Biomedical Engineering Reference
In-Depth Information
4.3 During diastole, heart chambers experience
(a) contractions that push blood into the downstream chamber
(b) a decrease in pressure, associated with muscle relaxation
(c) an opening of the left and right semilunar valves
(d) an increase in intracellular calcium
4.4 Discuss the differences between the cardiac muscle and skeletal muscle. Why are the
action potentials different in these two types of muscle?
4.5 Do the chordate tendineae play an active role in heart valve motion? What is the purpose
of these structures?
4.6 You are sitting outside on a warm day and are losing a great deal of fluid volume through
sweat. You decide to have your blood pressure taken and find that it is higher than nor-
mal. Why is this?
4.7 If your alarm clock wakes you up and you rise rapidly, why may you feel light-headed?
Under other conditions, such as voluntary waking without an alarm clock, this does not
occur, why?
4.8 A patient with congestive heart failure (severe myocardial infarction) has swollen ankles
and feet. What is the relationship between heart failure and fluid loss from the vascular
system?
4.9 A patient has an ECG and the physician finds that there are two P waves, followed by the
QRS complex and then the T wave. What is a possible reason behind this?
4.10 What are the principle valves in the heart and what are their functions?
4.11 Describe the salient aspects of the cardiac cycle.
4.12 Under normal physiological conditions, the pressure-volume relationship for the heart is
described by Figure 4.4 . Approximate the work associated with the left ventricle under
these conditions. Also, what is the cardiac work associated with a patient that is experienc-
ing high blood pressure, whose phase 1 starts at 2 mmHg and ends at 8 mmHg. Phase 2
ends when the left ventricular pressure reaches 110 mmHg, and at this point the aortic
valve opens. The maximum pressure associated with phase 3 reaches 175 mmHg and ends
at 125 mmHg, and follows a similar path as described in Figure 4.4 . Phase 4 closes the
work loop. Assume that the volumes under the disease condition remain the same.
4.13 Discuss the rates of change experienced in the left ventricular volume filling rate during
the cardiac cycle. Would this change during a disease condition?
4.14 A patient has a murmur in his ventricle that produces a loud gushing sound at the begin-
ning of systole. Which valve is most likely causing this sound and what is a possible rem-
edy for this murmur?
4.15 Calculate and plot the radial and circumferential stress distribution in the left ventricle at
the end of systole (p
80 mmHg; assume that the ventricle is a spherical shell). The inner
radius of the heart is 3.2 cm and the outer radius of the heart is 3.8 cm. The external pres-
sure surrounding the heart is
5
1 mmHg. Under a disease condition where the heart mus-
cle thickens, calculate the radial and the circumferential stress distribution in the left
ventricle at the end of systole and at peak systole. Under these conditions the pressure
remains the same, but the inner wall radius is 3 cm and the outer wall radius is 4.2 cm.
Compare this to normal conditions and comment.
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