Improved response to heat after moderate physical training in man.

7 young men marched for 6 days (35 km daily) in a cool climate at about 35% of their VO2max. Sweat output was measured at rest in a climatic chamber during a controlled hyperthemia test performed before and after the trial. 4 subjects served as controls. The main finding of the study was that sweat output increased 17.3% +/- 1.5 SEM on the post-trial test, without any change in VO2max. It is concluded that moderate physical training can improve heat responses in resting man.

Vigilance performance of men sleeping under arctic conditions.

This study investigated the effect of cold exposure on vigilance performance in men working and sleeping under Arctic conditions. The results were compared with changes in the amount of REM sleep. EEG sleep recordings were made on six subjects during five baseline nights in laboratory conditions, 16 experimental nights in Arctic conditions, and four recovery nights in the laboratory. Vigilance tests were administered every second day during the experimental period and two times during each of the baseline and recovery periods. During the first night in the Arctic, the amount of REM sleep fell to 50% of baseline and a large decrement occurred in detection performance on the following morning. During the remaining nights in the cold, REM deprivation averaged about 25% with somewhat greater deprivation occurring during colder nights. Reaction time measures generally increased throughout the experimental period and subsequently showed incomplete recovery. However, detection performance gradually improved during the experimental period but showed some regression following colder-than-usual nights, when REM deprivation increased. This suggested that performance on this type of task may be related to temperature variations and changes in REM deprivation.

Skin temperature changes in paradoxical sleep in man in the cold.

Mean skin temperature (Tsk) calculated from seven sites and rectal temperature (Tre) were recorded every minute for a total of 88 man-nights in eight young men sleeping at night in both cold (during the Artic winter) and neutral (laboratory) environments, and were related to the EEG stages of sleep, especially to paradoxical sleep (PS). In the neutral environment, Tre was always above 36 degrees C and Tsk increased during PS. In the cold conditions, during PS, Tsk increased when Tre was high, and decreased when Tre was below 36 degrees C. It was concluded that, although it is not known why a core temperature of about 36 degrees C is the critical point of change in the direction of Tsk variations during PS, the direction in which Tsk will vary during PS is dependent on the core temperature at the time.

Cold-induced diminution of paradoxical sleep in man.

Prolonged exposure to cold produced a chronic diminution in PS (PS-hyposomnia) primarily in the tonic component of PS. No significant change occurred in the REM (phasic or obligatory) component of PS. An inverse correlation was found in the activity of the pituitary-adrenal cortical system and the level of PS. The classical rebound phenomenon that occurs after PS deprivation was not observed in this study and it is suggested that the rebound effect characteristic of PS deprivation is related not to total PS but to its phasic (obligatory) component.

Cold-induced shivering in men with thermoneutral skin temperatures.

Twenty-two male Caucasians, aged 20-47 yr, were exposed in a cold room to air temperatures of -33 degrees C while lying in sleeping bags for 2 h. Skin and rectal temperatures as well as electromyographic activity of the chin, forearm, and thigh, were recorded. Shivering occurred in all the subjects, even though skin temperatures were maintained between 31 and 33 degrees C. It is suggested that a counter-current heat exchange occurs whereby the warm blood of the common carotid artery is cooled by cool venous blood in the jugular veins. This cooled arterial blood, in irrigating the hypothalamus, causes shivering.