Temperature最新文献

Occupational heat stress and hydration recommendations aim to prevent core temperatures from exceeding 38.0°C and dehydration in unacclimated workers. These guidelines do not consider individual differences in body composition. We hypothesized that core temperatures would be higher in adults with obesity during simulated occupational heat stress compared to adults without obesity when adhering to the current heat stress recommendations. Twenty-two unacclimated adults with [n = 10; 6 women; body fat % (37 ± 5%)] or without [n = 12; 7 women; body fat % (22 ± 6%)] obesity completed a 4-hour (half workday) exposure to a fixed wet-bulb globe temperature (WBGT) and work intensity. Work-rest ratio was 30 minutes of walking and 30 minutes of seated rest each hour. Work intensity [i.e. metabolic heat production (H_prod)] was prescribed as a function of WBGT (27.6 ± 0.5°C) and normalized to body mass (5.0 ± 0.4 W•kg^-1). All subjects were provided 237 mL of Gatorade every 15 min and drank ad libitum. Peak core temperature was higher in the obese (38.4 ± 0.3°C) compared to the non-obese (37.7 ± 0.4°C; p < 0.01) group. Mean core temperature was higher in the obese (37.9 ± 0.2°C) compared to the non-obese (37.4 ± 0.3°C; p < 0.01) group. Ad libitum drinking was not different between the obese (1.8 ± 0.8 L) and non-obese (1.8 ± 0.7 L; p = 0.94) groups. Percent change in body mass did not differ between the obese (-0.6 ± 0.6%) and non-obese (-0.4 ± 0.9%; p = 0.63) groups. Adherence to the heat stress recommendations during a 4-hour exposure resulted in elevated core temperature responses in adults with obesity compared to adults without obesity.

Exertional heat stroke (EHS) and Malignant Hyperthermia (MH) are potentially life-threatening conditions with overlapping clinical characteristics. In this study, we compared the thermoregulatory response to exercise under increased environmental temperatures in individuals with a history of EHS (n = 15) or MH (n = 14) to healthy controls (n = 15). Groups were age- and sex-matched (31 male, 13 female, 42 ± 10 years). A 60-min exercise test was performed on a cycle ergometer at an ambient temperature of 30.3 ± 0.6°C and a relative humidity of 33.5 ± 4.7%. A stepwise incremental exercise protocol was used to reach a metabolic heat production of 6, 8 and 9 W/kg body mass. Gastrointestinal (T_gi) and skin (T_sk) temperature were monitored continuously, and partitional calorimetry was used to calculate dry (H_dry) and respiratory heat loss (H_resp). Whole-body sweat rate (WBSR) was assessed by measuring body mass. Exercise-induced increases in T_gi (1.4 ± 0.5°C) and T_sk (1.9 ± 0.8°C) were observed, but the magnitude of increase across groups was comparable (p_time*group = 0.80 and p = 0.57, respectively). H_dry was significantly lower in EHS participants (54 ± 4 W) compared to controls (65 ± 11 W, p = 0.023). No differences were observed in H_resp and WBSR. Our results suggest that individuals with MH or a history of EHS do not have an altered thermoregulatory response to exercise in the heat in a controlled setting. Further research is required to determine to what extent the complex accumulation of risk factors contributes to EHS susceptibility.

This study assessed the effects of hydration and hydration/cooling on various psycho-physiological and cognitive responses in staff during a simulated burns surgery. Twelve participants completed three 2.5-h trials in the heat (33.6°C, 36.4% RH) whilst walking on a treadmill at a rating of perceived exertion of 12 on the Borg scale. Trials consisted of: i) ingestion of 37°C water (HYD); ii) ingestion of 5°C water (COLD); and iii) a no cooling/hydration control (CON). Water ingestion (0.9% of body-mass) was based on fluid loss calculated during a previous 2.5-h burn surgery. Results demonstrated that while treadmill distance was similar between trials (p > 0.05), cold water ingestion resulted in improved manual dexterity (p = 0.03), better thermal comfort (p < 0.01) and lower core and skin temperatures (p < 0.01), compared to CON. Skin temperature was also lower in COLD vs HYD (p < 0.01). Moderate to large effect sizes (ES, g = 0.38-0.77) were observed in favor of COLD versus CON and/or HYD for manual dexterity, counting span, grammatical reasoning and several perceived workload subsets at various time points, however associated 95% confidence intervals were wide and crossed zero, suggesting statistical uncertainty. Similarly, moderate to large ES (g = 0.45-0.77) favored HYD over CON for counting span (120 min) and various perceived workload outcomes, though again confidence intervals suggest that these effects were not statistically conclusive. No differences were observed between trials for sweat loss, thermal sensation, or heart-rate (p > 0.05). Overall, cold water ingestion resulted in benefit to numerous variables assessed here. Small boluses of cold water ingestion are recommended during hot burn surgeries.

To examine the suitability of common heat stress indicators, including wet-bulb globe temperature (WBGT), universal thermal climate index (UTCI), heat index (HI), and humidex, to (1) determine uncompensable heat stress and (2) the capability of the indicators to directionally match physiological and perceptual strain in varying thermal environments. Ten healthy, active males (2+/-7 y, 179+/-11 cm, 77.4+/-9.3 kg, 51.9+/-5.3 mL/kg/min) performed two randomized, crossover exercise trials (60-min cycling ~55% ṼO_2peak) in hot-dry (HD, 39.1°C, 33% RH) and warm-humid (WH, 34.5°C, 59% RH) conditions. Metabolic heat production (H_prod), evaporation required for heat balance (E_req), and maximum evaporative rate (E_max) were calculated. Estimated compensability was determined using E_req to E_max ratio. Physiological and perceptual measures occurredthroughout. There were no differences in WBGT (p = .83, d = .59), HI (p = .65, d = 1.9), and humidex (p = .73, d = 1.10) between HD and WH. UTCI in HD was significantly greater than in WH (p $<$ .001, d = 1.19). There were no differences inphysiological measures (p > .34) between HD and WH, indicating different environments with matched WBGT, HI, and humidex matched thermal, cardiovascular, and perceptual strain, but not UTCI. H_prod (p $=$ 0.04, $\eta$ _p ² = .38), E_req (p $<$ 0.001, $\eta$ _p ² = .75), and E_max (p $<$ 0.001, $\eta$ _p ² = .94) in HD were significantly greater than WH. E_req/E_max in both HD and WH indicated uncompensable heat stress. HI and humidex identified compensability, physiological, and perceptual strain adequately under HD and WH conditions.

We determined whether the time of day when students exercise in a tropical climate and the environmental conditions in which they attend theory classes (air conditioning vs. tropical climate) have an impact on athletic performance and physiological, psychological and perceptual parameters. Twenty-nine students took part in four experimental sessions consisting of outdoor exercises and theory classes from 7am-1pm, according to a randomized and counterbalanced order. Cognitive and exercise performances, perceptual responses, core temperature and heart rate were assessed in the air-conditioned and tropical climate conditions. Cognitive performance was lower in the tropical vs air-conditioned environment, including lower concentration, higher inattention and lower processing speed during the theory classes. During theory classes in a tropical climate, heart rate and core temperature were higher. Average concentration scores (i.e. mean: 107.0 vs. 234.0), and inattention (i.e. mean: 96.0 vs. 32.5) at end-morning (i.e. 11am-1pm) were negatively affected by tropical climate compared to air conditioning when it was preceded by physical exercise at 9am-11am, but not at 7am-9am. There was a momentary sensation of fatigue, with higher scores at 11am-1 pm than at 7am-9am, in both conditions. Core temperatures were higher during exercise performance at 9am-11 am (38.6°C ±4.9°C) than at 7am-9 am (38.3°C ±5.2°C), but there was no difference for exercise performance, heart rate. Climate conditions must be taken into account for (i) cognitive performance and physiological parameters in tropical climate, and (ii) the time of day for exercise when theory classes take place in late morning and young student-athletes must perform cognitively well.

Standby divers must be fully dressed in the appropriate ensemble during military and commercial diving operations. These garments are often fully encapsulating and may result in heat stress and hypohydration when worn in warm environments. We examined the physiologic responses to heat in subjects wearing a Viking HD drysuit during 1 hour of exposure to dry-bulb temperatures of 33°C, 36°C, 39°C, and 42°C. Euhydrated subjects donned a heavy rubber drysuit and chemical protective gloves over a lightweight base layer. The drysuit was appropriate for contaminated water diving with integrated boots and neck dam. Heart rate (HR), core (Tc), and skin (Tsk) temperatures were monitored. Eight subjects (4 males) aged 27 ± 5 y completed all study conditions. HR and Tc increased over time (p < 0.001). Seated HR peaked at 138 ± 17 bpm in the 42°C and at 114 ± 13 bpm in the 39°C condition. Peak Tc was 37.0 ± 0.2, 37.1 ± 0.2, 37.4 ± 0.3, and 37.9 ± 0.5°C in the 33°C, 36°C, 39°C, and 42°C conditions, respectively, and differed between all conditions (p < 0.001) except 33°C and 36°C (p = 0.60). Sweat rates progressively increased in the warmer conditions and corresponded with a -0.20 ± 0.10, -0.40 ± 0.19, -0.69 ± 0.46, and -0.99 ± 0.55% change in body mass. Even in the absence of radiant heating, significant hypohydration and heat stress occurs in standby divers after 30 min of exposure to 42°C and after 40 min at 39°C. Awareness of the conditions and rotation of standby divers could increase mission safety in these hot environments.

Despite increased female workforce engagement, research into physiological responses to thermally challenging environments has primarily focused on males. This study examined the combined impact of exercise-induced elevated core temperature and progressive dehydration on cognitive performance in naturally menstruating females. It was hypothesized that progressive increases in dehydration, heat and associated physiological responses would detrimentally affect cognitive performance. Twelve recreationally trained, naturally menstruating participants completed two experimental conditions - dehydrated (DEHY), and hydrated (HYD) - during the mid-luteal phase of their menstrual cycle. Participants cycled in a controlled environment (40°C, 20% humidity) for three 45-minute bouts at progressively reducing work intensity. Cognitive performance was assessed using the Parametric Go/No-Go (PGNG), Corsi Block Tapping (CBT), and Classic Stroop tasks, selected to represent the three key domains of executive function - cognitive inhibition, working memory, and cognitive flexibility. In DEHY, no fluid was permitted; in HYD, fluid was administered based on body mass loss. Body mass loss and serum osmolality was significantly higher in DEHY (-3.57[0.99] kg; 299[6] mOsm·kg^-1), compared to HYD (-0.48[0.30] kg; 283[5] mOsm·kg^-1) (p < .05). Contrary to the hypothesis, cognitive performance remained largely unaffected by exercise-induced dehydration and thermal strain. Only PGNG reaction time was significantly affected, with slower responses in the HYD condition. Despite physiological markers indicating significant dehydration, cognitive performance appeared to be largely preserved against the stressors of prolonged exercise and heat. Emphasizing the resilience of cognitive performance under these conditions strengthens understanding of sex-specific responses to environmental and physiological stress.