Single-breath resting diffusing capacities for CO (DlCO) and 18O2 (DlO2 ) were measured simultaneously with pulmonary capillary blood flow (Q̇c) in nine normal males at hypoxic alveolar O2 tensions (PO2 42 torr). DlCO (54 ± 5 ml stpd . min-1 . torr-1) was significantly higher than DlO2 (33 ± 11 ml stpd ± min-1 . torr-1). Extrapolation of the linear regressions between DlCO and DlO2 and cardiac output (range 4860 to 12,270 ml . min-1) suggest that DlO2 approximates DlCO at cardiac outputs of 18 L . min-1 in our subjects. No significant differences between the previously measured diffusing capacity for 18O16O (Hyde et al., 1966) and the present value for 18O18O was found. The discrepancy between the measured DlO2 and the predicted DlO2 calculated indirectly from the DlCO is confirmed. Inhomogeneity of pulmonary capillary diffusing surface area to capillary blood flow (Dl/Q̇c) probably accounts for this discrepancy. DL/Q̇c inhomogeneity, along with right-to-left shunts and V̇a/Qc inhomogeneities, must be taken into account when arterial-alveolar O2 gradients are evaluated.
- Diffusion/perfusion ratio
- Pulmonary capillary blood flow
- Pulmonary capillary blood volume
- Pulmonary diffusing capacity
ASJC Scopus subject areas
- Pulmonary and Respiratory Medicine