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The cardiac cycle
May 17
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The cardiac cycle
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The cardiac events that occur
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Each cycle is initiated
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by Spontaneous generation of AP in the
SAN.
There is delay of more than 1/10
second
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from the beginning of one heartbeat
to the beginning of the other.
between passages of cardiac impulses
from the atria into the ventricles.
This delay allows the atria
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to contract ahead of the ventricles.
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The cardiac cycle:
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Cardiac cycle consists of
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period of relaxation (diastole)
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during which the heart fills with blood,
followed by a period of contraction
(Systole)
Blood normally flows
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continually from the veins into the
atria.
75% before the atria contract.
Atria contraction causes addition
25% of ventricular filling
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Ventricular filling
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During ventricular systole
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large amount of Blood accumulate
in the atria.
Immediately after systole
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Ventricular pressures fall
Moderately increase pressure's in
the atria
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push the A-V valves open
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and allow blood to flow rapidly into the
ventricles
(period of rapid filling of ventricles).
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Ventricular Filling
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This period lasts
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During the middle 1/3
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for about the first 1/3 of diastole
only small amount of blood flows
from atria to ventricles.
During the last 1/3 of diastole
atria contract
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Ventricular emptying
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Immediately after Ventricular
contraction begins
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Ventricular pressure abruptly raises
causing A-V valves to close.
Additional 0.02 – 0.03Sec.
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Is required for the ventricles
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to push semi lunar valves open.
During this period contraction is
occurring
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to build up sufficient pressure,
but no emptying.
This period is called Isometric or
Isovolumic contraction
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Ventricular emptying
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When the Lt ventricular pressure
rises
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70% of emptying
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slightly above 80mmHg,
and Rt ventricular pressure
slightly above 8mmHg.
Semilunar valves open
Blood begins to pour out of the
ventricles
occur in the first third of ejection.
30% in the next two third.
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Ventricular emptying
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At the end of systole,
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For another 0.03 – 0.06Sec.
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ventricular relaxation begins suddenly,
allowing the intraventricular pressure to
fall rapidly.
Semilunar valves close
The ventricular muscle continues to relax
even though the volume does not change,
giving rise to the period of Isovolumic or
Isometric relaxation.
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Ventricular emptying
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The intraventricular pressures fall
rapidly
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back to their low diastolic level,
then A- V valve open
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to begin a new cycle, of ventricular
pumping.
End diastolic volume 110 – 120mls
Stroke volume ≈ 70mls
End systolic volume, 40 – 50mls
Ejection fraction, about 60%
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Ventricular pressure (mmHg)
60 -
20 -
Isovolumetric contraction
Isovolumetric relaxation
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120-
50
120
Ventricular volume (ml)
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Heart Sound
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Two are normally heard through a stethoscope
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during each cardiac cycle.
The first is a low, slightly prolonged “lub”
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fist sound
caused by vibrations set up by the sudden closure of
the mitral and tricuspid valves
at the start of ventricula systole
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Heart Sound
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The second is a shorter, high-pitched “dup”
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A soft, low-pitched the end of ventricular systole.
A soft, low-pitched third sound is
heard
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second sound
caused by vibrations associated with the end of ventricular
systole.
about one-third of the way through
diastole
in many normal young individuals.
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It coincides with the period of rapid ventricular filling
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and probably due to vibrations set up by the inrush of blood.
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Heart Sound
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A fourth sound can sometimes be heard
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immediately before the first sound
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when atrial pressure is high
or the ventricle is stiff
in conditions such as ventricular hypertrophy
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. It is due to ventricular filling
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rarely heard in normal adults.
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Heart sounds
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Standard areas of auscultation
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Aortic area – second intercostal
space Rt
Pulmonary area – second
intercostal space Lt
Mitral area – apex
Tricuspid area – fourth intercostal
space Rt
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