When red blood cells take unexpected detours 🔀

A Franco-American team has demonstrated that within the microcirculatory network, some red blood cells can take unexpected paths to travel from one point to another. This experimental observation is expected to lead to a more precise modeling of the mechanisms of oxygenation as well as the elimination of waste from cellular activity within the blood network.


The microcirculatory blood network is the prime location for exchanges between the blood and the organs: nutrients, respiratory gases, and waste products from metabolic activity are transferred to or from neighboring cells.

In this dense and redundant network of vessels, where the diameter is close to the size of circulating cells such as red and white blood cells, numerous physico-chemical interactions occur. Significant fluctuations in flow velocity and residence time of circulating elements are observed in vivo, though the mechanisms by which these fluctuations occur are not yet understood.

Due to their uneven distribution within vessels, red blood cells generate unique flow laws in terms of dissipation within the vessels or separation of cells/plasma at branches.

These behaviors have been theoretically studied for many years and serve as the foundation for current models aimed at predicting the distribution of red blood cells and dissolved molecules in the plasma within the network. By analogy with the flow of simple fluids, it is often assumed that the flow resulting from a constant condition at the network's entry would be unique and steady.

However, more advanced theoretical studies in recent years have shown the possibility of a more complex reality due to the highly nonlinear nature of the models, where multiple flow regimes can exist (and alternate randomly) under the same constant forcing conditions at the network's entry.


In a recent study, researchers from the Laboratoire Interdisciplinaire de Physique (LIPhy, CNRS / Université Grenoble Alpes) and the Laboratoire Rhéologie et Procédés (LRP, CNRS / Université Grenoble Alpes) developed an in vitro experiment highlighting these multiple flow solutions between which the system spontaneously oscillates.

In these flow configurations, a significant portion of the cells and fluid is diverted into transverse channels relative to the main flow direction, significantly increasing their residence time in the network.

These observations, supported by modeling developed by their American collaborators J. Geddes (Olin College) and N. Karst (Babson College), demonstrate the necessity of incorporating this intrinsic flow instability of blood within the capillary network into future models, even in non-pathological conditions. This transition between different hydrodynamic flows is likely to couple with various disruptive phenomena inherent to this environment: occlusions, the passage of white blood cells, vasodilation, etc. These results are published in the journal Physical Review Fluids.

Reference
Spatio-temporal instabilities of blood flow in a model capillary network.
Mathieu Alonzo, Nathaniel J. Karst, Thomas Podgorski, John B. Geddes, and Gwennou Coupier.
Physical Review Fluids, published on October 22, 2024.
Doi: 10.1103/PhysRevFluids.9.104401
Open archive: arXiv