Leg skin temperature and thigh sweat output: possible central influence of local thermal inputs

To demonstrate whether or not the skin temperature of one lower limb can have an influence on the sweat rate of the contralateral leg, the two legs of five subjects were exposed inside leg-chambers to specific local thermal conditions while sweat rates were measured on both limbs. Three experiments (C I,II,III) of 3 h were carried out: each included two phases A and B. During A, the right leg was not ventilated, while the left leg was (C I) or was not (C II–III) ventilated. During B, the legs were either removed from the leg-chambers (C I) or ventilated inside the chambers at differently controlled levels of leg skin temperature (C II–III). At all times, sweat capsules on both legs measured the sweat rates of local areas of the thigh which were also temperature-controlled. Results showed that, at constant or slightly increased mean skin and core temperatures, the sweat output of one leg could be decreased at constant (C II) or higher local skin temperature (C III) probably due to a decrease in the temperature of the opposite leg. This finding is interpreted as a consequence of a central negative effect, originating from contralateral thermal inputs.     

Differential heating of trunk and extremities. Effects on thermoregulation mechanisms

Experiments in which the whole human body was heated or cooled are compared with others in which one extremity (arm or leg) was simultaneously cooled or heated. With a warm load on the rest of the body resulting in general sweating, a cold load on one extremity did not evoke local shivering; with general body cooling, heating one limb did not stop the shivering. Skin temperatures of the other parts of the body were not influenced by warming or cooling one extremity. Evaporative heat loss was influenced by local, mean skin and core temperature, whereas shivering did not depend on local temperature, and vasomotor control seemed to be controlled predominantly by central temperatures. A cold load on an extremity during whole body heating in most cases induced an oscillatory behaviour of core temperature and of the evaporative heat loss from the body and the extremity. It is assumed that local, mean skin and core temperatures influence the three autonomous effector systems to very different degree.     

Control of sweating in man after work-induced thermal load and symmetrically applied cooling

To examine the compensatory effects of work-induced thermal load and symmetrically applied local cooling on local sweat rates, two kinds of experiment were carried out on eight male subjects in a climatic chamber: 1) Experiments at 36 degrees C ambient temperature with a work load of about 25 W by the right leg. 2) Experiments at 36 degrees C ambient temperature with a work load of about 25 W by the right leg as in 1., but with additional compensatory cooling of the left leg controlled throughout by heat balance calculations at 75-85 W, equal to the heat produced in the working leg, the necessary air temperature being dependent on local sweat rate. Work load without cooling brought about a significant increase in core temperatures, metabolism, heart rate and local sweat rates. With unchanged local skin temperatures local sweat rate increase was higher in the working leg. Therefore the existence of muscle thermoreceptors should be assumed, the afferent information from which is processed and weighted in a different way to that provided by skin receptors. Work load combined with additional cooling reduced local and mean skin temperatures and heart rate, but had no significant influence on core temperature or metabolism. However, local sweat rate was generally lower in both thighs, with a major reduction in the cooled leg confirming control of local sweat rate by local temperature.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influences of overall thermal balance on local inputs for drive of evaporation in men

Three kinds of experiments were carried out in a climatic chamber: experiments with warm load on the whole body at 36 degrees C (4 subjects); experiments at 36 degrees C with reduction of thermal load (28 degrees C) on the left leg (right leg at 36 degrees C) (8 subjects); and experiments at 36 degrees C with antisymmetric thermal load on the legs of 44 degrees C (right leg) and 28 degrees C (left leg), which resulted in additional thermal loads of +/- 30 W/leg (8 subjects). The additional thermal loads, which were applied via two climatic boxes, produced measurable effects on sweat rate when applied to one leg only. In comparison to the experiment 1, experiment 2 brought about a significant reduction of local evaporation on the left leg. With antisymmetric thermal loads on both legs (experiment 3), which did not influence the overall thermal balance, there was no significant influence on local evaporation, although significant changes of local temperatures were measured. It is suggested that the well-known regulatory models, declaring local, mean skin, and core temperatures as local evaporation drive should be supplemented with an important additional feature: local control of evaporation by local skin temperature may be blocked by an overall thermal balance.     

Sweat gland response to local heating during sleep in man

In order to assess whether the fluctuations in the sweating response occurring during sleep are related to changes in central drive or in peripheral sweat gland reactivity, 4 healthy male subjects spent 6 non-consecutive nights in a climatic chamber. Air temperature was 25 degrees C, dew-point temperature was 10 degrees C and air velocity was 0.3 m X s-1, while wall temperature was either 38 degrees C, 46 degrees C or 48.7 degrees C giving 3 levels of operative temperature (To = 30, 33 or 34 degrees C). During the whole night, 2 local sweating rates on the right and the left sides of the upper chest were continuously recorded from 12 cm2 area capsules using a dew-point hygrometer technique, while applying local thermal clamps, a constant 2 degrees C difference in local skin temperatures being imposed between the two symmetrical skin areas. Continuous measurements were made of rectal temperature, 10 local skin temperatures, 2 EEGs, 2 EOGs, 1 EMG and 1 ECG. Results show that the multiplicative relationship between the peripheral influence of local skin temperature and the central drive for sweating described in waking subjects, is still valid in sleeping subjects. No peripheral change appears in sweat gland reactivity between the different sleep stages. Changes in the sensitivity of the thermoregulatory system occurring during sleep cannot be explained by a local factor acting at the sweat gland level.     

Physiological and psychological thermal response to local cooling of human body

1. 1. In order to investigate the thermoregulatory responses to the non-uniform thermal environment of the human body, the effects of cooling 10 different body regions were compared by circulating cool water to the neck, breast, back, loin, upper-arms, lower-arms, hands, thighs, legs and feet, respectively. Tympanic temperature, regional (11 sites) and mean skin temperature, and the thermal sensations were measured during experiment in which 30 min local coolings were applied on 5 female students in a climatic chamber controlled at 30°C and 50% r.h.

2. 2. The skin temperature beneath the cooling pad decreased in the order of arms, legs, hands and feet, and trunk.

3. 3. The temperature drop was significantly correlated with the thermal sensation of the region itself.

4. 4. On the other hand, the tympanic temperature increased once by any local cooling. The increase of it was correlated with the change of the general thermal sensation.

5. 5. Results of principal component analysis of skin temperature showed that the peripheral cooling affected the skin temperature in the limited peripheral regions, while the effects of cooling of the breast and the back extended to both the central and peripheral.

Identification of local thermal conditions for sleeping comfort improvement in neutral to cold indoor thermal environments

The effect of the thermal environment on sleep quality has attracted considerable attention, as sleep forms one-third of human lifetime and the occupied space is largely constrained during sleep. With an increasing development of partial space regulation and task air conditioning systems and devices, thermal comfort demand concerning local thermal conditions has attracted more and more attention. In the present study, experiment was conducted and data mining technologies were performed to investigate correlations between local thermal conditions and whole body thermal comfort in sleeping state. The identification of local thermal condition included two steps: the first step was to clarify thermal sensation links between local and covered body, and the second step was to identify local thermal sensation inclination towards different thermal comfort levels. Thermal sensation correlations among local body parts and covered body were obtained. Back, face, and thigh were identified as three dominant linear-correlated local parts with weighting factors 0.488, 0.388, and 0.152, respectively; in addition, chest, arm, leg and foot were found as non-negligible local parts in the estimation of covered body thermal sensation. By dividing the sleeping human body into three parts as head, trunk and extremity, the proper local thermal sensations and their coupling relationships for whole body sleeping thermal comfort have been elaborated by three rules. The present study provides implications in sleeping thermal environment regulation in neutral to cold indoor conditions.     

Influence of isometric exercise on blood flow and sweating in glabrous and nonglabrous human skin.

The distribution of the reflex effects of isometric exercise on cutaneous vasomotor and sudomotor function is not clear. We examined the effects of isometric exercise by different muscle masses on skin blood flow (SkBF) and sweat rate (SR) in nonglabrous skin and in glabrous skin. The latter contains arteriovenous anastomoses (AVAs), which cause large fluctuations in SkBF. SkBF was measured by laser-Doppler flowmetry (LDF) and reported as cutaneous vascular conductance (CVC; LDF/mean arterial pressure). SR was measured by capacitance hygrometry. LDF and SR were measured at the sole, palm, forearm, and ventral leg during separate bouts of isometric handgrip (IHG) and isometric leg extension (ILE). CVC and its standard deviation decreased significantly during IHG and ILE in the palm and sole (P < 0.05) but not in the forearm or leg (P > 0.05). Only palmar SR increased significantly during IHG and ILE (P < 0.05). We conclude that the major reflex influences of isometric exercise on the skin include AVAs and palmar sweat glands and that this is true for both arm and leg exercise.     

Different thermal conditions of the extremities affect thermoregulation in clothed man

The effects of different types of clothing on human deep body temperature were studied with six healthy male subjects in a supine posture. Two clothing ensembles were employed for the present study: A covered the whole body area with garments except the face (1.97 clo) and B covered only the trunk and the upper half of the extremities with garments (1.53 clo). The experiment was carried out in a climatic chamber at 55% ± 5% relative humidity under cooling and warming temperatures: the temperature was changed from 22°C to 10°C (cooling) and returned to 22°C again (warming). The major findings were: rectal temperature (T _re) continued to decrease gradually in A throughout the experiment, whereas in B it increased during cooling, and returned to previous levels during warming. As a result, Tre and chest skin temperature were maintained at a higher level in B than in A. Internal tissue conductances were greater in A than in B both during cooling and during warming. Thermal comfort appeared to have been influenced more by the rate of skin temperature change than by the level of skin temperature per se. It was concluded that peripheral vasoconstriction in B induced less heat flow from core to shell, and, thus, the core temperature was maintained at a higher level in B than in A.     

Different responses in skin and muscle sympathetic nerve activity to static muscle contraction

We microneurographically recorded the traffic of sympathetic nerves leading to foot volar skin activity (SSA) and leg skeletal muscle activity (MSA) during isometric handgrip and simultaneously determined sweat rate by the ventilated capsule method and skin blood flow by laser-Doppler flowmetry in the innervating area of SSA. SSA increased abruptly and was almost constant during handgrip, accompanied by an increase in sweat rate, whereas skin blood flow showed no significant change during the handgrip. MSA showed a time-dependent increase during the course of handgrip. During arterial occlusion of the working forearm after handgrip, SSA decayed to the precontraction control level, whereas MSA remained at a higher level than during control. During involuntary biceps muscle contraction induced by electrical stimulation, both SSA and MSA increased. The results suggest that the SSA response during voluntary handgrip, which was demonstrated to contain mainly sudomotor activity, might be influenced by central command and input from peripheral mechanoreceptors but be influenced little by input from muscle chemoreceptors.     

Variations in corticomotor excitability in response to distal focal thermal stimulation

Abstract

Purpose: This study investigated the effects of thermal stimulation on corticomotor excitability with transcranial magnetic stimulation (TMS).

Material and methods: Participants consisted of healthy young adults (n?=?20) and seniors (n?=?15). Each experimental session consisted of a baseline (BL) assessment, followed by a warming and a cooling protocol. At BL, recordings of motor evoked potentials (MEPs) and skin temperature were performed with the index finger covered with a ‘neutral’ gel pack (24?°C). For warming, the same measurements were performed, but with the index covered with a warmed gel pack (45?°C). The gel pack was kept for 5?min, and the measurements were performed at 1?min during warming and 5 and 10?min post. After a break, participants were tested with the cooling protocol (gel pack 10?°C) by repeating the same sequence as in the warming.

Results: The two thermal protocols induced the desired range of skin temperatures (warming?=?35–45°; cooling?=?13–24°). For MEP modulation, the primary analysis revealed no main effects or interactions, owing to the variability of responses to either warming or cooling stimulation. Further analysis of individual responses revealed that modulation, when present, was short-lasting and was characterized by a depression in about half of the participants. Facilitation was also observed, but only in smaller clusters, especially with cooling (13/35). Modulation in MEP amplitude did not correlate with changes in skin temperature.

Conclusion: These results are consistent with previous reports regarding variability in response to sensory stimulation protocols. In the case of thermal stimulation, such variability likely reflects individual differences in the influences exerted by thermal afferents centrally.     

Comparison of thermoregulatory responses to heat between Malaysian and Japanese males during leg immersion

The objective of this study was to investigate thermoregulatory responses to heat in tropical (Malaysian) and temperate (Japanese) natives, during 60 min of passive heating. Ten Japanese (mean ages: 20.8 ± 0.9 years) and ten Malaysian males (mean ages: 22.3 ± 1.6 years) with matched morphological characteristics and physical fitness participated in this study. Passive heating was induced through leg immersion in hot water (42°C) for 60 min under conditions of 28°C air temperature and 50% RH. Local sweat rate on the forehead and thigh were significantly lower in Malaysians during leg immersion, but no significant differences in total sweat rate were observed between Malaysians (86.3 ± 11.8 g m⁻² h⁻¹) and Japanese (83.2 ± 6.4  g m⁻² h⁻¹) after leg immersion. In addition, Malaysians displayed a smaller rise in rectal temperature (0.3 ± 0.1°C) than Japanese (0.7 ± 0.1°C) during leg immersion, with a greater increase in hand skin temperature. Skin blood flow was significantly lower on the forehead and forearm in Malaysians during leg immersion. No significant different in mean skin temperature during leg immersion was observed between the two groups. These findings indicated that regional differences in body sweating distribution might exist between Malaysians and Japanese during heat exposure, with more uniform distribution of local sweat rate over the whole body among tropical Malaysians. Altogether, Malaysians appear to display enhanced efficiency of thermal sweating and thermoregulatory responses in dissipating heat loss during heat loading. Thermoregulatory differences between tropical and temperate natives in this study can be interpreted as a result of heat adaptations to physiological function.     

Effect of high local temperature on reflex cutaneous vasodilation

We examined the effect of high local forearm skin temperature (Tloc) on reflex cutaneous vasodilator responses to elevated whole-body skin (Tsk) and internal temperatures. One forearm was locally warmed to 42 degrees C while the other was left at ambient conditions to determine if a high Tloc could attenuate or abolish reflex vasodilation. Forearm blood flow (FBF) was monitored in both arms, increases being indicative of increases in skin blood flow (SkBF). In one protocol, Tsk was raised to 39-40 degrees C 30 min after Tloc in one arm had been raised to 42 degrees C. In a second protocol, Tsk and Tloc were elevated simultaneously. In protocol 1, the locally warmed arm showed little or no change in blood flow in response to increasing Tsk and esophageal temperature (average rise = 0.76 +/- 1.18 ml X 100 ml-1 X min-1), whereas FBF in the normothermic arm rose by an average of 8.84 +/- 3.85 ml X 100 ml-1 X min-1. In protocol 2, FBF in the normothermic arm converged with that in the warmed arm in three of four cases but did not surpass it. We conclude that local warming to 42 degrees C for 35-55 min prevents reflex forearm cutaneous vasodilator responses to whole-body heat stress. The data strongly suggest that this attenuation is via reduction or abolition of basal tone in the cutaneous arteriolar smooth muscle and that at a Tloc of 42 degrees C a maximum forearm SkBF has been achieved. Implicit in this conclusion is that local warming has been applied for a duration sufficient to achieve a plateau in FBF.     

Voluntary muscle activation is impaired by core temperature rather than local muscle temperature.

Fatigue during hyperthermia may be due in part to a failure of the central nervous system to fully activate the working muscles. We investigated the effects of passive hyperthermia on maximal plantar flexor isometric torque (maximal isometric voluntary contraction) and voluntary activation to determine the roles of local skin temperature, core temperature, and peripheral muscle temperature in fatigue. Nine healthy subjects were passively heated from 37.2 to 39.5 degrees C (core temperature) and then cooled back down to 37.9 degrees C using a liquid-conditioning garment, with the right leg kept at a thermoneutral temperature throughout the protocol, whereas the left leg was allowed to heat and cool. Passive heating resulted in significant decreases in torque from [mean (SD)] 172 N x m (SD 39) to 160 N x m (SD 44) and in voluntary activation from 96% (SD 2) to 91% (SD 5) in the heated leg, and maximal isometric voluntary contraction decreased similarly from 178 N xm (SD 37) to 165 N x m (SD 38) and voluntary activation from 97% (SD 2) to 94% (SD 5) in the thermoneutral leg. The initiation of cooling, which produced a rapid decrease in skin temperature and cardiovascular strain [heart rate reserve decreased from 58% (SD 12) to 31% (SD 12)], did not immediately restore either torque or voluntary activation. However, when core temperature was lowered back to normal, torque and voluntary activation were restored to baseline values. It was concluded that an increase in core temperature is a factor responsible for reducing voluntary activation during brief voluntary isometric contractions and that temperature-induced changes in the contractile properties of muscle and local thermal afferent input from the skin do not contribute significantly to the decrement in torque.     

Non-cutaneous peripheral thermosensitivity in the goat (Capra hircus)

1. A 0.2 m2 area of the trunk skin was denervated and its center was externally cooled or warmed, when central body temperature was lowered. 2. When the denervated skin was cooled, the central body temperature, at which shivering occurred, was significantly higher than with warming of the denervated skin. 3. It is concluded that the difference was caused by temperature signals originating from thermoreceptors in tissue layers underneath the denervated skin.     

Effects of chronic sympathectomy on locally mediated cutaneous vasodilation in humans.

In human skin, the vasodilator response to local heating includes a sensory nerve-dependent peak followed by a nadir and then a slower, nitric oxide-mediated, endothelium-dependent vasodilation. To investigate whether chronic sympathectomy diminishes this endothelium-dependent vasodilation, we studied individuals who had previously undergone surgical T(2) sympathectomy (n = 9) and a group of healthy controls (n = 8). We assessed the cutaneous vascular response (laser-Doppler) to 30 min of local warming to 42.5 degrees C on the ventral forearm (no sympathetic innervation) and the lower legs (sympathetic nerves intact). Lower body negative pressure (LBNP) was measured to confirm sympathetic denervation. During local warming in sympathectomized individuals, vascular conductance reached an initial peak at both sites [achieving 1.73 +/- 0.22 laser-Doppler units (LDU)/mmHg in the forearm and 1.92 +/- 0.21 LDU/mmHg in the leg]. It then decreased to a nadir in the innervated leg [to 1.77 +/- 0.23 LDU/mmHg (P < 0.05)] but not in the sympathectomized arm (1.69 +/- 0.21 LDU/mmHg; P > 0.10). The maximal vasodilation seen during the slower phase was not different between limbs or between groups. Furthermore, LBNP caused a 44% reduction in forearm vascular conductance (FVC) in control subjects, but FVC did not decrease significantly in sympathectomized individuals, confirming sympathetic denervation. These data indicate that endothelial function in human skin is largely preserved after sympathectomy. The altered pattern of the response suggests that the nitric oxide-dependent portion may be accelerated in sympathectomized limbs.     

Thermographic studies on patterns of skin temperature after exercise.

In six subjects thermograms of the thighs and the forearms were taken before, during and after 10 min ergometer exercise at 100 W at an ambient temperature of 23 degrees C. During exercise, an intra-individually constant and reproducible skin temperature pattern with local temperature differences exceeding 3 degrees C evolved. Reactions after external local cooling or after occlusion of blood flow and measurements with a laser Doppler-flowmeter showed dispersed convective heat transport to be the source of this irregular pattern. Temperature differences of 3.6 degrees C and deviations of blood flow in the skin microcirculation of 300% within a distance of a few centimetres reduce the value of single-spot measurements of skin temperature with reference to the whole extremity.     

Effects of head cooling on human sleep stages and body temperature

The purpose of this study was to confirm the effect of head cooling on human sleep stages and body temperature. Nine healthy male volunteers with a mean age of 25 +/- 3.77 years served as subjects. The experiments were carried out under three different sets of conditions: 26 degrees C, relative humidity (RH) 50% (26/50); 32 degrees C, RH 80% (32/80); and 32 degrees C RH 80% with the use of a cooling pillow (32/80 HC). The subjects slept from 2300 hours to 0700 hours with a cotton blanket, wearing short-sleeved pyjamas and shorts on a bed, which was covered with a sheet. Electroencephalograms, electro-ouclogram, and mental electromyelograms were recorded through the night. Rectal temperature (Tre) and skin temperature (Tsk) were measured continuously. Whole-body sweat and the tympanic temperature (Tty) were measured before and after sleep. Wakefulness significantly increased at 32/80 than at 26/50; however, no significant difference was observed between 32/80 HC and 26/50. Tre and mean Tsk were higher both at 32/80 and 32/80 HC than at 26/50. The whole-body sweat loss was significantly greater and Tty in the morning was higher at 32/80 than 32/80 HC and 26/50. These results suggest that head cooling during sleep may help to decrease the whole-body sweat rate during sleep under humid heat conditions.     

Active cutaneous vasodilation in resting humans during mild heat stress.

The role of skin temperature in reflex control of the active cutaneous vasodilator system was examined in six subjects during mild graded heat stress imposed by perfusing water at 34, 36, 38, and 40 degrees C through a tube-lined garment. Skin sympathetic nerve activity (SSNA) was recorded from the peroneal nerve with microneurography. While monitoring esophageal, mean skin, and local skin temperatures, we recorded skin blood flow at bretylium-treated and untreated skin sites by using laser-Doppler velocimetry and local sweat rate by using capacitance hygrometry on the dorsal foot. Cutaneous vascular conductance (CVC) was calculated by dividing skin blood flow by mean arterial pressure. Mild heat stress increased mean skin temperature by 0.2 or 0.3 degrees C every stage, but esophageal and local skin temperature did not change during the first three stages. CVC at the bretylium tosylate-treated site (CVC(BT)) and sweat expulsion number increased at 38 and 40 degrees C compared with 34 degrees C (P < 0.05); however, CVC at the untreated site did not change. SSNA increased at 40 degrees C (P < 0.05, different from 34 degrees C). However, SSNA burst amplitude increased (P < 0.05), whereas SSNA burst duration decreased (P < 0.05), at the same time as we observed the increase in CVC(BT) and sweat expulsion number. These data support the hypothesis that the active vasodilator system is activated by changes in mean skin temperature, even at normal core temperature, and illustrate the intricate competition between active vasodilator and the vasoconstrictor system for control of skin blood flow during mild heat stress.     

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.