Download 1 - ISpatula

Electrical Component
Phases of the Cardiac Cycle
Ventricular filling (mid-to-late diastole)
 Heart blood pressure is low as
blood enters atria and flows into
ventricles
 AV valves are open
 Atrial contraction - systole

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Phases of the Cardiac Cycle

Ventricular contraction
 Atria relaxation
 Rising ventricular pressure results
in closing of AV valves
 Early phase of ventricular systole
(isovolumic) phase
 Ventricular ejection phase opens
semilunar valves – ventricular filling
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Phases of the Cardiac Cycle

Ventricular relaxation
 Backflow of blood in aorta and
pulmonary trunk closes semilunar
valves
 Dicrotic notch – brief rise in aortic
pressure caused by backflow of blood
rebounding off semilunar valves
 Isovolumetric relaxation – early diastole
 Pressure lower than atria and AV valves
open
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Ventricular, Aortic and Atrial Pressures
0
0 .1
Time ( sec)
0 .3 0 .4 0 .5 0 .6 0 .7 0 .8
Aortic valve
closes
Dichrotic
notch
0 .2
Aortic
valve
opens
mmHg
120
Aorta
atrium
Pressure
100
Aort ic
80
60
Mitral
valve
closes
40
Mitral valve opens
20
Atrial
Vent ricular
0
a wave c wave
v wave
R
T
P
(a) ECG
1
4
8
Q
0.1
sec
Atrial
systole
0.3 sec
Ventricular
systole
120
0.4 sec
Relaxation
period
Atrial depolarization
2
Begin atrial systole
3
End (ventricular) diastolic volume
4
Ventricular depolarization
5
Isovolumetric contraction
6
Begin ventricular ejection
7
End (ventricular) systolic volume
8
Begin ventricular repolarization
9
Isovolumetric relaxation
9
Dicrotic wave
100
Aortic
pressure
5
80
6
(b) Pressure
(mmHg)
1
S
Left
ventricular
pressure
60
40
Left atrial
pressure
10
20
2
0
(c) Heart sounds
S1
S2
S3
S4
3 End (ventricular) diastolic volume
130
10 Ventricular filling
Stroke
volume
(d) Volume in
ventricle (mL)
60
7
0
(e) Phases of the
cardiac cycle
Atrial
contraction
Isovolumetric
contraction
UniversityIsovolumetric
of Jordan
Ventricular
ejection
relaxation
Ventricular
filling
Atrial
contraction
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Heart Sounds


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Auscultation – listening to heart sound via
stethoscope
Four heart sounds
 S1 – “lubb” caused by the closing of the AV
valves
 S2 – “dupp” caused by the closing of the
semilunar valves
 S3 – a faint sound associated with blood flowing
into the ventricles
 S4 – another faint sound associated with atrial
contraction
First Heart Sound (S1)
• Sudden closing of the mitral and
tricuspid valves during the onset of
systole will cause echo as a result of
blood oscillation and vibration of the
valves and walls of the ventricles.
• Loudest at the apex of the heart
• "lubb" of "lubb-dub"
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Second Heart Sound (S2)
• Sudden closing of the semilunar
valves at the end of systole caused
the sudden block of arterial blood
back into the ventricles. The elastic
recoil of the arteries cause the blood
to bounce forward which will vibrate
the blood, valves and ventricle walls.
•Best heard in the second thoracic
interspace just left and right of the
sternum (pulmonic area)
• Shorter duration than S1
• “dub" of "lubb-dub"
Heart Sounds
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5
Aortic Pressure Curve
o Aortic pressure starts increasing during
systole after the aortic valve opens
o Aortic pressure decreases toward the end
of the ejection phase
o After the aortic valve closes, an incisura
occurs because of sudden cessation of
back-flow toward left ventricle
o Aortic pressure decreases slowly during
diastole because of the elasticity of the
aorta
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Cardiac Cycle



ECG -
P - atrial wave
QRS - Ventricular wave
T - ventricular repolarization
Systole - muscle stimulated by action
potential and contracting
Diastole - muscle reestablishing
Na+/K+/Ca++ gradient and is relaxing
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6
Atrial Pressure

Atrial pressure waves (a-c-v waves)
a-wave - atrial contraction
c-wave – ventricular contraction
(A-V valves bulge)
v-wave - flow of blood into atria
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Ventricular Pressure and Volume Curves

Diastole
 Isovolumic relaxation
 A-V valves open (ventricular
pressure < atrial pressure)
 Rapid filling (first 1/3)
 Diastasis - slow flow into ventricle
 Atrial systole - extra blood in and
this just follows P wave (accounts
for less than 25% of filling)
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Ventricular Pressure and Volume Curves

Systole
 Isovolumic contraction
 A-V valves close (ventricular
pressure >atrial pressure)
 Aortic valve opens
 Rapid Ejection phase
 Slow ejection phase
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Ventricular Filling (Diastole)
Rapid filling phase
mmHg
Slow Filling Phase:
Diastasis
120
100
80
Aort ic
120 ml
60
40
Ventricular volume
50 ml
20
0
Stroke
volume
At rial
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Stroke Volume
• Stroke volume is the volume of blood
pumped out by the right/left ventricle in
one contraction.
• SV = end diastolic volume (EDV) end systolic volume (ESV)
– EDV = amount of blood collected in a
ventricle at the end of diastolic phase
– ESV = amount of blood remaining in a
ventricle after contraction
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Ejection fraction
• Fraction of the end-diastolic volume that
is ejected is called the ejection fraction
(EF) - usually greater than 55 %
• Ventricles empty during systole - the
volume decreases about 70 ml which is
called the stroke volume
EF = SV÷EDV
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Cardiac Output
• Is volume of blood pumped per minute by
each ventricle
• CO = volume of blood ejected from left (or
right) ventricle into aorta (or pulmonary trunk)
each minute
• CO = stroke volume (SV) x heart rate (HR)
• In typical resting male
5.25L/min = 70mL/beat x 75 beats/min
• Entire blood volume flows through pulmonary
and systemic circuits each minute
Ejection Fraction




20
End diastolic volume
= 125 ml
End systolic volume
= 55 ml
Ejection volume (stroke volume) = 70 ml
Ejection fraction = 70ml/125ml = 56%
(normally 60%)
 If heart rate (HR) is 70 beats/minute, what is
cardiac output?
 Cardiac output = HR * stroke volume
= 70/min * 70 ml
= 4900ml/min
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Maintain Flow (QIN = QOUT)
QIN
Vein
HEART
Aorta
QOUT
HEART
NORMAL
QIN
Aorta
Vein
QOUT
HEART
Vein
Aorta
QOUT
QIN
To maintain QIN = QOUT the heart must rapidly adjust its force of contraction on a
beat-to-beat basis. How does the heart do this?
FRANK – STARLING LAW
FRANK – STARLING LAW
Maintain Flow (QIN = QOUT)
QIN
QOUT
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Frank-Starling Mechanism




Within physiological limits the heart pumps all
the blood that comes to it without excessive
collection in the veins.
With increased stretch of cardiac muscle the
heart muscle contracts with more force
The actin and myosin filaments are brought to a
more optimal degree of overlap for force
generation
Stretch of the right atrial wall directly increases
the heart rate by 10 to 20%
Frank-Starling Law of the Heart

An increase in the end-diastolic volume




↑ sarcomere length
↑ increases the stroke volume
↑ ejection fraction
Failing hearts use the Frank-Starling
law
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Preload : the degree of stretch in the
heart before it contracts
Contractility: the forcefulness of
contraction of individual ventricular muscle
fibers
Afterload: the pressure that must be
exceeded if ejection of blood from the
ventricles is to occur
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Factors Affecting Stroke Volume
Preload – amount ventricles are
stretched by contained blood =EDV
 Contractility – cardiac cell contractile
force due to factors other than EDV
 Afterload – back pressure exerted by
blood in the large arteries leaving the
heart (Aortic pressure)

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Frank-Starling Law of the Heart
 Preload,
or degree of stretch, of cardiac
muscle cells before they contract is the
critical factor controlling stroke volume
 Slow heartbeat and exercise increase
venous return to the heart, increasing
SV
 Blood loss and extremely rapid
heartbeat decrease SV (↓Q)
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Autonomic Effects on Heart



Sympathetic stimulation causes increased HR
and increased contractility with HR = 180-200
and CO = 15-20 L/min.
Parasympathetic stimulation decreases HR
markedly and decreases cardiac contractility
slightly. Vagal fibers go mainly to atria
(hyperpolarization)
Fast heart rate (tachycardia) can decrease
CO because there is not enough time for
heart to fill during diastole
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Changes during Cardiac Cycle



Volume changes: End-diastolic volume, End-systolic
volume, Stroke volume and Cardiac output.
Aortic pressure: Diastolic pressure 80 mmHg, Systolic
pressure  120 mmHg (most of systole ventricular
pressure higher than aortic)
Ventricular pressure




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Diastolic  0
Systolic Lt. 120; Rt.  25 mmHg.
Atrial pressure: A wave =atrial systole, C wave=
ventricular contraction (AV closure), V wave= ventricular
diastole (AV opening)
Heart sounds: S1 = turbulence of blood around a closed
AV valves, S2 = turbulence of blood around a closed
semilunar valves.
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Phases of the Cardiac Cycle
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Factors that Increase Cardiac Output
CO = SV x HR
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Extrinsic Factors Influencing
Stroke Volume
 Contractility
is the contractile strength,
at fixed preload and afterload
 Increase in contractility comes from:
 Increased sympathetic stimuli
 Certain hormones (epinephrine)
 Ca2+ and some drugs
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Extrinsic Factors Influencing Stroke
Volume

Agents/factors that decrease contractility
include:
 Acidosis (H+)
 Increased extracellular K+
 Calcium channel blockers
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