Respiratory acclimatization to carbon dioxide

Twenty-one subjects were exposed to 1.5% CO 2 in 21% O 2 for 42 days with pre- and postexposure periods on air for 9 days. Respiratory minute volume (Ve) and alveolar pCO 2 were increased throughout the exposure to CO 2 . After transition to air Ve decreased, while pCO 2 remained elevated for 9 days. CO 2 retention with uncompensated respiratory acidosis lasted for 23 days. CO 2 excretion was increased during the 9-day recovery period indicating release of CO 2 from the CO 2 stores. Oxygen consumption did not change significantly during the experiment. Respiratory acclimatization to CO 2 involved a continuous increase in tidal volume while the respiratory rate declined slowly after an initial increase. Changes in respiratory pattern were associated with an increase in physiological and anatomical dead space. A significant increase in the arterial-alveolar pCO 2 and alveolar-arterial pO 2 gradient indicated the development of an alveolar dead space. The ventilatory response to 5% CO 2 was markedly reduced at the end of CO 2 exposure. chronic CO 2 exposure; chronic hypercapnia; chronic respiratory acidosis Submitted on August 31, 1961