Evaluating Carotid Artery Dynamics Using Pressure/Diameter Waveforms to Determine Stiffness and Viscoelastic Properties

Objective: Carotid stiffness as local Pulse Wave Velocity (cPWV), obtained by ultrasound during a scan, predicts risk of stroke and cognitive dysfunction independently of ambient blood pressure and age but remains pressure-dependent, complicating comparison between clinical groups. Our aim was to carry out multi-parametric analysis of carotid wall properties in healthy subjects and patients with different risk factors, compensating for the pressure-dependency of PWV. Design and method: Pressure (P) (PulsePen, DiaTecne, Milan, Italy, 500 or 1000 samples/s) and Diameter (D) (Aloka, Hitachi Ltd., Japan, 1000 samples/s, and MyLabOne, Esaote SpA, Italy, 660 samples/s) waveforms were acquired for the right and left common carotid artery of 210 subjects (117 men) at hospitals in Pisa and Massa (Tuscany, Italy). We included 81 age-matched healthy controls and patients treated for hypertension only (N = 28), hypertension with metabolic disorders (N = 31), dyslipidemia (mainly, hypercholesterolemia, N = 37), younger T1 diabetes (N = 19), and T2 diabetes (N = 14). The PD2-loop method was used to estimate cPWV, and the PD2 relationship was fitted with an exponential function P(t) = DBP*exp[γ(D(t)2/D_DBP2-1)]. The P-independent stiffness parameter γ was used for pressure normalization of cPWV to characterize the elastic component of arterial wall mechanical behaviour, as was the hysteresis area, defined as that within the plot of the PD-loop, for the viscous component.Results: In healthy subjects, cPWV increased with age from 4 m/s < 30 years to >=6 m/s in the eldest group. After pressure normalization to 110–75 mmHg, cPWV's increasing trend with age was still observed (Anova, p < 0.001) but total variation was reduced by 15% (left figure). Hypertensives and patients with metabolic disorders had higher cPWV than age-matched controls after pressure normalization and adjustment for age and heart rate. PD-loop hysteresis area was much greater in hypertension across the age range (right figure, p < 0.001). Conclusions: Overall, quantifying carotid wall viscosity through PD-loop assessment, in addition to pressure independent stiffness parameters, results in a promising tool to identify local mechanical pathology in hypertension and metabolic conditions.