Fast pulse thermal cautery probe and method

We claim:

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/.degree.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.

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DESCRIPTION

1. Technical Field

This invention relates to the coagulation of vascularized tissues, and more particularly to a miniaturized thermal cautery probe which is endoscopically deliverable and which applies precisly controlled heat to such tissues during a relatively short period.

2. Background Prior Art

The use of heat for the cauterization of bleeding wounds dates back to ancient times. Perhaps the simplest and most basic thermal cauterization technique involves the application of a hot iron to a bleeding wound. While this technique is somewhat effective in cauterizing large, external wounds, the technique is not applicable to internal wounds. Nor is the technique sufficiently precise or delimited to provide adequate cauterization without excessive tissue damage.

In the present century, the use of radio frequency electric current traveling through a portion of the body has been widely used to stop bleeding. The essential ingredient in radio frequency cauterization is the dissipation of electrical energy in resistive tissue. This dissipated electrical energy is converted into heat, which produces a rise in temperature of the tissue and blood. The plasma proteins in blood are denatured in a temperature range of from 50.degree. to 100.degree. C., producing a sticky or congealed mass of protein. This process is familiar in the cooking of egg white. Other processes may take place when tissue is heated. For example, vessels may contract or shrink, thereby further reducing the flow of blood.

Several radio frequency current generators are now commercially available and are widely used by surgeons for both cutting and coagulating tissue. Since the electrical current flow follows the path of least resistance, the resulting thermal damage, or necrosis, may at times be unpredictable, too deep and uncontrolled. The rationale for using radio frequency current for bleeding control is that the frequency is above that which would cause neuromuscular stimulation and yet permit sufficient power dissipation to produce a rapid rise in temperature. Thus, used properly, electrical shock does not occur and coagulation is accomplished.

There is currently much interest in the control of bleeding using the modern fiberoptic endoscope, which permits visualization and therapy in hollow organs of the body through a slender tube. Hollow channels with a few millimeters of inside diameter permit the insertion of instruments for the administration of therapy such as the coagulation of bleeding. Some investigators have reported good success using radio frequency coagulation through the endoscope in a clinical setting. But this technique has not been widely used in practice because of its inherent risks. Several groups have directed a laser beam through an endoscope using a special optical wave-guide with good success in both animals and humans. However, the high cost of laser coagulators and the as-yet unproven benefit in a controlled clinical trial are slowing the widespread adoption of this technique. Other problems associated with laser coagulators arise from the difficulty in precisely directing the laser beam to a moving target, the existence of optical hazards and the need for a gas injection system to wash away overlying blood. Furthermore, simple laser coagulators do not simultaneously apply heat and pressure to the wound; and the combination of heat and pressure is considered to be more effective than heat alone.

More recently, a miniaturized thermal probe has been developed which is endoscopically deliverable. This probe, which is described in an article by Protell, et al., "The Heater Probe: A New Endoscopic Method for Stopping Massive Gastro-Intestinal Bleeding" Gastroenterology, 74: 257-62 (1978), includes a heating coil mounted in a small cylindrical body with a thermocouple. The output of the thermocouple is compared to a temperature reference level, and the difference is used to control the power to the probe to achieve a preset probe temperature. In use, the probe is heated to the preset value and applied to the wound for a number of periods, each of approximately one second in duration. Alternatively, the cold probe is applied directly to the bleeding site, turned on and held there for a predetermined period after reaching a target temperature. The principal problem associated with the latter technique is the inability of the probe to reach coagulating temperature with sufficient speed and to then cool itself with sufficient speed to prevent excessive penetration of the heat by diffusion. Effective coagulation requires that the bleeding site be adequately heated. However, avoidance of thermal necrosis requires that the heat not penetrate too deeply. The only technique providing adequate heating of the bleeding site without producing excessive heat penetration is heating the bleeding site at a high temperature for an extremely short period of time. Presently existing thermal probes are not able to meet these requirements. The problem does not stem from an inability to heat the probe with sufficient speed as much as it does from an inability to cool the probe with sufficient speed. Any probe can be heated rapidly by merely utilizing a sufficiently large heater. However, the probe can be cooled only by the tissue with which it is in contact. Conventional probes have been incapable of being cooled by the surrounding tissue with sufficient speed due to their relatively high thermal mass.

Attempts have been made to design thermal cautery probes which are heated by passing a current through the body of the probe itself instead of through a separate heating element. An example of such probes is disclosed in U.S. Pat. No. 3,886,944, issued to Jamshidi. The disadvantages of such probes are twofold: first, the unavailability of a satisfactory probe material and, second, the nonuniformity of the probe temperature.

The choice of a probe material presents a problem because the resistance of the material must be high enough to dissipate sufficient power and the strength of the material must be high enough to withstand forces applied to the probe by the tissue and other objects. The Jamshidi probe utilizes a Nichrome alloy or stainless steel as the probe material. Either material has a relatively low resistivity, thereby making it difficult for the probe to dissipate sufficient power without applying a great deal of current to the probe. While probes requiring high current are acceptable under some circumstances, they are unacceptable where the probe is to be endoscopically deliverable since the high currents require wires which are larger than the endoscope channels. In fact, a probe having a resistance less than about 0.5 ohm will generally require more current than endoscopically deliverable power leads are capable of carrying.

A probe fabricated of a low-resistivity material can dissipate adequate power from relatively low current only by making the material extremely thin so that the resistance of the probe is high. Yet a probe having an extremely thin shell does not have sufficient strength to withstand clinical use.

A probe having a relatively thick shell of a higher resistivity or semiconductive material would be capable of dissipating adequate power at acceptably low currents. However, a material having these properties and which is inexpensive, easily worked, and sufficiently sturdy does not appear to be available.

The second disadvantage metioned above--the nonuniformity of probe temperature--is illustrated in the Jamshidi patent. In the Jamshidi probe, current flows outwardly from the center of the probe tip and then along the sides of the probe. The current density--and hence the power dissipation--varies from a maximum at the center of the probe to a minimum at the sides of the probe. As a result, the temperature of the probe decreases from a maximum at the center of the probe.

DISCLOSURE OF THE INVENTION

The primary object of the invention is to provide a thermal cautery probe having a heat capacity which is sufficiently low to allow rapid heating and cooling, thereby effectively coagulating vascularized tissue without undue thermal necrosis.

It is another object of the invention to provide a thermal probe which is powered for a predetermined period while measuring and displaying the total energy delivered to the probe during that period.

It is another object of the invention to provide a thermal cautery probe which is powered by a relatively low current.

It is another object of the invention to provide a low thermal mass cautery probe which has a uniform temperature distribution.

It is still another object of the invention to provide a thermal probe which receives a predetermined value of energy while measuring and displaying the duration of the period during which the energy is delivered.

It is yet another object of the invention to provide a low heat capacity cautery probe which receives energy over a relatively short period in the form of a large number of relatively short, equal energy pulses.

It is another object of the invention to provide a heating element for a thermal cautery probe which inherently provides an indication of the temperature of the probe's active heat transfer portion.

It is a further object of the invention to provide a washing system for a thermal cautery probe which effectively washes blood from the wound without interfering with cauterization, thereby facilitating identification of the bleeding site.

It is a still further object of the invention to provide a thermal cautery probe which does not have a tendency to adhere to coagulated tissue.

These and other objects of the invention are provided by an electrically powered thermal probe including an active heat-transfer portion having a low heat capacity which is in direct thermal contact with a heating element so that heat is transferred principally by conduction. The probe is heater active during a heating period having a duration of less than five seconds. Yet sufficient power is applied to the heat-transfer portion during the heating period to coagulate tissue, and the low heat capacity of the heat-transfer portion allows rapid cooling after the heating period. The effective impedance of the heater is greater than 0.5 ohm so that the heater can be powered through power lines that are capable of extending through the channels of an endoscope. The energy is delivered in the form of a large number of relatively short pulses, each delivering the same quantity of energy to the probe. The probe may be used in either of two modes. In a first mode the energy to be delivered to the probe is preset and the duration of the period during which the pulses are delivered is displayed. Accordingly, a down-counter is preset to a number indicative of the energy to be delivered, and each heating pulse decrements the down-counter until a zero count is reached. During this period, an oscillator is gated to an up-counter and the contents of the counter is displayed to indicate the duration of the period during which the heating pulses were delivered. In a second mode, the duration of the period that the heating pulses are applied to the probe is preset, and the energy delivered to the probe is displayed. Accordingly, the down-counter is preset to a number indicative of the period during which the pulses are to be delivered, and an oscillator is gated to the down-counter when the pulses are being delivered until a zero count is reached. Meanwhile, the heating pulses are applied to the up-counter, and the contents of the counter is displayed to indicate the energy delivered to the probe during the heating period. The heating element for the probe is preferably a controlled breakdown diode, such as a zener or avalanche diode, which provides good heat dissipation at low currents and has a breakdown voltage which is temperature dependent so that it provides an electrical indication of probe temperature. The probe temperature indication is used to inhibit the delivery of heating pulses to the probe where the temperature of the probe exceeds a target value. A plurality of water jets, which are circumferentially spaced about the body of the probe, direct water along the probe sidewalls in an axial direction, thereby clearing blood from the bleeding site. Finally, the end of the probe is coated with a special compound to prevent the probe from adhering to coagulated tissues.

In operation, one of the two operating modes is selected and the cauterization time or cauterization energy is preset, depending upon which mode is selected. The probe is then applied to the wound while cold, and a switch is activated to apply power to the probe. The low heat capacity of the probe's active heat-transfer portion allows it to quickly reach a sufficient temperature to effectively cauterize the wound and to rapidly cool after power is removed to prevent excessive thermal penetration, thereby minimizing necrosis.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of the fast pulse thermal cautery probe in operation;

FIG. 2 is an exploded isometric view of the thermal cautery probe;

FIG. 3 is an isometric view of the assembled thermal cautery probe;

FIGS. 4A and 4B is a schematic of the circuitry for supplying power to the thermal cautery probe;

FIG. 5 is a cross-sectional view taken along the line 5--5 of FIG. 3.; and

FIG. 6 is a graph showing the temperature at the heat transfer surface of the probe.

BEST MODE FOR CARRYING OUT THE INVENTION

The fast pulse thermal cautery probe is illustrated in use in FIG. 1. The probe includes a power supply and display unit 10 having a front panel 12 containing switches and indicators illustrated in greater detail in the enlarged view. A specially constructed catheter 14 extends from the power supply and display unit 10 to a headpiece 16 of a conventional fiberoptic endoscope 18 extending into the mount of a patient P to, for example, the patient's stomach. The headpiece 16 typically includes an eyepiece through which a surgeon S views internal cavities. However, the headpiece 16 may alternatively interface with various optical devices of conventional design. These devices may produce an image on a screen 20 of the position of the probe 22 within the stomach of the patient P. The endoscope 18 typically includes one or more passages or channels extending in parallel with the fiberoptic wave guide to allow various devices to be inserted into internal organs of a patient. The catheter 14 extends through one of these channels to the end of the endoscope 18 within an internal organ. A surgeon S may then position the probe 22 against a lesion such as an ulcer by manipulating actuator knobs generally positioned on the headpiece 16 of conventional endoscopes 18. The endoscope channels are necessarily limited in diameter so that the diameter of the power leads for applying power to the probe are also limited. In practice, the diameter of the power leads is limited to a size which is capable of delivering sufficient current for cauterization to a probe having a resistance of at least about 0.5 ohm. A probe having a lower resistance must receive a current which is in excess of that which endoscopically deliverable power leads are capable of efficiently carrying without producing excessive heating of the endoscope.

A foot switch 28 is also connected to the power supply and display unit 10 through a lead 29. As explained in greater detail hereinafter, the surgeon S actuates the foot switch 28 to apply power to the probe 22 after the probe has been applied to the lesion. A second switch, operating in conjunction with the switch 28, may be actuated to supply a washing fluid to the probe.

As best illustrated in the enlarged view of FIG. 1, the panel 12 includes an on-off switch 30 for applying power to the unit 10 and a mode switch 32 for selecting either a "time" mode or an "energy" mode. In the time mode, heating pulses are applied to the probe 22 for a period having a duration determined by the number preset with conventional thumb wheel switches 34. At the end of the period, the total energy delivered to the probe 22 during that period is shown on a conventional digital indicator 36. In the energy mode, the energy to be delivered to the probe each time the switch 28 is activated is seleted by the thumb wheel switches 34, and the duration of the period during which the pulses are delivered is shown on the indicator 36. The temperature of the probe during the heating period in either mode is selected by a temperature control knob 33.

The probe 22 is illustrated in assembled condition in FIG. 3. It is composed of an elongated cylindrical shell 40 having a smooth, round-ended forward portion and a cylindrical body 42 containing a number of circumferentially spaced-apart cleaning fluid nozzles 44. The catheter 14 abuts the body 42 of the probe 22 and supplies cleaning fluid to the nozzles 44 and heating pulses to an internal heating element in the shell 40, as explained in greater detail hereinafter.

The internal structure of the probe 22 is illustrated in greater detail in FIGS. 2 and 5. This structure is best explained in the context of the manufacturing procedure for the probe. Initially, a coaxial cable 50 is prepared by trimming a portion of an insulating sheath 52 back from an underlying coaxial metal braid 54, a coaxial dielectric insulator 56 and a center conductor 58. In a similar manner, the braid 54 is trimmed back from the underlying insulator 56 and conductor 58, and the insulator 56 is trimmed back from the underlying conductor 58. As a result, each component of the cable 50 is accessible.

After the cable 50 has been prepared as explained above, the body 42 of the probe 22 is loosely slipped over the cable 50, and the insulator 56 and center conductor 58 are inserted through a bore 60 of a coaxial braid anchor 62 with the braid 54 loosely fitting inside a cylindrical portion at the rear of the braid anchor 62. The braid 54 is then soldered to the walls of the bore 60 by conventional means to electrically and mechanically connect the braid anchor 62 to the braid 54 of cable 50.

A spring mount 102 is then soldered to the coax center conductor 58 and a spring 100 is soldered onto the spring mount 102. Next, the braid anchor 62 is slipped into the body 42 with resilient fingers 109 of the braid anchor 62 frictionally engaging the inside surface of the body 42. Next the assembly is placed in a vertical position and a small amount of epoxy is applied between spring mount 102 and braid anchor 62 to form a seal 70 having a shoulder 72. The seal 70 provides electrical insulation and a seal to prevent fluids from entering the interval cavity of the probe. A teflon seal 108 is then pressed into body 42 with the shoulder on seal 108 resting against the fingers 110 of body 42. The spring 100 now lies inside of the cylindrical bore 106 of seal 108 with the axial tip 105 of spring 100 protruding from the bore 106 a small amount.

After the rearward components of the probe 22 are prepared and assembled as explained above, the internal components of the shell 40 are assembled. As best illustrated in FIG. 5, the shell 40 is generally hollow to form a cylindrical cavity 80 surrounded by thin, cylindrical side walls 82. The front end of the shell 40 is a solid hemispherical heat transfer portion 84 having a planar, circular rear face 86. A controlled breakdown diode, such as a zener or avalanche diode 90, is then bonded within the cavity 80 against the rear face 86. The diode 90 includes a diode chip 92, a pair of cylindrical conductors 94, 96 connected to opposite faces of the diode chip 92, and an insulative coating 98 surrounding the diode chip 92 and conductors 94, 96. Although a diode 90 having the structure shown could be specially fabricated, the diode 90 is preferably formed by severing the ends of commercially available diodes having a cylindrical shape. A simpler and easier technique would be to solder a commercially available diode chip directly to cavity 80 against the rear face 86, although other heating devices, such as a thin film resistor or conventional diode, may also be used. However, such alternative heating devices generally require substantially more current to dissipate the same amount of power. For example, a 14-volt zener diode dissipates about twenty times more power for a given current than a diode having 0.7-volt forward breakdown voltage.

The diode 90 is mounted in the shell 40 by first tinning the rear face 86 of the heat transfer portion 84 with solder. The exposed surface of one diode conductor 94 is then also tinned and placed in the shell 40, preferably using an alignment jig to position the diode 90 at the center of the shell 40. The shell 40 is then heated to fuse the solder on the rear face 86 and the solder on the diode conductor 94. The diode 90 is thus in direct thermal contact with the heat-transfer portion 84 so that heat is transferred from the diode 90 to the heat-transfer por