Influence of pulmonary vasoconstriction on lung water and perfusion heterogeneity

To determine the influence of pulmonary vasoconstriction on lung tissue perfusion, we examined the effects of hypoxia, sympathetic nerve stimulation, and histamine on vascular resistance, blood, and extravascular volumes, weight, and the distribution of vascular transit times in dog left lower lung lobes perfused in situ. Hypoxia, sympathetic stimulation, and histamine increased pulmonary vascular resistance by 1.96, 1.42, and 2.02 times and increased the relative dispersion of the transit time distributions by 1.49, 1.30, and 1.71 times the control values, respectively. Hypoxia and sympathetic stimulation tended to decrease the blood volume accessible to indocyanine green dye and the lobe weight. On the other hand, histamine infusion, which also decreased the volume accessible to the dye, increased the lobe weight. Despite this increase in weight, histamine infusion resulted in a decrease in the extravascular volume accessible to ³HOH. These results indicate that these vasoconstrictor stimuli increased the heterogeneity of transit times through the lung lobe and decreased the flowing blood volume. In addition, histamine decreased the size of the perfused microvascular bed, indicating that pulmonary vasoconstriction can influence the local pattern of microvascular perfusion.