The effects on the respiratory and circulatory systems of rabbits of pulsed currents from two sources have been studied. The sources were an industrial high voltage test-set (source A) and an automobile ignition system (source B).
When the fore-limb to fore-limb pathway was used, source A produced complete arrest of respiration at the highest output voltage, 5kV (corresponding to a current of 392 mA), and at a pulse repetition rate of 30 per second. Progressive reduction of either of these factors resulted in progressively less interference with respiration. With the fore-limb to hind-limb pathway complete arrest of respiration occurred at an output voltage of 2 kV (corresponding to a current of 140 mA) and at a pulse repetition rate of 30 per second. Again progressive reduction of either current or pulse repetition rate resulted in progressively less interference with respiration, although at 30 per second even with the lowest voltage setting (1 kV; 64 mA) only diaphragmatic respiration occurred. Source B used on either pathway up to a pulse repetition rate of 16 per second did not cause complete arrest of respiration whether the current was taken straight from the ignition coil or off the distributor.
Neither source caused ventricular fibrillation either when delivering pulses at a preset rate or when the pulses were timed to coincide with successive T waves of the E.C.G. In these experiments the trains of pulses falling on the T waves lasted about 10 seconds.
With both sources the current and voltage waveforms were similar and in phase. With source A increase in current was directly related to increase in applied voltage. These findings suggest that under these experimental conditions, with minimum contact resistance, the animal impedance is resistive with no significant reactance.
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