Chronic intermittent hypercapnic hypoxia increases pulmonary arterial pressure and haematocrit in rats

Sleep-disordered breathing is associated with pulmonary hypertension and ra ised haematocrit. The multiple episodes of apnoea in this condition cause c hronic intermittent hypoxia and hypercapnia but the effects of such blood g as changes on pulmonary pressure or haematocrit are unknown. The present in vestigation tests the hypothesis that chronic intermittent hypercapnic hypo xia causes increased pulmonary arterial pressure and erythropoiesis. Rats were treated with alternating periods of normoxia and hypercapnic hypo xia every 30 s for 8 h per day for 5 days per week for 5 weeks, as a model of the intermittent blood gas changes which occur in sleep-disordered breat hing in humans. Haematocrit, red blood cell count and haemoglobin concentra tion were measured each week and systemic and pulmonary arterial blood pres sure and heart weight were measured after 5 weeks. In relation to control, chronic intermittent hypercapnic hypoxia caused a s ignificant increase in systemic (104.3 +/-4.7 mmHg versus 121.0 +/- 10.4 mm Hg) and pulmonary arterial pressure (20.7 +/-6.8 mmHg versus 31.3 +/-7.2 mm Hg), right ventricular weight (expressed as ratios) and haematocrit (45.2 /-1.0% versus 51.5 +/-1.5%). It is concluded that the pulmonary hypertension and elevated haematocrit as sociated with sleep-disordered breathing is caused by chronic intermittent hypercapnic hypoxia.