Increased stroke risk predicted by compromised cerebral blood flow reactivity

Abstract

The authors sought to determine risk for stroke in individuals with symptomatic carotid stenosis or occlusion based upon an assessment of cerebral blood flow (CBF) reserves. Vascular reserve was assessed by two consecutive xenon/computerized tomography (Xe/CT) CBF studies with intravenous acetazolamide introduced 20 minutes prior to the second study. Patients were assigned to one of two vasoreactivity groups. Group 2 included individuals who experienced a CBF reduction of more than 5% in at least one vascular territory and had a baseline flow of 45 cc/100 gm/min or less. Group 1 included all other individuals. Any territory with volume loss on CT of more than 50% was eliminated from analysis. Sixty-eight individuals were followed at 6-month intervals for a mean of 24 months. In Group 1 two strokes were observed contralateral to the side with lowest reserve, for a stroke incidence of 4.4%; in Group 2 eight strokes were observed ipsilateral to the side with lowest reserve, for a stroke incidence of 36%. The latter group had a 12.6 times greater chance of stroke (p = 0.0007). History of stroke, history of transient ischemic attacks, baseline CBF, and degree of stenosis were not associated with an increased stroke rate. In this study, significantly compromised vascular reserves accompanied by relatively low initial flow identified individuals who subsequently demonstrated a significantly increased rate of ipsilateral stroke.

MR assessment of cerebral vascular response: A comparison of two methods

“…Recently it was shown that a diminished CVR is a predictor of stroke in patients with symptomatic carotid artery occlusive disease (16). Furthermore, cerebral periventricular white matter lesions have been found to be correlated with decreased vasomotor reactivity in asymptomatic individuals (17), increased stroke risk (18), first-ever lacunar infarction (19), and deep white matter lesions (20). Apart from responding to hypercapnia, hypoxia, and hypotension, the CVR may also be challenged pharmacologically.…”

Comparison of CO2 in Air Versus Carbogen for the Measurement of Cerebrovascular Reactivity with Magnetic Resonance Imaging

“…We have found that intrasubject flow CVR as measured by ASL is affected by PO 2 and is not consistent between CO 2 in air and carbogen. Although the possibility remains that this inconsistency could be a result of imperfect estimation of tissue pressure of CO 2 and CBF under a combined hyperoxia and hypercapnia regime, particular care should be taken when comparing flow CVR values obtained from stimuli containing different fractions of oxygen. …”

Calibrated MRI to Evaluate Cerebral Hemodynamics in Patients with an Internal Carotid Artery Occlusion

“…1,3 Impaired CVR is a predictor for increased risk of ipsilateral stroke and transient ischemic attack (TIA) in patients with steno-occlusive carotid disease. 4,5 Similarly, increased OEF has been shown to predict recurrent ischemic stroke in patients with symptomatic occlusive disease of the cerebral vasculature. 6 Furthermore, a higher stroke risk has been observed in patients with impaired CVR and increased OEF when compared with patients with impaired CVR only.…”

“…As an alternative, perfusion or flow techniques combined with a vasodilatory stimulus have been proposed to evaluate the CVR. Invasive techniques such as xenon-enhanced computed tomography 5 or noninvasive techniques such as Doppler ultrasonography, 4 blood oxygen level-dependent (BOLD) magnetic resonance imaging (MRI), 9 or arterial spin labeling MRI 10 have been suggested. A dualecho arterial spin labeling (ASL) sequence can acquire perfusion data (first echo) and BOLD data (from the second echo which has T 2 * weighting) simultaneously.…”