A model of anemic tissue perfusion after blood transfusion shows critical role of endothelial response to shear stress stimuli

Development of in vitro microfluidic models to study endothelial responses to pulsatility with different mechanical circulatory support devices

Continuous-flow ventricular assist devices (CFVAD) and counterpulsation devices (CPD) are used to treat heart failure (HF). CFVAD can diminish pulsatility, but pulsatile modes have been implemented to increase vascular pulsatility. The effects of CFVAD in a pulsatile mode and CPD support on the function of endothelial cells (ECs) are yet to be investigated. In this study, two in vitro microfluidic models for culturing ECs are proposed to reproduce blood pressure (BP) and wall shear stress (WSS) on the arterial endothelium while using these medical devices. The layout and parameters of the two microfluidic systems were optimized based on the principle of hemodynamic similarity to efficiently simulate physiological conditions. Moreover, the unique design of the double-pump and double afterload systems could successfully reproduce the working mode of CPDs in an in vitro microfluidic system. The performance of the two systems was verified by numerical simulations and in vitro experiments. BP and WSS under HF, CFVAD in pulsatile modes, and CPD were reproduced accurately in the systems, and these induced signals improved the expression of Ca2+, NO, and reactive oxygen species in ECs, proving that CPD may be effective in normalizing endothelial function and replacing CFVAD to a certain extent to treat non-severe HF. This method offers an important tool for the study of cell mechanobiology and a key experimental basis for exploring the potential value of mechanical circulatory support devices in reducing adverse events and improving outcomes in the treatment of HF in the future.

Vascular pathophysiology of sickle cell disease

Sickle cell disease (SCD) is an hereditary disorder characterized by the production of an abnormal hemoglobin called hemoglobin S (HbS). HbS may polymerize in deoxygenated conditions, which leads to red blood cell (RBC) sickling. Sickled RBCs are more rigid and fragile, and prone to lysis. SCD patients exhibit various acute and/or chronic complications, which may affect several organs. The clinical presentation of SCD is highly variable from one patient to another and cannot be only explained by RBC sickling. Increased blood viscosity, caused by the presence of RBCs with abnormal deformability and aggregation, may increase vascular resistance and increase the risk of acute and chronic vascular complications. Chronic hemolysis results in decreased nitric oxide (NO) bioavailability which may compromise vasodilation and participate to the development of chronic vasculopathy. Furthermore, chronic hemolysis is responsible for increased inflammation and oxidative stress, which affect the vascular system and may promote the adhesion of circulating cells to endothelial cells. Extracellular vesicles and especially RBC microparticles (massively released in the context of SCD) are also at the origin of vascular damages and increased white blood cells adhesion to the endothelium, which may trigger vaso-occlusive crisis and other vascular-related complications. This review highlights the fact that SCD should not only be considered as a hematological disorder but also as a vascular disease.

Hypertonic treatment of acute respiratory distress syndrome

Many viral infections, including the COVID-19 infection, are associated with the hindrance of blood oxygenation due to the accumulation of fluid, inflammatory cells, and cell debris in the lung alveoli. This condition is similar to Acute Respiratory Distress Syndrome (ARDS). Mechanical positive-pressure ventilation is often used to treat this condition, even though it might collapse pulmonary capillaries, trapping red blood cells and lowering the lung's functional capillary density. We posit that the hyperosmotic-hyperoncotic infusion should be explored as a supportive treatment for ARDS. As a first step in verifying the feasibility of this ARDS treatment, we model the dynamics of alveolar fluid extraction by osmotic effects. These are induced by increasing blood plasma osmotic pressure in response to the increase of blood NaCl concentration. Our analysis of fluid drainage from a plasma-filled pulmonary alveolus, in response to the intravenous infusion of 100 ml of 1.28 molar NaCl solution, shows that alveoli empty of fluid in approximately 15 min. These modeling results are in accordance with available experimental and clinical data; no new data were collected. They are used to calculate the temporal change of blood oxygenation, as oxygen diffusion hindrance decreases upon absorption of the alveolar fluid into the pulmonary circulation. Our study suggests the extraordinary speed with which beneficial effects of the proposed ARDS treatment are obtained and highlight its practicality, cost-efficiency, and avoidance of side effects of mechanical origin.