Page 30 - Biomedical Engineering and Design Handbook Volume 1, Fundamentals

MODELING OF BIOMEDICAL SYSTEMS 7
Respiration, sensible Core (blood flow)
heat loss in the lungs

Convection

Convection
Heater air Air space Skin
Evaporation

Convection
Conduction
Radiation Convection

Wall Mattress

Free convection Conduction
& radiation
Surrounding Foundation
FIGURE 1.2 A lumped parameter model of the infant-incubator dynamics used by Simon et al.
(1994) to simulate the effect of various control modes in a convectively heated infant incubator.
Infant’s core and skin are modeled as two separate compartments. The incubator air space, the incu-
bator wall, and the mattress are treated as three compartments. Heat interactions occur between the
core (infant’s lungs) and the incubator air space through breathing. Skin-core heat interactions are
predominantly due to blood flow to the skin. Heat transfer between the infant’s skin and the incuba-
tor air is due to conduction and convection. Heat transfer from the skin to the mattress is via conduc-
tion, and heat transfer to the wall is via radiation from skin and convection from the air.

model of Simon et al. (1992) to evaluate the efficacy of air control, skin, control, and fuzzy logic
control which incorporates both skin and air temperatures.
Compartmental models have been used to model particle dynamics. The growing number of cases
of lung diseases, related to the accumulation of inhaled nonsoluble particles, has become a major
problem in the urban population. Sturum (2007) has developed a simple multicompartment model
for the clearance of nonsoluble particles from the tracheobronchial system (Fig. 1.3). While most of
the particles are rapidly transported toward the pharynx by the beating celia, the particles caught in
between celia in the highly viscous gel layer (compartment 1) may enter the low viscous sol layer
(compartment 2) via diffusion. From the sol layer, they could enter the epithelium (compartment 5)
and eventually enter the regional lymph node (compartment 6) or enter the blood circulation.
Alternatively, they could be captured by the macrophages (compartment 4) in any of these layers and
could reach the regional lymph node or the blood circulation (compartment 6) or the gastrointestinal
tract (GIT; compartment 3). Macrophages could release phagocytosed particles into any of these lay-
ers. In addition, the particles could defuse among all three layers (gel, sol, and epithelium) in both
directions. Sturum (2007) has derived model equations based on the diffusion of particles and other
modes of transport.

1.2 ELECTRICAL ANALOG MODELS OF CIRCULATION

Electric analog models are a class of lumped models and are often used to simulate flow through the
network of blood vessels. These models are useful in assessing the overall performance of a system
or a subsystem. Integration of the fluid momentum equation (longitudinal direction, in cylindrical