Biorheology

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.

Certains germes comme Diplococcus pneumoniae, fréquemment isolés dans les sécrétions bronchiques expectorées par les bronchitiques chroniques, possèdent un potentiel marqué d’activité d’exoenzymes, susceptibles de modifier la structure des glycoprotéines du mucus.

L’action de diverses glycosidases bactériennes: neuraminidases purifiées de Diplococcus pneumoniae et de Clostridium perfringens, β galactosidase et β-N-acétyl-hexosaminidase, a été étudiée in vitro sur les propriétés visco-élastiques des expectorations.

La neuraminidase purifiée de Diplococcus pneumoniae entraîne in vitro une réduction de la viscosité apparente ( η 0 ) et de la recouvrance globale (S _R); cette dernière est d’autant plus marquée que les sécrétions bronchiques sont riches en sialomucines. La présence d’autres glycosidases bactériennes (β-galactosidase et β-N-acétyl-hexosaminidase), bien que susceptibles de se conjuguer à celle de la neuraminidase, n’entraêne pas de modifications rhéologiques plus marquées que celles observées après action isolée de la neuraminidase purifiée.

Ces résultats soulignent l’importance des glycosidases bactériennes qui, au cours des processus suppuratifs bronchiques, peuvent perturber les qualités fonctionnelles de la sécrétion bronchique.

In order to understand more about the rheological properties of mucoid secretions and the mechanisms by which they are thickened or thinned by drugs, a model system based on hog gastric mucin has been employed. The consistency of a 10 per cent dispersion of mucin in tris buffer is little affected by changes in pH, ionic strength and the addition of specific ions such as Ca²⁺. The effect of mucolytic sulphydryl and proteolytic compounds has been followed using continuous shear viscometry and a new stress relaxation method. Other agents (surface active agent, and urea) have a similar effect to water. The model can be thickened by the addition of a disodium tetraborate, a cross-linking agent.

Effective application of the blood viscosity equation η r = ( 1 − k C T ) − 2.5 depends on accuracy of blood and plasma viscosity determinations, and on estimation of free volume of red cells, Ck. When microhaematocrits are used, term Tk can supply an estimate of the rigidity-deformability of the red cells. [n the unusual cases when the relative viscosity of blood is about equal viscosity of plasma, a hypothesis is given that this apparently “absurd” phenomenon might be due to heterogeneous distribution of plasma proteins and formation of “plasma atmosphere” around the red cells (especially in macroglobulinaemia).