Effect of vascular pressure and blood flow on CO diffusion in the perfused dog lung

¹ Department of Medicine, University of Chicago, Chicago, Illinois

The effects of blood flow and vascular pressure on the pulmonary diffusing capacity for carbon monoxide have been studied independently in 18 isolated perfused dog lungs, using the "equilibration technique" for Dl determination. The Dl is a function of mean vascular pressure over a wide range of vascular tensions, suggesting that there are some lung capillaries with high closing pressures or that patent pulmonary capillaries are capable of dilating in response to an increase in their transmural pressure. A maximum Dl could not be obtained. Measured Dl is reduced with low rates of pulmonary blood flow, but its dependence on perfusion rate becomes slight as physiologic flow rates are approached. Nonuniform diffusing capacity: lung volume ratios throughout the lung are noted at both low intravascular pressure and low blood flow, indicating nonuniformity of capillary filling and/or nonuniformity of capillary erythrocyte transit times. Under the conditions of these experiments, Dl appears to be dependent on blood flow per se as well as related to changes in pulmonary vascular resistance.