Authors: C.K. Hadjistassou, K. Moyle and Y. Ventikos
Affilation: University of Oxford, United Kingdom
Pages: 650 - 653
Keywords: microscopic, oxygen transport, haemodynamics, convection, diffusion
With the prospect of elucidating the Blood Oxygenation Level Dependent (BOLD) fMRI effect we consider cerebral oxygen transport at the microscopic scale. We concentrate on the transient response of a capillary-tissue system following brain activity. Model findings cast new light on the dynamics of BOLD fMRI. Diffusion and convection in the axial and radial directions are accounted for, over a range of blood velocities and cerebral oxygen utilisations (CMRO2). The model consists of a capillary, measuring 8μm in diameter by 200μm in length, surrounded tissue 25μm thick. The non-linear kinetics of oxygen release are modelled using the oxygen dissociation curve. Global oxygen conservation is ensured by coupling the oxy/deoxyhaemoglobin and free oxygen concentrations. Model sensitivity is quantified through a systematic study considering a range of blood velocities and CMRO2 values, with results showing good agreement with earlier studies. The transient response of the system to neuronal activation is quantitatively mapped and used to investigate various hypotheses from the literature. We show that an increase in CMRO2 requires a concomitant rise in blood velocity, suggesting a coupled CMRO2-blood flow rate dependence. The time lag between the stimulus onset and the haemodynamic response (and diffusion and convection) appear promising in explaining BOLD.