Biorheology

An earlier model of capillary tube viscometer was improved by (a) introducing a new indicating method, (b) increasing responsiveness through improved design and (c) eliminating some possible sources of error.

Meniscal resistance to movement observed in a bubble in a capillary filled with an aqueous solution of a surface active agent grows with bubble length up to a maximum. Development of meniscal resistance requires a definite length of free wall. This finding is of interest in the study of foams, emulsions and suspensions.

The deformability of red cells involves their elasticity, flexibility and internal viscosity. The viscosity of a dense pack of red cells involves not only red cell deformability but also intercellular friction. The results described in this paper are the product of a compromise method in which much but not all plasma has been removed before viscometry.

The appearances of blood flowing at high velocities in fine blood vessels are discussed and are supported by high speed photographs and tracings from series of such photographs. These indicate that blood flowing in the larger arterioles contains loose aggregates or groups of red cells separated by zones of relatively cell free plasma.

As these groups pass into the finer arterioles the blood cells become remarkably deformed and the diameter of the plastic masses, measured in the plane at right angles to the axis of the blood vessel, may be reduced to less than the diameter of a red cell at rest. Discrete red cells are also deformed. It is suggested that such deformation of columns of flowing red cells accounts for the low relative viscosity of whole blood previously observed in fine glass tubes.

In vitro tests on heparinized blood have shown that high molecular weight dextrans cause large increases in blood viscosity at low rates of shear. This may explain their deleterious effects on the perfusion of the capillaries in shock.

Low molecular dextrans do not diminish blood viscosity below the control value.

The experimental procedures employed constitute a rapid, simple method for testing in vitro the effects of plasma expanders on blood viscosity.

Vital microscopy accessories are described whereby blood pressure and respiration may be measured and temperature monitored and controlled in both conscious and anesthetized animals.