2007, Piran, Slovenia

Environmental Ergonomics XII
Igor B. Mekjavic, Stelios N. Kounalakis & Nigel A.S. Taylor (Eds.), © BIOMED, Ljubljana 2007
Invited presentation
266
REGIONAL DIFFERENCES IN HUMAN ECCRINE SWEAT
SECRETION FOLLOWING THERMAL AND NON-THERMAL
STIMULATION.
Nigel A.S. Taylor, Christiano A. Machado-Moreira
Human Performance Laboratories, University of Wollongong, Wollongong, Australia.
Contact person: nigel_taylor@uow.edu.au
INTRODUCTION
In a previous communication (Taylor, 2000), we have shown, under open-loop conditions,
that the skin has a generally uniform thermosensitivity. That is, with the exception of the face,
sensory awareness and the feedback-effector relationship for sweating was surprisingly
similar when body surfaces were presented with equivalent thermal stimuli (Cotter and
Taylor, 2005).
However, within the closed-loop state, there are many interactions between the cutaneous and
central thermosensitive tissues. In fact, warm- and cold-sensitive hypothalamic neurons
receive cutaneous, spinal and other central thermoafferent feedback, and these not only
modify the firing rate of hypothalamic neurons, but also affect their sensitivity to core
temperature changes. Thus, while open-loop experiments provide elemental detail pertaining
to the characteristics of discretely-controlled thermoafferent signals, they do not necessarily
inform us concerning the interaction of central and peripheral thermoafferents within closedloop
systems, either during steady states or thermal transients.
Therefore, the focus is this communication will be upon regional variations in human effector
function during both endogenous and exogenous (passive) thermal loading, but with feedback
loops closed (operating). The effector function of interest is eccrine sweat secretion, and we
shall briefly overview this topic with respect to thermal and non-thermal stimulations prior to,
and following thermal adaptation.
THERMAL STIMULATION
Sweat gland density: Eccrine gland density may powerfully affect segmental differences in
thermal sweating. Kuno (1956) suggested that, during the first two years of life, the number of
sweat glands present in adulthood is determined, with local climate influencing this process.
Knip (1977) provided supporting evidence, but these data require experimental verification.
While Szabo (1962) estimated that humans have about 3 million eccrine sweat glands, it has
been demonstrated that the average gland density is inversely related to body surface area
(Thompson, 1954; Kuno, 1956; Szabo 1962, 1967), with regional surface area growth during
adolescence reducing local gland density, while the gland count remains stable.
Thompson (1954) investigated active sweating using exercise and heating, and counted glands
at 11 sites using the plastic-impression technique. However, the most extensive analyses of
European skin specimens were performed by Szabo (1962, 1967), using surgical and biopsy
samples taken from 350 donors (N=66 for the present comparisons). A large Asian cadaveric
sample (N=74; Hwang and Baik, 1997) indicated lower gland density than reported by Szabo
(1962). Data from all three studies are contained in Table 1.