Plasma expander viscosity effects on red cell-free layer thickness after moderate hemodilution

The objective of the study was to investigate the effects of plasma viscosity after hemodilution on the thickness of the erythrocyte cell free layer (CFL) and on the interface between the flowing column of erythrocytes and the vascular endothelium. The erythrocyte CFL thickness was measured in the rat cremaster muscle preparation. Plasma viscosity was modified in an isovolemic hemodilution, in which the systemic hematocrit (Hct_sys) was lowered to 30%. The plasma expanders (PE) of similar nature and different viscosities were generated by glutaraldehyde polymerization of human serum albumin (HSA) at various molar ratios glutaraldehyde to HSA: (i) unpolymerized HSA; (ii) PolyHSA_24:1, molar ratio = 24 and (iii) PolyHSA_60:1, molar ratio = 60. The HSA viscosities determined at 200 s⁻¹ were 1.1, 4.2 and 6.0 dyn·cm⁻², respectively. CFL thickness, vessel diameter and blood flow velocity were measured, while volumetric flow, shear rate and stress were calculated. Hemodilution with PolyHSA_60:1 increased plasma viscosity and the blood showed marked shear thinning behavior. CFL thickness decreased as plasma viscosity increased after hemodilution; thus the CFL thickness with HSA and PolyHSA_24:1 increased compared to baseline. Conversely, the CFL thickness of PolyHSA_60:1 was not different from baseline. Blood flow increased with both PolyHSA's compared to baseline. Wall shear rate and shear stress increased for PolyHSA_60:1 compared to HSA and PolyHSA_24:1, respectively. In conclusion, PE viscosity determined plasma viscosity after hemodilution and affected erythrocyte column hydrodynamics, changing the velocity profile, CFL thickness, and wall shear stress. This study relates the perfusion caused by PolyHSA_60:1 to hemodynamic changes induced by the rheological properties of blood diluted with PolyHSA_60:1.