Patent Issued for System and Method for Electrosurgical Generator Power Measurement (USPTO 9375247)
By a News Reporter-Staff News Editor at Journal of Engineering -- From Alexandria, Virginia, VerticalNews journalists report that a patent by the inventors Orszulak, James H. (Nederland, CO); McGraw, Steven E. (Arvada, CO), filed on March 16, 2011, was published online on June 28, 2016.
The patent's assignee for patent number 9375247 is Covidien LP (Mansfield, MA).
News editors obtained the following quote from the background information supplied by the inventors: "The present disclosure is directed to electrosurgery and, in particular, to a system and method for electrosurgical generator power measurement. An active load device is employed with an automated control system to accurately measure generator output under simulated tissue impedance conditions.
"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 an 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., veins and/or soft tissue structures, such as lung, and intestine. A surgeon can 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. For the purposes herein, the term 'cauterization' is defined as the use of heat to destroy tissue (also called 'diathermy' or 'electro-diathermy'). The term 'coagulation' is defined as a process of desiccating tissue wherein the tissue cells are ruptured and dried.
"'Vessel sealing' or 'tissue fusion' is defined as the process of liquefying the collagen and elastin in the tissue so that it reforms into a fused mass with significantly-reduced demarcation between the opposing tissue structures (opposing walls of the lumen). Coagulation of small vessels is usually sufficient to permanently close them while larger vessels or tissue need to be sealed to assure permanent closure. It has been known that different waveforms of electrosurgical energy are suited for different surgical affects, e.g., cutting, coagulation, sealing, blend, etc. For example, the 'cutting' mode typically entails generating a continuous sinusoidal waveform in the frequency range of 250 kHz to 4 MHz with a crest factor in the range of 1.4 to 2.0. The 'blend' mode typically entails generating a periodic burst 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 a periodic burst 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 desired.
"In order to optimize sealing or tissue fusion without causing unwanted charring of tissue at the surgical site or possibly causing collateral damage to adjacent tissue, e.g., thermal spread, it is necessary to accurately control the output from the electrosurgical generator, e.g., power, waveform, voltage, current, pulse rate, etc. It follows that accurate measurement of the output power of an electrosurgical generator greatly benefits the design, manufacture, and use thereof.
"The task of acquiring power data from an electrosurgical generator unit typically involves coupling the RF output of the generator to a dummy load, and manually activating an output power mode and/or level via front panel controls or other actuator. The current value through the load is measured with an RMS voltmeter and recorded manually for each data point along a test sequence. Every data point must then be transferred into a form suitable for design analysis or individual product calibration by a design engineer or line technician. The entire series of measurements may be repeated for different power levels and with different dummy loads. For example, test data may be manually input into a spreadsheet or bench test equipment to calculate load power for each data point. Each power level and mode setting requires at least 20 data points to define a curve with a meaningful level of detail. Typically, at least three power levels are used to define a particular mode. Thus, for each electrosurgical mode, at least 60 data points need to be collected. This means that for an electrosurgical generator that can operate in a cut mode, a blend mode, a coagulation mode, and a sealing mode, 240 data points are required to meet the minimum level of precision required. The result is a time-consuming and labor-intensive product development cycle or manufacturing process which adds considerable cost to the product and negatively impacts time-to-market and margins."
As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventors' summary information for this patent: "It is an object of the present disclosure to provide a system and method that improves and automates the measurement of power generated by an electrosurgical energy source. It is a further object of the present disclosure to improve surgical tissue effect (e.g., cutting, coagulation, blending, sealing, etc.) by employing an automated method of continuum power measurement. In an embodiment, an active load device is operably coupled to the generator output under test. The active load is configured to simulate the change in tissue characteristics, e.g., an impedance change, that occurs when such tissue undergoes electrosurgical treatment. The active load faithfully simulates the change in tissue characteristics caused by a particular mode of electrosurgical energy delivery, such as without limitation, changes caused in response to a cutting mode, a coagulation mode, a blending mode, a sealing mode, and the like. Real-time measurements of generator voltage, current and computed power are recorded automatically to define and/or determine the accuracy of delivered generator power in view of dynamic changes in tissue characteristics, e.g., tissue impedance. An electrosurgical energy measurement system in accordance with the present disclosure may avoid potential power perturbations caused by discrete load impedances, because discrete load impedances do not provide a continuum energy measurement system. The disclosed measurement system may enable rapid prototyping, shorter manufacturing times, and may ultimately improve the precision and accuracy of electrosurgical generator.
"According to one aspect of the present disclosure, an active load device that simulates the tissue load impedance change is operably coupled to an output of a generator under test. Real time measurements of generator voltage, current and computed power are recorded automatically to define the delivered generator power accuracy over the dynamic changes in tissue impedance. A controller sweeps the active device load impedance in closed loop control, which is connected to the generator under test to establish a continuum power measurement process.
"In one embodiment, the disclosed system includes an instrumentation control section, and an active load with monitoring circuitry. A host configuration data file, a look-up table, a control processor, a proportional-integral-derivative (PID) controller (including a .SIGMA. error correction network), an input-output processor, and one or more analog to digital (A/D) and digital to analog (D/A) data conversion devices. The active load and monitoring circuitry includes voltage sense and current sense transducers, drive isolators, signal conditioning drivers and an active load element which simulates the dynamic tissue change corresponding to applied RF energy.
"An electrosurgical generator in accordance with the present disclosure includes a control interface adapted to establish a communication link between the generator and the instrumentation control section to enable the communication of operational commands and status reporting therebetween. The generator may be configured to respond to commands received by the control interface to facilitate automated testing thereof. For example, and without limitation, such commands may cause the generator to activate and deactivate energy generation, select an operating mode (cut, coagulation, blend, seal, etc.), set an output power, set an output frequency, and select a monopolar, bipolar, or polyphase operating mode.
"An embodiment of an electrosurgical generator measurement system according to the present disclosure includes an active load section and a control section. The active load section includes an input adapted to receive electrosurgical energy from an electrosurgical generator under test. The active load section further includes a voltage sensor in communication with the input and configured to output a voltage sensor signal, and a current sensor in communication with the input and configured to output a current sensor signal. The active load is operably coupled to the input and configured to present a variable load to the electrosurgical generator under test in response to an active load drive signal.
"The control section includes an input-output processor, a voltage sensor input in communication with the input-output processor and configured to receive a voltage sensor signal, and a current sensor input in communication with the input-output processor and configured to receive a current sensor signal. The control section further includes a PID control module in communication with the input-output processor, and is configured to output an active load drive signal. Also included in the control section is a lookup table in communication with the PID control module that is configured to store a test profile, and a control processor in communication with the input-output processor, the PID control module, and the lookup table, and is configured to output a generator control signal.
"In embodiments, the control section further includes a data record storage module in communication with the input-output processor. The data record storage module may be utilized to store the results of an electrosurgical generator measurement, which, in turn, may be communicated to an external device through a communication port that is operatively coupled to the input-output processor and/or the data storage module. The control section may include a communication interface operably coupled to the input-output processor that enables the communication of the measurement data to an external device. An analog to digital converter may be interdisposed between the voltage sensor input and the input-output processor and/or the current sensor input and the input-output processor. The active load may be galvanically isolated from the drive signal.
"The active load device may include an N-channel FET and a P-channel FET. In embodiments the drain of the N-channel FET is operably coupled to a positive terminal of the active load, the drain of the P-channel FET is operably coupled to the source of the N-channel FET, and the source of the P-channel FET is operatively coupled to a negative terminal of the active load.
"Also disclosed is a method for measuring the performance of an electrosurgical generator. In an example embodiment, the disclosed method includes the steps of describing a series of parameters defining a test sequence, the parameters including an impedance and a power level. The outputs of an electrosurgical generator under test are electrically coupled to an active load device having the capability to present a variable impedance to the output of the electrosurgical generator. The electrosurgical generator is activated in accordance with a parameter of the test sequence, and the output of the electrosurgical generator is measured. An impedance value based upon the output of the electrosurgical generator is computed and compared to an impedance parameter of the test sequence to determine a difference, if any, between the computed impedance and the target impedance, and, in turn, generate an active load control signal. The active load device is driven in accordance with the active load control signal, which causes an impedance in accordance with the test sequence to be presented to the output of the electrosurgical generator.
"In an embodiment, the measured output of the electrosurgical generator is recorded. Additionally or alternatively, the computed impedance may be compared to the impedance parameter of the test sequence to derive an error signal. The error signal and a test parameter may be provided as inputs to a proportional-integral-derivative controller, and an active load control signal is then computed utilizing the proportional-integral-derivative controller.
"In yet another embodiment, the series of parameters defining a test sequence may be acquired from a host configuration module. The host configuration module includes one or more series of parameters, or 'profiles', that describe an individual test sequence. The desire profile may be selectively loaded into a lookup table from the host configuration file.
"In still another embodiment, a calibration parameter may be derived in accordance with the error signal, and communicated to the electrosurgical generator wherein the calibration parameter may be stored in the electrosurgical generator for future use.
"Also disclosed herein is an electrosurgical generator adapted for use with an electrosurgical measurement system. The disclosed electrosurgical generator includes a processor, a controller interface in communication with the processor and adapted to receive a control signal, and an energy source operably coupled to the processor and configured to generate electrosurgical energy. The processor is configured to activate the energy source in accordance with a generator control signal received by the controller interface. The disclosed electrosurgical generator may include a memory operably coupled to the processor, wherein the processor is further configured to store a calibration parameter in the memory in accordance with a generator control signal received by the controller interface. The processor may be further configured to activate the energy source in accordance with a stored calibration parameter. In an embodiment, the electrosurgical measurement system is integral to the electrosurgical generator, which, in turn, enables the electrosurgical generator to perform self-testing and self-calibration."
For additional information on this patent, see: Orszulak, James H.; McGraw, Steven E.. System and Method for Electrosurgical Generator Power Measurement. U.S. Patent Number 9375247, filed March 16, 2011, and published online on June 28, 2016. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=9375247.PN.&OS=PN/9375247RS=PN/9375247
Keywords for this news article include: Covidien LP.
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