Showing papers by "I.M. Sechenov First Moscow State Medical University published in 1996"

Light-scattering anisotropy in the diagnostics of structural and orientational effects of RBCs in whole blood in Couette flow

Abstract: There are various optical methods to study the rheological properties of RBC's subjected to shear stress. The commonly used techniques are rheoscopy and ektacytometry, which use the diffraction pattern of light transmitted through the dilute suspension to study some changes in the shape and deformability of RBC's1. But the conditions of light scattering in the dilute suspensions are different from that in the concentrated suspensions or whole blood. The aggregometry method based on the regisration of light scattered from the blood layer is used for the monitoring of aggregational properties of erythrocytes in stasis and under the shear stress2'3. One of the methodological approaches in the development of aggregometry is based on the registration of light transmission through a thin blood layer in a cone-plate type viscometer4'5. Another method is based on the registration of the backscattered light from a blood layer in a Couette flow viscometer6'7. The differences in the flow geometry and in the modes of detection of the outcoming light have yielded different results in the study of hyperaggregational syndrome even in the in vitro experiments8. Comparative clinical approbation of the methods in three hemorheological centers have shown wide variation ofred blood cell aggregation characteristics9. We use the laser backscattering nephelometry technique to study the deformation and aggregation (or disaggregation induced by shear stress) of RBC's in whole blood in Couette flow. The estimated parameters of a blood sample are the characteristic times of aggregation T1 and T2, the index of hydrodynamic strength of aggregates β, and deformability of erythrocytes at high shear stress D. The measured parameters of the aggregation process in whole blood essentially depend on the degree of deformability of RBC's. The deformation and orientation of cells in a shear flow can be indirectly determined from the registration of the anisotropy in light scattering. Such measurements were carried out with a rotational viscometer10. These experiments with deformable erythrocytes showed the existence of an angular assymetry in the backscattering diagram. This assymetry was higher when the shear rate and the viscosity of the suspending medium increased. When performed with cells hardened with glutaraldehyde the backscattering experiments showed no changes in the backscattered diagram. In this paper we discuss a modified aggregometry technique which enables to register the anisotropy of light-scattering thus yielding additional information on deformation of RBC's under high shear stress and some parameters of the aggregation process in whole blood.