270
]. A. ]. STOLWIJK
ful for steady state studies. In man, steady state studies are made fairly
useless because of the close coupling between various body temperatures
whereas in animal studies, even with one control loop interrupted, other
control loops take over after only a small deviation of their signal temperatures and we no longer are dealing with an isolated component of the controlling system. In either case, simulation of such experiments with mathematical models will yield valuable insight.
In our current version of a thermoregulation model in man, we are
assuming that temperature signals come from the skin, from the brain stem
and from the muscle. There is no difficulty in deriving signals from other
locations, if desired. After integration these signals are used to cause appropriate changes in heat production, evaporative heat loss and blood flow.
These values, as modified by the controller system, are then used in the
calculation of heat flow rates and temperatures in the controlled system via
equations of the type given in (1).
All compartments are given a value TSET, a temperature at which the
output from the receptors is effectively considered to be zero. Deviations
from the set points are named ERROR as in (2).
ERROR (N) = T (N) - TSET (N)
(2)
ERROR (1) is the deviation of the brain temperature from its setpoint: a
negative value is then named SIG (1), a positive value is SIG (2). ERROR
(15) is the deviation of average skin temperature; if negative, this becomes
SIG (3); if positive SIG (4). Similarly, ERROR (16), the deviation in
average muscle temperature, is SIG (5) when negative and SIG (6) when
positive. Unless otherwise indicated, SIG (N) are all set to zero. The
physiological responses can now be expressed as combinations of signal
values SIG (N) and fixed coefficients which can be set to zero or to any
other value. The effector actions are represented by the symbols SWEAT,
CHILL, DILA T and STRIC. Appropriate fractions of each of these effector
actions are assigned to each of the compartments.
Blood flow, evaporative heat loss rates and metabolic heat production
are first set to their basal values and subsequently modified by the addition
of appropriate fractions of each of the effector actions. Both the head core
and trunk core are assigned an additional evaporative heat loss of 2 % of the
heat production due to work or shivering, reflecting the increased respiratory rate. Muscle compartments which have a variable metabolic rate are
given an addition in blood flow proportional to their extra metabolic rate,
thus reflecting the increased blood flow during exercise.
These newly developed values for heat production, evaporative heat
loss and blood flow are used in the computation of heat flows during the
next iteration interval.
]. A. ]. STOLWIJK
ful for steady state studies. In man, steady state studies are made fairly
useless because of the close coupling between various body temperatures
whereas in animal studies, even with one control loop interrupted, other
control loops take over after only a small deviation of their signal temperatures and we no longer are dealing with an isolated component of the controlling system. In either case, simulation of such experiments with mathematical models will yield valuable insight.
In our current version of a thermoregulation model in man, we are
assuming that temperature signals come from the skin, from the brain stem
and from the muscle. There is no difficulty in deriving signals from other
locations, if desired. After integration these signals are used to cause appropriate changes in heat production, evaporative heat loss and blood flow.
These values, as modified by the controller system, are then used in the
calculation of heat flow rates and temperatures in the controlled system via
equations of the type given in (1).
All compartments are given a value TSET, a temperature at which the
output from the receptors is effectively considered to be zero. Deviations
from the set points are named ERROR as in (2).
ERROR (N) = T (N) - TSET (N)
(2)
ERROR (1) is the deviation of the brain temperature from its setpoint: a
negative value is then named SIG (1), a positive value is SIG (2). ERROR
(15) is the deviation of average skin temperature; if negative, this becomes
SIG (3); if positive SIG (4). Similarly, ERROR (16), the deviation in
average muscle temperature, is SIG (5) when negative and SIG (6) when
positive. Unless otherwise indicated, SIG (N) are all set to zero. The
physiological responses can now be expressed as combinations of signal
values SIG (N) and fixed coefficients which can be set to zero or to any
other value. The effector actions are represented by the symbols SWEAT,
CHILL, DILA T and STRIC. Appropriate fractions of each of these effector
actions are assigned to each of the compartments.
Blood flow, evaporative heat loss rates and metabolic heat production
are first set to their basal values and subsequently modified by the addition
of appropriate fractions of each of the effector actions. Both the head core
and trunk core are assigned an additional evaporative heat loss of 2 % of the
heat production due to work or shivering, reflecting the increased respiratory rate. Muscle compartments which have a variable metabolic rate are
given an addition in blood flow proportional to their extra metabolic rate,
thus reflecting the increased blood flow during exercise.
These newly developed values for heat production, evaporative heat
loss and blood flow are used in the computation of heat flows during the
next iteration interval.