Biomedical Engineering Reference
In-Depth Information
4.24
The coronary arteries (~6-mm diameter and ~5 cm in length) supply the heart
muscle with oxygenated blood and nutrients. When they are obstructed, for
example 50% by area, not enough blood gets to the heart. Bypass surgery is
used to create a parallel flow around the obstruction and restore blood flow.
Before the bypass, the pressure
P
in
at the beginning of the coronary arteries is
90 mmHg, the pressure
P
out
at the end of the coronary arteries is 83 mmHg,
and the blood flow through the coronaries is 40 mL/min. Density and viscosity
(
) of blood are 1,060 kg/m
3
and 0.03 Poise (
μ
=
0.003 kg/m.s), respectively.
(a) What is the coronary arterial resistance?
(b) If the resistance of the bypass channel is 25% of the coronary arterial
resistance, what is the combined resistance of the coronary arteries and the
bypass channel?
(c) Assuming that the pressures
P
in
and
P
out
do not change when the bypass
is added, what is the blood flow to the heart with the bypass in place (in
mL/min)?
(d) Are the flows laminar in obstructed and unobstructed arteries?
4.25
During a period of relative inactivity, Janet is losing
300 kJ of enthalpy every
hour. This is due to the difference in metabolic and digestive waste products
leaving the body and the raw materials ingested and breathed into the body.
Janet is also losing heat to the surroundings given by
Q
−
T
0
), where
A is the body surface area (roughly 1.8 m
2
),
T
s
is the skin temperature (nor-
mally 34.2°C),
T
0
is the temperature of the body surroundings, and
h
is the
heat transfer coefficient. Assume that the typical values of
h
for the human
body are 8 kJ/(m
2
h°C) when fully clothed, a slight breeze blowing condition,
and 64 kJ/(m
2
h°C) when nude and immersed in water.
=
hA
(
T
s
−
(a) Assuming Janet's body as a continuous system at steady state, write an
energy balance on the body.
(b) Calculate the surrounding temperature for which the energy balance is
satisfied (i.e., at which Janet would feel neither hot nor cold) when Janet is
clothed and when Janet is immersed in water wearing a bikini.
(c) Comment on why Janet feels colder on a windy day than on a day when
the temperature is the same but there is no wind.
4.26
In order to perform a transplant operation, a surgeon wants to reduce the
patient's body temperature to 30°C. This is to be done by routing the blood
through a chiller. Assume that the blood leaving the chiller is cooled to 25°C,
how long will this take for a 70-kg patient?
4.27
A micro-organism is growing aerobically on glucose. When the overall growth
is written as glucose consumption kinetics, the following stoichiometry is
obtained:
6
H
12
O
6
+
1.473O
2
+
0.782NH
3
0.909C
4.4
H
7.3
N
0.86
O
1.2
+
3.854H
2
O
+
2CO
2
Based on this equation, determine the respiratory coefficient quotient for this
organism. Using the Weir equation, determine the energy expenditure.
