2007, Piran, Slovenia

Acute and chronic heat exposure
UNCOUPLING PHYSIOLOGICAL RESPONSES TO PRE-COOLING
FROM PERCEPTUAL SENSATIONS
Luke F. Reynolds, Stephen S. Cheung
Dalhousie University, Halifax, Canada
Contact person: stephen.cheung@brocku.ca
INTRODUCTION
Over the past decade, research interest has arisen on the direct effects of temperature per se
on exercise capacity and tolerance in the heat. One model of this relationship proposes that
thermal inputs and perception of heat strain modulates the regulation of self-paced workload
to minimize heat storage. To further investigate the relationship between thermal perception
versus physiological responses, it would appear advantageous to uncouple the two inputs.
This has previously been difficult to achieve in laboratory or field settings, as subjects could
not be blinded to ambient conditions or to whether they were being cooled or not. Namely,
one potential research model would be to achieve a state of sham cooling, where subjects
have the conscious perception of cooling without any changes in core temperature.
Relative to the entire body, the head and neck comprises a small percentage (7-9%) of the
total body surface area. However, this area is particular efficient at dissipating heat and
sensitive to thermal stimulus. For example, the face can dissipate 30% of resting heat load and
20% during moderate to intense exercise. It is hypothesized that the head, and especially the
face has a high concentration of temperature sensitive nerve endings, making it more sensitive
to thermal stimulus and especially cold than other parts of the body. In work on individuals
with Multiple Sclerosis (MS), passive exposure to head and neck cooling was able to decrease
rectal temperature by 0.2 o C over 30 min (Ku et al. 1999), suggesting that the head and neck
may be a useful site for pre-cooling without exposing the entire skin surface to cooling.
The purpose of the present study was to investigate whether it is possible to use a head
cooling device to not only passively cool individuals by a small but significant amount, but
also to achieve a condition of sham cooling, where subjects had the perception of thermal
cooling but without actual physiological cooling.
METHODS
The current study is part of a larger study on the clinical efficacy of pre-cooling on symptom
relief and functional capacity in individuals with MS. Four females with definite MS and with
self-reported heat sensitivity completed the study. Participants were told that they would
receive 2 bouts of cooling and 1 trial where they would receive no cooling. It was not
specified that the cooling strength would be different.
Experimental conditions included: (1) No Cooling, (2) True Cooling, and (3) Sham Cooling.
The three measurements occurred at the same time of day over 7 days and participants were in
the early-mid follicular phase of their menstrual cycle. Upon arrival, participants were
equipped with a heart rate monitor (Polar Vantage XL, Polar Electro Oy, Finland), selfinserted
a core probe (Mon-A-Therm Core, Mallinkrodt Medical, St. Louis, USA) 15 cm
beyond the anal sphincter, and thermistors (Mon-A-Therm Skin, Mallinkrodt Medical, St.
Louis, USA) were attached to the shoulder, chest, thigh and calf with one layer of 3M
hypoallergenic surgical adhesive tape. Participants were instructed to sit quietly and rest for
20 min to acclimate to room temperature before donning the head and neck cooling hood
(Life Enhancement Technologies, Santa Clara, USA). Perceptual thermal sensations were
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