Relationship between carotid artery mechanisms and the spontaneous baroreflex : a non-invasive investigation in humans

Objectives: This study addressed the relationship between spontaneous baroreflex sensitivity and carotid mechanical properties in a clinical setting. Methods: In 191 normal volunteers (age range 20-60 years, mean 44±13), spontaneous indices of baroreflex regulation were obtained noninvasively in the time (baroreflex slope, BRS) and frequency domains (α index and systolic arterial pressure-RR interval transfer gain) as well as using an exogenous autoregressive causal model (A.XAR); carotid mechanical properties were estimated by ultrasound. The link between mechanical measures and spontaneous baroreflex indices was explored by multivariate analysis and linear modeling. Results: Participants were divided into five groups according to age decades. With advancing age we observed a decrease in spontaneous baroreflex indices (BRS from 31.2 to 16.3; α index from 27.4 to 13.6; RR-SAP gain at high frequency from 31±3.0 to 14±3.0ms/mmHg all P<0.001) and increase in carotid intima-media thickness (IMT: from 0.53 to 0.69mm; P<0.001) and stiffness (local wave speed: from 4.0 to 6.9m/s; both P<0.001). A significant correlation was found between spontaneous indices of baroreflex sensitivity and carotid mechanical properties, particularly wave speed (r=-0.328, P<0.001). After adjusting for age and sex, a significant correlation remained between RR-SAP gain and wave speed and between A.XAR and IMT. Factor analysis and automatic linear modeling confirmed the observation that mechanical carotid properties are strong predictors of the age-related reduction of spontaneous baroreflex. Conclusion: A significant correlation between spontaneous baroreflex indices and local carotid mechanical properties supports the idea that they should be considered in the physiology of baroreflex regulation.