Page 14, Cardiac Performance, Dr. D. Penney


Increasing inotropicity alone (preload and afterload held constant) (Figure 2.05C) as in exercise or catecholamine infusion, increases stroke volume, and decreases end-systolic volume and usually end-diastolic volume as well. Because loop area is increased, stroke work is elevated (Figure 2.05).

Historically, the observation that end-diastolic volume decreased during exercise indicated that control of stroke volume was not primarily through the Frank-Starling mechanism, but rather due to enhanced contractility. Of course, preload, afterload and inotropicity usually all change to some degree in a given physiological situation.

Most recently, it has been found that the Frank-Starling mechanism becomes increasingly important in augmenting cardiac output with age; young people use it little, while aged individuals depend on it greatly.



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