Page 7, Cardiac Cycle, Dr. D. Penney


Not all of the blood in the heart is ejected during a cardiac cycle. Even utilizing the systolic reserve volume as during enhanced inotropicity, there remains a residual volume which cannot be ejected. The portion of blood ejected during one cardiac cycle is referred to as the ejection fraction. It is obtained by dividing stroke volume by end-diastolic volume (see Definitions),. Two-thirds (0.67) is a normal value of Ef.

Likewise, the heart can be filled to a greater extent by making use of the diastolic reserve volume, as is done in the Frank-Starling mechanism. Making use of both systolic reserve and diastolic reserve volumes, maximal stroke volume is achieved. Heart function is similar to lung function in this regard. By increasing both stroke volume and heart rate over rest values, cardiac output in excess of that at rest Cardiac Reserve can be called upon (Figure 1.04).




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