Lower Mean Skin Temperature 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.

Cognitive Performance During Night Work in the Cold.

Objective: The objective of this study was to investigate how night work at low ambient temperatures affects cognitive performance (short-term memory and reaction time), skin- and core temperature, thermal comfort, sleepiness, and cortisol. We hypothesized that cognitive performance is reduced at night compared with daytime and worsened when exposed to low ambient temperatures.Method: Eleven male subjects were recruited to perform three tests in a climatic chamber at night and daytime: Night –2°C, Night 23°C and Day 23°C. Each test lasted 6 h. Cognitive performance (short-term memory and reaction time), skin- and core temperature, thermal sensation and comfort, cortisol levels and sleepiness were measured during the tests.Results: A lower mean skin temperature and corresponding lower thermal sensation were observed at Night –2°C compared to Day 23°C and Night 23°C. Night work caused increased sleepiness and lower cortisol levels, but was not affected by changes in ambient temperatures, thermal comfort, or skin temperatures. There was no effect of either day/night work nor ambient temperature on the short-term memory or reaction time test.Conclusion: Lower skin- and core temperature were observed at night when exposed to low ambient temperature (–2°C), but there was no effect on short-term memory or reaction time. Increased sleepiness and lower cortisol levels were observed at night compared to daytime and was not influenced by low ambient temperature at night. The result from this study suggests that cognitive performance (short-term memory and reaction time) is not adversely affected by night work when exposed to low ambient temperatures if adequate protective clothing is worn.

Evaluation of the convective heat transfer coefficient of human body and its effect on the human thermoregulation predictions

Human thermoregulation models, particularly the Fiala model, are well accepted for the prediction of thermoregulatory responses and the assessment of clothing and building systems with regard to human thermal comfort. However, the convective heat transfer coefficients (hc), used for the heat transfer calculations, were obtained from measurements with a thermal manikin with poor body resolution from decades ago, and they were not distinguished between body postures. In this study, the overall and local hc of the human body in both standing and seated postures were evaluated by CFD simulations and implemented in the Fiala model to investigate the resultant influence on the predicted thermoregulatory responses by comparing the predictions with measurements of 14 human exposures. It was found that the original hc used in the Fiala model was similar to the simulated hc of the standing body, but higher than that of the seated body at most body parts. In 64% of the investigated human exposures, the root-mean-square-deviation of the skin temperature predicted by the Fiala model with the simulated hc was lower than that achieved with the original hc, indicating an improvement of the accuracy of the Fiala model. Additionally, the higher hc of the standing body resulted in a lower mean skin temperature by up to 1.5 °C when compared to the seated body in the environment of 10 °C and 2.5 m/s. This emphasises the necessity of ensuring the accuracy of the hc in the thermoregulation model in order to improve its validity for specific investigated conditions.

Development of heat stress charts for older people under indoor environmental conditions

It has been acknowledged that as outdoor temperature and relative humidity increase past threshold values, so do older people mortality and morbidity rates. Similarly, there exist indoor conditions of temperature (Tamb) and relative humidity (RH) that would pose a health-risk to older people when they are exposed to these conditions for extended periods. However, these indoor conditions need to be identified to set protective measures for this vulnerable population. The aim of this work is to develop heat stress indices for older people similar to the standard effective temperature (SET) for a wide range of indoor conditions, activity levels and clothing insulation. A robust and validated bioheat model for older people was used to predict thermal responses and deduce the limits of Tamb and RH that would present a heat-related health risk when the core temperature exceeds 38 °C, or percentage of body water loss exceeds 2%, or when skin wettedness and SET exceed given thresholds. The results were consistent with published experimental data. At relatively cool ambient conditions, Tamb < 21 °C, older people have higher mean skin temperatures and feel cooler than younger people. At Tamb ≥ 25 °C, older people have lower mean skin temperatures and SET values become greater than younger ones, indicating that older people would rate their indoor conditions more stressful than younger people.

Interindividual differences of male college students in thermal preference in winter

The purpose of the paper is to investigate the difference in thermal preferences and their effect on physiological response and thermal sensation. A questionnaire combined with reliability analysis was proposed to divide participants into the following groups: cool preference, neutral preference, and warm preference. Then, 18 participants with different thermal preferences (6 for each thermal preference) were selected from 180 university students based on the proposed questionnaire. Finally, the 18 participants performed human trials in three environments (21 °C, 19 °C, and 17 °C) wherein physiological parameters (core temperature, heart rate, skin temperature, and conductive heat flux), as well as thermal sensation and thermal comfort, were recorded during tests. The results demonstrated that the proposed questionnaire can be used to evaluate thermal preferences. Furthermore, thermal preferences significantly (p < 0.05) affected physiological parameters and thermal sensation. In particular, the participants who preferred cool temperatures had lower mean skin temperature, heart rate, and thermal comfort vote but higher mean conductive heat flux and thermal sensation votes than the warm preferred participants. The rates of the mean skin temperature and core temperature decline in the cool preferred participants were lower than in the warm preferred participants. The findings from this work can provide fundamental knowledge for individual thermal comfort assessment and personalized heating system development.

Investigation of sleep quality under different temperatures based on subjective and physiological measurements

This study investigated sleep quality at different indoor temperatures (17°C, 20°C, and 23°C [62.6°F, 68.0°F, and 73.4°F]) via subjective and physiological methods by evaluating the thermal comfort and sleep quality before and after sleep. Electroencephalograms were also obtained, and skin temperatures were measured throughout the entire sleep cycle. The quantitative powers of each electroencephalogram frequency rhythm were calculated, and the duration of every sleep stage was determined. Both results show that the ambient temperature has a significant effect on sleep quality. The subjective results show that 20°C (68.0°F) was the most comfortable temperature for the waking state and 23°C (73.4°F) was the most satisfactory temperature for sleeping. The objective results show that at 23°C (73.4°F), the relative power of the sleep δ band was the highest, the duration of sleep onset latency was the shortest, and the slow-wave sleep was the longest. All these results were highly consistent, indicating that sleep quality was highest at 23°C (73.4°F). The higher thermal comfort temperature in sleep compared with that in the waking time may be due to the lower mean skin temperature during sleep.

The effect of skin temperature on performance during a 7.5-km cycling time trial

Aerobic exercise performance is seriously compromised in the heat. Possibly, a high skin temperature causes a rating of perceived exertion (RPE)-mediated decrease in exercise intensity. The purpose of this study was to determine the effect of skin temperature on power output during a 7.5-km cycling time trial. Thirteen well-trained male subjects performed a 7.5-km cycling time trial at 15°C and 50% relative humidity (CONTROL), with radiative heat stress during the time trial, and with (PRECOOL) or without (HEAT) precooling. Heat stress was applied by infrared heaters positioned in front of the cycle ergometer between 1.5 and 6.0 km. Skin, rectal, and pill temperature, power output, heart rate, and RPE were measured during the trial. Despite the lower mean skin temperature at the start of the time trial for PRECOOL compared to HEAT (−2.1 ± 0.7°C; P < 0.01) and CONTROL (−1.8 ± 0.6°C; P < 0.05), and a greater increase in mean skin temperature during the heat stress period for PRECOOL (4.5 ± 1.0°C) and HEAT (3.9 ± 0.8°C) than for CONTROL (−0.3 ± 0.6°C; P < 0.01), no differences in power output were found between HEAT (273 ± 45 W) and CONTROL (284 ± 43 W; P = 0.11) and between HEAT and PRECOOL (266 ± 50 W; P = 0.47). Power output during the time trial was greater for CONTROL than for PRECOOL (P < 0.05). Additionally, no differences were observed in core temperature measures, HR, and RPE. Skin temperature does not affect the selection and modulation of exercise intensity in a 7.5-km cycling time trial.

Body regional influences of l-menthol application on the alleviation of heat strain while wearing firefighter’s protective clothing

The purpose of this study was to investigate the influences of menthol application according to the amount of surface area on physiological and psychological heat strains, along with body regional influences. Male students underwent two stages of experiments: [Experiment 1] Cutaneous thermal threshold test at rest on eight body regions with/without a 0.8% menthol application at T (a) 28°C and 50% RH; [Experiment 2] Six exercise tests with/without a 0.8% menthol spray at T (a) 28°C and 40% RH, while wearing firefighter's protective clothing (No menthol, PC(NO); Face and neck menthol, PC(FN); Upper body menthol, PC(UP); Whole body menthol application, PC(WB)) or wearing normal clothing (No menthol, NC(NO); Upper body menthol, NC(UP)). Experiment 1 showed that menthol caused no significant influence on cutaneous warm thresholds, while menthol applications evoked earlier detection of cool sensations, especially on the chest (P = 0.043). Experiment 2 revealed that NC(UP), PC(UP) and PC(WB) caused lower mean skin temperature, especially with higher peripheral vasoconstrictions on the extremities at rest. During exercise, NC(UP), PC(UP) and PC(WB) induced greater and earlier increases in rectal temperatures (T (re)) and a delayed sweat response, but lessened psychological burdens (P < 0.05). Both physiological and psychological effects of PC(FN) were insignificant. For a composite analysis, individual Menthol Sensitivity Index at cooling in Experiment 1 had significant relationships with the threshold for T (re) increase and changes in heart rate in NC(UP) of Experiment 2 (P < 0.05). Our results indicate that menthol's topical influence is body region-dependent, as well as depending on the exposed body surface area.

Anthropological and Thermoregulatory Changes Induced by a Survival Sojourn in a Tropical Climate

A survival sojourn in a tropical climate exposes subjects to 2 main constraints: food restriction and tropical climatic conditions. We hypothesized that such a sojourn could modify anthropological characteristics and thermoregulatory responses to heat and cold on return. Eight European male subjects were submitted to a sweating test (ST) for 90 minutes (dry bulb temperature [Tdb] = 47 degrees C, relative humidity (RH) = 10%, and wind speed = 0.8 m x s(-1)) and to a whole-body cold-air test (Tdb = 1 degrees C, RH = 40%, and wind speed = 0.8 m x s(-1)) for 120 minutes in thermoclimatic chambers both before and after a 4-week survival sojourn in French Guyana. The survival sojourn resulted in a decrease in lean body mass (P < .05) without any significant change in body fat content. Heat thermoregulatory changes studied during the ST were characterized both by a lower mean skin temperature (Tsk) (P < .05) and a higher sweat rate measured after the sojourn than before it (m(sw); P < .05). Cold thermoregulatory changes were characterized by a higher T(sk) value (P < .05) and a decreased onset for continuous shivering without any significant change in internal temperature or metabolic heat production (M). This study showed that this type of sojourn modifies not only biometrical characteristics of the subjects but also the thermoregulatory responses, inducing an adaptation of the thermoregulatory system to heat and an increase in the sensitivity of the thermoregulatory system to cold. This finding could have practical implications on return after such a sojourn.

MECHANISMS OF AGE-RELATED DECREMENTS IN SWEATING RESPONSES

1611 To approach the mechanisms underlying the age-related decrement of sweating function, 7 older (64-76 years) and 7 younger (20-24 years) men were exposed to standard heat stress for 60 min. The test consisted of placing the subjects' legs and feet in a 42 °C water bath while they sat in a constant air condition (35 °C, 45% rh). Rectal (Tre) and skin temperatures, local sweating rates (msw: on the forehead, chest, back, forearm and thigh) and the frequency of sweat expulsions ( fsw: as an indicator of central sudomotor activity) were measured during the test. No group differences were observed for mean body temperature (Tb) throughout the heating, although the older men had higher Tre( P<0.02) and lower mean skin temperature ( P<0.001) during the latter half of heating. The sweating responses were sluggish with a delayed onset in the older men compared to the younger men regardless of sites( P<0.04), especially on the thigh. During the latter half of the test, msw on the thigh was significantly lower in the older men than in the younger men ( P<0.001), but not on the other sites. The slope of the msw vs fsw relationship was significantly lower on the thigh for the older men ( P<0.03), but not on the other sites. No group difference was observed for the slope of fsw vs Tb relationship. These results suggest that the lower msw observed in older men was possibly due to age-related modification of peripheral mechanisms, including changes in the sweat glands themselves by atrophy and in their surroundings, rather than central drive activity related to sudomotor function.