Human thermoregulation in the heat: predictive models of physiological conductance and sweat rate
Date
2015-02-09
Authors
Cohen, Marc Harry
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Abstract
The literature pertaining to models of human thermoregulation is
critically reviewed. It is concluded that none of the models
investigated can be used to predict the physiological response of
acclimatized men required to work in the heat for extended periods
of time, the reasons being: (i) physiological conductance (the
lumped parameter describing internal heat transfer) has not been
completely described in terms of all the variables effecting it
(ii) the dynamic nature of the sweat rate response has never been
mathematically described.
A composite block diagram model for human thermoregulation, based
on a single cylinder core and shell model of the controlled
system, is postulated as a feasible solution to the problem of predicting
physiological responses to work in the heat. The controlling
system, consisting of physiological conductance and sweat
rate, is singled out for thorough investigation.
Detailed experimentation was carried out on a single nude acclimatized
man over a wide range of environments (13,6°C dry-bulb,
9,2°C wet-bulb to 38,5°C dry-bulb, 36,5°C wet-bulb) and work rates
(resting, 60 W/m2 to exercising, 240 W/m2 ). Each experiment
lasted four hours. Physiological conductance (K) is expressed as
a sigmoidal function of a weighted body temperature driving signal
(Tmb ) and metabolic rate (M), such that for the same Tmb, K
increases with increasing M. The saturation level of K at low Tm b
is expressed as a linear function of M, the saturation level of K
at high Tmb, is expressed as an exponential function of M. Because
of the dynamic nature of the sweat rate response to a step change
in environmental conditions and/or work rate, basic engineering
control theory is used tc formulate a block diagram model for
thermoregulatory sweating. The model introduces a rational
approach to combining Tmb, local effect of skin temperature, sweat
gland fatigue, skin wettedness and their time histories.