Study of Rheological and Electrical Behaviour of RBC Suspensions in Dextran and PEG under Non-steady Flow. Role of RBC Deformability and Morphology

A concurrent measuring system, using a Contraves Low Shear 30 rotational rheometer, previously described [1-2], was used in the study. It includes a resin replica of the Couette type measuring system MS 1/1 of the rheometer with a pair of platinum electrodes embedded into the wall; a device, constructed by the conductometric method and software (Data acquisition system) [1]. A method, based on dielectric properties of dispersed systems in Couette viscometric blood flow was applied to investigate the kinetics of RBC aggregation and the formation and break-up of the aggregates. Apparent viscosity and conductivity of normal human red blood cell (RBC) suspensions in dextran 70 (Dx 70) and polyethilenglycol (PEG) with various concentrations were evaluated in vitro under steady and unsteady flow conditions. Conductivity time and shear rate dependences in parallel with the rheological properties of the samples were studied under transient flow regimes at different local structure of the uniform Couette flow. Their dependence on dextrans concentrations were evaluated as well. Low shear viscosity and conductivity of RBC suspensions in dextrans were determined and compared to non-aggregating control RBC suspension in PBS. RBCs were treated with glutaraldehyde (GA) with different concentrations (from 0,01% to 1%). A time course of conductivity of normal RBCs and treated with GA suspended in dextran 70 was recorded under trapezoid change of shear rates. It provides experimental description of RBC aggregation-disaggregation processes and other cell-cell interactions. Dextrans induce morphological alterations in RBC shape and arrangement in the suspensions. Echinocytes are observed at low Dx 70 concentrations while spherocytes are found mainly in smears at higher Dx 70 concentrations. Their morphological characteristics affect blood electrical and mechanical properties.