Discrimination between orientation and elongation of RBC in laminar flow by means of laser diffraction,” OE/LASE'94

The elongation curve of RBC as determined by rheoscopy or ektacytometry (laser diffraction) resembles a rectangular hyperbola. The experimental data obtained so far included too large errors of measurement to allow precise mathematical description. The combination of laser diffraction with image analysis has im-proved ektacytometry considerably, such that the error of measurement is reduced to less than 0.5%. In laminar flow RBC of healthy donors are elongated elliptically (p ≤ 0.001). Using the precise data of elliptical deformation, the elongation curve can be described to be hyperbolic. Hence, the double reciprocal plot gives a linear curve which- over a wide range of shear stress (15 to 500 dyn/cm2)- fits well the experimental data (r ≥ 0.99: p ≤ 0.001). The stress strain characteristics (i.e. elongation curve) can be described by two parameters: maximum elongation ( Emax) and the shear stress needed for half-maximum elongation ( KE). Mechanical stress only slightly reduces Emax but significantly shifts KE to higher values. Hyper-osmolarity decreases Emax and increases KE. Mild hypo-osmolarity (>225 mOsm.) increases Emax and decreases KE, whereas strong hypo-osmolarity (≤225 mOsm.) decreases Emax and further decreases KE Inclusion of elongation data measured at shear stress < 15 dyn/cm2 detoriates the linear correlation. The elongation coefficients measured for low shear stress are higher than calculated by linear regression. The same holds true for range of shear stress between 15 and 25 dyn/cm2 if applied to RBC in hypertonic solu-tions or to cells which underwent mechanical stress. Further analysis of the laser diffraction patterns led us to suggest that at low shear stress the RBC become more or less oriented thereby presenting their side aspect (2.2 µm ⋅8 µm) to the laser beam. The diffraction pattern then resemble to those of elongated RBC. At shear stress exceeding 15 dyn/⋅cm2 the RBC rotate by 90 ° presenting their circular aspects ( ∅ 8 µm) which then become elliptically deformed by shear. 2