The LS300 viscometer permits automated measurements of viscosity at several shear rates of non-Newtonian fluids. We determined whole blood and plasma viscosity, aggregation, red blood cell deformability, and hematocrit of 66 healthy adults. The effects of the anticoagulants EDTA, heparin and citrate, and of centrifugation on blood viscosity (n=12) and red blood cell geometry (n=5) were investigated. With regard to the whole blood viscosity of adults, the best agreement was obtained by Casson's calculation compared to the methods of Ostwald, Bingham and Newton. The approximated flow curve of plasma showed only marginal differences between the method of Newton and Ostwald, whereas the latter gave the best quality of approximation. Centrifugation and the anticoagulants had a significant impact on whole blood viscosity and yield shear stress, whereas erythrocyte geometry remained unaffected. By linear regression of hematocrit with viscosity and yield shear stress, its impact on blood viscosity could be calculated in a hematocrit range of 0.32-0.50. Determination of whole blood viscosity should be performed in a standardized manner at several shear rates and without centrifugation of the blood samples.

Determination of shear stresses at given shear rates allow approximation of flow curves by mathematical models and to calculate viscosities of non-Newtonian fluids. In term neonates, the mean arterial blood pressure (MAP) is markedly below that of adults, therefore rheological properties of blood play an important role in maintaining perfusion. Whole blood viscosity was measured in umbilical cord blood taken from 62 term neonates using the LS 300 viscometer. Individual parameters that influence the viscosity of whole blood were measured: red blood cell (RBC) aggregation, plasma viscosity, hematocrit, and RBC deformability. The flow curve of whole blood of neonates was approximated by the method of Ostwald with the highest quality whereas in adults the best approximation was found by the method of Casson. With hematocrits of 0.40, the viscosity of whole blood in newborns approximated by Ostwald (9.84 ± 5.12 mPa·s) was significantly lower than that of adults (15.34 ± 3.01 mPa·s). The aggregation index of the blood of newborns was markedly lower (2.98 ± 2.12) than in adults (14.63 ± 3.50) whereas RBC deformability was higher in neonates. The viscosity of plasma determined by Ostwald revealed a lower exponent (n) in neonates (0.94 ± 022) compared to adults (1.01 ± 0.12) and the viscosity determined by Newton was lower in neonates (1.04 ± 0.16 mPa·s) than in adults (1.19 ± 0.07 mPa·s). The flow curve of neonatal blood which is best approximated by the model of Ostwald emphasizes its important viscous properties necessary for conditions with physiologically low blood pressure.

Abstract. The low shear viscometer LS300 permits measurements of viscosity with the same precision of the LS30 but is now fully controlled by the windows based software. That allows to determine viscosity at several shear rates and to establish flow curves enabling determination of the viscosity of non-Newtonian fluids. The viscosity of whole blood of ten adults was determined via flow curves approximated by Casson. The sensitivity of the LS300 was evaluated by determining the viscosity of water at rising temperatures and by establishing flow curves of ten specimen of the same blood sample. The low shear viscosimeters LS30/LS40 and with its latest development, the LS300 is sought-after in mineral oil industry, the cosmetic and food industry and in hemorheology, too. The technique of these devices based on the Couette principle ( Fig. 1) was described as golden standard technique (Pop et al. 2004) and most useful (Ernst et al. 1985) for determination of blood viscosity at single shear rates for the preceding models of the LS300. The new LS300 (KSPV-4, Rheomed GmbH, Aachen, Germany) is now fully controlled by the LS300 software and enables the operator to establish flow curves. Shear rate and viscosity are directly related to the properties of the fluid. Non-Newtonian fluids are governed by a non-linear relationship between shear stress and shear rate, whereas the viscosity of Newtonian fluids is independent from shear rate (Fig. 2), as indicated by the linear relation between shear rate and shear stress (Papaioannou et al. 2005). These flow curves can be approximated by mathematical models, which allow calculating the viscosity of a non-Newtonian fluid like whole blood (Shi et al. 1996;Baskurt et al. 2003;Marcinkowska-Gapinska et al. 2007).The LS300 (proRheo GmbH, Althengstett, Germany) is a rotational rheometer based on the Couette principle ( Fig. 1), equipped with a rotating measuring cup and a fixed measuring element. Thus, the measurements are not influenced by the Taylor vortex. The measuring principle is the same as the LS30 previously described (Aarts et al. 1984). The material number of the cup and the bob is steel (EN 1.4571).The radius of the measuring cup is 6 mm, the radius of the bob is 5.5 mm and the length of the bob is 8 mm. The sample volume was 0.9 ml. The bob was always covered with the tested sample. The software LS300 regulates the rotation count of the measuring cup. The number of measuring points at several shear rates and time may be selected as desired. The thermostat of the LS300 works with cryoregulation; its accuracy is ±0.1°C. The new technology of LS300 permits determination of shear forces at multiple shear rates during a single measuring run, over a wide range of shear rates from 0.018 to 125 s −1 (in steps of 0.01 s −1 ). By graphic presentation of shear rate versus shear stress one obtains data points which, when connected to each other, yield a flow curve (Fig. 3). The viscosity of non-Newtonian fluids can be determined by approximation of these flow curves with mathematical mo...

Red blood cells (RBC) of neonates have a shorter survival time and they are more susceptible to mechanical alterations than RBC of adults. Irreversible alteration of the membrane of RBC of preterm neonates, term neonates and adults due to tether formation was studied by means of a micropipette technique. Shear stress and forces were applied with this technique in an axisymmetric configuration and were calculated with an approximation method. The applied shear stress and forces that induced tether formation were lowest for RBC of preterm neonates (1.5 Pa, 1.8 pN), in between for RBC of neonates (1.7 Pa, 2.1 pN) and highest for RBC in adults (1.9 Pa, 2.6 pN). Decreased mechanical stability of the membrane of neonatal RBC may in part cause the shorter life span, the greater tendency to endocytosis and the higher amount of irregularly shaped cells of neonatal RBC compared to RBC in adults.