Effects of carbon dioxide on cold-exposed human subjects

Human subjects were exposed to an ambient temperature of 5 C for 75-min periods. Subjects breathed 2.5%—6% carbon dioxide for selected time periods during the exposure. Carbon dioxide appeared to inhibit shivering. After carbon dioxide inhalation, shivering and metabolism were greatly increased. When 6% carbon dioxide was inhaled for 30 min, the inhibition was overcome and shivering and metabolism approached high levels. The increased respiratory heat loss associated with carbon dioxide breathing may be one factor causing the breakthrough of the inhibition.