CORRELATION OF TRANSCRANIAL DOPPLER SONOGRAPHY MEAN FLOW VELOCITY WITH CEREBRAL BLOOD-FLOW IN PATIENTS WITH INTRACRANIAL PATHOLOGY

Several studies suggest that relative changes in cerebral blood flow ( CBF) may be assessed via transcranial Doppler sonography (TCD). The pr esent study investigates the correlation between changes In TCD-mean n ow velocity (Vm) and changes in CBF in patients with a variety of type s intracranial pathology undergoing cerebrovascular reactivity tests. After informed consent was obtained, 32 patients presenting with steno ses of brain-supplying arteries (n = 13), cerebral vascular malformati ons (n = 6), surgical decompression for subarachnoid hemorrhage (n = 2 ), brain edema after closed head injury (n = 8), or hepatic encephalop athy (n = 3) were studied. The patients were divided into mio groups f or different reactivity tests. Patients in group 1 (awake or sedated, n = 18) received a 1-g dose of acetazolamide intravenously. In group 2 (n = 14), mechanical ventilation was adjusted to produce a 20% decrea se in arterial CO2 tension compared with baseline. Regional CBF was me asured using xenon-enhanced computed tomography (Xe-CT). Xe-CT scans a t the levels of the basal ganglia and the lateral ventricles were perf ormed during a 4.5-min xenon wash-in period. Bilateral flow velocity w as measured in the middle cerebral artery using a 2-MHz pulsed TCD sys tem. Mean arterial blood pressure, heart rate, and end-tidal CO2 were continuously recorded during the procedure. After baseline measurement s and either alteration of CO2 or application of acetazolamide, the ce rebrovascular reactivity was assessed at 20 min by a second measuremen t of CBF, TCD, and all other physiologic variables. The correlation co efficient for relative changes of MCA territory CBF versus Vm and for the overall population was r = 0.82. In groups 1 and 2, the values wer e 0.39 and 0.5, respectively. Correlation coefficients did not exceed r = 0.4 in any subgroup-classification based on diagnosis. The close c orrelation between changes in CBF and Vm (r = 0.82) in patients with h eterogenous intracranial pathology seems to show that TCD is a measure of CBF. However, in groups 1 and 2, and in subgroups formed of patien ts classified according to diagnoses, data dispersion suggests that th e actual correlation is weaker. Relation of changes in Vm to those in CBF may depend on the underlying diagnosis. These data indicate that t he correlation between Vm and CBF may vary with intracranial pathology .