Objectives: To model the in vivo nonlinear mechanical behavior of human common carotid arteries (CCAs), to compute wall stresses and to deduce changes in wall micro-constituents (elastin-dominated matrix, collagen fibers, vascular smooth muscle cells (VSMC)) in normotensive subjects (NT) and hypertensive patients (HT).

Methods: Clinical data were obtained non-invasively from CCAs in 16 NT (21–64 years old) and 25 treated HT (44–69 years old). Medial diameter, intimal-medial thickness and blood pressure (BP) were measured during several cardiac cycles by high-resolution echotracking (Art.Lab®) and applanation tonometry (SphygmoCor®) systems, respectively. For the theoretical mechanical modeling, the CCAs were assumed to be hyperelastic, anisotropic, active-passive, and residually- stressed. We semi-analytically solved the boundary value problem to compute the intraluminal pressure from carotid distension, while accounting for perivascular tissue. Best-fit values of model parameters were adjusted by minimizing the difference between computed and measured inner BP over the cardiac cycle.

Results: In NT, age was positively correlated (p<0.05) with residual stresses and fibrillar collagen (stiffness and orientation). Despite treatment, HT had increased VSMC tone (p=0.003, +17.3%), a stiffer elastin-dominated matrix (p=0.01, +20.5%), and higher levels of stresses.

Conclusions: We were able to estimate wall stress fields and to quantify changes in mechanical characteristics of wall micro-constituents with aging and hypertension from non-invasive clinical data, though mechanical modeling of the wall behavior. Our results are consistent with prior reports on effects of age and hypertension, but provide increased insight into evolving contributions of cell and matrix mechanics to arterial behavior in vivo.