CHAPTER 9 • CARDIOVASCULAR INTEGRATION, ADAPTATION, AND PATHOPHYSIOLOGY
225
and may impair filling (i.e., produces diastolic
dysfunction). This is shown in the pressure-
volume loop as an elevated and steeper filling
curve (see Figs. 4.5 and 9.9). Whether end-
diastolic volume is increased or decreased
depends on the changes in compliance and
filling pressure. Recall from Chapter 4 that
an acute increase in afterload, which initially
leads to an increase in end-systolic volume,
usually causes a secondary increase in end-
diastolic volume that helps to preserve stroke
volume. But in chronic aortic stenosis, this
secondary increase in preload often will not
occur because
of the
reduced
ventricular
compliance.
In summary, aortic valve stenosis is char-
acterized by a large pressure gradient across
the aortic valve during systole, a systolic ejec-
tion murmur, reduced stroke volume, ven-
tricular hypertrophy (reduced compliance),
increased left ventricular filling pressure, and
increased left atrial and pulmonary vascular
pressures.
MITRAL VALVE STENOSIS
Mitral valve stenosis increases the pressure gra-
dient across the mitral valve during ventricular
filling, which leads to an increase in left atrial
pressure and a reduction in left ventricular
filling pressure (Fig. 9.12, left panel). During
ventricular filling, turbulence caused by the
narrowed mitral valve causes a diastolic mur-
mur. In moderate-to-severe mitral stenosis,
reduced ventricular filling causes a reduction
in ventricular preload (both end-diastolic vol-
ume and pressure decrease) (Fig. 9.12, right
panel). This leads to a decrease in stroke
volume
(width
of
pressure-volume
loop)
through the Frank-Star ling mechanism, and
a fall in cardiac output and aortic pressure.
Reduced afterload (particularly if aortic pres-
sure falls) enables the end-systolic volume to
decrease slightly, but not enough to overcome
the decline in end-diastolic volume. These
changes will be influenced by neurohumoral
activation, which increases blood volume,
systemic vascular resistance, cardiac inotropy,
and heart rate.
In summary, mitral valve stenosis impairs
ventricular filling, which reduces preload and
therefore stroke volume. A diastolic murmur
is present, and left atrial and pulmonary vas-
cular pressures are elevated.
PULMONIC AND TRICUSPID VALVE
STENOSIS
Pulm onic stenosis produces changes to the
right side of the heart that are analogous to
200
CD
I
E
E,
0
i_
3
C/)
C/)
CD
100
200
Time
CD
I
3
c
n
c
n
0
1
_
CL
>
100
100
200
LV Volume (mL)
0
0
0
■ FIGURE 9.12 Changes in cardiac pressures and volumes associated w ith chronic mitral valve stenosis in
the absence of systolic failure. The le ft panel shows that during ventricular filling, left atrial pressure
(LAP)
exceeds left ventricular pressure
(LVP)
(the gray area represents the pressure gradient generated by the
stenosis); a diastolic m urm ur is present between S2 and S1. A ortic pressure (AP) is reduced by severe mitral
stenosis because of decreased cardiac output. The rig ht panel shows the effects of mitral valve stenosis
(red loop)
on the left ventricular (LV) pressure-volume loop. End-diastolic volume is reduced because of
impaired ventricular filling, and end-systolic volume may be slightly reduced because of reduced after-
load; therefore, stroke volume is reduced.
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