The mechanical damage of red blood cells (hemolysis) remains a key challenge in the design of blood-contacting medical devices. This study aims to compare the predictive performance of the empirical power-law model and the physiologically motivated viscoelastic model in the FDA nozzle benchmark geometry, with a focus on how model parameters and shear stress definitions influence hemolysis predictions. Computational fluid dynamics (CFD) simulations were performed using a finite volume framework to resolve flow fields and shear stresses in the FDA nozzle. Both hemolysis models were implemented under identical geometry, mesh and boundary conditions. A parametric analysis was conducted by varying key model parameters, including the viscoelastic constants A, T_1 , T_2 , the shear stress threshold τ _S , and the power-law parameters. Predictions were evaluated using both total shear stress and turbulent viscous shear stress (TVSS) formulations, and compared against experimental data. The viscoelastic model demonstrated strong sensitivity to the relaxation time T_2 and to the choice of stress definition. A quasi-linear dependence on parameter A was identified, enabling calibration with experimental results. In contrast, the power-law model was less sensitive to stress definitions but strongly dependent on parameter fitting. The effect of τ _S differed between the two models: it reduced hemolysis in the power-law case but increased it in the viscoelastic formulation. The viscoelastic model offers a more mechanistic description of hemolysis but requires careful parameter calibration and is highly sensitive to stress definitions. The power-law model remains computationally efficient and easier to implement, though empirical by nature. Future research should refine parameter estimation and extend validation to more complex flow regimes, considering feedback effects of hemolysis on viscosity. Ultimately, CFD prediction of hemolysis remains a challenging unsolved problem.
Optical mapping is a high spatiotemporal resolution imaging technique used to study cardiac electrophysiology by recording fluorescent signals that correspond to changes in transmembrane potential, intracellular calcium, and metabolic activity. This review provides a comprehensive guide for beginners, covering the fundamentals of optical mapping system components, including dye selection, optical filters and mirrors, camera specifications, and system configurations. A range of tissue preparations, from single cells to whole hearts, is described, with attention to how preparation type affects experimental design, perfusion methods, and system setup. Pharmacological and computational strategies to reduce motion artifacts are discussed. Electrical stimulation protocols, such as pacing and restitution mapping, are described in the context of arrhythmia induction and rate dependent electrophysiological properties. Technical considerations including system maintenance and troubleshooting are also addressed. Finally, the review outlines current limitations, including dye cytotoxicity, tissue viability, and photobleaching, and explores future directions such as genetically encoded indicators and oxygen-enriched perfusates. This guide aims to equip new users with the foundational knowledge needed to design, perform, and interpret optical mapping experiments.
Traditional Computational Fluid Dynamics (CFD) methods used in the hydrodynamic design of blood-contacting medical devices create a bottleneck in optimization processes due to their heavy dependence on mesh structure and high computational costs. In this study, using a mesh-free Physics-Informed Neural Network (PINN) approach, complex flow fields and Turbulent Kinetic Energy (TKE) distributions in FDA reference nozzle geometries were mapped with high resolution. Unlike artificial intelligence algorithms that merely fit data, the proposed model directly integrates the axisymmetric mass conservation equation into the loss function as a mathematical constraint. The model was trained on experimental PIV/LDV data over a wide range covering laminar, transitional, and fully turbulent regimes ( Re = 500 - 6500 ). The model predicted sharp velocity gradients in the shear layers with high accuracy. Additionally, a practical empirical correlation for peak TKE was derived within the investigated conditions, serving as a rapid hydrodynamic indicator. The findings demonstrate that this physics-constrained approach reduces the need for mesh generation and offers a computationally lightweight framework for the continuity-constrained reconstruction and regularization of complex and inherently noisy experimental flow fields.
Biventricular assist devices (BiVADs) and total artificial heart (TAH) are the principal bridge-to-transplantation strategies for patients with advanced biventricular heart failure awaiting heart transplantation, but their comparative effectiveness and safety remain uncertain. This systematic review and meta-analysis compared pretransplant outcomes between the two approaches. A systematic review and meta-analysis was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. PubMed, Scopus, Web of Science, and Cochrane Library were searched from inception through January 2026 for studies comparing BiVADs and TAH as bridge-to-transplantation strategies. Study quality was assessed using the Newcastle–Ottawa Scale, and certainty of evidence was evaluated using the GRADE framework. Random-effects models were used to compare survival to transplantation, mortality during support, support-related complications, and duration of support. Ten retrospective studies involving 2,242 patients met the inclusion criteria. The overall analysis showed no significant difference in survival to transplantation between patients supported with BiVADs and TAH (RR = 0.97, 95
This study aimed to quantitatively investigate the role of marginal chordae of the mitral valve during static closure by analyzing the force within these chordae and its potential correlation with the transvalvular pressure. Porcine (n = 10) and human (n = 4) mitral valves were mounted in a saddle-shaped annulus clamp, while an in vitro system was utilized to replicate a physiological systolic blood pressure by vacuum pressure applied to the atrial side of the valve. A Millar pressure catheter and force transducers (“C-gauges”) were used to acquire the data. Strut chordal force was recorded simultaneously with the marginal chordal force, to serve as a verification of the employed equipment. The marginal chordal force in porcine and human averaged to 0.012 N ± 0.008 N and 0.006 N ± 0.008 N respectively at peak systolic pressure of 120 mmHg. Additionally, a simplified finite element study was conducted and supports low marginal forces relative to intermediary chords. This low force calls into question the traditionally-described role of the marginal chordae in preventing mitral prolapse at closure. The chords do, however, still show signs of assisting with the leaflets’ positioning. The relationship between marginal chordal forces and transvalvular pressure varies significantly across experiments, further obfuscating their role in normal valvular function.
