Abstract: Non-insulated surgical instruments are referenced to the electrical potential of a patient during minimally invasive electrosurgery to prevent unintentional patient burns, should the surgical instruments become accidentally energized during the electrosurgical procedure. An auxiliary safety electrode separate from the primary return electrode is attached to the patient at a location separate from the attachment point of the primary return electrode. Each non-insulated surgical instrument is preferably attached to the auxiliary electrode by a separate electrical conductor. The electrical conductor transfers to the auxiliary electrode any electrical energy which is accidentally applied to the instrument during the course of the electrosurgical procedure. The size of the auxiliary electrode is sufficient to safely disperse the electrical charge without burning the patient.

Abstract: A preferred embodiment of a self-balancing reflectometer is disclosed in conjunction with a system including an RF source, an RF load, and an RF transmission channel that carries RF signals transmitted by the source to the load. The self-balancing reflectometer includes a load current sampler that generates a first sample signal related to load current by a first fixed value of gain and a load voltage sampler that generates a second sample signal related to load voltage by a voltage-responsive second variable value of gain. The first sample signal is subtracted from the second sample signal and the resulting difference signal is applied to the RF port of a double balanced mixer. The RF voltage signal appearing at the load is applied to the LO port of the mixer, which generates an IF signal that varies with both rapid load impedance modulation corresponding to load data and long term basal variations in load impedance unrelated to load data.

Abstract: Apparatus for monitoring the resistance of the return part of the patient circuit of either a dual foil or single foil return electrode according to a user's selection is disclosed. The apparatus measures the quality of the contact between the return electrode and the patient. A DC or AC converter provides a substantially DC voltage at its input that varies in relation to the resistance of the return part of the patient circuit at its AC output. Preferably, a constant current fed sinusoidal oscillator with a low pass filter at its DC output provides a substantially DC voltage related to the resistance at its AC input. An analog to digital converter converts the substantially DC voltage to a corresponding binary digital signal that is input to a programmed microprocessor. A manually operable set point switch coupled to the microprocessor is acatuated by the user which actuation establishes a resistance level with the pad (return electrode) in place on the patient.

Abstract: A liquid conductivity sensor which features simply and inexpensively driving the excitation transformer of a two-transformer/fluid-loop remote conductivity sensor with a square wave excitation signal provided by a digital timer and a flip-flop. Also disclosed is using an electrodeless conductivity sensor to sense conductivity of dialysate.

Abstract: An electrosurgical unit having a power source, and an amplifier which includes a bipolar transistor and a FET in series with the amplifier load. In cut and blend modes, the power output of the unit is controlled by a variable voltage applied to the base terminal of the bipolar transistor. In coagulation, fulgration, and bipolar modes the power output is controlled by a variable duty cycle voltage applied to the gate terminal of the FET.

Abstract: An electrosurgical unit having feedforward power regulation. In one embodiment there is an amplifier which produces a pulse modulated electrosurgical output signal. A microprocessor calculates an adjusted pulse width (duty cycle) just sufficient to account for the power changes due to voltage fluctuations. The microprocessor controls the pulse width of the gate voltage of a power transistor in the amplifier to regulate the amplifier output. In another embodiment the supply voltage is fed into the base drive circuitry of an amplifier power transistor through the photo-resistor side of an optoisolator. The lamp brightness of the optoisolator and thus the gain of the base drive circuitry is adjusted by the amplifier power level control. The nonlinearity of the optoisolator complements the nonlinearity of the amplifier so that the net gain in the amplifier drive at any power setting is just sufficient to account for the voltage fluctuation.

Abstract: An electrosurgical unit including voltage control circuitry which operates to limit the voltage at the electrosurgical electrodes when the unit is not in coagulation mode. The electrosurgical unit includes sensing circuitry for providing a signal representative of the voltage at the electrosurgical electrodes, a mode setting switch or dial for changing between a cut mode setting and a coagulation mode setting, a circuit for producing a mode signal, and an RF power generator responsive to the mode setting switch for providing a cut mode waveform at the electrode outputs when the mode setting switch is in cut mode and a coagulation mode waveform when the mode setting switch is in the coagulation mode setting. A voltage limiting circuit is responsive to the signal from the sensing circuitry and limits the voltage at the outputs when the electrosurgical unit in cut mode. Suppression circuitry responsive to the mode signal prevents the voltage limiting circuitry from operating in coagulation mode.

Abstract: A pneumatic tourniquet which automatically adjusts the pressure in the tourniquet cuff and in which the pressure adjustment is variable and depends on the sign and magnitude of the pressure error. There is an inflatable cuff, a motor and pump for inflating the cuff, a valve for deflating the cuff, a transducer for sensing the pressure in the cuff, and a switch for setting a desired cuff pressure. A microprocessor is responsive to signals from the transducer and switches to calculate a duty cycle related to the pressure error. The microprocessor periodically applies a signal to the motor or valve during the calculated duty cycle to provide an adjustment to cuff pressure related to pressure error. The microprocessor also is responsive to motor speed and accumulated error history to provide further adjustments to the pressure.

Abstract: An automatic tourniquet with an improved occlusion detector. A pump and valve for inflating and deflating a tourniquet cuff are connected to a first port. A pressure transducer for sensing the pressure in the cuff is connected to a second port. A pair of pressure differential switches, which activate an alarm when a pressure difference developes across them, are connected anti-parallelly between the pump/valve and the transducer. The differential switches also deactivate the pump/valve upon detection of an occlusion.

Abstract: An automatic tourniquet including a mechanism for inflating and deflating a cuff, a pressure sensing mechanism, and a mechanism for displaying the pressure. The pressure sensing mechanism includes a pressure transducer producing a pair of digital signals, and a mechanism for adjusting the signals so that the pressures at which the transitions between the digital quanta occur for one signal are different from the pressures at which the transitions occur for the other signal. The mechanism for adjusting includes a mechanism for setting the signals to be equal at a selected pressure, and a mechanism for offsetting the signals from each other by a voltage corresponding to one-half a digital quantum. The offset signals are summed by a microprocessor to produce a display with twice the resolution of the individual signals.