Very mild exposure to hypoxia for 8 h can induce ventilatory acclimatization in humans

Ventilatory acclimatization to altitude is associated with a progressive in crease in ventilation, a progressive decrease in end-tidal PCO2 and a progr essive increase in the acute ventilatory sensitivity to hypoxia. Ventilator y acclimatization has been observed with mild exposure to hypoxia when the duration of exposure has been of some length (e.g. days), and with shorter duration exposures (e.g. 8 h) when the degree of hypoxia has been more seve re. The purpose of this study was to determine whether short-duration expos ures to very mild hypoxia, such as are commonly associated with the reducti on in cabin pressure during commercial airline night, can also induce some degree of ventilatory acclimatization. Twelve subjects were exposed in a ch amber to both 8 h mild hypoxia (inspired PO2 127 mmHg) and 8 h air-breathin g as a control. Exposures were on different days in random order. Following the hypoxic exposure, there was a significant reduction in end-tidal PCO2 during air breathing (from 39.2+/-1.8 to 38.1+/-1.5 mmHg, mean+/-SD, P<0.05 ), and a significant increase in ventilatory sensitivity to hypoxia (from 0 .84+/-0.54 l/min/% to 1.13+/-0.66 l/min/%, P<0.05). We conclude that short term exposures to very mild hypoxia do induce significant acclimatization w ithin the respiratory control system.