Fibrillating Parameters of Direct and Alternating (20 Hz) Currents Separately and in Combination--An Experimental Study

In an experimental Study on anesthetized mongrel dogs, the current levels of dc and 20-Hz ac, both singly and in combination, necessary to evoke ventricular fibrillation were investigated. The following shock durations were investigated: for dc; 50, 100, 200, 500, 1000, and 2000 ms, for 20-Hz ac; 100, 200, 500, 1000, and 2000 ms, and for combination dc and ac shocks; 200, 500, 1000, and 2000 ms. It is shown that threshold fibrillating currents of a given shock duration and type are apparently more nearly log normally than normally distributed. The tests of linear combinations of ac and dc resulted in the following working principles. The hazard of any shock of whatever combination of ac and dc is essentially the same as that of a pure ac shock of 1) the same duration and peak-to-peak current if the shock duration is 0.5 s or longer, or 2) the same peak current if the duration is 0.2 s (and possibly shorter).