Oxygen extraction fraction and acetazolamide reactivity in symptomatic carotid artery disease.

OBJECTIVE It has been proposed that cerebral blood flow (CBF) response to acetazolamide may be reduced according to the degree of autoregulatory vasodilation in regions with normal oxygen extraction fraction (OEF), whereas the CBF response may be absent in regions with increased OEF where vasodilation may be maximal in response to reduced perfusion pressure. The objective of this study was to test this hypothesis. METHODS Positron emission tomography (PET) was used to study 30 symptomatic patients with carotid artery steno-occlusive lesions. CBF at baseline and 10 minutes after an intravenous injection of 1 g acetazolamide was measured. The correlation between the change in CBF during acetazolamide administration and the baseline value of OEF in the affected hemisphere was examined. RESULTS The baseline OEF value was inversely and non-linearly correlated with the percentage change in CBF during acetazolamide administration (R(2) = 0.25, p = 0.02). There was an upward trend of OEF with diminishing acetazolamide response below a critical level around zero response. Acetazolamide response less than 6.65% over baseline (sensitivity 100%, specificity 89%, positive predictive value 50%, negative predictive value 100%) was established as most helpful in predicting abnormally high OEF. CONCLUSIONS The inverse, non-linear relationship between OEF and CBF response to acetazolamide suggests that these two measurements may not identify haemodynamic impairment in the same patients.