Fast pulse thermal cautery probe and method

• US 4,449,528 A
• Filed: 07/20/1981
• Issued: 05/22/1984
• Est. Priority Date: 03/20/1980
• Status: Expired due to Term

• Current Assignee: University of Washington
• Original Assignee: University of Washington
• Inventors: Auth, David C., Lawrence, Dale M., Majoch, Tim R.
• Primary Examiner(s): Cohen, Lee S.
• Application Number:
  US06/285,366
• Time in Patent Office: 1,037 Days
• Field of Search: 128/303.1, 128/303.13, 128/303.14, 128/303.17, 128/303.18, 128/399-401, 219/229, 219/230, 219/233, 219/240, 219/241, 219/242, 219/501
• US Class Current: 606/31
• CPC Class Codes: A61B 17/3203 Fluid jet cutting instruments
• CPC Class Codes: A61B 18/08 by means of electrically-heated probes
• CPC Class Codes: A61B 18/082 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 2018/00404 Blood vessels other than those in or around the heart
• CPC Class Codes: A61B 2018/00761 Duration
• CPC Class Codes: A61B 2018/0097 Cleaning probe surfaces
• CPC Class Codes: A61B 2018/087 using semiconductors as heating element

Abstract

A miniaturized, endoscopically deliverable thermal cautery probe for cauterizing internal vessels. The probe is applied to tissues cold, and a large number of electric heating pulses of equal energy are then applied to an internal heating element in the probe. The probe has an internal heating element in direct thermal contact with an active heat-transfer portion that has a low heat capacity to insure quick heating and subsequent cooling, thereby adequately coagulating tissue while minimizing heat penetration and resulting tissue damage. The electrical power applied to the probe is continuously measured and is terminated when the energy delivered reaches a preset value. The number of such pulses applied to the probe (and hence the total energy delivered) may be preset while the duration of the period during which the pulses were applied is displayed. Alternatively, the duration of the period during which such pulses are applied to the probe may be preset while the number of pulses applied (and hence the total energy delivered) is displayed. The heating element for the probe is a controlled breakdown diode which has a breakdown voltage that is a function of its temperature so that the temperature can be controlled. The heating element has a resistance of greater than 0.5 ohm to provide adequate power dissipation with relatively low currents. A washing fluid, preferably flowing along the outside of the probe toward its tip, cleans blood from the tissue to be coagulated to make the source of blood more readily visible.

Claims

1. An apparatus for heating tissue without causing deep tissue damage, comprising:

an electrically powered thermal probe having a heating element and an active heat-transfer portion which is in direct thermal contact with said heating element so that heat is transferred to said heat-transfer portion principally by conduction, said heat-transfer portion having a unit heat capacity of less than 1 joule/°

C. to allow said probe to cool from a temperature sufficiently high to coagulate within a sufficiently short period to prevent excessive heat penetration; and

power-generating means connected to the heating element of said probe applying an electric current pulse to said heating element during a heating cycle having sufficient energy to allow said probe to coagulate tissue during said heating cycle.

2. The apparatus of claim 1 wherein the effective resistance of said heating element is greater than 0.5 ohm so that said probe may dissipate sufficient power for coagulation from a relatively low current.

3. The apparatus of claim 1 wherein said heating element is a controlled breakdown diode connected to said power-generating means in reverse bias configuration.

4. The apparatus of claim 1 wherein the temperature range of said probe, when in contact with tissue, is between an initial temperature and a peak temperature, and wherein said apparatus further includes control means for controlling the duration of said electric current pulse so that the period during which the temperature of said probe rises from 40 percent of said range and subsequently falls to 40 percent of said range is less than 5 second.

5. The apparatus of claim 1 wherein said current is in the form of a train of pulses, each of which delivers a predetermined quantity of energy to said probe.

6. The apparatus of claim 5, further including temperature-sensing means for providing an electrical indication of the temperature of said probe, and inhibit means for preventing said current pulses from being generated when the temperature of said probe is above a predetermined value such that the frequency of said current pulses is adjusted to maintain the temperature of said probe constant during said heating cycle.

7. The apparatus of claim 5, further including an up-counter having a clock input connected to said power-generating means so that said up-counter is incremented by said current pulses, and display means for displaying the contents of said counter such that, at the termination of said heating cycle, said display means indicates the energy applied to said probe during said heating cycle.

8. The apparatus of claim 7, further including an oscillator generating a train of timing pulses, a down-counter, gating means for applying said timing pulses to said down-counter during said heating cycle, preset means for presetting said down-counter with a manually selectable number, and disable means for terminating said heating pulses when said down-counter decrements to zero, whereby the duration of said heating cycle may be manually preset.

9. The apparatus of claim 5, further including a down-counter having a clock input to which said current pulses are applied, preset means for presetting said down-counter with a manually selectable number, and disable means for terminating said current pulses when said down-counter decrements to zero, whereby the total energy delivered to said probe during said heating cycle may be manually preset.

10. The apparatus of claim 9, further including an oscillator generating a train of timing pulses, an up-counter, gating means for applying said timing pulses to said up-counter during said heating cycle, and display means for displaying the contents of said up-counter such that said display means indicates the duration of said heating cycle.

11. The apparatus of claim 5, further including gating means connected to said power-generating means for selectively applying said electric current pulses to said probe, voltage measuring means for providing a first signal which is proportional to the voltage across said probe, current measuring means for providing a second signal which is proportional to the current through said probe, multiplying means for multiplying said first and second signals together to generate an output which is proportional to the power delivered to said probe, an integrator connected to the output of said multiplying means for generating a signal which is proportional to the energy delivered to said probe, comparator means receiving the output of said integrator for disabling said gating means for a predetermined period when the energy delivered to said probe exceeds a predetermined value, thereby removing electric power from said probe, and reset means for resetting said integrator after said gating means is disabled such that a plurality of equal energy electric pulses are applied to said probe during said heating cycle.

12. The apparatus of claim 11, further including temperature regulating means for controlling the temperature of said probe during said heating cycle, said temperature regulating means comprising a temperature sensor generating a feedback voltage which is proportional to the temperature of said probe, temperature comparison means receiving said feedback voltage for disabling said gating means when the temperature of said probe exceeds a preset value whereby the frequency of said pulses is adjusted to maintain the temperature of said probe constant.

13. The apparatus of claim 12 wherein said heating element is a diode having a breakdown voltage which is proportional to its temperature, and wherein said temperature sensor includes means for applying a relatively low test current to said probe during said predetermined disabling period such that the voltage across said probe indicates the temperature of said probe during said disabling period.

14. The apparatus of claim 1 wherein said probe comprises a generally cylindrical, electrically conductive shell including a forward, active heat-transfer portion and a cylindrical cavity having a rear opening, and wherein said heating element comprises a diode mounted in said cavity in direct thermal contact with the active heat transfer portion of said probe.

15. The apparatus of claim 14 wherein the diode mounted in said cavity has a pair of opposed planar, conductive faces, one of which is soldered to the active heat-transfer portion of said shell while an electrically conductive spring bears against the other face of said diode.

16. The apparatus of claim 15 wherein said probe is connected to said power-generating means by a coaxial cable having a center conductor surrounded by a layer of insulation which is, in turn, surrounded by a coaxial braided conductor, and wherein a cylindrical braid anchor having its outer surface contacting said probe shell is soldered to said braided conductor, and wherein an electrically conductive spring mount is soldered to the end of said center conductor, said spring being mountd on said spring mount to establish a circuit from the center conductor, said spring, diode and shell to said braided conductor.

17. The apparatus of claim 4 wherein said shell is coated with a low-adhesion material to prevent said probe from sticking to tissue after coagulation.

18. The apparatus of claim 17 wherein said low-adhesion material is Dow Corning R-4-3117 conformal coating.

19. The apparatus of claim 17 wherein said low-adhesion material is a primer for Dow-Corning R-4-3117 conformal coating.

20. The apparatus of claim 14, further including a plurality of nozzles circumferentially spaced about the sides of said shell and pointing in an axial direction, and means for delivering a washing fluid to said nozzles such that said washing fluid flows axialy along the sides of said shell to said active heat-transfer portion in order to clean tissue to be coagulated and facilitate the identification of bleed points.

21. The apparatus of claim 20 wherein the inlets to said nozzles are at the rear end of said shell and said probe is connected to said power-generating means by coaxial cable, and wherein said means for delivering a washing fluid to said nozzles includes a tube tightly surrounding the rear portion of said shell and loosely surrounding said coaxial cable to provide a passage between said tube and cable, and a pump having an outlet communicating with said passage to deliver said washing fluid thereto.

22. The apparatus of claim 21 wherein said pump operates in a pulsating manner in order to apply said washing fluid to its outlet in pulses so that washing fluid pulses from said nozzles to clean blood from said tissue.

23. The apparatus of claim 1 wherein the heating cycle during which current is applied to said probe has a duration of less than three seconds.

24. An apparatus for heating tissue without causing deep tissue damage, comprising:

an electrically powered thermal probe having an internal heating element, said probe including an active heat-transfer portion in direct thermal contact with said heating element so that heat is transferred to said heat-transfer portion principally by conduction, said heat-transfer portion having a unit heat capacity which is sufficiently low so that the period during which the temperature of said probe rises from 40 percent of range between an initial temperature and a peak temperature, and subsequently falls to 40 percent of said range, can be less than 5 seconds; and

power-generating means connected to the heating element of said probe applying an electric current to said heating element during a heating cycle having a duration of less than 3 seconds and sufficient energy to allow said probe to coagulate tissue during said heating cycle.

25. The apparatus of claim 24 wherein said heating element is a controlled breakdown diode connected to said power-generating means in reverse bias configuration.

26. The apparatus of claim 24 wherein said heating element has an effective resistance of greater than 0.5 ohm so that said probe may dissipate sufficient power for coagulation from a relatively low current.

27. A method of heating tissue without causing deep tissue damage, comprising:

placing a thermal cautery probe in contact with said tissue, said probe having a thermal mass which is sufficiently low that tissue in contact with said probe reduces its temperature from a peak value to 50 percent of said peak value in less than one second after power is removed from said probe;

applying electric power to said probe for a heating period of less than 5 seconds, said power being of sufficient magnitude in relation to the thermal mass of said probe to cauterize said tissue during said heating period; and

removing said probe from said tissue at any time after said heating period since the low thermal mass of said probe allows said probe to quickly cool after said heating period to prevent deep pentration of said tissue regardless of the duration that said probe is applied to said tissue.

28. The method of claim 27 wherein said electric power is applied to said probe during said heating period in the form of a plurality of equal energy pulses.

29. The method of claim 28, further including the steps of measuring the temperature of said probe and adjusting the frequency of said pulses to maintain said temperature constant.

30. The method of claim 27, further including the step of applying a washing fluid to said tissue in a pulsating fashion during said heating period.