Effect of intermittent normoxia on chronic hypoxic pulmonary hypertension, right ventricular hypertrophy, and polycythemia in rats.

The effect of continuous and intermittent normoxia on chronic hypoxic pulmonary hypertension, right ventricular hypertrophy, and polycythemia was studied in rats. After 4 wk in a hypobaric chamber (380 mmHg), the mean right ventricular blood pressure (Prv) was 29.2 +/- 1.8 (SEM) mmHg (n = 10) compared with 11.1 +/- 1.1 mmHg in 10 untreated control animals. After recovery in room air (24 h/day) for 6 wk, the Prv was significantly reduced to 21.2 +/- 3.5 mmHg (n = 6). Recovery using intermittent normoxia (8 and 16 h/day) for 6 wk did not reduce Prv. In 10 control rats, the ratio of right to left ventricular weight (RV/(LV + S) was 28.8 +/- 1.1%. After 4 wk of chronic hypoxia the RV/(LV + S) was 48.5 +/- 2.4% (n = 10). Recovery using complete normoxia for 6 wk significantly reduced the RV/(LV + S) to 32.8 +/- 1.9% (n = 6). Intermittent normoxia (8 and 16 h/day) did not reduce RV/(LV + S). Chronic hypoxia (380 mmHg) for 4 wk elevated the hematocrit from 35 to 66%. The polycythemia was reversed by recovery using continuous normoxia for 6 wk. Intermittent normoxia (8 and 16 h/day) was ineffective.