Rheology of human foetal blood with reference to haematocrit,plasma viscosity,osmolality and pH 1

Abstract

Foetal blood was studied in a cone-in-cone viscometer. Calibration of the instrument required consideration of Reynold’s number at high rev./min.

In vitro adjustments were made to determine the separate effects of red cell concentration, plasma viscosity, pH and osmolality on the viscosity of blood.

Procedures designed to change pH also altered plasma osmolality.

Hyper- and hypotonicity of plasma both increased blood viscosity.

Fall in pH increased blood viscosity. The part which change in osmolality played in this was calculable.

The mechanism of the increase in viscosity with fall in pH could not be certainly deduced.

It was, however, greater by a factor of 50 per cent or more, depending on the shear rate at which tested, than that accountable by the swelling of cells from fall in pH.

It is therefore suggested that an important factor in the elevated viscosity of blood at low pH is an increased rigidity of the erythrocyte from an effect of H⁺ on the cell membrane or contents.