Influence of age on pulmonary diffusing capacity

¹ Joint Cardiorespiratory Service, Royal Victoria Hospital and Montreal Children's Hospital, McGill University, Montreal, Canada

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.