Final answer:
Increasing preload involves either lengthening the filling time during diastole or increasing venous return through venoconstriction. Preload can be decreased by raising heart rate to lower filling time or by inducing vasodilation to reduce venous return.
Step-by-step explanation:
To increase preload in the heart, which refers to the end-diastolic volume (EDV) that stretches the ventricles, two methods can be employed. One way is to increase the duration of ventricular diastole, allowing more time for the ventricles to fill. The other method is to enhance venoconstriction, which increases the return of blood to the heart, subsequently increasing the preload and stretching of the cardiac muscle. In contrast, to decrease preload, the heart rate could be increased to reduce the filling time, or conditions that lower venous return could be introduced, such as vasodilation.
According to Starling's Law of the Heart, an increase in preload, within physiological limits, leads to an increased contractility and stroke volume due to the greater initial stretch of the ventricular muscle fibers. While modifying preload, it's essential to maintain it within physiological limits to ensure efficient heart function.