No large effects on cognitive performance in high versus low solar green-flag WBGT conditions.

Excessive solar radiation negatively affects cognitive performance. Occupational guidelines typically combine environmental components into one value, such as wet-bulb globe temperature (WBGT). Here, we evaluated cognitive performance in two similar 28.6 °C WBGT-effective (WBGTeff) that were designed differently; using high or low levels of solar radiation. Eight soldiers were exposed to a virtual-reality environment in a climate chamber set to high (900 Wm-2) or low solar radiation conditions (300 Wm-2). Soldiers walked 3 x 30 min at 5 kmh-1. Cognitive performance was evaluated using a virtual-reality scenario and a computerised test battery. There was no statistically significant effect of condition on the cognitive tasks (p > 0.05). Associations were found between mean body temperature (Tb) and visual detection (P ≤ 0.01). Differences in solar radiation with similar WBGTeff (28.6 °C) do not cause large systematic differences in cognitive performance. Certain aspects of cognitive performance (i.e. response inhibition) seem to be partly associated with Tb rather than solar radiation.Practitioner summary: Cognitive performance was evaluated in two similar WBGT conditions that were designed differently; using high or low levels of solar radiation. Differences in solar radiation with similar WBGT do not cause systematic differences in cognitive performance. Certain aspects of cognition were partly associated with mean body temperature rather than solar radiation.

Sweat rate and sweat composition during heat acclimation.

The purpose of this study was to determine local sweat rate (LSR) and sweat composition during heat acclimation (HA). For ten consecutive days of HA, eight participants cycled in 33 °C and 65% relative humidity at an intensity such that a rectal temperature of 38.5 °C was reached within ~40 min, followed by a 60-min clamp of this rectal temperature (i.e., controlled hyperthermia). Four participants extended HA by a 28-day decay period and five consecutive days of heat re-acclimation (HRA) using controlled hyperthermia. Sweat from the upper arm and upper back was collected three times during each heat exposure session. LSR and sweat sodium, chloride, lactate, and potassium concentrations were determined. Relative to HA day 1, LSR was increased at the final day of HA (day 10) (arm: +58%, P < 0.001; back: +36%, P < 0.05). Concentrations of sodium, chloride, and lactate significantly (P < 0.05) decreased to ~60% at HA day 10 compared to day 1 on the arm and back. Potassium concentration did not significantly differ on HA day 10 compared to day 1 (arm: +11%, P > 0.05; back: +8%, P > 0.05). The induction patterns of the sudomotor adaptations were different. Whilst LSR increased from HA day 8 on the arm and from HA day 7 on the back, sodium and chloride conservation already occurred from HA day 3 on both skin sites. Lastly, the sweat lactate reduction occurred from HA day 6 on the arm and back. Initial evidence is provided that adaptations were partly conserved after decay (28 days) and that a 5-day HRA may be sufficient to restore HA adaptations. In conclusion, ten days of exercise-induced HA using controlled hyperthermia led to increases in LSR and concomitant reductions of sweat sodium, chloride, and lactate concentrations, whilst potassium concentrations remained relatively constant.

Integrated assessment of simultaneous threshold exceedance of heat, air pollution and airborne allergenic pollen across Europe.

BACKGROUND: Climate change is expected to elevate exposure to several environmental health risk factors, including extreme environmental temperatures, air pollution and airborne allergenic pollen. Given their interconnected effects on respiratory and cardiovascular diseases, it is crucial to evaluate these exposures simultaneously. Yet, comprehensive efforts to do so remain limited. This research aims to develop an approach using modelled data, in conjunction with health-based threshold values, to assess whether, where and when there is simultaneous threshold exceedance of heat, air pollution and airborne allergenic pollen in Europe. METHODS: Hourly exposure data for the three stressors were sourced from three models (air pollution: LOTOS-EUROS, pollen: Copernicus Atmosphere Monitoring Service, meteorological conditions: ECMWF) for 2021 and 2022. Thresholds for each stressor that indicate the boundary of acceptable limits were based on officially established tresholds or literature recommendations. The result is a 0.1°x0.1° resolution grid (approximately 10 km x 10 km) for each stressor, with each cell representing whether exposure met or exceeded the threshold. FINDINGS: Simultaneous threshold exceedance of air pollution and heat is occurring in various degrees throughout Europe. In the summer of 2022, the exceedances ranged from below 1% in large parts of Northern Europe to as much as 25% of the time in the Mediterranean area. An assessment of monthly threshold exceedance patterns shows a dynamic and changing co-exposure pattern across the year, which differs per region. INTERPRETATION: This work lays out a robust approach to assess simultaneous threshold exceedances of multiple environmental health risk stressors. This approach can guide policy makers in pinpointing high-risk areas particularly vulnerable to simultaneous threshold exceedances, and develop mitigation strategies for those areas. FUNDING: Internal funding from TNO.

Efficiency of three cooling methods for hyperthermic military personnel linked to water availability.

PURPOSE: Three feasible cooling methods for treatment of hyperthermic individuals in the military, that differed considerably in water volume needed (none to ~80 L), were evaluated. METHODS: Ten male soldiers were cooled following exercise-induced hyperthermia (rectal temperature (Tre) ∼39.5 °C) using ventilation by fanning (1.7 m s-1), ventilation by fanning (1.7 m s-1) while wearing a wet t-shirt (250 mL-27 °C water) and tarp assisted cooling with oscillations (80 L of 27.2 ± 0.5 °C water; TACO). RESULTS: Cooling rates were higher using TACO (0.116 ± 0.032 °C min-1) compared to ventilation (0.065 ± 0.011 °C min-1, P<0.001) and ventilation in combination with a wet t-shirt (0.074 ± 0.020 °C min-1, P=0.002). Time to cool (TTC) to Tre=38.2 °C for TACO was shorter (14 ± 4 min) compared to ventilation only (20 ± 5 min; P=0.018), but not to ventilation while wearing a wet t-shirt (18 ± 6 min; P=0.090). CONCLUSIONS: TACO may be an acceptable, efficient and feasible cooling method in case of exertional heat stroke. However, in case of limited water availability, transportat should be prioritized, and cooling of any form should be implemented while waiting for and during transport.

The effect of short and continuous absorbent patch application on local skin temperature underneath.

Objective. By attaching absorbent patches to the skin to collect sweat, an increase in local skin temperature (Tsk) underneath the patches seems unavoidable. Yet this effect has not been quantified. The present study investigates the effect of absorbent patch application on localTskunderneath.Approach. Ten healthy participants cycled for 60 min at an exercise intensity relative to their body surface area (40 W.m-2) in three environmental conditions (temperate: 25 °C 45% RH, hot-humid: 33 °C 65% RH and hot-dry: 40 °C 30% RH). The effect of short sweat sampling (i.e. from min 25-30 to min 55-60) onTskwas examined on the right scapula.Tskof the left scapula served as control. The effect of continuous sweat sampling (i.e. four consecutive 15 min periods) onTskwas examined on the right upper arm.Tskof the left upper arm served as control.Main results. Neither short nor continuous application of absorbent sweat patches affectedTskunderneath the patches in the hot-humid and hot-dry condition (P > 0.05). In the temperate condition, continuous application led to a significant increase inTskunderneath the patches during the first and second minute. This increase remained throughout the experiment (1.8 ± 0.6 °C;P < 0.001). Short application of sweat patches did not affect the localTskunderneath (P > 0.05) in the temperate condition.Significance. To avoid a significant increase in localTskunderneath sweat patches, continuous application should be prevented in, especially, a temperate condition. Timely removal of sweat patches should be taken into account during longer periods of collecting sweat in field or laboratories settings.

The effect of sweat sample storage condition on sweat content.

Due to time and logistical constraints sweat samples cannot always be analyzed immediately. The purpose of this study was to investigate the effect of storage temperature and duration on sweat electrolyte and metabolite concentrations. Twelve participants cycled for 60 min at 40 W.m-2 in 33°C and 65% RH. Using the absorbent patch technique, six sweat samples were collected from the posterior torso. Sweat from the six samples was mixed, divided again over six samples and placed in sealed vials. Sweat sodium, chloride, potassium, ammonia, lactate and urea concentrations in one sample were determined immediately. Two samples were stored at room temperature (~25°C, 42% RH) for 7 and 28 days respectively. The remaining samples were frozen at -20°C for 1 h, 7 or 28 days respectively before analysis. Sweat sodium, chloride, potassium and urea concentrations were not affected by storage temperature and duration. Sweat lactate decreased (-1.8 ± 1.8 mmol.L-1, P = 0.007) and ammonia concentrations increased (5.1 ± 3.9 mmol.L-1, P = 0.017) after storage for 28 days at 25°C only. The storage temperature and duration did not affect sodium, chloride, potassium and urea concentrations. However, sweat samples should not be stored for longer than 7 days at 25°C to obtain reliable sweat lactate and ammonia concentrations. When samples are frozen at -20°C, the storage duration could be extended to 28 days for these components.

Sweat rate and sweat composition following active or passive heat re-acclimation: A pilot study.

The purpose of this study was to investigate local sweat rate (LSR) and sweat composition before and after active or passive heat re-acclimation (HRA). Fifteen participants completed four standardized heat stress tests (HST): before and after ten days of controlled hyperthermia (CH) heat acclimation (HA), and before and after five days of HRA. Each HST consisted of 35 min of cycling at 1.5W·kg-1 body mass (33°C and 65% relative humidity), followed by a graded exercise test. For HRA, participants were re-exposed to either CH (CH-CH, n = 6), hot water immersion (water temperature ~40°C for 40 min; CH-HWI, n = 5) or control (CH-CON, n = 4). LSR, sweat sodium, chloride, lactate and potassium concentrations were determined on the arm and back. LSR increased following HA (arm +18%; back +41%, P ≤  0.03) and HRA (CH-CH: arm +31%; back +45%; CH-HWI: arm +65%; back +49%; CH-CON arm +11%; back +11%, P ≤ 0.021). Sweat sodium, chloride and lactate decreased following HA (arm 25-34; back 21-27%, P < 0.001) and HRA (CH-CH: arm 26-54%; back 20-43%; CH-HWI: arm 9-49%; back 13-29%; CH-CON: arm 1-3%, back 2-5%, P < 0.001). LSR increases on both skin sites were larger in CH-CH and CH-HWI than CH-CON (P ≤ 0.010), but CH-CH and CH-HWI were not different (P ≥ 0.148). Sweat sodium and chloride conservation was larger in CH-CH than CH-HWI and CH-CON on the arm and back, whilst CH-HWI and CH-CON were not different (P ≥ 0.265). These results suggest that active HRA leads to similar increases in LSR, but more conservation of sweat sodium and chloride than passive HRA. Abbreviations: ANOVA: Analysis of variance; ATP: Adenosine triphosphate; BSA (m2): Body surface area; CH: Controlled hyperthermia; CH-CH: Heat re-acclimation by controlled hyperthermia; CH-CON: Control group (no heat re-acclimation); CH-HWI: Heat re-acclimation by hot water immersion; CV (%): Coefficient of variation; dt (min): Duration of a stimulus; F: Female; GEE: Generalized estimating equations; HA: Heat acclimation; HRA : Heat re-acclimation; HST: Heat stress test; LSR (mg·cm-2·min-1) : Local sweat rate; LOD (mmol·L-1): Limit of detection; M: Male; m x (mg): Mass of x; RH (%): Relative humidity; RT: Recreationally trained; SA (cm2): Surface area; t (min): Time; T: Trained; Tsk (°C): Skin temperature; Tre (°C): Rectal temperature; USG : Urine specific gravity; VO2peak (mL·kg-1·min-1): Peak oxygen uptake; WBSL (L): Whole-body sweat loss; WBSR (L·h-1): Whole-body sweat rate.

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

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.