2007, Piran, Slovenia

Acute and chronic heat exposure
PHYSIOLOGICAL AND COGNITIVE FUNCTION WHEN AUXILIARY
COOLING IS USED DURING AN EXERCISING HEAT STRESS.
Joanne N. Caldwell, Nigel A.S. Taylor
Human Performance Laboratories, University of Wollongong, Wollongong, Australia
Contact person: nigel_taylor@uow.edu.au
INTRODUCTION
When exposed to environmental heat stress, one’s ability to perform physical and mental
tasks can be compromised. In relation to a helicopter pilot, a slight decrement in flight
performance can result in devastating consequences. Previously, Froom et al. (1993) found
environmental heat stress elevated pilot error, whilst Caldwell et al. (2005) have described
impaired flight simulator performance during progressive hyperthermia. Such changes can
reflect reduced cognitive function, and Faerevik and Reinertsen (2003) have shown that heat
stress can contribute to deficits in both vigilance and multi-choice reaction time. Presumably,
the use of biological and chemical (BC) protective clothing will exacerbate this state.
Notwithstanding these observations, the literature does not provide a consensus concerning
the interaction of heat strain and cognitive function. This state may result from experimental
design limitations. For example, the quantification of, and control over the thermal
environment, and the resultant thermal strain, are often poorly addressed. In this regard, one
could consider both static and dynamic states, since thermoreceptor feedback possesses such
information. In the former case, and to the best of our knowledge, the impact of elevated and
clamped core and shell temperatures on cognitive function has rarely been considered
(Caldwell et al. 2005). This is important since, only when thermal strain is controlled, can one
be certain that it is the thermal energy content per se, and not thermal transients that affect
cognition. Furthermore, one must choose suitably sensitive cognitive-function indices, so that
the affects of various thermal treatments can be determined.
Accordingly, this project had two aims. First, the experimental design and cognitive-function
measures were chosen to optimise the identification of an interaction between thermal strain
and cognitive function during uncompensable heat stress, whilst wearing biological and
chemical protective clothing. Second, assuming an interaction, the effectiveness of an
auxiliary cooling system, as a possible means of reducing cognitive and physical performance
decrements, was evaluated.
METHODS
Eight males (27.1 SD 6.2 y; 80.0 SD 8.4 kg; 179.2 SD 6.4 cm) completed trials involving 120
min of low-intensity exercise (total metabolic rate ~180 W: semi-recumbent cycling), with a
2-min rest after every 13 min of work. Subjects wore the standard combat uniform (insulation
0.29 m 2 K.W -1 ), a liquid-cooling garment (Cool Tubesuit, Med-Eng, Ottawa, Canada), and the
Australian Defence Force biological and chemical ensemble, including over boots, gloves and
face mask.
Trials differed in the environmental conditions (temperate versus hot-dry), and the activation
state of the liquid-cooling garment (active versus inactive), and were administered in a
balanced order: (i) trial one: temperate environment (control: 20ºC, 30% relative humidity),
inactive liquid cooling; (ii) trial two: hot-dry environment (48ºC, 20% relative humidity),
inactive liquid cooling; and (iii) trial three: hot-dry environment (48ºC, 20% relative
humidity), active liquid cooling. In the heat, a substantial radiant heat source was also applied
(infra-red lamps ~750W.m -2 ). Subjects consumed 200 mL of water (at room temperature)
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