Abstract:
In this study, a computational model of the human thermoregulatory system is developed
to predict the temperature distribution within tissues, on the skin and the arterial net-
work. It is based on an anatomically accurate whole human body geometry comprising
various tissue structures, organs and its vascular network. The governing equations that
couple energy transfer between the blood and surrounding tissues were implemented
in OpenCMISS, an open-source computational library that provides an environment
to utilise the nite element method (among other specialised numerical methods) to
solve partial di erential equations in complex bioengineering problems. Moreover, an
open standard framework built using the XML mark-up language known as CellML
was used to impose appropriate regulatory or control actions and update heat transfer
mechanisms accordingly. The framework was also used to prescribe di erent types of
boundary conditions as it is primarily used to solve di erential-algebraic equations.
An extensive literature review is included in this thesis to provide an overview
of the existing mathematical models used for studying the thermoregulation of
the human body. The review covers the strengths, limitations and scope of ap-
plications of these models.
The computational model was formulated by coupling the bioheat equation describing
the di usion of heat in three-dimensional tissue structures with the energy equation that
is responsible for advection and di usion of heat along the one-dimensional blood
ow
in the arterial network. It can simulate the heat exchange between the body surface
and surrounding environment due to conduction, convection, radiation and evapora-
tive cooling or moisture transfer.
Furthermore, it is capable of simulating blood
ow under di erent conditions which is
essential for evaluating heat exchange between the blood and surrounding tissues. This
functionality of the model allows us to investigate how physiological conditions in the
arterial network in
uence the human thermal system and a ect its performance. Functionally the model is organised into two subsystems. The passive subsystem pri-
marily deals with various modes of heat transport within tissues, between tissues and
blood (arterial system and perfusion) and between the body and the surrounding en-
vironment. The governing equations that mathematically describe the passive subsys-
tem are based on the laws of conservation. The active subsystem, on the other hand,
prescribes physiological phenomena in the body, namely, shivering, sweating, vasodila-
tion and vasoconstriction and facilitates maintaining the body core temperature. These
physiological activities are based on empirical formulations from previous studies.
The blood
ow and heat transfer included in the passive system was simulated using
OpenCMISS and the active system was implemented by using CellML capabilities that
enable to input controlling parameters and prescribe and update the boundary conditions
to OpenCMISS (passive system). The model results were veri ed against closed-form so-
lutions obtained for topologically simple domains and validated against published exper-
imental data acquired under controlled conditions. In the latter case, a reasonably good
agreement was seen between the model predictions and experimental observations.
The structure of the model allows for investigation of the thermoregulatory responses
of the human body under a multitude of ambient environmental conditions. Further-
more, it would be possible to investigate temperature distribution in the vital organs
and skin that can be used to diagnose heat-related conditions and make informed de-
cisions to plan suitable treatments.
The models capability of simulating the human thermoregulatory system with the abil-
ity to obtain realistic skin and internal temperature distribution was demonstrated by
considering a number of exposure scenarios. These included neutral condition, high
and low temperatures. In all cases, local skin temperature distributions were eval-
uated. The e ect of body shape and distribution of the thermophysical properties
were also investigated.
An important aspect of the current model development is that an open-source
code and libraries were used in this thesis research. As such, any contribution
made through this study allows other researchers to modify, improve and extend
the model for other applications.