VARIATIONS IN THE PULMONARY CAPILLARY BLOOD VOLUME AND MEMBRANE DIFFUSION COMPONENT IN HEALTH AND DISEASE*

Abstract
By measuring the steady state CO diffusing capacity at various O2 tensions during moderate exercise, the pulmonary capillary blood volume (Vc) and membrane diffusion component (Dm) have been computed in normal subjects and in patients suffering from a variety of diseases. In 14 normal subjects walking at 3 mph on the flat, Vc averaged 143 ml and Dm 50 mlCO/min/mmHg. Repeated measurements on 4 normal subjects showed that the Vc determination had a standard deviation of about [plus or minus] 12 ml and the Dm a standard deviation of about [plus or minus] 10 mlCO/min/ mmHg in any one subject. Variations in Vc between subjects were greater than could be explained by method error. Abnormalities found in Vc and Dm in lung disease and in mitral stenosis indicate that this technique of study may prove useful in the detailed evaluation of a variety of conditions.