Measurement of arterial aging in hypertensive patients.

Roach and Burton (1) described two important changes in arterial walls with advancing age. One is an increase in collagenous fibers causing loss of distensibility with increase in the slope dP/ dV of arterial pressure-volume curves. The other is a decrease in the unstretched length of these collagenous fibers as the "slack" in them is taken up, possibly by cross linkages and adhesions. This change results in a more rapid decrease in distensibility with stretch and an increase in the rate of change in slope (or the curvature) of pressure-volume curves toward the pressure axis. An indirect clinical index of the latter effect of aging on arterial walls has been described (2, 3) and referred to, arbitrarily, as an "index of arterial rigidity." It does not measure the slope dP/dV of arterial pressure-volume curves but the rate of change in slope (or the curvature) with pressure. Thus, it is not directly related to distensibility of the large arteries but it represents the differential of their stiffness with respect to pressure. Conway and Smith (2) applied this test to a study of "aging of arteries in relation to hypertension" and found that the rigidity indices of older hypertensive patients exceeded those of a control group of 16 young medical students. Their observations (2, 4) supported the hypothesis (5) that in the majority of patients with essential hypertension the elevated diastolic pressure is the consequence of aging of arteries. More recently (3) we demonstrated a strong correlation between this index and age which made us suspect that a number of the hypertensives in their studies might be considered to have normal rigidity indices when compared with normal subjects of the same age. Knowing the variation of this index