Characteristics of adjustment of lung diffusing capacity to work

The response of lung diffusing capacity for CO (DL(CO)) to the onset of exercise or a change in work load was studied in four healthy males. Single-breath DL(CO) was measured during the transients 1) from rest to 40% of maximum O₂ uptake V̇O₂(max)); 2) from rest to 80% V̇O₂ max; and 3) from steady-state exercise at 40 to 80% V̇O₂(max). Protocols 1 and 2 consisted of 8.5 min of exercise while 3 consisted of 10.5 min of exercise at 40% V̇O₂(max) followed by 8.5 min at 80% V̇O₂(max). DL(CO) was measured at 10, 20, 30, 60, 90, 240, and 510 s after onset of change in load. Half times of the responses (1, 39; 2, 43; 3, 56 s) were not statistically different. The percentage of the total response completed at each time interval indicated that 3 was significantly (P<0.05) slower than 1 and 2 at 10 and 20 s. The rapid response of DL(CO) at the onset of exercise may reflect a neural component in pulmonary vascular control during exercise.