Pulmonary hypertension and right ventricular hypertrophy caused by intermittent hypoxia and hypercapnia in the rat.

This study reports the effects in an animal model of intermittent exposure to hypoxic, hypercapnic gas mixture on pulmonary artery pressure, packed cell volume, ventricular weights, and lung growth. Rats were exposed in chambers for 8 hours to an inspired O2 fraction of 0.10 and an inspired CO2 fraction of 0.06 in alternation with exposure for 16 hours to room air during 21 to 22 days. Control animals were exposed in chambers for 8 hours to compressed air at flow rates similar to those for the test animals, then for 16 hours to room air. Packed cell volume, right ventricular systolic pressure, and the ratio of the right ventricular weight to the weight of the left ventricle plus septum were all significantly greater in the test animals than in the control animals. Lung volume, alveolar number, and surface area were also significantly increased, but only when adjusted for body weight. The increase in right ventricular weight appeared to be due in part to the fact that right ventricular pressure was still increased 16 hours after removal of the hypoxic-hypercapnic gas mixture. The cause of this sustained increase in right ventricular systolic pressure is unclear.