Journal of Applied Physiology, Vol 79, Issue 5 1736-1743, Copyright © 1995 by American Physiological Society
Human intramuscular temperature and heat flow transients at rest
T. Binzoni, E. Hiltbrand, B. Kayser, G. Ferretti and F. Terrier
Department of Radiology, Hopital Cantonal Universitaire de Geneve, Switzerland. tiziano@medsun.unige.ch
A general model for heat exchange, comprising the major models in the
literature, was developed. Temperature changes as a function of space and
time were determined in six resting humans (age 32.7 +/- 4.5 yr) during
temperature transients by magnetic resonance imaging (MRI), so that the
exact solution of the model was obtained. These results allowed application
of the model, e.g., the analysis of transient muscle heat flow changes,
which could not be assessed by previous steady-state analyses. A
microthermocouple was inserted in muscle vastus lateralis 2-3 cm below the
skin surface. The measured temperature was used for calibrating the pixel
intensity of a temporal series of transaxial magnetic resonance images
obtained with a spin echo sequence around the microthermocouple position.
After muscle temperature was increased by immersion in a controlled water
bath, MRI acquisition was performed while muscle temperature was
decreasing. Temperature maps relative to space and time inside a
homogeneous region of interest were reconstructed by neural networks,
showing specific temperature patterns. Subsequently calculated heat flows
(with negative sign) appeared to increase linearly as temperature
decreased, until a maximum was attained at a critical temperature, below
which dramatic consistent heat flow changes were found. In conclusion, MRI
is indeed a powerful technique, useful to study the determinants of muscle
temperature and heat flow changes in space and time.
