Phystut10 - Cardiovascular Physiology II Andrew MacDonald...

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Cardiovascular Physiology – II Andrew MacDonald [email protected]
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An ECG is the sum of all of the  electrical events in the heart, both  depolarizing and repolarizing  events.  Such electrical events can be detected  by external electrodes placed on  the surface of the skin.  This can be picked up because body  fluids and tissues are good  conductors of electricity.  Hence,  the conduction from the heart  passes through the various layers  to the surface and is ultimately  picked up by these electrodes.  P QRS T waves  P Q R S T
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It can be used to tell you numerous details about  the function of the heart, including… Heart Rate Effects of Drugs Extent and location of myocardial damage.  Extent and type of disturbances of rhythm or  conduction. 
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Cardiac Cycle:  It describes all of the  electrical and mechanical events in the  heart.  The two phases of the cardiac cycle  are diastole ( dialation;  relaxation) and  systole ( contraction). Intervals (waves & segements) ….. segements (baseline portion)…. waves (deflection from baseline).
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The ECG broken down…
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1) Atrial Systole –  The artia contract and force the remaining 20-30% of the blood into  the ventricles (EDV), this value goes up during exercise or periods of physical  exertion.  2) Early Ventricular Systole (isovolumic ventricular contraction) –  There is no change in  ventricular blood volume.  However, the blood is pushed from the apex (bottom of the  ventricles) up towards the atrioventricular valves, slamming the shut.  This prevents  blood from flowing back into the atria and creates the “lub” sound when listening to  the heartbeat with a stethoscope.  3) Ventricular Systole (Rapid ventricular ejection) –  The force of contraction by the  ventricles becomes high enough to push open the semi-lunar valves, injecting blood  into the arterial system.   4) Early Ventricular Diastole (isovolumic ventricular relaxation) –  As the ventricles begin  to relax the blood in the arteries starts to flow backwards, slamming shut the cusp-like  semi-lunar valves, the closing of these valves creates the “dub” sound when listening  to the heartbeat with a stethoscope. 
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