Role of positive airway pressure on pulmonary acinar perfusion heterogeneity

Perfusion of the pulmonary acinus has been shown to be generally homogeneou s, but there is a significant component that is heterogeneous. To investiga te the contribution of the alveolar septal capillary network to acinar perf usion heterogeneity, the passage of fluorescent dye boluses through the sub pleural microcirculation of isolated dog lung lobes was videotaped using fl uorescence microscopy. As the videotapes were replayed, dye-dilution curves were recorded from each of the tributary branches of Y-shaped venules that drained single acini. For each Y-shaped venule, the mean appearance time d ifference between the pair of tributary branches was calculated from the dy e curves. When the complex septal capillary networks were derecruited by hi gh positive airway pressure, venular perfusion became proportionally more h omogeneous. This result shows that septal capillary resistance and pathleng th differences are important contributors to intra-acinar perfusion heterog eneity.