Lung membrane conductance and capillary volume derived from the NO and CO transfer in high-altitude newcomers

Acute exposure to high altitude may induce changes in carbon monoxide (CO) membrane conductance (DmCO) and capillary lung volume (Vc). Measurements were performed in 25 lowlanders at Brussels (D-0), at 4,300 m after a 2-or 3-day exposure (D-2,D-3) without preceding climbing, and 5 days later (D-7,D-8), before and after an exercise test, under a trial with two arterial pulmonary vasodilators or a placebo. The nitric oxide (NO)/CO transfer method was used, assuming both infinite and finite values to the NO blood conductance (theta NO). Doppler echocardiogra-phy provided hemodynamic data. Compared with sea level, lung diffusing capacity for CO increased by 24% at D-2,D-3 and is returned to control at D-7,D-8. The acute increase in lung diffusing capacity for CO resulted from increases in DmCO and Vc with finite and infinite theta(NO) assumptions. The alveolar volume increased by 16% at D-2,D-3 and normalized at D-7,D-8. The mean increase in systolic arterial pulmonary pressure at rest at D-2,D-3 was minimal. In conclusion, the acute increase in Vc may be related to the increase in alveolar volume and to the increase in capillary pressure. Compared with the infinite theta(NO) value, the use of a finite theta(NO) value led to about a twofold increase in DmCO value and to a persistent increase in DmCO at D-7,D-8 compared with D-0. After exercise, DmCO decreased slightly less in subjects treated by the vasodilators, suggesting a beneficial effect on interstitial edema.