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Salinet A.S.M.,University of Leicester | Salinet A.S.M.,Royal Infirmary | Haunton V.J.,University of Leicester | Panerai R.B.,University of Leicester | And 3 more authors.
Journal of Neurology

The aim of this study was to systematically review CBF studies, assess their methodological quality, and identify trends in the association between task-related brain activation patterns and CBF changes in ischemic stroke (IS) patients. We searched the MEDLINE, EMBASE, CINAHL, and Web of Sciences databases for studies of functional recovery with quantification of CBF responses to brain activation paradigms after IS. Titles, abstracts and full text of articles were scrutinised according to pre-defined selection criteria. Two independent reviewers (AS, VH) undertook the methodological quality screening and data extraction of the included studies. Sixteen of the 1,521 identified studies were relevant. Studies showed weaknesses in key methodological criteria (e.g. population size, discussion of limitations), and only seven studies compared responses with a control population. Overall, there was no agreement between CBF responses in either the affected or unaffected hemisphere and prediction of post-IS recovery. Some studies have shown a higher CBF increase in the unaffected hemisphere when the affected hemisphere was stimulated compared to the healthy control responses. However, CBF responses in the affected hemisphere were inconsistent. Many post-IS CBF studies are of poor methodological quality, and do not demonstrate a consistent response post-IS or a relationship with recovery. Further longitudinal studies assessing the natural history of CBF responses to brain paradigms following IS should be undertaken to determine prognostic significance, and to inform future therapeutic strategies. © 2013 Springer-Verlag Berlin Heidelberg. Source

Maggio P.,Biomedical University of Rome | Salinet A.S.M.,University of Leicester | Panerai R.B.,University of Leicester | Panerai R.B.,National Institutes for Health Research NIHR | And 2 more authors.
Journal of Applied Physiology

Does hypercapnia- induced impairment of cerebral autoregulation affect neurovascular coupling? A functional TCD study. J Appl Physiol 115: 491-497, 2013. First published June 6, 2013; doi:10.1152/japplphysiol.00327.2013.- Neurovascular coupling (NVC) and dynamic cerebral autoregulation (dCA) are both impaired in the acute phase of ischemic stroke, but their reciprocal interactions are difficult to predict. To clarify these aspects, the present study explored NVC in a healthy volunteer population during a surrogate state of impaired dCA induced by hypercapnia. This study aimed to test whether hypercapnia leads to a depression of NVC through an impairment of dCA. Continuous recordings of middle cerebral arteries cerebral blood flow velocity (CBFv), blood pressure (BP), heart rate, and end-tidal CO2 WERE performed in 19 right-handed subjects (aged >45 yr) before, during, and after 60 s of a passive paradigm during normocapnia and hypercapnia. The CBFv response was broken down into subcomponents describing the relative contributions of BP (VBP), critical closing pressure (V CrCP), and resistance area product (VRAP). VRAP reflects myogenic activity in response to BP changes, whereas VCrCP is more indicative of metabolic control. The results revealed that hypercapnia significantly affected NVC, with significant reductions in the relative contribution of VCrCP to the paradigminduced increase in CBFv. The present study suggests that hypercapnia impairs both dCA and NVC, probably acting through an impairment of the metabolic component of CBF control. Copyright © 2013 the American Physiological Society. Source

Salinet A.S.M.,University of Leicester | Robinson T.G.,University of Leicester | Robinson T.G.,National Institutes for Health Research NIHR | Panerai R.B.,University of Leicester | Panerai R.B.,National Institutes for Health Research NIHR
Journal of Applied Physiology

Cerebral blood flow (CBF) regulation can be impaired in acute ischemic stroke but the combined effects of dynamic cerebral autoregulation (CA), CO2 cerebrovascular reactivity (CVR), and neurovascular coupling (NVC), obtained from simultaneous measurements, have not been described. CBF velocity in the middle cerebral artery (MCA) (CBFv, transcranial Doppler), blood pressure (BP, Finometer), and end-tidal PCO2 (PETCO2, infrared capnography) were recorded during a 1-min passive movement of the arm in 27 healthy controls [mean age (SD) 61.4 (6.0) yr] and 27 acute stroke patients [age 63 (11.7) yr]. A multivariate autoregressive-moving average model was used to separate the contributions of BP, arterial PCO2 (PaCO2), and the neural activation to the CBFv responses. CBFv step responses for the BP, CO2, and stimulus inputs were also obtained. The contribution of the stimulus to the CBFv response was highly significant for the difference between the affected side [area under the curve (AUC) 104.5 (4.5)%] and controls [AUC 106.9 (4.3)%; P = 0.008]. CBFv step responses to CO2 [affected hemisphere 0.39 (0.7), unaffected 0.55 (0.8), controls 1.39 (0.9)%/mmHg; P = 0.01, affected vs. controls; P = 0.025, unaffected vs. controls] and motor stimulus inputs [affected hemisphere 0.20 (0.1), unaffected 0.22 (0.2), controls 0.37 (0.2) arbitrary units; P = 0.009, affected vs. controls; P = 0.02, unaffected vs. controls] were reduced in the stroke group compared with controls. The CBFv step responses to the BP input at baseline and during the paradigm were not different between groups (P = 0.07), but PETCO2 was lower in the stroke group (P < 0.05). These results provide new insights into the interaction of CA, CVR, and NVC in both health and disease states. Copyright © 2015 the American Physiological Society. Source

Salinet A.S.M.,Royal Infirmary | Robinson T.G.,Royal Infirmary | Robinson T.G.,National Institutes for Health Research NIHR | Panerai R.B.,Royal Infirmary | Panerai R.B.,National Institutes for Health Research NIHR
Journal of Neurology

We tested two hypotheses: (1) neurovascular coupling is impaired after acute ischemic stroke, (2) subcomponent analysis of cerebral blood flow velocity can reveal significant differences between acute ischemic stroke and healthy controls. This was explored through the comparison of nineteen acute ischemic stroke patients with healthy controls. Recordings of cerebral blood flow velocity, blood pressure and end-tidal CO2 were obtained during 60s of passive elbow flexion. Cerebral blood flow velocity changes were decomposed into standardized subcomponents describing the contributions of blood pressure (V BP), resistance area product (V RAP) and critical closing pressure (V CrCP). The passive paradigm led to a bilateral cerebral blood flow velocity increase in both groups, but in acute ischemic stroke the magnitude of change was significantly lower. Blood pressure increases were shown to be an important contributor to cerebral blood flow velocity response throughout the paradigm in both groups, with no significant difference between groups. The V CrCP contribution was not different between groups or hemispheres; its continuous rise during activation indicating a vasodilatory effect. On the other hand, the V RAP contribution showed significant differences (p = 0.03), thus suggesting myogenic impairment in acute ischemic stroke. Cerebral blood flow velocity responses to passive elbow flexion suggest an impairment of neurovascular coupling in acute ischemic stroke. Subcomponent analysis suggests an impairment of the myogenic pathways, giving a greater insight into the different mechanisms contributing to neurovascular coupling. Further research is needed to assess the clinical value of subcomponent analysis of neurovascular coupling and the natural history of such changes following acute ischemic stroke. © 2013 Springer-Verlag Berlin Heidelberg. Source

Salinet A.S.M.,University of Leicester | Panerai R.B.,University of Leicester | Panerai R.B.,National Institutes for Health Research NIHR | Robinson T.G.,University of Leicester | Robinson T.G.,National Institutes for Health Research NIHR
Ultrasound in Medicine and Biology

This study aimed to compare the response of metabolic-induced cerebral hemodynamic changes measured using transcranial Doppler (TCD) ultrasonography during passive, active and motor imagery paradigms, and associated peripheral hemodynamic responses. Continuous recordings of bilateral cerebral blood flow velocity (CBFv), blood pressure, heart rate and end-tidal CO2 were performed in 12 right-handed subjects (aged ≥45 y) before, during and after 60 s of active, passive and mental-imagined paradigms. The results revealed no significant difference in CBFv responses between the paradigms and, furthermore, the temporal patterns of the hemodynamic responses showed some degree of similarity. Moreover, significant changes were seen in cerebral and peripheral hemodynamic responses for all paradigms. Our results suggest that active, passive and motor imagery paradigms can be used interchangeably to assess hemodynamic responses. This will enable more detailed noninvasive assessment in patients, where voluntary movement is not possible, but where abnormalities of cerebral hemodynamic control mechanisms can be anticipated. © 2012 World Federation for Ultrasound in Medicine & Biology. Source

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