Year

1997

Degree Name

Doctor of Philosophy

Department

Department of Biomedical Science

Abstract

Human skin has afferent and efferent roles in thermoregulation, but neither is fully determined. This project examined regional sudomotor (sweat) power, then used mainly the sudomotor mechanism to examine regional cutaneous thermosensitivities.

Regional sudomotor power was examined during cycling in the heat (N=$). Despite large inter-individual variability, sweat rates (rhsw: ventilated capsules) elicited from the forehead and dorsal hand were higher than from other sampled regions (p<0.05), which was also consistent with the pattern of skin blood flow in upper-body regions during supine, thermoneutral rest (N=6; p<0.05). Inter- regional and inter-individual rhsw variability was unaffected (p>0.05) by a 5-day heat acclimation regimen, as was the distribution of sweating.

A technique was then evaluated for clamping mean skin (Tsk: 15 sites) and deep body (Tc: 3 sites) temperatures, for up to 3 hr, whilst manipulating the local skin temperature (Tskl) of discrete regions (274 cm2). Mean body temperature (Tb = 0.8*TC + 0.2*Tsk) was clamped for individual Tskl manipulations (within ±0.05°C) and for 3 hr (+0.09°C). Local muscle temperature was little affected (up to + 1.05°C at 3 cm). It was then possible to investigate cutaneous thermosensitivities in sudomotor control. Tsld was increased or decreased by 4.07°C (at. 10 min) from 36.28 ±0.08°C, or decreased from 40.36±0.43°C to 29.45±0.19°C (at 4 min), for each of ten regions: face, arm, forearm, hand, chest, abdomen, back, thigh, leg and foot (N=13). The ms w was sensitive to the rate of Tsk] change for cooling, but only to the displacement of Tskl for warming. The ms w responses were greatest within treatment patches (p<0.05), and at precisely contralateral sites (4-min cooling only; p<0.05), but were otherwise bilaterally equivalent (p>0.05). The findings support a dominant role by one thermal integrator, but also a possible spinal mediation. The regional nature of cutaneous thermosensitivity, heretofor undetermined, was examined using regional groupings (segments). Inter-segmental sensitivities were equivalent (p>0.05), with three clear exceptions. Firstly, facial sensitivity was high, for both rhsw and whole-body thermal discomfort. Secondly, warmth sensitivity was equivalently high for the face and torso, compared with limbs (msw only; p<0.05). Thirdly, local warm sensation sensitivities were equivalently high for the face and limb extremities, being higher than the torso or proximal limbs (p<0.05), yet the limb extremities often ranked as the least sensitive segment for influencing wholebody thermal discomfort and sweating.

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.