Background: Numerous publications have documented the usefulness of carotid ultrasonography. However, few studies report on criteria of flow evaluation in vertebral arteries. One reason is the greater anatomical variety of vertebral arteries, particularly the often encountered diameter asymmetry between sides. The purpose of this study was to assess the dependence of hemodynamics in vertebral arteries on their side-to-side diameter asymmetry.Material and Methods: Prospective color Doppler ultrasonography examinations of the vertebral arteries were performed on 113 adult volunteers (69 females, 44 males, mean age: 29.1±6.9 SD), free of symptoms of vertebrobasilar insufficiency, atherosclerotic lesions, anatomic anomalies, or signs of significant stenosis in spectral Doppler. The subjects were divided into four groups according to the degree of asymmetry between sides.
Results: There were no statistically significant differences in the hemodynamics of the arteries with side-to-side diameter asymmetry of less than 25% (or 0.5 mm). In the remaining three groups, flow parameters differed considerably between sides. End diastolic velocity revealed the greatest dependence on diameter asymmetry. Conclusions: Assessment of the hemodynamics of vertebral arteries should take side-to-side asymmetry into consideration. Arteries differing in diameter by up to 25% or 0.5 mm can be considered symmetrical. The most vulnerable flow parameter to side-to-side diameter asymmetry is the end diastolic velocity.

Keywords: Blood Flow Velocity - physiology, Hemodynamics, Regional Blood Flow, Vertebral Artery - ultrasonography