Final answer:
Increased preload results in a shift of the pressure-volume loop to the right, indicating more blood within the ventricle at the end of diastole and enhanced contractility of the cardiac muscle. This increased ventricular filling leads to greater stroke volume in accordance with the Frank-Starling law, within physiological limits.
Step-by-step explanation:
The effect of increased preload on the pressure-volume loop involves enhancing the cardiac muscle contraction according to the Frank-Starling mechanism. When the preload or end-diastolic volume (EDV) increases, it leads to an increased stretch of the ventricular muscle fibers, thereby increasing their contractility and stroke volume (SV). A higher preload shifts the starting point of the pressure-volume loop to the right, indicating a higher volume of blood in the ventricle at the end of diastole. However, it's essential to note that this improved contractility is within physiological limits; beyond this, the effectiveness can decrease, leading to potential cardiac dysfunction.
Several factors can affect preload, including blood volume, venous return, and ventricular compliance. Increasing factors such as the volume of blood and venous return, or decreasing the resistance in veins, will result in a higher preload. This, in turn, leads to an increased pressure during ventricular systole and raises the stroke volume, as postulated by the Starling's Law of the Heart. Conversely, increasing afterload (resistance in the arteries) without adequate cardiac compensation can lead to a decreased blood flow. Factors that can affect afterload include blood vessel length and diameter, viscosity of the blood, and the overall pressure in the arterial system.