Thermal balance effects on vigilance during 2-hour exposures to -20 degrees C

Human mental performance is markedly affected by environmental temperature, body temperature, body heat content, and comfort, but the effects of these different factors are not entirely clear. A liquid conditioning garment (LCG) can be used to manipulate these factors independently. We hypothesized that cold exposure (coldEX) has negative effects on vigilance which can be alleviated by increasing body heat content throughout or prior to coldEX.

Subjects (n = 10) were tested for vigilance during a 130-min coldEX to -20 degrees C while warmly clothed; a period of moderate exercise occurred at minutes 64-74. An LCG was used to provide heating either before coldEX (prior heating, PH) or throughout coldEX (heating, H); the control condition involved no heating (NH).

There were significant differences among conditions for rectal temperature (PH: 37.3 +/- 0.26 degrees C, H: 37.0 +/- 0.24 degrees C, NH: 37.05 +/- 0.26 degrees C) and mean skin temperature (PH: 33.85 +/- 1.21 degrees C, H: 35.11 +/- 1.35 degrees C, NH: 32.84 +/- 0.65 degrees C). Reaction time decreased significantly after the 45th minute of coldEX in H and NH. At the same time, signal detection criteria in all conditions demonstrated considerable alterations, indicating bias in favor of 'target-present' responses, which were associated with lower mean skin temperature and thermal comfort vote. PH was more effective than H and NH in preserving reaction time and response consistency. Relative to men, women demonstrated increased heat loss and more deteriorated vigilance and signal detection.

Vigilance deteriorates in cold conditions within 45 min of exposure. Increasing body heat content prior to coldEX is efficacious in preserving vigilance performance during exposures lasting up to 2 h.