Higher cerebral function and hemispheric blood flow during awake carotid artery balloon test occlusions

Objectives-Measures capable of detecting early alterations of brain functio n during acute cerebral ischaemia have not been adequately defined. Interna l carotid artery (ICA) test occlusions provide a well controlled environmen t to investigate the effects of reversible acute hemispheric hypoperfusion on brain function. A continuous time estimation task was developed that rel iably demonstrated alterations in higher cerebral function before developme nt of any deficits in elementary neurological function during ICA balloon c atheter test occlusions. In the present study, we hypothesised that alterat ions in our behavioural task would correlate significantly with absolute le vel of ipsilateral CBF. Methods-Twenty five patients underwent awake ICA test occlusions during whi ch sustained attention and ipsilateral CBF were measured simultaneously usi ng our time estimation task and the intracarotid Xe-133 washout method. Alt eration in sustained attention was correlated with CBF after occlusion usin g Fisher's exact test. Results-Deterioration in sustained attention was significantly associated w ith ipsilateral CBF below 30 ml/g/min (Fisher's exact test, p=0.047). Chang es in individual patients' performance on the behavioural task correlated i n real time with changes occurring either at the point of occlusion or at a specific threshold of induced hypotension. Sensitivity for our behavioural test in predicting CBF was 75%; specificity 70%. Conclusions-Monitoring sustained attention during carotid balloon test occl usions seems to be a sensitive means to detect decreases in CBF as measured by Xe-133 washout. Correlation between higher cerebral function and CBF ca n allow more detailed investigations of physiological relations between cer ebral haemodynamics and brain function in human conditions of cerebral isch aemia.