Repeated Cold Exposure Research Articles

Exertional fatigue and cold exposure: mechanisms of hiker's hypothermia

Participants in prolonged, physically demanding activities in cold weather are at risk of a condition known as "hiker's hypothermia". During exposure to cold weather, the increased gradient favoring body heat loss to the environment must be balanced by physiological responses, clothing, and behavioral strategies that conserve body heat stores, or else body temperature will decline. The primary human physiological responses elicited by cold exposure are shivering and peripheral vasoconstriction. Shivering increases thermogenesis and replaces body heat losses, while peripheral vasoconstriction improves thermal insulation of the body and retards the rate of heat loss. A body of scientific literature supports the concept that prolonged and (or) repeated cold exposure, fatigue induced by sustained physical exertion, or both together can impair shivering and vasoconstrictor response to cold. The mechanisms accounting for this thermoregulatory impairment are not clear, but the possibility that changes in blood glucose availability or sympathetic responsiveness to cold due to exertion and fatigue merit further research.

Local cold acclimation during exercise and its effect on neuromuscular function of the hand

Most acclimation research is performed on resting individuals, whereas in real life, cold exposure is often accompanied by physical activity. We examined the effects of 2 weeks of repeated cold exposure of the hand with or without an elevated core temperature from exercise on neuromuscular function of the first dorsal interosseus (FDI) muscle and manual performance of the hand. The experimental group (4 female, 6 male; age, 25.1 +/- 6.9 y) cooled their hands in 8 degrees C water for 30 min daily while cycling (50% of heart rate reserve); the control group (4 female, 4 male; age, 25.1 +/- 5.7 y) remained still. Manual function testing consisted of tactile sensitivity, grip strength, manual dexterity, and evoked twitch force in a custom-made myograph. Thermal sensation, skin temperature of index finger (Tif) and hand (Tfdi), as well as rectal temperature (Tre), were recorded daily. Tre increased significantly during bicycling, by 0.6 +/- 0.2 degrees C. Minimal Tif and Tfdi of the groups combined increased significantly during exposure days from 8.7 +/- 0.7 degrees C and 12.4 +/- 2.8 degrees C to 10.1 +/- 1.3 degrees C and 15.0 +/- 3.0 degrees C, respectively (p=0.04), with no significant difference between groups. Thermal ratings improved significantly on exposure days. Manual function was impaired with cooling, but with no significant difference between groups or across time. Deterioration of twitch characteristics with cooling did not change with repeated cold exposure. Although the increasing core temperature during cold water immersion changed the acute temperature response and thermal ratings, it had no effect on local cold acclimation or manual function.

Effect of cold acclimation on neuromuscular function of the hand

The research in this thesis investigated the effects of cold stress on neuromuscular function with the main focus on cold acclimation. In total, 6 studies, 1 field study and 5 experiments, were conducted. The field study showed that during manual work in cold weather, finger and hand temperature can drop to levels that may impair manual function. The first 2 experiments were conducted to investigate the effect of acute local cold stress on force control and to investigate the effect of cold-induced vasodilatation (CIVD) on neuromuscular function. In experiment 1, it was found that cooling of the hand in 10 °C cold water for 10 min did not improve force control, although neuromuscular function was significantly impaired after cooling. In experiment 2, cold-induced vasodilatation, occurring after 20 min of 8 °C cold-water immersion of the hand, was confined to the finger tip and had no effect on the temperature of the first dorsal interosseus (FDI) muscle or its neuromuscular function. A series of cold acclimation studies was conducted to investigate the effect of repeated cold-water hand immersions on neuromuscular function. In these experiments, neuromuscular function was tested before and after 2–3 weeks of daily hand immersion in 8 °C cold water for 30 min. In experiment 3, it was found that 3 weeks of cold-water immersion resulted in a decrease in minimum and mean index finger temperature and CIVD was attenuated. Neuromuscular function was not affected by this change in temperature response. In experiment 4, one hand was exposed daily to cold water and compared with the opposite control hand. Blood plasma catecholamine concentrations were increased after 2 weeks in the cold-exposed hand, but no changes in temperature response or neuromuscular function were found after repeated cold exposure. Thermal comfort after 30 min of cold-water immersion significantly improved after repeated cold exposure causing a discrepancy between actual and perceived temperature and it was suggested that this may impose a greater risk of cold injury owing to a change in behavioural thermoregulation. In the last experiment, core temperature was elevated by bicycling at a submaximal level during the cold hand immersion. Exercise had a direct effect on the temperature response during cold-water immersion, decreasing the minimum FDI temperature and slowing down the deteriorating effect of cold on neuromuscular function; however, exercise showed was no effect on local cold acclimation. It is concluded that local repeated cold exposures may improve finger and hand temperature and subjective thermal ratings, but that these changes are too small to improve neuromuscular function. The best remedy to maintain manual function is to limit or avoid cold stress as much as possible. If sufficient protection of the hands is impossible, core heating through exercise or passive heating may be a solution.

Central and peripheral factors in thermal, neuromuscular, and perceptual adaptation of the hand to repeated cold exposures

We investigated the role of central and peripheral factors in repeated cold exposure of the hand and their effects on temperature response, neuromuscular function, and subjective thermal sensation. Eleven subjects immersed their left hand repeatedly in 8 degrees C cold water for 30 min, 5 d/week, for 2 weeks. Before and following the 2 weeks of exposure, neuromuscular function, blood markers, thermal sensation, and temperature responses of both acclimated (left) and control (right) hands were tested. Minimum index finger temperature pre-acclimation was 10.9 +/- 3.4 degrees C and 10.0 +/- 2.0 degrees C in the left and right hand, respectively, and did not change significantly post-acclimation (left, 12.8 +/- 4.2 degrees C; right, 10.2 +/- 1.1 degrees C). Neuromuscular function was impaired with cooling, but this was significantly different neither between the hands nor over time. Central factors, measured by catecholamines and changes in temperature and cardiovascular response over time, did not change and there were no differences in responses between the exposed and non-exposed hand over time (peripheral adaptation) nor were there any differences in local factors endothelial-1 and nitric oxide. Subjective thermal comfort was improved and the discrepancy that was found between the change in actual and perceived temperature may increase the risk of cold injury in partially acclimatized individuals, owing to an adjustment in behavioural thermoregulation.

Caterpillars benefit from thermal ecosystem engineering by wandering albatrosses on sub-Antarctic Marion Island

Wandering albatrosses (Diomedea exulans) nest on Southern Ocean islands, building elevated nests upon which they incubate eggs and raise chicks, and which the chicks occupy through winter. The nests support high invertebrate biomass, including larvae of the flightless moth Pringleophaga marioni. Here we argue that high biomass of P. marioni in the nests is not associated with nutrient loading as previously suspected, but that higher temperatures in the nests increase growth and feeding rate, and decrease deleterious repeated cold exposure, providing fitness advantages for P. marioni. Thus, wandering albatrosses may be serving as thermal engineers, modifying temperature and therefore enabling better resource use by P. marioni.

Deleterious effects of repeated cold exposure in a freeze-tolerant sub-Antarctic caterpillar

Multiple freeze-thaw cycles are common in alpine, polar and temperate habitats. We investigated the effects of five consecutive cycles of approx. -5 degrees C on the freeze-tolerant larvae of Pringleophaga marioni Viette (Lepidoptera: Tineidae) on sub-Antarctic Marion Island. The likelihood of freezing was positively correlated with body mass, and decreased from 70% of caterpillars that froze on initial exposure to 55% of caterpillars that froze on subsequent exposures; however, caterpillars retained their freeze tolerance and did not appear to switch to a freeze-avoiding strategy. Apart from an increase in gut water, there was no difference in body composition of caterpillars frozen 0 to 5 times, suggesting that the observed effects were not due to freezing, but rather to exposure to cold per se. Repeated cold exposure did not result in mortality, but led to decreased mass, largely accounted for by a decreased gut mass caused by cessation of feeding by caterpillars. Treatment caterpillars had fragile guts with increased lipid content, suggesting damage to the gut epithelium. These effects persisted for 5 days after the final exposure to cold, and after 30 days, treatment caterpillars had regained their pre-exposure mass, whereas their control counterparts had significantly gained mass. We show that repeated cold exposure does occur in the field, and suggest that this may be responsible for the long life cycle in P. marioni. Although mean temperatures are increasing on Marion Island, several climate change scenarios predict an increase in exposures to sub-zero temperatures, which would result in an increased generation time for P. marioni. Coupled with increased predation from introduced house mice on Marion Island, this could have severe consequences for the P. marioni population.

Type I cryoglobulinemia and multiple myeloma presenting with widespread livedo reticularis and skin necrosis

Cryoglobulins are reversibly cold-precipitating, circulating immunoglobulins which can lead to clinical symptoms. such as recurrent palpable purpura. polyarthralgia and renal disease. A 65-year-old Taiwanese man presented with widespread, severe livedo reticularis of all four extremities with acrocyanosis, Raynaud's phenomenon, and eventuated in necrosis of auricular helices, scrotum and fingers after repeated cold exposure. Biopsy of livedo reticularis revealed dermal thrombosis with mixed inflammatory infiltrates in and around vessel walls, and biopsy of a gangrenous lesion showed similar occlusive vasculopathy with ischemic necrosis the skin. Further studies confirmed the presence of type I cryoglobulinemia and the diagnosis of IgG-kappa multiple myeloma. Due to the frequent association with underlying hematological disorders, autoimmune diseases and infections, thorough examination in a patient with cryoglobulinemia should be performed.

Comparative Characterization of Cytokine Production by Concanavalin A-Activated Splenocytes from BALB/c and C57Bl/6 Mice after Cold Exposure

The level of cytokines produced by ConA activated splenocytes was studied in male BALB/c and C57Bl/6 mice after single and repeated cold exposure (-20 degrees C, 3 min). Single cold exposure significantly decreased IL-2, -3, -4, -5, -10, -12, IFN-gamma production in BALB/c mice and decreased IL-2 content and increased TNF-alpha level in C57Bl/6 mice. Repeated cold exposure normalized the content of IL-2, -4, -10, -12, and IFN-gamma in BALB/c mice, which reflects the development of adaptive immune reactions. In C57Bl/6 mice IL-2, -3, -5, -10, -12, and IFN-gamma production remained significantly decreased, which attested to dysadaptive processes.

Work in Artificial Cold Environments

The physiological characteristics of work in cold stores, as a typical artificial cold environment, are reviewed mainly from our various field and experimental studies. There are about 4,000 cold stores in Japan, and 85% of them are kept at temperatures below -20 degrees C. Although the duration of cold exposure per stay in a cold store was very short, forklift workers entered the cold stores very frequently. Cold stress and the decrease in workers' performance were the same as for continuous exposure to cold. Since the peripheral skin temperature of subjects at night is higher than that in the afternoon, they are less likely to feel cold or pain sensation at night. However, there was a marked decrease in rectal temperature and in manual performance. There is an increased risk of both hypothermia and accidents for those who work at night. The cold store workers, however, had adapted to cold through daily repeated cold exposures.

Morphofunctional Characteristic of Mast Cells in BALB/c and C57Bl/6 Mice during Cold Exposure

Mast cells of the mesentery and subcutaneous tissue in BALB/c and C57Bl/6 mice were studied after single and repeated cold exposure (-20 degrees C, 3 min). Immediate adaptive reactions of mast cells in BALB/c and C57Bl/6 mice did not differ after single cold exposure and were manifested in increased degranulation. Repeated cold exposure of BALB/c mice was followed by an adaptive reaction, which included an increase in the count of mast cells in subcutaneous tissue and normalization of the degranulation index. In C57Bl/6 mice the count of mast cells in subcutaneous tissue decreased, while the degranulation index remained high. These changes reflect the disadaptive response of mast cells to repeated cold exposure.

Anti-stress effects of 3,4,5-trimethoxycinnamic acid, an active constituent of roots of Polygala tenuifolia (Onji).

3,4,5-trimethoxycinnamic acid (TMCA) is one of the constituents in Onji (roots of Polygala tenuifolia WILLD), an herbal medicine used for sedative in Japanese traditional Kampo medicine. Our previous study revealed that oral administration of this compound prolongs sleeping time induced by hexobarbital in mice to exhibit sedative action. In the present study, we investigate the effects of TMCA on the stress induced with repeated cold exposure or intracerebroventricular injection of corticotrophin-releasing hormone (CRH). Both types of stress significantly reduced the sleeping time induced with pentobarbital in rat, which was significantly prolonged by intraperitoneal injection of TMCA. The intracerebroventricular injection of CRH significantly augmented the content of norepinephrine (NE) in locus coeruleus (LC) of rats, which was significantly suppressed by the intracerebroventricular injection of TMCA. These findings suggest that TMCA would exhibit sedative effects by suppressing NE content in LC.

Nordic Society for Arctic Medicine. The effects of cold adaptation on human performance

Objectives. Repeated exposure to cold is known to provoke adaptation, reflected as changes in thermoregulatory and endocrine responses. These adaptive mechanisms are relatively well known. However, the functional impact on performance has not been studied.Methods. The first study is a cross-sectional population study conducted in 1997 (n=2624) and 2002 (n=6825), in which Finns, aged from 25 to 74 years, were queried about their habitual cold exposure. The material from the questionnaire is combined with meteorological information. In the second study, we examined the type of cold acclimatisation, if any, that prevails in urban circumpolar residents. A controlled laboratory study was conducted where subjects were exposed to three 24-h periods of either warm, or cold, bright and dim light, during winter (n = 7) and summer (n = 8). Thermoregulatory responses, physical and cognitive performance, and circulating hormones were assessed. Finally, cold acclimation was studied by exposing ten subjects to cold, on ten successive days. Responses in thermoregulation, autonomic nervous system, physical and cognitive performance, mood and hormones, were followed.Results. New information is obtained about the magnitude of habitual cold exposure and how it is affected by age, gender, place of residence, as well as by the degree of cold exposure. In addition, knowledge of the prevailing pattern of cold adaptation of modern circumpolar residents and its effects on physicial performance, cognitive functioning and mood is received. The repeated cold exposure study reveals information on the successive stages of cold acclimatisation, as well as the interrelations between thermoregulation and performance.Significance. The medical community managing the health care of residents living in high latitude environments will have an improved understanding of the functional significance of cold adaptation, the specific environmental conditions and physiological mechanisms that affect performance and behaviour in these regions.

繰り返し寒冷暴露が、体温・循環機能・主観的応答・作業パフォーマンスにおよぼす影響

繰り返し寒冷暴露が、体温・循環機能・主観的応答・作業パフォーマンスにおよぼす影響

The effect of exercise training in a cold environment on thermoregulation in adult and aged C57BL/6J mice.

We studied the effect of exercise training in cold environment (six weeks of daily, one-hour runs on a treadmill at ambient temperature of 6 +/- 1 degrees C at 60-65% of VO2max) on cold-induced metabolic heat production, heat loss, and cold tolerance in adult and aged C57BL/6J male mice. In adult mice, exercise training in cold environment resulted in greater cold-induced heat production and cold tolerance without changes in heat loss, similar to the effects of daily cold exposure without exercise. In aged mice, daily cold exposures did not affect cold tolerance and cold-induced heat production, but exercise training in the cold resulted in greater cold-induced heat production and cold tolerance. Heat loss in aged mice increased similarly after both repeated cold exposures and exercise training in the cold. Therefore, mechanisms of effect of exercise training on cold tolerance are different in adult and aged animals. Exercise training in cold environment does not affect cold-induced heat production and cold tolerance in adult mice, but improves them in aged animals.

Change in heat loss as a part of adaptation to repeated cold exposures in adult and aged male C57BL/6J mice.

Previous studies have shown that adult mice increase cold-induced heat production as a result of repeated exposures to cold, but that aged mice do not. The objective of the present study was to investigate changes in heat loss during repeated cold exposures in adult and aged C57BL/6J mice. Mice were partially restrained for three hours at 6 degrees C, three times at one-week intervals. Dry heat loss was inferred from measurements of differential temperature between the incoming and outgoing air in the experimental chamber. During the first cold exposure, aged mice showed less heat loss (both total and adjusted for body temperature) than adult animals, suggesting greater peripheral vasoconstriction in aged mice. With repeated cold exposures, both age groups showed increased heat loss, but the aged mice showed greater increase of heat loss, so that by the third cold stress test, no significant differences in heat loss between adult and aged mice were observed. The increase of heat loss after repeated cold exposures in aged mice might reflect a lesser peripheral vasoconstriction, serving to reduce the possibility of tissue necrosis in the cold.

Cold Acclimation-Associated Changes in Brown Adipose Tissue do Not Necessarily Indicate an Increase of Nonshivering Thermogenesis in C57BL/6J Mice

We have reported previously that a cold acclimation procedure (3-hr partial restraint at 6°C, repeated 3 times at 2-week intervals) usually improves the cold tolerance of adult C57BL/6J mice. Those mice that did not improve their cold tolerance had lower cold-induced sympathetic nervous outflow to the interscapular brown adipose tissue (IBAT), suggesting a failure in the mechanisms of nonshivering thermogenesis. To understand the origin of this failure, this study was intended to measure nonshivering thermogenesis in mice that did not improve their cold tolerance after the cold acclimation procedure. After being subjected 3 times to a partial restraint at 6°C, mice were anesthetized with urethane, immobilized with vecuronium bromide, and placed on artificial ventilation. The VO2 and VCO2 in expired air were measured and metabolic heat production (MHP) was calculated while body temperature was artificially lowered to 7.5°C below control level. In a separate group of mice, the total amount and concentration of mitochondrial uncoupling protein, thermogenin (UCP), in IBAT was measured immediately after completion of the cold-acclimation procedure. The concentration and the amount of UCP in the mitochondria of IBAT was significantly higher in all mice that had been presented to the cold acclimation procedure, regardless of its outcome, than in mice that had never been exposed to an environment below room temperature (NAIVE). MHP increased significantly during body cooling in all mice. However, MHP before and during cold stimulation in mice that did not improve their cold tolerance as a result of the cold-acclimation procedure was significantly lower than the MHP of animals in which cold tolerance was improved, and was not different from MHP of the NAIVE group. Therefore, in mice in which cold tolerance did not improve after repeated cold exposure, the anatomical and biochemical changes in brown adipose tissue typical of cold acclimation were not associated with a cold-induced increase in MHP. We infer that the expression of UCP in brown adipose tissue is a necessary, but not sufficient, attribute of cold acclimation. Cold acclimation, measured as increased cold tolerance, occurs only if synthesis of UCP in BAT is associated with an increased cold-induced response of the sympathetic nervous system.

Stimulus conditions influencing the development of tolerance to repeated cold exposure in rats

Tolerance to an environmental cold challenge in rats is eliminated when cold exposure occurs in a context different from the adaptation context, indicating that learning mechanisms play a role in thermoregulation (Riccio, MacArdy, & Kissinger, 1991). This finding, analogous to outcomes obtained with drug tolerance, was investigated in the present study. Experiment 1 demonstrated that a change in both proximal and distal contextual cues disrupts an established cold adaptation, an outcome consistent with the view that associative processes contribute to the tolerance. In Experiment 2, although cold tolerance persisted over a 7-day retention interval, the disruption of tolerance by a shift in context was attenuated with the delay of testing. This finding suggests that the precise stimulus attributes of the context were forgotten over the interval. Experiment 3 demonstrated that cold-tolerance disruption is due to the actual change in context and not to novelty of the test context. Experiment 4 showed that changing the context associated with each cold exposure impaired the development of tolerance. The results of these experiments provide additional evidence that cold tolerance is regulated at least partially by associative learning processes.

Changes in the activity of the adrenal cortex in fasted echidnas ( Tachyglossus aculeatus) exposed to low ambient temperatures

1. 1. The adrenal cortex is necessary for survival of echidnas at low ambient temperatures. In this study, adrenal gland activity was investigated in echidnas exposed to 2 days of cold (14°C) and fasting, alternating with 2 days at room temperature and feeding ad lib. 2. 2. In the cold. 2.75 ± 0.29% (SD) of the initial body weight was lost daily. Plasma amino acid concentration did not change while glucose concentration decreased from 2.6 ± 0.3 to 1.5 ± 0.3 mmol/l with consecutive sessions of cold. 3. Plasma concentrations of corticosterone (7.2 ± 1.4 nmol/l) and cortisol (4.4 ± 1.9 nmol/l) were unchanged by repeated cold exposure. However, the adrenal response to ACTH stimulation decreased and the clearance of corticosteroids increased after cold exposure. 4. It was concluded that exposure to cold increases the utilization of glucocorticoids and decreases the capacity for their biosynthesis.

Alteration of nyctohemeral changes in body core temperature by repeated cold exposure given at a fixed time daily in rats [corrected

The effects of cold exposure for several hours at a fixed time once a day on nyctohemeral variations of hypothalamic temperature (Thy), heat balance, and feeding and locomotor activities were examined in rats. The cold-exposed group was subjected to an ambient temperature of 3 degrees C for about 5 h in the last half of the dark phase daily for 10 or more than 21 consecutive days, while the control rats were kept constant at 24 degrees C. The 10-d cold exposure had little effect on nyctohemeral changes in Thy and locomotor activity. However, after completing a 3- to 4-week cold exposure schedule, the levels of Thy, heat loss, heat production, and feeding and locomotor activities of the cold-exposed rats significantly decreased for 1-2 h during the period of the previous cold exposure time. These decreases lasted for at least 2 d after the end of the cold exposure schedule. These results suggest that the patterns of nyctohemeral changes in body core temperature and feeding and locomotor activities were altered after repeated cold exposure at a fixed time once a day in rats.

Cold tolerance and metabolic heat production in male C57BL/6J mice at different times of day

Nine-month-old male C57BL/6J mice were subjected to three-hour cold stress tests (partial restraint at 6°C) at 9:00 a.m. or at 1:00 p.m. Tests were repeated three times at two-week intervals at the same time of day. Body temperature was measured by colonic thermoprobe, and metabolic heat production was measured by indirect calorimetry during each test. All mice showed habituation to repeated cold exposures (an improvement of cold tolerance across tests) due to an increase in metabolic heat production. The levels of metabolic heat production were similar during morning and afternoon testing; however, mice tested in the afternoon had consistently poorer cold tolerance, which indicated increased heat loss. Increased heat loss in mice of similar body weight and presumably similar body composition, suggests that there is less effective cold-induced skin vasoconstriction during the afternoon. We hypothesize that the compromised skin vasomotor response during the afternoon cold exposure results from competing effects of vasodilation due to local autoregulation stimulated by a circadian reduction of cardiac output during the sleep phase, and vasoconstriction due to the cold stress.