Changes in systolic time intervals during stepwise increasing hypoxia.

Determinations of the reciprocal value of the square of the pre-ejection period (1/PEP-2) and the pre-ejection period/left ventricular ejection time-ratio (PEP/LVET-ratio) during stepwise increasing hypoxia showed in seven mongrel dogs in a decrease in PEP/LVET-ratio and an increase in 1/PEP-2 as an expression of a stimulation of the cardiac function. Significant changes were not observed before the arterial oxygen tension (Pao2) was below 40 mmHg. During severe hypoxia (Pao2 15-20 mmHg), some deterioration in the systolic time intervals occurs with time, but a stimulation persists at the time of death compared to the prehypoxic values.