OCT 2009Dr Nyoman W / Dr DENNY AGUSTININGSIH1 THE CARDIAC CYCLE What is the cardiac cycle. The cardiac cycle is the sequence of events that occur when the heart beats. There are two phases of this cycle: DiastoleDiastole - Ventricles are relaxed. SystoleSystole - Ventricles contract.

OCT 2009DENNY AGUSTININGSIH2 Electrocardiography Atria Ventricles TWO SEPARATE PUMPS

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OCT 2009DENNY AGUSTININGSIH5 Heart Sounds are Produced by the Closing of the Valves Normal heart sounds are produced when valves snap closed: LUB-DUP LUB = closing of AV valves: beginning of systole DUP = closing of semilunar valves: end of systole Abnormal valve sounds: – Leakage of valve -> swishing sound (murmur) – Narrowing of valve (stenosis) -> high pitched sound

OCT 2009DENNY AGUSTININGSIH6 Heart sounds:

OCT 2009DENNY AGUSTININGSIH7 Ventricular Volumes End Diastolic Volume-(EDV)‏ – volume in ventricles at the end of filling End Systolic Volume- (ESV)‏ – volume in ventricles at the end of ejection Stroke volume (EDV-ESV)‏ – volume ejected by ventricles Ejection fraction – % of EDV ejected (SV/EDV X 100%)‏ – normal 50-60%

OCT 2009DENNY AGUSTININGSIH8 Cardiac Output Normally about 5 liters/min The cardiac output per minute (CO) is the product of the size of a single output, the stroke volume (SV), and the heat rate (HR) in beats/minute: – CO = HR X SV – = 70 beats/min X.07 liters/beat = 5 liters/min

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OCT 2009DENNY AGUSTININGSIH10 Factors Affecting Cardiac Output Rate: – Factors affecting HR – Last topics Rhythm – Sinus rhythm from SA node – Arrhythmia

OCT 2009DENNY AGUSTININGSIH11 Factors Affecting Cardiac Output Preload – Equal to EDV – Depends on Venous Return – Frank-Starling Law – Contractility Afterload – TPR

OCT 2009DENNY AGUSTININGSIH12 VENOUS RETURN

OCT 2009DENNY AGUSTININGSIH13 Muscle pump

OCT 2009DENNY AGUSTININGSIH14 Frank-Starling Law of the Heart Relationship between EDV, contraction strength, and SV. Within physiologic limits the heart will pump all the blood that returns to it without allowing excessive damming of blood in veins

OCT 2009DENNY AGUSTININGSIH15 Mechanism of Frank-Starling Increased venous return causes increased stretch of cardiac muscle fibers. (Intrinsic effects)‏ – increased cross-bridge formation – increased calcium influx both increases force of contraction – increased stretch on SA node increases heart rate

OCT 2009DENNY AGUSTININGSIH16 Extrinsic Control of Contractility Contractility: – Strength of contraction at any given fiber length. Depends upon sympathoadrenal system: – NE and Epi produce an increase in contractile strength. + inotropic effect: – More Ca 2+ available to sarcomeres.

OCT 2009DENNY AGUSTININGSIH17 TPR Total Peripheral Resistance: – Impedance to the ejection of blood from ventricle. – Afterload. In order to eject blood, pressure generated in the ventricle must be greater than pressure in the arteries. – Pressure in arteries before ventricle contracts is a function of TPR. SV inversely proportional to TPR. – Greater the TPR, the lower the SV.

OCT 2009DENNY AGUSTININGSIH18 RV wall cerscent LV wall 3x thicker cylindrical Interventricular septum

OCT 2009DENNY AGUSTININGSIH19 Cardiac output distribution