Engineering simulation of the viscous behavior of whole blood using suspensions of flexible particles.

Highly flexible model red cells were molded of acrylamide gel and suspended in a mixture of castor oil and diiodomethane to produce a neutrally buoyant fluid suspension in which the particles behaved mechanically very much like living erythrocytes. The various suspensions were permitted to flow down long cylindrical tubes while measurements of flow rate and pressure drop were made for various concentrations. The fluid suspensions were found to exhibit nonNewtonian viscous behavior which agrees very well with that of whole blood under comparable conditions. The fluid suspensions also exhibited a yield stress below which particle motion ceases. The yield stress was found to depend strongly on particle concentration, as is the case for whole blood. ADDITIONAL KEY modeling of blood non-Newtonian flow WORDS erythrocyte behavior stasis pressure-flow relation yield stress microcirculation laminar flow • It is well known that whole blood, even during steady flow through rigid cylindrical tubes, does not behave as a Newtonian fluid (1-4). Instead, the velocity profile for blood changes from the parabolic shape of an ideal liquid to a blunter one, and along with this, there is a migration of erythrocytes away from the vessel wall (5) . This change increases progressively as the vessel diameter decreases. Palmer (6), Bloch (7), Monro (8) , and Branemark and Lindstrom (9) have clearly shown that erythrocytes passing through the microcirculation often undergo large radial excursions, significant distortions, or both. Although there is a wealth of qualitative information available on this subject, little is known about the pressure-flow relationships for these conditions, nor is there much information on the influence of the flexibility of the red corpuscles on the viscous fluid