CONTRIBUTION OF AN ULTRASONIC INTERFEROMETRY METHOD (ECHOCELL) TO THEDETERMINATION OF RED-BLOOD-CELL SEDIMENTATION-RATE AT LOW HEMATOCRIT

The sedimentation rate (SR) of red blood cells (RBCs) in suspension wa s determined at low volume fractions (1%-5%) by a new ultrasonic inter ferometry method (EchoCell). This method is based on A-mode echography and measures the accumulation rate of RBCs on a solid plate during RB C settling. The RBC accumulation rate, which is related to the SR, is obtained from interference of waves reflected by the two interfaces '' plate / sedimented particles'' and ''sedimented particles / suspension ''. The method allows to distinguish SR of RBCs with high and mean set tling velocity. Present results are compared (i) to the experimental S R measured by using a cylindrical tube of same geometry as the EchoCel l cavity and (ii) to the theoretical SR predicted by some models, espe cially the Kermack et al. one: the linearly relationship found between the volume fraction of RBCs (or hematocrit) and SR, obtained at low h ematocrit using the ultrasonic interferometry method, agrees with the cylindrical tube method.