Abstract
Changes of the heart excitability were observed in dogs poisoned acutely with the inhalation of CO gas.
1) Due to the inhalation of 0.05 to 1% CO gas for 60 minutes, the remarkable prolongation of refractory periods was observed in all animals and the elevation of resting threshold was seen in a few animals. The lowering of heart excitability was shown not only during the gas inhalation but after its cessation. Then the strength-interval curve shifted to the right.
2) Due to the inhalation of 2.5% CO gas for 15 minutes, the heart excitability was decreased slightly during the gas inhalation and recovered soon by the inhalation of pure oxygen. Then the absolute refractory period was reduced.
It requires a definite time duration for which the CO-Hb level is maintained at a certainly high level, to produce the lowering of the heart excitability.
3) Lowering of the heart excitability continued and became severe after the cessation of gas inhalation. The disturbances of heart muscles due to CO poisoning may be attributed to disturbances of myoglobin and/or cytochrome c.
4) The reduction of absolute refractory period was observed by the inhalation of 2.5% CO gas for 15 minutes and this may be attributed to the compensatory function in the early stage of hypoxemia.
