Thermophysiological Responses Research Articles

Validation of the Fiala multi-node thermophysiological model for UTCI application

The important requirement that COST Action 730 demanded of the physiological model to be used for the Universal Thermal Climate Index (UTCI) was its capability of accurate simulation of human thermophysiological responses across a wide range of relevant environmental conditions, such as conditions corresponding to the selection of all habitable climates and their seasonal changes, and transient conditions representing the temporal variation of outdoor conditions. In the first part of this study, available heat budget/two-node models and multi-node thermophysiological models were evaluated by direct comparison over a wide spectrum of climatic conditions. The UTCI-Fiala model predicted most reliably the average human thermal response, as shown by least deviations from physiologically plausible responses when compared to other models. In the second part of the study, this model was subjected to extensive validation using the results of human subject experiments for a range of relevant (steady-state and transient) environmental conditions. The UTCI-Fiala multi-node model proved its ability to predict adequately the human physiological response for a variety of moderate and extreme conditions represented in the COST 730 database. The mean skin and core temperatures were predicted with average root-mean-square deviations of 1.35 ± 1.00°C and 0.32 ± 0.20°C, respectively.

Computational fluid dynamics analysis of drag and convective heat transfer of individual body segments for different cyclist positions

This study aims at investigating drag and convective heat transfer for cyclists at a high spatial resolution. Such an increased spatial resolution, when combined with flow-field data, can increase insight in drag reduction mechanisms and in the thermo-physiological response of cyclists related to heat stress and hygrothermal performance of clothing. Computational fluid dynamics (steady Reynolds-averaged Navier–Stokes) is used to evaluate the drag and convective heat transfer of 19 body segments of a cyclist for three different cyclist positions. The influence of wind speed on the drag is analysed, indicating a pronounced Reynolds number dependency on the drag, where more streamlined positions show a dependency up to higher Reynolds numbers. The drag and convective heat transfer coefficient (CHTC) of the body segments and the entire cyclist are compared for all positions at racing speeds, showing high drag values for the head, legs and arms and high CHTCs for the legs, arms, hands and feet. The drag areas of individual body segments differ markedly for different cyclist positions whereas the convective heat losses of the body segments are found to be less sensitive to the position. CHTC–wind speed correlations are derived, in which the power-law exponent does not differ significantly for the individual body segments for all positions, where an average value of 0.84 is found. Similar CFD studies can be performed to assess drag and CHTCs at a higher spatial resolution for applications in other sport disciplines, bicycle equipment design or to assess convective moisture transfer.

Numerical Analysis of Specific Absorption Rate and Heat Transfer in the Human Body Exposed to Leakage Electromagnetic Field at 915 MHz and 2450 MHz

In recent years, society has increased utilization of electromagnetic radiation in various applications. This radiation interacts with the human body and may lead to detrimental effects on human health. However, the resulting thermophysiologic response of the human body is not well understood. In order to gain insight into the phenomena occurring within the human body with temperature distribution induced by electromagnetic field, a detailed knowledge of absorbed power distribution is necessary. In this study, the effects of operating frequency and leakage power density on distributions of specific absorption rate and temperature profile within the human body are systematically investigated. This study focuses attention on organs in the human trunk. The specific absorption rate and the temperature distribution in various tissues, obtained by numerical solution of electromagnetic wave propagation coupled with unsteady bioheat transfer problem, are presented.

DOMINANT FACTORS AFFECTING TEMPERATURE ELEVATION IN ADULT AND CHILD MODELS EXPOSED TO SOLAR RADIATION IN HOT ENVIRONMENT

The number of children sufiering from heat-related illness has been increasing in recent years. Children are more susceptible to heat-related illness than adults, which is considered to be caused by morphological and functional difierences between adults and children. In the present study, the temperature change and perspiration in adult and child models during a simultaneous exposure to solar radiation and a hot environment are evaluated computationally. First, the power absorbed in the human body due to solar radiation is computed by the FDTD method for the Maxwell equations. Then, the temperature distribution inside the human body is modeled by the bioheat equation taking into account the thermophysiological response. Anatomically- based Japanese adult male and 3-year-old child phantoms are used. An approximative analytical solution for the core temperature elevation is also derived to clarify the dominant factors afiecting the temperature elevation. From our computational results, the core temperature elevation in the child phantom for both the solar and hot-environment exposures was larger than that in the adult phantom. The temperature elevation in the child was found to be mainly caused by the exposure

Can the PHS model (ISO7933) predict reasonable thermophysiological responses while wearing protective clothing in hot environments?

In this paper, the prediction accuracy of the PHS (predicted heat strain) model on human physiological responses while wearing protective clothing ensembles was examined. Six human subjects (aged 29 ± 3 years) underwent three experimental trials in three different protective garments (clothing thermal insulation Icl ranges from 0.63 to 2.01 clo) in two hot environments (40 °C, relative humidities: 30% and 45%). The observed and predicted mean skin temperature, core body temperature and sweat rate were presented and statistically compared. A significant difference was found in the metabolic rate between FIRE (firefighting clothing) and HV (high visibility clothing) or MIL (military clothing) (p < 0.001). Also, the development of heart rate demonstrated the significant effects of the exposure time and clothing ensembles. In addition, the predicted evaporation rate during HV, MIL and FIRE was much lower than the experimental values. Hence, the current PHS model is not applicable for protective clothing with intrinsic thermal insulations above 1.0 clo. The results showed that the PHS model generated unreliable predictions on body core temperature when human subjects wore thick protective clothing such as firefighting clothing (Icl > 1.0 clo). The predicted mean skin temperatures in three clothing ensembles HV, MIL and FIRE were also outside the expected limits. Thus, there is a need for further extension for the clothing insulation validation range of the PHS model. It is recommended that the PHS model should be amended and validated by individual algorithms, physical or physiological parameters, and further subject studies.

How to measure thermal effects of personal cooling systems: human, thermal manikin and human simulator study

Thermal effects, such as cooling power and thermophysiological responses initiated upon application of a personal cooling system, can be assessed with (i) humans, (ii) a thermal manikin and (iii) a thermophysiological human simulator. In order to compare these methods, a cooling shirt (mild cooling) and an ice vest (strong cooling) were measured using human participants and a thermal manikin. Under all conditions, cooling was provided for 45 min, while resting at a room temperature of 24.6–25.0 °C and a relative humidity of 22–24%. Subsequently, the thermophysiological human simulator was used under the same conditions to provide data on thermophysiological responses such as skin and rectal temperatures. The cooling power determined using the thermal manikin was 2 times higher for the cooling shirt and 1.5 times higher for the ice vest compared to the cooling power determined using human participants. For the thermophysiological human simulator, the cooling power of the cooling shirt was similar to that obtained using human participants. However, it was 2 times lower for the ice vest when using the thermophysiological human simulator. The thermophysiological human simulator is shown to be a useful tool to predict thermophysiological responses, especially upon application of mild cooling intensity. However, the thermophysiological human simulator needs to be further improved for strong cooling intensities under heterogeneous conditions.

Effects of Two Different Kinds of Bed on Thermophysiological Responses and Heart Rate during Night Sleep

Effects of Two Different Kinds of Bed on Thermophysiological Responses and Heart Rate during Night Sleep

EFFECTS OF COOLING THE UPPER TORSO ON THERMOPHYSIOLOGICAL RESPONSES AND CLOTHING MICROCLIMATE IN SUBJECTS WEARING PROTECTIVE CLOTHING FOR PESTICIDE

INTRODUCTION Farmers need protective clothing while spraying pesticide in order to protect themselves against agricultural chemicals. However, wearing the protective clothing often causes hyperthermia. because heat loss, especially wet heat loss through the protective clothing does not occur effectively from the human body to the environment. Although various cooling systems which can prevent the core temperature and the sweat rate from rising have been studied (1,2), these are not necessarily practical or appropriate for field use. With these in mind, we tried to study the thermophysiological effects of cooling the upper torso with a portable frozen gel strip in exercising and resting subjects.

The Effects of Wearing Hat on Thermophysiological Responses in Sedentary and Exercising Women under Warm and Radiant Environments

The Effects of Wearing Hat on Thermophysiological Responses in Sedentary and Exercising Women under Warm and Radiant Environments

Effects of Air Temperature and Clothing on Thermophysiological Responses and Thermal Comfort Vote during Rest and Physical Exercise

Effects of Air Temperature and Clothing on Thermophysiological Responses and Thermal Comfort Vote during Rest and Physical Exercise

Thermo-Physiological Responses of the Foot under 2234°C Thermal Conditions

Thermo-Physiological Responses of the Foot under 2234°C Thermal Conditions

Effects of the Jet Air Mattress on Thermophysiological Responses and Microclimate inside Bed

Effects of the Jet Air Mattress on Thermophysiological Responses and Microclimate inside Bed

Prediction of human thermophysiological responses during shower bathing

This study develops a model to predict the thermophysiological response of the human body during shower bathing. Despite the needs for the quantitative evaluation of human body response during bathing for thermal comfort and safety, the complicated mechanisms of heat transfer at the skin surface, especially during shower bathing, have disturbed the development of adequate models. In this study, an initial modeling approach is proposed by developing a simple heat transfer model at the skin surface during shower bathing applied to Stolwijk's human thermal model. The main feature of the model is the division of the skin surface into three parts: a dry part, a wet part without water flow, and a wet part with water flow. The area ratio of each part is decided by a simple formula developed from a geometrical approach based on the shape of the Stolwijk's human thermal model. At the same time, the convective heat transfer coefficient between the skin and the flowing water is determined experimentally. The proposed model is validated by a comparison with the results of human subject experiments under controlled and free shower conditions. The model predicts the mean skin temperature during shower fairly well both for controlled and free shower bathing styles.

Effect of Ceramics on the Physical and Thermo-physiological Performance of Warm-up Suit

The purpose of this study was to develop a warm-up suit that is comfortable as well as having a good thermal performance. Heat-insulating water vapor-permeable fabrics for warm-up suit were developed by applying ceramic powders to hydrophilic polyurethane films, which were then incorporated into textiles. Two types of ceramic compounds were used in this study: MU-4N and RT-3. The infrared emissivity was 92.6 for MU-4N and 94.8 for RT-3. In order to evaluate the effectiveness of using ceramics in a warm-up suit, we examined the effects of ceramics on selected variables: thermo-physiological properties of the clothing systems (using thermal manikin), and thermo-physiological responses and subjective sensations of human subjects. The infrared emissivity of textiles increased when ceramics were added to the film laminate. Ceramics slightly increased the thermal insulation value and decreased the water vapor transmission rate. The thermal manikin test also showed that ceramics enhanced the thermal insulation of the clothing system without increasing the evaporative resistance. The microclimate temperature was kept higher when subjects wore the warm-up suit with ceramics.

THE INFLUENCE OF ROOM HEATING CHARACTERISTICS ON THE PHYSIOLOGICAL REACTION OF YOUNG CHILDREN AND THEIR MOTHER

This paper investigates young children's thermoregulatory capabilities through a comparison of young children's thermal responses and heat balances with their mother's. The following results were obtained: 1) The majority of children's local skin temperatures were significantly higher than that of the mother's during the 24°C and 32°C conditions. 2) In the 32°C and 28°C condition there was no significant difference between the child and mother's thermo-physiological responses. However there was a difference in blood flow to the skin through contraction of blood vessels in the cold conditions of 24°C and 20°C, which suggested an undeveloped thermo-physiological response in the children. 3) It was found when investigating the heat diffusion of children and mothers that there were significant differences in the 24°C and 32°C conditions in regards to metabolic rate, convection, radiation and evaporation.

Thermophysiological Responses Caused by Ballistic Bullet-Proof Vests

Little data is available concerning the heat stress experienced by members of staff who wear bullet-proof vests in a warm or hot environment. For this reason, knowledge is limited and, consequently, preventative advice on how to avoid heat sickness or hyperthermia is required. Skin and body temperatures, fluid loss and the heart rate of 30 persons (15 test persons versus 15 control persons) were measured in three situations typical of the test participants' job situations. Environmental data (wind velocity, air humidity, air temperature) were measured during the tests as well. Whereas there was a significant increase in skin temperatures, there was no difference in the core body temperatures of both groups. Maximum core body temperature remained well below 38 degrees C in all subjects. Test persons wearing vests showed a fluid loss of 1.1 l on average (non-vest wearers in the control group 1.0 l). There is no increased risk of heat stroke or hyperthermia for employees wearing bullet-proof vests in comparison with employees who do not wear them. Both groups, however, should be advised to ensure an adequate intake of fluid to maintain a healthy body fluid balance when working in hot environments.

Effect of glucocorticoid depletion on heat-induced Hsp70, IL-1β and TNF-α gene expression

When exposed to heat, conscious naive rats may develop lethal heatstroke, depending on heat load, i.e., time spent at high body core temperature. The occurrence of heatstroke was hypothesized to result from a defective glucocorticoid secretion related to altered heat-stress responses. We thus investigated the potential involvement of glucocorticoids in heat tolerance and its consequences on physiological responses, heat shock protein 70 (Hsp70), and cytokine mRNA expressions. Two hours before heat exposure, the animals were injected either with metyrapone, an inhibitor of corticosterone synthesis, or with its vehicle. Heat exposure lasted for 15, 30, 45 or 60 min. Thereafter, the rats were distributed into three groups according to their heat load: null, moderate (without any lethal risk) and intense (with lethal risk). Physiological responses were evaluated with colonic temperature, plasma lactate and hematocrit. Brain responses were assessed in frontal cortex through Hsp70, interleukin-1beta (IL-1β) and tumor necrosis factor-alpha (TNF-α) mRNA expressions. The animals with a severe heat load exhibited a high hematocrit, increased plasma lactate level and enhanced brain IL-1β and Hsp70 mRNA expressions. Independent of the heat load, Metyrapone rats showed the same thermophysiological responses and IL-1β and Hsp70 mRNA expressions when compared with vehicle rats. However, the Metyrapone rats experiencing an intense heat load exhibited an increased TNF-α mRNA expression. In conclusion, these data (i) confirm that heat load is important in the calibration of the risk attached to heat exposure; and (ii) suggest that corticosterone synthesis inhibition may favor TNF-α mRNA expression without any effect on Hsp70 mRNA expression.

Effects of fabric surface energy on human thermophysiological responses during exercise and recovery

The present paper reports a study on influences of fabric surface energy of cotton and polyester garments on clothing microclimates and human thermophysiological responses during intermittent exercise and recovery. Eight healthy males wearing the garments prepared performed exercises and rest according to the following protocol: rest for 30 min, run on treadmill for total 60 min of three sessions with different intensity and duration, and then sit quietly for 30 min for recovery, all at 30 °C and relative humidity of 30 %, while the microclimate humidity (H mc ) and temperature (T mc ), the clothing outside surface humidity (H co ) and temperature (T co ), the skin temperatures and ear canal temperature (T ear_canal ) were measured. The garments are made of: (a) hydrophilic and hydrophobic cotton knitted fabrics, and (b) hydrophilic and hydrophobic polyester knitted fabrics. During and after exercise, for cotton, hydrophilic garment resulted in significant lowerΔH mc , ΔH co , ΔT mc during recovery, higher $$\Delta \overline {\rm T} _{sk} $$ , lowerΔT ear_canal andΔT forehead . For polyester, hydrophilic garment resulted in significantly lowerΔH co , ΔT co , higher $$\Delta \overline {\rm T} _{sk} $$ , higherΔT forehead during E1, E2 and recovery session but lower during E3. In summary, surface energy of cotton garments had significant influences on human thermophysiological responses during exercise and recovery, and hydrophilic cotton garment was better than hydrophobic one to reduce heat stress. Surface energy of polyester garments had influences of lower significance, and hydrophilic garment appeared better than hydrophobic garment.

Effect of Fabric Liquid Water Transfer Behavior on Human Thermophysiological Responses and Clothing Microclimate during Exercise and Recovery

This paper reports a study on the effects of fabric liquid water transfer behavior on human thermophysiological responses and clothing microclimate. Both cotton and polyester fabrics were treated to have different liquid water transfer properties. With moisture management (MM) treatment, the fabrics can transfer liquid water from inner surface (close to skin) to outer surface (close to surrounding environment) during wearing while keeping skin dry. With reversed moisture management (RMM) treatment, the inner layer of the fabric is water absorbency, liquid water is difficult to be transferred to outer surface. Two sets of garments were made of MM and RMM fabrics for both cotton and polyester respectively. A series of wear trials were conducted by asking human subjects to wear these garments according to a specially designed experimental protocol. The microclimate humidity and temperature, skin temperature and ear canal temperature were recorded. MM cotton garment caused significant lower absolute humidity outside clothing (Hco) during exercise and recovery, higher temperature outside clothing (Tco), higher mean skin temperature (Tsk) and lower ear canal temperature (Tear_canal) during recovery than RMM cotton. Polyester MM garment caused significant higher Hco during exercise and higher Tsk than RMM polyester. For both cotton and polyester, MM garment is better than RMM garment to reduce heat stress during exercise and recovery in temperature of 30 °C and relative humidity of 30%.

Human thermophysiological response to high intensity radiation fluxes near a forest fire line

Human thermophysiological response to high intensity radiation fluxes near a forest fire line