Manabu Shibasaki

Modulation of the thermoregulatory sweating response to mild hyperthermia during activation of the muscle metaboreflex in humans.

1 To investigate the effect of the muscle metaboreflex on the thermoregulatory sweating response in humans, eight healthy male subjects performed sustained isometric handgrip exercise in an environmental chamber (35 °C and 50% relative humidity) at 30 or 45% maximal voluntary contraction (MVC), at the end of which the blood circulation to the forearm was occluded for 120 s. The environmental conditions were such as to produce sweating by increase in skin temperature without a marked change in oesophageal temperature. 2 During circulatory occlusion after handgrip exercise at 30% MVC for 120 s or at 45% MVC for 60 s, the sweating rate (SR) on the chest and forearm (hairy regions), and the mean arterial blood pressure were significantly above baseline values (P < 0.05). There were no changes from baseline values in the oesophageal temperature, mean skin temperature, or SR on the palm (hairless regions). 3 During the occlusion after handgrip exercise at 30% MVC for 60 s and during the occlusion alone, none of the measured parameters differed from baseline values. 4 It is concluded that, under mildly hyperthermic conditions, the thermoregulatory sweating response on the hairy regions is modulated by afferent signals from muscle metaboreceptors.

Regional differences in age-related decrements of the cutaneous vascular and sweating responses to passive heating

Ten older (aged 64–76 years) and ten younger (aged 20–24 years) healthy men were exposed to a standard heat stress [by placing the lower legs and feet in a water bath at 42°C while sitting in a controlled environment (ambient temperature 35°C and 45 % relative humidity) for 60 min]. During passive heating, the rectal temperature of the older men was significantly greater (P < 0.05) and mean skin temperature was lower (P < 0.001), compared to the younger men. Skin blood flow by laser Doppler flowmetry (LDF) was significantly lower on the chest and thigh for the older men (P < 0.001), but forehead LDF did not differ between the groups. The percentages of total LDF in the older men to total LDF in the younger men for the last 30 min were 99%, 58% and 50% on the forehead, chest and thigh, respectively. The age-related differences in LDF responses mirrored cutaneous vascular conductances (CVC), since no group and time effects were observed in mean arterial blood pressure during the test. During the last 30 min the local sweat rates (msw) on the back and thigh were significantly lower for the older men (P < 0.02), but not on forehead, chest and forearm, although the older men had lower msw during the first 30 min exposure regardless of site (P < 0.03). The percentages of total msw in the older men to total msw in the younger men during the last 30 min were 105%, 99%, 63%, 106% and 88% on the forehead, chest, thigh, forearm, and back, respectively. During the latter half of the exposure, the older men had similar LDF, CVC and msw on the forehead, lower LDF and CVC and a similar msw on the chest, and lower LDF, CVC and msw on the thigh, compared to the younger men. These results suggest firstly that regional differences exist in the age-related decrement of cutaneous vasodilatation as well as sweat gland function, secondly that the age-related decrement in cutaneous vascular function may precede a decrement in sweat gland function, and thirdly that the successive decrements may develop sequentially from the lower limbs to the upper body, and head.

Thermoregulatory responses of prepubertal boys and young men during moderate exercise

Abstract Seven prepubertal boys (aged 10–11 years)␣and eleven young men (aged 21–25 years), matched for skinfold thickness and maximal oxygen uptake (O2max) per unit of mass, cycled at an intensity of approximately 40% O2max for 45 min in a warm condition (30 °C, 45% relative humidity). During exercise no age-related differences were observed for the increases in rectal temperature (Tre) and heart rate (HR), although the absolute Tre and HR were significantly greater for the boys because of a higher initial baseline (P < 0.05). Total body sweating rate [181 (SEM 12) vs 245 (SEM 12) g · m−2 · 45 min−1; P < 0.002] and local sweating rates (sw) on chest, back, and forearm were significantly lower for the boys (P < 0.001), as was metabolic heat production [203 (SEM 9) vs 276 (SEM 9) W · m−2; P < 0.01]. The lower sw in the boys was due to a lower output per activated sweat gland, even though they had a higher activated sweat gland density regardless of site. In contrast, cutaneous blood flow by laser Doppler flowmetry (LDF) in the boys was significantly greater on the chest and back, compared to the men (P < 0.003). The age-related differences in cutaneous vascular conductance (CVC) were more marked because of lower mean arterial pressure in the boys during exercise. However, forearm LDF and CVC were significantly lower for the boys (P < 0.008). No significant differences in LDF among sites were observed for the boys, whereas for the men LDF on the forearm was significantly greater than on the chest and back (P < 0.01). The boys showed lower mean skin temperatures (especially on the back and chest despite greater increments of LDF) after starting to sweat, whereas the men remained unchanged, suggesting that the heat loss on the trunk in the boys was promoted by greater increments of LDF despite lower sw, compared to the young men. It was concluded that during moderate exercise in an air temperature at 30 °C, prepubertal boys could thermoregulate as efficiently as young men by greater vasodilatation on their trunk despite lower sw. Furthermore regional differences may exist in the maturation-related modification of vasodilatation.

Relationship between skin blood flow and sweating rate, and age related regional differences

Abstract To examine the mechanisms and regional differences in the age-related decrement of skin blood flow, 11 young (age 20–25 years) and 10 older (age 64–76 years) men were exposed to a mild heat stress by immersing their feet and lower legs in water at 42°C for 60 min, while they were sitting in near thermoneutral conditions [25°C and 45% relative humidity (rh)]. During the equilibrium period (25°C and 45% rh) before the heat test, no group differences were observed in rectal (Tre) and mean skin (Tsk) temperatures or mean arterial pressure (MAP). During passive heating, Tsk was significantly lower in the older men 20 min after commencing exposure (P < 0.001), although there were similar increases in Tre in both groups. Exposure time and age did not affect MAP. The local sweating rate (m˙sw) and the percentage change in skin blood flow by laser Doppler flowmetry (%LDF) relative to baseline values on the chest, back, forearm and thigh were significantly lower in the older men (P < 0.001), especially on the thigh. After starting the heat exposure, three temporal phases were observed in the relationship between %LDF and m˙sw at most sites in each subject. In phase A, %LDF increased but with no increase in m˙sw. In phase B, m˙sw increased but with no secondary increase in %LDF. Finally, in phase C, there were proportional increases in %LDF and m˙sw. The increase in %LDF in phase A was significantly lower on the forearm and thigh (P < 0.05) for the older men, but not on the chest and back. In phase C, the slopes of the regression lines between %LDF and m˙sw were lower for the older men on the back (P < 0.03), forearm (P = 0.08) and thigh (P < 0.03), but not on the chest. These results would suggest that the age-related decrement in skin blood flow in response to passive heating may be due in part to a smaller release of vasoconstrictor tone and to less active vasodilatation once sweating begins. Regional differences exist in the impaired vasoconstriction and active vasodilatation systems.

Kinetics of oxygen uptake and cardiac output at onset of arm exercise

Pulmonary oxygen uptake (V O2) kinetics at onset of exercise is reported to be slower for arm than for leg exercise. This could be attributed to reduced cardiac output (Q) or reduced arteriovenous O2 content difference or both. To test this, V O2 mean tissue oxygen consumption (V O2T) and Q kinetics in arm cranking were compared with corresponding values found in leg cycling. The increase in V O2 during phase 1 (abrupt increase after onset of exercise) was less in arm than in leg exercise, suggesting that immediate Q adjustments to arm exercise were less pronounced. Mean response times (MRT, the relative rates at which a steady state was attained) for V O2, V O2T, and Q were prolonged during arm exercise. The MRT of VO 2 in arm exercise at a given blood lactate increase was higher than in leg exercise. The delayed V O2 kinetics in arm exercise might be due to delayed Q kinetics and higher anaerobic glycolysis occurring early during arm exercise.

Sweating responses to passive and active limb movements

The changes in esophageal and mean skin temperatures did not show a marked difference between active limb movement (ALM) and passive limb movement (PLM). Increase in heart rate was significantly greater during ALM than PLM at 30 and 60 rpm (P < 0.05). Sweating rate on the chest and forearm were significantly greater during ALM than PLM at each pedalling frequency (P < 0.05). The result suggests that the greater increase in sweating rate during ALM relative to PLM may in part be of a consequence of non-thermal factors.

Circadian Variation in Skin Blood Flow Responses to Passive Heat Stress

To examine whether there is a circadian variation in skin blood flow response to passive heat stress and maximal skin blood flow, which was measured by local warming to 42 degrees C for 45 min, we studied six men at an ambient temperature of 28 degrees C at four different times of day [0400-0700 (morning), 1000-1300 (daytime), 1600-1900 (evening), and 2200-0100 hours (night)], each time of day being examined on separate days. Heat stress at rest was performed by immersing the legs below the knee in hot water (42 degrees C) for 60 min. The esophageal temperature (Tes) at rest was significantly higher in the evening than in the morning. The maximal skin blood flow (SkBFmax) on both sites, back and forearm, did not show a significant difference among the four times of day. The variation in Tes thresholds for cutaneous vasodilation to heat stress was similar to the circadian rhythm in resting Tes. The relationship of the percentage of SkBFmax (%SkBF) with Tes was significantly lower in the morning than in the evening. The results suggest that the maximal skin blood flow during local warming does not show variation over the day, but the sensitivity of vasodilation to passive heat stress shows a circadian variation.

The effect of diurnal variation on the regional differences in sweating and skin blood flow during exercise

AbstractThe aim of the present study was to examine changes in the control of heat-dissipation responses to exercise associated with the diurnal variation in core temperature from the viewpoint of the regional response patterns. We studied seven men during exercise on a cycle ergometer at 100 W for 40 min at 25°C at 0630 (morning) 1630 (evening) hours on 2 separate days. Oesophageal temperature (Toes), local skin temperature, local sweating rate (

Circadian variation of sweating responses to passive heat stress

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