Investigating the non-linearity of the BOLD cerebrovascular reactivity response to targeted hypo/hypercapnia at 7T. A., Froeling M., Luijten P., Philippens M., et al. The cerebrovascular response to carbon dioxide in humans. Glial and neuronal control of brain blood flow. M., Charpak S., Lauritzen M., Macvicar B. Reversed robin hood syndrome in acute ischemic stroke patients. The dashed vertical line shows the subject’s resting P ETCO 2.Īlexandrov A. The flow patterns of response for the voxel branch and reference resistance branch are then calculated from the resistance response patterns (voxel, blue line and reference black dashed line) The resistance sigmoids graphs show the relation of the fitted voxel sigmoid resistances (blue line) to the reference resistance sigmoid (black line), with their respective midpoints indicated by the vertical lines. P ETCO 2 (magenta points), is converted to resistance (blue points), then fitted with a sigmoid (blue line). The analysis graph shows the model fitting process, using the reference resistance (black solid line) and its calculated flow (black dashed line): model voxel branch flow pattern of response to P ETCO 2, scaled from the % changes in BOLD vs. The maps show the locations of example voxels 1 (high amplitude, midpoint at resting P ETCO 2) and 2 (low amplitude, high midpoint). We suggest that these maps provide physiological insight into the regulation of CBF distribution.Ĭarbon dioxide cerebrovascular reactivity cerebrovascular resistance humans magnetic resonance imaging model.Įxample maps for a single axial slice and their color scales from a healthy control subject with analysis graphs and resistance sigmoids from two example voxels. We show an example for a healthy subject and for a patient with steno-occlusive disease to illustrate. The sigmoid parameters of the resistance response pattern of examined voxels may be mapped to their anatomical location. Using the model to calculate resistance response patterns of the examined branch showed sigmoidal patterns of resistance response, regardless of the measured CBF response patterns. The other branch has a CBF equal to the measured CBF response to CO 2 of any voxel under examination. One branch has a reference resistance with a sigmoidal response to CO 2, representative of a voxel with a robust response. The model, which has been used previously to explain the steal phenomenon, consists of two vascular branches in parallel fed by a major artery with a fixed resistance unchanging with CO 2. We propose a method using a simple model to convert these CBF response patterns to the pattern of resistance responses that underlie them. As a result, the CBF responses to CO 2 take on various non-linear patterns that are not well-described by straight lines. Consequently, local CBF responses reflect not only changes in the local vascular resistance but also the effect of changes in local perfusion pressure resulting from redistribution of flow within the network. However, the ability of CVR to reflect the responsiveness of a particular vascular region is confounded by that region's inclusion in the cerebral vascular network, where all regions respond to the global CO 2 stimulus. Cerebrovascular reactivity (CVR), the ratio of cerebral blood flow (CBF) response to CO 2 stimulus is currently used as a performance metric. Deliberate changes in carbon dioxide (CO 2) partial pressure may be used to challenge this regulation and assess its performance since CO 2 also acts to change vessel diameter. The cerebral vascular network regulates blood flow distribution by adjusting vessel diameters, and consequently resistance to flow, in response to metabolic demands (neurovascular coupling) and changes in perfusion pressure (autoregulation).
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