The pulmonary diffusing capacity (DL) increases with exercise. This was first shown by Krogh in 1915 (1) and has been confirmed by investigators who have studied the matter since that time, using both carbon monoxide and oxygen (2-5). The mechanism by which exercise increases the diffusing capacity is not altogether clear, however, and the apparent amount of increase with exercise is dependent on the technique used for determining the diffusing capacity, and on the severity of the exercise.
Two methods widely used for estimating the pulmonary diffusing capacity for carbon monoxide are the steady state method of Filley, MacIntosh and Wright (3) and the Krogh breath holding technique as modified by Ogilvie, Forster, Blakemore and Morton (5). In the steady state technique, the subject breathes continuously throughout the test period, which makes minute ventilation a variable factor. In the breath holding method, however, the breath is held and minute