Download Cardiac Cycle

Cardiac Cycle
Dr. Wasif Haq
Introduction
• Cardiac events that occur from beginning of one
heartbeat to the beginning of the next.
• Inversely proportional to heart rate.
• Consists of systole & diastole.
• Systole: Period of contraction.
• Diastole: Period of relaxation, heart fills with blood.
Some Essential Concepts
• Delay between the impulse passage and actual
contraction.
• Whenever the pressure in one region falls, blood will
flow into lower region pressure from higher region
pressure.
• Valve distal to high pressure region open.
• All valves closed in “Iso” states.
Phases of Cardiac Cycle
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Consists of 4 phases
1. Period of rapid filling of ventricles.
2. Period of isovolumic/isometric contractions.
3. Period of ejection.
4. Period of isovolumic/ isometric relaxation.
1. Rapid Filling of Ventricles
• Ventricular pressure falls after systole, pushing
blood from atria into ventricle.
• A.V. valve open causing filling of ventricles with
blood.
• Rapid filling consists of 3 portions/parts; 1/3 rapid
filling occurs( 80% of atrial blood without
contraction of atria), 2/3 some quantity of blood
flows, 3/3 atrial contraction occurs (causing
remaining 20% of blood to flow as well)
2. Isovolumic/ Isometric Contractions
• All valves closed (A.V. and semilunar valves)
• Some delay before opening of semilunar
(pulmonary & aortic valves) needed to build
sufficient pressure to open these valves.
• Ventricular fibers are contracting, but no
volume change inside the ventricle because
of closure of both the valves.
3. Period of ejection
• When ample pressure has been built in
ventricle(>80 mm Hg in left ventricle & > 8 mm Hg
in right ventricle), contraction occurs to eject blood
into arteries.
• Two phases; 1. Period of rapid ejection (70% of
blood emptied), followed by 2. Period of slow
ejection (remaining 30% blood ejected).
• Semilunar valves (aortic & pulmonary) open.
4. Isovolumic/Isometric relaxation
• All valves closed.
• After systole, increased pressure in arteries force
closure of semilunar (aortic & pulmonary) valves,
A.V. valves are also closed at this time, preventing
any volume change inside ventricle.
• Ventricular fibers relax during this phase.
Volumes
• End systole volume: Residual volume of blood in
each ventricle at end of contraction/systole. Usually
50 ml.
• End diastole volume: Filled volume of blood prior
to contraction 110-120 ml.
• Stroke volume output: Amount of blood pumped
by heart with each heartbeat.70 ml.
• Stroke volume= End diastolic volume- End systolic
volume
Electrocardiogram, Atrial
Pressure Changes,
Ventricular Volume,
Ventricular pressure
curve, aortic pressure
curve & heart sounds.
Electrocardiogram
• Graphic tracing of variations in electrical potential
caused by excitation of heart & detected at body
surface.
• Consists of P, QRS complex, T and U wave.
Waves Significance
• P waves represent ‘atrial depolarization’ , wave
appears before atria actually contract.
• Q.R.S. Complex represent ‘ventricular
depolarization’, occurs slightly before ventricular
depolarization.
• T wave represent ‘ventricular repolarization’, occurs
before the termination of ventricular contraction.
• U wave represent ‘Purkinjee fibers repolarization’,
not always present.
P wave= Atrial depolarization, Q.R.S. complex=
Ventricular depolarization, T wave= Ventricular
repolarization, U wave = Purkinjee fibers repolarization
Atrial Pressure Changes
• a wave represents atrial contraction, increasing atrial
pressure.
• c wave represents regurgitation of blood from
ventricles into atrium due to sliding/closure of A.V.
valves towards atrium due to increased ventricular
pressure.
• v wave represents the flow of blood from atria to
ventricle after ventricles stop contracting.
Aortic Pressure Changes
• Opening of aortic valve: Rise in left ventricular
pressure upon ventricular contraction (Q.R.S.)
causes aortic valve opening, pressure in aorta will
rise to 120 mm Hg.
• Closing of aortic valve: After ventricular systole,
aortic valve close, causing pressure dissipation
slowly to 80 mm Hg before next ventricular
contraction.
Ventricular Pressure Changes
• During ventricular systole, the ventricular pressure
increases which causes closing of A.V. valve ( c
wave in atrial pressure changes) and opening of
aortic valve, pumping blood to the systemic
circulation.
Ventricular Volume Changes
• The ejection of blood from ventricle during systole
(aortic valve opening & A.V. valve closure) causes
drop in ventricular volume, followed by rapid filling of
ventricles (A.V. valve open & aortic valve closure).
Phonocardiogram
• 1st heart sound: A.V. valve close, semilunar valves open,
systole begins. “Lub”
• 2nd heart sound: Semilunar valve close, A.V. valve
opens, systole finishes. “Dub”.
• 3rd heart sound: Rapid flow of blood from atria into
ventricles, mitral valve is open, normal in children but in
adults, may mark pathology.
• 4th heart sound: Filling of ventricles by atrial systole, not
normal.
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