Generalization of the Fahraeus principle for microvessel networks

TLDR

The vessel Fahraeus effect arises from velocity differences between red cells and plasma within individual vessel segments, while the network Fahraeus effect stems from velocity and hematocrit heterogeneity across vessels in a complete-flow cross section. The study mapped hematocrit and diameter in every segment between bifurcations of three rat mesenteric microvascular networks, classifying them by flow direction and using photographic and videomicroscopic imaging to analyze hematocrit distribution across consecutive-flow cross sections. Mean hematocrit decreases in peripheral cross sections, with the network Fahraeus effect contributing about 20 % of the total reduction and becoming more pronounced toward the most distal cross sections.

Abstract

Microvessel hematocrits and diameters were determined in each vessel segment between bifurcations of three complete microvascular networks in rat mesentery. Classification of the segments as arteriolar, venular, or arteriovenular (av) was based on flow direction at branch points. Photographic and videomicroscopic mapping was used to obtain quantitative information on the architecture and topology of the networks. This topological information allowed the analysis of hematocrit distribution within a series of consecutive-flow cross sections, each of which carried the total flow through the network. The observed reduction of mean hematocrit in the more peripheral cross sections is explained by the presence of a “vessel” and a “network” Fahraeus effect. The vessel Fahraeus effect results from velocity difference between red cells and blood within the individual vessel segments due to the existing velocity and cell concentration profiles. The network Fahraeus effect is based on the velocity difference of red cells and blood caused by velocity and hematocrit heterogeneity between the vessels constituting any of the complete-flow cross sections. The network Fahraeus effect is found to account for approximately 20% of the total hematocrit reduction and increases toward the most distal cross sections.