Reduced Vasomotor Reactivity in Cerebral Microangiopathy

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Abstract
Background and Purpose —Reduction of cerebral blood flow and vasomotor reactivity (VMR) are thought to play an important role in the pathogenesis of cerebral microangiopathy. The aim of our study was to determine whether near-infrared spectroscopy (NIRS) can detect a reduced VMR in patients with microangiopathy, whether NIRS reactivities correlate with VMR assessed by transcranial Doppler sonography (TCD), and whether the differing extents of patients’ microangiopathy demonstrated on MRI or CT can be distinguished by both noninvasive techniques. Methods —We compared the VMR of 46 patients with cerebral microangiopathy with 13 age-matched control subjects. Patients were classified with the Erkinjuntti scale. We monitored cerebral blood flow velocity (CBFV) in both middle cerebral arteries by TCD, changes in concentration of oxyhemoglobin (Hb o 2 ), deoxyhemoglobin (Hb) and blood volume (HbT) by NIRS, mean arterial blood pressure, and end-tidal CO 2 (Et co 2 ) during normocapnia and hypercapnia. VMRs were calculated as percent change of CBFV (NCR) and as absolute change in concentration of HbO 2 , Hb, and HbT per 1% increase in Et co 2 (CR-HbO 2 , CR-Hb, CR-HbT). Results —NCR and NIRS reactivities were significantly reduced in patients with cerebral microangiopathy. CR-HbO 2 and CR-Hb showed a close correlation with NCR, and NCR and NIRS reactivities were related to the severity of cerebral microangiopathy according to the Erkinjuntti scale. Validity of NCR and NIRS reactivities were similar. Conclusions —VMR is reduced in patients with cerebral microangiopathy and can be noninvasively assessed in basal arteries (with TCD) and brain parenchyma (with NIRS). Reduction of CO 2 -induced VMR, as measured by NIRS and TCD, may indicate the severity of microangiopathy.