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 (DmCO), and pulmonary-capillary blood volume (Vc) were measured at rest before maximal oxygen consumption (V̇O2max) was determined in seven adults. Then, DLCO, DmCO and Vc were measured pre- and post-exhaustive incremental exercise at 5,150 m after ~40 days of acclimatization. Results. Immediately after exercise at high-altitude, there was an increase in group mean DmCO (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 Vc (151 ± 28 vs. 158 ± 37 ml, P = 0.693). There was, however, a ~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 DmCO (123 ± 2 vs. 156 ± 4 ml/min/mmHg) and Vc (157 ± 3 vs. 180 ± 8 ml) in 2 of the 7 participants. There was a significant positive relationship between the decrease in V̇O2max 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.