TEMPORAL CAPILLARY PERFUSION PATTERNS IN SINGLE ALVEOLAR WALLS OF INTACT DOGS

Pulmonary gas exchange reserve in the form of recruitable capillaries was first described in the 1930s, when in vivo microscopy was used to demonstrate that not all capillaries were perfused during basal condit ions and that perfusion of individual capillaries varied over time. Th ese important observations have never been directly confirmed, nor hav e the hemodynamic causes of the variation been investigated. We used v ideomicroscopy to record nine consecutive pulmonary capillary perfusio n patterns during a 40-min period. Confirming the original work, we fo und considerable perfusion variation in about one-half of the capillar ies. These variations did not correlate with changes in pulmonary arte rial pressures or cardiac outputs, suggesting that factors more subtle than large-vessel hemodynamics affected capillary perfusion consisten cy. In contrast to this variable group, one-half of the capillary segm ents were consistently perfused during at least eight of the nine obse rvations and were interconnected to form preferential pathways across the alveolar wall.