Acute Carbon Dioxide Exposure in Healthy Adults: Evaluation of a Novel Means of Investigating the Stress Response

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Abstract
Acute hypercapnia was studied to assess its potential as a noninvasive and simple test for evoking neuroendocrine, cardiovascular and psychological responses to stress in man. A single breath of four concentrations of carbon dioxide (CO2), 5%, 25%, 35% and 50%, was administered to nine healthy volunteers in a randomized, single‐blind fashion. Although no adverse effects occurred, most subjects were unable to take a full inspired vital capacity breath of 50% CO2. In response to the remaining exposures, subjective and somatic symptoms of anxiety increased in a dose‐dependent manner. Unlike 5% and 25% CO2, 35% CO2stimulated significant adrenocorticotropic hormone and noradrenaline release at 2 min and cortisol and prolactin release at 15 min following inhalation. This same dose also provoked a significant bradycardia that was followed by an acute pressor response. No significant habituation of psychological, hypothalamic‐pituitary‐adrenal (HPA) or cardiovascular responses following 35% CO2was seen when this dose was repeated after 1 week. A single breath of 35% CO2safely and reliably produced sympathetic and HPA axis activation and should prove a useful addition to currently available laboratory tests of the human stress response.