Data reduction methods for ektacytometry in clinical hemorheology

Abstract

Laser-diffraction ektacytometry is a generally accepted technique for measuring RBC deformability induced by fluid shear stress (SS) and yields paired elongation index-SS data at several levels of stress. Unfortunately, comparison of results is hindered by the lack of simple indices that accurately characterize these data. Several mathematical models have been proposed, including those developed for analysis of enzyme kinetics (Lineweaver-Burk, Eadie-Hofstee) and curve fitting (Streekstra-Bronkhorst). All of these analytical approaches provide a value for cell deformation at infinite stress (EI max ) and the shear stress required to achieve one-half of this deformation (SS 1/2 ); the use of non-linear regression is essential when calculating these parameters. While the current models provide equivalent results for normal RBC if used with non-linear regression, EI max and SS 1/2 are not always concordant for cells with abnormal mechanical behavior. This technical note examines such differences for three conditions: glutaraldehyde treatment, mechanical stress and non-isotonic media. It was found that none of the models yield completely satisfactory values for EI max and SS 1/2 , especially if there are large changes of EI max . However, the ratio of SS 1/2 to EI max (SS 1/2 /EI max ) is much less affected by these problems, has similar power (i.e., standardized difference) as SS 1/2 and EI max and is more robust in reflecting alterations of deformability. We thus conclude that the SS 1/2 /EI max ratio can be used when reporting and comparing various populations of RBC or cells obtained from subjects having different clinical states.

The Effect of Alcohols on Red Blood Cell Mechanical Properties and Membrane Fluidity Depends on Their Molecular Size

“…Figure 2B and 2D demonstrate that EI max values are also altered significantly by alcohols. Given that both SS 1/2 and EI max are affected, SS 1/2 /EI max ratios were calculated in order to allow comparisons of the effects of the four alcohols at various concentrations [22]. The concentration-dependent influence of alcohols with different molecular weights is presented in Figure 3: the SS 1/2 /EI max ratio reaches a minimum (i.e., the maximum of deformability) at a concentration specific to each alcohol, with reversal of the effects with further increase of concentration.…”

“…Additionally, the maximum EI (EI max ) and the shear stress required to cause one-half of this maximum (SS 1/2 ) were determined using the Lineweaver-Burk approach and non-linear curve fitting [21]. The SS 1/2 /EI max ratio was calculated as a normalized measure of SS 1/2 [22]; SS 1/2 /EI max is inversely related to RBC deformability such that a lower value indicates better deformability.…”

Impact of Type of Sport, Gender and Age on Red Blood Cell Deformability of Elite Athletes

“…The theoretical maximal EI at infinite shear stress (EI max ) and the shear stress at half-maximum deformation (SS 1/2 ) were calculated using non-linear regression according to Baskurt and colleagues [1]. EI Ratio = SS 1/2 / EI max was finally calculated according to Baskurt and colleagues [2] with higher values representing lower RBC deformability. This EI Ratio was shown to be more robust in reflecting alterations of deformability and having similar power compared to the individual values EI max and SS 1/2 , while reducing data to one parameter [2].…”

“…EI Ratio = SS 1/2 / EI max was finally calculated according to Baskurt and colleagues [2] with higher values representing lower RBC deformability. This EI Ratio was shown to be more robust in reflecting alterations of deformability and having similar power compared to the individual values EI max and SS 1/2 , while reducing data to one parameter [2].…”

Shear stress-induced improvement of red blood cell deformability

“…Data are expressed as EI-SS curves. These EI-SS data were characterized by the maximum EI at infinite SS (EI max ) and the SS needed to achieve one-half of this maximum (SS 1/2 ) using the Lineweaver-Burk approach and non-linear curve fitting [3]; the SS 1/2 /EI max ratio was calculated as a normalized measure of SS 1/2 [6]; (2) RBC were subjected to constant shear stress of 5, 10 or 20 Pa and EI-time data were obtained during this period. For some experiments, EI-time data were recorded at 5 Pa SS for 10, 20 or 30 s, then the recording was repeated at the same 5 Pa shear stress following a waiting time of 10 or 60 s.…”