Rheo-optical studies of blood cells 1

Abstract

This paper is concerned with the optical properties of suspensions of blood cells subjected to flow, under conditions where rates of shear are non-uniform and undefined, as for stirred or swirled suspensions, or where they are rigorously defined, as for suspensions flowing between counter-rotating glass discs in a microCouette device. A detailed example of each of these two types of investigations is presented: (i) the determination of light transmission constants of suspensions of blood cells as a function of particle concentration, particle shape and stirring rate with a platelet aggregometer. This device measures light transmittance in suspensions contained in a cylindrical cuvette maintained at 37’C and stirred with a magnetic bar. Both light transmission and associated stirring-dependent scintillations are related directly to the particle shape and pharmacologically-induced shape changes, as well as aggregation; (ii) the measurement of the period of damping and associated relaxation time of the rheo-optical transients observed for dilute suspensions of erythrocytes subjected to Couette flow. These are shown to be quantitatively related to particle geometry and particle interactions in terms of theoretically-derived rheological parameters. Other related rheo-optical methods are compared with these two specific examples, and summarized in terms of the optical parameters studied and the associated suspension or particle property being described for erythrocytes and platelets. It is seen that particle concentration, volume, shape and state of aggregation can generally be measured, depending on the parameters being analyzed. Shear-dependent scintillations or transient oscillations are found to reflect essentially the asymmetric shape of cells. The advantages and limitations of these different methods are presented. Finally, the future possible directions of rheo-optical studies are indicated.