Cognitive Correlates of Cerebral Vasoreactivity on Transcranial Doppler in Older Adults

Background: This study was performed to explore the possible contributions of cerebral hemodynamic changes to the cognitive impairment in patients with Alzheimer's disease (AD). Methods: A total of 194 participants were included: 52 controls, 75 patients with mild cognitive impairment (MCI), and 67 patients with AD. Demographic characteristics, vascular risks, mini-mental state examination MMSE), and clinical dementia rating (CDR) were assessed, and magnetic resonance imaging of the brain was performed to evaluate white matter hyperintensities (WMHs). Using transcranial Doppler (TCD) ultrasonography, cerebrovascular reactivity (CVR) was evaluated with a breath-holding test, in addition to the mean blood flow velocity (MFV), pulsatility index (PI), and resistance index (RI) of the middle cerebral artery. Results: After adjusting for covariates such as age, education, WMH severity, and vascular risks, TCD parameters such as MFV, PI, and RI did not differ between the 3 groups. However, CVR was significantly reduced in the AD group (45.33 +/- 11.49%), compared with the other groups (56.36 +/- 14.65%, controls; 53.84 +/- 15.47%, MCI group; P < .001). Multiple regression analyses also showed that CVR was associated with MMSE scores. CVR differed according to the CDR scores (P < .001). Conclusions: Our finding may be suggestive of an underlying microangiopathic mechanism in AD patients. Furthermore, there was an association between the impaired function of cerebral microvessels and cognitive impairment. Further research is needed to fully establish whether altered cerebral hemodynamics may be considered an independent factor in predicting cognitive decline or an effect of pathologic processes involved in AD.