Pulmonary capillary reserve and exercise capacity at high altitude in healthy humans

Purpose We determined whether well-acclimatized humans have a reserve to recruit pulmonary capillaries in response to exercise at high altitude. Methods At sea level, lung diffusing capacity for carbon monoxide (DLCO), alveolar-capillary membrane conductance (Dm(CO)), and pulmonary capillary blood volume (V-c) were measured at rest before maximal oxygen consumption ((V)over dotO(2max)) was determined in seven adults. Then, DLCO, Dm(CO) and V-c were measured pre- and post-exhaustive incremental exercise at 5150 m after similar to 40 days of acclimatization. Results Immediately after exercise at high altitude, there was an increase in group mean Dm(CO) (14 +/- 10 %, P = 0.040) with no pre- to post-exercise change in group mean DLCO (46.9 +/- 5.8 vs. 50.6 +/- 9.6 ml/min/mmHg, P = 0.213) or V-c (151 +/- 28 vs. 158 +/- 37 ml, P = 0.693). There was, however, a similar to 20 % increase in DLCO from pre- to post-exercise at high altitude (51.2 +/- 0.2 vs. 61.1 +/- 0.2 ml/min/mmHg) with a concomitant increase in Dm(CO) (123 +/- 2 vs. 156 +/- 4 ml/min/mmHg) and V-c (157 +/- 3 vs. 180 +/- 8 ml) in 2 of the 7 participants. There was a significant positive relationship between the decrease in. (V)over dotO(2max) from sea level to high altitude and the change in DLCO and lung diffusing capacity for nitric oxide (DLNO) from rest to end-exercise at high altitude. Conclusion These data suggest that recruitment of the pulmonary capillaries in response to exercise at high altitude is limited in most well-acclimatized humans but that any such a reserve may be associated with better exercise capacity.