## 4 Discussion  
RBC deformability is the ability of cells to adjust their shape to pass through microvessels, especially capillaries, which are narrower than erythrocyte diameter. Increased rigidity interferes with blood perfusion and impairs oxygen delivery to peripheral tissues [48; 49; 50; 51]. Rigid RBCs can weaken tissue perfusion and block capillaries [51; 52; 53]. Deformability is a function of some basic properties of the erythrocyte, such as membrane surface area-to-volume ratio, cytosol viscosity, and binding stability between the lipid bilayer and cytoskeleton [51; 70]. All these factors are affected by the cell environment and external conditions. Additional factors include the shear stress level applied to the RBC and the flow pattern. RBCs are subjected to mechanical stress as they pass through the cardiovascular system but do not sustain significant damage. However, normal erythrocytes can be damaged in non-physiological conditions such as high mechanical stress created by flow in artificial organs or auxiliary devices. This can cause deterioration in the vital properties of RBCs, which reduces their ability to resist further damage and leads to impairment of cell integrity and subsequent hemolysis. The physiological level of shear stress (up to 5 Pa [71]) enables RBC deformation, detachment of red cells from the endothelium, and disaggregation of rouleaux without inducing immediate or long-term injury to blood components [31]. In contrast, supraphysiological shear stress can impair RBC deformability without initiating hemolysis [31; 72]. RBC damage is always observed when blood is exposed to shear stress levels above 5 Pa but below a \"hemolytic threshold\" [12; 39; 31; 72]. The destruction of RBCs (i.e., hemolysis) can occur when the RBC is exposed to shear stress that exceeds the hemolytic thresh \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Parameters \({}^{*}\)**} & \multicolumn{2}{c}{**After Salvage**} & \multicolumn{2}{c}{**Before Salvage**} & \multirow{2}{*}{\(\mathbf{p}\)**Values**} \\ \cline{2-2} \cline{4-5}  & **Average** & \(\pm\)**SD** & **Average** & \(\pm\)**SD** & \\ \hline UDFC, \% & 3.23 & 1.75 & 2.31 & 1.60 & \(>0.05\) \\ \hline \hline \end{tabular} \({}^{*}\)UDFC—fraction of un-deformable (ER \(\leq\) 1.1) cells in RBC population %.  
\end{table} 
Table 1: Characterizing of RBC deformability for salvaged blood (RBC\({}_{\text{Si}}\)) and freshly-collected cells (RBC\({}_{\text{B}}\)). Figure 7: Percentage of undeformable cells (%UDFC) in RBC population before and after salvage. old [15; 21]. At the same time, it is essential to point out that two factors determine the outcome of a mechanical effect: the level of applied stress and the duration of its application [15]. Although most authors indicate a deterioration in cell deformability following mechanical stress [31; 72], some publications report an improvement in deformability [73; 22]. A comparison of the various results allows us to conclude that moderate mechanical stress (5-10 Pa) should lead to an improvement in cell deformability [22; 73] and high stress should lead to its deterioration [31; 72]. [PERSON] et al. [72] showed that RBC deformability begins to decrease when the shear stress exceeds 30 Pa and suggests that deformability measurement can be a marker for showing erythrocyte sub-hemolytic damage. One of the clinical setups in which mechanical stress is applied to RBCs outside of the body is blood salvage. Intraoperative autologous blood transfusion has expanded in recent decades [9; 74]. There are conflicting results regarding the effect of blood salvage on red cell properties [18; 75; 76]. [PERSON] et al. [76] report that cell savage \"does not severely alter the rheological properties of blood.\" In line with these results, [PERSON] et al. [75] demonstrated (for patients undergoing cardiac surgery) that transfusion of salvaged RBCs does not lead to a decrease in deformability and an increase in aggregation of a recipient's red cells. In contrast, [PERSON] et al.