Journal of Applied Physiology, Vol 77, Issue 4 1617-1622, Copyright © 1994 by American Physiological Society
Efficiency function: improvement of classical bioheat approach
H. Brinck and J. Werner
Institut fur Physiologie, Ruhr-Universitat, Bochum, Germany.
In view of the complex vascular architecture and the intricate physical
heat transfer processes in the human body, convective heat transfer via the
blood is generally described by simple substitutional processes
("non-vascular models"). The classical "bioheat" approach of Pennes (J.
Appl. Physiol. 1: 93-122, 1948), defining the heat flow to or from the
tissue as being proportional to the product of perfusion rate and the
difference of arterial and tissue temperature, has been seriously
questioned after having been used for > 40 yr in many applications. In
our laboratory, we have at our disposal a complex three-dimensional
vascular model for the special case of tissue in a human extremity. This
was used to test the performance of simple nonvascular models. It turned
out that the Pennes approach may deliver acceptable results if the body is
in the thermoneutral zone or if heat stress acts uniformly on the whole
body. However, when cold stress or local hyperthermia is present,
unreliable results must be expected. As the vascular model is not generally
practicable because of its extreme complexity, we offer the efficiency
function concept as a simple way of correcting the classical bioheat
approach by factor multiplication. Efficiency function is determined as a
function of perfusion rate and tissue depth in a way that compensates for
the deficiencies of the Pennes bioheat term. The results are reasonable
compared with those of the vascular model and experimental results.
