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Transcript
Cardiac Cycle: one complete heartbeat, consisting of the
contraction/relaxation of both atria, followed by the
contraction/relaxation of both ventricles. The average duration is
0.8 sec.
What are the events that occur during one heart beat?
The Cardiac Cycle: Definitions
Systole: phase of myocardial contraction (atrial systole, ventricular
systole); during systole, the pressure in a chamber is elevated
and blood is ejected
Diastole: phase of myocardial relaxation; during diastole, the pressure in a
chamber falls and the chamber fills with blood
Systole
Diastole
Cardiac cycle points to remember:
1.
The purpose of the myocardium is to contract to provide pressure for the
ejection of blood (systole) and to relax to reduce pressure and allow
filling (diastole).
2.
Blood moves from regions of high pressure to regions of low pressure.
3.
The contraction of the myocardium is coordinated by the cardiac
conduction system.
4.
The valves of the heart (atrioventricular and semilunar) ensure that blood
moves in a forward, not backward, direction.
The cardiac cycle
Event
Value
# cardiac cycles/minute
75
Duration of one cardiac cycle
0.8 second
Duration of
0.1 sec
atrial systole
Duration of atrial diastole
Duration of ventricular systole
0.7 second
0.3 second
Duration of
0.5 sec.
ventricular diastole
Duration of cardiac quiescence
(the atria and ventricles are in
diastole at the same time)
0.4 second
Note: the events of the cardiac cycle are traditionally described
in terms of the left heart. Pressure changes occurring in the
right heart are 1/5th as great as the changes in the left heart
The Cardiac
Pressure Curve
End Diastolic Volume
(EDV)
The volume of blood
received by a ventricle
during the period of
ventricular filling
End Systolic Volume
(ESV)
The volume of blood
remaining in a ventricle
after the period of
ventricular ejection
Ventricle Diastole
Passive ventricular filling
Active ventricular filling
Blood flow
From atrium into ventricle Contraction of atrium
pumps additional 2025% of blood
Pressures
Atrial>ventricular
Atrial>ventricular
Why? Atrial systole
Valve state
ECG
Heart Sound
Comments
A-V open (pressure in
atrium greater than
pressure in ventricle
Semilunar closed
(pressure in aorta >
pressure in ventricle
A-V open
Why? Atrial
pressure > than
ventricular pressure
Pre-P wave
P-wave
none
Semilunar -
Closed -pressure in
aorta > than
ventricle
none
End Diastolic volume
The volume of
blood received by
a ventricle during
the period of
ventricular filling
Ventricular Systole
Early Ventricular
diastole
Period of isovolumetric
contraction
Period of ejection
Ventricles begin to contract
– no volume change
Ventricle continue to
contract – blood ejected
into aorta
Ventricular >aorta
Ventricular pressure > atrial Atrial starting to rise
A-V closes (pressure in
ventricle is greater than
atrium)
Semilunar Closed -pressure in
aorta is still > than
ventricle
QRS
A-V closed (pressure in
ventricle>pressure in
atrium
Semilunar opens–
why?
Pressure in ventricle is
now > than aorta
T-wave
1st heart sound
Period of isovolumetric
contraction – all valves
closed, ventricular volume
does not change (an
isometric contraction?)
none
End-systolic
Volume
The volume of blood
remaining in a
ventricle after the
period of ventricular
ejection
Period of isovolumetric
relaxation
Mid Ventricular Diastole
a. The atria and ventricles are in diastole
b.
Atrial pressure is greater than
ventricular pressure
Thus, blood moves from atria into
ventricles through open AV valves
Note: the ventricles receives about
75%
of its final blood
volume during this time
Late Ventricular Diastole
a.
the atria contract and eject the
remaining volume of blood into the
ventricles
Note: the ventricles receive the
remaining 25%
blood
during atrial systole
The arteries during this entire time
period are losing
pressure as
blood circulates to smaller vessels
Ventricular Systole
a.
Ventricular pressure
as the ventricles contract
b. When ventricular pressure
is greater than atrial
pressure, the AV valves
close
c.
When ventricular pressure
is greater than arterial
pressure, the semilunar
valves open
and
blood is ejected into the
arteries
Isovolumetric Period of
Contraction:
period of time, during ventricular
systole, after the AV valves close
but before the semilunar valves
open, when ventricular volume
remains unchanged
Early Ventricular Disatole
Ventricular pressure falls during
ventricular diastole
When ventricular pressure is less
than arterial pressure, the
semilunar valves close
When ventricular pressure is
less than atrial pressure, the
atrioventricular valves open ;
the ventricles begin to fill
Isovolumetric Period of Relaxation
Period of time, during ventricular
diastole, after the semilunar valve
closes but before the AV valve
opens, when ventricular volume
remains unchanged
A Few Other Things ..
Dicrotic Notch:
A brief rise in arterial pressure
that results from arterial blood
rebounding off of newly closed
semilunar valves
End Diastolic Volume (EDV)
The total volume of blood that a
ventricle receives during its
filling period
End Systolic Volume (ESV)
The total volume of blood left in
a ventricle after ventricular
contraction
Stroke Volume (SV)
The total volume of blood that
ejected into arteries as a result
of ventricular contraction
E. Heart Sounds
There are two easily and consistently heard heart sounds:
Normal valves have two
characteristcs:
1. Unimpeded flow
2. Unidirectional flow
First Sound (S1)
Second Sound (S2)
Generated By
closure of the AV valves
closure of the
Sounds like
“lub”
“dup”
When heard
at the beginning of ventricular
systole
at the beginning of ventricular
diastole
semilunar
valves
F. Valve Abnormalities
Stenosis:
A narrowed valve
a significant amount of pressure must be generated
to eject blood though a narrowed valve
this can lead to:
1.
Increased residual volume of blood in a chamber
2.
Cardiac cell hypertrophy
3.
Low pulse pressure
Rheumatic mitral stenosis: note
thickened leaflets and shortened
chordae
Calcification of the aortic semilunar
valve
Note the turbulance
(red spirals) of the
blood as it flows
through the stenotic
aortic semilunar valve
It is the turbulance
that creates the
mumur
At which point in the cardiac cycle would you expect
to hear a murmur associated with
a. Stenosis of the mitral valve?
Ventricular diastole
b. Stenosis of the aortic semilunar valve?
Ventricular systole
Answer choices are:
Ventricular diastole
Ventricular systole
B. Insufficiency (Incontinence):
A valve that does not close properly
This can lead to:
1.
The backward flow of blood
2.
Increased volume of blood in the affected chamber
3.
Cardiac cell hypertrophy
4.
Low pulse pressure
Ruptured chords – mitral valve
prolapse secondary to a
Haemophilus infection
At which point in the cardiac cycle would you expect to
hear a murmur associated with
a. Insufficient mitral valve?
Ventricular systole
a. Insufficient aortic semilunar valve?
Ventricular diastole
Answer choices are:
Ventricular diastole
Ventricular systole
Causes of valve abnormalities include:
1.
Coronary atherosclerosis (papillary muscle dysfunction)
2. Rheumatic fever (most common cause, mitral valve)
3. Autoimmune diseases
4. Congenital malformations of valves
5. Connective tissue defects (eg, Marfan’s syndrome)
6. Aging (calcification)