CHAPTER 4 • CARDIAC FUNCTION
63
Dias
Sys
Dias
I- - - - - ►M- - - - - - - - - - - - - - - - - - - H- - - - - - - - - - - - - - - - - - - - - - - - - - - - M
Phase:
1
2
3
4
5
6
7
■ FIGURE 4.2 Cardiac cycle. The seven phases of the cardiac cycle are (?) atrial systole; (2) isovolumetric
contraction;
(3)
rapid ejection;
(4)
reduced ejection; (5), isovolumetric relaxation;
(6)
rapid filling; and
(7) reduced filling. Sys, systole;
Dias,
diastole;
AP,
aortic pressure;
LVP,
left ventricular pressure;
LAP,
left
atrial pressure; a,
a
wave;
c, c
wave;
v,
v wave;
x, x
descent;
X, x
descent; y,
y
descent;
LV,
left ventricle;
ECG,
electrocardiogram;
LVEDV,
left ventricular end-diastolic volume;
LVESV,
left ventricular end-systolic
volume,
S -S 4,
four heart sounds.
chambers increase; this drives blood from the
atria, across the open AV valves, and into the
ventricles. Retrograde atrial flow back into the
vena cava and pulmonary veins is impeded
by the inertial effect of venous return and by
the wave of contraction throughout the atria,
which has a “milking effect.” Atrial contrac-
tion produces a small transient increase in left
and right atrial pressure that is called the “a
wave.” The
a
wave is also reflected proximally
into the venous vessels (i.e., pulmonary veins
and vena cava). On the right side of the heart,
this produces the
“a
wave” of the jugular
pulse. This can be observed when a person is
recumbent and the jugular vein in the neck
expands with blood, which permits pulsa-
tions to be visualized.
Atrial contraction normally accounts for
only about 10% of left ventricular filling
when a person is at rest and the heart rate
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