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Unformatted text preview: Lecture 20: Cardiovascular System - Cardiac Physiology Reading: chapter 9, section: mechanical events, pgs 315-320 (pgs 320-325, if using 5th edition) chapter 9, section: cardiac output and its control, pgs 320-326 (pgs 325-332, if using 5th edition) Mechanical Events of the Cardiac Cycle - The cardiac cycle consists of alternate periods of contraction and emptying (systole) and relaxation and filling (diastole). These events occur in both the atria and the ventricles. A well-defined sequence of changes in pressure, volume, electrical activity and valve activity occur during each cycle (Figure 9-17,9-18). The sequence is often described with respect to ventricular activity as a reference. Several key events of the cycle are defined below. end-diastolic volume - the volume of blood in the chamber at the end of diastole. This is equivalent to the maximum amount of blood that the chamber will hold during the cycle. isovolumetric ventricular contraction - period of time during contraction when the chamber remains closed, and therefore no blood can enter or leave. Chamber pressure increases during this period. end-systolic volume - the amount of blood remaining in the chamber at the end of systole when ejection is complete. stroke volume - the amount of blood pumped out of the chamber with each contraction. Equal to the end-diastolic volume minus the end-systolic volume. isovolumetric ventricular relaxation - period of time during relaxation when the chamber remains closed, and therefore no blood can enter or leave. Chamber pressure decreases during this period. ...
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- Fall '08