Skin Heat Loss Research Articles

Developing thermal prediction models for the elderly under temperature step changes

Daily transitions between indoor and outdoor environments involving temperature step changes have been extensively studied in young people, but little attention has been given to age-related differences and the development of thermal prediction models specifically for the elderly. To address this knowledge gap, a study was conducted in a climate chamber using warm-neutral-warm experimental sessions. Twenty-four elderly participants were selected from volunteers who met the health and body shape requirements. Thermal sensation vote (TSV) and mean skin temperature (MST) responses of the elderly were collected and analyzed. The results demonstrate that temperature step changes (3–9 °C) and neutral thermal experiences significantly influence the thermal responses of the elderly. Compared to the young, the elderly exhibit lower TSV, lower MST, lower skin heat loss, and different associations between TSV and skin heat loss. Leveraging these age-related differences, an MST prediction model was established for the elderly. The predicted MST can also serve as an input for the TSV prediction model established in this study. The TSV prediction model is based on skin heat loss and applicable to both transient and steady-state conditions. This study introduces a new approach for predicting the thermal responses of the elderly and enhances understanding of age-related differences in thermal responses.

Angiotensin-(1−7) improves tail skin heat loss and increases the survival of rats with polymicrobial sepsis

Sepsis is a serious syndrome, characterized by the excessive release of inflammatory mediators and thermoregulatory changes, being fever the most common sign. However, despite the importance of Angiotensin (Ang)-(1−7) in controlling the inflammation, the role of the peptide in the febrile response and mortality in animals submitted to experimental model of sepsis is still not clear. In this way, we evaluate the effect of continuous infusion of Ang-(1−7) in inflammatory response, thermoregulation and in mortality of Wistar male rats submitted to colonic ligation puncture (CLP). Before CLP surgery, the infusion pumps (Ang-(1−7), 1.5 mg/mL or saline) were inserted into the abdominal cavity and maintained for 24 h. CLP rats showed a febrile response starting from 3 h after and persisted until the 24th hour of experiment. Continuous treatment with Ang-(1−7) attenuated the febrile response and reestablished the euthermia 11 h after CLP, until the end of experiment, which coincided with an increased heat loss index (HLI). This effect was associated with a decrease in production of pro-inflammatory mediators in liver, white adipose tissue (WAT) and hypothalamus. Moreover, an increase in norepinephrine (NE) content in interscapular brown adipose tissue (iBAT) was observed in CLP animals, which was attenuated with treatment with Ang-(1−7), and decreased mortality in CLP animals treated with Ang-(1−7). Taken together, the present study demonstrates that continuous infusion treatment with Ang-(1−7) can promote a global anti-inflammatory effect, reestablishing the tail skin heat loss as a key thermo-effector function, resulting in an increased survival of animals submitted to experimental sepsis.

The role of peripheral transient receptor potential vanilloid 1 channels in stress-induced hyperthermia in rats subjected to an anxiogenic environment

Anxiety resulting from psychogenic stimuli elicit stress-induced hyperthermia in rats, often called “psychogenic fever”, which is part of a coordinated response to situations seen as novel or distressing. Brain transient receptor potential vanilloid 1 (TRPV1) channels modulate both thermoregulation and animal behavior; however, the role of peripheral TRPV1 channels in regulating these responses during exposure to an anxiogenic environment has not been determined. Thus, the present study aimed to investigate the involvement of abdominal TRPV1 channels in stress-induced hyperthermia and behavior in rats subjected to an unconditioned anxiety test. Desensitized rats (peripheral desensitization of TRPV1 channels with resiniferatoxin; RTX) and their respective controls were subjected to a 15-min open field (OF) test. The core body temperature (Tcore), tail skin temperature (Tskin), and rats’ movements inside the arena were recorded. The OF test induced a similar increase in Tcore in both groups throughout the exposure time; however, at the recovery period, the RTX-treated rats had a slower reduction in Tcore due to lower tail skin heat loss. Tskin decreased significantly in both groups during exposure to OF but, during recovery, the RTX-treated rats showed impaired skin vasodilation. Also, RTX-treated rats entered fewer times and spent less time in the OF center square, suggesting an anxiety-related behavior. Our findings indicate that, under stressful conditions, peripheral TRPV1 channels modulate thermoregulatory and behavioral responses. The TRPV1 desensitization induces a more prolonged hyperthermic response due to lower cutaneous heat dissipation, alongside a more evident anxiety-like behavior in rats subjected to the OF apparatus.

A Case Study on Assessment Performance and Energy Efficient Recommendations for Industrial Boiler

As India is a developing country, industrialization is increasing day by day and there is a great need for industry energy audit. Audit helps to maintain and save energy from being wasted and helps in achieving highest efficiency of industrial equipment. This paper contains an actual industry audit report on boiler performance. This paper contains a report on Thermal analysis of boilers, thermal skin heat loss of boilers, O2 percentage control in flue gases to standard values, effect of coal additive, etc. This paper also contains a report on waste heat recovery options for thermal boiler, flue efficiency monitor, infrared thermometer, ultrasonic peak detector IR thermal imager. These equipment are used for energy assessment of boilers. Thermography survey of boiler surface is carried out to estimate the radiation and the other losses and the result of this total annual saving after insulation repairing or maintenance is Rs.8.48 lakh and investment is around Rs.6.31 lakh. Economizer performance of both the ISGEC and Thermax boiler can be improved with the help of suggested measures. It will help to save approximately rupees Rs.38.42 Lakh annually and investment on maintenance cost is negligible. In short, this paper deals with assessment of all boilers, evaluates their efficiencies and losses to identify energy saving opportunities and presents them in a report with their payback periods. Keywords: Energy, Energy audit, assessment, boiler.

Human Responses to 5 Heated Hypothermia Wrap Systems in a Cold Environment

We compared the effectiveness of 5 heated hypothermia wrap systems. Physiologic and subjective responses were determined in 5 normothermic subjects (1 female) for 5 heated hypothermia wraps (with vapor barrier and chemical heat sources) during 60 min of exposure to a temperature of -22°C. The 5 systems were 1) user-assembled; 2) Doctor Down Rescue Wrap; 3) hypothermia prevention and management kit (HPMK); 4) MARSARS Hypothermia Stabilizer Bag; and 5) Wiggy's Victims Casualty Hypothermia Bag. Core and skin temperature, metabolic heat production, skin heat loss, and body net heat gain were determined. Subjective responses were also evaluated for whole body cold discomfort, overall shivering rating, overall temperature rating, and preferential ranking. The Doctor Down and user-assembled systems were generally more effective, with higher skin temperatures and lower metabolic heat production; they allowed less heat loss, resulting in higher net heat gain (P<0.05). HPMK had the lowest skin temperature and highest shivering heat production and scored worse than the other 4 systems for the "whole body cold discomfort" and "overall temperature" ratings (P<0.05). The user-assembled and Doctor Down systems were most effective, and subjects were coldest with the HPMK system. However, it is likely that any of the tested systems would be viable options for wilderness responders, and the choice would depend on considerations of cost; volume, as it relates to available space; and weight, as it relates to ability to carry or transport the system to the patient.

Moisture in clothing and its transient influence on human thermal responses through clothing microenvironment in cold environments in winter

Air humidity produces conditions of varying moisture contents in clothing, which affects the heat and moisture transfer between human body, clothing and environment, as well as the wearers’ comfort. This study was designed to evaluate the moisture effects in clothing in cold environments. A series of wearing experiments were conducted in a climate chamber, simulating transient moisture absorption and desorption in experimental clothes. Totally 20 subjects were involved in three temperature levels (16 °C/20 °C/24 °C) and two relative humidity levels (15% RH/85% RH) during winter, with physiological measurement and subjective evaluation. The results showed that moisture in clothing under 85% RH significantly reduced subject mean skin temperatures (MST) and increased the local blood flow, due to enhanced heat loss by vapour evaporation. The initial skin wettedness was approximately 0.7 at 85% RH and stabilised at 0.33 after 90min exposure. The skin heat loss (Qskin) at 85% RH was almost twice as high as that at 15% RH under the same temperature conditions, owing to larger sensible and evaporative heat loss caused by moist clothing. The inner clothing effective temperature Teff was proposed to relate to TSV that the TSV increased by 1.12 units with an increase of 1 °C of Teff, which quantified the coupled effects of air temperature and humidity in clothing microenvironment on human thermal comfort. The findings address the negative effect of clothing absorbing a large amount of moisture, which should be considered for indoor heating temperature designs in cold-humid environments.

Reduction in predicted survival times in cold water due to wind and waves

Recent marine accidents have called into question the level of protection provided by immersion suits in real (harsh) life situations. Two immersion suit studies, one dry and the other with 500 mL of water underneath the suit, were conducted in cold water with 10–12 males in each to test body heat loss under three environmental conditions: calm, as mandated for immersion suit certification, and two combinations of wind plus waves to simulate conditions typically found offshore. In both studies mean skin heat loss was higher in wind and waves vs. calm; deep body temperature and oxygen consumption were not different. Mean survival time predictions exceeded 36 h for all conditions in the first study but were markedly less in the second in both calm and wind and waves. Immersion suit protection and consequential predicted survival times under realistic environmental conditions and with leakage are reduced relative to calm conditions.

The development and initial validation of a virtual dripping sweat rate and a clothing wetness ratio for use in predictive heat strain models

This paper applies the heat balance equation (HBE) for clothed subjects as a linear function of mean skin temperature (t sk ) by a new sweating efficiency (η sw ) and an approximation for the thermoregulatory sweat rate. The equation predicting t sk in steady state conditions was derived as the solution of the HBE and used for a predictive heat strain scale. The heat loss from the wet clothing (WCL) area was identified with a new variable of 'virtual dripping sweat rate VDSR' (S wdr ). This is a subject's un-evaporated sweat rate in dry clothing from the regional sweat rate exceeding the maximum evaporative capacity, and adds the moisture to the clothing, reducing the intrinsic clothing insulation. The S wdr allowed a mass balance analysis of the wet clothing area identified as clothing wetness (w cl ). The w cl was derived by combining the HBE at the WCL surface from which the evaporation rate and skin heat loss from WCL region are given. Experimental results on eight young male subjects wearing typical summer clothing, T-shirt and trousers verified the model for predicting t sk with WCL thermal resistance (R cl,w ) identified as 25 % of dry clothing (R cl,d ).

Apparent latent heat of evaporation from clothing: attenuation and “heat pipe” effects

Investigating claims that a clothed person's mass loss does not always represent their evaporative heat loss (EVAP), a thermal manikin study was performed measuring heat balance components in more detail than human studies would permit. Using clothing with different levels of vapor permeability and measuring heat losses from skin controlled at 34 degrees C in ambient temperatures of 10, 20, and 34 degrees C with constant vapor pressure (1 kPa), additional heat losses from wet skin compared with dry skin were analyzed. EVAP based on mass loss (E(mass)) measurement and direct measurement of the extra heat loss by the manikin due to wet skin (E(app)) were compared. A clear discrepancy was observed. E(mass) overestimated E(app) in warm environments, and both under and overestimations were observed in cool environments, depending on the clothing vapor permeability. At 34 degrees C, apparent latent heat (lambda(app)) of pure evaporative cooling was lower than the physical value (lambda; 2,430 J/g) and reduced with increasing vapor resistance up to 45%. At lower temperatures, lambda(app) increases due to additional skin heat loss via evaporation of moisture that condenses inside the clothing, analogous to a heat pipe. For impermeable clothing, lambda(app) even exceeds lambda by four times that value at 10 degrees C. These findings demonstrate that the traditional way of calculating evaporative heat loss of a clothed person can lead to substantial errors, especially for clothing with low permeability, which can be positive or negative, depending on the climate and clothing type. The model presented explains human subject data on EVAP that previously seemed contradictive.

Increase of heat loss by wearing gloves and boots in wet-suited subjects working in cold water.

The effect of wearing protective gloves and boots on thermal exchanges of wet-suited subjects in cold water was evaluated. Four male subjects, clad in 5 mm-thick neoprene wet suits and either with or without neoprene gloves (5 mm-thick) and boots (5 mm-thick) were immersed up to the neck in water at 13 degrees C while resting for 3 h or exercising for 2 h. Rectal temperature, oxygen consumption and local (chest, back, upper arm, thigh, forearm, calf, hand and foot) skin temperatures, skin heat fluxes and thermal insulations were determined during immersion. The rectal temperature was not different between conditions but the skin temperature was significantly higher with gloves and boots, especially at the distal extremities (forearm, calf, hand and foot). Consequently, the core-to-skin temperature gradient was reduced by wearing gloves and boots, but the skin heat loss was markedly increased. Calculated overall body insulation was significantly lowered by wearing gloves and boots. These results indicate that in wet-suited subjects resting or exercising in cold (13 degrees C) water, gloves and boots increase the overall rate of body heat loss. Attenuation of cold-induced vasoconstriction is proposed as the mechanism.

Heat Loss in an Animal Experimental Model

Heat loss leading to hypothermia is common during surgery, particularly when a body cavity is exposed. To determine the principal site of heat loss we used heat flux transducers to measure heat loss from the skin and the exposed abdominal cavity of seven pigs. Heat loss from the skin was 74 +/- 15 W/m2, and from the abdominal cavity, 350 +/- 122 W/m2 (p less than 0.002; ratio = 1:4.7). The area of the skin was 0.52 +/- 0.06 m2, and of the abdominal cavity, 0.04 +/- 0.006 m2 (ratio = 13.6:1). For every 13.6 watts lost from the skin, 4.7 watts were lost from the abdominal cavity; i.e. skin heat loss accounted for 74% of total heat loss. Therefore adequate insulation would reduce the incidence of hypothermia. Evaporation accounted for the largest heat loss from the abdominal cavity. Evaporative losses could be minimised by enclosing the bowel in a plastic bag.

Changes in thermal insulation during underwater exercise in Korean female wet-suit divers.

The present work was undertaken to examine the effect of wet suits on the pattern of heat exchange during immersion in cold water. Four Korean women divers wearing wet suits were immersed to the neck in water of critical temperature (Tcw) while resting for 3 h or exercising (2-3 met on a bicycle ergometer) for 2 h. During immersion both rectal (Tre) and skin temperatures and O2 consumption (VO2) were measured, from which heat production (M = 4.83 VO2), skin heat loss (Hsk = 0.92 M +/- heat store change based on delta Tre), and thermal insulation were calculated. The average Tcw of the subjects with wet suits was 16.5 +/- 1.2 degrees C (SE), which was 12.3 degrees C lower than that of the same subjects with swim suits (28.8 +/- 0.4 degrees C). During the 3rd h of immersion, Tre and mean skin temperatures (Tsk) averaged 37.3 +/- 0.1 and 28.0 +/- 0.5 degrees C, and skin heat loss per unit surface area 42.3 +/- 2.66 kcal X m-2 X h. The calculated body insulation [Ibody = Tre - Tsk/Hsk] and the total shell insulation [Itotal = (Tre - TW)/Hsk] were 0.23 +/- 0.02 and 0.5 +/- 0.04 degrees C X kcal-1 X m2 X h, respectively. During immersion exercise, both Itotal and Ibody declined exponentially as the exercise intensity increased. Surprisingly, the insulation due to wet suit (Isuit = Itotal - Ibody) also decreased with exercise intensity, from 0.28 degrees C X kcal-1 X m2 X h at rest to 0.12 degrees C X kcal-1 X m2 X h at exercise levels of 2-3 met.(ABSTRACT TRUNCATED AT 250 WORDS)

Suprabulbar and bulbar integration of ventilation and ear vascular control during thermoregulation in the rabbit

Suprabulbar and bulbospinal integration of cardiorespiratory responses to cold and heat stress was studied in groups of normal, thalamic and pontine rabbits. The animals sat in an airconditioned environmental chamber in which ambient temperature (T A) was maintained sequentially at 22°C, 12°C, 22°C and 35°C, with an accuracy of ±1°C. Neither thalamic nor pontine rabbits could maintain core temperature in cold or heat. At T A 35°C, thalamic and pontine animals did not pant, indicating that telencephalic responses were necessary for the integration of mechanisms promoting respiratory heat loss. Thalamic animals, however, could inhibit ear vascular sympathetic tone in the heat, but the response was absent in pontine animals, suggesting diencephalic responses were essential for the integration of mechanisms promoting ear skin heat loss. Thus, the neural adjustments to thermal stress depend on mechanisms of integration distributed longitudinally throughout the central nervous sytem, and different components of the reflex cardiorespiratory response depend on different sites in the central nervous system for their full expression.

PHYSICAL INSULATION OF HEALTHY MEN AND WOMEN OVER 60 YEARS.

Maximal body insulation [ I = (rectal temp. – skin temp.)/rate of skin heat loss] of healthy Korean men and women (17 each) over 60 years of age was determined by a method applied earlier to diving women of Korea (Rennie et al. J. Appl. Physiol. 17: 961, 1962). The critical water temperature was similar for males and females, ranging from 28–33 C. The water temperature at which 50% of subjects shivered was 31.2 C for both groups. This value is identical to that of young Korean men but is significantly higher than that of young Korean women. When a comparison was made at 31 C water, the extent of reduction in rectal temperature was, in the aged group, greater in males than in females, and was also greater in the aged than in the young. However, these differences could be accounted for mostly by the difference in subcutaneous fat thickness. When the values of I were considered as a function of the subcutaneous fat thickness, there was no difference either between old males and females or between the aged and young Korean subjects. This indicates that maximal body insulation due to physical factors does not change as a function of age. Note: (With the Technical Assistance of Jin Kyung Kim) temperature regulation; aging process; subcutaneous fat; cold; shivering threshold Submitted on January 15, 1964

Physical insulation of Korean diving women

Human cold adaptation was studied by comparing maximal body insulation [ I = (rectal temp. – skin temp.) /rate of skin heat loss] of Korean diving women to insulation of Korean nondiving men and women and American men and women. Appropriate measurements were made during immersion in a constant-temperature bath cool enough to induce maximal cutaneous vasoconstriction without shivering. Subcutaneous fat was estimated from measurements of skin-fold thickness. Within each racial group there is a significant regression of I on fat thickness. Koreans had a significantly greater I than Americans of comparable fat thickness. Korean diving women had the same I as nondivers of comparable fat thickness. Korean women had significantly greater I than Korean men due, we believe, to thicker subcutaneous fat. This may be the reason why women and not men engage in diving. The only evidence for cold adaptation among diving women was their ability to withstand colder water immersion without shivering. Submitted on March 22, 1962