Reduced Heat Production Research Articles

Cocoa husks in diets of Italian heavy pigs

The aim of the present study was to evaluate the effect of cocoa husks feeding on liver composition of the Italian heavy pig. Cocoa husks are by-products derived from chocolate production and have a high content of proteins, lipids, and NDF. Cocoa husks are also rich in antioxidants, polyphenols in particular. Eight finishing pigs were divided into 2 groups: control group fed a traditional diet, based on cereals, and treatment group fed a diet obtained by substitution of 10% of the control diet with coarsely ground cocoa husks. The trial was conducted during the hot season and lasted 6 wk, at the end of which all the pigs were slaughtered. Cocoa husks diet reduced dry matter intake (P < 0.01) and energy intake (P < 0.01) but neither body weight nor backfat thickness was affected by cocoa husks diet. Treatment did not influence carcass weight and hot dressing percentage but reduced liver weight (P < 0.05), liver dry matter percentage (P < 0.01), DNA (P = 0.01), and glycogen content (P = 0.01). By contrast, cocoa husks increased liver ether extract (P = 0.05) without affecting cholesterol content. Liver weight loss, reduction of protein synthesis, and a shift toward glycogen use instead of fat oxidation are considered metabolic strategies to reduce heat production under hot conditions. It is possible, therefore, that cocoa husks feeding promoted the process of acclimation because pigs needed less feeding to reach similar body and carcass weight as control pigs.

Superimposition of Postnatal Calorie Restriction Protects the Aging Male Intrauterine Growth- Restricted Offspring from Metabolic Maladaptations

Intrauterine growth restriction (IUGR) results in dysregulated glucose homeostasis and adiposity in the adult. We hypothesized that with aging, these perturbations will wane, and superimposition of postnatal growth restriction (PNGR) on IUGR [intrauterine and postnatal growth restriction (IPGR)] will reverse the residual IUGR phenotype. We therefore undertook hyperinsulinemic-euglycemic clamp, energy balance, and physical activity studies during fed, fasted, and refed states, in light and dark cycles, on postweaned chow diet-fed more than 17-month aging male IUGR, PNGR, and IPGR vs. control (CON) rat offspring. Hyperinsulinemic-euglycemic clamp revealed similar whole-body insulin sensitivity and physical activity in the nonobese IUGR vs. CON, despite reduced heat production and energy expenditure. Compared with CON and IUGR, IPGR mimicking PNGR was lean and growth restricted with increased physical activity, O(2) consumption (VO(2)), energy intake, and expenditure. Although insulin sensitivity was no different in IPGR and PNGR, skeletal muscle insulin-induced glucose uptake was enhanced. This presentation proved protective against the chronologically earlier (5.5 months) development of obesity and dysregulated energy homeostasis after 19 wk on a postweaned high-fat diet. This protective role of PNGR on the metabolic IUGR phenotype needs future fine tuning aimed at minimizing unintended consequences.

Hyposensitization and Desensitization in Allergic Contact Dermatitis

Acquired allergic contact dermatitis (ACD) causes significant morbidity. Certain occupations predispose workers to ACD, especially those that may damage the skin barrier. Allergic contact dermatitis has significant socioeconomic effects. Allergic contact dermatitis is difficult to treat, particularly if exposure is unavoidable. The objective of this study was to establish the efficacy of intradermal steroid injections in inducing specific antigen hyposensitization when administered weekly into shifted patch-test sites. Prospective, open-label trial included 10 patients with ACD. Each week for up to 8 weeks, patients were patch-tested to their known allergen, and the patch-test site was injected with triamcinolone. Primary outcomes were clinical score, reaction size, erythema, and thermal characteristics. Statistical analysis included regression, correlation, repeated measures, and analysis of variance with contrast variables. Overall results suggest significant decreases in patch-testing reactions as evidenced by improved clinical scores, reaction sizes, and reduced heat production. In 3 patients, the patch test became negative. This desensitized state persisted for 2 months in 1 patient and for 4 months in the other 2 patients. Repetitive treatments of weekly, shifted, positive patch test sites with intradermal steroid injections show a tendency toward allergen-specific hyposensitivity and in some cases to nonreactivity at repeat patch testing. This finding may influence future management of ACD.

Viewpoint: Are there valid concerns for completing a marathon at 39 weeks of pregnancy?

recently, widespread media attention has been given to Amber Danielle Miller, a 27-yr-old woman (163 cm tall), who, at 39 wk of pregnancy, gave birth following her completion of the Chicago Marathon on October 9, 2011 ([17][1], [19][2], [21][3]). She completed the Marathon in 6 h, 25 min, and 50 s

Heat stress and feeding strategies in meat-type chickens

Heat stress can induce hyperthermia in poultry. A reduction in heat load can be achieved by increasing the possibilities for dissipation, decreasing the level of heat production or by changing the thermal production pattern within a day. Strategies to reduce the negative effects of heat stress can be based on a specific feeding strategy, such as restricted feeding. Feed that is offered long enough before a hot period can ameliorate the harmful effects of high temperature. Another strategy may be to use choice feeding from different feed ingredients, rich in protein or in energy. With such self-selection, the chicken may adjust its intake of individual components, allowing the bird to optimise the heat load associated with the metabolism of the ingested nutrients. Additional promising strategies involve offering a choice between feeds with a different feed particle size or structure. A large particle size contributes to the development of the gastro-intestinal tract (GIT), especially the gizzard and the caeca. A large gizzard will maximize the grinding process and potentially ease digestion down the GIT, thereby reducing heat production associated with digestive processing. Also wet feeding may be profitable under heat stress conditions as well. Feeding wet diets may facilitate an increased water intake and larger particle sizes can limit water excretion in droppings, resulting in more water being available for evaporation during panting, hence cooling the bird. In conclusion, these feeding strategies may help to reduce heat production peaks, facilitate evaporative activity and/or decreases the heat load, resulting in beneficial effects on performance and health of the bird kept in more tropical areas worldwide.

Sex Differences in the Metabolic Effects of Testosterone in Sheep

Adiposity is regulated in a sexually divergent manner. This is partly due to sex steroids, but the differential effects of androgens in males and females are unclear. We investigated effects of testosterone on energy balance in castrated male (n = 6) and female sheep (n = 4), which received 3 × 200 mg testosterone implants for 2 wk or blank implants (controls). Temperature probes were implanted into retroperitoneal fat and skeletal muscle. Blood samples were taken to measure metabolites and insulin. In males, muscle and fat biopsies were collected to measure uncoupling protein (UCP) mRNA and phosphorylation of AMP-activated protein kinase and Akt. Testosterone did not change food intake in either sex. Temperature in muscle was higher in males than females, and testosterone reduced heat production in males only. In fat, however, temperature was higher in the castrate males compared with females, and there was no effect of testosterone treatment in either sex. Preprandial glucose levels were lower, but nonesterified fatty acids were higher in females compared with males, irrespective of testosterone. In males, the onset of feeding increased UCP1 and UCP3 mRNA levels in skeletal muscle, without an effect of testosterone. During feeding, testosterone reduced glucose levels in males only but did not alter the phosphorylation of AMP-activated protein kinase or Akt in muscle. Thus, testosterone maintains lower muscle and fat temperatures in males but not females. The mechanism underlying this sex-specific effect of testosterone is unknown but may be due to sexual differentiation of the brain centers controlling energy expenditure.

Sustainable ICT: Micro and Nanoscale Energy Management

State of the art ICT basic devices are dominated by power dissipated in heat. Presently the main effort is aimed at cooling down the heat produced during computation with specific attention to the charge transport on one hand and on the other hand on reducing the voltage operating levels up to the point of not compromising the error rate due to voltage fluctuations. In this scientific session we proposed to address the problem at a very fundamental level: what are the basic mechanisms behind the heat production? How can we take advantage of the fluctuations instead of avoiding them? These questions should convey the idea that the proposed approach is way beyond the state of the art. It is not simply an incremental progress toward the reduction of heat production in room temperature conductors or new technology beyond CMOS. It is a new, visionary approach that challenges the very basic foundation of thermodynamics.

Nitrous oxide causes a regulated hypothermia: Rats select a cooler ambient temperature while becoming hypothermic

An initial administration of 60% nitrous oxide (N(2)O) evokes hypothermia in rats and if the administration continues for more than 1-2h, acute tolerance typically develops such that the initial reduction in core temperature (Tc) reverses and Tc recovers toward control values. Calorimeter studies at normal ambient temperature indicate that hypothermia results from a transient reduction in heat production (HP) combined with an elevation in heat loss. Acute tolerance develops primarily due to progressive increases in HP. Our aim was to determine whether rats provided a choice of ambient temperatures would behaviorally facilitate or oppose N(2)O-induced hypothermia. A gas-tight thermally-graded alleyway (range, 6.7-37.0°C) enabled male Long-Evans rats (n=12) to select a preferred ambient temperature during a 5-hour steady-state administration of 60% N(2)O and a separate paired control gas exposure (order counterbalanced). Tc was measured telemetrically from a sensor surgically implanted into the peritoneal cavity >7days before testing. Internal LED lighting maintained the accustomed day:night cycle (light cycle 0700-1900h) during sessions lasting 45.5h. Rats entered the temperature gradient at 1100h, and the 5-h N(2)O or control gas period did not start until 23h later to provide a long habituation/training period. Food and water were provided ad libitum at the center of the alleyway. The maximum decrease of mean Tc during N(2)O administration occurred at 0.9h and was -2.05±0.25°C; this differed significantly (p<0.0001) from the corresponding Tc change at 0.9h during control gas administration (0.01±0.14°C). The maximum decrease of the mean selected ambient temperature during N(2)O administration occurred at 0.7h and was -13.58±1.61°C; this differed significantly (p<0.0001) from the corresponding mean change in the selected ambient temperature at 0.7h during control gas administration (0.30±1.49°C). N(2)O appears to induce a regulated hypothermia because the selection of a cool ambient temperature facilitates the reduction in Tc. The recovery of Tc during N(2)O administration (i.e., acute tolerance development) could have been facilitated by selection of ambient temperatures that were warmer than those chosen during control administrations, but interestingly, this did not occur.

Schistosoma mansoni: Antischistosomal activity of the four optical isomers and the two racemates of mefloquine on schistosomula and adult worms in vitro and in vivo

Recent studies have shown that mefloquine (MQ) reveals interesting antischistosomal properties. We examined the antischistosomal activities of the erythro and threo isomers and racemates of MQ on newly transformed schistosomula (NTS) and adult Schistosoma mansoni in vitro and in mice harbouring adult S. mansoni. The in vitro effects in the presence and absence of haemin were monitored by means of microcalorimetry, scanning electron microscopy and phenotypic evaluation. Incubation of NTS with the erythro derivatives at concentrations of 3 μg/ml and above resulted in convulsions, granularity, decrease in heat flow, and death while NTS incubated with the threo derivatives were only affected at high concentrations (100 μg/ml). Extensive tegumental alterations, decrease in metabolic activity, viability, and death were observed when adult schistosomes had been exposed to 10 μg/ml of the erythro compounds. Moderate tegumental and viability changes but reduced heat production rates were observed with the threo derivatives at 10 μg/ml. In the presence of haemin, all MQ derivatives showed pronounced antischistosomal properties against adult S. mansoni in vitro. In vivo, MQ derivatives achieved statistically significant total and female worm burden reductions ranging between 65.4% and 100%. The highest total worm burden reductions of 93.4% and 90.2% were observed following treatment with the erythro and threo racemates, respectively. In conclusion, the optical isomers and racemates of MQ show only moderate stereoselectivity, in particular in vivo. Our results may enhance our understanding of the mechanism of action and therapeutic profile of MQ derivates on schistosomes.

Metabolic and hormonal acclimation to heat stress in domesticated ruminants

Environmentally induced periods of heat stress decrease productivity with devastating economic consequences to global animal agriculture. Heat stress can be defined as a physiological condition when the core body temperature of a given species exceeds its range specified for normal activity, which results from a total heat load (internal production and environment) exceeding the capacity for heat dissipation and this prompts physiological and behavioral responses to reduce the strain. The ability of ruminants to regulate body temperature is species- and breed-dependent. Dairy breeds are typically more sensitive to heat stress than meat breeds, and higher-producing animals are more susceptible to heat stress because they generate more metabolic heat. During heat stress, ruminants, like other homeothermic animals, increase avenues of heat loss and reduce heat production in an attempt to maintain euthermia. The immediate responses to heat load are increased respiration rates, decreased feed intake and increased water intake. Acclimatization is a process by which animals adapt to environmental conditions and engage behavioral, hormonal and metabolic changes that are characteristics of either acclimatory homeostasis or homeorhetic mechanisms used by the animals to survive in a new ‘physiological state’. For example, alterations in the hormonal profile are mainly characterized by a decline and increase in anabolic and catabolic hormones, respectively. The response to heat load and the heat-induced change in homeorhetic modifiers alters post-absorptive energy, lipid and protein metabolism, impairs liver function, causes oxidative stress, jeopardizes the immune response and decreases reproductive performance. These physiological modifications alter nutrient partitioning and may prevent heat-stressed lactating cows from recruiting glucose-sparing mechanisms (despite the reduced nutrient intake). This might explain, in large part, why decreased feed intake only accounts for a minor portion of the reduced milk yield from environmentally induced hyperthermic cows. How these metabolic changes are initiated and regulated is not known. It also remains unclear how these changes differ between short-term v. long-term heat acclimation to impact animal productivity and well-being. A better understanding of the adaptations enlisted by ruminants during heat stress is necessary to enhance the likelihood of developing strategies to simultaneously improve heat tolerance and increase productivity.

Chronic increase of circulating galanin levels induces obesity and marked alterations in lipid metabolism similar to metabolic syndrome

Galanin (GAL) has a role in the regulation of food intake by way of acting on the central nervous system in rodents. High serum GAL levels have been observed in obese human subjects, suggesting that peripheral GAL has a role in the regulation of energy balance and that elevated circulating GAL levels contribute to the development of obesity and obesity-associated metabolic impairments. Currently, it is not known how chronically increased levels of circulating GAL affect energy balance. The purpose of this study is to clarify the importance of chronically increased levels of circulating GAL on energy balance in a transgenic mouse model. Male wild-type and homozygous galanin transgenic (GAL-Tg) mice were used to study the peripheral effects of a 10-fold increase in circulating GAL on food intake, body weight, lipid metabolism, hepatic steatosis, glucose homeostasis and energy expenditure. In the absence of an orexigenic effect, GAL-Tg mice had increased body weight, visceral adiposity, total serum cholesterol, total serum triglycerides and hyperinsulinemia, as well as impaired glucose tolerance. Compared with wild-type mice, the obese phenotype observed in the GAL-Tg mice was attributed to decreased oxygen consumption and carbon dioxide production, and this effect was independent of any changes in food intake or horizontal activity. In this obese model, GAL contributed to the development of fatty liver disease, which was associated with impaired glucose tolerance, as well as a reduction in heat production and metabolic rate. Chronically elevated GAL may regulate body weight, metabolic rate, and lipid and carbohydrate metabolism through a mechanism that is independent of feeding regulation. The obese phenotype in the GAL-Tg mice is related to the reduced energy expenditure and insulin resistance. These findings support the hypothesis that increased circulating GAL levels contribute to the development of metabolic syndrome.

Behavioral responses of neonatal chicks exposed to low environmental temperature

Research has shown that on exposure to low environmental temperature, neonatal chicks (Gallus gallus) show hypothermia and absence of gene transcript enhancement of putative thermogenic proteins, mitochondrial fatty acid transport, and oxidation enzymes. Various behavioral abnormalities may also decrease the thermogenic capacity of low-temperature-exposed neonatal chicks. Therefore, to investigate behavioral irregularities in low-temperature-exposed (20 degrees C) neonatal chicks, we studied behavioral responses when compared with the control kept at thermoneutral temperature (30 degrees C). Two-day-old chicks (n = 5) were exposed to either low or thermoneutral temperature for 3 h and were then immediately placed in an acrylic monitoring cage (40 x 30 x 20 cm). The monitoring cage was fitted with a 3-dimensional mirror (to prevent isolation-induced stress) and maintained either at 20 or 30 degrees C. Behavioral responses were monitored for 10 min. Behavioral observations revealed that low-temperature exposure decreased distress vocalizations and spontaneous activity. Low-temperature exposure induced sleep-like behavior in neonatal chicks; active wakefulness was decreased while standing or sitting motionless with eyes closed or open and sleeping posture was significantly increased. In conclusion, there is evidence that on exposure to low-temperature, neonatal chicks decrease behavioral activity. Increased sleep-like behavior and decreased activity may reduce heat production in low-temperature-exposed neonatal chicks and could potentiate the sensitivity to cold exposure.

The effect of thermal manipulations during the development of the thyroid and adrenal axes on in-hatch and post-hatch thermoregulation

This study aimed to elucidate the effects of thermal manipulation (TM) during the development and maturation of the thyroid and adrenal axis on broiler chicks hatchability and thermoregulation during hatch, and to evaluate the improvement of thermotolerance acquisition of TM chicks by thermally challenging them post-hatch. Fertile Cobb eggs were divided into three treatments: control, 12 and 24 H. The control eggs were incubated under standard conditions, whereas the 12 and 24 H eggs were incubated from 7 d of incubation (E7) until E16 (inclusive) at 39.5 °C and 65% RH for 12 h/d (12 H) or continuously (24 H). Hatchability, BW and quality of the hatched 24 H chicks were negatively affected, but exhibited significantly improved thermotolerance on heat stress at 3 and 10 d of age for males and females, respectively. It can be concluded that continuous TM during embryogenesis impaired broiler chick performance, but improved their ability to thermoregulate in response to thermal challenge mainly by reducing heat production.

Hypothermia in Trauma

The human core temperature is maintained by highly controlled regulatory mechanisms that balance heat production and heat loss. When this balance is interrupted, there are consequences for human physiology that are not yet fully understood. Extremes of temperature have a physiological impact on human cells. In some instances, such as cardiac arrest, traumatic brain injury, and organ transplantation, controlled hypothermia can be physiologically beneficial, but hypothermia in traumatic injury is distinctly different. In trauma, hypothermia often begins at the time of injury as a result of increased heat loss by conduction and convection due to exposure and reduced heat production due to decreased motor activity.

Stress-induced changes important for effective androgenic induction in isolated microspore culture of triticale (×Triticosecale Wittm.)

The accumulation of abscisic acid (ABA) and the activities of antioxidative enzymes along with cell metabolic activity were monitored during androgenesis induction in triticale (×Triticosecale Wittm.). Tested cultivars ‘Mieszko’ and ‘Wanad’ were selected due to their significantly different responses to androgenic induction. Significant variation was observed in respect of superoxide dismutase activity and endogenous ABA content in anthers isolated from freshly cut tillers. For both cultivars, tillers pretreatment with low temperature decreased peroxidase activity by 36%, highly accelerated respiration rate and reduced heat production. At the same time, the level of ABA in ‘Mieszko’ was increased to the level measured in ‘Wanad’. This effect was associated with higher microspore culture viability and increased stress tolerance in ‘Mieszko’. Low temperature and metabolic starvation during 4-day anther preculture did not influence activities of antioxidative enzymes, while it resulted in slight decrease in respiration rate and heat emission. The importance of these changes for effective androgenesis induction is discussed.

THERMOREGULATORY RESPONSES OF SHEEP TO STARVATION AND HEAT STRESS CONDITIONS

The present study was carried out at Sakha Animal Production Experimental Station belonging to Animal Production Research Institute. The experiment was conducted under thermoneutral conditions (TNZ) in winter (THI< 74) and during moderate heat stress (MHS, THI 74 <88) in summer season on 9 and 6 Ossimi rams, respectively. Body weight, thermoregulatory parameters and blood parameters were determined at the start of the experiment and after 48 and 96 hrs of starvation in each experiment. Ambient temperature (Ta), relative humidity (RH %) and Temperature-Humidity Index (THI) were measured simultaneously during the experiment. Under TNZ, starvation had no significant effect on rectal temperature (RT), due to a significant and insignificant reduction in heat production (HP) and evaporative cooling (minute ventilation, MV), respectively. While under MHS, starvation reduced the effect of heat stress on RT by decreasing MV and respiration rate (RR), while, HP remained almost unchanged. Under TNZ, starvation caused an insignificant and significant decrease in plasma total cholesterol (Tcho.) and total lipids (Tl), respectively. Meanwhile under MHS, starvation had no significant effect on plasma Tcho. and Tl concentrations. Before starvation, moderate heat stress caused a significant increase in RT; meanwhile, respiratory evaporation (MV) and heat production (HP) were lower than that in the TNZ. Moderate heat stress (MHS) did not affect significantly blood hematocrit (Ht) and plasma proteins (plasma total proteins (Tp), albumin (Alb) and globulin (Gl)) while it increased significantly plasma glucose concentration. It could be concluded that starved sheep can tolerate moderate heat stress by decreasing evaporative cooling; meanwhile normal fed sheep depends on heat storage to tolerate moderate heat stress.

Correlation of systemic inflammation with local inflammatory activity in non-culprit lesions: Beneficial effect of statins

Background In patients with acute coronary syndromes (ACS) increased systemic and local inflammatory activation in culprit lesions is observed. It is unknown, however, whether systemic inflammation is correlated with non-culprit lesion inflammatory activation. Moreover, the effect of statins on non-culprit lesion inflammation has not been extensively investigated. The aim of the present study was to investigate in non-culprit lesions 1) the correlation between plaque temperature measurements with the levels of C-reactive protein (CRP) and 2) whether statin administration is associated with reduced heat production. Methods We included 71 patients with ACS or stable angina (SA) undergoing percutaneous coronary intervention in culprit lesions, having an intermediate non-culprit lesion. Forty patients were treated with statin and 31 patients were not treated. Systemic inflammatory status was assessed by CRP, and local inflammatory activation by measuring the temperature difference of non-culprit lesion (Δ T), assigned as the difference between the maximal temperature of the atherosclerotic plaque from the proximal vessel wall temperature. Results Mean Δ T was 0.08 ± 0.07 °C. Patients with ACS had higher Δ T compared to patients with SA (ACS: 0.10 ± 0.07 °C vs SA: 0.05 ± 0.06, p < 0.01). Δ T was less in patients treated with statin in both groups (ACS: 0.07 ± 0.04 °C vs 0.13 ± 0.08 °C p = 0.009; SA: 0.04 ± 0.05 °C vs 0.09 ± 0.07 °C, p = 0.04). CRP was higher in patients with ACS compared to SA (1.18 ± 1.12 vs 0.47 ± 0.37 mg/dL, p = 0.001). There was a positive correlation of Δ T and CRP values ( R = 0.46, p < 0.001). Conclusions Local inflammatory activation in non-culprit lesions is correlated with systemic inflammation. Moreover, statins have a beneficial effect on non-culprit lesion heat production.

Variations of strength and localized deformation in cratons: The 1.9 Ga Kapuskasing uplift, Superior Province, Canada

The Kapuskasing Structural Zone was the site of local crustal thrusting and uplift within the Superior craton, presumably in response to stresses applied at the margin of the craton during the Paleoproterozoic ca. 1.9 Ga. We use the present-day heat flow data in the Superior Province to calculate the strength of the lithosphere and to show that the uplift took place in the weakest part of the craton. After eliminating heat flow data that were affected by the uplift and later events (Keweenawan rifting), we calculate the heat flow and the temperature field in the lithosphere at 1.9 Ga. We show that the Kapuskasing region was in the center of a “thermal anomaly” at this time. The strength of the lithosphere in this region may have been up to 2–3 orders of magnitude lower than in surrounding parts of the craton, depending on crustal heat source distribution. Uplift and the resulting erosion of the upper crust, as evidenced by geothermobarometry data from around Kapuskasing, led to a reduced crustal heat production compared to the average crust of the southern Superior Province. This reduced heat production resulted in low crustal temperatures and a strong lithosphere permitting the long term preservation of a crustal root.

Metabolism after injury. I. Effects of severity, nutrition, and environmental temperatue on protein potassium, zinc, and creatine.

AbstractThe effect of an environmental temperature of 28–30°C. and a relative humidity of 35–45 per cent on the protein metabolic response to injury of one or more major long bones of the lower limbs has been studied in 29 male patients and 28 similar controls housed at 20–22°C. The metabolic response was reduced at the higher temperature compared with the controls, the more severely injured showed a greater metabolic response than the less severely injured, and the ameliorating influence of environmental temperature was more noticeable in the former. The metabolic response seems to be principally one of catabolism of muscle, with increased urinary excretions of potassium, creatine, and zinc in the urine correlating well with those of nitrogen at 20°C. but not at 30°C. The response (i.e., catabolism of muscle) was not affected by post-injury diet at 20°C. ambient temperature. There was a reduction in the disturbance of the plasma proteins.In general, the patients tolerated the warm drier conditions. Owing to the intrinsic difficult in assessing minor changes in bone healing it was not possible to assess what, if any, beneficial change occurred in the fracture site. From our experimental observations on the rat and the work of others on burned patients the reduction in heat production at the higher ambient temperature is accompanied by an enhanced rate of healing of surface wounds.

Human thermoregulatory function during exercise and immersion after 35 days of horizontal bed-rest and recovery

The present study evaluated the effect of 35 days of experimental horizontal bed-rest on exercise and immersion thermoregulatory function. Fifteen healthy male volunteers were assigned to either a Control (n = 5) or Bed-rest (n = 10) group. Thermoregulatory function was evaluated during a 30-min bout of submaximal exercise on a cycle ergometer, followed immediately by a 100-min immersion in 28 degrees C water. For the Bed-rest group, exercise and immersion thermoregulatory responses observed post-bed-rest were compared with those after a 5 week supervised active recovery period. In both trials, the absolute work load during the exercise portion of the test was identical. During the exercise and immersion, we recorded skin temperature, rectal temperature, the difference in temperature between the forearm and third digit of the right hand (DeltaT(forearm-fingertip))--an index of skin blood flow, sweating rate from the forehead, oxygen uptake and heart rate at minute intervals. Subjects provided ratings of temperature perception and thermal comfort at 5-min intervals. Exercise thermoregulatory responses after bed-rest and recovery were similar. Subjective ratings of temperature perception and thermal comfort during immersion indicated that subjects perceived similar combinations of Tsk and Tre to be warmer and thermally less uncomfortable after bed-rest. The average (SD) exercise-induced increase in Tre relative to resting values was not significantly different between the Post-bed-rest (0.4 (0.2) degrees C) and Recovery (0.5 (0.2) degrees C) trials. During the post-exercise immersion, the decrease in Tre, relative to resting values, was significantly (P < 0.05) greater in the Post-bed-rest trial (0.9 (0.5) degrees C) than after recovery (0.4 (0.3) degrees C). DeltaT(forearm-fingertip) was 5.2 (0.9) degrees C and 5.8 (1.0) degrees C at the end of the post-bed-rest and recovery immersions, respectively. The gain of the shivering response (increase in VO(2) relative to the decrease in Tre; VO(2)/Tre) was 1.19 l min(-1) degrees C(-1) in the Recovery trial, and was significantly attenuated to 0.51 l min(-1) degrees C(-1) in the Post-bed-rest trial. The greater cooling rate observed in the post-bed-rest trial is attributed to the greater heat loss and reduced heat production. The former is the result of attenuated cold-induced vasoconstriction and enhanced sweating rate, and the latter a result of a lower shivering VO(2) response.