Effects of transient change in carotid arterial stiffness on arterial baroreflex during mild orthostatic stimulation

Abstract

Stiffening of central conduit arteries –areas where the mechanoreceptors are embedded (e.g., ascending aorta and carotid artery) – is considered to be associated with the impaired baroreflex control in response to hypotensive stress. Arterial stiffness is modulated by vascular tone transiently and dynamically, however, it is unknown whether a transient change in the carotid artery stiffness influences the cardiac baroreflex response to a rapid hypotension. We measured (n = 11) carotid arterial stiffness (via concurrent applanation tonometory and ultrasound imaging) at supine rest and during 20-degree head-up tilt (HUT). To evaluate the cardiac baroreflex response, acute hypotension was evoked by releasing bilateral thigh cuffs after 3 min of suprasystolic resting ischemia at each posture; cardiac baroreflex sensitivity (e.g., change in heart rate for a given change in mean arterial pressure, ΔHR/ΔMAP) and latency (e.g., the time to peak HR response) was estimated. Carotid β-stiffness index, a measure of arterial stiffness, was reduced by 14% during HUT (P < 0.05 vs. supine position). Although cardiac baroreflex responses were unaltered, the within-group biological variability in the cardiac baroreflex sensitivity and latency from the supine to HUT was correlated with the corresponding changes in carotid arterial stiffness (r = 0.66 and r = 0.64, respectively, both P < 0.05). These findings suggest that a transient change in carotid arterial stiffness, at least in part, influences changes in the cardiac baroreflex response to a rapid hypotension.