Sweat Evaporation Research Articles

Evaporation-Induced Clogging of an Artificial Sweat Duct.

Metal-based antiperspirants have been in use for centuries; however, there is an increasing consumer demand for a metal-free alternative that works effectively. Here, we develop an artificial sweat duct rig and demonstrate an alternative, metal-free approach to antiperspiration. Instead of clogging sweat ducts with metal salts, we use a hygroscopic material to induce the evaporation of sweat as it approaches the outlet (i.e. pore) of the sweat duct. As a result, the sweat dehydrates almost completely while still being inside of the duct, forming a natural gel-like salt plug that halts the flow. We show that the critical pressure gradient within the duct (∼3 kPa), beneath which clogging occurs, can be rationalized by balancing the mass flow rates of the liquid (Poiseuille's law) and the evaporative vapor (Fick's law).

AN INVESTIGATION OF SEASONAL VARIATIONS IN THE FITNESS TEST PERFORMANCE OF LAW ENFORCEMENT RECRUITS

The purpose of this research was to determine whether different seasons could influence fitness test performance in law enforcement recruits. Retrospective examination was conducted on data from four classes, which included 375 recruits (302 males, 73 females) from an agency. The classes were fitness tested during four different seasons in southern California (Fall: n=89, temperature=22-28°C, humidity=20-32%; Winter: n=84, temperature=18-26°C,humidity=8-11%; Spring: n=102, temperature=22-29°C, humidity=23-50%; Summer: n=100, temperature=21-25°C, humidity=39-71%). Fitness testing occurred in the week prior to academy and included: the vertical jump (VJ); push-ups and sit-ups completed in 60 s; and the 20-m multistage fitness test (20MSFT). A one-way ANOVA was used with Bonferroni post hoc (p<0.05) adjustment to calculate any between-class differences. There were no significant between-class differences for the VJ (p=0.197) and sit-ups (p=0.352). Winter and Summer recruits completed 16% and 19% significantly more push-up repetitions than Spring recruits (p≤0.029). Winter recruits completed 16-22% significantly more MSFT shuttles than Fall, Spring and Summer classes recruits (p≤0.009, 16%, 22%, and 18%, respectively). Variability in fitness test performance across the seasons may be due to class-to-class fitness variations in recruits. However, recruits in the Winter class were clearly superior in the 20MSFT, which is an aerobic maximal running test. Hotter temperatures can increase cardiovascular strain, while humidity can decrease sweat evaporation rates, which can impact a test such as the 20MSFT. Law enforcement staff may need to consider ambient temperatures and humidity during fitness tests due to potential negative effects on recruit performance.

Substrate-Free Multilayer Graphene Electronic Skin for Intelligent Diagnosis.

Current wearable sensors are fabricated with substrates, which limits the comfort, flexibility, stretchability, and induces interface mismatch. In addition, the substrate prevents the evaporation of sweat and is harmful to skin health. In this work, we have enabled the substrate-free laser scribed graphene (SFG) electronic skin (e-skin) with multifunctions. Compared with the e-skin with the substrate, the SFG has good gas permeability, low impedance, and flexibility. Only assisted using water, the SFG can be transferred to almost any objects including silicon and human skin and it can even be suspended. Many through-holes like stomas in leaf can be formed in the SFG, which make it breathable. After designing the pattern, the gauge factor (GF) of graphene electronic skin (GES) can be designed as the strain sensor. Physiological signals such as respiration, human motion, and electrocardiogram (ECG) can be detected. Moreover, the suspended SFG detect vibrations with high sensitivity. Due to the substrate-free structure, the impedance between SFG e-skin and the human body decreases greatly. Finally, an ECG detecting system has been designed based on the GES, which can monitor the body condition in real time. To analyze the ECG signals automatically, a convolutional neural network (CNN) was built and trained successfully. This work has high potential in the field of health telemonitoring.

Effects of Pre-Cooling on Thermophysiological Responses in Elite Eventing Horses.

Simple SummaryHorses have a high metabolic capacity for exercise, producing a great deal of heat, and have a small surface area for heat loss. Under limited circumstances, the regulation of heat loss (i.e., across the respiratory tract and by the evaporation of sweat) means heat build-up in the body is reduced. Thermoregulation can be assisted by cooling the horses down to safely perform exercise in thermally challenging environments. The present study showed that pre-cooling (i.e., cooling between the warm-up and exercise performance) slightly reduced the rise in rectal, shoulder and rump skin temperatures of ten international eventing horses during moderately intense canter training in moderate environmental conditions. During the canter training, heart rate, sweat rate and sweat composition were unaffected by pre-cooling. The pre-cooling strategy chosen here was cold-water rinsing for a short period of time (~8 min). Considering the limited time and space at equestrian events, such a pre-cooling strategy could easily be implemented. Reducing heat strain by pre-cooling may potentially improve equine welfare during events.In this study, we examined the effects of pre-cooling on thermophysiological responses in horses exercising in moderate environmental conditions (average wet bulb globe temperature: 18.5 ± 3.8 °C). Ten international eventing horses performed moderate intensity canter training on two separate days, and were either pre-cooled with cold-water rinsing (5–9 °C for 8 ± 3 min; cooling) or were not pre-cooled (control). We determined velocity (V), heart rate (HR), rectal temperature (Tre,), shoulder and rump skin temperature (Tshoulder and Trump), plasma lactate concentration (LA), gross sweat loss (GSL), and local sweat rate (LSR), as well as sweat sodium, chloride and potassium concentrations. The effect of pre-cooling on Tre was dependent on time; after 20 min of exercise the effect was the largest (estimate: 0.990, 95% likelihood confidence intervals (95% CI): 0.987, 0.993) compared to the control condition, resulting in a lower median Tre of 0.3 °C. Skin temperature was also affected by pre-cooling compared to the control condition (Tshoulder: −3.30 °C, 95% CI: −3.739, −2.867; Trump: −2.31 °C, 95% CI: −2.661, −1.967). V, HR, LA, GSL, LSR and sweat composition were not affected by pre-cooling. In conclusion, pre-cooling by cold-water rinsing could increase the margin for heat storage, allowing a longer exercise time before a critical Tre is reached and, therefore, could potentially improve equine welfare during competition.

Wearable Multifunction Sensor for the Detection of Forehead EEG Signal and Sweat Rate on Skin Simultaneously

In this paper, we designed a multifunction wearable sensor for detecting electroencephalogram (EEG) and sweat rate simultaneously. Conductive fabric electrode was combined on the multifunction sensor for EEG signal measurement. The conductive material on the fabric was metallic Ag, which has low contact impedance and noise. The EEG electrode was connected to an EEG signal recording module, which was based on ADS1299 converter. There were 8 signal recording channels on the module. One of the channels was connected to the multifunction sensor and the other 7 channels could be connected to independent EEG electrodes. Because of the gaps between the fibers, the conductive fabric electrode could record EEG signals while allowing sweat to permeate through it. The sweat passed through EEG electrode could get into the internal of multifunction sensor. A piece of microporous PDMS was used to accelerate the evaporation of sweat in the multifunction sensor. The microporous PDMS was coated with super hydrophilic coating to help sweat diffusion in it. CaCl2 desiccant was used in the sensor to absorb sweat vapor continuously and generate a humidity diffusion gradient. A circuit board based on SHT20 chip was embedded in the sensor for relative humidity measurement in the path of sweat vapor diffusion. The sweat rate was measured by indirect estimation from relative humidity. By measuring the relative humidity in the multifunction sensor, we could realize the continuously measurement of sweat rate simultaneously with EEG signal recording. Both the EEG signal and sweat rate data could be transferred out wirelessly.

Global warming, heat-related illnesses, and the dermatologist.

Global warming, provoked by the greenhouse effect of high levels of atmospheric gases (most notably carbon dioxide and methane), directly threatens human health and survival. Individuals vary in their capacity to tolerate episodes of extreme heat. Because skin is the organ tasked with heat dissipation, it is important for dermatologists to be versed in the physiology of cutaneous heat dissipation and cognizant of clinical settings in which the skin’s thermoregulatory responses may be impaired. When the external temperature is lower than that of the skin, the skin releases internal heat through direct thermal exchange with the environment, a process that is aided by an expansion of cutaneous blood flow and eccrine sweating. Cooling through the evaporation of sweat is effective even when the external temperature exceeds that of skin. Many factors, including environmental and physiological (e.g., age and sex), and pathological (e.g., preexisting illnesses, disorders of eccrine function, and medications) considerations, affect the skin’s capacity to thermoregulate. Identification of individuals at increased risk for heat-related morbidity and mortality will become increasingly important in the care of patients.

Mechanisms of thermal dysregulation in primary hyperhidrosis and hypohidrosis.

Mechanisms of thermal dysregulation in primary hyperhidrosis and hypohidrosis.

Aggregation kinetics of diesel soot nanoparticles in artificial and human sweat solutions: Effects of sweat constituents, pH, and temperature

Soot nanoparticles (SNPs) are airborne contaminants that could potentially penetrate skin, but their aggregation after contact with sweat may lower their health risks. This study investigated SNP aggregation kinetics in 4 artificial sweat standards and 21 human sweat samples. Effects of sweat inorganic (NaCl, Na2HPO4, and NaH2PO4) and organic (L-histidine, lactic acid, and urea) constituents, pH, temperature, and concentrations were examined. Results showed that SNP aggregation rates in 4 standards followed American Association of Textile Chemists and Colorists (AATCC) > British Standard (EN) > International Standard Organization (ISO) pH 5.5 > ISO pH 8.0, and could be described by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The aggregation rates increased with concentrations of SNPs, inorganic salts, L-histidine, and lactic acid, decreased with increasing pH and concentration of urea, and were weakly influenced by temperature. Systematic characterizations revealed SNP adsorption for organic sweat constituents. SNPs aggregated rapidly to ∼1000 nm in AATCC, but remained stable in ISO pH 8.0 and > 14/21 human sweat fluids over 20 min. The SNP aggregation rates correlated negatively with pH (r = -0.531*) and |ζ potential| (r = -0.464*) of human sweat samples. Sweat evaporation could promote aggregation of SNPs, hence lowering their potential harm via dermal exposure.

Testing traditions in cycling: newspapers are effective thermal insulators during simulated downhill cycling

Cycling downhill accelerates heat loss and requires lower work rates leading to cold discomfort. Historically, cyclists have behaviorally thermoregulated prior to cycling downhill by inserting newspapers into their jerseys. Yet, there is no experimental data to support such a method showing improvements in thermal perception and profile; we hypothesized it would. Two cohorts (N.=8 each) of male participants completed two main trials each involving 30-minutes simulated uphill cycling (65% VO<inf>2peak</inf> 188 [41] W; no fan) followed by 15-minutes downhill cycling (35% VO<inf>2peak</inf> 41 [12] W) in front of an industrial fan (wind speed: 4.6 [0.1] m·s-1). In one trial participants inserted one (study 1) or two (study 2) tabloid newspapers into their jerseys (PAPER) prior to downhill cycling; the other was a control (NOPAPER). Whole body and torso thermal sensation (TS) and comfort (TC), aural temperature (T<inf>au</inf>), skin temperature (T<inf>skin</inf>), and newspaper mass change (∆) were measured. Data were compared using ANOVA and t-test to 0.05 alpha level. After uphill cycling thermal and perceptual profiles were similar. In study 1, only TC was transiently improved 1-minute after newspaper insertion. In study 2, T<inf>skin</inf> rate of decline was lower in the PAPER condition (-0.11 [0.12] °C.min-1 cf -0.53 [0.16] °C.min-1; P=0.001) and T<inf>chest</inf> remained higher (28.83 [3.17] °C cf 24.39 [3.22] °C). This improved TS but not TC. Newspaper mass increased indicating impaired sweat evaporation (∆<inf>mass</inf>: 5.7 [4.9] g; P=0.01). Thermal perception and profile during downhill cycling was improved by inserting two newspapers but not one newspaper into the jersey, supporting our hypothesis.

Heat, moisture and air transport through clothing textiles

The body generates sweat and heat that must be removed from the surface of the skin to the outside environment in order to maintain body temperature. The transfer of sweat, heat and air through the fabric is important for the wearer’s comfort. The fabric transports moisture by absorption or wicking processes. Moisture is absorbed by the fabric and when it evaporates it cools the body. Wicking occurs when moisture is transported in between the pores of the fabrics or by capillary action in yarns. Heat transfer involves conduction, convection and radiation and because air movement by convection facilitates the evaporation of sweat, it can make a substantial contribution to causing the body temperature to decrease. Clothing impairs the transfer of heat and moisture from the skin surface to the external environment. Restricting heat transfer to the external environment helps to keep the wearer warm but excessive accumulation of moisture causes clothing to stick to the skin, while the accumulation of heat causes heat stress making the wearer feel uncomfortable. Moisture, heat and air transmission are affected by fibres, fabrics and finishing properties and hydrophilic fibres absorb more moisture than lipophilic fibres. Rapid transportation of sweat and heat helps the body to cool down and the wearer to feel comfortable but protective clothing tends to have lower moisture, heat and air transmission and as a result the accumulation of moisture and heat makes them uncomfortable to wear. Traditional methods of evaluating the effects of moisture, heat and air transmission by clothing use bench-top tests on flat fabric, however, the more-recent use of manikins enables consideration to be taken of body shape as well as fit of the garments.

Improving the Performance of Terry Fabrics for use in Pilgrimage Clothes

Terry fabric is a kind of soft pile fabrics. It is distinguished with uncut or cut loops which must have required usage properties such as higher water absorption, bacterial resistance, high wet strength, ability to dye well, good colorfastness, wash ability, soft hand, and hypoallergenic, low cost, and easy availability. Terry fabric is the most popular fabric for home textiles like bath towels, hand towels, kitchen towels, medical towels. One of the popular applications of terry fabrics is pilgrimage (IHRAM) terry cloths. It should have physiological comfort properties; like the breathability, quick absorption and evaporation of sweat, softness, air and water vapor permeability, antibacterial especially in hot weather of Mecca. Terry fabrics are produced by three yarn systems: pile warp, ground warp weft yarns. Pile structure mainly affect the functional properties of terry fabrics. The main factors should be considered in the designing of a terry fabric are the fabric materials, type of ground warp yarns, type of pile warp yarns, type of weft yarns, pile length, pile height and pile structure. This research concerns with improving the performance of terry towels used as pilgrimage (Ihram) cloths by measuring the weight (GSM), fabric thickness and air permeability of the fabric. Three parameters were used in executing the research samples to compare them with a common control sample in the market to achieve the research aims. The first factor is using bamboo fibers as pile warp yarns. The second parameter is using different heights of pile (5.5 mm-6.5mm-7.5 mm). The third parameter is using different types of materials as wefts (Cotton-Lyocel-Bamboo). The result of the research showed that decreasing the pile height improves air permeability. In addition, using bamboo yarns as pile warp and picking by using bamboo and Lyocel yarns improves the performance and physiological comfort characteristics of terry towels such as absorption, evaporation, thermal conductivity, anti-microbial and anti-bacterial abilities. Research Problem: High degrees of temperature in Mecca during the year leads to significant suffering to people during the pilgrimage season. This leads to sweating heavily which is considered an ideal environment for Bacterial growth and thus causes physiological in comfort for them.Antibacterial treatments should be done during final finishing processes for traditional cotton terry towels to provide these fabrics with antibacterial properties, but the efficiency of this treatments is temporary especially with continuous laundering. So, this requires terry towels which provide physiological comfort and durable antibacterial without chemical treatments by using antibacterial natural materials such as bamboo and Lyocel.Objectives: This research aims to producing terry towels used as pilgrimage (IHRAM) cloths which achieve physiological characteristics for people during pilgrimage as following: Improve the ability of water absorption and evaporation, Improve the ability of air permeability which improve thermal conductivity, Improve the anti-bacterial and anti-microbial properties.Methodology: The research follows the practical methodology . Results: Decreasing pile height leads to improve air permeability of the fabric, Using bamboo fibers as pile warp improves air permeability of fabric comparing to the usage of cotton fibers, Using bamboo and Lyocel fibers as wefts improves air permeability of the fabric.

Heat Strain Assessment Under Three Different Wet Bulb Globe Temperatures With Protective Clothing

Personal protective clothing is an important part of personal protective equipment worn by health care workers and first receivers. Wearing a vapor-barrier layer of protective clothing inhibits sweat evaporation and impairs physiological and perceptual responses. PURPOSE: To evaluate thermoregulatory responses and heat strain indices during simulated healthcare and first receivers’ tasks under three different wet bulb globe temperatures (WBGT). METHODS: Four men (25.8±6.8 yrs, 176.5±6.1 cm, 75.3±16.9 kg) wore an ensemble consisting of a loose-fitting powered air-purifying respirator, chemical resistant coverall vapor-barrier ensemble, double gloves, boots, and an apron, while performing a battery of first receiver and health care simulation activities (walking, cutting and removing clothing, scrubbing, placing a splint and cervical collar, and weight carrying) for three repetitions under three different WBGT (18, 26, and 34°C) in counterbalanced order. These environmental conditions were intended to simulate healthcare workplace conditions during mass casualty incidents. Rectal temperature (Tre) and heart rate were continuously monitored and averaged during the last 1-minute of each activity and presented as mean ± standard deviation. Physiological (PSI) and perceptual strain index (PeSI) were calculated at the end of each activity. RESULTS: Over time, Tre, PSI, and PeSI all gradually increased. At the end of the trial, Tre was significantly higher in the 34°C condition (38.5±0.4°C) than the 18°C condition (37.8±0.4°C, p=0.029) but did not differ from the 26°C conditions (38.2±0.6°C, p=0.104). The PSI was significantly higher in 34°C (6.4±1.0) than 26°C (5.1±1.2, p=0.002) and 18°C conditions (2.6±1.1, p=0.001). The PeSI was significantly higher in 34°C (7.6±1.8) than 18°C conditions (3.3±1.8, p=0.006) but did not differ between 34°C (7.6±1.8) and 26°C conditions (5.7±1.4, p=0.075). CONCLUSIONS: Tre and heat strain indices gradually increased over time across all environmental conditions. Tre and PeSI did not differ between 26°C and 34°C WBGT conditions. Tre and PeSI responses may be blunted by wearing a vapor-barrier ensemble. Future studies should examine this hypothesis to clarify the current findings.

Super-hygroscopic film for wearables with dual functions of expediting sweat evaporation and energy harvesting

Despite the boom in atmospheric water-harvesting techniques, few attempts have been made with a broader horizon–absorbing the moisture from sweatevaporation, which has substantial implications for human comfort and wearable electronics. Herein, a cobalt-complex-based super-hygroscopic material (Co-SHM) is developed to expedite sweat evaporation and fabricate moisture-triggered energy harvesting devices. The Co-SHM features transparent thin-film structure, fast absorption kinetics and high water uptake of 4.6 g g−1. The material regeneration can be driven by natural sunlight, making the Co-SHM an energy-efficient moisture absorbent. Integrating the Co-SHM into breathable and waterproof PTFE membranes, we design new kinds of armpit pad, shoe lining, and insole, which can rapidly absorb the moisture from sweat to prevent sweat accumulation, thereby providing a dry and comfortable microclimate for people. Furthermore, the absorbed sweat can be transduced to energy through a Co-SHM based wearable energy harvesting devices. The harvested energy can power a light-emitting diode. This work holds significant economic potential in the fields of functional clothing, footwear, and wearable electronics.

Relationship of Hot Work Climate with Employee Blood Pressure in Binat Installation, Dr. Sardjito

Blood pressure in each individual varies, and depends on age and daily activities such as when blood pressure activity will rise and when the remaining blood pressure will drop. Laundry installations are workplaces where there is a physical hazard in the work process in the form of a hot working climate. In a hot working climate, the body regulates its temperature by accelerating the evaporation of sweat by widening (vasodilation) of blood vessels which results in increased blood circulation and increased capillaries accompanied by physiological responses, such as increased pulse and blood pressure. This study aims to analyze the relationship between the work of heat and blood pressure of workers in the Laundry Installation of RSUP Dr. Sardjito Yogyakarta. This study uses quantitative research design using a cross sectional approach. The population in this study were Laundry Installation workers with a sample of 35 respondents taken with total sampling. Data analysis using Chi-Square. The results showed that there was a relationship between the hot work climate and workers’ blood pressure (p = 0.03) and there was a relationship between the hot working climate and diastolic blood pressure of workers in the Laundry in RSUP Installation. Sardjito Yogyakarta (p = 0.01).

On the Effect of Sex on Heat Strain During Prolonged Work in the Heat

Workers in many industries commonly experience excessive elevations in core temperature and heart rate (heat strain), which can compromise productivity and safety. These elevations in heat strain could be exacerbated in women, due to impairments in evaporative heat loss (sweat evaporation) relative to men, which exacerbate body heat storage during semi‐nude, short duration (30 min) exercise at a moderate metabolic rate (~200 W/m2). However, in an occupational setting, work is often performed for prolonged periods (&gt;180 min) at a similar intensity (on average) while wearing protective clothing that can impede sweat evaporation. As such, the extent to which such sex‐related impairments in heat dissipation may be exacerbated during prolonged, moderate‐intensity work while wearing protective clothing remains unclear. This is a critical knowledge gap, as such information is necessary to inform sex‐specific occupational heat stress guidelines, which are currently unavailable. We therefore sought to evaluate whether core (rectal) temperature and heart rate (% heart rate reserve, HRR) would be exacerbated in women relative to men during prolonged, moderate‐intensity work in non‐heat stress and high‐heat stress conditions while wearing standard work clothing. To evaluate this hypothesis, 15 healthy women (18–42 years) and 19 men (18–45 years) completed two trials (separated by &gt;48 hours) involving 180‐min of treadmill walking at a moderate metabolic rate (200 W/m2) in a non‐heat stress (21.9°C, 35% relative humidity; wet‐bulb globe temperature [WBGT] 16°C) and high‐heat stress (41.4°C, 35% relative humidity; WBGT 32°C) environment, while wearing single‐layer cotton coveralls (~1 Clo). Trials were terminated upon completion of 180‐min work, volitional fatigue, or a core temperature ≥39.5°C. Mann‐Whitney U‐tests were used to identify between‐group differences in work duration, while unpaired t‐tests (2‐tailed) were used to assess between‐group differences in peak core temperature and HRR (average of the final 5‐min of work). All participants completed 180 min in the WBGT 16°C however, in the WBGT 32°C, 7 men and 7 women terminated prematurely. Nonetheless, median (range) work duration was similar between groups (women: 158 min [75 – 180] vs. men: 145 min [78–180]; p=.79). Peak core temperature (mean [SD]) was similar between women and men in the WBGT 16°C (37.8°C [0.3] and 37.6°C [0.3], respectively; p=.07) however, contrary to our hypothesis, this response was also similar between men and women in the WBGT 32°C (38.8°C [0.4] and 39.0°C [0.4], respectively; p=.23). Peak HRR was also similar between women and men in the WBGT 16°C (47% [11] and 43% [16]; p=.44) and WBGT 32°C (81% [13] and 86% [16]; p=.41), respectively. Our preliminary findings indicate that sex‐related impairments in heat loss (previously observed in dry heat) do not appear to exacerbate heat strain in women relative to men during prolonged, moderate‐intensity work while wearing standard protective clothing. However, whether a given level of heat strain is equally detrimental to the health of women and men has yet to be determined, and this should be considered prior to implementing or dismissing sex‐specific guidelines for industrial workers.Support or Funding InformationThe Government of Ontario.

Use of a Water‐soaked Garment, with and without an Electric Fan, to Mitigate Thermal Strain in Older Individuals under Heat Wave Conditions

As average global surface temperatures are projected to rise, and heat waves are expected to increase in frequency, duration, and intensity, exposure to high levels of heat stress will occur with greater regularity. Older individuals are particularly vulnerable to heat stress, evidenced by excess hospitalizations and mortality among individuals aged &gt;60 years. With the continue rise of electricity costs coupled with vulnerable regions that do not have easy access to air conditioning, it is imperative to find alternative cooling strategies that are cost‐effective and accessible for older individuals. The present study evaluated whether wearing a water‐soaked t‐shirt, with and without electric fan use, mitigates thermal and cardiovascular strain under heat wave conditions. Nine healthy older individuals (68 ± 4 years; five females) completed three, 120‐min heat exposures (42.4 ± 0.2°C, 34.2 ± 0.9% relative humidity) on separate occasions while wearing either a dry t‐shirt (CON), a t‐shirt soaked with 500 ml of tap water (WET), or a t‐shirt soaked with 500 ml of tap water while facing an electric fan forcing air at 2.4 ± 0.4 m/s (WET+FAN). Measurements included core and mean skin temperatures, evaporative mass loss, heart rate, and blood pressure. The rise in core temperature was attenuated by ~0.3°C in WET compared to DRY and WET+FAN during the first hour of heat stress (P &lt; 0.01). At 120 min, the rise in core temperature remained attenuated by ~0.2 °C in WET compared to DRY (P=0.0016), while other comparisons were not different. After the 120‐min heat exposure, changes in body mass, which largely reflect evaporation of sweat and moisture trapped in clothing, were greatest in WET+FAN, followed by WET, and then DRY (P &lt; 0.01). However, sweat losses were lowest in WET, followed by DRY, and then WET+FAN (P &lt; 0.01). Heart rate was lower during the first hour in WET vs. DRY, and at 30 min only in WET vs. WET+FAN (P &lt; 0.01). No differences in mean arterial pressure were found (P = 0.51). In conclusion, simply wearing a water‐soaked t‐shirt is an effective heat management strategy to mitigate thermal and cardiovascular strain and lower sweat losses in older people exposed to heat wave conditions. Conversely, the cooling benefits of a water‐soaked t‐shirt are eliminated when used in combination with a fan.Support or Funding InformationFunding: National Institutes of Health (R01GM068865) and Department of Defense – US Army (W81XWH‐15‐1‐0647)

Blunted Effects of Elevated Serum Osmolality on Whole‐body Heat Loss and Rectal Temperature in Middle‐aged‐to‐older Men Exercising in Dry Heat

We recently demonstrated that sweating‐induced hypohydration attenuated whole‐body heat loss (via reduced sweat evaporation) in young but not middle‐aged men during exercise‐heat stress. In that work, we reasoned that this divergent response may stem from an attenuated influence of intravascular osmolality (elevated during hypohydration) on heat dissipation in the middle‐aged. This hypothesis is supported by previous studies showing i) increased osmolality attenuates sweating in young adults and ii) fluid‐regulatory responses to osmotic stimuli are blunted with aging. However, the independent effect of intravascular osmolality on whole‐body heat loss and thermal strain in middle‐aged men during exercise has not been directly evaluated. On two separate occasions, six young (25 years [SD 4]) and eight middle‐aged‐to‐older (61 years) men underwent a 90‐min intravenous infusion of either 0.9% saline (200 [5] μmL·min−1·kg−1; ISO) or 3.0% saline (125 μmL·min−1·kg−1; HYP). Participants then performed 60 min of cycling at a fixed metabolic heat production of 250 W·m−2 in dry heat (40ºC, ~15% relative humidity). Serum osmolality and plasma volume responses were determined from venous blood samples procured at baseline (prior to infusion) and end‐exercise (60‐min). Heat production and whole‐body heat loss (evaporative + dry heat loss) were measured via indirect and direct calorimetry, respectively. Rectal temperature was monitored continuously. End‐exercise serum osmolality was elevated in HYP compared to ISO in the young (309 [4] vs 299 [3] mOsm·kg−1; p&lt;.001) and middle‐aged‐to‐older (312 [2] vs 300 [4] mOsm·kg−1; p&lt;.001) men and was similar between age‐groups (both p≥.07). In the young, the reduction in plasma volume from baseline at end‐exercise was greater in ISO relative to HYP (−8 [3] vs −4 [3]%; p=.014). By contrast, no differences in the plasma volume response were detected between ISO and HYP in the older group (−9 [4] vs −4 [6]%; p=.14). Changes in plasma volume were similar between age‐groups in each condition (both p≥.75). Whole‐body heat loss was attenuated in HYP compared to ISO in the young (233 [13] vs 251 [15] W·m−2; p=.012), whereas no effect of osmolality was observed in the middle‐aged‐to‐older men (225 [14] vs 227 [16] W·m−2; p=.74). Further, heat loss was attenuated in the middle‐aged‐to‐older vs young in ISO (p=.017) but was comparable between groups in HYP (p=.26). Similarly, a greater end‐exercise rectal temperature was noted in HYP vs ISO in the young (38.2 [0.3]°C vs 37.9 [0.3] °C; p=.037) but not the middle‐aged‐to‐older men (38.3 [0.3]°C vs 38.3 [0.3]°C; p=.88). The rectal temperature response was greater in the middle‐aged‐to‐older during ISO (p=.013) whereas no difference between age‐groups was observed in HYP (p=.59). Our findings indicate that whole‐body heat loss and rectal temperature responses to exercise in dry‐heat are not appreciably modified by increased serum osmolality in middle‐aged‐to‐older men. An age‐related reduction in osmotic sensitivity may therefore explain the blunted effect of hypohydration on heat loss previously observed in this population.Support or Funding InformationNatural Sciences and Engineering Research Council of Canada.

75 Burn Survivors Can Exercise for 30 Min, Even in the Heat, Without a Risk of Excessive Hyperthermia

Abstract Introduction Excision of burned skin and subsequent grafting removes sweat glands and thereby impairs thermoregulation. Consequently, rehabilitation and associated exercise may be accompanied by a greater risk of hyperthermia, depending on exercise duration, intensity and environmental temperature. Current physical activity guidelines recommend adults perform at least 150 min of moderate-intensity exercise per week, which is often divided into 30-min daily sessions. This project tested the hypothesis that burn survivors could exercise for 30 min without excessive elevations in core body temperature, regardless of the total body surface area (%TBSA) burned or environmental temperature. Methods Ten subjects cycled for 60 min at 1) a moderate intensity (97±8 watts) in a thermoneutral environment (24°C, MOD_NEU), 2) a moderate intensity (100±17 watts) in a hot environment (39°C, MOD_HOT), and 3) a low intensity (65±10 watts) in a hot environment (39°C, LOW_HOT). Burn injuries were simulated by covering 0%, 20%, 40%, or 60% of the individual’s TBSA with an absorbent material that prevented sweat evaporation. Changes in gastrointestinal temperature (ΔTcore) were analyzed at 15-min increments throughout exercise. Results For the MOD_NEU trial, there were no differences in ΔTcore between the %TBSA coverage bouts at any time point during exercise. For the MOD_HOT trial, there were no differences in ΔTcore at 15 and 30 min of exercise regardless of the %TBSA coverage, while ΔTcore was appreciably elevated (P&amp;lt; 0.05) at 45 and 60 min of exercise for 20%+ TBSA bouts. For the MILD_HOT trial, there were no differences in ΔTcore at any time point between %TBSA bouts, with the sole exception of 60% simulated burn having a slightly greater ΔTcore (0.3±0.34°C; P&amp;lt; 0.05) at 60 min of exercise relative to the 0% TBSA bout. Conclusions These data indicate that individuals with up to 60% of their TBSA burned could exercise at a moderate intensity for 30 min, even in hot environmental conditions, without excessive elevations in body core temperature. Applicability of Research to Practice Individuals with significant burn injuries can benefit from exercise, without the risk of excessive hyperthermia, for up to 30 min in the heat or at least 60 min in an air conditioned space. Funding: DOD W81XWH-15-1-0647

The Suitability of Porous Material to Simulate Evaporation in Human Sweating Mechanisms

This study aims to determine the suitable porous material that can simulate human sweat evaporation rate for preliminary thermal comfort assessment. The objective of the study was to identify the relationship of human sweat evaporation rate with porous material evaporation rate. Field experimental has been conducted to measure the evaporation rate of porous material such as red clay, white clay, plaster and human sweat. Then, the correlation analysis was conducted between porous material evaporation rate and human sweat evaporation rate. The collected data were analyzed by using SPSS 20 and Microsoft Excel 2016 tools. Pearson correlation were used as statistical analysis to find the relationship between both variable. The statistical significance level was set at P&lt; 0.01. Based on the findings, human sweat evaporation rate had a moderate correlation with red clay (r = 0.583) and white clay (r = 0.503) with statistically significant but very weak correlation with plaster (r = 0.020). The porous characteristics of red clay and white clay has the capillary effect which is almost like human skin by showing a good correlation between human sweat and porous material evaporation rate. As this is preliminary study, in future more research to be done to obtain higher correlation between porous material and the human body by modifying the material. To minimize heat stress, it would be a step forward in evaluating outdoor thermal comfort and raising awareness of society and government.

The influence of air humidity on human heat stress in a hot environment

This article aims to present the physical adaptation capabilities of a human, seen as a response to extreme hot and dry or hot and humid conditions. Adaptation capabilities are expressed as safe exposure time in two variants: at rest and during physical activity. The study shows the results of calculations of the variability over time of the core temperature and skin temperature as well as heat balance. Calculations were made according to Standard No. EN ISO 7933:2005 on the basis of assumed and actual meteorological data. The results of the calculations show that in these conditions a hot but dry environment enables a human (although to a limited extent) to stay and perform low physical activity, provided access to drinking water is ensured. In contrast, a hot but humid environment causes more serious problems, due to the inability to reduce skin temperature by evaporation of sweat from the skin surface.