Effects of Pulmonary Vascular Congestion on Postural Changes in the Perfusion and Filling of the Pulmonary Vascular Bed.

Measured by a variety of techniques, the overall ventilation-perfusion relationship of the normal human lung is different in supine and upright positions, and in the upright position, the upper regions of the lung are relatively poorly perfused (1-4). Similarly, pulmonary diffusing capacity (DL) is reduced when normal subjects change from supine to upright positions (5, 6); in the upright position, carbon monoxide absorption is greater in the lower portions of the lung than in the upper portions (7). These differences are probably related to a gravity dependent gradient of perfusion and capillary filling caused by the inability of the normally low pulmonary arterial pressure to provide uniformly adequate perfusion against the hydrostatic gradient that must be present in the pulmonary vascular bed of normal adult humans in an upright position (2, 8). The present investigation was undertaken to determine a) whether the normal postural changes in physiologic dead space and diffusing capacity are present in patients in whom the pulmonary vascular pressure should be great enough to insure perfusion of the entire lung in the upright position and b) whether an acute increase in pulmonary vascular pressures affects the arterialalveolar CO2 gradient and alveolar dead space of normal men in an upright position.