Multiscale modeling of cerebral blood flow and oxygen transport

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The overall goal of this proposal is to gain quantitative understanding of the relationship between neural activation, blood flow and tissue oxygenation in the brain cortex, using multiscale theoretical models for blood flow, oxygen transport and flow regulation in networks of microvessels. Adequate blood flow to meet spatially and temporally varying demands of brain tissue is crucial, since lack of oxygen quickly leads to irreversible damage. The mechanisms by which blood flow is controlled are poorly understood. Multiple interactions between neural activity, metabolite levels, changes in vascular tone, network blood flow, and oxygen transport are difficult to unravel, and cannot be understood just by observing behavior of individual blood vessels. In the proposed work, the detailed structure of microvessel networks with thousands of segments in the mouse cerebral cortex will be imaged using two-photon microscopy. Observations using phosphorescence quenching nanoprobes will yield high resolution maps of tissue oxygen levels. Spectral domain optical coherence tomography will be used to measure blood flows. The multiscale modeling approach simulates biological and physical processes at the capillary diameter and cellular scale (~10 μm, including flow mechanics and active responses of vessel walls to hemodynamic, neural and metabolic stimuli), at the vessel scale (~100 μm, including segment flow resistance, oxygen loss and propagation of conducted responses along vessel walls) and at the network and tissue scale (~1000 μm, including entire network flows, perfusion, oxygen extraction and tissue hypoxic fraction). Specific Aim 1 is to develop predictive multiscale models for blood flow and oxygen transport in the mouse cerebral cortex, and validate these models using experimental data derived from multimodal imaging of the cortex microvasculature. The proposed studies will provide a model that will reconcile available data at the microscopic level with macroscopic level variables such as perfusion and oxygen extraction and will allow prediction of tissue oxygenation and occurrence of hypoxia for a range of blood perfusion and oxygen demand. Specific Aim 2 is to develop multiscale models for blood flow autoregulation and neurovascular coupling in the mouse cerebral cortex, and to test and refine these models using experimental data derived from multimodal imaging of the cortical microvasculature. The models will include effects of myogenic, metabolic, shear-dependent and conducted responses, as well as the possible role of capillary-level regulation. Models including or excluding these mechanisms will be tested for their ability to represent actual regulatory responses, as reported in the literature and as observed in multimodal imaging experiments under varying physiological conditions. Improved understanding of the mechanisms of flow regulation could lead to improved strategies for disorders related to neurovascular function, including stroke and neurodegenerative diseases, and for interpreting fMRI brain imaging.