Perfusion heterogeneity in the pulmonary acinus

There is little information on the distribution of acinarperfusion because it is difficult to resolve blood flow within such small regions. We hypothesized that the known heterogeneity of arteriolar blood flow and capillary blood flow would result in heterogeneous acinar perfusion. To test this hypothesis, the passage offluorescent dye boluses through the subpleural microcirculation ofisolated dog lobes was videotaped by using fluorescence microscopy. Asthe videotapes were replayed, dye-dilution curves were recorded fromeach of the tributary branches of Y-shaped venules that drained anacinus. From the dye curves, we calculated the mean appearance time ofeach curve. The difference in mean appearance times between venulartributary branches was small in most cases. In 43% of the observedvenular branch pairs, the dye curves were essentially superimposable(the mean appearance-time difference was <5%); and in another 42%,the mean appearance-time difference between curves was 5-10%.From these results, we conclude that acinar perfusion is unexpectedlyhomogeneous.