20 in response thereto to achieve the desired and optimal electrosurgical effect.
• In general, the system according to the present disclosure regulates the application of energy to achieve the desired tissue treatment based on properties (e.g., electrical and/or physical) of tissue. In embodiments, the application of energy to tissue is regulated based on the electrical conductivity of that tissue as a function of the tissue temperature. Tissue conductivity as a function of tissue temperature may be represented as a conductivity vs. temperature curve. Tissue conductance is inversely related to tissue impedance if the material tissue properties (e.g., length of tissue, area of tissue, etc.) remain constant. Specifically, tissue conductance and tissue impedance are related by the following equation:
• 
  Z=L/(σ*A);
• where Z is impedance of tissue undergoing treatment;
• L is the length of tissue undergoing treatment;
• σ is electrical conductance of tissue undergoing treatment; and
• A is the surface area of tissue undergoing treatment.
• FIG. 3 illustrates the relationship between a typical conductivity vs. temperature curve and a corresponding (i.e., over the same temperature range) impedance vs. temperature curve for tissue undergoing ablation (e.g., utilizing electrosurgical instrument2). The illustrated curves demonstrate that, for tissue undergoing ablation, the lowest impedance value on the impedance vs. temperature curve corresponds to the highest conductance value on the conductance vs. temperature curve.
• The conductance vs. temperature curve for tissue undergoing ablation may be dynamically changing due a variety of factors such as, for example, the changes in energy applied to tissue. The present disclosure provides for a control algorithm that actively tracks this curve to allow for the application of energy to maintain an optimal positioning on the curve (e.g., peak tissue conductance) despite the dynamic nature of the curve.
• FIG. 4 shows a flow chart illustrating acontrol algorithm200 for regulating the application of energy to tissue, according to one embodiment of the present disclosure. In embodiments,algorithm200 may be a software application residing in thememory26 and executable by the controller24 (e.g., via the microprocessor25).
• The control algorithm defines a state variable (SV) to express a real-time value of one or more physical properties of the tissue undergoing ablation (e.g., tissue impedance, voltage across tissue, current through tissue) and/or one or more electrical properties related to the applied energy (e.g., amplitude and/or phase of power applied to tissue, etc.). In embodiments, the SV may be defined in any one or more so-called “states”. For example, the SV may represent the real-time state of tissue resistance as being either “decreasing” or “rising”.
• In the embodiment illustrated inFIG. 4A, thealgorithm200 initially defines the SV as decreasing and increases the application of energy to tissue (e.g., thecontroller24 increases the output of the generator20). Subsequently, thecontrol algorithm200 enters aswitch loop210 wherein thealgorithm200 continuously monitors the SV to be in any one of two states (e.g., decreasing or rising). Based on the detected state of the SV, thealgorithm200 switches between two control loops to control the application of energy to tissue.
• In the illustrated embodiment, thealgorithm200 enters one of twocontrol loops220 and230 to correspond to decreasing and rising states of the SV, respectively, as detected by thealgorithm200 via theswitch loop210. More specifically, thealgorithm200 enters a decreasingcase control loop220 if theswitch loop210 detects the state of the SV as decreasing. Upon enteringcontrol loop220, thealgorithm200 continuously detects (e.g., via the sensor module22) the slope of the control curve (e.g., the impedance vs. temperature curve ofFIG. 3). If the detected slope of the control curve is negative, thealgorithm200 increases the application of energy to tissue (e.g., thecontroller24 increases the output of the generator20) and subsequently defines the SV as decreasing. In this manner, the decreasingcase control loop220 is repeated as long as the SV is defined as decreasing and the slope of the control curve is negative.
• Conversely, if the detected slope of the control curve is not negative (e.g., slope=0 or slope>0), thealgorithm200 decreases the application of energy to tissue and subsequently defines the SV as rising. In this manner, theswitch loop210 detects the SV as rising and, thus, triggers thealgorithm200 to enter a risingcase control loop230.
• Upon entering the risingcase control loop230, thealgorithm200 continuously detects the slope of the control curve. The risingcase control loop230 is configured such that the response to the detected slope of the control curve is directly opposite to that of the decreasingcase control loop220. More specifically, if the detected slope of the control curve is negative during the risingcase control loop230, thealgorithm200 continues to decrease the application of energy to tissue (e.g., thecontroller24 further decreases the output of the generator20) and subsequently defines the SV as decreasing. Continuing to decrease the application of energy to tissue in this scenario allows thealgorithm200 to effectively track the optimal point on the control curve (e.g., lowest possible tissue impedance as a function of temperature). Conversely, if the detected slope of the control curve is not negative (e.g., slope=0 or slope>0), thealgorithm200 increases the application of energy to tissue and subsequently defines the SV as decreasing. Increasing the application of energy to tissue in this scenario allows thealgorithm200 to effectively deliver the maximum energy to tissue. In either scenario (i.e., slope<0; and slope>0) of the risingcase control loop230, the SV is reset to decreasing such that thealgorithm200 enters or re-enters the decreasingcase control loop220. In this way, thealgorithm200 aggressively applies energy to tissue to achieve maximal tissue heating while tracking the optimal point on the control curve (e.g., the lowest possible tissue impedance).
• In embodiments wherein a tissue impedance vs. temperature curve (e.g.,FIG. 3) is utilized as the control curve, the decreasingcase control loop220 recognizes that a slope detected as negative corresponds to the tissue impedance as decreasing and, thus, thealgorithm200 increases the application of energy to tissue accordingly and re-enters the decreasingcase control loop220. Conversely, the decreasingcase control loop220 recognizes that a slope detected as not negative corresponds to the tissue impedance as rising and, thus, thealgorithm200 decreases the application of energy to tissue accordingly and enters the risingcase control loop230. The risingcase control loop230 recognizes that a slope detected as negative corresponds to the tissue impedance as decreasing and, thus, thealgorithm200 further decreases the application of energy to tissue to ensure thealgorithm200 finds the lowest possible tissue impedance. Conversely, the risingcase control loop230 recognizes that a slope detected as not negative corresponds to the tissue impedance as not changing or continuing to rise and, thus, thealgorithm200 increases the application of energy to tissue to ensure that the maximum energy is delivered to tissue.
• In embodiments, in the case of the SV being defined as rising, if the slope of the control curve is negative, energy applied to tissue is decreased and the SV is reset to rising rather than decreasing, as is the case in the embodiment illustrated inFIG. 4A.FIG. 4B shows a flow chart illustrating analternative algorithm300 according to embodiments of the present disclosure. Thealgorithm300 operates similarly to thealgorithm200 illustrated inFIG. 4A and is only described to the extent necessary to illustrate the differences between the embodiments. Thealgorithm300 utilizes the identical initialization as that of thealgorithm200 illustrated inFIG. 4A. Further, thealgorithm300 includes aswitch loop310 configured to switch between two control loops, namely, a decreasingcase control loop320 and a risingcase control loop330 corresponding to the SV being defined as decreasing and rising, respectively.
• As illustrated inFIGS. 4A and 4B, the difference between thealgorithms200 and300 lies in the respective risingcase control loops230 and330. In the case of the SV being defined as rising in theswitch loop310 of thealgorithm300, if the slope of the control curve is negative, thealgorithm300 decreases the energy applied to tissue and maintains the SV as rising rather than reset to decreasing, as is the case in thealgorithm200 embodied inFIG. 4A. In this manner, the risingcase control loop330 will continue to loop until the slope of the control curve is not negative (e.g., slope=0 or slope>0). In embodiments wherein a tissue impedance vs. temperature curve (e.g.,FIG. 3) is utilized as the control curve, if the tissue impedance is decreasing (e.g., slope of the control curve<0), the risingcase control loop330 will continue until thealgorithm300 detects that the tissue impedance is not negative (i.e., slope of the control curve>0). Upon detection that the tissue impedance is not negative, thealgorithm300 increases the application of energy to tissue and resets the SV to decreasing.
• In embodiments, a high priority control loop may be layered over thealgorithms200 and300 to run concurrently therewith. During the ablation of tissue, conditions may exist that lead to continued energy increases. Such energy increases may cause tissue properties (e.g., impedance) to rise and/or fall outside of the peak conductance range or into a so-called “runaway state.” The high priority control loop monitors the control curve for the runaway state and adjusts the application of energy (e.g., thecontroller24 decreases the output of the generator20) accordingly. More specifically, the high priority loop interrupts the algorithm (e.g.,algorithm200 and300) to check for the runaway state, and decreases the application of energy in the event that such a state is detected. In embodiments wherein an impedance vs. temperature curve (FIG. 3) is utilized as the control curve, the high priority loop continually interrogates whether tissue impedance is rising more than a pre-determined threshold value. The pre-determined threshold value may be pre-determined by the surgeon via thegenerator20 input controls and/or reside in thememory26 for execution by themicroprocessor25.
• With reference toFIG. 5, another embodiment of the present disclosure is shown. In the illustrated embodiment, energy application is regulated by thecontroller24 pursuant to a closedloop control system400 stored within thememory26. Thesystem400 continuously monitors tissue impedance as an indicator of tissue conductance and automatically adjusts output to create the lowest possible tissue impedance and/or the highest possible tissue conductance. Upon the initialization of a given procedure or at some predetermined time delay thereafter, thesystem400 processes and stores a baseline impedance Z_BASEdetermined by thesensor24. Thesystem400 determines deviations in average tissue impedance from the baseline impedance Z_BASEas a function of time and adjustsgenerator20 output in response to such deviations. This allows peak tissue conductance to be maintained independent of tissue changes, variations ingenerator20 output, and device accessory selection.
• Further, thesystem400 continually interrogates whether detected impedance has risen above a threshold value, and reduces generator output in response to any such threshold breaches. Finally, thesystem400 may commence a treatment termination sequence upon detection of specific tissue conditions which indicate a completed treatment. Treatment completion may be indicated by an equilibrium between the level of energy applied to the tissue (e.g., via the forceps10) and the level of energy dissipated from the tissue. Based on this equilibrium, thesystem400 determines that the detected tissue impedance has achieved its lowest sustainable level and has remained at that level without change for a substantial amount of time.
• Accordingly, the closedloop control system400 of the present disclosure provides continual control of thepower supply27 and/or the output stage28 (FIG. 2) in response to so-called “sensed” physical or electrical properties at the surgical site and/or proximate theoutput stage28. In embodiments of the present disclosure and in particular reference toFIG. 5, thecontroller24 may be provided with and/or in operative communication with an innerloop control module402 and an outerloop control module404 through which various priority tasks (e.g., loops) may be executed. The inner and outerloop control modules402,404 may be software modules executable by themicroprocessor25 of the controller24 (FIG. 2) and both may receive signals generated by thesensor module22.
• The inner and outerloop control modules402,404 continually receive real-time sensed values, such as current I and voltage V, from thesensor module22 as well as a time t. Themodules402,404 perform calculations on the sensed values to derive additional real-time values, such as power P and impedance Z. For example, the value for change in impedance (dz/dt) is obtained in accordance with:
• 
  dz/dt=(Z−Z_OLD)/(t−t_OLD); and
• 
  Z_OLD=Z;
• where Z is the impedance in accordance with values measured at time t; and
• Z_OLD is the stored impedance in accordance with values measured at a previous time interval at time t_OLD. The inner and outerloop control modules402,404 process the real-time sensed values and output an RF command to thegenerator20 which controls the output power needed for achieving a desired tissue effect.
• FIG. 6A shows anormal priority task410 controlled by the innerloop control module402 for automatic power adjustment to achieve peak conductance. Thenormal priority task410 adjusts the power output by thegenerator20 to continuously achieve peak tissue conductance (i.e., lowest tissue impedance) irrespective of changes to tissue (e.g., thickness, bubble formation, temperature, etc.), variations in generator output (e.g., manual adjustment of generator output power), and device and/or accessory selection (e.g., monopolar device, bipolar forceps, etc.). The innerloop control module402 utilizes thenormal priority task410 to continuously monitor average tissue impedance over a period of time (e.g., a dZ_AVE/dt waveform) as an indicator of tissue conductance since tissue conductance is inversely proportional to tissue impedance. Themodule402 then automatically adjusts the output power of thegenerator20 to provide the lowest possible tissue impedance and, thus, the highest possible tissue conductance. Thenormal priority task410 is characterized by a dual-control loop that continuously interrogates (e.g., via the sensor module22) the slope of the average impedance waveform over a particular window of time and adjusts the output power of thegenerator20 in response to the direction of the slope (e.g., m=0, m<0, or m>0) detected over the duration of that particular window of time.
• During operation of thenormal priority task410, an initial increase of the output power of thegenerator20 is made over the duration of a first sample window of time (e.g., a user-defined time delay). During the first sample window of time, thesensor module22 determines a first slope of the average impedance waveform in response to the initial increase in output power of thegenerator20. During a second sample window of time, a second adjustment is made to the power output by thegenerator20 and a second slope of the average impedance waveform is determined. If the second slope of the average impedance waveform is substantially the same as the first slope of the average impedance waveform, a third adjustment to the output power of thegenerator20 is made. In this scenario, the second adjustment made to the power output by thegenerator20 is a “reverse” adjustment to that of the first adjustment made to the power output by thegenerator20.
• During a first sampled time delay “t1,” the tissue ablation procedure is activated (e.g., by pressing of a foot pedal or handswitch) and a host processor (e.g., microprocessor5) activates thenormal priority task410 to monitor changes in average impedance as a function of time (e.g., dz/dt). More specifically, an initial increase ΔP_iin output power of thegenerator20 is made during time delay t1 while thesensor module22 continuously monitors a first sampled average tissue impedance Z1_AVEto detect changes therein in response to the initial increase ΔP_iin output power of thegenerator20 as a function of time delay t1. The change in Z1_AVEmay be embodied as a waveform interpreted by the innerloop control module402 which represents the first average impedance Z1_AVEas a function of time delay t1 (e.g., dZ1_AVE/dt1). In this manner, thenormal priority task410 may monitor the slope of the impedance waveform as an indication of changes in average tissue impedance over a sample window of time.
• In embodiments, time delay t1 may be up to four (4) seconds during which the initial increase ΔP_iin output power of thegenerator20 is made at a rate of twenty (20) watts per second. In this configuration, the output power of thegenerator20 may be gradually increased to eighty watts (80) over the duration of the time delay t1.
• If, over the duration of the first time delay t1, the first average impedance Z1_AVEdecreases (e.g., the slope of dZ1_AVE/dt1<0) in response to the initial increase ΔP_iin power output, thecontroller24 makes a first adjustment ΔP₁to increase the power output over the duration of a second time delay “t2.” In certain embodiments, the second time delay t2 may be up to four (4) seconds to allow thesensor module22 to record a sufficient sample of data related to changes in tissue impedance.
• Conversely, if over the duration of the first time delay t1, the first average tissue impedance Z1_AVEeither increases or is unchanged (e.g., the slope of dZ1_AVE/dt1>0) in response to the initial increase ΔP_iin power output, thecontroller24 makes a second adjustment ΔP₂to decrease the power output over the duration of the second time delay t2.
• As thecontroller24 makes the second adjustment ΔP₂to decrease the power output over the duration of the second time delay t2, thesensor module22 continuously monitors for changes in a second sampled average tissue impedance Z2_AVE. In embodiments, the second adjustment ΔP₂may be as much as a five (5) watt decrease over the duration of the second time delay t2. If, over the duration of the second time delay t2, the second average tissue impedance Z2_AVEeither increases or is unchanged (e.g., the slope of dZ2_AVE/dt2>0) in response to the second adjustment ΔP₂to decrease the power output, thecontroller24 makes a third adjustment ΔP₃to increase the power output by thegenerator20 over the duration of a third time delay “t3.” Thenormal priority task410 is thereafter repeated. If, over the duration of the second time delay t2, the second average tissue impedance Z2_AVEdecreases (e.g., the slope of dZ2_AVE/dt2<0) in response to the second adjustment ΔP₂to decrease the power output, thecontroller24 makes a fourth adjustment ΔP₄to decrease the power output over the duration of the third time delay t3, and thenormal priority task410 is repeated.
• In this way, thenormal priority task410 performs a reverse adjustment of power output by thegenerator20 over the duration of the third time delay t3 relative to the adjustment made over the duration of the second time delay t2 in response to the same direction of the change (e.g., same slope direction) in the average tissue impedance as detected by thecontroller24 during the first time delay t1. That is, over the duration of the first time delay t1, if the first average tissue impedance Z1_AVEeither increases or is unchanged in response to the initial increase ΔP_iin power output thecontroller24 makes the second adjustment ΔP₂to decrease the power output over the duration of the second time delay t2. Conversely, if the second average tissue impedance Z2_AVEeither increases or is unchanged in response to the second adjustment ΔP₂to decrease the power output thecontroller24 makes the third adjustment ΔP₃to increase the power output over the duration of the third time delay t3. It is in this manner that thenormal priority task410 operates to control the power output by thegenerator20 to achieve the highest possible tissue conductance and, thus, the lowest possible tissue impedance throughout the duration of a given procedure.
• In embodiments, the duration of the time delays t1, t2, t3, the amount of the power adjustments ΔP_i, ΔP_i, ΔP₂, ΔP₃, ΔP₄, the rate at which the power adjustments ΔP_i, ΔP₁, ΔP₂, ΔP₃, ΔP₄are made, and the maximum level to which the power output may be increased by ΔP_imay be pre-determined by the user via the user inputs of thegenerator20 and/or a software-based user interface, as will be discussed in further detail below.
• The outerloop control module404 is layered over the innerloop control module402 and runs concurrently therewith to provide additional control of thegenerator20 to reach a desired output value or effect. The outerloop control module404 utilizes ahigh priority task420 to prevent tissue properties (e.g., impedance) from rising and/or falling outside the peak conductance range or a so-called “run-away state.” Upon activation, thesensor module22 records a baseline impedance value Z_BASEand transmits this value to thecontroller24 for storing in thememory26. Thehigh priority task420 processes the base impedance Z_BASEstored in thememory26 and continually monitors deviations in average tissue impedance Z_AVEfrom the base impedance Z_BASEas a function of time (e.g., a dz/dt waveform). Thehigh priority task420 compares the deviations to a threshold impedance value Z_MAX, and automatically adjusts the output power of thegenerator20 to counteract increases in the average impedance Z_AVEthat breach the threshold value Z_MAX. That is, if a rise in average tissue impedance Z_AVEover a sample window of time exceeds the threshold value Z_MAX, the output power of thegenerator20 is decreased by thecontroller24. In embodiments, the threshold impedance value Z_MAXmay be determined by detecting a change in average impedance Z_AVEover some period of time (e.g., an average change of 20 ohms over seven seconds), and comparing this change in average impedance Z_AVEto the base impedance value Z_BASEstored inmemory26.
• FIG. 6B shows thehigh priority task420 controlled by the outerloop control module404 for automatic power adjustment based on detected rises in average tissue impedance Z_AVEthat exceed the threshold impedance value Z_MAX. Thehigh priority task420 is layered over thenormal priority task410 and runs concurrently therewith. Specifically, the outerloop control module404 utilizes thehigh priority task420 to continuously monitor average tissue impedance as a function of time (e.g., a dz/dt waveform). The average tissue impedance may be an average peak impedance Z_PEAKsampled over a substantially short period of time, e.g., 0.05 seconds. If the rise in peak impedance Z_PEAKexceeds or is equal to a predetermined impedance value ΔP (e.g., 20 ohms nominal) above the base impedance Z_BASE, thecontroller24 makes a fifth adjustment ΔP₅to decrease the power output.
• In embodiments, the output level of thegenerator20 at which the base impedance Z_BASEwill be determined, the impedance value ΔP, and the fifth adjustment ΔP₅may be pre-determined by the user via the user inputs of thegenerator20 and/or a software-based user interface, as will be discussed in further detail below.
• In embodiments, the outerloop control module404 may utilize alow priority task430 to determine when to terminate the power output by thegenerator20 to end a given tissue treatment. Thelow priority task430 is based on a determination that an equilibrium exists between the energy applied by the generator20 (e.g., via the forceps10) and the energy that is dissipated from the tissue site. Thelow priority task430 may determine whether average tissue impedance has achieved its lowest sustainable level and remains at that level without substantial change for a substantial period of time.
• Discussed below with reference toFIG. 6C, thelow priority task430 is layered over thenormal priority task410 and runs concurrently therewith. The outerloop control module404 utilizes thelow priority task430 to continuously monitor average tissue impedance as a function of time (e.g., over the duration of a given procedure). Specifically, thecontroller24 continually receives a current average tissue impedance value Z_AVEnfrom thesensor module22. Upon processing the current average tissue impedance value Z_AVEn, thelow priority task430 compares the current tissue impedance value Z_AVEnto a historical tissue impedance value Z_AVEn-1stored in thememory26 from the previous iteration through thelow priority task430. Thereafter, the current average tissue impedance value Z_AVEnis stored in thememory26 as the historical tissue impedance value Z_AVEn-1. In operation, after the expiration of a fourth time delay “t4” following the activation of thegenerator20, thelow priority task430 monitors average tissue impedance for certain criteria that may indicate that a given treatment is complete and, thus, the power output may be terminated. In certain embodiments of the present disclosure, this criteria may include determining that the current tissue impedance value Z_AVEnis substantially equivalent to the historical tissue impedance value Z_AVEn-1stored in thememory26 over the duration of a fifth time delay “t5” after thegenerator20 is activated. In response, thegenerator20 may continue to output power over the duration of a sixth time delay “t6.” Following the time delay t6, thegenerator20 is turned “off” and the procedure is terminated. In certain embodiments of thelow priority task430, the power output may be terminated immediately by thecontroller24 upon the expiration of the fifth time delay t5. Alternatively, output may be adjusted by thecontroller24 to a predetermined level by the user (e.g., via the user inputs of thegenerator20 and/or a software-based user interface).
• In embodiments, the duration of the time delays t4, t5, t6 may be pre-determined by the user via the user inputs of thegenerator20 and/or a software-based user interface, as will be discussed in further detail below.
• According to embodiments of the present disclosure, the interrogation of impedance may be achieved via single pole recursive filtering.FIG. 7A illustrates asoftware system500 embedded in thememory26 and executed by themicroprocessor25 which utilizes anormal priority task510, ahigh priority task520, andlow priority task530 to controlgenerator20 output based on changes in average tissue impedance as a function of time. Eachtask510,520,530 processes averaged impedance data received from a plurality of single pole recursive impedance filters that continuously filter and/or average tissue impedance data sensed by thesensor module22.
• In the illustrated embodiment, eight impedance filters Zf1-Zf8 are used in conjunction with thesoftware system500. Each of the impedance filters Zf1-Zf8 may be formatted for use with the following data averaging formula (I):
• 
  ZfX_n=Zin*A+ZfX_n-1*B  (1)
• A and B are dependent on a time constant and may be specified by the user, via the input controls of thegenerator20, for each particular impedance filter ZfX. When calculating A and B, the following formulas may be used:
• 
  B=ê(−1/number of samples);
• 
  A=1−B.
• The sample rate may also be specified by the user for calculating the number of samples. In formula (I), Zin is the new impedance value (e.g., Z_RMS) just calculated, and ZfX_n-1is the filtered impedance, for the filter number specified by X, from the previous iteration through the loop, and ZfX_nis the new filtered impedance value for the filter number specified by X.
• Referring now toFIG. 7B, thenormal priority task510 is made up of three states, namely, an initializingstate550, arun state560, and apeak state570. During the initializingstate550, the ablation procedure is activated (e.g., by pressing of a foot pedal or handswitch) and a host processor (e.g., microprocessor5) activates thesoftware system500 for monitoring the plurality of impedance filters Zf1-Zf8. Upon activation of thestate550, a first timer “T1” is initialized to run concurrently with the initializingstate550. The first timer T1 may be set by the user (e.g., via the user inputs of thegenerator20 and/or a software-based user interface) as the amount of time thesoftware system500 waits during thestate550, after initial activation, before interrogating the plurality of impedance filters, as will be discussed in further detail below.
• Once turned on, thegenerator20 operates at a baseline level of power P_BASE. It is at this baseline level of power P_BASEthat thesensor module22 records a baseline impedance Z_BASEand transmits this value to thecontroller24 for storing in thememory26. Once the baseline impedance Z_BASEhas been recorded, the power output by thegenerator20 is ramped by thecontroller24 to an initial level P_INIT. The user may be able to specify (e.g., via the user inputs of thegenerator20 and/or a software-based user interface) the rate at which the power output by thegenerator20 is ramped as well as a maximum level of power P_MAXto which thegenerator20 may be ramped. The power output by thegenerator20 is ramped by thecontroller24 until either the first timer T1 expires or P_MAXis reached.
• Upon expiration of the first timer T1, thenormal priority task510 stores the baseline impedance Z_BASEinto thememory26 as impedance value Zf1_n-1and enters therun state560. Once therun state560 is initialized, thenormal priority task510 starts a second timer “T2” which runs concurrently with therun state560. The second timer T2 may be predetermined by the user (e.g., via the user inputs of thegenerator20 and/or a software-based user interface) as the amount of time thenormal priority task510 operates in therun state560 prior to interrogating the plurality of impedance filters for average impedance data.
• If therun state560 is entered from the initializingstate550, thesoftware system500 immediately calculates the difference between the current filtered impedance Zf2_nand the previous filtered impedance Zf1_n-1and compares this difference to a first impedance reference Zdelta1. The first impedance reference, Zdelta1, is the amount of change from the previous filtered impedance Zf1_n-1to the current filtered impedance Zf2_nwhich is a threshold for triggering an increase or decrease in power output by thegenerator20. The impedance reference Zdelta1 may be predetermined (e.g., via the user inputs of thegenerator20 and/or a software-based user interface) by the user.
• If the difference between the current filtered impedance Zf2_nand the previous filtered impedance Zf1_n-1is less than or equal to Zdelta1, thecontroller24 makes a first adjustment P1 to increase the power output by thegenerator20 and thenormal priority task510 reenters therun state560. Upon reentering therun state560, thesoftware system500 restarts the second timer T2 and waits for the second timer to expire before interrogating impedance filters Zf1 and Zf2 for filtered impedance data.
• If the difference between the current filtered impedance Zf2_nand the previous filtered impedance Zf1_n-1is greater than Zdelta1, thecontroller24 makes a second adjustment P2 to decrease the power output by thegenerator20 and thenormal priority task510 enters thepeak state570. Upon entering thepeak state570, thesoftware system500 starts a third timer “T3”, as will be discussed in further detail below.
• In embodiments, the duration of the third timer T3, the amount of the first and second power adjustments P1, P2 may be pre-determined by the user via the user inputs of thegenerator20 and/or a software-based user interface, as will be discussed in further detail below.
• Upon exiting therun state560, thesoftware system500 stores the current filtered impedance value Zf1_ninto thememory26 as the previous filtered impedance Zf1_n-1and stores the filtered impedance Zf3ninto thememory26 as the previous filtered impedance Zf3_n-1. That is, prior to the exiting of therun state560, the current filtered impedances Zf1_nand Zf3_ndetermined during the present iteration through therun state560 become the respective previous filtered impedances Zf1_n-1and Zf3_n-1once therun state560 is reentered (i.e., once the present iteration through therun state560 becomes the previous iteration through the run state).
• The third timer T3 is initialized by thesoftware system500 to coincide with the initialization of thepeak state570 and to run concurrently therewith. Once the third timer T3 expires, thesoftware system500 calculates the difference between the current filtered impedance Zf4_nand the previous filtered impedance Zf3_n-1and compares this difference to a second impedance reference Zdelta2. The second impedance reference, Zdelta2, is the amount of change from the previous filtered impedance Zf3_n-1to the current filtered impedance Zf4_nwhich is a threshold for triggering an increase or decrease in power output.
• If the difference between the current filtered impedance Zf4_nand the previous filtered impedance Zf3_n-1is less than the second impedance reference Zdelta2, thecontroller24 makes a third adjustment P3 to decrease the power output and thenormal priority task510 reenters therun state560 and thesoftware system500 restarts the second timer T2.
• If the difference between the current filtered impedance Zf4_nand the previous filtered impedance Zf3_n-1is greater than or equal to the second impedance reference Zdelta2, thecontroller24 makes a fourth adjustment P4 to increase the power output and thenormal priority task510 reenters therun state560 and thesoftware system500 restarts the second timer T2.
• In embodiments, the second impedance reference Zdelta2 and the third and fourth power adjustments P3, P4 may be pre-determined by the user via the user inputs of thegenerator20 and/or a software-based user interface, as will be discussed in further detail below.
• Upon exiting thepeak state570, thesoftware system500 stores the current filtered impedance Zf1_ninto thememory26 as the previous filtered impedance Zf1_n-1and stores the current filtered impedance Zf3_ninto thememory26 as the previous filtered impedance Zf3_n-1.
• In embodiments, the duration of the first, second, and third timers T1, T2, T3 and the amount of the first and second power adjustments P1, P2 may be pre-determined by the user via the user inputs of thegenerator20 and/or a software-based user interface, as will be discussed in further detail below.
• Referring now toFIG. 7C, thehigh priority task520 is layered over thenormal priority task510 and runs concurrently therewith to provide additional control of thegenerator20 to reach a desired output value or effect. A fourth timer “T4” is initialized by thesoftware system500 to coincide with the initialization of thehigh priority task520 and to run concurrently therewith. Once the fourth timer T4 expires, thesoftware system500 calculates the difference between the current filtered impedance Zf6_nand the current filtered impedance Zf5_nand compares this difference to a third impedance reference Zdelta3. The third impedance reference, Zdelta3, is the amount of change from the current filtered impedance Zf5_nto the current filtered impedance Zf6_nwhich is a threshold for triggering a decrease in power output. In this manner, the third impedance reference Zdelta3 operates in a threshold capacity to prevent dangerous conditions such as a run-away state that may arise and lead to continued power increases and impedance rises.
• If the difference between the current filtered impedance Zf6_nand the current filtered impedance Zf5_nis greater than or equal to the third impedance reference Zdelta3, thecontroller24 makes a fifth adjustment P5 to decrease the power output and thesoftware system500 reenters thehigh priority task520 and restarts the fourth timer T4.
• If the difference between the current filtered impedance Zf6_nand the current filtered impedance Zf5_nis less than the third impedance reference Zdelta3, thesoftware system500 enters thenormal priority task510. Hence, thenormal priority task510 is only entered from thehigh priority task520 if the third reference impedance Zdelta3 threshold is not equaled or exceeded.
• In embodiments, the duration of the fourth timer T4, the third impedance reference Zdelta3, and the amount of the fifth power adjustment P5 may be pre-determined by the user via the user inputs of thegenerator20 and/or a software-based user interface, as will be discussed in further detail below.
• Thelow priority task530 is layered over thenormal priority task510 and runs concurrently with both thehigh priority task520 and thenormal priority task510 to provide additional control of thegenerator20 to terminate the procedure once a desired output value or effect has been achieved. A fifth timer “T5” is initialized to coincide with the initialization of the vessel sealing procedure (e.g., by pressing a foot pedal or handswitch), and to run concurrently therewith. Once the fifth timer T5 expires, thesoftware system500 continuously interrogates whether particular impedance conditions indicative of a desired tissue effect exist for the duration of a sixth timer “T6” and, if such criteria is met, accordingly initiates a process to terminate the power output. Specifically, thesoftware system500 calculates the difference between the current filtered impedance Zf8_nand the current filtered impedance Zf7_nand compares this difference to a fourth impedance reference Zdelta4. The fourth impedance reference Zdelta4 is the amount of change from the current filtered impedance Zf7_nto the current filtered impedance Zf8_nthat initiates a seventh timer “T7,” the expiration of which triggers thegenerator20 to shut off and the procedure to be terminated.
• If the absolute value of the difference between the current filtered impedance Zf8_nand the current filtered impedance Zf7_nis less than or equal to the impedance reference Zdelta3 for the duration of the sixth timer T6, the seventh timer T7 is initialized. In addition, atermination state535 of thelow priority task530 is triggered to provide for a plurality of options which allow the user to predetermine (e.g., via the user inputs of the generator20) how thegenerator20 will behave once the condition discussed above is satisfied for the duration of the sixth timer T6. Options available to the user with respect to thetermination state535 may include allowing thegenerator20 to operate at it's current output level for the duration of the seventh timer T7, specifying an output level at whichgenerator20 is to operate for the duration of the seventh timer T7, and continuing with thelow priority task530 until the seventh timer T7 expires.
• If the absolute value of the difference between the current filtered impedance Zf8_nand the current filtered impedance Zf7_nis not less than or equal to the impedance reference Zdelta3 for the duration of the sixth timer T6, thesoftware system500 continues to execute thelow priority task530 concurrently with the high priority andnormal priority tasks520 and530.
• In embodiments, the duration of the fifth, sixth, and seventh timers T5, T6, T7 and the fourth impedance reference Zdelta4 may be pre-determined by the user via the user inputs of thegenerator20 and/or a software-based user interface, as will be discussed in further detail below.
• In embodiments of the present disclosure, an eighth timer T8 may be specified by the user (e.g., via the user inputs of thegenerator20 and/or a software-based user interface) as a “master” timer (i.e., total procedure time) for the operation of thegenerator20 in a given procedure. In this configuration, thegenerator20 is shut off upon the expiration of the procedure timer T8 regardless of whether or not thetermination state535 is entered.
• With reference now toFIG. 8, a software-basedgraphical user interface600 is shown for use with embodiments of thesoftware system500 of the present disclosure. Theinterface600 may include a plurality of editable parameters to allow the user to provide specific values (e.g., via the user inputs of the generator20) for controlling the power output by thegenerator20 via thesoftware system500. Theinterface600 allows the user to test and/or validate thesoftware system500 of the present disclosure. Specifically, theinterface600 may be organized by priority level and/or task level including anormal priority interface610, ahigh priority interface620, and alow priority interface630, as shown inFIG. 8. Further, acontrol interface640 may be provided to allow the user to specify various control parameters such as, for example, the procedure time (e.g., the eighth timer T8) and the file path and/or location of a file to be executed by thesoftware system500, etc.
• Thenormal priority interface610 is configured to be edited by the user to provide specific parameters for predetermining the behavior of thenormal priority task510 during a given procedure. Thenormal priority interface610 may be divided into three sub-interfaces, namely, aninitialization state interface650, arun state interface660, and apeak state interface670, to coincide with the threestates550,560, and570 of thenormal priority task510, respectively. Theinterfaces650,660, and670 may be edited by the user to provide specific parameters for further predetermining the behavior of thenormal priority task510 during a given procedure.
• Referring now to interface650, the user may be able to specify parameters related to theinitialization state550 of thenormal priority task510, such as the duration of the first timer T1 and power levels of P_BASE, P_INIT, P_RATE, and P_MAX. With reference tointerface660, the user may be able to specify parameters related to therun state560 of thenormal priority task510, such as the duration of the second timer T2, the first impedance reference Zdelta1, and the amount of the first and second power adjustments P1, P2. With reference tointerface670, the user may be able to specify parameters related to thepeak state570 of thenormal priority task510, such as the duration of the third timer T3, the second impedance reference Zdelta2, and the amount of the third and fourth power adjustments P3 and P4.
• Thehigh priority interface620 is configured to be edited by the user to provide specific parameters for predetermining the behavior of thehigh priority task520 during a given procedure. In particular, the user may be able to specify parameters such as the duration of the fourth timer T4, the third impedance reference Zdelta3, and the fifth power adjustment P5.
• Thelow priority interface630 is configured to be edited by the user to provide specific parameters for predetermining the behavior of thelow priority task530 during a given procedure. In particular, the user may be able to specify parameters such as the duration of the fifth, sixth, and seventh timers T5, T6, T7 and impedance reference Zdelata4. Further, with respect to thetermination state535 of thelow priority task530, the user may be able to choose from a menu of options (not explicitly shown) to select how thegenerator20 will behave over the duration of the seventh timer T7 once thetermination state535 is entered (e.g., continue current output level, adjust to a predetermined output level, shut off upon the expiration of the seventh timer T7, etc.).
• While several embodiments of the disclosure have been shown in the drawings and/or discussed herein, it is not intended that the disclosure be limited thereto, as it is intended that the disclosure be as broad in scope as the art will allow and that the specification be read likewise. Therefore, the above description should not be construed as limiting, but merely as exemplifications of particular embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.

Claims (15)

1. A method for controlling an electrosurgical waveform generated by an electrosurgical generator comprising the steps of:

activating an electrosurgical generator to produce an electrosurgical waveform;

increasing power of the electrosurgical waveform during a first sample window;

determining a direction of change in a first average impedance during the first sample window in response to the increase in power of the electrosurgical waveform;

performing a first adjustment of power of the electrosurgical waveform in response to the direction of change in the first average impedance during a subsequent sample window;

determining a direction of change in a subsequent average impedance during the subsequent sample window in response to the first adjustment of power; and

performing a subsequent adjustment of power of the electrosurgical waveform in response to the direction of change in the subsequent average impedance, wherein the subsequent adjustment of power is reverse to that of the first adjustment of power when the direction of change in the first and subsequent average impedances is the same.

2. A method according toclaim 1, wherein the step of adjusting power further comprises the steps of:

increasing the power of the electrosurgical waveform in response to a decrease in the first average impedance curve; and

decreasing the power of the electrosurgical waveform in response to an increase in the average impedance.

3. A method according toclaim 1, wherein the step of performing a subsequent adjustment of power further comprises the steps of:

decreasing the power of the electrosurgical waveform in response to a decrease in the first average impedance; and

increasing the power of the electrosurgical waveform in response to an increase in the average impedance.

4. A method according toclaim 1, wherein after the step of performing a subsequent adjustment of power, the method further comprises the steps of:

continuously measuring peak impedance during a third sample window; and

comparing the peak impedance to a predetermined threshold change in impedance to determine a rapid rise in impedance.

5. A method according toclaim 1, wherein after the step of performing a subsequent adjustment of power, the method further comprises the steps of:

determining a third average impedance during a third sample window;

determining a fourth average impedance during a fourth sample window; and

applying the electrosurgical waveform for a fifth sample window if the third and fourth average impedance are substantially equal.

6. A method for controlling an electrosurgical waveform generated by an electrosurgical generator comprising the steps of:

activating an electrosurgical generator to produce an electrosurgical waveform;

increasing power of the electrosurgical waveform during a first sample window of a normal priority task;

determining a direction of change in a first average impedance during the first sample window of the normal priority task in response to the increase in power of the electrosurgical waveform;

performing a first adjustment of power of the electrosurgical waveform in response to the direction of change in the first average impedance during a subsequent sample window of the normal priority task;

determining a direction of change in a subsequent average impedance during the subsequent sample window of the normal priority task in response to the first adjustment of power; and

performing a subsequent adjustment of power of the electrosurgical waveform in response to the direction of change in the subsequent average impedance, wherein the subsequent adjustment of power is reverse to that of the first adjustment of power when the direction of change in the first and subsequent average impedances is the same.

7. A method according toclaim 6, wherein after the step of activating an electrosurgical generator to produce an electrosurgical waveform, the method further comprises the steps of:

continuously measuring peak impedance during a first sample window of a high priority task, wherein the high priority task is layered over the normal priority task and configured to operate concurrently therewith; and

comparing the peak impedance to a predetermined threshold change in impedance to determine a rapid rise in impedance.

8. A method according toclaim 6, wherein after the step of activating an electrosurgical generator to produce an electrosurgical waveform, the method further comprises the steps of:

determining a first average impedance during a first sample window of a low priority task, wherein the low priority task is layered over the normal priority task and configured to operate concurrently therewith;

determining a second average impedance during a second sample window of the low priority task; and

applying the electrosurgical waveform for a third sample window of the low priority task if the third and fourth average impedance are substantially equal.

9. A control system for use with an electrosurgical generator adapted to generate an electrosurgical waveform for application to tissue comprising:

a controller configured to adjust power of an electrosurgical waveform generated by an electrosurgical generator, wherein the controller increases power of the electrosurgical waveform during a first sample window;

a sensor module configured to continually sense tissue impedance resulting from the application of the electrosurgical waveform to the tissue and generate at least one signal relating thereto; and

at least one loop control module in operative communication with the controller for receiving the at least one signal from the sensor module to determine a direction of change in a first average impedance during the first sample window in response to the increase in power of the electrosurgical waveform made by the controller, wherein the controller performs a first adjustment of power of the electrosurgical waveform in response to the direction of change in the first average impedance during a subsequent sample window;

wherein the at least one loop control module is further configured to determine a direction of change in a subsequent average impedance during the subsequent sample window in response to the first adjustment of power made by the controller; and

wherein the controller is further configured to perform a subsequent adjustment of power of the electrosurgical waveform in response to the direction of change in the subsequent average impedance, wherein the subsequent adjustment of power is reverse to that of the first adjustment of power when the direction of change in the first and subsequent average impedances is the same.

10. A control system according toclaim 9, further comprising:

a plurality of impedance filters configured to receive the at least one signal generated by the sensor module and filter at least one of the first average impedance and the subsequent average impedance and generate at least one signal relating thereto for transmitting to the controller.

11. A control system according toclaim 9, further comprising:

a user interface in bidirectional communication with the controller which allows a user to select at least one pre-surgical parameter, the at least one pre-surgical parameter including at least one of a level of increase of power of the electrosurgical waveform during the first sample window, a level of the first adjustment of power of the electrosurgical waveform during the subsequent sample window, and a level of the subsequent adjustment of power of the electrosurgical waveform.

12. A control system according toclaim 9, wherein the controller is further configured to increase the power of the electrosurgical waveform in response to a decrease in the first average impedance and decrease the power of the electrosurgical waveform in response to an increase in the first average impedance.

13. A control system according toclaim 9, wherein the controller is further configured to decrease the power of the electrosurgical waveform in response to a decrease in the first average impedance and increase the power of the electrosurgical waveform in response to an increase in the first average impedance.

14. A control system according toclaim 9, wherein the sensor module is configured to continuously measure a peak impedance during a third sample window and generate at least one signal relating thereto and wherein the at least one loop control module is configured to receive the at least one signal relating to the peak impedance from the sensor module to compare the peak impedance to a predetermined threshold change in impedance to determine a rapid rise in impedance.

15. A control system according toclaim 9, wherein the sensor module is further configured to determine a third average impedance during a third sample window and determine a fourth average impedance during a fourth sample window and wherein the controller applies the electrosurgical waveform for a fifth sample window if the third and fourth average impedance are substantially equal.

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