Effects of altitude, acidosis, and alkalosis upon hypoxic threshold.

Abstract

Summary1. Inspired oxygen tensions which produce the first discernible increases in ventilation (hypoxic thresholds) were measured in subjects acclimatized to Mt. Evans, Colo. (14,150 feet) and to Denver, Colo. (5300 feet). In addition thresholds were measured in subjects living in Denver who were in chronic metabolic acidosis (NH4CI) and in chronic metabolic alkalosis (NaHCO3). 2. Mt. Evans subjects showed an average threshold of 179 mm tracheal PO2 and those at Denver 127 mm. Reports in the literature pinpoint the threshold for sea level dwellers at about 93 mm. Furthermore the threshold for Denverites ingesting NH4CI was 163 mm and for those ingesting NaHCO3 was 107 mm. 3. Since NH4CI changed PAO2 and pH in the opposite direction from altitude but changed the hypoxic threshold in the same direction, these agents were ruled out as threshold governors. It was suggested that probably the hypoxic threshold is a function of either the resting PCO2 or the bicarbonate level to which the individual had acclima...