Changes In Heat Loss Research Articles

Change in Heat Loss after Light-Short Exercise and Food Intake

Changes in heat loss after light-short exercise and unwarmed food intake were investigated using partitional calorimetry to test the hypothesis that heat loss following these treatments is due to sweat evaporation (Esk). Four Japanese male subjects exercised at 30% of their maximum workload for 10 min and rested for 60 min. They ate 200 g almonds, drank 100 g green tea and rested for 120 min on different occasion. Rectal temperature, oxygen consumption, body weight, skin temperatures and local heat flow rates at seven sites on the skin surface were measured at 2-min intervals. The results demonstrated that the heat stored during exercise was dissipated by Esk with a 16 min delay whereas the heat produced by diet induced thermogenesis was dissipated by Esk without delay. Therefore, it was demonstrated that the supplemental heat loss pathway after both light-short exercise and unwarmed food intake was Esk.

Upper ocean heat content in the Nordic seas

Seven years of temperature profiles are obtained from the Argo float project and are used to study the vertically integrated heat content for the Nordic seas which is broken up into the Norwegian Basin, Greenland Sea, Lofoten region, and Iceland Plateau. The World Ocean Atlas 2005 (WOA05) is used as the climatological baseline for temperature and hence heat content. Temporally and spatially averaged temperature profiles within the Norwegian and Iceland basins show good agreement between the Argo and WOA05 data sets. For the Greenland and Lofoten basins, the WOA05 data show cooler surface temperatures (by 1–2°C) but still lie within 1 standard deviation of each other over the 7‐year period. The Argo float data show circulation within each of the basins that is counterclockwise, and some of the floats eventually disperse toward the outer edges of the basins. Vertically integrated heat content from 0 to 1200 m shows similar characteristics as the WOA05 results including the timing and strength of the seasonal variability. The anomalous heat content for the Greenland and Norwegian sea basins is calculated in depth bins of 400 m. The Greenland Sea shows a warming trend over the 7 years of study, which corresponds to a temperature increase of (4.1 ± 0.3) × 10−2 °C/yr. The Norwegian Sea basin shows interannual variability in heat content for the surface layer (0–400 m) that may be related to the North Atlantic Oscillation (NAO). During an NAO+ phase, the Norwegian Basin shows a warm phase, and during an NAO− phase, the Norwegian Basin is in a cold phase; the correlation is small (r = 0.32) but different from zero correlation only at the 90% level, implying that the variability in the AHC may be due to (1) local atmospheric forcing and hence changes in heat loss, (2) atmospheric pressure differences that are not resolved by the NAO index, and (3) exchange of heat with the basin boundaries.

Direct evidence for systems-level modulation of initial drug (in)sensitivity in rats

Some argue that pharmacological effects trigger corrective regulatory responses of varying strength. If so, some commonly used in vivo measures of initial drug sensitivity are difficult to interpret because the measured effects represent a combination of underlying pharmacological effects and regulatory counter-responses with the relative contribution of each influenced by individual and dose-related factors. The objective of this study was determine if core temperature (T (core)), a common measure in drug research, can mask the variability both in underlying pharmacological effects and physiological counter-responses during an initial administration of the hypothermia-promoting drug, nitrous oxide (N(2)O). T (core) was measured synchronously with its determinants, heat production (HP) and heat loss (HL) during steady-state N(2)O administration. Drug-naive rats received a 90-min exposure to 0, 15, 30, 50, 60, or 75% N(2)O plus a paired control gas exposure (n > or = 8 per group). HP was measured via indirect calorimetry, HL via direct calorimetry, and T (core) via telemetry. T (core) was unaltered by concentrations < or =50% N(2)O, but at 30 and 50% N(2)O, this stability masked significant increases of HL that were offset by increases of HP. On average, hypothermia accompanied 60 and 75% N(2)O inhalation owing to uncompensated increases of HL. However, some rats administered with these doses also exhibited T (core) stability via significant opposing changes of HL and HP. A common in vivo measure of initial drug sensitivity can fail to disclose underlying pharmacological sensitivity owing to regulatory counter-responses. This concept has implications for understanding relationships between phenotypic variation in initial drug sensitivity and subsequent drug-taking phenotypes.

高炉低還元材比操業に向けた周辺流制御と原材料品質設計

Concepts and targets of operational conditions and burden qualities for reduction of exhaust carbon dioxide (CO2) are discussed with consideration of an energy balance at Steel works. Lowering a reducing agent rate (RAR) with reduction of a heat loss and increase in a shaft efficiency is desirable measures to decrease in the exhaust CO2. Suppressed gas flow at a peripheral part of furnace contributes to improvement of both heat loss and shaft efficiency, however, promoted gas flow at that part is necessary for a stable state of gas permeability with low quality burden against degradation behavior. To apply for the operational design, effects of sinter RDI and coke TI on the RAR and exhaust CO2 through the changes in peripheral gas flow are clarified on the basis of analyses of the operational results and simulations by using of the mathematical model. For example, improvement with -10.4% of RDI and 0.69% of TI contributes the reduction of RAR by 10 kg/t through changes of heat loss by 78.3 MJ/t and shaft efficiency by 0.014.

High-resolution scanning thermal probe with servocontrolled interface circuit for microcalorimetry and other applications

This article presents a scanning thermal microscopy sensing system equipped with a customized micromachined thermal imaging probe and closed loop interface circuit. The micromachined thermal probe has a thin film metal bolometer sandwiched between two layers of polyimide for high thermal isolation and mechanical flexibility, and a tip with a diameter of approximately 50 nm which provides fine spatial resolution. The circuit includes a proportional-integral (PI) controller which couples to a Wheatstone bridge circuit in which the bolometer forms one leg. The PI controller adjusts power supplied to thermal probe, compensating change in heat loss from probe tip to sample and keeping the resistance bridge balanced. It permits precise control of probe temperature to within 2.3 mK, and widens its applications to microcalorimetry. The probe is used in thermal mapping and microcalorimetry applications. A calibration method based on microcalorimetric measurements of melting temperature is presented for the probe. Scanning thermal images show a high signal-to-noise ratio of 15.7 for 300 nm thick photoresist in which the minimum detectable thermal conductance change is &amp;lt;23 pW/K (which corresponds to a topographic change of 7.2 nm). Subsurface scans show a signal-to-noise ratio of 15.5 for variation of 1.0% in thermal resistance for a topographically smooth surface.

Neurotensin analog NT77 induces regulated hypothermia in the rat

The potential use of hypothermia as a therapeutic treatment for stroke and other pathological insults has prompted the search for drugs that can lower core temperature. Ideally, a drug is needed that reduces the set-point for control of core temperature (T c) and thereby induces a regulated reduction in T c. To this end, a neurotensin analog (NT77) that crosses the blood brain barrier and induces hypothermia was assessed for its effects on the set-point for temperature regulation in the Sprague–Dawley rat by measuring behavioral and autonomic thermoregulatory responses. Following surgical implanation of radiotransmitters to monitor T c, rats were placed in a temperature gradient and allowed to select from a range of ambient temperatures (T a) while T c was monitored by radiotelemetry. There was an abrupt decrease in selected T a from 29 to 16 °C and a concomitant reduction in T c from 37.4 to 34.0 °C 1 hr after IP injection of 5.0 mg/kg NT77. Selected T a and T c then recovered to control levels by 1.5 hr and 4 hr, respectively. Oxygen consumption (M) and heat loss (H) were measured in telemetered rats housed in a direct calorimeter maintained at a T a of 23.5 °C. Injection of NT77 initially led to a reduction in M, little change in H, and marked decrease in T c. H initially rose but decreased around the time of the maximal decrease in T c. Overall, NT77 appears to induce a regulated hypothermic response because the decrease in T c was preceded by a reduction in heat production, no change in heat loss, and preference for cold T a's. Inducing a regulated hypothermic response with drugs such as NT77 may be an important therapy for ischemic disease and other insults.

Light masking of circadian rhythms of heat production, heat loss, and body temperature in squirrel monkeys.

Whole body heat production (HP) and heat loss (HL) were examined to determine their relative contributions to light masking of the circadian rhythm in body temperature (Tb). Squirrel monkey metabolism (n = 6) was monitored by both indirect and direct calorimetry, with telemetered measurement of body temperature and activity. Feeding was also measured. Responses to an entraining light-dark (LD) cycle (LD 12:12) and a masking LD cycle (LD 2:2) were compared. HP and HL contributed to both the daily rhythm and the masking changes in Tb. All variables showed phase-dependent masking responses. Masking transients at L or D transitions were generally greater during subjective day; however, L masking resulted in sustained elevation of Tb, HP, and HL during subjective night. Parallel, apparently compensatory, changes of HL and HP suggest action by both the circadian timing system and light masking on Tb set point. Furthermore, transient HL increases during subjective night suggest that gain change may supplement set point regulation of Tb.

Thermal effects of steel toe caps in footgear

This study investigated cold weather safety footwear and the possible thermal effects of steel toe caps in footwear. Two models of boots were used. Both models were manufactured in two variants – with and without steel toe cap. The boot insulation was measured with an artificial, heated foot (AHF). One model was used in experiment with subjects ( n=6). Cold exposure consisted of sitting for 60 min at −10°C. There were no differences between insulation levels of boots with and without steel cap for one boot model, but the differences were statistically significant for the second model showing slightly higher insulation values for the boot without steel cap. No significant differences due to insulation dissimilarities could be found from the measurements on subjects. Statistically significant differences were found for both models regarding the rate of change of heat loss from AHF when its location was changed from warm to cold and back to warm. The rise and decrease of heat loss from AHF depended on the rate of temperature change of the boots. The results showed that a faster change in heat loss from AHF occurred for boots without steel toe caps. Data from subjects seemed to confirm this by a somewhat faster, though not significant, rise in toe skin temperatures after cold exposure in boots without steel toe caps. The effect may be attributed to the higher mass and heat contents of the boots with steel toe cap. Relevance to industry Many jobs need additional protection of the toes or shins. The steel toe cap and its alleged cooling effect have been a frequent subject of complaints. This study discusses reasons that could explain the complaints, and presents a standard method for evaluating thermal properties of footwear.

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.

The physiology of heat regulation

Heat regulation is presented as the physiological method of handling metabolic heat, instead of temperature regulation. Experimental evidence of heat regulation from the literature is reviewed, including more than 20 years of calorimetric studies by the author. Changes in heat production are followed by slow exponential changes in heat loss, which produce changes in body heat storage. Heat balance occurs at many levels of heat production throughout the day and night, and at each level there is a related level of rectal temperature. Heat flow can be sensed by the transcutaneous temperature gradient. The controller for heat loss appears to operate like a servomechanism, with feedback from heat loss and possibly feedforward from heat production. Physiological responses defend the body heat content, but heat content varies over a range that is related to heat load. Changes in body heat content drive deep body temperatures.

Metabolic and febrile responses to typhoid vaccine in humans: effect of beta-adrenergic blockade.

Fever and activation of acute phase responses were induced in human volunteers by intramuscular injection of typhoid vaccine. Vaccine injection caused a rapid (within 1 h) and sustained rise in metabolic rate (peak response 16%, 6-8 h), followed by later increases in white blood cell count (3-4 h), skin temperature (4-5 h), oral temperature (5-6 h), heart rate (6-8 h), and plasma cortisol (5-8 h). A peak fever [1.2 +/- 0.2 degree C (SE) rise] was recorded 12 h after vaccine injection. The involvement of the sympathetic nervous system in the development of these responses was investigated by the oral administration of propranolol before (80 mg) and 3 h after (40 mg) vaccine injection. Propranolol prevented the increases in metabolic rate, heart rate, and skin temperature but did not inhibit the rise in oral temperature or white cell count after vaccine administration. These data indicate that the sympathetic nervous system is responsible for the rise in energy expenditure associated with fever in humans. However, the rise in body temperature can develop in the absence of this increase in metabolic rate possibly by changes in heat loss.

Blunted febrile response to intravenous endotoxin in starved rats

The effects of fasting on the febrile responses to intravenous injection of bacterial lipopolysaccharide (LPS; endotoxin) of Escherichia coli were investigated in rats. Ad libitum-fed rats (C) produced a biphasic fever with an increase in the temperature difference between brown adipose tissue and colon and shivering activity (SA). Measurement by a direct calorimeter showed no particular changes in heat loss. Rats starved for 4 days (F4) responded to intravenous LPS with a monophasic fever accompanied by an increase in SA only. However the maximal rise in colonic temperature (Tco) did not differ from C rats. Subsequent 2-day fasting reduced SA and the maximal fever height. Endogenous pyrogen (EP) injected intravenously produced a prompt rise in Tco followed by prolonged hyperthermia in C rats. In the F4 rats, there was no such sustained rise in Tco as a result of intravenous EP. The response in Tco to intravenous prostaglandin E2 (PGE2) was the same in fed and starved rats. The administration of LPS, EP, and PGE2 into the lateral ventricle evoked a similar extent of hyperthermia in C and F4 rats. Because the second phase of fever has been shown to occur after pyrogens are translated into a febrile stimulus within the blood-brain barrier, it is assumed that the functional changes of the blood-brain barrier such as in the permeability of pyrogens or in the sensitivity of pyrogen receptors resulted in the absence of the second phase of fever in starved rats.

Total calorimetry and temperature regulation in the nine-banded armadillo.

Cold exposure in the nine-banded armadillo causes vigorous shivering and a rise in core temperature (Tc). The increase in metabolic rate and Tc depends upon exposure temperature, but may be as much as six times and 3 degrees C respectively (Johansen 1961). These findings might indicate an insensitivity to Tc, which is puzzling since internal temperature is thought to be the primary and regulated variable. It is suggested that positive feedback may play a role in temperature regulation in these animals. To investigate this problem two series of experiments were performed in the same species. Series 1. Measurements of changes in heat loss (direct calorimetry) and heat production (indirect calorimetry) following transferral from a thermoneutral to a cold environment. The difference between these measurements determines whether heat storage is positive due to the increased core temperature or negative due to reduction in the size of the core with the increased temperature. Series 2. Investigation of core thermosensitivity (body core cooling using colonic thermode) under different environmental conditions. The results of the first series showed that the rise in Tc was accompanied by positive heat storage in the body. The second series demonstrated core thermosensitivities similar to those previously reported for a variety of other homeothermic mammals.

The effect of staged burn wound closure on the rates of heat production and heat loss of burned children and young adults.

The sequential metabolic studies of nine severely burned patients were examined retrospectively. Information analyzed included heat production (M), partitioned heat loss (HL), the percentage of the body surface area open wound (% open wound) and skin (TS) and rectal (TR) temperatures. The reduction in the hypermetabolic response correlated with the number of days postburn (DPB), % open wound, average body temperature (TB = 0.8TR + 0.2TS) and evaporative heat loss (EV) (r = 0.62, 0.55, 0.56, 0.63, respectively). However, decrements in metabolic rate between sequential studies correlated only with the change in % open wound and the change in EV (r = 0.41 and 0.49, respectively). While changes in heat loss are not capable of predicting all of the variation in metabolic rate, burned patients demonstrate an increase in heat production largely secondary to the inability to conserve heat effectively in the periphery. This response is compounded by an altered central thermoregulation.

Effects of fasting on heat balance and nonshivering thermogenesis in febrile adult guinea pigs

1. 1. The calorigenic responses of 60-h fasted (F) and control (C) guinea pigs to E. coli endotoxin (5 μg·kg −1 i.v.) injection were compared at T a = 25° C. 2. 2. In contrast to fed (C) guinea pigs, the F group showed significantly lower calorigenic response. 3. 3. The brown adipose tissue (BAT) thermogenesis judge by the BAT temperature did not change significantly. Shivering activity was not different from that in the C group. 4. 4. The results conclude that fasting attenuates endotoxin-induced fever and this attenuation is due to suppression of nonshivering thermogenesis (NST) in guinea pigs. 5. 5. The results from direct calorimetry indicate that endotoxin injection evoked a prominent increase in heat production, while the changes in heat loss do not have an important role.

Hypothalamic temperature during desynchronized sleep.

The influence of changes in heat loss at specific heat exchangers, appraised by recording ear skin temperature (Ts), on the hypothalamic temperature (Thy) rise during desynchronized sleep (DS) was studied in unrestrained cats at different ambient temperatures (Ta). The correlations of initial and final Thy changes (delta iThy and delta fThy) with initial and final Ts changes (delta iTs and delta fTs), respectively, are statistically not significant. However, a significant negative correlation was found between delta fiThy, i.e. delta fThy-delta iThy, and delta fiTs, i.e. delta fTs-delta iTs. The latter result shows that only after its initial rise is Thy affected by changes in heat loss at specific heat exchangers during DS. Accordingly, delta fThy and delta fiThy are positively correlated with Ta. However, also delta iThy, although not affected by heat loss changes at specific heat exchangers, shows a positive correlation with Ta. On the basis of these results and of the data in the literature, it is concluded that three independent factors underlie Thy changes during DS, namely heat loss at specific heat exchangers, hypothalamic blood flow and thermogenesis.

The use of meteorological records in estimating the effects of weather on sensible heat loss from sheep

The weather components that influence heat loss from an animal out-of-doors include air temperature, wind, sun, cloud and precipitation. An expression is derived that allows an estimate to be made of sensible heat loss from sheep exposed to weather, with particular reference to cool conditions. The environmental variables used in the expression are all obtained directly from standard meteorological data; hourly data are appropriate to the time-scale of adaptation of the sheep to changing conditions. The expression is based on the ratio of the deep body—air temperature difference to the total insulation of the animal; the latter consists of the tissue, coat and surface insulations acting in series. The effects of sun and cloud are included in the temperature difference and the effects of wind and rain are included in the coat and surface insulations. Changes in heat loss that occur throughout the year are described, including 24-hourly and geographical variations. The influences of individual weather factors and of the animal's fleece depth are quantified.

高圧ヘリウム混合ガス空間の温熱環境に関する基礎的研究

The purpose of this paper is to determine quantitatively heat exchange between human skin surface and thermal environment in a hyperbaric helium environment In a hyperbaric helium environment the rate of convective heat loss changes by substitution of helium for nitrogen, for example, the rate of convective heat loss by the respiration becomes significant heat loss path, on the other hand, evaporative capacity decreases by reduction of mass diffusivity for water to gas with barometric pressure. Data on the thermal environment of a hyperbaric helium environment was obtained from a series of experiments which were carried out at the Japan Marine Science & Technology Center, in 1977 to 1978. We discussed these experimental results, in comparison with the previous results. Results of this research are as follows; 1) A comfort temperature increases with barometric pressure. 2) Convective heat transfer coefficient, ambient gas movement in 0.1m/s〜0.3m/s, increasees with barometric pressure. 3) The clothing insulation decrease with barometric pressure. 4) The clothing permeation efficiency factor decreases slightly with barometric pressure.

Penetration of external thermal perturbations into homeothermic organisms, part II (author's transl)

The penetration of external thermal perturbations into parts of the body with different surface curvatures is discussed. For areas with approximate rotational symmetry a theoretical treatment by means of the variation theory is possible. the mean surface curvature on the rotation axis is constant. Therefore the solution of the partial differential equation given in part I can be applied without change, if the correct value of the mean surface curvature of the body part is used. Also for an exponential form of alteration of the heat loss a solution is deduced. Combining small parts of sudden and exponential changes of heat loss it is possible to approximate almost any reasonable type of external thermal perturbation. Superimposing single solutions with different parameters allows then a complete solution of the problem. The importance of the theoretical results in view of homeothermia is discussed.