Pulmonary Gas Exchange

altitude either during physical maturation (at age 10±4 yr) or as adults (at age 26±4 yr). The relative degree of acclimatization achieved in these lowland residents was assessed through their comparison both with normal sea-level values and with two additional groups of short-term sojourners and natives to 3,100 m. DLco at rest and work was significantly elevated above normal and above sojourner values in both groups of resident lowlanders at 3,100 m. The high DLCo in the native to 3,100 m was closely approximated in the younger resident lowlander at rest, but only during exercise in the adult resident lowlander. The high DLco at rest and during exercise in the resident lowlanders was not attributable to differences in Hb concentration or in alveolar lung volume; and was accompanied primarily by an increased estimated Dmco and to a lesser extent by an expanded Vc. The interpretation and implications of these findings were limited by the low quantitative capability of Vc and Dmco estimates and by the cross-sectional nature of the study. Nevertheless, the higher than normal DLco and Dmco in the non-native, long-term resident of 3,100 m was substantial, highly significant statistically, and consistent over a wide range of metabolic rates at rest and work. These data provide, then, a reasonable rationale upon which longitudinal experiments may be based to determine the true effects of chronic hypoxia on pulmonary gas exchange in man. This work was presented in part at the FASEB National Meeting, Atlantic City, N. J., April 1972. (Fed. Proc. 31: 389). Received for publication 25 September 1972 and in revised form 25 July 1973. INTRODUCTION A higher than normal alveolar-capillary diffusion for CO (DLco) ' has been observed consistently in healthy humans native to high altitude (3,100-4,200 m) (1-4). This elevated DLco has been associated with a high pulmonary capillary blood volume (Vc) and/or so-called membrane diffusing capacity (Dmco) (1, 2), an altered lung structure (5), and during exercise in ambient hypoxia, was reflected in a narrowed alveolar to arterial Po2difference (1). This study was directed to the question of postnatal adaptability of the lung to hypoxia in the native lowlander. Several studies have shown negligible or relatively minor alterations in DLCO in the native lowlander as a result of short-term (< 3 mo) sojourn to high altitude (1, 2, 6, 7). On the other hand, we have reported data on a limited number of subjects which suggested that the native lowlander who began long-term residence at 3,100 m during early maturation was characterized by a higher than normal DLco (1). The present study extends these previous preliminary observations and represents an initial attempt, by means of cross-sectional investigation, to answer two specific questions concerning the effects of chronic high altitude exposure on alveolar gas exchange in healthy man. Can the healthy, nonnative, long-term resident of high altitude acclimatize in a manner approaching that of the native to high altitude? Is the completeness of his adaptation dependent upon the stage of physical maturation present at the initiation of residency at high altitude? To these ends, DLco and its components were determined at rest and during muscular work in two groups of sea level natives who had initiated long-term residence at 'Abbreviations used in this paper: DLco, alveolar-capillary diffusion for CO; Dm, membrane diffusing capacity; CI, confidence interval; PB, barometric pressure; PIO2, pressure of inspired oxygen; Po2, pressure of oxygen; TLC, total lung capacity; Vc, pulmonary capillary blood volume. The Journal of Clinical Investigation Volume 52 December 1973 2993-2999 2993 Downloaded from http://www.jci.org on July 7, 2017. https://doi.org/10.1172/JCI107497