THE EFFECT OF CHANGES IN VENTILATION AND PULMONARY BLOOD FLOW ON THE DIFFUSING CAPACITY OF THE LUNG*†

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Abstract
The effect of changes in minute ventilation and pulmonary blood flow on the diffusing capacity of the lung for CO was investigated at rest and during exercise by steady state methods. For this purpose, normal human subjects were, contrasted with patients in whom pulmonary blood flow was restricted by mitral stenosis. In order to vary ventilation and blood flow independently, special methods, such as voluntary hyperpnea and unilateral balloon occlusion of a pulmonary artery were also employed. The results indicate that diffusing capacity for CO is affected by changes in pulmonary blood flow only when flow is markedly curtailed. In contrast, increases in ventilation are associated with increases in diffusing capacity, and seem to account for the rise in diffusing capacity during graded exercise.
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