Disposable laser-diffraction ektacytometry to measure red blood cell deformability

The laser-diffraction technique has been applied to design a slit rheometer for measuring red blood cell deformability over a range of shear stress. A laser beam traverses a diluted blood suspension and is diffracted by RBCs in the volume. The diffraction patterns are captured by a CCD-video camera, linked to a frame grabber integrated with a computer. When deforming under decreasing shear stress, RBCs change gradually from the prolate ellipsoid towards a circular biconcave morphology. Both the laser-diffraction image and pressure were measured with respect to time. Which enable to determine the elongation index (El) and the shear stress. The range of shear stress is 0-35 Pa and the measuring time is less than 2 min. The elongation index(EI) is determined from an isointensity curve in the diffraction pattern using an ellipse-fitting program. The key advantage of this design is the incorporation of a disposable element that holds the blood sample, which enables the present system to be easily used in a clinical setting.