The effects of face cooling on the prolactin response and subjective comfort during moderate passive heating in humans

Abstract

The purpose of the present study was twofold: first, to determine the extent to which elevated skin temperature is responsible for the hormonal and perceptual responses to passive heating; and second, to determine to what extent face-cooling can override the effects of raised skin temperature. Sixteen recreationally active, non-heat-acclimated volunteers (12 male, 4 female; age, 29 ± 9 years, [mean ± S.D.]) underwent a passive heat exposure for 60 min in a sauna maintained at 58 • C (13% relative humidity), conditions under which sweating effectively maintains core temperature. Subjects were allocated to one of two experimental groups which were matched for sex, age, body mass index, body surface area and sweating response; one group received face cooling (FC) every 5 min, whilst the other control group (CON) received none. Mean skin temperatures were elevated by ∼4 • C for the 60 min duration (CON, 36.5 ± 0.1 • C; FC, 35.7 ± 0.1 • C; P < 0.05) but core temperature rose by only ∼0.25 • C with no difference between groups. Circulating prolactin remained stable and showed no increase for the FC group, whereas concentrations increased by 102 ± 34% (P < 0.05) for the CON group. No differences were observed between groups for heart rate, but the sensation of heat was less (P < 0.05) with FC. We suggest that a significant component of the prolactin response to moderate passive heating is mediated by facial skin temperature, and selective cooling of the face is associated with improved perception of thermal comfort. These results indicate that the temperature of only a small part of the total skin area (∼10%) has a disproportionately large effect on the hormonal and perceptual responses to heat stress.

The Influence of Selective Cooling of the Body Surface on the Improvement of Physiological Indicators of the Body and the Subjective Assessment of Thermal Comfort During Activities Carried Out in the Hot Climatic Zone

“…Therefore, selective cooling of a small area (180 cm 2 ) and the size of the thermal stimulus in the range of 16-17°C in hot conditions (40°C) combined with moderate eff ort did not have a signifi cant infl uence on the change in the temperature of the interior of the body. No signifi cant changes in this physiological indicator are consistent with the observations of other authors [7,14,15]. The total sweat loss based on body weight measurements (without the necessity to take into account the amount of fl uid absorbed) showed a tendency to lower water loss after cooling.…”

“…Previous studies suggest that cooling of the head area in warm conditions has a particular impact on subjectively assessed whole-body thermal comfort [14,15]. This is due to the fact that the head area is relatively heat sensitive, i.e.…”

“…thermodetectors) located in the thermoregulation centre in the hypothalamus [14] by passing the impulse through the skin nerves. This region of the brain is more sensitive to signals from cold receptors than to heat.…”

“…menthol) and have diff erent thermosensitivity ranges. The TRPM8 channel plays an important role in the feeling of cold, thermoregulation and cold pain [4,14]. It is strongly expressed in sensory surface neurons and is involved in receiving stimuli at extremely low temperatures, but can also be activated at low cooling.…”

Heat Stress and Cardiovascular, Hormonal, and Heat Shock Proteins in Humans

“…The increase in heart rate with heat stress was consistent with previous findings. 18 Researchers have shown that during heat stress, peripheral vascular resistance is reduced and blood volume shifts from the central body to the periphery to facilitate heat exchange. 19 The increase in heart rate is compensatory to avoid a large drop in mean arterial blood pressure so cardiac output can be maintained even with a reduced stroke volume.…”