High frequency electrosurgical apparatus for thermal coagulation of biologic tissues

High frequency electro surgical apparatus for thermal coagulation of biologic tissues comprising a high frequency electric generator having a fundamental frequency (f.sub.1) of operation and having an output circuit equipped with a coagulation electrode for contact with biological tissues of a patient and with switching means for manual or automatic activation of said generator to produce an output of high frequency current and for automatic switching off of a coagulation operation in dependence upon changes in electric conductivity of said tissues of said patient, and further comprising, in accordance with the invention:

• electrical monitoring means (25) having an input coupled to said output circuit of said high frequency generator for monitoring amplitude fluctuations of the output of said high frequency electric generator during each coagulation operation by monitoring at least one of the current and voltage of said output, said monitoring means including means (50, 51, 52) for deriving from the output high frequency current (I.sub.HF) of said generator, a voltage proportional to the amplitude fluctuations (A(t)2) of said high frequency current (I.sub.HF), first detection means (53, 55, 58, 60, 62) coupled for being responsive to the output of said voltage deriving means for producing, at an output of said first detection means, a first DC voltage (U.sub.a) proportional to said amplitude fluctuations (A(t)) of said high frequency current (I.sub.HF) and second detection means (54, 56, 61, 63) coupled for response to rising portions of fluctuations of said high frequency current and constituted as a peak value detector, for producing, at an output of said second detection means, a second DC voltage (U.sub.b) which rises proportionally to the rising portion of fluctuations of said high frequency current;
• voltage comparison means (67) coupled for response to said respective outputs of said first and second detection means for comparing said first DC voltage (U.sub.a) and a predetermined adjustable fraction (kU.sub.b) of said second DC voltage and producing a comparison result signal at an output of said comparison means;
• a bistable switching control circuit (70) coupled to said output of said comparison means and connected for being set by the comparison result signal of said voltage comparison means (67) when said first DC voltage (U.sub.a) becomes smaller than said predetermined fraction (kU.sub.b) of said second DC voltage and thereby to produce an output control signal (Q);
• means coupled for response to said bistable circuit (70) and connected to said high frequency generator for shutting off the output of said high frequency generator in response to said output control signal (Q) of said bistable circuit (70), and
• means (23) for reactivating, and usable for initially activating, the output of said high frequency generator in response to operation of a manual switch (21), to operation of an automatic switch (22) or to both said manual switch and said automatic switch.