What causes passive hyperemia?

Passive hyperemia is primarily caused by a problem with venous outflow. When there is an obstruction or impairment in the veins that prevents blood from flowing out of a particular area, it leads to an accumulation of blood in the capillaries and surrounding tissues. This condition causes the affected area to become engorged with blood, resulting in passive hyperemia.

In contrast, venous patency refers to the open and unobstructed state of veins, which would not lead to hyperemia because blood would be able to flow freely. Increased capillary perfusion indicates a rise in blood flow through the capillaries, which usually would not result in passive hyperemia but rather active hyperemia. Decreased capillary perfusion suggests a reduction in blood flow to the tissues, which would not lead to an increase in blood volume and therefore wouldn't cause passive hyperemia either. Thus, the correct answer emphasizes the importance of proper venous drainage in the maintenance of normal blood flow and tissue perfusion.