A resistively heated thermally cutting and coagulating surgical instrument which may be employed with a conventional electrosurgical generator having bipolar output ports and a bipolar cable. The instrument utilizes a heating element which is heated to a predetermined upper temperature limit while in still air under a starting condition. Under this condition, heat dissipation by radiation, convection, and conduction through the instrument itself provides a high temperature end form of regulation. Under a subsequent working condition wherein the heated component or element is in contact with the tissue, heat dissipation is by thermal conduction both into the tissue and through the thermally conductive components of the instrument. A preferred heating element is formed with a ferromagnetic material which, when at the upper limit temperature is maintained at a value restricted to a temperature below curie temperature and which does not invoke surface oxidation or scaling within the time interval of heating experienced in the starting condition. However, the temperature is high enough to sustain a temperature effective for cutting and coagulation when in the working condition. A handle is employed which contains impedance matching circuit components. In one embodiment, the heating component of the instrument incorporates an integrally formed probe which is retained at lower temperatures through the use of a current restricting neck.

Resistively heated cutting and coagulating surgical instrument

An improved performance ferromagnetic self-­regulating heater. Constant alternating current is applied to a layered structure including at least one ferromagnetic layer. One or more layers of non-magnetic material is added to the ferromagnetic layer in such a way that the power factor of the heater is very sig­nificantly increased above its value in the absence of at least one of the layers. The alternating current flows through the different layers in varying quantities depending on layer composition, temperature and Curie point of the ferromagnetic layer. The structure generates heat by resistive heating as a function of the power applied. In one embodiment a single layer of non-­magnetic, high-resistance material is in intimate electrical and thermal contact with one surface of the ferromagnetic material. Below the effective Curie temperature of the ferromagnetic layer the current is mainly confined in the non-magnetic layer which heats with greater efficiency due to better resistive and impe­dance characteristics. In a second embodiment a further non-magnetic, low-resistance layer is added to the opposite surface of the ferromagnetic material. Here the majority of the current is switched from the high-­resistance to the low-resistance layer as the heater approaches effective Curie. By these means impedance matching circuit losses can be substantially reduced and energy is saved in high power systems based on the power factor.

High power self-regulating heater

A self-redulanting heater includes an electrically-conductive substrate (11), having a magnetic surface layer (13) of one skin depth, folded 180 degrees to define two heater sections joined by a fold section. The magnetic material has a considerably higher resistance than the substrate material. The surfaces of the two sections clad with the surface layer are in closely spaced parallel relation and connected in series by the fold section (23) such that a constant amplitude alternating energizing current flows in opposite directions through the two sections at any instant of time to thereby establish an electric field between the two heaters. The field concentrates current flow at the two facing surfaces. Depth of the current is determined by the skin effect phenomenon and increases significantly at temperatures above the Curie temperature of the magnetic material.

Generating electromagnetic fields in a self regulating temperature heater by positioning of a current return bus

A power supply for use with resistively-heated surgical instruments is provided, wherein the desired operating conditions of the surgical instrument are determined by a set-point determination circuit in combination with a set-point indicator element. The power supply includes an impedance matching circuit and current step-up transformer for reducing power loss in the cable connecting the surgical instrument to the power supply. A method of regulating the output of a power supply used with resistively-heated surgical instruments is also provided.

Regulated-current power supply and methods for resistively-heated surgical instruments

An instrument for use in endoscopic surgery is provided. The instrument has a heating element with a working surface for providing hemostasis at an auto-regulated temperature. The working surface may include a tapered edge for providing thermally-enhanced cutting and a non-stick coating for operating the instrument at low auto-regulation temperatures. A process for making the instrument is also provided. Additionally, a method of performing endoscopic surgery on a patient's internal tissue is also provided.

Endoscopic instrument with auto-regulating heater and method of using same

The present invention achieves constant voltage at radio frequencies to drive a constant voltage to constant current converter, by employing a tightly coupled d.c. feedback loop to control the voltage via a transformer to the drain of a FET operated as a Class C amplifier in the saturated mode whereby among other advantages, the amplifier can withstand, without damage, very high VSWRs. Control is affected by a high gain differential amplifier which compares a d.c. voltage derived from the r.f. output of the system against a highly stable d.c. voltage reference. A controller, responding to the output of the differential amplifier causes a first level of voltage to be applied to the drain of the FET when the system is not loaded and causes a second voltage varying between said first level and a higher level when the system is loaded. In the lower voltage condition the controller is effectively removed from the system so that it does not have to drop a high voltage to a low voltage; the low voltage being supplied effectively from a separate source.

Steven J. Smith

Papers

Constant current r.f. generator