Studies of the electrocardiogram and the toxicity of cardiac glycosides in animals exposed to hyperbaric helium

Abstract The effects of hyperbaric helium on the toxicity of cardiac glycosides were investigated in animals equilibrated with 19.0 ata (atmospheres absolute) helium/0.2 ata oxygen in a hyperbaric chamber. Control animals were exposed to air at 1 ata, but otherwise were treated the same as pressurized animals. Restrained, unanesthetized rats with indwelling jugular vein catheters were infused with ouabain until cessation of respiratory movements occurred. Guinea pigs, anesthetized with Dial-urethane, received a slow iv infusion of either ouabain or digoxin, and the toxic effects of these drugs on the electrocardiogram (ECG) were monitored until asystole ensued. Studies with cats were essentially the same as those in guinea pigs, but only ouabain was infused. The ECG and heart rate were also observed during compression and throughout the equilibration period. Results of these experiments showed that pressurization alone had virtually no effect on heart rate or ECG in guinea pigs and cats. In addition, pressure did not alter the lethal dose in the rat or the doses required to elicit specific ECG disturbances in guinea pigs and cats. An effect of pressure on the chronotropic response to ouabain and digoxin was observed in guinea pigs, but this was considered to be relatively unimportant. Thus it appears that hyperbaric helium does not affect the toxicity of cardiac glycosides.