Abstract
O 2 diffusing capacity (D O 2 ) was measured in anesthetized, unidirectionally ventilated ducks during hypercapnic hypoxia. D O 2 averaged 78.2 μmol·(min·Torr) −1. This value increased to 97.3 μmol·(min·Torr) −1 after correction for ventilation-perfusion inequality. D O 2 increased when pulmonary O 2 exchange (M O 2 ) and pulmonary blood flow (Ṁ) were increased by either 2,4 dinitrophenol (DNP, ca. 5 mg/kg i.v.) or temporary unilateral pulmonary artery occlusion (TUPAO). D O 2 increased with M O 2 42.4 μmol·(mmol·Torr) −1 (R=0.664), and with Q̇ 80.3 μmol·(L·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 D O 2 to Q̇ reflects a reduction of functional lung heterogeneity at higher blood flows, perhaps due to better matching of V̇ to D, or D to Q̇.
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