Final answer:
Plaque buildup in an artery causes a reduction in its radius, which in turn decreases blood flow through the artery.
Step-by-step explanation:
When an artery is clogged with an atherosclerotic plaque, it causes a reduction in the radius of the artery. The plaque buildup narrows the space through which blood can flow, decreasing the radius of the artery. This reduction in radius leads to a decrease in blood flow through the artery.