Assessing arterial distensibility using ultrasound wall-tracking diameter distension: an urgent need for direct stiffness measurement!

Background: Arterial stiffness is increasingly used as an early marker of atherosclerosis and for the individual's assessment of cardiovascular risk. Ultrasound wall tracking allows assessing the distensibility coefficient DC = (ΔD/D)/ΔP with D diastolic diameter, ΔD cyclic diameter change and ΔP the local pulse pressure. Although DC depends on intrinsic stiffness, it also depends on vessel geometry. In this study, we reconcile DC of the common carotid artery measured within the framework of the Asklepios population study. Methods: Diameter, intimamedia thickness (IMT) and DC of the left common carotid artery were assessed in 2315 (1191women) apparently healthy subjects (age 35-56), using vascular ultrasound (Vivid 7, 12L probe) and wall tracking (media-adventitia transition) techniques. Evolution of DC and IMT/D with age was evaluated within the context of a theoretical framework linking DC, IMT/D and the Young elasticity modulus E [DC =1/(2.E.IMT/D)]. Results DC was higher in women than in men for age (35-40), while the inverse was true at age (51-56), suggesting a more rapid increase in stiffness in women. This evolution in DC is partly explained by arterial remodelling (increase in IMT/D) accompanied by an increase in intrinsic stiffness. While DC decreases by >30%, our data suggest an increase in intrinsic stiffness of about 25% over the studied age range. Conclusions: Clinically used measures of arterial stiffness are intrinsically dependent on arterial geometry. Direct measurements of stiffness are highly needed to avoid the ambiguity between an artery's kinematic behavior and its intrinsic mechanical properties