Adaptive Changes in Physiological Responses of Men to Heat Induced by Heat Acclimatization and Physical Training.

Korean J Physiol Pharmacol

Kim

Shin

et al. 2010

Tropical inhabitants are able to tolerate heat through permanent residence in hot and often humid tropical climates. The goal of this study was to clarify the peripheral mechanisms involved in thermal sweating pre and post exposure (heat-acclimatization over 10 days) by studying the sweating responses to acetylcholine (ACh), a primary neurotransmitter of sudomotor activity, in healthy subjects (n=12). Ten percent ACh was administered on the inner forearm skin for iontophoresis. Quantitative sudomotor axon reflex testing, after iontophoresis (2 mA for 5 min) with ACH, was performed to determine directly activated (DIR) and axon reflex-mediated (AXR) sweating during ACh iontophoresis. The sweat rate, activated sweat gland density, sweat gland output per single gland activated, as well as oral and skin temperature changes were measured. The post exposure activity had a short onset time (p＜ 0.01), higher active sweat rate [(AXR (p＜ 0.001) and DIR (p＜ 0.001)], higher sweat output per gland (p ＜ 0.001) and higher transepidermal water loss (p＜ 0.001) compared to the pre-exposure measurements. The activated sweat rate in the sudomotor activity increased the output for post-exposure compared to the pre-exposure measurements. The results suggested that post-exposure activity showed a higher active sweat gland output due to the combination of a higher AXR (DIR) sweat rate and a shorter onset time. Therefore, higher sudomotor responses to ACh receptors indicate accelerated sympathetic nerve responsiveness to ACh sensitivity by exposure to environmental conditions.

Section: Discussionmentioning

confidence: 99%

Effect of the Heat-exposure on Peripheral Sudomotor Activity Including the Density of Active Sweat Glands and Single Sweat Gland Output

Korean J Physiol Pharmacol

Kim

Shin

et al. 2010

“…This is recognized as one type of short-term heat acclimation. Thermoregulation to the same given heat stress in summer and winter induced changes similar to short-term heat acclimation (Hori et al 1993;Inoue et al 1995;Shiraishi et al 1990;Tsurutani-Midorikawa 1981). In this study, a higher T sk in summer than in winter was assessed in the neutral environment room before 276 Seasonal Effects of Sleep Deprivation on Thermoregulatory Responses in a Hot Environment MeanϮSD (nϭ8) * Significant differences between sleep conditions assessed from main effect of sleep factor, PϽ0.05.…”

Section: Discussionmentioning

confidence: 98%

“…Therefore, diurnal variation of thermoregulatory responses is affected also by seasonal changes in body-temperature circadian rhythm (TsurutaniMidorikawa 1981). Besides, thermoregulatory responses to heat stress are seasonally changed because of humans' advanced ability to adapt to heat or cold according to the season (Hori et al 1993;Inoue et al 1995;Shiraishi et al 1990;Tsurutani-Midorikawa 1981). However, there are fewer studies observing thermoregulation effected by sleep deprivation on a seasonal basis.…”

Section: Introductionmentioning

confidence: 99%

Seasonal Effects of Sleep Deprivation on Thermoregulatory Responses in a Hot Environment

Fujita

Ismail

et al. 2003

J. Physiol. Anthropol.

Effects of sleep deprivation and season on thermoregulation during 60 min. of leg-bathing (water temperature of 42°C, air temperature of 30°C, and relative humidity of 70%) were studied in eight men who completed all 4 experiments for normal sleep and sleep deprivation in summer and winter. Rectal temperature (T re ), skin temperature, total body sweating rate (M sw-t ), local sweating rate on the back (M sw-back ) and forearm (M sw-forearm ), and skin blood flow on the back (SBF back ) and forearm (SBF forearm ) were measured. The changes in T re (DT re ) were smaller (PϽ0.05) for sleep deprivation than for normal sleep regardless of the season. This decrease in DT re was significant only in summer (PϽ0.05). Mean skin temperature (T sk ) was higher (PϽ0.05) for sleep deprivation than for normal sleep regardless of the season. M sw-t was smaller (PϽ0.05) for sleep deprivation than for normal sleep regardless of season, although M sw-back and M sw-forearm were similar. SBF back and SBF forearm tended to be higher for sleep deprivation than normal sleep. The sensitivity of SBF to T re was higher (PϽ0.05) for sleep deprivation than for normal sleep. These data indicate that seasonal differences in thermoregulation were small because of morning time. Sleep deprivation increased dry heat loss and restrained T re rise, in spite of decreased sweating rate.

“…When short-term acclimation is complete, the increase in the volume of sweat allows the body to compensate for the increase in body temperature [ 31 ]. The reduction of the Na+ concentration reduces the loss of Na+ due to sweating [ 9 36 ]. In addition to changes in sweating, lowered heart rate and slower rise in core temperature during heating aspects of heat resistance acquired by short-term acclimation [ 1 5 6 37 ].…”

Section: Discussionmentioning

confidence: 99%

“…In Japan, where the four seasons are obvious, seasonal acclimation is observed in summer, which is a kind of short-trem acclimation. Comparing sweating reponse to heating in summer and winter, in summer, onset time of sweating is short and sweat rate is higher [ 9 10 ], and Na + concentration of sweat is lower [ 9 ]. It is well known that basal metabolic rate (BMR) also shows seasonal variation of lower values in summer and higher values in winter [ 11 12 ].…”

Section: Introductionmentioning

confidence: 99%

Seasonal acclimation in sudomotor function evaluated by QSART in healthy humans

Shin

Korean J Physiol Pharmacol

Kim

2016

The quantitative sudomotor axon reflex testing (QSART) is a classic test of routine postganglionic sudomotor function. We investigated sudomotor function by QSART after summer (July 2012) and winter (January 2013) seasonal acclimation (SA) in the Republic of Korea. QSART with acetylcholine (ACh) iontophoresis were performed to determine directly activated (DIR) and axon reflex-mediated (AXR1, 2) sweating rate. Onset time of axon reflex, activated sweat gland density (ASGD), activated sweat gland output (ASGO), tympanic and skin temperatures (Tty, Tsk), basal metabolic rate (BMR), and evaporative loss volume changes were measured. Tympanic and mean body temperature (b; calculated from Tty, Tsk) were significantly lower after summer-SA than that of winter-SA. Sweat onset time was delayed during winter-SA compared to that after summer-SA. BMR, AXR(1), AXR(2), and DIR sweat rates, ASGD and ASGO, and evaporative loss volume were significantly diminished after winter-SA relative to after summer-SA. In conclusion, changes in sweating activity measured by QSART confirmed the involvement of the peripheral nervous system in variation of sudomotor activity in seasonal acclimation.