RESUMEN
Recent work employing the computational fluid-particle modeling of the hepatic arteries has identified a correlation between particle release position and downstream branch distribution for direct tumor-targeting in radioembolization procedures. An experimental model has been constructed to evaluate the underlying simulation theory and determine its feasibility for future clinical use. A scaled model of a generalized hepatic system with a single inlet and five outlet branches was fabricated to replicate the fluid dynamics in the hepatic arteries of diseased livers. Assuming steady flow, neutrally buoyant microspheres were released from controlled locations within the inlet of the model and the resulting output distributions were recorded. Fluid and particle transport simulations were conducted with identical parameters. The resulting experimentally and simulation-derived microsphere distributions were compared. The experimental microsphere distribution exhibited a clear dependence on injection location that correlated very strongly with the computationally predicted results. Individual branch targeting was possible for each of the five outputs. The experimental results validate the simulation methodology for achieving targeted microsphere distributions in a known geometry under constant flow conditions.
Asunto(s)
Braquiterapia/instrumentación , Portadores de Fármacos/química , Arteria Hepática/fisiopatología , Microesferas , Modelos Cardiovasculares , Radiofármacos/química , Reología/métodos , Animales , Velocidad del Flujo Sanguíneo/fisiología , Fenómenos Fisiológicos Sanguíneos , Simulación por Computador , Humanos , Movimiento (Física)RESUMEN
A novel annuloplasty ring with a shape memory alloy core has been developed to facilitate minimally invasive mitral valve repair. In its activated (austenitic) phase, this prototype ring has comparable mechanical properties to commercial semi-rigid rings. In its pre-activated (martensitic) phase, this ring is flexible enough to be introduced through an 8-mm trocar and easily manipulated with robotic instruments within the confines of a left atrial model. The core is constructed of 0.50 mm diameter NiTi, which is maintained below its martensitic transition temperature (24 °C) during deployment and suturing. After suturing, the ring is heated above its austenitic transition temperature (37 °C, normal human body temperature) enabling the NiTi core to attain its optimal geometry and stiffness characteristics indefinitely. This article summarizes the design, fabrication, and evaluation of this prototype ring. Experimental results suggest that the NiTi core ring could be a viable alternative to flexible bands in robot-assisted minimally invasive mitral valve repair.
Asunto(s)
Prótesis Valvulares Cardíacas , Procedimientos Quirúrgicos Mínimamente Invasivos/instrumentación , Níquel/química , Titanio/química , Aleaciones/química , Diseño Asistido por Computadora , Módulo de Elasticidad , Diseño de Equipo , Análisis de Falla de Equipo , HumanosRESUMEN
PURPOSE: An in vitro study using explanted porcine hearts was conducted to evaluate a novel annuloplasty band, reinforced with a two-phase, shape memory alloy, designed specifically for minimally invasive mitral valve repair. DESCRIPTION: In its rigid (austenitic) phase, this band provides the same mechanical properties as the commercial semi-rigid bands. In its compliant (martensitic) phase, this band is flexible enough to be introduced through an 8-mm trocar and is easily manipulated within the heart. EVALUATION: In its rigid phase, the prototype band displayed similar mechanical properties to commercially available semi-rigid rings. Dynamic flow testing demonstrated no statistical differences in the reduction of mitral valve regurgitation. In its flexible phase, the band was easily deployed through an 8-mm trocar, robotically manipulated and sutured into place. CONCLUSIONS: Experimental results suggest that the shape memory alloy reinforced band could be a viable alternative to flexible and semi-rigid bands in minimally invasive mitral valve repair.
Asunto(s)
Implantación de Prótesis de Válvulas Cardíacas/instrumentación , Prótesis Valvulares Cardíacas , Ensayo de Materiales/métodos , Procedimientos Quirúrgicos Mínimamente Invasivos/métodos , Insuficiencia de la Válvula Mitral/cirugía , Animales , Modelos Animales de Enfermedad , Modelos Teóricos , Diseño de Prótesis , Robótica , PorcinosRESUMEN
OBJECTIVE: The development of a novel surgical tool or technique for mitral valve repair can be hampered by cost, complexity, and time associated with performing animal trials. A dynamically pressurized model was developed to control pressure and flowrate profiles in intact porcine hearts in order to quantify mitral regurgitation and evaluate the quality of mitral valve repair. METHODS: A pulse duplication system was designed to replicate physiological conditions in explanted hearts. To test the capabilities of this system in measuring varying degrees of mitral regurgitation, the output of eight porcine hearts was measured for two different pressure waveforms before and after induced mitral valve failure. Four hearts were further repaired and tested. Measurements were compared with echocardiographic images. RESULTS: For all trials, cardiac output decreased as left ventricular pressure was increased. After induction of mitral valve insufficiencies, cardiac output decreased, with a peak regurgitant fraction of 71.8%. Echocardiography clearly showed increases in regurgitant severity from post-valve failure and with increased pressure. CONCLUSIONS: The dynamic heart model consistently and reliably quantifies mitral regurgitation across a range of severities. Advantages include low experimental cost and time associated with each trial, while still allowing for surgical evaluations in an intact heart.