A new method for blood viscosity measurement
Sangho Kim a , Young I. Cho a,∗ , Abraham H. Jeon a , Bill Hogenauer b , Kenneth R. Kensey b
Department of Mechanical Engineering & Mechanics, Drexel University, Philadelphia, PA 19104, USA b Visco Technologies, Inc., Exton, PA 19341, USA Received 21 February 2000; received in revised form 10 May2000
Abstract The present study introduces the concept of a newly designed scanning viscometer with a capillary tube for use in measuring whole blood viscosity without the use of anticoagulants in a clinical setting. Both ﬂow rate and pressure drop measurements that are usually required for the operation of a capillary tube viscometer are replaced with a single measurement of liquid-heightvariation with time. In addition, the present method overcomes the drawbacks of conventional viscometers in the measurement of the whole blood viscosity. First, with the present study, whole blood viscosity can be accurately and consistently measured at 37◦ C over a wide shear rate range including shear rates as low as 1 s−1 . Second, the present method can measure whole blood viscosity over a range ofshear rates in less than 2 min without any anticoagulants so that one can measure the viscosity for unadulterated blood. © 2000 Elsevier Science B.V. All rights reserved.
Keywords: Scanning capillary tube viscometer; Blood viscosity; Anticoagulant; Pressure drop; Shear rate
1. Introduction Viscometers that are currently available may be grouped into three broad categories [1–4]: (1) capillarytube viscometers, (2) rotating viscometers, and (3) falling ball or needle viscometers. Most of these viscometers can produce viscosity measurements at a speciﬁed, constant shear rate. Therefore, in order to measure the viscosity over a range of shear rates, one needs to repeat the measurement by varying either the pressure in the reservoir tank of capillary tube viscometers, the rotating speedof the cone or cup in rotating viscometers, or the density of the falling objects. Such operations make viscosity measurements difﬁcult and labor intensive. In addition, these viscometers require anticoagulants in blood to prevent blood clotting. Hence, the viscosity results include the effects of anticoagulants, which may increase or decrease blood viscosity depending on the type of anticoagulant[5–8].
∗ Corresponding author. Tel.: +1-215-895-2425; fax: +1-215-895-1478. E-mail address: firstname.lastname@example.org (Y.I. Cho).
0377-0257/00/$ – see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 7 - 0 2 5 7 ( 0 0 ) 0 0 1 2 7 - 0
S. Kim et al. / J. Non-Newtonian Fluid Mech. 94 (2000) 47–56
Nomenclature d g h ht =∞ k L n P P Q t V inner diameter of tubeacceleration due to gravity ﬂuid height ﬂuid height difference as time goes to inﬁnity consistency index for power-law model length of tube power-law index pressure pressure drop volumetric ﬂow rate time ﬂuid velocity
Greek letters ˙ γ shear rate η non-Newtonian viscosity µ Newtonian viscosity ρ density Subscripts c capillary tube r riser tube
The present study introduces an innovative conceptof a capillary tube viscometer that is capable of measuring whole blood viscosity continuously over a range of shear rates with an emphasis on obtaining low shear rate viscosity. The present study measured the viscosity of unadulterated blood at body temperature, 37◦ C. Blood is a ﬂuid consisting primarily of plasma and cells such as erythrocytes, leukocytes and platelets. Erythrocytes (i.e. redblood cells, RBC) constitute the majority of the cellular content and account for almost one half of the blood volume. The presence of such a high volume of RBC makes blood a non-Newtonian ﬂuid whose viscosity varies with shear rate . Whole blood viscosity decreases as shear rate increases, a phenomenon called ‘shear-thinning characteristics’. In other words, whole blood behavior may be...