Studies on blood viscosity during extracorporeal circulation.

Blood viscosity was studied during extracorporeal circulation by means of a cone in cone viscometer. This rotational viscometer provides sixteen kinds of shear rate, ranging from 0.05 to 250.2 sec-1 • Merits and demerits of the equipment were described comparing with the capillary viscometer. In experimental study it was well demonstrated that the whole blood viscosity showed the shear rate dependency at all hematocrit levels. The influence of the temperature change on the whole blood viscosity was clearly seen when hemato· crit was high and shear rate low. The plasma viscosity was 1.8 cp. at 37°C and Newtonianlike behavior was observed at the same temperature. ·In the hypothermic condition plasma showed shear rate dependency. Viscosity of 10% LMWD was over 2.2 fold as high as that of plasma. The increase of COz content resulted in a constant increase in whole blood viscosity and the increased whole blood viscosity after C02 insufflation, rapidly decreased returning to a little higher level than that in untreated group within 3 minutes. Clinical data were obtained from 27 patients who underwent hypothermic hemodilution perfusion. In the cyanotic group, w hole blood was much more viscous than in the noncyanotic. During bypass, hemodilution had greater influence upon whole blood viscosity than hypothermia, but it went inversely upon the plasma viscosity. The whole blood viscosity was more dependent on dilution rate than amount of diluent in mljkg. The venous mixture was a little higher as to its viscosity than that of the oxygenated whole blood and the above phenomenon became more pronounced within low shear rate range. Peripheral circulation was discussed in relation to the b lood viscosity.