Effects of altitude acclimatization on pulmonary gas exchange during exercise.
Pulmonary gas exchange was studied in eight normal subjects both before and after 2 wk of altitude acclimatization at 3,800 m (12,470 ft, barometric pressure = 484 Torr). Respiratory and multiple inert gas tensions, ventilation, cardiac output (Q), and hemoglobin concentration were measured at rest and during three levels of constant-load cycle exercise during both normoxia [inspired PO2 (PIO2) = 148 Torr] and normobaric hypoxia (PIO2 = 91 Torr). After acclimatization, the measured alveolar-arterial PO2 difference (A-aPO2) for any given work rate decreased (P less than 0.02). The largest reductions were observed during the highest work rates and were 24.8 +/- 1.4 to 19.7 +/- 0.8 Torr (normoxia) and 22.0 +/- 1.1 to 19.4 +/- 0.7 Torr (hypoxia). This could not be explained by changes in ventilation-perfusion inequality or estimated O2 diffusing capacity, which were unaffected by acclimatization. However, Q for any given work rate was significantly decreased (P less than 0.001) after acclimatization. We suggest that the reduction in A-aPO2 after acclimatization is a result of more nearly complete alveolar/end-capillary diffusion equilibration on the basis of a longer pulmonary capillary transit time.
Bebout
D E
DE
Department and School of Medicine, University of California, San Diego, La Jolla 92093.
Story
D
D
Roca
J
J
Hogan
M C
MC
Poole
D C
DC
Gonzalez-Camarena
R
R
Ueno
O
O
Haab
P
P
Wagner
P D
PD
D000064:Acclimatization / Q000502:physiology*; D000328:Adult; D000531:Altitude; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D008176:Lung Volume Measurements; D008297:Male; D008875:Middle Aged; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D012123:Pulmonary Ventilation / Q000502:physiology