What two factors predict the resistance offered by an arteriovenous fistula (AVF)?

The correct choice is based on understanding the fundamental principles of vascular resistance. The resistance offered by an arteriovenous fistula (AVF) is primarily determined by the diameter and length of the AVF. According to Poiseuille's law, the resistance to flow in a vessel is inversely related to the fourth power of the radius (or diameter) of that vessel. This means that even a small increase in diameter can lead to a significant decrease in resistance. Additionally, the longer the vessel (the length of the AVF), the greater the resistance encountered by the flow, as there is more surface area for friction to occur along the length of the AVF.

In contrast, the other options do not directly address the factors that fundamentally influence resistance in this context. Flow rates and pressure gradients are more related to the effects of resistance rather than the resistance itself. Proximity to the heart and vein size could influence flow dynamics but do not directly determine the resistance offered by the fistula. Aneurysm size and patient age are also unrelated to the inherent resistance characteristics of the AVF. Therefore, diameter and length are the critical factors in assessing the resistance of an arteriovenous fistula.