Abstract
Blood from patients with diabetes has been found in many studies to offer more resistance to flow at low shear rate than blood from healthy subjects. Such shear-thinning has been proposed to decrease the stability of high Reynold’s non-Newtonian fluid flow. Flow destabilization could affect arterial flow patterns. Because of this possibility, diabetic and nondiabetic blood were compared for flow stability. When the inner cylinder of a Couette system (viscometer) is rotated rapidly, pairs of counter-rotating toroidal vortices develop at a critical rotation rate, as shown by Taylor. Newtonian fluid Taylor-Couette instability is very regular in onset compared to turbulence in pipe flow, making it convenient for evaluating the flow stability of non-Newtonian fluids. The critical Taylor number (Tc) of blood was determined in our Couette viscometer following shear-thinning assessment. Tc of blood from 88 diabetic and 100 nondiabetic subjects was measured using a computer-automated determination of torque inflection. Blood’s steady flow viscosity was measured at 25 rotation rates from .03 to 360 sec−1 . Low shear rate viscosity elevation in diabetes was again demonstrated, but Tc and the ratio in rotation rate to Tc at which wavy vortices first formed were highly comparable, Tc differing by 0.3% between the groups. A previously published technique for adjusting for variation in hematocrit was examined and found more useful for healthy than diabetic blood. Diabetes has no effect on blood’s essentially normal flow stability even though it alters its shear-thinning and viscoelastic behavior.
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