The effects of carbon dioxide on sleep and thermoregulation in cold environments.

Abstract

In order to study the effects of mild hypercapnia on sleep and thermoregulation, 5 male volunteers (23.6 +/- 1.96 yrs) were exposed to air containing 0, 2, or 4% CO2, while sleeping in a double (9.0 clo) or single (4.5 clo) Canadian Forces sleeping ensemble (1 clo = 0.155°C·m 2·W-1) at -20°C. Each condition was presented twice in a completely randomized manner on non-consecutive nights. Standard polysomnographic EEG, EMG and EOG measures were monitored as well as rectal (Tr), mean skin (T¯sk) and toe (T toe) temperatures. Hypercapnia was associated with enhanced body cooling as indicated by a decreased time to minimal Tr and Ttoe (p < .05). In agreement with current knowledge of sleep in cold environments, sleeping in the single bag resulted in a significantly decreased percentage of REM sleep (p < .05) and trends towards decreases sleep efficiency and total sleep time (TST). Slow wave sleep (%SWS) tended to increase in the single bag condition. CO2 exposure was associated with a trend towards decreased TST and suppression of the cold induced increase in %SWS. The possible effects of body temperatures being mediated through sleep processes as opposed to direct CO2 effects, and the possible importance of SWS on thermoregulation were discussed.