Respiratory and Cardiovascular Function in Patients with Severe Pulmonary Hypertension

Abstract

The significance of impaired lung function and its contribution to disability in hypertensive pulmonary vascular disease are obscure. Hemodynamics, ventilation, lung volumes, ventilation blood flow relations, and steady state carbon monoxide diffusion capacity (Dco) were studied in 12 patients with severe pulmonary hypertension of varied etiology. There was normal ventilation, increased residual volume, high residual/total lung capacity ratio, chronic hyperventilation, respiratory alkalosis, increased physiologic dead space, arterial O2 unsaturation at rest, and elevated end tidal-arterial PCO2 gradients with exercise. Dco at rest was normal or only slightly decreased, mean 13.7 [plus or minus]3.4 ml/min/mm Hg. The increase of DCO with exercise was normal and one exception, a patient with maximal Dco at rest and maximal alveolar ventilation and QO2 with mild exercise. The data are consistent with a distribution defect characterized by under and/or nonperfusion of ventilated alveoli. There is no restrictive ventilatory pattern or obstruction to airflow. Analysis of the alveolar-arterial pO2 difference and O2 tension-time curves along the pulmonary capillary suggest the absence of alveolar capillary block or insufficient contact time. With exercise, a reduced contact time between alveolar gas and pulmonary capillary blood might contribute to incomplete equilibration of the capillary blood. It is concluded that evaluation of pulmonary gas exchange at different exercise levels best reflects the overall degree of disability in patients with hypertensive pulmonary vascular disease.