Relative organ blood flow in rats exposed to intermittent high altitude hypoxia.

Circulating blood volume, cardiac output and relative organ perfusion changes were studied, using the Sapirstein method of 86RB tissue uptake, in male 75-day-old rats exposed to intermittent high altitude hypoxia (gradually up to 7000 m, 4 h daily, 5 days a week; the total number of exposures was 24). Intermittent hypobaric exposure caused a significant rise of the erythrocyte volume, whereas the plasma volume remained unchanged. The relative perfusion of the left and particularly of the right ventricular myocardium, as well as of the spleen, liver, lung, small intestine and skeletal muscle, was significantly higher. The cardiac output determined in other experimental animals similarly treated was significantly higher after 24 exposures to the intermittent high altitude hypoxia. We suggest that these changes are triggered by tissue hypoxia and a greater blood flow demand.