12 Biomedical Engineering Fundamentals
587
more than 50% of thermal energy and about 20% by the skin and muscles,
whereas the contribution of the skin and muscles may reach to 90% during physical
work [34].
On the other hand, the heat loss is represented by heat radiation, heat convection,
and evaporation. The heat radiation and evaporation are proved more powerful
at room temperature and warm environment. The heat loss cannot be efficiently
realized by the proximal skin surface because its shape is too flat for efficient heat
transfer to the environment. Hence, the heat loss mostly occurs from distal body
parts such as fingers and toes which have high surface to volume ratio in order
to conduct heat to the environment. In other words, the body consists of a heatproducing core which regulates the temperature at 37 ◦ C homeostatically. The core
body temperature reflects a circadian variation of about ±0.6 ◦ C with a maximum in
the early evening nearly around 6 p.m. and a minimum during 3 a.m. The regulating
mechanisms involve a readjustment of the target temperature value of 37 ◦ C during
the whole day. This target value is instructed by the central nervous system of
the brain (hypothalamus region), while the actual value registration of core body
temperature by the thermal receptors is also carried out in hypothalamus region [34].
12.5.2 Parameter Behavior
The vital physiological phenomena of the heartbeat, respiration, blood circulation,
blood oxygenation, and body temperature represent specific changes in their reflexive and tonic behavior. The typical behavior and interrelations of the physiological
parameters are also a major concern in order to coordinate and integrate body
functions. The physiological parameter behavior with their mutual coordination
facilitates vital physiological functions, limited resources of body energy, limited
space and time in organs and cells for life-supporting functions, environmental
changes adaptation, adaptation to physical and mental stress, and regeneration task
of the body with sleep [34].
The behavior and coordination of the physiological parameters can be explained
with a feedback control loop represented in Fig. 12.36. The hypothesis behind the
control loop is that the central nervous controls the physiological phenomenon or
function through a quantitative feedback such as thermal, chemical, and pressure
receptors. The desired performance can be obtained by minimizing the error calculated with the difference between the target and actual value of the physiological
parameters. In this way, controlled body functions can be achieved with the help
of the central nervous system. In Fig. 12.36, the controller comprises neurogenic,
myogenic, and hormonal controls. The neurogenic control yields a fast response
with the help of the autonomic nervous system while as myogenic control through
muscle excitation. The slow response is obtained with hormonal control with the
release of hormones [34].
The cardiovascular system is an example of this feedback control system in
which when blood pressure drops below the normal value, the arterial stretch-
587
more than 50% of thermal energy and about 20% by the skin and muscles,
whereas the contribution of the skin and muscles may reach to 90% during physical
work [34].
On the other hand, the heat loss is represented by heat radiation, heat convection,
and evaporation. The heat radiation and evaporation are proved more powerful
at room temperature and warm environment. The heat loss cannot be efficiently
realized by the proximal skin surface because its shape is too flat for efficient heat
transfer to the environment. Hence, the heat loss mostly occurs from distal body
parts such as fingers and toes which have high surface to volume ratio in order
to conduct heat to the environment. In other words, the body consists of a heatproducing core which regulates the temperature at 37 ◦ C homeostatically. The core
body temperature reflects a circadian variation of about ±0.6 ◦ C with a maximum in
the early evening nearly around 6 p.m. and a minimum during 3 a.m. The regulating
mechanisms involve a readjustment of the target temperature value of 37 ◦ C during
the whole day. This target value is instructed by the central nervous system of
the brain (hypothalamus region), while the actual value registration of core body
temperature by the thermal receptors is also carried out in hypothalamus region [34].
12.5.2 Parameter Behavior
The vital physiological phenomena of the heartbeat, respiration, blood circulation,
blood oxygenation, and body temperature represent specific changes in their reflexive and tonic behavior. The typical behavior and interrelations of the physiological
parameters are also a major concern in order to coordinate and integrate body
functions. The physiological parameter behavior with their mutual coordination
facilitates vital physiological functions, limited resources of body energy, limited
space and time in organs and cells for life-supporting functions, environmental
changes adaptation, adaptation to physical and mental stress, and regeneration task
of the body with sleep [34].
The behavior and coordination of the physiological parameters can be explained
with a feedback control loop represented in Fig. 12.36. The hypothesis behind the
control loop is that the central nervous controls the physiological phenomenon or
function through a quantitative feedback such as thermal, chemical, and pressure
receptors. The desired performance can be obtained by minimizing the error calculated with the difference between the target and actual value of the physiological
parameters. In this way, controlled body functions can be achieved with the help
of the central nervous system. In Fig. 12.36, the controller comprises neurogenic,
myogenic, and hormonal controls. The neurogenic control yields a fast response
with the help of the autonomic nervous system while as myogenic control through
muscle excitation. The slow response is obtained with hormonal control with the
release of hormones [34].
The cardiovascular system is an example of this feedback control system in
which when blood pressure drops below the normal value, the arterial stretch-