Determinants of pulmonary blood volume. Effects of acute changes in pulmonary vascular pressures and flow

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Abstract
To examine the effects of pulmonary vascular pressures and flow on pulmonary blood volume (PBV), experiments were performed at constant heart rate and zone 3 conditions (mean left atrial pressure (LAP) above airway pressure) in 6 anesthetized, open-chest dogs. PBV was calculated as the product of electromagnetic aortic flow and pulmonary mean transit time for ascorbate, obtained without blood withdrawal by polarographic recording of aortic ascorbate changes. In 3 series of experiments LAP was raised similarly in 3 steps, from 4.5 to 14.8 mm Hg; by mitral constriction which reduced pulmonary blood flow, by blood volume expansion which more than doubled pulmonary blood flow, or by a combination of the 2 procedures which kept pulmonary blood flow constant. In all 3 series, LAP and mean pulmonary arterial pressure (PAP) rose in proportion, but PBV was better correlated to PAP (r = 0.87 .+-. 0.02) than to LAP (r = 0.66 .+-. 0.90). PAP is possibly the most important factor in determining PBV under zone 3 conditions, whether PAP is raised by increasing pulmonary blood flow or by mitral constriction.