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.

Newhouse D ，Mihalcin E ，Lefebvre K ，Nucci M ，Ravanelli N ... -  《-》

Erratum: Eyestalk Ablation to Increase Ovarian Maturation in Mud Crabs.

《Jove-Journal of Visualized Experiments》

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

Johnson DA ，Cable TG ，Funnell MP ，Peden DL ，Thorley J ，Ferreira de Cunha M ，Reynolds KM ，Harris L ，Wood M ，Chavez-O'Reilly T ，Carrington J ，Bailey SJ ，Clifford T ，Heaney LM ，James LJ ... -  《-》

The Significance of Body Surface Area to Mass Ratio for Thermal Responses to a Standardized Exercise-Heat Stress Test.

To evaluate the significance of body surface area-to-mass ratio (BSA/mass) on the heat-tolerance test (HTT) results. We hypothesized that individuals defined as heat tolerant (HT) would have on average higher BSA/mass compared to heat intolerant (HI) individuals. A retrospective reanalysis of the HTT results of 517 soldiers (age: 18-38 yrs., M/F: 96/4%), who were tested by the Israel Defense Forces (IDF) HTT protocol. The criterion for heat tolerance in the current analysis was a rectal temperature (Tre) plateau during the second hour of the test. A logistic regression analysis to evaluate the predictive power of BSA/mass for heat intolerance was performed; the spline model was applied to show the odds for heat intolerance across BSA/mass. In men BSA/mass of HI individuals was lower than HT individuals (248 ± 19 vs. 262 ± 18 cm2/kg, p < 0.01, d = 0.76). In women a similar trend was noted but with no statistical significance between HT and HI groups. The odd ratio for heat intolerance for every unit increase in BSA/mass was 0.97 (CI 95% 0.95-0.99). The spline model plateaued above BSA/mass of 270 cm2/kg. The results imply that body-core temperature responses to a standard exercise-heat stress (fixed external work rate and climatic conditions) are influenced by BSA/mass. More specifically, lack of a steady state in Tre (indicating heat intolerance) was more likely to occur with every unit decrease in BSA/mass. These findings contribute to a better understanding of the role of body anthropometry in the response to a standard exercise-heat task that might have an implication on clinical decision-making about return to duty/play of soldiers, athletes and others who deemed to be identified as HI.

Akavian I ，Epstein Y ，Rabotin A ，Peretz S ，Charkoudian N ，Ketko I ... -  《-》

The index of maximum sweat ion reabsorption rates of sweat glands does not correlate to whole body sweat sodium concentration in exercising young healthy men.

Factors explaining individual variations in whole body sweat sodium ion concentration ([Na+]) during exercise are not fully understood. Galvanic skin conductance (GSC) reflects the electrical properties of the skin influenced by sweat rate (SR) and the presence of ions. Initiation of increases in this response to elevating sweating may reflect exceeding the maximal capacity of sweat ion reabsorption in sweat glands. We investigated whether the SR threshold for increasing GSC, an indirect measure of maximum ion reabsorption rates of sweat glands, explains the variations in whole body sweat [Na+]. Thirty young healthy males cycled for 90 min at incremental exercise intensities of 30, 45, and 60% peak oxygen uptake (30 min each) in the heat (32°C, 50% relative humidity). Whole body sweat [Na+] was measured using a whole body washdown technique. The SR threshold for increasing GSC was determined from the relationship between the local SR (ventilated capsule) and GSC on the forearm and chest. The average whole body sweat [Na+] was 42.8 ± 18.9 (range: 14.4-81.0) mmol L-1, and the SR threshold for increasing GSC was 0.29 ± 0.20 (range: 0.02-0.62) and 0.35 ± 0.30 (range: 0.01-1.40) mg cm-2 min-1 for the forearm and chest, respectively. Whole body sweat [Na+] was not correlated with the SR threshold for increasing GSC in the forearm or chest (r2 ≤ 0.001, P ≥ 0.921). We conclude that the SR threshold for increasing GSC at the forearm and chest does not explain the individual variation in whole body sweat [Na+] during exercise in the heat.NEW & NOTEWORTHY Galvanic skin conductance is influenced by sweat rate and sweat ions, and the sweat rate at which this response begins to increase may reflect the exceeding capacity of sweat ion reabsorption in sweat glands. However, we show that this indirect measure of the sweat gland's capacity of ion regulation on the forearm and chest does not correlate with whole body sweat sodium concentration during exercise, excluding its role as a determinant of systemic sweat sodium loss.

Oshima S ，Okamoto Y ，Otsuka J ，Yokoyama S ，Hashimoto Y ，Ishihara T ，Togo H ，Amano T ... -  《-》