CHAPTER II: CARDIAC MECHANICS Asst. Prof. Dr. Emre Hamurtekin EMU Faculty of Pharmacy.
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Transcript of CHAPTER II: CARDIAC MECHANICS Asst. Prof. Dr. Emre Hamurtekin EMU Faculty of Pharmacy.
CHAPTER II: CARDIAC MECHANICS
Asst. Prof. Dr. Emre HamurtekinEMU Faculty of Pharmacy
1. CARDIAC CYCLE2. CARDIAC OUTPUT 3. DETERMINANTS of CARDIAC OUTPUT4. CARDIAC WORK
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• Cardiac cycle can be divided into seven phases:1.Atrial systole2.Isovolumic ventricular contraction3.Rapid ventricular ejection4.Reduced ventricular ejection5.Isovolumic ventricular relaxation6.Rapid ventricular filling7.Reduced ventricular filling
• Atrial systole is initiated by …………………... • Atrial systole follows the crest of P wave on the
ECG.• Atrial contraction forces a small additional blood
into the venticular chamber (atrial kick).
• Ventricular systole begins with isovolumic isovolumic ventricular contractionventricular contraction.
• In isovolumic ventricular contraction, when intraventricular pressure rises, mitral valve closes.
• In isovolumic ventricular contraction, aortic valve is still held closed by higher aortic pressure.
atrial excitation
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• In Rapid Ventricular Ejection Rapid Ventricular Ejection phase, aortic valve finally opens and blood exits the ventricle.
• In this phase, atrium relaxes and the blood starts to fill the atrium.
• In Reduced Ventricular Ejection Reduced Ventricular Ejection phase, ejection velocity decreases (reduced ejection).
• At the end of this phase, aortic valve is finally closed.
• Once the aortic valve is closed, Isovolumic Isovolumic Ventricular Relaxation Ventricular Relaxation period starts.
• In this period, LV volume is lowest.
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• Once intraventricular pressure drops below atrial pressure, mitral valve opens.
• Blood in the atrium starts to move into the ventricle in Rapid Ventricular Filling Rapid Ventricular Filling phase.
• In Reduced Ventricular Filling (Reduced Ventricular Filling (diastasisdiastasis) ) phase, atrium and ventricle are both fully relaxed.
• Arterial pressure continues to fall as blood flows into capillary beds.
• This phase typically disappears when HR increases.
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• LV does not empty completely during systole.• ESV is around 50 ml.• EDV - ESV EDV - ESV = = SV (stroke volume).SV (stroke volume).• SV is the amount of blood transferred from LV to
the arterial system during systole.• In healty person SV should be > 60 ml.• EF (ejection fraction) = SV \ EDV EF (ejection fraction) = SV \ EDV (normally
about 55% - 75%.• EF is an important measurement of cardiac
efficiency.• EF is used clinically to assess cardiac status in
patients with heart failure.
• CO (L/min) = HR CO (L/min) = HR x x SVSV• HR is established on the SA node and is controlled by ANS.• SV is dependent onSV is dependent on,
• LV preload• LV afterload• Contractility
• PreloadPreload: Muscle length before contraction begins. • Preload is related with the volume of blood entering the
chamber (EDVEDV)• AfterloadAfterload: The load against which a myocyte must shorten.• The principal component of afterload is arterial pressure.• ContractilityContractility: measure of a muscle’s ability to shorten
against a afterload.• Contractility equates with the cytoplasmic free Ca
concentration.
Ability of a muscle cell to develop force (contractility)
(+) inotropic agents(+) inotropic agents
-Epinephrine-Norepineprine-Digoxin
(-) inotropic agents(-) inotropic agents
-β- blockers-Ca channel blockers
Contractility equates with intracellular free CaCa concentration
SNS norepinephrine ββ-1 receptors -1 receptors cAMPcAMP PKA activationPKA activation
PKA activationPKA activation L - type Ca channelsL - type Ca channels, , Ca release channelsCa release channels, SERCA , SERCA
• Heart performs two kinds of work:I. Internal workII. External work
• Internal workInternal work:• Expended in «isovolumic contraction»• The force necessary to open the aortic and pulmonary
valves• Accounts for ˃ 90% of total cardiac workload.
• External work External work (pressure-volume work)(pressure-volume work):• Expended in transferring blood to the arterial system
against a resistance.• Accounts for ˂ 10% of total cardiac workload.