RHEOLOGICAL PROPERTIES OF BLOOD AS ASSESSED WITH A NEWLY DESIGNED OSCILLATING VISCOMETER

A newly designed type of oscillating viscometer was tested for blood v iscosity measurements. The viscometer consists of a probe (either a tu be or a rod) oscillating at a resonance frequency with amplitudes in t he micro- and nanometer range. The torsional oscillations are dampened by fluids flowing through the tube or surrounding the rod. The degree of damping depends on the viscosity of the fluid, which allows to mea sure viscosity. Data obtained with these instruments were compared wit h those obtained with a conventional Couette viscometer. An increase o f erythrocyte aggregation by the addition of dextran 70 in vitro led t o the expected increase of viscosity in the Couette viscometer; in the oscillating tube viscometer, however, it remained unchanged, which ma y be explained by a decreased erythrocyte concentration near the tube wall due to increased aggregation and flow of erythrocytes in the tube center. In ex vivo experiments on blood flowing without anticoagulant directly through the tube viscometer an inverse correlation between v iscosity and fibrinogen concentration was found. This is in contrast t o actual knowledge and may indicate that high fibrinogen levels have a beneficial rheological effect at the tube or vessel wall. Our data su ggest that the new oscillating tube viscometer is an interesting tool, which may contribute to a more comprehensive understanding of blood f low.