Abstract: An external defibrillator (8) with an output circuit (14) having four legs arrayed in the form of an "H" (an "H-bridge") is disclosed. Each leg of the output circuit contains a solid-state switch (31, 32, 33, 34). By selectively switching on pairs of switches in the H-bridge, a biphasic defibrillation pulse may be applied to a patient. The switches in three of the legs of the H-bridge output circuit are preferably silicon controlled rectifiers (SCRs). Gate drive circuits (51, 53, 54) are coupled to the SCRs to bias the SCRs with a voltage that allows the SCRs to remain turned-on even when conducting low current. The switch in the fourth leg is preferably a pair of insulated gate bipolar transistors (IGBTs) coupled in series. A gate drive circuit (52) is coupled to the gate of the IGBTs to provide a slow turn-on and a fast turn-off of the IGBTs.

Abstract: A defibrillator method and apparatus wherein a patient's measured transthoracic impedance (TTI) is used to control the amount of energy contained in a defibrillation pulse applied to the patient. Prior to delivering a defibrillation pulse, the patient's TTI is measured by an impedance measuring circuit (11). The patient's TTI may also be measured during delivery of a prior defibrillation pulse. A microprocessor (23) uses the measured patient TTI to control the shape of the defibrillation pulse by controlling: (i) the phase duration of the defibrillation pulse; and (ii) the voltage level to which the defibrillator's capacitor bank (15) is charged. The defibrillation pulse shape is controlled so that the energy conveyed by the defibrillation pulse to the patient is near or exceeds a desired value. The desired value may be set by an operator via an energy selector (25).

Abstract: An external defibrillator with a microprocessor for testing the integrity of an output circuit prior to and during the delivery of a multiphasic defibrillation pulse from an energy storage capacitor coupled to the output circuit is disclosed. The output circuit contains a plurality of switches. The integrity of the output circuit and the output switches is determined by selectively monitoring the changes in the voltage level on the energy storage capacitor while certain tests or functions are being performed. A scaling circuit steps down the voltage level of the high-energy storage device so that it can be measured and monitored by the microprocessor. The microprocessor may compensate for the failure of an output switch by locating a usable set of output switches and using them to provide a discharge path through the output circuit for application of a monophasic pulse.

Abstract: An external defibrillator (8) with an output circuit (14) having four legs arrayed in the form of an "H" (an "H-bridge") is disclosed. Each leg of the output circuit contains a solid-state switch (31, 32, 33, 34). By selectively switching on pairs of switches in the H-bridge, a biphasic defibrillation pulse may be applied to a patient. The switches in three of the legs of the H-bridge output circuit are preferably silicon controlled rectifiers (SCRs). Gate drive circuits (51, 53, 54) are coupled to the SCRs to bias the SCRs with a voltage that allows the SCRs to remain turned-on even when conducting low current. The switch in the fourth leg is preferably a pair of insulated gate bipolar transistors (IGBTs) coupled in series. A gate drive circuit (52) is coupled to the gate of the IGBTs to provide a slow turn-on and a fast turn-off of the IGBTs.