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Foot cooling does not improve vigilance but may transiently reduce sleepiness
Author(s) -
Sixtus Ryan P.,
Galland Barbara C.,
Cotter James D.
Publication year - 2019
Publication title -
journal of sleep research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.297
H-Index - 117
eISSN - 1365-2869
pISSN - 0962-1105
DOI - 10.1111/jsr.12701
Subject(s) - vigilance (psychology) , alertness , wakefulness , psychology , crossover study , psychomotor vigilance task , sleep deprivation , audiology , somnolence , analysis of variance , medicine , anesthesia , physical therapy , adverse effect , psychiatry , electroencephalography , cognition , alternative medicine , pathology , neuroscience , placebo
Summary Temperature of the skin ( T Sk ) and core ( T C ) play key roles in sleep–wake regulation. The diurnal combination of low T Sk and high T C facilitates alertness, whereas the transition to high T Sk and low T C correlates with sleepiness. Sleepiness and deteriorating vigilance are induced with peripheral warming, whereas peripheral cooling appears to transiently improve vigilance in narcolepsy. This study aimed to test the hypothesis that foot cooling would maintain vigilance during extended wakefulness in healthy adults. Nine healthy young adult participants with habitually normal sleep completed three constant‐routine trials in randomized crossover order. Trials began at 22:30 hours, and involved continuous mild foot cooling (30°C), moderate foot cooling (25°C) or no foot cooling, while undertaking six × 10‐min Psychomotor Vigilance Tasks and seven × 7‐min Karolinska Drowsiness Tasks, interspersed with questionnaires of sleepiness and thermal perceptions. Foot temperatures in control, mild and moderate cooling averaged 34.5 ± 0.5°C, 30.8 ± 0.2°C and 26.4 ± 0.1°C (all p < .01), while upper‐limb temperatures remained stable (34–35°C) and T C declined (approximately −0.12°C per hr) regardless of trial ( p = .84). Foot cooling did not improve vigilance (repeated‐measures‐ANOVA interaction for response speed: p = .45), but transiently reduced subjective sleepiness (−0.8 ± 0.8; p = .004). Participants felt cooler throughout cooling trials, but thermal comfort was unaffected ( p = .43), as were almost all Karolinska Drowsiness Tasks’ encephalographic parameters. In conclusion, mild or moderate cooling of the feet did not attenuate declines in vigilance or core temperature of healthy young adults during the period of normal sleep onset and early sleep, and any effect on sleepiness was small and transient.