Cardiac Cycle Dr. Wasif Haq. Introduction Cardiac events that occur from beginning of one heartbeat...
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![Page 1: Cardiac Cycle Dr. Wasif Haq. Introduction Cardiac events that occur from beginning of one heartbeat to the beginning of the next. Inversely proportional.](https://reader035.fdocuments.in/reader035/viewer/2022062322/5697bfeb1a28abf838cb8197/html5/thumbnails/1.jpg)
Cardiac Cycle
Dr. Wasif Haq
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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.
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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.
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Phases of Cardiac Cycle• 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.
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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)
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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.
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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.
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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.
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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
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Electrocardiogram, Atrial Pressure Changes,
Ventricular Volume, Ventricular pressure
curve, aortic pressure curve & heart sounds.
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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.
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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.
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P wave= Atrial depolarization, Q.R.S. complex= Ventricular depolarization, T wave= Ventricular
repolarization, U wave = Purkinjee fibers repolarization
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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.
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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.
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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.
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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).
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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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