Blood viscosity modelling: influence of aggregate network dynamics under transient conditions.

This paper reports on a theoretical examination of the hypothesis that red blood cell network characteristics influence the mechanical properties of the fluid. For this purpose a newly developed energy-rate based blood viscosity model, which incorporates network dynamics, was used to predict the transient behaviour of blood viscosity (steady-state results of this model have been reported in Biorheology 46 (2009), 487-508). The main network characteristic examined in the present work was the inter-aggregate branch size and its relationship to the evolving aggregates.

An energy-rate based blood viscosity model incorporating aggregate network dynamics.

Existing time-dependent blood viscosity models that involve aggregation dynamics are mainly based on structural variables and/or viscoelastic models in order to describe the bulk mechanical properties of the fluid, but the implications of important characteristics of blood microstructure, such as the time- and flow-dependent characteristics of the red blood cell network developed due to aggregation at low shear rates, have not been thoroughly investigated. In this paper a time-dependent blood viscosity model is developed based on an energy-rate model previously proposed (Skalak et al., Biophys.

Erythrocyte aggregation at non-steady flow conditions: a comparison of characteristics measured with electrorheology and image analysis.

In the present study electro-rheology (Contraves LS30 viscometer-based system) and optical shearing microscopy (Lincam CSS450 system and image analysis) techniques have been utilized in order to provide quantitative data on the behaviour of the microstructural properties of whole normal human blood at non-steady flow conditions. The objective of this work is to contribute towards a better understanding of red blood cell aggregation at flow conditions similar to that occurring in a circulatory system and to aid the interpretation and validation of electro-rheological data through a quantitative comparison with data acquired with optical shearing microscopy. Electro-rheology is a promising technique that has been used to provide bulk fluid properties, showing potential for basic research and diagnostic purposes, whereas optical shearing techniques offer a direct assessment of blood microstructure at a cellular level.

Coupled human erythrocyte velocity field and aggregation measurements at physiological haematocrit levels.

Simultaneous measurement of erythrocyte (RBC) velocity fields and aggregation properties has been successfully performed using an optical shearing microscope and Particle Image Velocimetry (PIV). Blood at 45% haematocrit was sheared at rates of 5.4< or =gamma < or = 252 s(-1) and imaged using a high speed camera.

On the effect of microstructural changes of blood on energy dissipation in Couette flow.

Red blood cell aggregation affects the flow of blood at low shear rates; not only the behaviour of the fluid deviates from its Newtonian characteristics, but, depending on the shearing history of the flow, the non-Newtonian characteristics may be influenced. It is not clear how the time and flow-dependent characteristics of the microstructural network developed in blood affect its mechanical properties. The present study aims to improve understanding of the effect of dynamic flow conditions on microstructural characteristics and consequently on the mechanical properties of the fluid.