Experimental characterization of blood rheology and development of a computational rheological Index during progressive hemorrhagic shock

Background: Hemorrhagic shock is associated with profound disturbances of microcirculatory perfusion in which alterations of blood rheology may contribute to tissue hypoxia and organ dysfunction. Historically, the concept of hemorrhagic shock has evolved from an initial focus on systemic hemodynamic failure toward recognition of the critical role of microcirculatory dysfunction and impaired tissue oxygen delivery. More recent experimental and clinical research has further emphasized the contribution of blood rheological abnormalities to the progression of hemorrhagic shock and organ dysfunction. However, the relative contribution of individual hemorheological parameters during progressive hemorrhagic shock remains insufficiently characterized. Objective: To investigate stage-dependent changes in blood rheology in an experimental rat model of hemorrhagic shock and to evaluate the relationship between conventional hemorheological parameters and a newly proposed computational rheological index derived from routine hematological variables. Methods: Hemorrhagic shock was induced in 60 anesthetized rats by controlled withdrawal of 2.0, 2.5, or 3.5 mL of arterial blood, corresponding to progressive stages of shock. 20 intact animals served as controls. Erythrocyte aggregation, erythrocyte deformability, plasma viscosity, hematocrit, and the computational rheological index were assessed 15 min after blood withdrawal. Results: Progressive blood loss resulted in stage-dependent deterioration of hemorheological properties. Erythrocyte aggregation demonstrated the greatest relative increase and was strongly associated with shock severity. Changes in erythrocyte deformability were less pronounced, whereas plasma viscosity and hematocrit remained relatively stable throughout the experimental stages. The computational rheological index exhibited changes parallel to erythrocyte aggregation, suggesting that it reflects progressive rheological impairment. Conclusions: Experimental hemorrhagic shock is accompanied by progressive deterioration of blood rheology, with erythrocyte aggregation representing the most sensitive laboratory marker. The proposed computational rheological index demonstrated a close association with experimentally observed rheological alterations and warrants further validation in independent experimental and clinical studies.