Non-linear control systems and methods for heating and ablating body tissue

• US 5,702,386 A
• Filed: 06/28/1996
• Issued: 12/30/1997
• Est. Priority Date: 11/08/1991
• Status: Expired due to Term

• Current Assignee: EP Technologies Incorporated (Boston Scientific Corporation)
• Original Assignee: EP Technologies Incorporated (Boston Scientific Corporation)
• Inventors: Panescu, Dorin, Swanson, David K., Stern, Roger A.
• Primary Examiner(s): Bahr, Jennifer
• Assistant Examiner(s): PEFFLEY, MICHAEL F
• Application Number:
  US08/670,985
• Time in Patent Office: 550 Days
• Field of Search: 606/27-34, 606/37-42, 606/45-52, 607/100-102
• US Class Current: 606/34
• CPC Class Codes: A61B 18/00 Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body eye surgery A61F9/007; ear surgery A61F11/00
• CPC Class Codes: A61B 18/1206 Generators therefor
• 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 2017/00017 Electrical control of surgical instruments
• CPC Class Codes: A61B 2017/00084 Temperature
• CPC Class Codes: A61B 2017/00101 using an array of thermosensors
• CPC Class Codes: A61B 2017/00292 mounted on or guided by flexible, e.g. catheter-like, means
• CPC Class Codes: A61B 2017/003 Steerable
• CPC Class Codes: A61B 2017/00482 with a code
• CPC Class Codes: A61B 2018/00083 low, i.e. electrically insulating
• CPC Class Codes: A61B 2018/00095 high, i.e. heat conducting
• CPC Class Codes: A61B 2018/00101 low, i.e. thermally insulating
• CPC Class Codes: A61B 2018/00178 Electrical connectors
• CPC Class Codes: A61B 2018/00351 Heart
• CPC Class Codes: A61B 2018/00357 Endocardium
• CPC Class Codes: A61B 2018/00577 Ablation
• CPC Class Codes: A61B 2018/00642 with feedback, i.e. closed loop control
• CPC Class Codes: A61B 2018/00666 using a threshold value
• CPC Class Codes: A61B 2018/00684 using lookup tables
• CPC Class Codes: A61B 2018/0069 : using fuzzy logic
• CPC Class Codes: A61B 2018/00702 : Power or energy
• CPC Class Codes: A61B 2018/00779 : Power or energy
• CPC Class Codes: A61B 2018/00791 : Temperature
• CPC Class Codes: A61B 2018/00797 : measured by multiple temperature sensors
• CPC Class Codes: A61B 2018/00803 : with temperature prediction
• CPC Class Codes: A61B 2018/00815 : measured by a thermistor
• CPC Class Codes: A61B 2018/00827 : Current
• CPC Class Codes: A61B 2018/00869 : Phase
• CPC Class Codes: A61B 2018/00875 : Resistance or impedance
• CPC Class Codes: A61B 2018/00892 : Voltage
• CPC Class Codes: A61B 2018/00916 : with means for switching or controlling the main function of the instrument or device
• CPC Class Codes: A61B 2018/00988 : Means for storing information, e.g. calibration constants, or for preventing excessive use, e.g. usage, service life counter
• CPC Class Codes: A61B 2018/124 : switching the output to different electrodes, e.g. sequentially
• CPC Class Codes: A61B 2018/1253 : monopolar
• CPC Class Codes: A61B 2018/126 : bipolar
• CPC Class Codes: A61B 2018/1425 : Needle
• CPC Class Codes: A61B 2018/1435 : Spiral
• CPC Class Codes: A61B 2090/0803 : Counting the number of times an instrument is used
• CPC Class Codes: A61B 2562/08 : Sensors provided with means for identification, e.g. barcodes or memory chips
• CPC Class Codes: A61M 2205/273 : preventing reuse, e.g. of disposables
• CPC Class Codes: A61M 2205/6018 : providing set-up signals for the apparatus configuration
• CPC Class Codes: A61M 2205/6027 : Electric-conductive bridges closing detection circuits, with or without identifying elements, e.g. resistances, zener-diodes
• CPC Class Codes: A61M 2205/70 : with testing or calibration facilities
• CPC Class Codes: A61M 2230/50 : Temperature

Abstract

Systems and methods employ an energy emitting electrode to heat tissue. The systems and methods control the application of energy to the electrode using adjustments that take into account, in a non-linear fashion, changes in monitored operating conditions.

Claims

1. An apparatus for supplying energy to an electrode for ablating tissue comprising

a generator adapted to be electrically coupled to an electrode to supply energy to the electrode for ablating tissue, and

a controller coupled to the generator to adjust power to the generator and thereby adjust energy supplied to the electrode, the controller comprising

a sampling element to monitor a selected operating condition resulting from supplying energy to the electrode and derive from it an operating value (V_D),

a processing element coupled to the sampling element to compare the derived operating value V_D to a preselected value (V_S) for the operating condition to establish an error signal (Δ

), where;

space="preserve" listing-type="equation">Δ

=V.sub.S -V.sub.D

an output element coupled to the processing element to incrementally adjust power to the generator according to the following expression;

space="preserve" listing-type="equation">Δ

P=f(S.sub.SCALE ×

Δ

)

where;

Δ

P is the incremental power adjustment;

f is a mathematical function; and

S_SCALE is a nonlinear scaling factor that equals a first value (X) when Δ

>

Z and equals a second value (Y), different than X, when Δ

<

Z, where Z is a desired Δ

.

2. An apparatus according to claim 1

wherein Y>

X.

3. An apparatus according to claim 1 or 2

wherein Z=0.

4. An apparatus according to claim 1

wherein the sampling element includes a sensing element supported in proximity with the electrode for measuring temperature at the electrode.

5. An apparatus according to claim 4

wherein the sampling element monitors changes in temperature measured by the sensing element over time to derive V_D.

6. An apparatus according to claim 5

wherein V_D comprises a temperature prediction for a future time derived from one or more temperatures measured by the sensing element.

7. An apparatus according to claim 1

wherein V_S remains essentially constant over time.

8. An apparatus according to claim 1

wherein the apparatus further includes means for changing the value of V_B and wherein V_B changes at least once as a function of time.

9. An apparatus for supplying energy to an electrode for ablating tissue comprising

a generator adapted to be electrically coupled to an electrode to supply energy to the electrode for ablating tissue, and

a controller coupled to the generator to adjust power to the generator and thereby adjust energy supplied to the electrode, the controller comprising

sampling means for monitoring operating conditions resulting from supplying energy to the electrode,

a first processing element coupled to the sampling means to derive a power control signal S_DERIVED based upon a first operation condition monitored by the sampling means,

a second processing element coupled to the sampling means to compare a second operating condition monitored by the sampling means with preselected criteria for the second operating condition and to generate an error signal (E) when the second operating condition fails to meet the preselected criteria, and

an output element coupled to the first and second processing elements to issue a command signal S_COMMAND to set power supplied to the generator,

wherein, absent the error signal E, S_COMMAND sets the power according to S_DERIVED, and

wherein, when the error signal E is generated, S_COMMAND sets the power at a prescribed low power condition (P_LOW), regardless of S_COMMAND, P_LOW being a value above zero.

10. An apparatus according to claim 9

wherein the sampling means includes a sensing element supported in proximity with the electrode for measuring temperature at the electrode,

wherein the second monitored operating condition includes a measurement of temperature at the electrode by the sensing element, and

wherein the preselected criteria includes an established maximum temperature value.

11. An apparatus according to claim 9

wherein the sampling means includes a sensing element supported in proximity with the electrode for measuring temperature at the electrode,

wherein the second monitored operating condition includes a measurement of temperature at the electrode by the sensing element, and

wherein the preselected criteria includes an established set temperature value adjusted by an established incremental value.

12. An apparatus for supplying energy to an electrode for ablating tissue comprising

a generator adapted to be electrically coupled to an electrode to supply energy to the electrode for ablating tissue, and

a controller coupled to the generator to adjust power to the generator and thereby adjust energy supplied to the electrode, the controller comprising

first sampling means for monitoring operating conditions resulting from supplying energy to the electrode,

second sampling means for deriving impedance resulting from supplying energy to the electrode,

a first processing element coupled to the first sampling means to derive a power control signal S_DERIVED based upon a first operation condition monitored by the first sampling means,

a second processing element coupled to the first processing element to compare a second operating condition monitored by the first sampling means with preselected criteria for the second operating condition and to generate an error signal (E) when the second operating condition fails to meet the preselected criteria, and

an output element coupled to the first and second processing elements to issue a command signal S_COMMAND to set power supplied to the generator,

wherein, absent the error signal E, S_COMMAND sets the power according to S_DERIVED, and

wherein, when the error signal E is generated, S_COMMAND sets the power at a prescribed low power condition (P_LOW), regardless of S_COMMAND, P_LOW being a value above zero to permit derivation of impedance by the second sensing means.

13. An apparatus according to claim 12

wherein the first sampling means includes a sensing element supported in proximity with the electrode for measuring temperature at the electrode,

wherein the second monitored operating condition includes a measurement of temperature at the electrode by the sensing element, and

wherein the preselected criteria includes an established maximum temperature value.

14. An apparatus according to claim 12

wherein the first sampling means includes a sensing element supported in proximity with the electrode for measuring temperature at the electrode,

wherein the second monitored operating condition includes a measurement of temperature at the electrode by the sensing element, and

wherein the preselected criteria includes an established set temperature value adjusted by an established incremental value.

15. An apparatus according to claim 9 or 12

wherein the second monitored operating condition includes a measurement of the power delivered to the generator, and

wherein the preselected criteria includes an established maximum power value.

16. A method for ablating body tissue comprising the steps of

applying ablating energy to an electrode,

monitoring a selected operating condition of the electrode and derive from it an operating value (V_D),

comparing the derived operating value V_D to a preselected set value (V_S) for the operating condition to establish an error signal (Δ

), where;

space="preserve" listing-type="equation">Δ

=V.sub.S -V.sub.D

issuing a command signal S_COMMAND to adjust power to the electrode above a zero value, thereby maintaining power to the electrode without interruption, where;

space="preserve" listing-type="equation">S.sub.COMMAND =f(S.sub.SCALE XΔ

)

where S_SCALE is a nonlinear scaling factor that equals a first value (X) when Δ

>

Z and equals a second value (Y), different than X, when Δ

<

Z, and Z is a desired Δ

.

17. A method according to claim 16

wherein Y>

X.

18. A method according to claim 16

wherein Z=0.

19. A method for ablating body tissue comprising the steps of

applying ablating energy to an electrode,

monitoring first and second operating conditions for the electrode, each operating condition resulting from applying ablating energy, the first operating condition being different than the second operating condition,

deriving a power control signal S_DERIVED based upon the first monitored operation condition,

comparing the second monitored operating condition with preselected criteria for the second operating condition to generate an error signal (E) when the second operating condition fails to meet the preselected criteria,

issuing a command signal S_COMMAND to set power supplied to the electrode,

wherein, absent the error signal E, S_COMMAND sets the power according to S_DERIVED, and

wherein, when the error signal E is generated, S_COMMAND sets the power at a prescribed low power condition (P_LOW), regardless of S_COMMAND, P_LOW being a value above zero.

21. A method according to claim 19 or 20

wherein the second monitored operating condition includes a measurement of the power delivered to the generator, and

wherein the preselected criteria includes an established maximum power value.

22. A method according to claim 19 or 20

wherein the second monitored operating condition includes a measurement of temperature at the electrode, and

wherein the preselected criteria includes an established maximum temperature value.

23. A method according to claim 19 or 20

wherein the second monitored operating condition includes a measurement of temperature at the electrode, and

wherein the preselected criteria includes an established set temperature value adjusted by an established incremental value.

20. A method for ablating body tissue comprising the steps of

applying ablating energy to an electrode,

monitoring first and second operating conditions for the electrode, each operating condition resulting from applying ablating energy, the first operating condition being different than the second operating condition,

measuring impedance resulting from applying ablating energy to the electrode, deriving a power control signal S_DERIVED based upon the first monitored operation condition,

comparing the second monitored operating condition with preselected criteria for the second operating condition to generate an error signal (E) when the second operating condition fails to meet the preselected criteria,

issuing a command signal S_COMMAND to set power supplied to the electrode,

wherein, absent the error signal E, S_COMMAND sets the power according to S_DERIVED, and

wherein, when the error signal E is generated, S_COMMAND sets the power at a prescribed low power condition (P_LOW), regardless of S_COMMAND, P_LOW being a value above zero so that measurement of impedance can continue.