Increased Metabolism and Dead Space as Components of Ventilation at High Altitude.

摘要

Ventilatory acclimatization to high altitude results in alveolar hyperventilation, which is an increase in alveolar ventilation per unit of carbon dioxide production and is associated with a fall in the PC02. A measurement frequently made during acclimatization to high altitude is the total volume of air expired per minute, the minute ventilation. However, the relation of total to alveolar ventilation and the influence of C02 production on the latter at high altitude is unclear. We sought to determine the contribution of changes in metabolism and in dead space ventilation to the increase in minute ventilation observed with ascent and 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 (+35% by day 5) and arterialized venous PC02 fell. Resting metabolic rate (VC02) increased 16% by day 5 and could account for approximately half of the increase in minute ventilation. The increases in ventilation on days 1, 2 and 4 were positively correlated with increased C02 production; they were not correlated with arterial oxygen saturation on any day. During exercise at high altitude, minute ventilation rose above low altitude values but less than 10% of the increase in ventilation could be attributed to increased C02 production. Dead space ventilation at high altitude was the same as at low altitude in resting subjects.