Changes in Respiratory Response to CO₂ During Natural Sleep at Sea Level and at Altitude

¹ From the Department of Physiology, University of California, Berkeley, and the White Mountain Research Station, Big Pine, California

The effect of natural sleep on the breathing of three adult, male, sea level residents was studied at sea level, during a 4-week sojourn at 14,250 feet and after return to sea level. In each case the respiratory minute volume decreased by about 2 l/min. during sleep. To investigate the role of altered responsiveness to CO₂ in this effect of sleep, graded CO₂ mixtures containing sufficient O₂ to preclude hypoxia during the test were administered to the subjects awake and asleep. At sea level, sleep shifted the curve relating respiratory minute volume to alveolar CO₂ tension (CO₂ response curve) to the right by 3–5 mm Hg, so that higher CO₂ tensions were required to stimulate a given level of ventilation. In the tests at altitude the waking CO₂ response curve was 10–12 mm Hg to the left of its sea level position. During sleep at altitude the curve shifted to the right from this new position by 3–5 mm Hg, suggesting that the effects of sleep were superimposed on the respiratory readjustment accompanying altitude acclimatization. There was little if any change in shape or slope of the CO₂ response curve with sleep either at sea level or altitude.

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