2007, Piran, Slovenia

Gravitational Physiology
THERMOREGULATORY RESPONSES TO COLD WATER
IMMERSION ARE NOT AFFECTED BY 35 DAYS OF
HORIZONTAL BED REST
Stelios Kounalakis 1,2 , Michail E. Keramidas 1,2 , Gianni Biolo 3 ,
Pietro E. di Prampero 4 , Marco Narici 5 , Rado Pisot 6 , Ola Eiken 7 and Igor B.
Mekjavic 1
1 Jozef Stefan Institute, Ljubljana, Slovenia;
2 National and Kapodistrian University of Athens, Greece;
3 Università di Trieste - Ospedale di Cattinara, Trieste, Italy;
4 MATI Centro di Eccellenza – Università di Udine, Udine, Italy;
5 Manchester Metropolitan University, Alsager Campus, Cheshire, UK;
6 Institute for Kinesiology Research, University of Primorska, Koper, Slovenia;
7 Swedish Defence Research Agency, Karolinska Institutet, Stockholm, Sweden
Contact person: igor.mekjavic@ijs.si
INTRODUCTION
We have previously investigated the post-exercise thermoregulatory responses during
immersion in 28°C water (Mekjavic et al., 2005) immediately after 35 days of
horizontal bed rest and following a full recovery within 5 weeks. In both trials
subjects were immersed in the bath with an end-exercise rectal temperature (Tre)
approximately 0.5 °C higher than the pre-exercise value. During the 100 min
immersion in a well-stirred bath of water maintained at 28°C, Tre decreased by as
much as 0.9°C. During this cooling phase we monitored the cessation of sweating at
the forehead, the onset of shivering thermogenesis as reflected in the oxygen uptake,
and the forearm-fingertip skin temperature gradient, an index of peripheral vasomotor
tone. We observed no effect on either the core temperature threshold or gain of the
sweating response. In contrast, there was a significant attenuation of the cold-induced
vasoconstriction and shivering thermogenesis, which we concluded was responsible
for the greater cooling rate of Tre following bed-rest.
The aim of the present study was to investigate whether the observed attenuation of
shivering and cold-induced vasoconstriction would prevail during a much greater
thermogenic drive, established by colder skin and core temperatures.
METHODS
Ten healthy male subjects with average (SD) age of 23.0 (1.7) yrs, height 181.2 (5.2)
cm, body mass 76.3 (9.0) kg, and V & O2max 4.1 (0.7) L·min -1 participated in the study.
Following a medical examination they were housed in a separate wing of the
Orthopaedic Hospital Valdoltra (Ankaran, Slovenia). Subjects remained in a
horizontal position for a 35-day period and were under 24-hour medical supervision
during the study. Prior to, and immediately after the bed rest, they participated in an
immersion in 15°C water for 60 min, or until their core temperature as measured
rectally (Tre) decreased to 35°C, or by 2°C from pre-immersion levels.
During the 10 minute pre-immersion rest period, and throughout the immersion phase
of the trial we monitored rectal temperature (Tre; MSR 12, Switzerland) 12 cm
beyond the anal sphincter, skin temperatures (MSR 12, Switzerland) from 4 sites
(arm, chest, thigh, calf), forearm (proximal) - fingertip (distal) temperature gradient
(ΔTdiff) as an index of cutaneous vasomotor tone (Rubinstein and Sessler, 1990), and
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