CARBON MONOXIDE DIFFUSING CAPACITY IN PERMANENT RESIDENTS AT HIGH ALTITUDES

DL, DM and VC were determined by the steady-state carbon monoxide method in five residents of 3700 m and in four residents of 4500 m. Observed DL (PaO2; 100-150 mm Hg) and derived DM were greater than normal in residents of 3700 m but were nearly equal to sea level normal values in residents of 4500 m. Derived VC was near normal in the first group, but was greatly increased in the second group. These differences most likely result from differences in true DM and VC, with the exception that apparent DL and DM for the residents of 4500 m may be spuriously low. The changes in VC agree well with the differences in predicted central blood volume, but the greater DM in residents of high altitude is difficult to reconcile with anatomical measurements in other high altitude species. It is concluded that in permanent residents at high altitude the diffusion and reaction components of the total resistance to oxygen uptake in the lung are decreased, an adaptation not present in acclimatized low-landers. © 1969.