Respiratory Response to Inspired CO2 During Acclimatization to an Altitude of 12,470 Feet

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Abstract
The respiratory stimulation produced by adding graded amounts of CO2 to the inspired gas was studied in four adult male subjects at sea level and during acclimatization to an altitude of 12,470 feet. During acclimatization, the curve relating respiratory minute volume to inspired or alveolar CO2 shifted to the left by 8 to 11 mm Hg, while the shape and slope of the curve did not change significantly. This indicates primarily a change in the CO2 levels to which the regulatory mechanisms respond, rather than a change in the magnitude of the response to a given level of CO2. Most of the change occurred in the first 2 days at altitude. A possible mechanism depending primarily on the initial hypoxic stimulation of the chemoreceptors, which might explain the shift in CO2 response, is discussed. Submitted on November 20, 1956