Reliability of ultrasonographic measurement of vertebral artery blood flow
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Clinical tests involving sustained cervical spine rotation and/or extension are commonly applied pre-manipulatively to screen for patients at risk of stroke due to vertebral artery pathology. This is despite the fact that the validity of these manoeuvres is disputed and their effect on vertebral artery blood flow poorly understood. Recent research has mployed duplex ultrasound (Doppler with Bmode real-time imaging capability) to quantify positional haemodynamic parameters and determine whether subjects testing positive differ from negative subjects. However, the reliability of Doppler sampling of the upper cervical part of the vertebral artery in positions involving rotation and extension has not been established. Thus the aim of this study was to evaluate the reliability and measurement variability associated with this investigative procedure. Methods: Twenty normal subjects volunteered to participate in the study. Haemodynamic measurements were taken of a randomly selected vertebral artery using duplex ultrasound with colour flow and power Doppler imaging capabilities. Blood flow was recorded at both the atlanto-axial and the C2/3 regions of the vessel in neutral, end-range extension and end-range contralateral rotation. The protocol was then repeated. Results: Intraclass correlation coefficients (2, 1) and 95% limits of agreement indicated that sampling at the more vulnerable but less accessible atlanto-axial site was generally more repeatable, notably in end-range contralateral rotation. In particular, the key measures of atlanto-axial peak systolic velocity and resistance index in end-range rotation demonstrated excellent reliability (0.82; 0.76). Between group differences of -12.9 to 16.6 cm/s and -0.11 to 0.17 respectively would be necessary to discount measurement variability. Conclusions: Accurate interpretation of the results of ultrasonographic investigation of vertebral artery tests utilising rotation and extension requires consideration of measurement variability and reliability. Haemodynamic parameters of acceptable reliability and associated ranges of measurement variability have been identified for use in future research.
New Zealand Journal of Physiotherapy