Effect of pulmonary blood flow on the exchange between the circulating and marginating pool of polymorphonuclear leukocytes in dog lungs.

The effect of pulmonary blood flow on the exchange between the circulating was marginating pool of polymorphonuclear leukocytes (PMN) was examined in three sets of experiments. In the first we used the double indicator dilution technique with labeled PMN and erythrocytes (RBC) to calculate the percent extraction and percent recovery of PMN at different levels of cardiac output (CO). In the second group of experiments we took advantage of the wide range of blood flow in the lung to determine the effect of regional blood flow on regional PMN retention, and in the third set we measured total leukocyte (WBC) and PMN counts in simultaneous samples from the pulmonary artery and aorta over a wide range of cardiac output. The studies showed that 80-90% of the labeled PMN were removed in a single pass through the lung and that regional retention of labeled PMN and A-V differences for unlabeled PMN increased with decreasing blood flow. The data for regional retention of labeled PMN and the A-V differences observed for unlabeled cells both fit the equation Y = A + Be-cx (where A + B = 100), which showed that PMN accumulate in the lung as blood flow is reduced. We conclude that a dynamic equilibrium exists between the circulating and marginating pools of leukocytes in the lung and that blood flow primarily effects the reentry of cells into the circulating pool so that the marginating pool of PMN within the lung accumulates cells when blood flow is reduced below 7 ml/min per g.