Rheogoniometric studies of whole human blood at shear rates from 1000 to 0.0009 sec −1

Abstract

Extensive rheogoniometric measurements of undiluted blood, anticoagulated with heparin, Paul’s oxalate mixture and ethylene diamine tetra acetate, are presented. The blood was secured from healthy adult human subjects and measurements were made at shear rates from 1000 to 0.0009 sec⁻¹. In the minimal shear rate range from 0.01 to 0.0009 sec⁻¹, and in some cases down to 0.0006 sec⁻¹, three different slopes were obtained in the shear stress versus the shear rate plots, as compared to merely a single slope which we reported earlier. No appreciable differences were found by the use of the three anticoagulants. Although two different gap widths in the combined Couette and cone and plate geometry were employed on samples from different blood withdrawals, all three types of slopes were found. The typical data were plotted in 6 figures which characterize our findings. A discontinuity or slope change was observed in three out of the 6 figures, when the shear rate is below 10⁻² sec⁻¹. This continuity appears to confirm the presence of a yield stress. The importance of minimal shear rates in the flow properties of blood concerns physiological and pathological conditions, in which the flow of blood approaches a standstill and the shear rate progresses to zero.