EFFECT OF BLOOD-FLOW ON CAPILLARY TRANSIT-TIME AND OXYGENATION IN EXCISED RABBIT LUNG

We used an isolated perfused lung preparation of the rabbit to study t he effect of increasing blood flow on pulmonary capillary transit time by two methods. In one method, capillary transit time was measured fr om fluorescent dye dilution curves from arterioles and venules of the subpleural microcirculation. Values of transit time were similar to th ose for the whole lung determined by dividing capillary blood volume b y blood flow. Capillary transit times averaged 0.50-0.62 sec at a cont rol blood flow of 80 ml min(-1) kg(-1) and decreased to 0.14-0.18 sec as blood flow increased to 6 times control. To determine whether the r educed transit time would limit O-2 transport, we studied the effect o f blood flow on oxygenation. Two isolated rabbit lungs were perfused i n series. Blood from one lung deoxygenated by ventilation with a N-2-C O2 mixture was oxygenated by the test lung ventilated with air. Ventil ation was matched to blood flow P-O2 and P-CO2 were measured in blood flowing into and out of the test lung. At all flows, no significant al veolar gas-to-end-capillary blood PO2 gradient (A-aDO(2)) was measured . The isolated perfused rabbit lung showed no transit time limitation to oxygenation for blood flows that are consistent with heavy exercise in vivo.