Download Cardiovascular System

Cardiovascular system- L4
Faisal I. Mohammed, MD, PhD
Yanal A. Shafagoj MD, PhD
University of Jordan
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Cardiac Output
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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
University of Jordan
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Phases of the Cardiac Cycle
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Systole has three phases
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Isovolumic contraction phase
Rapid ejection phase
Reduced or slow ejection phase
Diastole has four phases
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Isovolumic relaxation phase
Rapid filling phase
Reduced or slow filling phase
Atrial contraction phase
Phases of the Cardiac Cycle
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Ventricular filling – mid-to-late diastole
 Intra-ventricular pressure is low as
blood enters atria and flows into
ventricles
 AV valves are open, then atrial systole
occurs
Phases of the Cardiac Cycle
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Ventricular systole
 Atria relax
 Rising ventricular pressure results in
closing of AV valves…→ S1
 Early phase of ventricular systole
(isovolumic) phase
 Ventricular ejection phase opens
semilunar valves →opening of the
valves is silent…no sound
Phases of the Cardiac Cycle
Isovolumetric relaxation – early diastole
 Ventricles relax
 Backflow of blood in aorta and
pulmonary trunk → closes semilunar
valves → S2
 Dicrotic notch – brief rise in aortic pressure
caused by backflow of blood rebounding off
semilunar valves
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Cardiac Cycle
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Systole - muscle stimulated by action potential
and contracting
Diastole - muscle reestablishing Na+/K+/Ca++
gradient and is relaxing
EKG - P - atrial wave
QRS - Ventricular wave
T - ventricular repolarization
Cardiac Cycle (cont’d)
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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
Ventricular Pressure and Volume Curves
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Diastole
Isovolumic relaxation
A-V valves open
Rapid filling
Diastasis - slow flow into ventricle
Atrial systole - extra blood in and this
just follows P wave. Accounts for less
than 25% of filling
Ventricular Pressure and Volume Curves
(cont’d)
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Systole
Isovolumic contraction
A-V valves close (ventricular pressure >
atrial pressure)
Aortic valve opens
Rapid Ejection phase
Slow ejection phase
Ejection Fraction
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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Aortic Pressure Curve
Aortic pressure starts increasing during systole
after the aortic valve opens.
Aortic pressure decreases toward the end of the
ejection phase.
After the aortic valve closes, an incisura occurs
because of sudden cessation of back-flow
toward left ventricle.
Aortic pressure decreases slowly during diastole
because of the elasticity of the aorta.
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Autonomic Effects on Heart
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Sympathetic stimulation causes increased HR and
increased contractility with HR = 180-200
and
C.O. = 15-20 L/min.
Parasympathetic stimulation decreases HR
markedly and decreases cardiac contractility
slightly. Vagal fibers go mainly to atria.
Fast heart rate (tachycardia) can decrease C.O.
because there is not enough time for heart to fill
during diastole….there is the so called maxHR
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Changes during Cardiac cycle
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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: 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.
Heart Sounds
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Heart Sounds
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Heart sounds
(lub-dup) are
associated
with closing
of heart valves
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
Cardiac Output: Example
CO (ml/min) = HR (75 beats/min) x SV
(70 ml/beat)
 CO = 5250 ml/min (5.25 L/min)
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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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Frank-Starling Law of the Heart
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Within physiological limits an increase in the
stretch of the muscle before it contracts
increases the force of contraction
An increase in the end-diastolic
volume→↑sarcomere length →↑ increases the
stroke volume →↑ejection fraction
Failed heart utilizes Frank-Starling law
Cardiac Output
Phases of the Cardiac Cycle
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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
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Agents/factors that decrease contractility
include:
 Acidosis
 Increased extracellular K+
 Calcium channel blockers
Thank You
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