Transcranial Doppler measurement of middle cerebral artery blood flow velocity: a validation study

Measurement of intracranial arterial blood flow velocity is a new technique with potentially a number of very useful applications. This study validates the technique by comparing it to cerebral blood flow (CBF) measured using intravenous Xenon133 and extracranial clearance recording. We have measured the middle cerebral artery (MCA) blood flow velocity in 17 symptomatic patients with the EME TC 264 transcranial Doppler velocimeter and compared these measurements to the ipsilateral hemispheric cerebral blood flow measured with an intravenous Xenon133 technique (Novo Cerebrograph 10A). Measurements were made at rest and during hypercapnia. The absolute measurement of MCA velocity and hemispheric CBF showed a poor correlation (r = 0.424, p less than 0.01) due to wide between-patient variations at rest but the blood flow response to hypercapnia, expressed as a reactivity index, showed a good correlation (r = 0.849, p less than 0.001). Thus changes in MCA velocity reliably correlate with changes in cerebral blood flow but the absolute velocity cannot be used as an indicator of CBF.