"Hardening of the arteries," or arteriosclerosis (as distinct from atherosclerosis), is apparently an inevitable change of aging. The walls of blood vessels become stiffer as time passes, as does all connective tissue of the body. This is caused by (1) cross-linkage of collagen, the protein which makes up the connective tissue of artery walls, and (2) by the slow steady difuse deposition of calcium in the walls of the arterial tree.

With arteriosclerosis, calcium builds up and becomes many times more concentrated in the wall of the normal artery than it was in childhood. We are not alking about plaque formation but rather a diffuse deposition of calcium in the walls of arteries, finally resulting in an arterial system that is said to be as stiff as a lead pipe. This is has sometimes been called "lead pipe disease." Calcium content is what atherosclerosis and arteriosclerosis have in common, but in atherosclerosis it occurs in concentrations called plaques; in arteriosclerosis it occurs diffusely.

Aging can be thought of as a progressive dysfunction of calcium metabolism. As the body ages, more and more calcium is concentrated in the interior of cells. Dying of old age is, in a very real way, dying of calcium poisoning.

Of course, the most well known result of calcium deposit is heart attack, also called myocardial infarction. In most heart attacks both atherosclerosis and arteriosclerosis are present. Atherosclerosis provides the plaque which narrows the artery and arteriosclerosis stiffens the arteries so that they cannot expand with each heart beat to compensate for the blockage caused by plaque formation.

While arteriosclerosis by itself does not cause hear attack or stroke, the condition potentiates the effect of atherosclerosis to produce these results. This potentiation is by virtue of the fact that when plaque develops in the presence of arteriosclerosis, the stiffened and inflexible blood vessel wall does not have the ability to compensate by expanding with the increased blood pressure of each heart beat. Thus the flow of blood is less than it would otherwise be due to the absence of flow around the plaque.

The diagnosis of arteriosclerosis is best made using a Doppler machine. This ingenious device listens to the sound of blood as it rushes through an artery at speeds which vary with the phase of the heart cycle of contraction and relaxation. The frequency of the sound varies with the speed of the blood cell's transit through the artery which is being listened to. Higher speed produces a higher frequency. From these changing frequencies the Doppler machine constructs a graph and from the shape of the graph the flexibility or inflexibility of the arterial system can be accurately inferred.