Generation of Rectangular Biphasic Waveform to Decrease Defibrillation Threshold for External Defibrillator

Abstract

Studies have shown that de¯brillation threshold for current amplitude of biphasic truncated exponential (BTE) waveform has a hyperbolic strengthÀduration relationship. Theoretical and experimental results have shown that decreasing the tilt of BTE waveforms decreases the de¯brillation threshold. On the other hand, low peak current waveform reduces probability of myocardium damage and burn. Therefore, achieving a waveform with low tilt and low peak current is desired. All DC de¯brillators use a capacitor to store and deliver required energy. Because of capacitor discharging nature, the tilt of waveforms is high. In rectilinear biphasic waveform (RBW), which was generated by ZOLL M-series de¯brillator, the tilt of the¯rst phase was decreased using an adjustable resistor connected in series with current path. But the de¯brillator cannot keep the current constant in the second phase and in the both phases for high transthoracic impedances (TTI) either. In this paper, for solving these problems, a circuit that generates rectangular biphasic waveform is designed. In this circuit,¯ve resistors are used and connected in series. Then an IGBT switch is connected to each resistor in parallel. Also, control of minimum current ripple is applied in order to decide which resistors should be worked in each time. The circuit is simulated in MATLAB/Simulink and a prototype model is constructed. Results demonstrate that the tilt of the waveform is notably reduced to a value less than 10%.