Intrinsic Stiffness of the Carotid Arterial Wall Material in Essential Hypertensives

We have previously shown that the decrease in large artery distensibility observed in patients with essential hypertension (HT group) was primarily due to an increase in distending pressure and not to hypertension-associated structural modifications of the artery, suggesting a functional adaptation of the wall material. To evaluate the elastic properties of the wall material of the common carotid artery, we determined Young's incremental elastic modulus (Einc) in the HT group and in normotensive subjects (NT group) as a function of blood pressure and circumferential wall stress. In 102 HT patients with never-treated essential hypertension and 40 age- and gender-matched NT subjects, the Einc-pressure and Einc-stress curves were calculated from intima-media thickness and from diameter and pressure waveforms, determined with echo tracking and aplanation tonometry, respectively. The "effective" stiffness of the wall material, determined through Einc calculated at mean blood pressure, was significantly higher in the HT than in the NT group. The "intrinsic" stiffness of the wall material, determined through Einc calculated at a common circumferential wall stress, did not differ between the 2 groups. However, when each group (HT and NT) was analyzed according to tertiles of age, the "intrinsic" stiffness of the arterial wall material was increased only in younger HT patients. In middle-aged and older HT patients, the intrinsic mechanical properties of the carotid arterial wall material were unchanged, and the increased stiffness of the common carotid artery in the HT group was due primarily to the increased level of blood pressure. These results also indicate that the deleterious effects of aging and hypertension on "intrinsic" stiffness are not additive.