An automated tube-type blood viscometer: Validation studies

The technical complexity of previous rheometers has tended to limit the availability of blood viscosity data obtained over a wide range of shear rates. However, an automated tube-type viscometer, the Rheolog™, has been developed; it employs a disposable flow assembly and less than five minutes are required to obtain blood viscosity results over a shear rate range of 1-1500 s^-1. We have carried out validation studies of the Rheolog™ using normal human blood and have compared these results with those obtained by cone-plate and Couette viscometers; storage time and temperature effects were also evaluated. Replicate measurements indicated mean CV levels less than 5%, and were independent of hematocrit and shear rate. Rheolog™ blood viscosity data agreed closely with those from other viscometers: average Rheolog™ differences from mean cone-plate and Couette values were -0.3% at 28% hematocrit, -1.4% at 41% hematocrit (i.e., native), and 1.0% at 56% hematocrit. Storage at room temperature up to 8 hours and at 4°C up to 4 days had minimal effects whereas notable changes were observed when stored for 3 hours at 37°C. Our results indicate that, within the hematocrit and shear rate limits employed herein, the Rheolog™ provides rapid, accurate and reproducible blood viscosity data, and suggest its usefulness for both basic science and clinical studies.