Abstract:
Surgical cutting instrument includes an electrically heated cutting edge and an automatic control system for maintaining the cutting edge at a constant high temperature for sterilizing the blade, cutting tissue, and cauterizing the incised tissue to reduce hemorrhage from the cut surfaces of the tissues (hemostasis).

Description:
RELATED APPLICATIONS 
     This application is a division application of U.S. patent application Ser. No. 05/534,756 filed Dec. 2, 1974, now U.S. Pat. No. 4,089,336, which is a continuation of U.S. patent application Ser. No. 05/063,645 filed Aug. 13, 1970, now abandoned, which is a continuation of U.S. patent application Ser. No. 04/681,737 filed Nov. 9, 1967, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The control of bleeding during surgery accounts for a major portion of the total time involved in an operation. The bleeding that occurs when tissue is incised obscures the surgeon&#39;s vision, reduces his precision and often dictates slow and elaborate procedures in surgical operations. Each bleeding vessel must be grasped in pincer-like clamps to stop the flow of blood and the tissue and vessel within each clamp must then be tied with pieces of fine thread. These ligated masses of tissue die and decompose and thus tend to retard healing and promote infection. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention provides a surgical cutting instrument having a cutting edge which is electrically heated to a constant high temperature for sterilizing the blade, cutting the tissue and cauterizing the surfaces of the incision, thereby allowing surgery to be more rapidly performed. This is accomplished in accordance with the illustrated embodiment of this invention by providing an electrically heated element disposed as the cutting edges of he blade and by providing a control system witch maintains the cutting edge at a high substantially constant temperature during its use. The hot cutting edge according to the present invention decreases the amount of tissue that is damaged and reduces the tendency of the instrument to stick to the heated tissue in the incision. The material used in the electrically heated cutting edge has a negative temperature coefficient of resistance to insure that electrical power applied to the cutting edge is dissipated primarily in the regions thereof which tend to be cooled by contact with tissue. The temperature at which the cutting edge of the blade is maintained depends upon such factors as the nature of the tissue to be cut, the speed of cutting desired, the degree of tissue coagulation desired, and the non-adherence of the blade to the incised tissue and generally is maintained between 300°-1000° Centigrade for typical incisions. The instantaneous temperature of the cutting edge is monitored by measuring the resistance of the heating element itself or through the use of thermocouple elements disposed in the blade near the cutting edge, and the monitoring signal thus derived controls the power applied to the heating element. The handle of the cutting instrument is thermally insulated from the blade to permit comfortable use of the instrument and the handle and blade with its electrically heated cutting edge are detachable for easy replacement and interchangeability with blade, scoops and cutting edge of various shapes and sizes determined by the nature of the incision to be made and the tissue to be cut. 
    
    
     DESCRIPTION OF THE DRAWING 
     FIG. 1 is a schematic diagram showing the cutting instrument and the temperature control system therefor, according to the preferred embodiment of the present invention, and FIGS. 2 and 3 are pictorial views of other embodiments of cutting instruments according to the present invention for use with circuitry as shown in FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1 of the drawing, there is shown the surgical cutting instrument  9  connected to a temperature-measuring and power-controlling system  11 . The cutting instrument  9  includes a thin ceramic card  12  in the desired shape of a surgical cutting blade which is detachable from the handle or holder  10 . An electrically heated element  13  is disposed along the leading edge of the card  12  to form its cutting edge and is electrically connected to the control circuit through the cable  14  and the connectors  16 . The element  13  may be a single filament attached to the edge of the card  12 , for example, using conventional ceramic welding materials or may be a layer of electrically conductive material vapor-deposited along the edge of the card  12 . Also, the heating element  13  may have sufficient cross-sectional area to be self-supporting as shown in FIG. 2, so that the blade  18  is formed entirely by the element  13  alone. The material used in the element  13  ideally should have a negative temperature coefficient of resistance so that as selected portions of the element cool when in contact with tissue, the resistance of such portions will increase and thereby localize the portions of the element  13  in witch additional power supplied by the control system will be dissipated. The temperature of the element may thus be maintained substantially constant over the entire length thereof as portions of the element  13  contact tissue. Suitable materials having negative temperature coefficients of resistance include silicon carbide, carbon, boron silicate and such semiconductor materials as silicon and germanium. Of course, material having a positive coefficient of resistance may also be used. However, when materials of this type are used, care should be taken to shape the element  13  so that substantially the entire length of the element  13  contacts tissue in use. This is required to prevent the additional power supplied by the control system  11  from being dissipated in the portions of the element which do not cool when in contact with tissue and, hence, which have higher resistance than the cooler portions. For cutting applications where it is not convenient to shape the element  13  so that its entire length is in contact with tissue each time it is used, the element  13  may consist of a plurality of electrically isolated elements  13  and  13 ′, as shown in FIG. 3, with each of the elements  13  and  13 ′, connected to a separate temperature measuring and power-controlling system of the type shown in FIG.  1 . 
     The resistance of the element  13  is included in a bridge circuit  15  which is connected to receive alternating signal appearing on lines  17  and  19 . The level of alternating signal appearing on lines  17  and  19  and, hence, the power applied to element  13  is determined by the conduction angles of the controlled rectifiers  21  and  23  which are connected in conduction opposition in parallel across the series resistor  25 . Power is supplied to the control system  11  through the primary and secondary windings  26  and  27  of power input transformer  29 . Alternating line signal  28  applied to the transformer  29  is stepped down typically to about 24 volts for the safety of the patient and the surgeon and the average current flow per half cycle of the alternating signal is determined in part by the series resistor  25  and by the conduction angle of a silicon-controlled rectifier  21 ,  23 . 
     The operating temperatures the element  13  may be determined by adjusting one of the resistors, say resistor  31 , in the bridge circuit  15 . Any variation in the operating temperature of element  13  front a set value unbalances the bridge  15  and produces a control signal  33  across the diagonal terminals  35 ,  37  of the bridge circuit  15  which is either in phase or out of phase with the applied line signal, depending upon whether the operating temperature of the element is above or below the set value of operating temperature. A phase-shifting network  39  is connected to the output terminals of the bridge circuit  15  for applying the error signal  44  with respect to ground to the input of error amplifier  41  with a small amount of phase shift relative to the applied line signal  28 . This provides control of the conduction angle of the controlled rectifiers  21 ,  23  over a greater portion of a half cycle of the applied line signal. The output of amplifier  41  is applied to the threshold detectors  43 ,  45  which respond to the amplified error signal attaining selected value slightly above and below zero. The threshold detectors  47  and  49  thus activate the trigger pulse generators  47  and  49  at the proper times in alternate half cycles of applied line signal  28  to apply conduction-initiating pulses to the gate electrodes  51 ,  53  of the controlled rectifiers  21 ,  23 . Thus, increased conduction angle of the controlled rectifiers  21  and  23  increases the power applied to the element  13  to maintain the element at a preselected operating temperature as the element tends to cool down in contact with sin tissue. However, if the operating temperature of the element  13  should exceed the set value due, for example, to thermal overshoot upon removal of the element  13  from contact with skin tissue, the phase of the error signal  33  with respect to the applied line signal reverses. This causes the trigger pulse generators to supply conduction-initiating pulses to the gate electrodes of the controlled rectifiers  21 ,  23  during alternate half cycles when these rectifiers are back biased. This causes a decrease in the power delivered to the element  13  with a concomitant drop in its operating temperature to about the set value of operating temperature. When this occurs, the proper phase relationship between error signal and line signal is restored and power is again supplied to the element  13 . Conversion of the control system  11  for operation with elements  13  having negative or positive temperature coefficients of resistance merely requires that the trigger pulses from the generators  47  and  49  be applied through reversing switch  55  to the proper controlled rectifier  21 ,  23  during the forward-biasing half cycle of line signal  28 . 
     It should be apparent that other temperature control systems may also be used to maintain the operating temperature of the element  13  substantially constant at a preselected value. For example, a thermocouple sensor may be disposed on the card  12  in close proximity with the element  13  or a thermocouple element may ever be formed on element  13  using another material or dissimilar work function to form the thermocouple junction. The signal from such thermocouple may then be used to control the operating temperature of the element  13  by controlling the power supplied thereto.