Determinants of Pulmonary Vascular Volume

Abstract

This study attempted to evaluate the relative roles of vessel distensibility and vessel recruitment in the changes in pulmonary blood volume induced by changes in pulmonary intravascular pressure. Pulmonary blood volume was determined by a double-injection indicator-dilution technique in eight anesthetized open-chest dogs with a right and left ventricular bypass which allowed independent control of pulmonary artery and left atrial pressures. In three dogs, measurements were also taken during reverse perfusion (from the left atrium to the pulmonary artery). During forward perfusion, when left atrial pressure was increased from 7 to 26 cm H 2 O, and, by reducing flow from 3.4 to 1.2 liters'/min, pulmonary artery pressure was maintained at 30 cm H 2 O so that recruitment could be considered constant, pulmonary blood volume did not change but remained at about 260 ml. Pulmonary blood volume also did not change during reverse perfusion when pulmonary artery pressure was increased from 8 to 27 cm H 2 O at a constant left atrial pressure (inflow pressure). By contrast, when pulmonary artery pressure was raised by increasing flow, so that vessel recruitment could occur, pulmonary blood volume increased 12 ml for each 1-cm H 2 O increase in pulmonary artery pressure at a constant left atrial pressure of 5 cm H 2 O, and pulmonary blood volume increased 7 ml for each 1-cm H 2 O increase in pulmonary artery pressure at a constant left atrial pressure of 33 cm H 2 O. Therefore, in the range of pressures that we explored, the role of large-vessel distensibility in the changes in pulmonary blood volume observed when intravascular pressures were raised was small.

Effects of exercise on lung lymph flow in sheep and goats during normoxia and hypoxia.

“…It is well established from measurements of carbon monoxide uptake by the lung (6), and changes in mean transit time of tracers through the lung (4,5) that exercise causes a two-to threefold increase in lung blood volume in animals and man. The relative contribution of capillary dilation and capillary recruitment to this increased pulmonary blood volume is debated (41). Regardless of the mechanism, it would result in a significant increase in perfused microvascular surface area and comparable increase in fluid movement out of vessels.…”

Pulmonary vascular impedance analysis of adaptation to chronically elevated blood flow in the awake dog.

“…Thus, as pulmonary blood flow increases, the PVR and Z m typically fall, representing the more distal (small vessel) mechanism for adaptation to changing flow: recruitment of pulmonary vascular channels (Maseri et al, 1972). It is well accepted that significant vasomotor activity exists in small precapillary resistance ves- sels; however, there also is evidence of changes in mechanical properties of the larger pulmonary arteries under physiological stress and adrenergic stimulation (Ingram et al, 1968).…”

Interrelationships of flow, intravascular pressure, and tissue perfusion in the measurement of capillary permeability to sodium in isolated dog lung lobes.

“…For example, pulmonary blood volume (PBV) increases as a function of pulmonary artery pressure (Rosenzweig et al, 1970;Maseri et al, 1972;Vreim and Staub, 1974). This increase in PBV may occur by distention of open perfused channels, by recruitment of additional vessels, or by a combination of both mechanisms.…”