Laboratoire Matière et Systèmes Complexes

There will be a live diffusion with Zoom.

Broad distributions of blood flow and transport properties as a fundamental component of brain microcirculation.

Sylvie Lorthois, Groupe Milieux Poreux et Biologiques , Institut de Mécanique des Fluides de Toulouse

The cerebral microvascular system is essential to a large variety of physiological processes in the brain, including blood delivery, neurotoxic waste clearance and blood flow regulation as a function of neuronal activity (neuro-vascular coupling). Recent evidence suggests it is also involved in the onset an progression of Alzheimer’s disease. In this talk, I will present recent theoretical results which may help understand the underlying mechanisms. These results have been obtained during F. Goirand’s PhD thesis, in collaboration with T. Le Borgne (Univ. Rennes) on one hand and B. Georgeot (LPT Toulouse) and O. Giraud (LPTMS Saclay) on the other hand.

First, the microvascular architecture combines tree-like arteriolar and venular structures with a dense capillary network. I will show that this yields highly heterogeneous blood flow and travel time distributions. I will then discuss how these heterogeneities control the appearance of critical intravascular regions, whether hypoxic or with abnormally high concentrations of metabolic waste, a signature of microvascular dysfunction. I will finally show that such regions appear much earlier than anticipated by current models under pathological stress, such as mild hypoperfusion.

Second, brain microvascular networks have been shown to display a community structure, with some vertices being more connected to each other than with the rest of the vasculature. I will introduce a class of model networks which enables to reproduce this community structure. I will use these model networks to study the global flow reduction induced by the removal of a single edge. The latter can be expressed as a function of the initial flow rate in the removed edge and of a topological quantity, both of which display probability distributions following Cauchy laws. As a result, I will show how the distribution of blood flow reductions is influenced by the community structure, and discuss the consequences on the resilience of the system.