Dynamic regulation of cerebral tissue oxygenation is associated with neurocognitive dysfunction in aMCI patients.

C erebral autoregulation (CA) is essential to maintain a constant cerebral blood flow (CBF) in the context of changes in cerebral perfusion pressure.1 Assessment of CA reflects cerebrovascular function and has been used widely in hypertension studies and other clinical settings. 2,3 Quantitative assessment of CA is challenged by the methods used for CBF measurement. Modern imaging modalities such as single-photon emission computed tomography, positron emission tomography, perfusion computed tomography, and MRI are difficult to be applied for CBF measurement in clinical studies of CA because of the cumbersome experimental conditions, the limitations of using radioactive isotopes (single-photon emission computed tomography and positron emission tomography), or other imaging contrast agents (computed tomography and MRI) for repeated measurements. 4 Recently, transcranial Doppler (TCD) has been used to assess CA because of its bedside availability, noninvasiveness, and high temporal resolution in measuring changes in cerebral blood flow velocity (CBFV) in the basal cerebral arteries. 5 However, because the diameter of the insonated vessels cannot be measured directly using TCD, the validity of using this technique to assess CA is based on a fundamental assumption that changes in CBFV represent changes in volumetric CBF, that is, by assuming that the diameter of basal cerebral arteries does not change significantly in the face of changes in blood pressure. 5 For its importance, this assumption has been evaluated repeatedly by using a variety of imaging modalities to measure CBF and to compare with TCD measurement of CBFV during changes in arterial pressure. 6,7 However, the findings so far are inconsistent. [8][9][10] One of the major limitations of these studies is that CBF and CBFV often were not measured simultaneously or were measured with different temporal and spatial resolutions, thus making it difficult or even impossible for direct comparisons between CBF and CBFV Abstract-The validity of using transcranial Doppler measurement of cerebral blood flow velocity (CBFV) to assess cerebral autoregulation (CA) still is a concern. This study measured CBFV in the middle cerebral artery using transcranial Doppler and volumetric cerebral blood flow (CBF) in the internal carotid artery (ICA) using color-coded duplex ultrasonography to assess CA during steady-state changes in mean arterial pressure (MAP 7 However, this study was conducted only in 7 patients with cerebrovascular diseases under surgical conditions, and these observations need to be confirmed.Color-coded duplex ultrasonography (CDUS) is a noninvasively bedside available technology that has been used to measure volumetric CBF in the ICA.12,13 Similar to TCD, CDUS also has high temporal resolution.14 In addition, changes in CBF in the ICA most likely reflect those in the MCA and anterior cerebral artery, which are the major branches of ICA.In this study, we simultaneously measured changes in CBFV in the MCA and ICA and CBF in the ICA to assess CA during stepw...

Key pointsr Cerebral autoregulation (CA) is a key mechanism to protect brain perfusion in the face of changes in arterial blood pressure, but little is known about individual variability of CA and its relationship to the presence of brain white matter hyperintensity (WMH) in older adults, a type of white matter lesion related to cerebral small vessel disease (SVD).r This study demonstrated the presence of large individual variability of CA in healthy older adults during vasoactive drug-induced changes in arterial pressure assessed at the internal carotid and vertebral arteries. We also observed, unexpectedly, that it was the 'over-' rather than the 'less-reactive' CA measured at the vertebral artery that was associated with WMH severity.r These findings challenge the traditional concept of CA and suggest that the presence of cerebral SVD, manifested as WMH, is associated with posterior brain hypoperfusion during acute increase in arterial pressure.Abstract This study measured the individual variability of static cerebral autoregulation (CA) and determined its associations with brain white matter hyperintensity (WMH) in older adults. Twenty-seven healthy older adults (13 females, 66 ± 6 years) underwent assessment of CA during steady-state changes in mean arterial pressure (MAP) induced by intravenous infusion of sodium nitroprusside (SNP) and phenylephrine. Cerebral blood flow (CBF) was measured using colour-coded duplex ultrasonography at the internal carotid (ICA) and vertebral arteries (VA). CA was quantified by a linear regression slope (CA slope) between percentage changes in cerebrovascular resistance (CVR = MAP/CBF) and MAP relative to baseline values. Periventricular and deep WMH volumes were measured with T2-weighted magnetic resonance imaging. MAP was reduced by −11 ± 7% during SNP, and increased by 21 ± 8% during phenylephrine infusion. CA demonstrated large individual variability with the CA slopes ranging from 0.37 to 2.20 at the ICA and from 0.17 to 3.18 at the VA; no differences in CA were found between the ICA and VA. CA slopes measured at the VA had positive correlations with the total and periventricular WMH volume (r = 0.55 and 0.59, P < 0.01). Collectively, these findings demonstrated the presence of large individual variability of CA in older adults, and that, when measured in the posterior cerebral circulation, it is the higher rather than lower CA reactivity that is associated with WMH severity.