Effect of endothelial glycocalyx layer redistribution upon microvessel poroelastohydrodynamics

• Published in: Journal of fluid mechanics Vol. 798; pp. 812 - 852
• Main Authors: Lee, T. C., Long, D. S., Clarke, R. J.
• Format: Journal Article
• Language: English
• Published: Cambridge, UK Cambridge University Press 10.07.2016
• Subjects: Bioavailability; Blood cells; Blood vessels; Boundary element method; Cell junctions; Circulatory system; Computational fluid dynamics; Confocal microscopy; Disease; Dynamics; Endothelium; Erythrocytes; Experiments; Fluid flow; Hemodynamics; Hyperglycemia; Lines; Macromolecules; Mass transport; Mathematical models; Mechanical stimuli; Mechanotransduction; Microscopy; Microvasculature; Molecular sieves; Physiological functions; Protection; Proteins; Standard deviation; Stokes flow; Stokes law (fluid mechanics); Stress; Thin films; Transducers; low-Reynolds-number flows; blood flow; boundary integral methods
• ISSN: 0022-1120; 1469-7645
• DOI: 10.1017/jfm.2016.337

The endothelial glycocalyx layer (EGL) is a macromolecular layer that lines the inner surface of blood vessels. It is believed to serve a number of physiological functions in the microvasculature, including protection of the vessel walls from potentially harmful levels of fluid shear, as a molecular sieve that acts to regulate transendothelial mass transport, and as a transducer of mechanical stress from the vessel lumen. To best fulfil some of its roles, it has been suggested that the EGL redistributes, so that it is thickest at the cell–cell junctions. It has also been suggested that the majority of mechanotransduction occurs through the solid phase of the EGL, rather than via its fluid phase. The difficulties associated with measuring the distribution of the EGL in vivo make these hypotheses difficult to confirm experimentally. Consequently, to gauge the impact of EGL redistribution from a theoretical standpoint, we compute the flow through a porous-lined microvessel, the endothelial surface of which has been informed by confocal microscopy images of a postcapillary venule. Following earlier studies, we model the poroelastohydrodynamics of the EGL using biphasic mixture theory, taking advantage of a recently developed boundary integral representation of these equations to solve the coupled poroelastohydrodynamics using the boundary element method. However, the low permeabilities of the EGL mean that viscous effects are confined to thin layers, thereby also enabling an asymptotic treatment of the dynamics in this limit. In this asymptotic regime, we also consider a two-layer Stokes flow model for the lumen flow to approximate the effect of red blood cells within the lumen. We demonstrate that redistribution of the EGL can have a substantial impact upon microvessel haemodynamics. We also confirm that the bulk of the mechanical stress is indeed carried through the solid phase of the EGL.