Effects of Altitude,Acidosis,and Alkalosis upon Hypoxic Threshold. ∗

Abstract

Summary

1. 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 acclimatized.