Heart As A Pump and Blood Vessels

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Heart As A Pump and Blood Vessels

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University of Southern California
Bisc 307l - General Physiology
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BISC 307L 2nd Edition Lecture 27 Current Lecture Pressure – Volume Changes in the Left Ventricle Y axis = pressure in L ventricle. X axis = volume of L ventricle. Start at point A – the left ventricle has completed its relaxation and has not yet begun to fill. Its pressure is at a minimum. Its volume is also at a minimum because the ejection phase just ended. The ventricles start to fill with blood and increase in volume from 65 to 135, between A and B. The volume of the L ventricle is increasing as it is filling, but over most of this time, the pressure in the left ventricle isn’t changing. At the tail end of this process, when the L atrium contracts, the boost in pressure and volume results in the additional filling of the LV, so you get to point B. Point B, which is the maximum volume the heart has, is called the end diastolic volume. Then, the ventricle begins contracting. As soon as it starts contracting, the atrioventricular valve closes. Between B until C, the pressure is building up to 80mmHg, but there is no change in volume. This is called the isovolumic ventricular contraction phase. B->C is like phase 3 in the last figure in the last set of notes. From B->C, the pressure builds due to the contraction, and from C->D there is ventricular ejection, which is phase 4 in the previous diagram in the last set of notes. Volume goes down from 135->65. At the end of systole, you have the ESV(end systolic volume) at point D. The difference between the ESV and EDV is the stroke volume, which is how much blood is ejected per cycle. So in D, we start the relaxation of the left ventricle, and the pressure starts to fall. The valve to the aorta closes, and as the heart relaxes, the pressure in the ventricles go down, and there is an isovolumic change in pressure (D->A). Until ventricular pressure falls below 4 or 5 mmHg down here, the AV valve to the left atrium is also closed. This is an isovolumic ventricular relaxation – no change in volume, just pressure going down, which is phase 5 in the previous diagram in the last set of notes. And then the cycle repeats. **There is a slide called the Wigger’s Diagram in this set of powerpoints – Herrera told us to study it ourselves and that it is a useful diagram that correlates to mechanical and electrical events during the cardiac cycle, but didn’t mention anything about it beyond that. Cardiac Output Cardiac output is one of the most important parameters in measuring heart health – it is the measure of how much blood is pumped out by either side of the heart per unit of time. It is equal to the heart rate x stroke volume, and is usually ~5L/minute. CO regulation is important, and accomplished by varying the heart rate, stroke volume, or both. Regulation of ...

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