Neuropsychological Sequelae of Carotid Stenosis and the Outcome Evaluations Following Revascularization

Project: National Science and Technology CouncilNational Science and Technology Council Academic Grants

Project Details


Background: The notion that carotid artery stenosis can lead to cognitive deficits remains controversial. Most evidence for cognitive changes as a result of carotid artery stenosis has come from the outcome studies of carotid revascularization. In addition to the differences in surgical procedures, the diversity in the sensitivity of the neuropsychological tests and control of moderator variables of cognitive performance in these studies are also likely to contribute to the inconsistent findings. A model of timed cognition seems to offer an innovative approach with potential application to tackle these limitations. The model assumes that most of the total standardized variance for every diverse cognitive task can be accounted for by a general speed factor. Indeed, speed or reaction times have long been known to be sensitive to mild cerebral dysfunction including transient ischemic attacks and cerebral circulation disorders. Since one of the direct impacts from carotid artery stenosis to the brain is circulation deficiency, it is quite possible that slowness in cognition is more likely to manifest earlier in these patients than inability to complete the cognitive tasks. Aims: The general purposes of this proposed project intend to elucidate whether carotid stenosis can lead to any cognitive deficits by extensively examining a wide range of specific cognitive functions in patients with this condition. In particular, the model of cognitive speed will be extensively tested to ascertain whether or not the changes of cognitive efficiency can be established as a consequence of carotid artery stenosis, and be reflected by the physiological changes observed from the investigations of cerebral perfusion and the cerebrovascular reactivity. In addition, the long-term effects of carotid revascularization on cognitive functions and/or cognitive speed will be studied to examine if improvement in cerebral circulation can result in better cognitive efficiency. Methods: A series of studies will be carried out to i) examine if differences in severity of carotid stenosis will result in differences in the scopes of cognitive deficits and/or cognitive speed; the relationships between cerebral circulation, cerebrovascular reactivity and cognitive speed will also be investigated; ii) explore the predictive power of various moderating variables (e.g. age, education, general intelligence, general medical conditions and severity of stenosis) on cognition. The interacting effects between each moderator variable and stenosis severity on cognition will also be examined. iii) to examine the long term effects of revascularization on cognition. The research protocols and data analyses of the studies listed above will be based on between-group or mixed designs. We estimate that at least 150 subjects with different grades of carotid stenosis will be needed throughout the project. They will be allocated to three different groups: the revascularization intervention group (N=60), the medication group (N=45) and the control group (N=45) based on their severity of stenosis and choice of treatments. All subjects will undergo three phases of neuropsychological assessments in 12 months, each with 6 months apart. The first assessment will be carried out prior to surgery for the subjects receiving revascularization; and within one month after enrollment for the other two groups. Most tests used for the assessment will be modified or computerized to incorporate measures of speed. The cerebral circulation and cerebrovascular reactivity investigations for each subject will also be taken for three times in agreement with the assessment phases, but these investigations will only be applied to the control group once during the first phase. The data continuously accumulated throughout the project will be analyzed to attest to the above questions by ANOVA, ANCOVA or t-tests where appropriate. In some cases, correlation and multiple regression analyses will be performed when examining the predictive power of several moderator variables and stenosis severity on Form C011 page 2 of 2 pages cognition. Expected outcomes: We anticipate that by application of the model of timed cognition may prove to be more sensitive and helpful than conventional neuropsychological test scores to reveal the cognitive changes produced by carotid artery stenosis. However, these effects may be liable to be obscured by the interactions between some moderator variables (e.g. age, education, general intelligence and general medical conditions). We hope that diminished cognitive efficiency observed in subjects with more severe stenosis can be more directly reflected by the physiological measures of cerebral circulation and cerebrovascular reactivity. Finally, we also anticipate that the restoration of cerebral circulation efficiency by carotid revascularization may improve certain aspects of cognitive functions and cognitive speed at least for a short term (e.g. 6 months).

Project IDs

Project ID:PF9902-0815
External Project ID:NSC98-2410-H182-006-MY2
Effective start/end date01/08/1031/07/11


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