ESTIMATION OF ARTERIAL STIFFNESS, COMPLIANCE, AND DISTENSIBILITY FROMM-MODE ULTRASOUND MEASUREMENTS OF THE COMMON CAROTID-ARTERY

Background and Purpose Arterial stiffness may indicate early vascular changes that predispose to the development of major vascular disease. The repeatability of a variety of indices of arterial stiffness calcul ated from a standard carotid arterial M-mode ultrasound image was inve stigated. Methods Twenty-six asymptomatic normal subjects were imaged and had blood pressure recordings on each of two separate occasions at least 1 day apart. Using a computer-assisted method, the maximum and minimum internal diameter and average wall thickness of the right comm on carotid artery were measured over several cardiac cycles, and the f ollowing indices of arterial stiffness and distensibility (compliance) were derived: the pressure-strain elastic modulus (Ep), Young's modul us (E), cross-sectional compliance (CC), and the distensibility coeffi cient (DC). Results The repeatability of these measures, expressed as coefficients of variation, was as follows: Ep, 18%; E, 24%; CC, 14%; a nd DC, 13%. In another group of 20 subjects, the coefficient of variat ion for repeat examination by different sonographers was Ep, 19%; E, 2 0%; CC, 14%; and DC, 17% and for the one sonographer using two ultraso und machines was Ep, 13%; E, 13%; CC, 11%; and DC, 13%. These values i ndicate a moderate level of repeatability. In a univariate analysis ea ch of these indices was significantly related to increasing age (Ep=1. 0+12.9xAGE, r=.80; E=314.5+13.9xAGE, r=.48; CC=22.6-0.26xAGE, r=-.63; DC=64.0-0.65xAGE, r=-.78) but not to wall thickness (all P>.47). Using multiple regression techniques to adjust for age, wall thickness is a significant predictor of distensibility (P=.017), cross-sectional com pliance (P<.001), and the pressure-strain elastic modulus (P=.019). Be cause Young's modulus is calculated from wall thickness, it could not be included in the multivariate analysis. Conclusions We conclude that estimates of carotid artery distensibility and cross-sectional compli ance derived from M-mode ultrasound recordings are moderately repeatab le and may provide useful additional end points for trials of atherosc lerotic progression.