Spin-label studies of erythrocyte deformability. IV. Relation of electron spin resonance spectral change with deformation and orientation of erythrocytes in shear flow.

Electron spin resonance (ESR) spectra of spin-labeled human erythrocytes in shear flow are simulated to derive semi-empirical relations of the ESR spectral change with deformation and orientation of the cells by using a modified theoretical model developed for deformation and orientation of liquid drops. The six observed spectra at different shear stress values were simultaneously simulated by adjusting only two parameters. One parameter can be related to the ratio of the internal to the external viscosity, and the other to the elastic property of the cell membrane. From these results we have derived a semi-empirical relationship between the average deformation index or the orientation angle with a spectral measure, which characterizes the spectral shape change induced by shear stress. Thus, it becomes possible to obtain improved quantitative information on the rheological behavior of red blood cells by using the spin-label ESR method.