Influence of age and end-stage renal disease on the stiffness of carotid wall material in hypertension

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Abstract
Incremental elastic modulus, which is the slope of the relationship between stress and strain of arterial vessels, is a marker of wall material stiffness. The radial artery incremental elastic modulus, which is not influenced by age, is normal or reduced in patients with essential hypertension but increased in patients with end-stage renal disease. Authors of studies on hypertension largely ignore the question of whether the incremental elastic modulus, measured in the common carotid artery as typical of a central artery site, differs according to age or to the presence of end-stage renal disease or both. The carotid incremental elastic modulus was measured in 208 hypertensive patients divided into four groups according to age (≤ or > 55 years) and the presence or absence of end-stage renal disease. The incremental elastic modulus was calculated from transcutaneous measurements of arterial internal diameter and wall thickness (echo-tracking device) and carotid pulse pressure (tonometry). Because the four groups of subjects had the same mean arterial pressure, the static incremental elastic modulus was calculated both in isobaric conditions and for the same wall stress. In nonuremic subjects, lumen diameter, wall thickness and the incremental elastic modulus were significantly (P < 0.001) increased in older subjects whereas compliance and distensibility were decreased. The mean (± SD) elastic modulus was 0.41 ± 0.14 × 103 kPa in younger and 0.71 ± 0.28 × 103 kPa in older subjects. In uremic subjects, the corresponding values were 0.48 ± 0.30 and 0.90 ± 0.49 × 103 kPa, and therefore higher than in nonuremic subjects, irrespective of age. Multiple regression analysis showed that age, mean arterial pressure and the presence of end-stage renal disease independently influenced carotid diameter, distensibility and the incremental elastic modulus. In hypertensive patients, the carotid incremental elastic modulus is increased independently in aging men and women and in the presence of uremia. This increase is not dependent on mechanical factors such as the level of mean blood pressure.