13 14 Heart and Circulation I and II (1)

Preload preload is the load stretch filling on the

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Preload Preload is the load (stretch, filling) on the ventricle prior to ventricular ejection Preload is dependent on venous return to the ventricle Measures of Preload: End-diastolic volume, end- diastolic pressure, right atrial pressure Frank-Starling’s Law: An increase in preload leads to an increase in stroke volume. That is, greater filling of the ventricle leads to greater volume of blood that is ejected to the circulation
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Frank-Starling’s Law of the Heart Basic Mechanism of Frank-Starling’s Law : Length-force relations of cardiac muscle Functional Implication : The extent of ventricular filling is an important determinant of stroke volume - and therefore cardiac output.
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Afterload Definition : The load against which the LV ejects after the opening of the aortic valve Simple Measure of Afterload : mean arterial pressure For a normal heart , cardiac output is relatively insensitive to afterload up to 140 mmHg mean arterial pressure. For a failing heart , cardiac output is significantly reduced by an increase in afterload. For both normal and failing hearts , an increase in afterload leads to an increase in cardiac work and therefore oxygen consumption afterload
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Cardiac Contractility Definition : Contractile capability of the heart Index of Cardiac Contractility : ejection fraction Ejection Fraction = Stroke Volume / End-Diastolic Volume
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Enhancement of Cardiac Contractility by Sympathetic Stimulation (Family of Frank-Starling Curves) Increased contractility is associated with higher SV/EDV ratio
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Effects of Sympathetic Stimulation on Ventricular Contraction and Relaxation
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Mechanism of Sympathetic Stimulation-Induced Enhancement of Cardiac Muscle Contractility
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Summary of the Major Determinants of Cardiac Output (Preload) (Contractility)
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Heart Failure
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Prevalence of Heart Failure (From: Am. J. Med. 122: 713-723, 2009)
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Diastolic and Systolic Heart Failure Diastolic Heart Failure : Normal ejection fraction – major problem is abnormal ventricular filling (stiff heart) Systolic Heart Failure : Abnormal ejection fraction – major problem is abnormal ventricular ejection (weak heart)
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