Sweat Loss Research Articles

Evaluating a novel portable semiconductor liquid cooling garment for reducing heat stress of healthcare workers in a hot-humid environment

Limited research focused on exploring personal cooling garments (PCGs) that offer excellent portability, along with a substantial, long-lasting, and consistent cooling effect for healthcare workers exposed to extreme heat while combating the COVID-19 pandemic. To address this gap, a novel, energy-efficient, and portable semiconductor liquid cooling garment (SLCG) was introduced, which incorporates a semiconductor-powered cold source and a cooling vest crafted from a semi-transparent thermoplastic polyurethane (TPU) film that offers extensive body coverage. Its practical cooling efficacy was assessed through a human trial involving ten male participants engaging in two protocols under a hot-humid environment (i.e., 30 ± 0.5 °C, RH = 80 ± 5 %). These protocols included both low-intensity (Prot.1) and moderate-intensity (Prot.2) exercises, mimicking the physical demands faced by healthcare workers. SLCG significantly reduced the mean, torso and local skin temperatures during both Prot.1 and Prot.2 (p < 0.05), also with a notable reduction in heart rate and sweat loss during Prot.1 (p < 0.05). Rating of perceived exertion as well as thermal sensations, wetness sensations and comfort sensations in the whole-body and local-body (i.e., head & neck, trunk, arms and legs) were all remarkably improved using SLCG during Prot.1 (p < 0.05). These perceptual sensations in SLCG were only improved in the whole body during the resting stage, and in the trunk region during Prot.2 (p < 0.05). Furthermore, participants felt no significant added weight or movement restrictions with SLCG in either protocol.

Effects of Cannabidiol Ingestion on Thermoregulatory and Inflammatory Responses to Treadmill Exercise in the Heat in Recreationally Active Males.

Exertional heat stress can induce systemic endotoxin exposure and a pro-inflammatory cascade, likely impairing thermoregulation. Cannabidiol (CBD) is protective in pre-clinical models of tissue ischaemia and inflammation. Therefore, this study examined the effects of CBD ingestion on exercise-induced thermoregulatory and inflammatory responses. In a randomised, double-blinded study, thirteen active males (age 25 ± 5 y; peak oxygen uptake [V̇O2peak] 50.4 ± 3.2 mL/kg/min) ingested 298 mg CBD or placebo 105 minutes before 1 h treadmill exercise (60-65% V̇O2peak) in 32 °C and 50% relative humidity. Core temperature, skin temperature, heart rate, subjective outcomes and sweat loss were assessed during/after exercise. Plasma osmolality, plasma volume changes and plasma markers of intestinal damage (I-FABP), monocyte activation (CD14) and inflammatory cytokine responses (IL-6, IL-8 and TNF-α) were assessed at baseline, pre-exercise, 20- and 90-min post-exercise. Core temperature (∆ 1.69 ± 0.48 °C [CBD] and 1.79 ± 0.53 °C [Placebo]) and I-FABP increased during exercise, with no differences between conditions (p > 0.050). Mean (95% CI) CD14 was 1776 (463 to 3090) pg/mL greater 90 min post-exercise in placebo (p = 0.049). Median (interquartile range) peak IL-6 concentration was -0.8 (-1.1, -0.3) pg/mL less in CBD (p = 0.050), whilst the between-conditions difference in IL-6 area under curve was -113 (-172, 27) pg/mL·270 min (p = 0.054). CBD did not affect thermoregulation during exertional heat stress but appeared to elicit minor immunosuppressive effects, reducing CD14 and IL-6 responses, warranting investigation in humans under more severe heat strain and other pro-inflammatory scenarios.

Kidney effects of triple CFTR modulator therapy in people with cystic fibrosis.

Elexacaftor/tezacaftor/ivacaftor (ETI) is a new cystic fibrosis transmembrane conductance regulator (CFTR) modulator that has transformed the respiratory prognosis of people with cystic fibrosis (pwCF). However, its impact on other organs such as the kidneys, where CFTR is expressed, remains unclear. Since pwCF are risk of both kidney disease and urolithiasis, we aimed to study the potential effects of ETI on renal function, volume status, and risk factors for urolithiasis. This prospective, observational, single-center, before-after cohort study, involved adult pwCF eligible for ETI. The changes in plasma and urinary profiles were assessed by comparing renal function (using 2021 CKD-EPIcreatinine and 2021 CKD-EPIcreatinine-cystatin C formulas), volume status (using aldosterone/renin ratio and blood pressure), and risk factors for urolithiasis, at the time of ETI introduction (M0) and 7 months after (M7). Nineteen pwCF were included. No significant change in renal function was observed between M0 and M7 (2021 CKD-EPIcreatinine: 105.5ml/min/1.73 m² at M0 vs. 103.3ml/min/1.73 m² at M7; P=.17). There was a significant reduction in aldosterone level (370.3pmol/l at M0 vs. 232.4pmol/l at M7; P=.02) and aldosterone/renin ratio (33.6 at M0 vs. 21.8 at M7; P=.03). Among the risk factors for urolithiasis, a significant reduction in magnesuria level was found (4.6mmol/d at M0 vs. 3.8mmol/d at M7; P=.01). These findings suggest that ETI seem to have no short-term impact on the renal function of adult pwCF and appears to correct secondary hyperaldosteronism due to excessive sweat losses. Further investigations are needed to determine the potential impact of decreased magnesuria observed under ETI therapy on the risk of urolithiasis.

(Keynote) Soft Microfluidic Analysis Systems for the Skin

Recent advances in materials science, chemical engineering and mechanics design establish the foundations for high performance classes of microfluidic lab-on-a-chip technologies that have physical properties matched those of the human skin. The resulting devices can integrate with the surface of the skin in a water-tight yet physically imperceptible fashion, to provide real-time measurements of sweat rate and total sweat loss, along with continuous, clinical-quality biochemical information on physiological status using a combination of colorimetric and electrochemical techniques. This talk summarizes the key ideas and presents application examples in sports performance, worker safety, medical diagnostics and nutritional monitoring.

Thermal and Cardiovascular Responses during Exertional Heat Stress after Diphenhydramine Use: A Randomized Crossover Trial.

Despite sparse systematic evidence, current exercise heat safety recommendations suggest that antihistamines blunt sweating and increase the risk for heat-related injury during exertional heat stress. The primary purpose of the present study was to examine whether diphenhydramine hydrochloride (DPH), a first-generation antihistamine, effects the sweating, core temperature, and heart rate response during exertional heat stress using a double-blind randomized crossover design. On two occasions separated by >48 h, 20 healthy adults (10 females, 23 ± 3 y, BSA: 1.9 ± 0.2 m2, BMI: 23.7 ± 2.2 kg·m-2) orally consumed either 50 mg of DPH or placebo (PLA), and then rested for 2 h in a climate-controlled room maintained at 30 °C and 35%RH (Heat Index of ~29 °C), followed by a 60-minute fixed-heat production treadmill walk (6.3 ± 1.0 W·kg-1). Whole-body sweat loss (WBSL), local sweat rate (LSR), rectal temperature (Trec), and heart rate (HR) were measured. WBSL was not different between conditions (PLA: 406 ± 78 g; DPH: 396 ± 75 g, P = 0.26, treatment effect: -10 g 95%CI [-28, 8]). No differences were observed for the onset for sweating (PLA: 13.5 ± 2.4 min; DPH: 13.3 ± 2.7 mins, P = 0.79), and steady-state LSR (PLA: 0.83 ± 0.26 mg·cm-2·min-1; DPH: 0.82 ± 0.27 mg·cm-2·min-1, P = 0.99). No difference in baseline Trec was observed (PLA: 37.09 ± 0.35 °C, DPH: 37.13 ± 0.33 °C, P = 0.68), and the 60-min ΔTrec was not different (P = 0.99) between PLA (0.83 ± 0.29 °C) and DPH (0.81 ± 0.30 °C). HR was similar at baseline (PLA: 86 ± 13 BPM, DPH: 84 ± 11 BPM, P = 0.30) and end-exercise (PLA: 134 ± 28 BPM, DPH: 132 ± 26BPM, P = 0.90). 50 mg of DPH does not modify the sweating, core temperature, and heart rate response during exertional heat stress in young healthy adults.

Physical and mental demand during direct anterior total hip arthroplasty: Comparison of robotic-assisted and conventional techniques

IntroductionThe adoption of new techniques, such as the direct anterior (DA) approach, and technologies, such as robotic assistance, in total hip arthroplasty (THA) has the potential to alleviate the intraoperative physical and mental demand that surgeons experience. Therefore, the aim of this study is to compare the physical and mental demand of surgeons performing conventional DA THA with fluoroscopy and robotic-assisted DA THA without fluoroscopy. MethodsTwo orthopaedic surgeons completed bilateral DA THA's on six cadaveric specimens. To assess physical demand, heart rates (HR), respirations, HR variability (stress), calories burned, and sweat loss were recorded using smartwatches. Surgeons completed a modified SURG-TLX questionnaire to assess physical and mental demand. Data were pooled together and two-sample t-tests were performed. ResultsPhysical and mental demand metrics such as maximum HR, maximum stress, mean caloric expenditure and sweat loss were lower in robotic-assisted DA THA without fluoroscopy. Robotic-assisted THA was associated with a decreased percentage change for both the overall procedure and all surgical steps. Robotic-assisted THA also resulted in a significant difference in percentage change for maximum HR during acetabular reaming.Via questionnaire results, surgeons reported that robotic-assisted DA THA was significantly less physically and mentally demanding compared to conventional DA THA for the overall procedure and acetabular reaming. DiscussionIt is important to understand how robotic-assisted THA impacts the health of the surgeons using them. Robotic-assisted DA THA without fluoroscopy resulted in less physical and mental demand for orthopaedic surgeons for the overall procedure and individual surgical steps.

A crosstalk-free dual-mode sweat sensing system for naked-eye sweat loss quantification via changes in structural reflectance

A crosstalk-free dual-mode sweat sensing system for naked-eye sweat loss quantification via changes in structural reflectance

Autonomic impairment in primary lateral sclerosis.

Prior studies reported evidence of autonomic involvement in motor neuron disease and suggested more severe dysfunction in upper motor neuron predominant syndromes. Hence, we sought to characterize autonomic impairment in primary lateral sclerosis. Neurological evaluations, thermoregulatory sweat tests, and autonomic reflex screens were analyzed retrospectively in 34 primary lateral sclerosis patients (28 definite and 6 probable). Patients with other potential causes of autonomic failure and patients with autonomic testing results compromised by artifact were excluded. A total of 17 patients reported autonomic symptoms. Orthostatic lightheadedness was most frequent (8 patients), followed by bladder (7), bowel (5), and erectile dysfunction (3). The autonomic reflex screens of 33 patients were reviewed; 20 patients had abnormal studies. The thermoregulatory sweat tests of 19 patients were reviewed; 11 patients had abnormal studies. Composite Autonomic Severity Score was calculated for 33 patients and found abnormal in 20/33 patients (60.6%): 15/20 patients (75%) had mild impairment, and 5/20 patients (25%) had moderate impairment. The frequencies of testing abnormalities were: sudomotor 18/20 (90%), cardiovagal 9/20 (45%), and adrenergic 6/20 (30%). Sweat loss pattern analysis showed global, regional, and mixed patterns to be more common than length-dependent and distal patterns. We found evidence of frequent autonomic dysfunction in primary lateral sclerosis, which is generally of modest severity akin to prior reports for amyotrophic lateral sclerosis, but more commonly in a pattern consistent with preganglionic/ganglionic localization. This suggests that primary lateral sclerosis, as with amyotrophic lateral sclerosis, is a multisystem disease that affects the autonomic nervous system.

Thermal and cardiovascular heat adaptations in active adolescents following summer

ABSTRACT This study aimed to investigate seasonal heat acclimatization in active adolescents following summer. Fifteen (5 females) active adolescents (14.6 ± 1.0 y) completed a 45-min heat response test (HRT) walking at 60% V ˙ O2peak in 40°C and 30% relative humidity before and after summer (i.e. November 2022 and March 2023). During the HRT, gastro-intestinal temperature (Tgi), skin temperature (Tsk), heart rate, local sweat rate (LSR) and whole-body sweat loss (WBSL) were recorded. Carbon monoxide rebreathing and dual-energy X-ray absorptiometry scans determined resting hematological measures and body composition. Participants completed physical activity (PA) diaries and wore an accelerometer for two one-week periods (pre- and post-summer). Daytime wet-bulb globe temperature (WBGT) was calculated for each summer day. Data are presented as posterior mean and 90% credible intervals. Participants reported 7 ± 4 h·wk−1 of outdoor PA, and daytime WBGT was 21.2 ± 4.6°C. Following summer, resting Tgi and heart rate were reduced by 0.2°C [−0.3, −0.1; probability of direction = 99%] and 7 beats·min−1 [−10, −3; 100%], respectively. During the HRT, there was an earlier onset of sweating (−0.2°C [−0.3, −0.0; 98%]), an attenuated rise of Tgi (0.2°C [−0.5, 0.0; 92%]) and mean Tsk changed by −0.2°C [−0.5, 0.1; 86%]. There was minimal evidence for heat adaptations in LSR or WBSL, hematological parameters or perceptual measures. This is the first study to demonstrate seasonal heat adaptations in active adolescents. Reductions in resting Tgi and exercising Tsk and a lower Tgi at the onset of sweating were associated with a smaller rise in Tgi during the HRT following summer.

Cold-water foot immersion and physiological strain of adults with coronary artery disease during hot and humid heat exposure

Introduction: Heat extremes are associated with a greater risk of adverse cardiovascular outcomes, especially among adults with coronary artery disease. While air-conditioning provides exceptional protection during heat extremes, it is neither sustainable nor widely accessible. Cold-water foot immersion reduces physiological heat strain in healthy young adults but its effect in more vulnerable populations remains unknown. Objective and hypotheses: This study aims to identify the effect of cold-water foot immersion on markers of physiological heat strain in adults with coronary artery disease. We hypothesized that cold-water foot immersion would reduce physiological heat strain when used on its own and that this effect would be greater when combined with an electric fan. Methods: 17 adults living with stable coronary artery disease (2 females/15 males; 67±8 years) were exposed to a 38°C, 60% relative humidity environment for 3 hours on three separate, randomized occasions: i) no cooling (control; CON); ii) cold-water foot immersion (20 min of immersion each 30 min, ~30 cm in water kept at ~18°C; FI); iii) cold-water foot immersion and fan use (FI+FAN). Rectal and skin temperatures, heart rate (5-lead ECG), and whole-body sweat loss (change in nude weight) were measured. Results: The increase in rectal temperature did not differ between conditions (CON: 0.40±0.24°C, FI: 0.41±0.29°C, and FI+FAN: 0.36±0.22°C; p≥0.49). The increase in skin temperature was reduced with FI and FI+FAN compared to CON (CON: 4.9±0.8°C, FI: 4.1±1.2°C, and FI+FAN: 4.3±0.8°C; p≤0.01), with no difference between FI and FI+FAN (p=0.15). Similarly, the increase in heart rate was reduced with FI and FI+FAN compared to CON (CON: 8±6 bpm, FI: 4±6 bpm, and FI+FAN: 3±6 bpm; p≤0.01), with no difference between FI and FI+FAN (p=0.45). Sweat loss was also reduced by FI and FI+FAN compared with CON (CON: 823±114 g, FI: 544±174 g, and FI+FAN: 671±255 g; p≤0.03), with sweat loss during FI sweat loss being lower than during FI+FAN (p=0.03). Conclusion: The results show that cold-water foot immersion, used alone or in combination with an electric fan, reduces the increase in heart rate and whole-body sweat loss of adults living with coronary artery disease exposed to a hot and humid environment for 3 hours. This could be linked to the lower increase in skin temperature with foot immersion. National Health and Medical Research Council of Australia (APP1147789). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

ACUTE INTERMITTENT HEAT EXPOSURE WITH MORE FREQUENT AND SHORTER COOLING BREAKS ENHANCES PERFORMANCE AND ELICITS COMPARABLE PHYSIOLOGICAL RESPONSES TO CONTINUOUS HEAT EXPOSURE

INTRODUCTION &amp; AIMS Heat acclimation (HA) is critical to mitigate the adverse effects of heat on exercise performance. While these methods yield physiological adaptations to heat, it also results in greater internal training load. This can potentially compromise training quality and lead to overreaching. Therefore, there is a need for HA protocols that address situations where training quality is crucial, yet the heat stimulus is necessary. The aim of this study was to investigate the influence of shorter, more frequent rest breaks with per-cooling (PerC) as an alternative HA session on physiological, perceptual, and self-paced maximal cycling performance, compared to continuous heat exposure. METHODS Thirteen participants completed one continuous and three intermittent heat exposure (IHE) maximal self-paced cycling protocols matched for total exercise and rest duration, in a random order in heat (36°C, 80% relative humidity): 1 x 60-min exercise (CON), 3 x 20-min exercise with 7.5-min rest between sets (IHE-20), 4 x 15-min exercise with 5-min rest between sets (IHE-15), 6 x 10-min exercise with 3-min rest between sets (IHE-10). Mixed-method PerC (crushed-ice ingestion and cooling vest) was applied during rest periods of all IHE protocols. RESULTS Total distance completed was greater in IHE-10, IHE-15, and IHE-20 compared to CON (+11%, +9%, and +8%, respectively), with no difference observed between IHE protocols. Total time spent above 38.5°C core temperature (Tc) was longer in CON compared to IHE-15 and IHE-20 (+62% and +78%, respectively), but similar to IHE-10 (+5%). Furthermore, a longer time above 38.5°C Tc occurred in IHE-10 versus IHE-15 and IHE-20 (+54% and +69%, respectively). Sweat loss did not differ between conditions. CONCLUSION Intermittent heat exposure with PerC may be a viable alternative HA protocol in situations where training quality takes precedence over thermal stimulus, or when both factors hold equal priority.

Does diphenhydramine exert a sex-dependent effect on sudomotor responses during exertional heat stress?

Introduction: The first-generation H1 antihistamine diphenhydramine hydrochloride (DPH) is a potent antimuscarinic agent which may compromise sweat output during heat stress. DPH consumption prior to exertional heat stress could further suppress the sweating response in females due to their lower postjunctional cholinergic sensitivity of the sweat glands relative to males. Objective and Hypothesis: The purpose of the present study was to test the hypothesis that DPH would reduce sweating to a greater extent in females relative to males due to differences in cholinergic sensitivity at the sweat gland. Methods: Equal groups (10 per group) of males (24±3 y; 82.6±10.1 kg; 182±5 cm) and females (22±3 y, 67.7±7.8 kg, 171±6 cm) completed two experimental trials presented in a randomized double-blind fashion. Upon arrival to lab, participants consumed either i) a placebo (PLA) pill or ii) 50 mg DPH and then rested in a room maintained at ~29.5°C &amp; 35% RH for 2 hours before conducting a 60-minute treadmill march at a fixed rate of heat production relative to body surface area (~245 W/m2). Rectal temperature (Trec), local sweat rate of the forearm (LSR), and whole body sweat loss (WBSL) were measured. Sex-segregated analysis was conducted for each outcome variable as the difference between PLA and DPH. Results: Baseline Trec did not differ within sex between PLA and DPH (males: -0.10±0.26°C; females: -0.05±0.33°C, P=0.70), however a higher absolute baseline Trec was observed in females compared to males (P=0.006). In comparison to PLA, DPH did not exert a sex-dependent effect on ΔTrec following 60-min of exercise (males: 0.04±0.11°C; females: 0.02±0.37°C, P=0.90). No sex-dependent effect on the onset of sweating was observed between DPH and PLA (males: -0.4±2.6 min; females: 0.6±2.4 min, P=0.34). DPH did not exert a sex-dependent effect on LSR at steady-state (males: 0.03±0.25 mg/cm2/min; females: -0.01±0.21 mg/cm2/min, P=0.71). Lastly, no sex-dependent effect on WBSL was observed between PLA and DPH (males: 14±34 g; females: 6±43 g, P=0.98). Conclusion: Current evidence suggests that sex does not independently modulate the sweating response during exertional heat stress following the consumption of 50 mg of DPH. This research is supported by Dr. Ravanelli’s Research Seed Grant from the Centre for Research in Occupational Safety &amp; Health, and Dr. Ravanelli’s Natural Sciences and Engineering Research Council of Canada Discovery Grant (PIN#2022-05096). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Does acute heat stress alter lactation performance in postpartum mothers?

Introduction: Heat stress has been shown to acutely decrease lactation performance in various mammalian species, however whether a similar effect is present in humans remains largely unexplored. Objective and hypothesis: The objective of the present study was to determine whether an acute whole-body heat stress reduces lactation performance in postpartum mothers in the proceeding 24 h. Methods: To date, 9 postpartum mothers (32±4 y; 1.6 ±0.1 m; 67±13 kg; 8±3 months postpartum) have participated in the study. During the 24 h period before and after the acute passive heat stress, participants were asked to record their voluntary fluid intake and their milk production defined as the volume of expressed milk and/or breastfeeding volume based on the baby’s weight before and immediately after nursing, accounting for evaporative water losses. The passive heat stress protocol involved participants laying supine while donning a tube-lined garment continuously perfused with 49°C water for 60 minutes. Rectal temperature and heart rate were measured during the passive heat stress intervention to confirm thermal strain, and whole-body sweat losses were calculated as the net difference in body mass following passive heat stress. Results: The 60-minute passive heat stress protocol increased rectal temperature by 0.4±0.3°C, increased heart rate (17±12 BPM), and resulted in a whole-body sweat loss of 278±201 g. The frequency of lactation was similar during the 24 h before (5.4±1.6 times) and 24 h after (5.1±1.1 times, P=0.20) acute passive heat stress. The total volume of human milk production in the 24 h prior to heat stress was not different to the 24 h following heat stress (pre: 327±123 ml, post: 312±148 ml, P=0.33). Maternal fluid intake was higher during the 24 h after passive heat stress (1561±73 ml) in comparison to the 24 h before (1377±244 ml, P=0.05). Conclusion: Preliminary data suggests that an acute bout of whole-body heat stress does not modulate lactation performance in postpartum mothers. This research was supported by Dr. Ravanelli’s Natural Sciences and Engineering Research Council of Canada Discovery Grant (PIN#2022-05096). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

The Physiological and Perceptual Responses During Acute Heat Stress Following Alcohol Consumption

Introduction: Alcohol consumption has been suggested to increase the risk of heat-related injury during heat waves, however, current evidence remains inconclusive on the underlying mechanisms. The purpose of the proposed study was to investigate whether alcohol consumption would alter physiological and perceptual responses during heat stress relative to a volume matched placebo. Methods: 5 participants (2 females 25.2±7.8 y; 77.9±23.1 kg; 1.7±0.2 m) have completed two experimental trials presented in random order on separate days. Participants voided their bladder upon arrival to the lab, were instrumented and entered a climate room maintained at 40°C &amp; 25%RH, completed a 20 minute baseline to equilibrate with the environment, and then consumed either i) an alcoholic beverage (ALC, orange juice and 80-proof gin) suffcient to target a blood alcohol concentration of 0.08 mg/ml, or ii) a volume matched placebo (PLA, orange juice and tonic) over 30 minutes, and rested for an additional 120 minutes in the heat. Blood alcohol concentration, core and mean skin temperature, heart rate, blood pressure, thermal comfort, and thermal sensation were assessed before beverage consumption, and every 30 minutes thereafter. Urine production was calculated as the sum of all micturition during and immediately following the heat exposure. Whole-body sweat loss was calculated as the net difference in mass following the 120-min heat exposure accounting for urine output. Results: No differences were observed at baseline for core temperature (PLA: 37.0±0.3°C, ALC: 36.9±0.2°C, P=0.12), heart rate (PLA: 82±10 BPM, ALC: 81±12 BPM, P=0.89), mean arterial pressure (PLA: 95±5 mmHg, ALC: 97±9 mmHg, P=0.61), and thermal comfort (P=0.21) and sensation (P&gt;0.55). Blood alcohol concentration was 0.10±0.02 mg/ml at 30 minutes following alcohol consumption, and remained elevated at 120-min (0.09±0.01 mg/ml). Throughout heat exposure, core (P&gt;0.49) and mean skin (P&gt;0.61) temperature were not different between PLA and ALC. Thermal comfort was not different between PLA and ALC throughout heat exposure (P≥0.16), however a reduced thermal sensation was observed with ALC compared to PLA at 120-min (P=0.02). Heart rate was higher with ALC compared to PLA at 60-min (ALC: 94±12 BPM, PLA: 88±10 BPM, p&lt;0.02), and remained higher with ALC compared to PLA throughout the remaining heat exposure (p&lt;0.001). Mean arterial pressure was lower at 30-min with ALC (86±10 mmHg) compared to PLA (98±5 mmHg, p&lt;0.001), and remained lower with ALC throughout heat exposure (p&lt;0.001). Urine production was not different between PLA (559±254 ml) and ALC (681±101 ml, P=0.32). Whole-body sweat losses were not different between PLA (398±161 g) and ALC (477±242 g, P =0.52). Conclusion: Preliminary results suggest that the consumption of alcohol does not alter whole-body sweating, core and skin temperature, thermal comfort, and urine production during acute heat stress. However, relative to placebo, alcohol consumption increased heart rate and reduced mean arterial pressure during acute heat stress, and reduced thermal sensation. This research was supported by Dr. Ravanelli’s Lakehead University Research Funding and the Natural Sciences and Engineering Research Council of Canada Discovery Grant (PIN#2022-05096). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Thermoregulatory Responses to Very Hot and Dry Heat Exposure: Interactions Between Age and Sex

Extreme heat events can cause mass morbidity and mortality. Older adults are more susceptible to the adverse effects of heat. Additionally, sex is known to independently influence the physiological responses to heat stress. However, less is known regarding the interaction between age and sex on thermoregulation. Purpose: This study investigated differences in thermoregulatory responses between males and females in older and younger individuals exposed to a hot and dry environment with accompanying activities of daily living. Methods: Twenty older (70 ± 4 yrs) and twenty younger (29 ± 5 yrs) adults (10 males and 10 females per group) were exposed to 3-hours of ambient heating, replicating peak environmental conditions during the 2018 Los Angeles heat wave (47 °C, 15% relative humidity). Participants performed seven 5-minute periods of light exercise (≍3 METS; metabolic heat production: 2.99 ± 0.33 W/kg) dispersed throughout the heat exposure to simulate heat generation associated with activities of daily living. Participants ingested 3 mL/kg/hr of tap-temperature water throughout the trial. Core temperature, skin temperature, and heart rate changes were assessed from pre-post heat exposure. Whole-body sweat rate and forearm blood flow changes were indexed to changes in core temperature. Data were analyzed using a two-way ANOVA (Age x Sex) Results: Delta core temperature was greater in older individuals (males: 1.43 ± 0.47°C, females: 1.31 ± 0.39°C) than in younger (males: 0.83 ± 0.22°C, females: 0.53 ± 0.24°C, p&lt;0.001) but there was no difference between sex (p = 0.063) nor was there an interaction (p = 0.423). There was an interaction of age and sex on delta heart rate (p = 0.019). Older females (32 ± 9 bpm) had greater increases in heart rate than older males (18 ± 8 bpm), younger males (18 ± 6 bpm), and younger females (18 ± 12 bpm, p ≤ 0.009 for all comparisons). There was no effect of age (p = 0.529), sex (p = 0.670), or interaction (p = 0.422) on delta skin temperature. There was an interaction between age and sex for whole-body sweat loss (WBSL) indexed to changes in core temperature and body surface area (p = 0.009). Younger females (1688 ± 685 mL/m2/°C) had greater WBSL than older females (612 ± 211 mL/m2/°C, p &lt; 0.0001), older males (694 ± 327 mL/m2/°C, p &lt; 0.0001), and younger males (1038 ± 282 mL/m2/°C, p &lt; 0.0001). There was a main effect of sex (p = 0.003) and age (p &lt; 0.0001), but no interaction (p = 0.152) on delta forearm blood flow indexed to changes in core temperature (older males: 116 ± 67 mL/min/°C, older females: 194 ± 73 mL/min/°C, younger males: 263 ± 72 mL/min/°C, younger females: 468 ± 243 mL/min/°C). Conclusion: These data suggest that many thermoregulatory responses to heat stress are influenced by the interaction between age and sex. Supported by NIH R01AG069005 (CGC). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

The Critical Ambient Temperature Threshold for Safe Fan Use in Young Adults During Extreme Heat Exposure

Introduction: The electric fan may be an effective, low-cost heat resilience solution during extreme heat. Fans have been shown to attenuate the rise in cardiovascular and thermal strain relative to still air in young adults, particularly during exposure to more humid conditions. When ambient temperature exceeds skin temperature, a fan improves sweat evaporation from the skin surface, which counterbalances the increased rate of convective heat gain. However, at higher air temperatures, the increased convective heat gain may exceed the rate of evaporative heat loss resulting in net heat gain and increasing physiological strain. The purpose of the present study was to identify the critical ambient temperature limit, where increased physiological strain will be observed, with a fan in comparison to still air. Method: To date, 6 participants (4 females; 24±9 y; 72.8±17.8 kg; 1.8±0.2 m) have completed two 180-minute temperature ramp heat-exposures (37°C to 47°C at ~0.05°C/min, 25%RH) on separate days. Wearing standardized t-shirts and shorts, the participants remained seated while either i) facing an electric fan (5.3±0.9 m/s) or ii) in still air (0.1±0.0 m/s). Rectal and skin temperature, heart rate, blood pressure, whole-body sweat loss, thermal comfort, and thermal sensation were measured every 10 minutes. Results: Rectal temperature was similar between fan and still air up to 43°C (P&gt;0.92), however was greater with a fan from 44°C onwards (p&lt;0.05). Skin temperature was higher with a fan compared to still air throughout the exposure (p&lt;0.001). Heart rate was similar between fan and still air until 44°C (P&gt;0.61), after which heart rate was higher with a fan (p&lt;0.05). Mean arterial pressure was not different between fan and still air at any air temperature (P=0.53). The rate pressure product was higher with a fan compared to still air when the ambient temperature exceeded 44°C (p&lt;0.05). Whole-body sweat losses were greater with a fan (1215±250 g) compared to still air (675±103 g, P=0.006). No differences between fan and still air were observed for thermal comfort (P=0.22) or thermal sensation (P=0.73) throughout the temperature ramp protocol. Conclusion: When ambient temperature exceeds 43°C, electric fan use results in greater physiological strain at rest in young healthy adults relative to still air. This research was supported by Dr. Ravanelli’s Natural Sciences and Engineering Research Council of Canada Discovery Grant (PIN#2022-05096). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

The effect of 8-day oral taurine supplementation on thermoregulation during low-intensity exercise at fixed heat production in hot conditions of incremental humidity

PurposeTo determine the effect of taurine supplementation on sweating and core temperature responses, including the transition from compensable to uncompensable heat stress, during prolonged low-intensity exercise of a fixed-heat production (~ 200W/m2) in hot conditions (37.5 °C), at both fixed and incremental vapour-pressure.MethodsFifteen females (n = 3) and males (n = 12; 27 ± 5 years, 78 ± 9 kg, V˙\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\dot{V}$$\\end{document}O2max 50.3 ± 7.8 mL/kg/min), completed a treadmill walking protocol (~ 200W/m2 heat production [Ḣprod]) in the heat (37.5 ± 0.1 °C) at fixed-(16-mmHg) and ramped-humidity (∆1.5-mmHg/5-min) following 1 week of oral taurine supplementation (50 mg/kg/bm) or placebo, in a double-blind, randomised, cross-over design. Participants were assessed for whole-body sweat loss (WBSL), local sweat rate (LSR), sweat gland activation (SGA), core temperature (Tcore), breakpoint of compensability (Pcrit) and calorimetric heat transfer components. Plasma volume and plasma taurine concentrations were established through pre- and post-trial blood samples.ResultsTaurine supplementation increased WBSL by 26.6% and 5.1% (p = 0.035), LSR by 15.5% and 7.8% (p = 0.013), SGA (1 × 1 cm) by 32.2% and 29.9% (p < 0.001) and SGA (3 × 3 cm) by 22.1% and 17.1% (p = 0.015) during the fixed- and ramped-humidity exercise periods, respectively. Evaporative heat loss was enhanced by 27% (p = 0.010), heat-storage reduced by 72% (p = 0.024) and Pcrit was greater in taurine vs placebo (25.0-mmHg vs 21.7-mmHg; p = 0.002).ConclusionTaurine supplementation increased sweating responses during fixed Ḣprod in hot conditions, prior to substantial heat strain and before the breakpoint of compensability, demonstrating improved thermoregulatory capacity. The enhanced evaporative cooling and reduced heat-storage delayed the subsequent upward inflection in Tcore—represented by a greater Pcrit—and offers a potential dietary supplementation strategy to support thermoregulation.

Paper-based microfluidic chip for sweat volume, ECG and EMG monitoring

With the development of wearable devices, the application of non-invasive wearable devices to monitor sweat in real time is the most important for human health. Here, a paper-based microfluidic chip for monitoring of sweat loss during exercise is proposed. Highly absorbent rice paper is selected as the paper-based material, and the capillary action of the paper base is used to actively adsorb sweat, and it can be used repeatedly. As the electrode material, the conductive cloth has good tensile properties and bending resistance, which ensures that the change of resistance is caused by the amount of sweat entering. Other materials of the chip are highly hydrophobic, ensuring that all sweat will be absorbed by the paper base. The sweat volume monitored by the microfluidic chip in real time is 0.5μl-225μl. Compared with rigid electrodes and wet electrodes, the application of flexible electrodes allows the chip to fit well with the skin, the ECG waveform is clearer and has greater amplitude, and the EMG is smoother and has a greater signal-to-noise ratio.

Living in Western Australia induces some physiological adaptations of seasonal acclimatisation in the surgical burns team

ABSTRACT Seasonal acclimatization is known to result in adaptations that can improve heat tolerance. Staff who operate on burn injuries are exposed to thermally stressful conditions and seasonal acclimatization may improve their thermoeffector responses during surgery. Therefore, the aim of this study was to assess the physiological and perceptual responses of staff who operate on burn injuries during summer and winter, to determine whether they become acclimatized to the heated operating theater. Eight staff members had physiological and perceptual responses compared during burn surgeries conducted in thermoneutral (CON: 24.1 ± 1.2°C, 45 ± 7% relative humidity [RH]) and heated (HOT: 31.3 ± 1.6°C, 44 ± 7% RH) operating theaters, in summer and winter. Physiological parameters that were assessed included core temperature, heart rate, total sweat loss, sweat rate, and urinary specific gravity. Perceptual responses included ratings of thermal sensation and comfort. In summer, CON compared to winter CON, baseline (85 ± 15 bpm VS 94 ± 18 bpm), mean (84 ± 16 bpm VS 93 ± 18 bpm), and peak HR (94 ± 17 bpm VS 105 ± 19 bpm) were lower (p < 0.05), whereas core temperature was not different between seasons in either condition (p > 0.05). In HOT, ratings of discomfort were higher in summer (15 ± 3) than winter (13 ± 3; p > 0.05), but ratings of thermal sensation and sweat rate were similar between seasons (p > 0.05). The surgical team in burns in Western Australia can obtain some of the physiological adaptations that result from seasonal acclimatization, but not all. That is most likely due to a lower than required amount of outdoor heat exposure in summer, to induce all physiological and perceptual adaptations.

Experimental investigation on physiological and perceptual thermal responses through simulated hot-humid deep mine conditions

Miners in underground space often experience discomfort and heat strain due to combination of hot-humid environment and strenuous physical intensity. To investigate the impacts of manipulated variables, amounts of trials were conducted in a controlled climate chamber, with air temperatures of 29 °C and 32 °C, air velocities of 0.8 m/s and 1.8 m/s, and labor intensities of 3 km/h and 5 km/h, respectively. The physiological responses of mean skin temperature (Tmsk), oral temperature (Tor), sweat loss (SW), and heart rate (HR) were measured during these trials, along with the perceptual responses of thermal sensation vote, thermal comfort vote, thermal satisfaction vote, thermal acceptability vote, air movement expectation vote. The results indicate that Tmsk, Tor, SW and HR exhibit an upward trend in response to increasing air temperature and labor intensity, but decrease with rising air velocity. Tmsk and Tor are primarily affected by air temperature, while SW and HR are predominantly influenced by labor intensity. Notably, increased air temperature and labor intensity have negative effects on perceptual sensations, whereas augmentation in air velocity can marginally mitigate perceptual sensations. Tmsk and sweating rate exhibit the potential to serve as an indicator for evaluating and forecasting perceptual sensation. Tmsk values of 36 °C and 35 °C can be identified as the maximum thresholds for miners' thermally acceptable and comfortable skin temperatures. The findings can provide valuable references for understanding thermal responses of individuals in hot-humid deep mine conditions, and establish a robust basis for promoting working safety and comfort of miners.