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Research Papers

Heat Loss Through the Glabrous Skin Surfaces of Heavily Insulated, Heat-Stressed Individuals

[+] Author and Article Information
D. A. Grahn1

Department of Biology, Stanford University, Stanford, CA 94305dagrahn@stanford.edu

J. L. Dillon

Department of Civil and Mechanical Engineering, United States Military Academy, West Point, NY 10996

H. C. Heller

Department of Biology, Stanford University, Stanford, CA 94305

1

Corresponding author.

J Biomech Eng 131(7), 071005 (Jun 29, 2009) (7 pages) doi:10.1115/1.3156812 History: Received November 17, 2008; Revised May 06, 2009; Published June 29, 2009

Insulation reduces heat exchange between a body and the environment. Glabrous (nonhairy) skin surfaces (palms of the hands, soles of the feet, face, and ears) constitute a small percentage of total body surface area but contain specialized vascular structures that facilitate heat loss. We have previously reported that cooling the glabrous skin surfaces is effective in alleviating heat stress and that the application of local subatmospheric pressure enhances the effect. In this paper, we compare the effects of cooling multiple glabrous skin surfaces with and without vacuum on thermal recovery in heavily insulated heat-stressed individuals. Esophageal temperatures (Tes) and heart rates were monitored throughout the trials. Water loss was determined from pre- and post-trial nude weights. Treadmill exercise (5.6 km/h, 9–16% slope, and 25–45 min duration) in a hot environment (41.5°C, 20–30% relative humidity) while wearing insulating pants and jackets was used to induce heat stress (Tes39°C). For postexercise recovery, the subjects donned additional insulation (a balaclava, winter gloves, and impermeable boot covers) and rested in the hot environment for 60 min. Postexercise cooling treatments included control (no cooling) or the application of a 10°C closed water circulating system to (a) the hand(s) with or without application of a local subatmospheric pressure, (b) the face, (c) the feet, or (d) multiple glabrous skin regions. Following exercise induction of heat stress in heavily insulated subjects, the rate of recovery of Tes was 0.4±0.2°C/h(n=12), but with application of cooling to one hand, the rate was 0.8±0.3°C/h(n=12), and with one hand cooling with subatmospheric pressure, the rate was 1.0±0.2°C/h(n=12). Cooling alone yielded two responses, one resembling that of cooling with subatmospheric pressure (n=8) and one resembling that of no cooling (n=4). The effect of treating multiple surfaces was additive (no cooling, ΔTes=0.4±0.2°C; one hand, 0.9±0.3°C; face, 1.0±0.3°C; two hands, 1.3±0.1°C; two feet, 1.3±0.3°C; and face, feet, and hands, 1.6±0.2°C). Cooling treatments had a similar effect on water loss and final resting heart rate. In heat-stressed resting subjects, cooling the glabrous skin regions was effective in lowering Tes. Under this protocol, the application of local subatmospheric pressure did not significantly increase heat transfer per se but, presumably, increased the likelihood of an effect.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figure 1

Photographs of the experimental setup and experimental devices. Left panel: a subject clad in MOPP gear, balaclava, winter glove, and boot covers, and one hand in the experimental heat transfer device during postexercise rest in the experimental chamber (Tes=41°C). Right panel: two hands placed in the experimental devices (see Sec. 2 for description of devices). The external neoprene insulation covering the experimental device had been removed for the photograph to better display the details of the device.

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Figure 2

Tes versus time during recovery after exercise in thermally stressful conditions. Treatments: control (no cooling), heat extraction from one hand, and heat extraction from two hands (n=17). Heat extraction entailed the combined application of a heat sink to the glabrous skin of the hand and subatmospheric pressure to the entire hand (mean±SD). t-test results: (a) control versus one hand, p<0.001; (b) one hand versus two hands, p<0.005.

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Figure 3

Tes versus time during recovery after exercise in thermally stressful conditions; the effect of cooling one hand, with or without application of subatmospheric pressure. Left: group results n=12. Right: cooling only (no pressure differential) group data sorted according to effect and compared with the complete data set for one hand cooling with a pressure differential and no cooling. In eight subjects the response to cooling-alone resembled the response to cooling with subatmospheric pressure. In four subjects, the response to cooling-alone resembled the no treatment response.

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Figure 4

Tes versus time during recovery after exercise in thermally stressful conditions; the effect of cooling the various combinations of glabrous skin regions (n=8, mean±SD). FFH: foot, face, and hand cooling.

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