SYSTEM AND METHOD FOR CONTROLLING POWER BASED ON IMPEDANCE DETECTION, SUCH AS CONTROLLING POWER TO TISSUE TREATMENT DEVICES

• US 20090030477A1
• Filed: 07/24/2008
• Published: 01/29/2009
• Est. Priority Date: 07/24/2007
• Status: Active Grant

• Current Assignee: Boston Scientific Scimed (Boston Scientific Corporation)
• Original Assignee: Asthmatx, Inc. (Boston Scientific Corporation)
• Inventors: Jarrard, Jerry
• Granted Patent: US 9,108,052 B2
• Time in Patent Office: Days
• US Class Current: 607/42
• CPC Class Codes: A61B 18/1206 Generators therefor
• CPC Class Codes: A61B 18/1233 with circuits for assuring patient safety
• CPC Class Codes: A61B 18/14 Probes or electrodes therefor
• CPC Class Codes: A61B 18/1492 having a flexible, catheter-like structure, e.g. for heart ablation A61B18/1477 takes precedence
• CPC Class Codes: A61B 2018/00214 Expandable means emitting energy, e.g. by elements carried thereon
• CPC Class Codes: A61B 2018/00267 having a basket shaped structure
• CPC Class Codes: A61B 2018/00541 Lung or bronchi
• CPC Class Codes: A61B 2018/00577 Ablation
• CPC Class Codes: A61B 2018/00595 Cauterization
• CPC Class Codes: A61B 2018/00642 with feedback, i.e. closed loop control
• CPC Class Codes: A61B 2018/00702 Power or energy
• CPC Class Codes: A61B 2018/00791 Temperature
• CPC Class Codes: A61B 2018/00875 Resistance or impedance
• CPC Class Codes: A61B 2018/00898 Alarms or notifications created in response to an abnormal condition
• CPC Class Codes: A61N 1/32 alternating or intermittent currents applying electric fields by inductive or capacitive coupling A61N1/40; microwave apparatus A61N5/02
• CPC Class Codes: A61N 1/36128 Control systems
• CPC Class Codes: A61N 1/36146 specified by the stimulation parameters

Abstract

A system and method of controlling the application of energy to tissue using measurements of impedance are described. The impedance, correlated to the temperature, may be set at a desired level, such as a percentage of initial impedance. The set impedance may be a function of the initial impedance, the size and spacing of the electrodes, the size of a targeted passageway, and so on. The set impedance may then be entered into a PID algorithm or other control loop algorithm in order to extract a power to be applied to a treatment device.

Claims

1. A method of controlling power supplied to an energy delivery device used to treat tissue of a human body, the method comprising:

determining an impedance value that correlates to a desired state of the treated tissue; and

identifying a power value based on the determined impedance value; and

controlling the energy delivery device using the identified power value.

2. The method of claim 1, further comprising:

determining an initial impedance value that correlates to a temperature of the tissue before treatment; and

determining the impedance value that correlates to the desired state by selecting the impedance value as a percentage less than 100 percent of the initial impedance value.

3. The method of claim 1, further comprising:

applying energy to the tissue of the internal passageway using the energy delivery device, wherein the applied energy relates to the identified power value.

4. The method of claim 1, wherein the power value is identified using a PID algorithm.

5. The method of claim 1, wherein the energy delivery device contains two or more electrodes placed proximate to two or more tissue locations and wherein determining the impedance value includes:

determining an impedance value at each of the tissue locations; and

averaging the impedance values at the tissue locations.

6. The method of claim 1, wherein the desired state comprises a temperature between 50 and 80 degrees Celsius.

7. The method of claim 1, wherein identifying a power value includes identifying the power value based on an inverse relationship between impedance and the state of the tissue.

8. A closed loop impedance feedback power control system, the system comprising:

an energy delivery apparatus having an electrode;

an energy supply apparatus that powers the energy delivery apparatus; and

an energy supply controller that controls the power from the energy supply apparatus to the energy delivery apparatus based on desired impedance values that correlate to temperatures that fall within a desired non-ablative range.

9. The system of claim 8, wherein the energy supply controller determines the desired impedance values based on initial impedance values.

10. The system of claim 8, wherein the desired impedance values are a percentage of an initial impedance value based on voltage and current measurements related to the energy delivery apparatus.

11. The system of claim 8, wherein the desired impedance values are between 70 percent and 90 percent of an initial impedance value.

12. The system of claim 8, wherein the desired impedance values are based on characteristics of the energy delivery apparatus.

13. The system of claim 8, wherein the desired impedance values are based on characteristics of a passageway that surrounds the energy delivery apparatus during treatment.

14. The system of claim 8, wherein the desired impedance values are based on a time rate change of an initial impedance value.

15. The system of claim 8, wherein the desired impedance values are based on an initial pulse impedance, an average pulse impedance, an ending pulse impedance, a rate of change of the pulse impedance, or a pulse energy.

16. A closed loop impedance feedback power control system used to treat tissue within an airway of a human lung, the system comprising:

an energy delivery device having an elongated body and an electrode unit having a plurality of electrodes; and

a control device, wherein the control device outputs power to the energy delivery device based on a difference between a desired impedance value and a present impedance value.

17. The system of claim 16, wherein the control device includes a PID algorithm that determines an output power value based on the difference between the impedance values.

18. The system of claim 16, wherein the desired impedance value is a percentage of an initial impedance value determined at a normal body temperature of the tissue.

19. The system of claim 18, wherein the initial impedance is based on geometry of the electrodes of the treatment device.

20. The system of claim 18, wherein the initial impedance is based on a diameter of the airway.

21. The system of claim 16, wherein the control device is configured to deliver energy in a bipolar or monopolar fashion.

22. The system of claim 16, wherein the control device is configured to deliver energy for an activation time period of less than 20 seconds.

23. The system of claim 16, wherein the desired impedance value correlates to a temperature within the range of 50-80 degrees Celsius.

24. The system of claim 16, wherein the output power is less than 40 Watts.

25. The system of claim 16, wherein the energy comprises radio frequency energy.

26. A method of delivering energy to tissue within an airway in a lung using an energy delivery apparatus, the method comprising:

transmitting a low energy pulse to the tissue to determine an initial impedance value;

determining a desired impedance value based on a desired tissue state related to the delivery of the energy and on the initial impedance value; and

adjusting power output to the energy delivery apparatus based on a difference between a current impedance value and the desired impedance value.

27. A method of adjusting the power output to an energy delivery device used to deliver energy to tissue at a first location in an airway of a patient, the method comprising:

identifying a difference between a current impedance value and a set impedance value; and

modifying the power output based on the identified difference between the current impedance value and the set impedance value.

28. The method of claim 27, wherein modifying the power output includes inserting the difference into a PID algorithm in order to determine a value of the power to output to the energy delivery device.

29. The method of claim 27, further comprising:

moving the energy delivery device to a second location in the airway;

determining a new set impedance value; and

repeating the identifying and modifying steps based on the new set impedance value.

30. A method of delivering energy to tissue within an airway in a lung using an energy delivery apparatus, the method comprising:

transmitting a pre-treatment low energy pulse to the tissue;

determining a desired impedance value based on one or more parameters of the transmitted low energy pulse; and

adjusting power output to the energy delivery apparatus based on a difference between a current impedance value and the desired impedance value.

31. The method of claim 30, wherein the one or more parameters of the low energy pulse include an initial pulse impedance, an average pulse impedance, an ending pulse impedance, a rate of change of the pulse impedance, or a pulse energy.