Systems and methods for measuring tissue impedance through an electrosurgical cable

• US 9,655,670 B2
• Filed: 02/14/2014
• Issued: 05/23/2017
• Est. Priority Date: 07/29/2013
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Covidien LP (Medtronic Plc)
• Inventors: Waskiewicz, Alexander M., Larson, Eric J., Ford, Carolyn G.
• Primary Examiner(s): Stoklosa, Joseph
• Assistant Examiner(s): Kim, Eunhwa
• Application Number:
  US14/180,965
• Publication Number:
  US 20150032098A1
• Time in Patent Office: 1,194 Days
• CPC Class Codes: A61B 18/1233 with circuits for assuring patient safety
• CPC Class Codes: A61B 18/1442 Probes having pivoting end effectors, e.g. forceps
• CPC Class Codes: A61B 18/16 Indifferent or passive electrodes for grounding
• CPC Class Codes: A61B 2018/00577 Ablation
• CPC Class Codes: A61B 2018/00607 Coagulation and cutting with the same instrument
• CPC Class Codes: A61B 2018/00875 Resistance or impedance

Abstract

The electrosurgical systems and methods of the present disclosure include a tissue resistance measurement system that compensates for capacitive parasitics in a cable connecting an electrosurgical generator to and electrosurgical cable to estimate the real resistance of a tissue load. The electrosurgical generator includes an output stage coupled to an electrical energy source and generates electrosurgical energy. The electrosurgical generator includes a plurality of sensors sensing a voltage and current of the electrosurgical energy and a controller controlling the output stage. The controller includes a calculator that calculates a real part of an impedance based on the sensed voltage and current, an estimator that estimates a resistance of the tissue using a solution to a quadratic equation that is a function of the real part of the impedance, and a control signal generator configured to generate a control signal for the output stage based on the resistance of the tissue.

Claims

1. An electrosurgical generator for delivering electrosurgical energy to a tissue via an electrosurgical cable and an electrosurgical instrument, the electrosurgical generator comprising:

an output stage coupled to an electrical energy source and configured to generate the electrosurgical energy to the electrosurgical instrument;

a plurality of sensors configured to sense a voltage waveform and a current waveform of the electrosurgical energy; and

a controller configured to control the output stage to generate a desired level of the electrosurgical energy, the controller comprising;

a calculator configured to calculate a real part of an impedance based on the sensed voltage and current waveforms;

an impedance compensator configured to modify a target impedance profile using a solution to a quadratic equation that models reactive components of the electrosurgical cable; and

a control signal generator configured to generate a control signal to control the output stage so that the calculated real part of the impedance tracks the modified target impedance profile,

wherein the solution to the quadratic equation is

2. The electrosurgical generator according to claim 1, wherein the resistance of the tissue is a larger solution to the quadratic equation when a phase difference between the voltage waveform and the current waveform is less than or equal to −

45 degrees, or a smaller solution when the phase difference is greater than −

45 degrees.

3. The electrosurgical generator according to claim 1, wherein the reactive components of the electrosurgical cable is modeled as an inductor in series with the tissue and a shunt capacitor in parallel with the tissue.

4. The electrosurgical generator according to claim 1, further comprising an inductor coupled to the output stage and tuned to a shunt capacitance and a series inductance of the electrosurgical cable so that the calculated real part of the impedance is sufficiently resistive.

5. The electrosurgical generator according to claim 4, wherein the shunt capacitance of the electrosurgical cable is a capacitance value measured when electrodes of the electrosurgical instrument are not in contact with tissue.

6. The electrosurgical generator according to claim 4, wherein an inductance value of the inductor is equal to

7. The electrosurgical generator according to claim 4, wherein an inductance value of the inductor is equal to

8. A method of controlling an electrosurgical generator that delivers electrosurgical energy to a tissue via an electrosurgical cable and an electrosurgical instrument, the method comprising:

sensing a voltage waveform and a current waveform of the electrosurgical energy;

calculating a real part of an impedance based on the sensed voltage and current waveforms;

modifying a target impedance profile using a solution to a quadratic equation that models reactive components of the electrosurgical cable; and

generating a control signal to control an output from an output stage of the electrosurgical generator so that the calculated real part of the impedance tracks the modified target impedance profile,

wherein the solution to the quadratic equation is

9. The method according to claim 8, wherein the resistance of the tissue is a larger solution to the quadratic equation when a phase difference between the voltage waveform and the current waveform is less than or equal to −

45 degrees, or a smaller solution when the phase difference is greater than −

45 degrees.

10. The method according to claim 8, wherein the reactive components of the electrosurgical cable are modeled as an inductor in series with the tissue and a shunt capacitor in parallel with the tissue.

11. The method according to claim 8, further comprising an inductor coupled to the output stage and tuned to a shunt capacitance and a series inductance of the electrosurgical cable so that the calculated real part of the impedance is sufficiently resistive.

12. The method according to claim 11, wherein the shunt capacitance of the electrosurgical cable is a capacitance value measured when electrodes of the electrosurgical instrument are not in contact with tissue.

13. The method according to claim 11, wherein an inductance value of the inductor is equal to

14. The method according to claim 11, wherein an inductance value of the inductor is equal to

15. A non-transitory computer-readable storage medium storing a program that, when executed by a processor, performs a method of controlling an electrosurgical generator that delivers electrosurgical energy to tissue via an electrosurgical cable and an electrosurgical instrument, the method comprising:

sensing a voltage waveform and a current waveform of the electrosurgical energy;

calculating a real part of an impedance based on the sensed voltage and current waveforms;

modifying a target impedance profile using a solution to a quadratic equation that models reactive components of the electrosurgical cable; and

generating a control signal to control an output from an output stage of the electrosurgical generator so that the calculated real part of the impedance tracks the modified target impedance profile,

wherein the solution to the quadratic equation is