Thermal effects of dorsal head immersion in cold water on nonshivering humans.

Personal floatation devices maintain either a semirecumbent flotation posture with the head and upper chest out of the water or a horizontal flotation posture with the dorsal head and whole body immersed. The contribution of dorsal head and upper chest immersion to core cooling in cold water was isolated when the confounding effect of shivering heat production was inhibited with meperidine (Demerol, 2.5 mg/kg). Six male volunteers were immersed four times for up to 60 min, or until esophageal temperature = 34 degrees C. An insulated hoodless dry suit or two different personal floatation devices were used to create four conditions: 1) body insulated, head out; 2) body insulated, dorsal head immersed; 3) body exposed, head (and upper chest) out; and 4) body exposed, dorsal head (and upper chest) immersed. When the body was insulated, dorsal head immersion did not affect core cooling rate (1.1 degrees C/h) compared with head-out conditions (0.7 degrees C/h). When the body was exposed, however, the rate of core cooling increased by 40% from 3.6 degrees C/h with the head out to 5.0 degrees C/h with the dorsal head and upper chest immersed (P < 0.01). Heat loss from the dorsal head and upper chest was approximately proportional to the extra surface area that was immersed (approximately 10%). The exaggerated core cooling during dorsal head immersion (40% increase) may result from the extra heat loss affecting a smaller thermal core due to intense thermal stimulation of the body and head and resultant peripheral vasoconstriction. Dorsal head and upper chest immersion in cold water increases the rate of core cooling and decreases potential survival time.     

The effect of clothing on "diving bradycardia" in man during submersion in cold water

Eighteen healthy male volunteers undertook three seated submersions into stirred water at 5 degrees C. Whilst submerged, the subjects attempted to hold their breath for 20 s. They wore a different clothing assembly for each submersion, viz: a cotton overall assembly, a "wet suit" assembly and a "dry suit" assembly. During the experiments the breath-hold time, heart rate, skin and rectal temperatures of the subjects were recorded. The results showed that significantly (P less than 0.05) more subjects developed a diving bradycardia--defined as five or more consecutive R-R intervals of over 1.2 s--when wearing the dry suit. It is concluded that increasing the cold stress experienced by individuals during cold-water submersion decreases the incidence of diving bradycardia but not the magnitude of the bradycardia when it occurs.     

Only UCP1 can mediate adaptive nonshivering thermogenesis in the cold.

Adaptive nonshivering thermogenesis may have profound effects on energy balance and is therefore therefore is a potential mechanism for counteracting the development of obesity. The molecular basis for adaptive nonshivering thermogenesis has remained a challenge that sparked acute interest with the identification of proteins (UCP2, UCP3, etc.) with high-sequence similarity to the original uncoupling protein-1 (UCP1), which is localized only in brown adipose tissue. Using UCP1-ablated mice, we examined whether any adaptive nonshivering thermogenesis could be recruited by acclimation to cold. Remarkably, by successive acclimation, the UCP1-ablated mice could be made to subsist for several weeks at 4C during which they had to constantly produce heat at four times their resting levels. Despite these extreme requirements for adaptive nonshivering thermogenesis, however, no substitution of shivering by any adaptive nonshivering thermogenic process occurred. Thus, although the existence of, for example, muscular mechanisms for adaptive nonshivering thermogenesis has recurrently been implied, we did not find any indication of such thermogenesis. Not even during prolonged and enhanced demand for extra heat production was any endogenous hormone or neurotransmitter able to recruit any UCP1-independent adaptive nonshivering thermogenic process in muscle or in any other organ, and no proteins other than UCP1-not even UCP2 or UCP3-therefore have the ability to mediate adaptive nonshivering thermogenesis in the cold.     

Thermoregulatory model for immersion of humans in cold water

The mathematical models of thermoregulation of Stolwijk and Hardy, and Montgomery were used to develop a model suitable for the simulation of human physiological responses to cold-water immersion. Data were obtained from experiments where 13 healthy male volunteers were totally immersed under resting and nude conditions for 1 h in water temperatures of 20 and 28 degrees C. At these temperatures, the mean measured rectal temperature (Tre) fell by approximately 0.9 and 0.5 degrees C, respectively, yet mean measured metabolic rate (M) rose by approximately 275 and 90 W for the low body fat group (n = 7) and 195 and 45 W for the moderate body fat group (n = 6). To predict the observed Tre and M values, the present model 1) included thermal inputs for shivering from the skin independent of their inclusion with the central temperature to account for the observed initial rapid rise in M, 2) determined a thermally neutral body temperature profile such that the measured and predicted initial values of Tre and M were matched, 3) confined the initial shivering to the trunk region to avoid an overly large predicted initial rate of rectal cooling, and 4) calculated the steady-state convective heat loss by assuming a zero heat storage in the skin compartment to circumvent the acute sensitivity to the small skin-water temperature difference when using conventional methods. The last three modifications are unique to thermoregulatory modeling.     

Implications of nonshivering thermogenesis for energy balance regulation in humans

The incidence of the metabolic syndrome has reached epidemic levels in the Western world. With respect to the energy balance, most attention has been given to reducing energy (food) intake. Increasing energy expenditure is an important alternative strategy. Facultative thermogenesis, which is the increase in energy expenditure in response to cold or diet, may be an effective way to affect the energy balance. The recent identification of functional brown adipose tissue (BAT) in adult humans promoted a renewed interest in nonshivering thermogenesis (NST). The purpose of this review is to highlight the recent insight in NST, general aspects of its regulation, the major tissues involved, and its metabolic consequences. Sustainable NST in adult humans amounts to 15% of the average daily energy expenditure. Calculations based on the limited available literature show that BAT thermogenesis can amount to 5% of the basal metabolic rate. It is likely that at least a substantial part of NST can be attributed to BAT, but it is possible that other tissues contribute to NST. Several studies on mitochondrial uncoupling indicate that skeletal muscle is another potential contributor to facultative thermogenesis in humans. The general and synergistic role of the sympathetic nervous system and the thyroid axis in relation to NST is discussed. Finally, perspectives on BAT and skeletal muscle NST are given.     

Comparative aspects of cold acclimation and nonshivering thermogenesis in homeotherms

In some small animals (rat, guinea,pig) adaptation to cold entails an increased ability to produce heat through nonshivering thermogenesis. This is closely associated with the calorigenic action of noradrenaline (NA), In bigger animals (rabbit) the magnitude of nonshivering thermogenesis governed by NA is smaller and these animals rely mostly on adaptation by means of increased insulation. In some other species (white mouse, hedgehog, dog, young fowl)the role of NA in cold acclimation is either not clear or dubious. The last group of homeotherms involves species which do not show either nonshivering thermogenesis or increased insulation after cold adaptation although the resistance to cold has been found to be increased (pigeon, chickens, miniature swine, new born pig). An entirely new mechanism of cold adaptation must be anticipated in these species.

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Zusammenfassung In einigen kleineren Tierarten (Ratte, Meerschweinchen) schliesst die Anpassung an Kälte eine erhöhte Fähigkeit zur Wärmebildung ohne Muskelzittern ein. Dieser Beitrag zur Wärmebildung ist zusätzlich zu dem durch Muskelzittern und eng mit der kalorigenen Wirkung von Noradrenalin (NA) verbunden. Grössere Tiere passen sich an Kälte vorwiegend durch Verbesserung der Isolation an (Kaninchen). Der Anteil der durch NA gesteuerten Thermogenese ist gering. Bei anderen Tieren (Maus, Igel, Hund, junges Geflügel) ist die Rolle des NA entweder noch nicht abgeklärt oder zweifelhaft. Schliesslich gibt es Tiere (Taube, Huhn, junge Schweine), die bei Kälteakklimatisation weder eine Verbesserung der Isolation noch zitterfreie Thermogenese aufweisen. Bei diesen Tierarten muss ein völlig neuer Mechanismus der Kälteanpassung angenommen werden.

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Resume Pour quelques espèces de petits animaux (rats, cobaye), l'adaptation au froid englobe la possibilité accrue de production de chaleur sans tremblement musculaire. Cette contribution à la production de chaleur se greffe à celle provenant du tremblement musculaire et est étroitement liée à l'effet calorigène de la noradrénaline (NA). De plus gros animaux s'adaptent au froid surtout par une amélioration de l'isolation (lapin). La part de chaleur due à l'effet de la NA y est faible. Pour d'autres espèces (souris, hérisson, chien, jeune volaille), le rôle joué par la NA est ou peu clair ou douteux. Enfin, certains animaux (pigeons, poules,porcelets) ne présentent ni amélioration de l'isolation ni production de chaleur par tremblement musculaire au cours de l'acclimatation au froid. Dans ces cas-là, il faut admettre un mécanisme entièrement nouveau d'adaptation au froid.

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Presented during the Fifth International Biometeorological Congress, 1–7 September 1969, Montreux, Switzerland.     

Thermal balance and survival time prediction of man in cold water.

Metabolic rates and rectal temperatures were continuously monitored for humans immersed in cold ocean water (4.6--18.2 degrees C) under stimulated accident conditions. The subjects wore only light clothing and a kapok lifejacket while either holding-still or swimming. While holding-still, metabolic heat production (Hm,kcal-min--1) was inversely related to water temperature (Tw, degrees C) according to the equation Hm equals 4.19 minus-0.117 Tw. This temperature response pattern is shown to be similar to that for exposure to air of the same temperature when air velocity is just over 5 m.p.h. (2.24 m/s). The thermogenic response was one-third efficient in balancing the calculated heat loss in cold water, resulting in hypothermia at a rectal temperature cooling rate (C, degrees C-min--1) dependent on water temperature (Tw, degrees C) according to the relation C equal 0.0785 - 0.0034Tw. Although swimming increased heat production to 2.5 times that of holding-still at 10.5 degrees C water temperature, cooling rate was 35% greater while swimming. A prediction equation for survival time (ts, min) of persons accidentally immersed in cold water (Tw, degrees C) has the form ts equal 15 + 7.2/(0.0785-0.0034Tw), based on the findings of this study, and it is compared to pre-existing models.     

朱砂叶螨成螨在水中的耐受力

【目的】明确朱砂叶螨Tetranychus cinnabarinus(Boisduval)在雨水中的耐受能力,为评价雨水对朱砂叶螨的控制作用提供理论依据。【方法】本文通过采用玻片浸渍法和录像技术,对朱砂叶螨沉于水中的沉浮比例、耐受力以及足的摆动频率进行研究。【结果】在棉花叶片上接螨饲养5 d后(92.79%±0.55%)的朱砂叶螨沉于水中的比例极显著高于2 d后(42.72%±2.37%)的;3日龄的雌(297.4±16.1)min、雄(297.7±7.4)min成螨之间在水中存活时间差异不明显。雌雄成螨在水中最短存活时间分别为48 min和45 min;雌雄成螨数量大约在300 min内死亡达到一半,雌雄成螨在水中最长存活时间分别为773 min和856 min;雌雄成螨死亡数在时间上分布不均匀。沉在水中朱砂叶螨雌雄成螨死亡过程中表现为:足的摆动频次由高到低,足的摆动时间也非连续状态。【结论】朱砂叶螨成螨在水中有一定的耐受能力。     

Conductive and convective heat flows of exercising humans in cold water

The apparent conductance (Kss, in W.m-2.degrees C-1) of a given region of superficial shell (on the thigh, fat + skin) was determined on four nonsweating and nonshivering subjects, resting and exercising (200 W) in water [water temperature (Tw) 22-23 degrees C] Kss = Hss/(Tsf-Tsk) where Hss is the skin-to-water heat flow directly measured by heat flow transducers and Tsf and Tsk are the temperatures of the subcutaneous fat at a known depth below the skin surface and of the skin surface, respectively. The convective heat flow (qc) through the superficial shell was then estimated as qc = (Tsf - Tsk).(Kss - Kss,min), assuming that at rest Kss was minimal (Kss,min) and resting qc = 0. The duration of immersion was set to allow rectal temperature (Tre) to reach approximately 37 degrees C at the end of rest and approximately 38 degrees C at the end of exercise. Except at the highest Tw used, Kss at the start of exercise was always Kss,min and averaged 51 W.m-2.degrees C-1 (range 33-57 W.m-2.degrees C-1) across subjects, and qc was zero. At the end of exercise at the highest Tw used for each subject, Kss averaged 97 W.m-2.degrees C-1 (range 77-108 W.m-2.degrees C-1) and qc averaged 53% (range 48-61%) of Hss (mean Hss = 233 W.m-2).(ABSTRACT TRUNCATED AT 250 WORDS)     

Immune changes in humans during cold exposure: effects of prior heating and exercise.

This study examined the immunological responses to cold exposure together with the effects of pretreatment with either passive heating or exercise (with and without a thermal clamp). On four separate occasions, seven healthy men [mean age 24.0 +/- 1.9 (SE) yr, peak oxygen consumption = 45.7 +/- 2.0 ml. kg(-1). min(-1)] sat for 2 h in a climatic chamber maintained at 5 degrees C. Before exposure, subjects participated in one of four pretreatment conditions. For the thermoneutral control condition, subjects remained seated for 1 h in a water bath at 35 degrees C. In another pretreatment, subjects were passively heated in a warm (38 degrees C) water bath for 1 h. In two other pretreatments, subjects exercised for 1 h at 55% peak oxygen consumption (once immersed in 18 degrees C water and once in 35 degrees C water). Core temperature rose by 1 degrees C during passive heating and during exercise in 35 degrees C water and remained stable during exercise in 18 degrees C water (thermal clamping). Subsequent cold exposure induced a leukocytosis and granulocytosis, an increase in natural killer cell count and activity, and a rise in circulating levels of interleukin-6. Pretreatment with exercise in 18 degrees C water augmented the leukocyte, granulocyte, and monocyte response. These results indicate that acute cold exposure has immunostimulating effects and that, with thermal clamping, pretreatment with physical exercise can enhance this response. Increases in levels of circulating norepinephrine may account for the changes observed during cold exposure and their modification by changes in initial status.     

Antimutagenic effects in humans.

The application of antimutagenicity studies to human somatic mutation is discussed, with emphasis on the potential for future studies. Five assay-gene combinations are now available for measuring human somatic mutation in lymphocytes and erythrocytes. Results with these combinations have defined the human background levels, and show clear responses of mutant frequency to a variety of mutagens. The testing of antimutagenic effects on background frequencies is feasible, but has not yet been done. The major uncertainty in such studies is the unknown age of mutant cells in the background, since only the newly forming mutants are potentially susceptible to most antimutagenic treatments. Intervention studies in the face of active mutagenicity and the use of other genotoxicity endpoints, such as chromosome aberrations, micronuclei and DNA adducts, are considered briefly.     

Effect of photoperiod and melatonin on cold resistance,thermoregulation and shivering/nonshivering thermogenesis in Japanese quail

Summary The effect of photoperiod and melatonin treatment on cold resistance and thermogenesis of quails was studied. The birds were acclimated for 8 weeks to short day (8L:16D) or long day (16L:8D) conditions, and 8 of 16 quails in each group were implanted with melatonin capsules. One group of quails was maintained outside in an aviary during winter. Oxygen consumption ( ) body temperature (T _b, recorded with temperature transmitters) and shivering (integrated pectoral EMG) were recorded continuously, and samples of heart rate and breathing rate were picked up when ambient temperature was decreased stepwise from 27 down to –75 °C. Heat production maximum (HP_max), cold limit, lower critical temperature, basal metabolic rate (BMR) and thermal conductance were determined.The results show that short day, cold and melatonin treatment improved cold resistance and thermal insulation of quils when compared with quails acclimated to long day conditions. An increase in HP_max was induced only by melatonin treatment. The results suggest that the acclimatization of quails is under control of the pineal gland.The linear increase of shivering intensity with at moderate cold load shows that shivering is the primary source for thermoregulatory heat production in the quail. AtT _a's below –40 °C shivering remained constant although , heart rate and breathing rate continued to increase with increasing cold load. This could indicate the existence of a nonshivering thermogenesis in birds. Unlike to mammals, this non-shivering thermogenesis in birds would serve as secondary source of heat supporting shivering thermogenesis in severe coldAbbreviations BMR basal metabolic rate - ECG electrocardiogram - EMG electromyogram - NST nonshivering thermogenesis - SMR standard metabolic rate