Gas exchange during exercise in healthy people. I. The physiological dead-space volume.

1. Physiological dead-space volume (V D) was measured in twenty-four healthy men and women aged from 20 to 71 years, at rest and at two rates of work on a treadmill, whilst breathing air and breathing oxygen. 2. The effect of correction of arterial carbon dioxide tension (Pa,CO2) to pulmonary capillary temperature on the resulting value for V D was investigated. We find that the effect is substantial and that a correction should be made. 3. Equations have been derived for the prediction of normal V D during exercise. The best prediction was given by a regression on height, age, carbon dioxide output, ventilation and respiratory frequency, with an upper 95% confidence limit of +81 ml.