Static versus Dynamic Distensibility of the Carotid Artery in Humans

Abstract

In clinical studies, the elastic behavior of central arteries is usually assessed by measuring dynamic distensibility. In this study, we aimed to investigate how dynamic and static distensibility of the common carotid artery (D_dyn and D_stat, respectively) are related in 28 healthy volunteers of 20–71 years. The carotid diameter and its change with the pressure pulse were measured using an ultrasound echo-tracking device. Arterial blood pressure was measured by Finapres and carotid pressure was determined by applanation tonometry. D_dyn was determined at rest using the pressure pulse, while D_stat was determined during pressor responses induced by handgrip or cold pressor test. Data are given as mean ± 1 SD. In younger subjects (<35 years), D_stat did not differ from D_dyn (7.0 ± 3.4 vs. 6.5 ± 2.1·10^–3·mm Hg^–1, respectively), whereas in older subjects (>35 years), D_stat was significantly higher than D_dyn (3.8 ± 1.4 vs. 2.1 ± 0.9· 10^–3·mm Hg^–1, p < 0.001). For all subjects, D_stat and D_dyn decreased with increasing age and mean arterial pressure (MAP). Using stepwise multiple regression analysis, the strongest predictor of D_stat proved to be MAP, while that of D_dyn was age. D_stat was found to be linearly related to the hysteresis loop area of the pressure-diameter relation (r = 0.94), i.e. to vessel wall viscosity. It is concluded that, with increasing age, static distensibility overestimates the distension capacity of large arteries.

Mechanical and neural contributions to hysteresis in the cardiac vagal limb of the arterial baroreflex

“…It has been proposed that barosensory vessel mechanics may contribute significantly to this phenomenon, since a similar pattern is manifested in the pressure-diameter relationship of large elastic arteries (Bonyhay et al 1997). For example, within the cardiac cycle, diameters are larger with pressure falls than with pressure rises (Lénárd et al 2000). It is not known, however, whether this pattern appears with slower changes in pressure across cardiac cycles.…”

“…It has been proposed that the pattern of baroreflex hysteresis derives from the viscoelastic nature of compliant barosensory vessels (Bonyhay et al 1997;O'Leary et al 2005). For example, within a pulse interval, carotid artery diameters are larger at any given pressure when pressure is falling than when pressure is rising (Lénárd et al 2000). If greater barosensory vessel diameters across falling versus rising pressures generate proportional cardiac vagal outflows, this would generate longer RR intervals during falls and hence a higher set point.…”

Static and dynamic changes in carotid artery diameter in humans during and after strenuous exercise

“…Wall viscosity results in hysteresis of the pressure‐diameter relationship (i.e. at the same pressure level the vessel diameter is larger for falling than for rising pressures; Lénárd et al . 2000).…”

The repeated sit-to-stand maneuver is a superior method for cardiac baroreflex assessment: a comparison with the modified Oxford method and Valsalva maneuver

“…Our study was not designed to isolate these components, their interactions, or relative contributions to hysteresis, but others have demonstrated the mechanical and neural components exhibit frequency dependence. The concept of mechanical frequency dependence is supported by studies showing the arterial wall (mechanical component) becomes stiffer when it is stretched quickly, which lowers BRS INT (5,27,35). The concept of neural frequency dependence is supported by studies showing that the recruitment of baroreceptor afferents (Type A and C) is influenced by the rate of stretch (4,8,46).…”