Alterations in Distribution of Blood Flow to the Lung's Diffusion Surfaces During Exercise

breath methods, pulmonary capillary blood flow (QC), carbon monoxide diffusing capacity (DLCO), and iso-topic oxygen (180180) diffusing capacity (DLlso,) in five normal males during conditions of rest and moder-ate exercise at mixed venous 02 tensions (Po2 33-44 mm Hg). During moderate exercise at a work load of 100 W, pulmonary capillary blood flow increased from 6.9+1.5 to 12.9+3.4 min- and DL 802 increased from 25+4 to 434+3 ml min'*mm Hg-1, whereas DLCo showed no significant change (45+-5 to 49+410 ml * mingl mm Hg-1). DL1802 increased proportionally to QC (r = 0.74), where DLcO did not (r = 0.08). The greater increase in DL180, during exercise can be ex-plained by a more homogeneous diffusion/perfusion (DLO2/Q) distribution in the individual respiratory exchange units during exercise. This improved distri-bution of DL02/Q acts to help prevent an increase in alveolar-arterial 02 tension difference from developing despite the decrease in pulmonary erythrocyte transit times that occur during exercise. The insignificant rise in DLco with exercise under these hypoxic breath-holding conditions may result from pulmonary vasomotor responses to short-term hypoxia or from relative insensitivity of DLCO to moderate levels of exercise