Chapter 4 Of course the autoregulation parameters evaluated in this study will never be a single diagnostic parameter identifying which MCI patient will develop Alz- heimer’s disease and which one doesn’t, but these parameters could help in determining the influence of vascular components in the disease spectrum of cognitive disorders and together with other factors could disentangle the com- plex relationship between cerebral blood flow and cognition. A multidisciplinary approach is needed to study vascular cognitive impairment 12. We also per- formed extensive duplex and neuropsychological investigations. These results will be published in successive papers. Limitations TCD measures only relative velocity instead of absolute flow due to the un- known vessel diameter and insonation angle. Therefore, the assumed diameter of 3 mm for the WKM parameters increases noise and could mask differences in e.g. compliance. The small number of patients in this study could limit the power to show signifi- cant differences. For the autoregulation parameter GainLF gain a post hoc analy- sis showed that at least twice the number of subjects would be needed to show a significant difference for this parameter. Since the recruitment was from an existing cohort of both AD and MCI the MRI data were not always acquired within the same time frame as the autoregulation measurement were performed. In only 9 patients the MRI was acquired maximally one year before the autoregu- lation test. This means that the condition of the cerebrovascular system could have been worsened with respect to the MRI results. Medication can influence the relation between disease groups and their cere- brovascular results. Therefore, use of psychopharmacological medication was an exclusion criterion. Medication use was asked and almost every AD patient used a cholinesterase inhibitor. Due to ethical reasons this could not be stopped for the present study. A few AD patients (12%) and MCI patients (32%) used statines, which could influence autoregulation performance. Conclusion This is the first study comparing cerebralautoregulation in three subject groups namely AD, MCI and matched controls in which distinct changes in cerebral hemodynamics in patients with AD were observed. Increased cerebrovascular resistance is found, possibly due to enhanced vasoconstriction in AD. CVRi values for MCI showed to be in between AD and controls but not significantly different from controls. In MCI decreased mCBFV and increased CVRi might be 74
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