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Operations in Iraq, Afghanistan and Bosnia reveal that soldiers are exposed to extreme, complex and sustained operations, crossing the limits of human capabilities. During these operations the operational readiness or status of the soldier is estimated by the commander based on subjective observations of the physical and mental capabilities of the soldier. This commander evaluation can be biased by personal experiences and commanders own physical and mental status.

Introduction: Subjects with a weak cold-induced vasodilatation response (CIVD) to experimental cold-water immersion of the fingers in a laboratory setting have been shown to have a higher risk for local cold injuries when exposed to cold in real life. Most of the cold injuries in real life, however, occur in the foot in cold air rather than in the hand in cold water. Therefore, an experiment was conducted to investigate the within-subject relation between CIVD in the fingers and toes exposed to cold water and cold air. Methods: In 4 experimental sessions, 11 healthy male subjects immersed their toes and fingers in 5°C water and exposed the fingers and toes to -18°C cold air for 30 min. The pad temperature of the middle three digits was measured. Results: CIVD in water was more pronounced in the fingers (onset time 5.1 ± 1.8 min; amplitude 5.0 ± 2.1°C) than in the toes (onset time 10.6 ± 6.0 min; amplitude 3.0 ± 1.0°C). Out of 22 skin temperature responses to cold air, 13 were not identifiable as CIVD. The mean skin temperatures for fingers and toes during the last 20 min of cold exposure were 25.6 ± 7.1°C and 20.9 ± 6.8°C, respectively, for air and 9.3 ± 1.9°C and 7.1 ± 1.3°C for water immersion. There was a strong relation between the mean temperature of the fingers during cold-water immersion and toes during cold air exposure (r = 0.83, P < 0.01), showing that a weak CIVD response in the hand is related to a weak response in the foot. Discussion: We conclude that the cold-water finger immersion test is related to the temperature response in the toes and may thus continue to serve as a valid indicator for the risk of local cold injuries.

Milde huidverwarming verhoogt de slaperigheid en slaapdruk niet alleen bij volwassenen maar ook bij ouderen, maar ouderen met slaapproblemen kunnen deze milde veranderingen in huidtemperatuur niet of nauwelijks waarnemen, waardoor het buiten de experimentele setting/in het dagelijks leven dus mogelijk is dat ouderen met slaapproblemen wellicht in een te koud slaapomgeving proberen te slapen.

Peripheral cold injuries are often reported in mountaineers. Not only low ambient temperatures, but also the hypobaric circumstances are known to be major environmental risk factors. When the fingers are exposed to extreme cold for several minutes, cold induced vasodilation (CIVD) occurs, that is reported to have protective properties for cold injuries. Repeated immersion in cold water may lead to improved finger blood flow. In the latter study, the subjects immersed their phalanxes in ice water four times daily for one month. In this study we investigated if two weeks of repeated immersions of the hand in cold water prior to a mountain expedition to the Ama Dablam in Nepal enhanced finger blood flow response to cold.

Study Objectives: To investigate the effect of mild manipulations of core and skin temperature on psychomotor vigilance (PVT) in young adults, elderly, and elderly insomniacs. Design: 432 PVTs were obtained during a 2-day semi-constant routine protocol, while differentially manipulating core and skin temperatures within a comfortable thermoneutral range. Setting: Sleep laboratory of the Netherlands Institute for Neuroscience. Patients or Participants: Groups of 8 sex-matched young adults (27.0±2.4 years, mean±s.e.m.), elderly (65.8±2.8 years), and insomniacs (59.1±1.9 years). Measurements and Results: During the 7-minute PVTs, response speed typically declined with increasing time-on-task. Proximal skin warming by only ±0.6'C accelerated this decline by 67% (P = 0.05) in young adults and by 50% (P

The deployment of military operational personnel to hot environments has increased markedly since 1990. Several countries dispatch military personnel In-Theatre (e.g. Iraq and Afghanistan) in order to help the local population or to ensure a safe environment. In these hot climates it is hard for military personnel coming from colder environments to adapt immediately to the new environmental situation. Furthermore, military personnel have to be alert for seven days a week and 24 hours a day. Military personnel work and perform better when they are well rested1. High ambient temperatures during the night may have an influence on sleep and consequently may lead to sleep deprived military personnel. We tested whether a cooler night ambient temperature would be beneficial for the sleep of acclimated subjects as compared to a high ambient night temperature. All measurements performed in this study were specifically chosen to be also applicable for field studies in the military environment and the sleeping conditions was made comparable to the field situation by using field bed, sleeping bags and multiple sleepers in one room.

Sleep occurs in close relation to changes in body temperature. Both the monophasic sleep period in humans and the polyphasic sleep periods in rodents tend to be initiated when core body temperature is declining. This decline is mainly due to an increase in skin blood flow and consequently skin warming and heat loss. We have proposed that these intrinsically occurring changes in core and skin temperatures could modulate neuronal activity in sleep-regulating brain areas (Van Someren EJW, Chronobiol Int 17: 313-54, 2000). We here provide results compatible with this hypothesis. We obtained 144 sleep-onset latencies while directly manipulating core and skin temperatures within the comfortable range in eight healthy subjects under controlled conditions. The induction of a proximal skin temperature difference of only 0.78 +/- 0.03 degrees C (mean +/- SE) around a mean of 35.13 +/- 0.11 degrees C changed sleep-onset latency by 26%, i.e., by 3.09 minutes [95% confidence interval (CI), 1.91to 4.28] around a mean of 11.85 min (CI, 9.74 to 14.41), with faster sleep onsets when the proximal skin was warmed. The reduction in sleep-onset latency occurred despite a small but significant decrease in subjective comfort during proximal skin warming. The induction of changes in core temperature (delta = 0.20 +/- 0.02 degrees C) and distal skin temperature (delta = 0.74 +/- 0.05 degrees C) were ineffective. Previous studies have demonstrated correlations between skin temperature and sleep-onset latency. Also, sleep disruption by ambient temperatures that activate thermoregulatory defense mechanisms has been shown. The present study is the first to experimentally demonstrate a causal contribution to sleep-onset latency of skin temperature manipulations within the normal nocturnal fluctuation range. Circadian and sleep-appetitive behavior-induced variations in skin temperature might act as an input signal to sleep-regulating systems.