Functional analysis of the common carotid artery: relative distension differences over the vessel wall measured in vivo
Objectives Absolute (ΔD) and relative (ΔD/D) arterial diameter distension, parameters related to the elasticity of the vessel, can be measured in superficial arteries using ultrasound-based vessel ‘wall tracking’ techniques. Currently available systems (e.g. the Wall Track System; WTS) measure the displacement of the media-adventitia transition (outer wall). We hypothesize that, given volume incompressibility of the vessel wall, ΔD and ΔD/D measured at the outer wall, significantly underestimate vessel distension at the lumen–intima interface (inner wall).
Methods We measured ΔD and ΔD/D at both the inner and outer wall of the common carotid artery in 39 subjects (aged 18–83 years) using a new prototype ‘wall tracking’ system based on the Vivid-7 scanner (GE Vingmed Ultrasound, Horten, Norway). In addition, ΔD and ΔD/D were also measured using WTS.
Results As anticipated, tracking the inner wall yielded lower diastolic diameters than when tracking the outer wall (Ddia = 5.70 ± 0.80 and 6.91 ± 0.98 mm, respectively, P< 0.0001). ΔD (0.54 ± 0.16 versus 0.49 ± 0.16 mm; P< 0.0001) and ΔD/D (0.096 ± 0.030 versus 0.071 ± 0.026, P< 0.0001) were indeed larger at the inner than at the outer wall. For WTS, Ddia, ΔD and ΔD/D were 7.04 ± 1.02 mm, 0.45 ± 0.14 mm and 0.066 ± 0.022, respectively.
Conclusions On average, ΔD and ΔD/D are 10 and 25% higher on the inner than on the outer wall, respectively. Follow-up studies in larger cohort trials are mandatory to assess whether tracking the inner wall yields arterial function parameters with a higher cardiovascular prognostic potential.