An increase in fibrinogen, a coagulation factor in blood, enhances erythrocyte aggregation. However, no previous studies have fully investigated erythrocyte aggregation at low plasma fibrinogen concentrations (<150 mg/dL), which can be caused by severe hemorrhage and induce coagulopathy. The purpose of this study was to reveal erythrocyte aggregability at low fibrinogen concentrations that occur in severe hemorrhage by syllectometry, an optical method for measuring erythrocyte aggregation. Fifty-six blood samples with a fibrinogen concentration of 129.4 ± 88.3 mg/dL were prepared by mixing serum and plasma from 12 healthy volunteers, and the relationship between fibrinogen concentration and erythrocyte aggregation parameters obtained by syllectometry was examined. At low fibrinogen concentrations (<150 mg/dL), erythrocyte aggregation parameters (amplitude and aggregation index) decreased almost linearly with decreasing fibrinogen concentration (r = 0.808 and 0.745), and a time constant parameter (t_1/2) increased with decreasing fibrinogen concentration (r = –0.827), similar to previously reported results for normal to high fibrinogen concentrations. Relaxation time (t₀) increased exponentially with decreasing fibrinogen concentration (r = –0.608). These results suggest that erythrocyte aggregability decreases with decreasing fibrinogen concentration even at low fibrinogen levels that can cause coagulopathy, and that syllectometry can be used to detect decreases in fibrinogen.

The brain requires O₂ and nutrition to keep functioning. It is known that O₂ concentration converts the polarity of vessel response near the activated neuron in the hippocampus. However, it remains unclear whether O₂ concentration converts the polarity in the cortex. We investigated the comparison of the arteriole response near the stimulated neurons in cerebral cortex slices between 95% and 20% O₂ concentration in medium. We showed that the diameter of the blood vessels decreased under 95% O₂ concentration when the pyramidal cells near the blood vessels were stimulated and increased under 20% O₂ concentration with the same stimulation.

Red cell distribution width (RDW) is a simple, inexpensive, and unique laboratory parameter. This hematologic parameter reflecting the heterogeneity of red cell size was used conventionally to differentiate anemic diseases but is used currently as a prognostic marker of common as well as cardiac diseases. Higher RDW is associated with lower therapeutic response in patients with acute myocardial infarction undergoing percutaneous coronary intervention, those with atrial fibrillation undergoing catheter ablation, and those with heart failure under drug therapy. RDW showing such wide usefulness is linked to the chronic inflammation, which dysregulates normal erythropoiesis and impairs deformability of red cells within the microcirculation. Disturbed microcirculation causes persistent and systemic tissue hypoxia-reoxygenation insult impairing redox homeostasis, which induces chronic inflammation and clonal hematopoiesis of intermediate potential as a stress memory. Therefore, higher RDW is sustained in many cardiac diseases by hemorheological insult causing chronic inflammation under the clonal expansion of erythroid cells leading to the reduced deformability and increased RDW of red cells by unknown mechanisms.

There still remains uncertainty about the result of hemodynamic analysis of the intracranial aneurysm by computational fluid dynamics (CFD) because a variety of computational conditions are used by different analysts. In particular, the impact of the outflow boundary condition imposed at the outlets has not been fully elucidated, although it is considered to play an important role in determining the hemodynamic state in a bifurcation aneurysm. The purpose of this study is to discuss quantitative influences of different outflow boundary conditions on computed wall shear stress (WSS) in the aneurysm in terms of rupture risk assessment. Using three patient-specific models of aneurysms, the authors conducted hemodynamic analysis and compared the maximum, minimum and mean WSSs evaluated with seven outflow boundary conditions: the zero-pressure condition, five power laws with different exponents and Windkessel model. In one of the three models, even a slight difference in the power-law exponent caused a significant difference larger than 0.2 Pa in the minimum WSS, which could lead to misjudgement in rupture risk assessment. No particular outflow condition proved superior to the others. However, it was suggested that the Windkessel could perform better if the patient-specific information about the distal flow resistance were available.