Increased metabolism contributes to increased resting ventilation at high altitude

Ventilatory acclimation to high altitude results in an increase in total or minute ventilation, and is associated with a fall in alveolar PCO2, i.e. alveolar hyperventilation. However, the extent to which the increase in total ventilation is matched by a greater metabolic rate (VO2, VCO2) vs alveolar hyperventilation is unclear. We sought to determine the contribution of changes in metabolic rate to the increase in minute ventilation observed during exposure to high altitude. In 12 healthy male subjects taken from Denver, Colorado (1600 m) to Pikes Peak, Colorado (4300 m) for 5 days, resting minute ventilation increased from low to high altitude (+ 26% for the 5 days) and arterialized PCO2 fell. Resting metabolic rate increased 16% for the 5 days and could account for more than half of the increase in minute ventilation. Among subjects the increases in ventilation on days 1, 2 and 4 were positively correlated with increased CO2 production; they were not correlated with arterial oxygen saturation on any day. During exercise at high altitude, PCO2 values were not different from those at rest and minute ventilation rose above low altitude values (+ 58% by day 5), but the increase could not be accounted for by an increased CO2 production. Thus at rest but not during exercise a substantial portion of the rise in minute ventilation could be attributed to increased metabolic rate.