Preload, contractility, and afterload as determinants of stroke volume during elevation of aortic blood pressure in dogs

Aortic blood pressure was raised at various end-diastolic volumes at high and low myocardial contractility, and after autonomic blockade. Elevation of aortic blood pressure elicited a stroke volume-increasing effect by raising end-diastolic volume (preload) and a stroke volume-reducing effect by raising afterload. Large end-diastolic volume and low myocardial contractility favoured a fall in stroke volume, whereas stroke volume rose during elevation of aortic blood pressure at high myocardial contractility, especially at small end-diastolic volume. The interactions of preload, contractility, and afterload on stroke volume are predictable from an analysis of ventricular function curves (relationship between stroke volume and end-diastolic volume).