Influence of age on pulmonary diffusing capacity

The pulmonary function of 24 normal subjects ranging in age from 20 to 50 years has been studied at rest and during exercise. At rest there is a significant decrease with age in the pulmonary diffusing capacity and the level of diffusing capacity attained on exercise at any particular oxygen uptake decreases with increasing age. Simultaneous measurements of O2 uptake, ventilation, end tidal O2 and CO2 concentration and calculated alveolar CO2 concentration, using the Bohr equation, show no evidence that any of these measurements are significantly influenced by age. The predicted maximal O2 diffusing capacity ( J. Appl. Physiol. 6: 588, 1954) predicts with fair accuracy the diffusing capacity for carbon monoxide that will be found in any given individual at an O2 uptake of about 2.8 l/min. It correctly predicts the change in CO diffusing capacity with increasing age. Reasons are given for suggesting that the decrease in pulmonary diffusing capacity observed may be explained by a diminution in cardiac output with increasing age. Submitted on November 21, 1958