Resting values of left ventricular work to coronary blood flow ratio in rats exposed to intermittent high altitude hypoxia and swimming.

Total hemodynamic values and left ventricular blood flow were studied using Sapirstein's method of 86Rb uptake in female rats 24 h after a last exposure to high altitude. A stimulated altitude of 1350 m was used, initial exposure being for 30 min, gradually increased by 30 min daily up to 330 min daily for 5 days a week; the total number of exposures was 32. In another animal group the hypobaric exposure was combined with swimming in water at 37 degrees C. In both experimental groups the cardiac output and stroke volume increased, and in rats undergoing swimming the total peripheral resistance decreased as well. In the rats exposed to intermittent hypoxia only, left ventricular blood flow increased by about the same proportion as the cardiac output. The ratio of left ventricular work to coronary blood flow was significantly increased. In rats exposed to the combined influence of hypoxia and swimming, the increase in left ventricular blood flow did not match either the increase in cardiac output, or the weight gain of the left ventricle. The ventricular work to coronary blood flow ratio was the same as in controls.