Residence at 3,800-m altitude for 5 mo in growing dogs enhances lung diffusing capacity for oxygen that persists at least 2.5 years

Mammals native to high altitude (HA) exhibit larger lung volumes than their lowland counterparts. To test the hypothesis that adaptation induced by HA residence during somatic maturation improves pulmonary gas exchange in adulthood, male foxhounds born at sea level (SL) were raised at HA (3,800 m) from 2.5 to 7.5 mo of age and then returned to SL prior to somatic maturity while their littermates were simultaneously raised at SL. Following return to SL, all animals were trained to run on a treadmill; gas exchange and hemodynamics were measured 2.5 years later at rest and during exercise while breathing 21% and 13% O₂. The multiple inert gas elimination technique was employed to estimate ventilation-perfusion (V̇A/Q̇) distributions and lung diffusing capacity for O₂ (DL_O2). There were no significant intergroup differences during exercise breathing 21% O₂. During exercise breathing 13% O₂, peak O₂ uptake and V̇A/Q̇ distributions were similar between groups but arterial pH, base excess, and O₂ saturation were higher while peak lactate concentration was lower in animals raised at HA than at SL. At a given exercise intensity, alveolar-arterial O₂ tension gradient (A-aDO₂) attributable to diffusion limitation was lower while DLO₂ was 12-25% higher in HA-raised animals. Mean systemic arterial blood pressure was also lower in HA-raised animals; mean pulmonary arterial pressures were similar. We conclude that 5 mo of HA residence during maturation enhances long-term gas exchange efficiency and DL_O2 without impacting V̇A/Q̇ inequality during hypoxic exercise at SL.