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CARDIOVASCULAR PHYSIOLOGY CONCEPTS
velocity, and SV at a given preload and
afterload.
*
Ventricular afterload can be estimated
by ventricular wall stress, which is
the product of ventricular pressure
and ventricular radius divided by the
ventricular wall thickness. Increased
afterload decreases the velocity of
fiber shortening during contraction,
which decreases the SV.
*
Inotropy is the property of a cardiac
myocyte that enables it to alter its
tension development independent of
changes in preload length. Increased
inotropy enhances active tension
development by individual muscle
fibers and increases ventricular
pressure development, ejection
Preload, afterload, and inotropy are
interdependent, meaning that a change
in one usually leads to secondary
changes in the others.
Myocardial oxygen consumption can
be calculated using the Fick Principle,
in which oxygen consumption equals
the product of the CBF and the
arteriovenous oxygen difference.
Myocardial oxygen consumption
is strongly influenced by changes
in arterial pressure, heart rate, and
inotropy; it is less influenced by changes
in SV.
REVIEW QUESTIONS
For each question, choose the one best
answer:
1.
During the phase of rapid ventricular
filling,
a. S4 may sometimes be heard.
b. The aortic valve is open.
c. The mitral valve is open.
d. Ventricular pressure is higher than
aortic pressure.
2.
A patient with valve disease undergoes car-
diac catheterization to compare vascular
and intracardiac pressures against normal
values. Which of the following is found in
a heart with normal valve function?
a. Aortic diastolic pressure is less than
pulmonary artery systolic pressure.
b. Left ventricular end-diastolic pressure
is less than mean right atrial
pressure.
c. Mean left atrial pressure is normally
greater than mean right atrial pressure
by <10 mm Hg.
d. Pulmonary artery diastolic pressure is
less than mean right atrial
pressure.
3.
Right ventricular preload is increased by
which of the following?
a. Decreased atrial contractility
h. Decreased blood volume
c. Decreased heart rate
d. Decreased ventricular compliance
4.
A 78-year-old female patient with a his-
tory of left ventricular failure complains
of difficulty breathing when lying down.
Which of the following occurs to the
cardiac muscle fibers that can lead to an
increase in right ventricular output and
pulmonary congestion when this patient
lies down?
a. Active tension development increases,
h. Degree of muscle shortening is dimin-
ished.
c. Preload decreases.
d. Velocity of shortening decreases.
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