Cardiac Performance, Dr. D. Penney

Table 2.01. Similarities / Differences between Increased Preload and Afterload, Pressure-Volume changes, Incidence, Mechanism, and Consequences.

Comparison Increased Preload Increased Afterload

Similarities Increased tension on muscle fibers (related to pressure and volume) Increased tension on muscle fibers (related to pressure and volume

Pressure-volume changes Primarily an increase in volume (= volume load) Primarily an increase in pressure (= pressure load)

Incidence At the end of ventricular diastole During ventricular ejection

Mechanism Increased end-diastolic volume (heart failure, aortic insufficiency, etc.) Increased output resistance (constriction, etc.)

Consequence Increased product of mean ejection pressure and stroke volume; Increased stroke work Increased mean ejection pressure; Decreased stroke volume; Little change in stroke work

Comparison	Increased Preload	Increased Afterload
Similarities	Increased tension on muscle fibers (related to pressure and volume)	Increased tension on muscle fibers (related to pressure and volume
Pressure-volume changes	Primarily an increase in volume (= volume load)	Primarily an increase in pressure (= pressure load)
Incidence	At the end of ventricular diastole	During ventricular ejection
Mechanism	Increased end-diastolic volume (heart failure, aortic insufficiency, etc.)	Increased output resistance (constriction, etc.)
Consequence	Increased product of mean ejection pressure and stroke volume; Increased stroke work	Increased mean ejection pressure; Decreased stroke volume; Little change in stroke work

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