226
CARDIOVASCULAR PHYSIOLOGY CONCEPTS
those produced on the left side of the heart
by aortic stenosis. Stenosis of the pulm onic
valve results in a pressure gradient across
that valve
during right ventricular
ejec-
tion, as w ell as a systolic murmur. Reduced
right ventricular stroke volum e decreases
left ventricular filling and stroke volum e,
w hich leads to activation of neurohumoral
com pensatory mechanism s. The right ven-
tricle hypertrophies, w hich contributes to
elevated filling pressures that are transmit-
ted back into the right atrium and system ic
venous circulation.
Tricuspid stenosis impairs right ventricular
filling and stroke volume, and elevates right
atrial and systemic venous pressures. Because
right ventricular output is reduced, left ven-
tricular stroke volume is also diminished,
which can trigger compensatory neurohu-
moral mechanisms. As with mitral stenosis,
there is a diastolic murmur.
Valve Regurgitation
Valvular insufficiency can occur with out-
flow valves (aortic or pulm onic) or inflow
valves (mitral or tricuspid). In this condi-
tion, the valve does not close completely,
which
permits
blood
to
flow
backward
(regurgitate)
across
the
valve.
Aortic
or
pulmonary
insufficiency
m ost
com m only
occurs through disease processes that alter
valve structure. Mitral and tricuspid valve
regurgitation can occur following rupture of
the chordae tendineae, following ischem ic
damage to the papillary m uscles, in response
to infective or degenerative disease of the
valve tissue, or when the ventricles are path-
ologically dilated (e.g., as occurs in dilated
cardiomyopathy).
AORTIC VALVE REGURGITATION
Aortic valve regurgitation causes blood to enter
the left ventricle from the aorta (backward
flow) during the time that the valve would
normally be closed. Because blood leaves the
aorta by two pathways (back into the ventricle
as well as down the aorta), the aortic pressure
falls more rapidly than usual during diastole,
thereby
reducing
aortic
diastolic
pressure
(Fig. 9.13, left panel). Ventricular (and aortic)
peak systolic pressures are increased because
there is an increase in stroke volume into the
aorta because of increased ventricular filling.
The increased systolic pressure and decreased
200
I
E
E,
0
100
m
m
0
CL
>
0
0
100
200
LV Volume (mL)
■ FIGURE 9.13 Changes in cardiac pressures and volumes associated w ith chronic aortic valve regur-
gitation in the absence of systolic failure. The le ft panel shows that during ventricular relaxation, blood
flows backwards from the aorta into the ventricle, causing a more rapid fall in aortic pressure (AP), which
decreases diastolic pressure and increases aortic pulse pressure; left atrial pressure
(LAP)
increases
because of blood backing up into the atrium as left ventricular end-diastolic volume and pressure
increase. An increase in ventricular stroke volume (because of increased filling) leads to an increase in
peak ventricular and aortic pressures; a diastolic murm ur is present between S2 and Sr The rig ht panel
shows the effects of aortic valve regurgitation
(red loop)
on the left ventricular
(LV)
pressure-volume
loop. End-diastolic volume and stroke volume are greatly increased, and there are no true isovolumetric
phases because blood flows across the valve whenever there is a pressure difference across the valve.
previous page 239 Cardiovascular Physiology Concepts  2nd Edition read online next page 241 Cardiovascular Physiology Concepts  2nd Edition read online Home Toggle text on/off