76
CARDIOVASCULAR PHYSIOLOGY CONCEPTS
Outflow
Resistance
& Afterload
t Ventricular
Compliance
Î Atrial
Inotropy
\
Heart
Rate
' l
Ventricular
Inotropy
Venous
Pressure
/
\
Venous
Venous
Compliance
Blood Volume
i
Inflow
Resistance
• Total blood volume
• Venous return
FIGURE 4.12 Factors that increase ventricular preload.
5. Inflow Resistance. Elevated inflow resistance
(e.g., tricuspid valve stenosis; see Chapter
9) reduces the rate of ventricular filling and
therefore decreases ventricular preload.
6. Outflow Resistance. An increase in out-
flow resistance, as caused by pulmonic
valve stenosis (see Chapter 9) or elevated
pulmonary artery pressure
(pulmonary
hypertension), impairs the ability of the
right ventricle to empty, leading to an
increase in preload.
7. Ventricular Inotropy. In ventricular systolic
failure (see Chapter 9), when ventricular
inotropy is diminished, the ventricular
preload increases because of the inability
of the ventricle to eject normal volumes of
blood. This causes blood to back up in the
ventricle and proximal venous circulation.
Left ventricular preload is determined by the
same factors as for right ventricular preload,
except that the venous pressure is pulmonary
venous pressure instead of central (or tho-
racic) venous pressure, the inflow resistance is
the mitral valve, and the outflow resistance is
the aortic valve and aortic pressure.
CASE 4-1
Echocardiography reveals that the left ventricle of a chronically hypertensive patient is
significantly hypertrophied. Using left ventricular pressure-volume loops, describe how
end-diastolic pressure and volume and SV will be altered by the hypertrophy. Assume
no change in heart rate, inotropy, or aortic pressure.
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