Cardiac Cycle 0207080 - Cardiac Cycle, Preload/Afterload,...

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Cardiac Cycle, Preload/Afterload, Inotropic State Rebecca Keller, PhD 262-8105 kellerRe@mail.amc.edu Review of Cardiac Anatomy Heart consists of 4 chambers: a. right atrium – receives blood from the superior and inferior vena cava, is highly distensible (compliant), and maintains a low pressure b. right ventricle – blood flows from the right atrium across the tricuspid valve into the right ventricle, walls are not as thick as the left ventricle, outflow tract is the pulmonary artery c. left atrium – blood flows from the lung to the left atria via pulmonary veins, highly compliant although less compliant than the right atrium, left atrial pressure is higher than right atrial pressure d. left ventricle – blood flows from the left atrium across the mitral valve and into the left ventricle, thick muscular walls generate high pressures during contraction, outflow tract is the aorta through the aortic valve e. tricuspid and mitral valves – also called AV valves, have fibrous strands (cordae tendinae) on the leaflets that attach to the papillary muscles 1
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Cardiac Cycle (Wiggers Diagram) - depicts changes in aortic pressure (AP), left ventricular pressure (LVP), left atrial pressure (LAP), left ventricular volume (LV Vol), and heart sounds during a single cycle of cardiac contraction and relaxation - changes are related in time to the electrocardiogram - Aortic pressure is measured by inserting a pressure catheter into the aorta from a peripheral artery, and the left ventricular pressure is obtained by placing a pressure catheter inside the left ventricle and measuring changes in intraventricular pressure as the heart beats - A single cycle of cardiac activity can be divided into two basic stages: Diastole and systole i. diastole, which represents ventricular filling and a brief period just prior to filling at which time the ventricles are relaxing ii. systole , which represents the time of contraction and ejection of blood from the ventricles - cardiac cycle is usually divided into seven phases 1. Atrial Systole : A-V Valves Open; Semilunar Valves Closed The p-wave of the electrocardiogram (ECG), which represents electrical depolarization of the atria, initiates contraction of the atrial musculature. As the atria contract, the pressure within the atrial chambers increases so that a pressure gradient is generated across the open atrioventricular (AV) valves, thereby 2
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causing a rapid flow of blood into the ventricles. Retrograde atrial flow back into the vena cavae is impeded by venous return (inertial effect) and by the wave of contraction ("milking effect") throughout the atria. However, atrial contraction does produce a small increase in venous pressure that can be noted as the "a-wave" of the jugular pulse. Just following the peak of the a-wave is the x-descent. Atrial contraction normally accounts for only about 10% of left
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This note was uploaded on 04/07/2008 for the course BMED 4200 taught by Professor Keller during the Spring '08 term at Rensselaer Polytechnic Institute.

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Cardiac Cycle 0207080 - Cardiac Cycle, Preload/Afterload,...

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