Capillary filling kinetics in the rabbit heart during normoxemia and hypoxemia

In experiments on anesthetized rabbits the kinetics of capillary plasma filling in the heart during normoxemia and hypoxemia were studied. Three gamma globulins originating from three different species were infused into the left atrium for various periods of time. The hearts were shock frozen, and the respective globulins were immunohistochemically identified in parallel sections. The anatomic capillary density was determined by staining the capillary basement membrane. During normoxemia 69 and 66% (subepicardium and subendocardium, respectively) of the capillaries were labeled within 2 s, 84 and 78% within 5 s, and 96 and 92% within 10 s. Labeling was complete after 20 s. Hypoxemia (arterial PO2 27 mmHg, 5 min) led to a significant acceleration of capillary filling kinetics: 93 and 95% within 2 s, 98 and 99% within 5 s, 100 and 99% within 10 s. During hypoxemic conditions the entire left coronary flow was found increased by a factor of 2.3. The data may best be explained by the fact that hypoxemia does not lead to mobilization of previously nonperfused capillaries but induces either an amplification of capillary flow velocities or an increased frequency of periods with high capillary blood flow.