2007, Piran, Slovenia

Gravitational Physiology
THE EFFECTS OF BED-REST ON THERMAL COMFORT AND
CUTANEOUS THERMAL SENSITIVITY.
Daniel (Wolowske) Yogev 1 , Rado Pisot 2 , Ola Eiken 3 & Igor B. Mekjavic 1
1 Department of Automation, Biocybernetics and Robotics, Jozef Stefan Institute,
Ljubljana,
2 Institute for Kinesiology Research, University of Primorska, Koper, Slovenia;
3 Swedish Defence Research Agency, Karolinska Institutet, Stockholm, Sweden.
Contact person: daniel.wolowske@ijs.si
INTRODUCTION
Thermal studies in spaceflights as well as experimental bedrests (BRs) show that
although maintenance of normothermia is not jeopardized, some thermoregulatory
responses, particularly after exercise, are attenuated. Exercise-induced heat loss
responses (sweating and vasodilatation) and heat production responses (immersioninduced
shivering) were shown to be modified after BR (Mekjavic et al. 2005,
Fortney et al. 1998, Lee et al. 2002 and Crandall et al. 1994). Changes in the
efficiency and/or sensitivity of these autonomic responses were suggested to
contribute to the elevation in core temperature observed in spaceflights and in BR
experiments (Ertl et al. 2000, Fortney 1987 and Greenleaf 1989). Theoretically, such
thermal imbalance can develop as a result of inappropriate behavioural
thermoregulatory responses due to altered thermal sensation (i.e. the ability to sense
thermal stimuli) or changes in the perception of thermal comfort. Changes in thermal
comfort and thermal sensation during hypokinesia (Panferova 1976) and experimental
BR (Mekjavic et al. 2005, Fortney et al. 1996) have been reported in previous studies,
however, the effects on behavioural responses is not yet clear. Thus, the aim of the
present study was to assess the effects of BR on behavioural thermoregulatory
responses and on cutaneous thermal sensitivity.
METHODS
Ten healthy males (age 22.3 ± 2.2 years) participated in the study. They were tested
on day 1 and day 22 of an experimental bed-rest in the Orthopaedic Hospital
Valdoltra, Ankran, Slovenia. Subjects were tested at identical time of the day in a
temperature controlled room adjacent to the BR dormitories. A supine position was
maintained throughout the experiment. Subjects refrained from large meals, caffeine
containing drinks and cigarette smoking 2 hours prior to testing. After 10 min of
habituation to the room temperature (~26°C) two thermal sensitivity tests (cold and
warm) were performed using a Middlesex Thermal Testing System (MTTS, Howe
Institute, Canvey Island, Essex, UK). Thermal stimuli to the skin were provided by a
Peltier element thermode positioned on the volar side of the right forearm between the
elbow and the wrist. Thereafter, Skin temperature sensors (thermistors, YSI 409AC,
YSI Inc., OH, USA) were attached (toe, calf, thigh, abdomen, chest, fingertip,
forearm, arm) and subjects donned a WPS. The WPS was designed to allow the
subject control over the temperature of water perfusing the suit by a remote-control.
The starting temperature was set to 27°C (perceived as slightly uncomfortably cold)
for 5 minutes. Then it was programmed to fluctuate in a sinusoidal manner between
27°C and 42°C at 2°C min -1 . Subjects were instructed to repetitively interfere with the
cooling or warming of the WPS whenever it reached a slightly uncomfortable level
(i.e. threshold of their thermal comfort zone; TCZ) by pushing a button on the remote
controller. Subjects were instructed to continuously regulate the temperature of the
WPS to achieve maximal thermal comfort during the entire 60 minute period. The
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