Influence of pulmonary blood flow and O2 flux on DO2 in avian lungs.

O2 diffusing capacity (DO2) was measured in anesthetized, unidirectionally ventilated ducks during hypercapnic hypoxia. DO2 averaged 78.2 mumol X (min X Torr)-1. This value increased to 97.3 mumol X (min X Torr)-1 after correction for ventilation-perfusion inequality. DO2 increased when pulmonary O2 exchange (MO2) and pulmonary blood flow (Q) were increased by either 2,4 dinitrophenol (DNP,ca. 5 mg/kg i.v.) or temporary unilateral pulmonary artery occlusion (TUPAO). DO2 increased with MO2 42.4 mumol X (mmol X Torr)-1 (R = 0.664), and with Q 80.3 mumol X (L X Torr)-1 (R = 0.895). Since there is evidence against expansion of membrane diffusing capacity through recruitment and distention of pulmonary capillaries in avian lungs, we suggest that the close coupling of DO2 to Q reflects a reduction of functional lung heterogeneity at higher blood flows, perhaps due to better matching of V to D, or D to Q.