Static versus dynamic distensibility of the carotid artery in humans

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 x 10(-3) x 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 x 10(-3) x 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.