Evaluation of the Biaxial Mechanical Properties of the Mitral Valve Anterior Leaflet Under Physiological Loading Conditions

It is a fundamental assumption that a repaired mitral valve (MV) or MV replacement should mimic the functionality of the native MV as closely as possible. Thus, improvements in valvular treatments are dependent on the establishment of a complete understanding of the mechanical properties of the native MV. In this work, the biaxial mechanical properties, including the viscoelastic properties, of the MV anterior leaflet (MVAL) were explored. A novel high-speed biaxial testing device was developed to achieve stretch rates both below and beyond in-vitro values reported for the MVAL (Sacks et al, ABME, Vol. 30,pp. 1280-90, 2002). Experiments were performed with this device to assess the effects of stretch rate (from quasi-static to physiologic) on the stress-stretch response in the native leaflet. Additionally, stress-relaxation and creep tests were performed on the MVAL under physiologic biaxial loading conditions.The results of these tests showed that the stress-stretch responses of the MVAL during the loading phases were remarkably independent of stretch rate. The results of the creep and relaxation experiments revealed that the leaflet exhibited significant relaxation, but unlike traditional viscoelastic biological materials, exhibited negligible creep.These results suggested that the MVAL may be functionally modeled as an anisotropic quasi-elastic material and highlighted the importance of performing creep experiments on soft tissues. Additionally, this study underscored the necessity of performing biaxial experiments in order to appropriately determine the mechanical properties of membranous tissues

In vitro hemodynamic evaluation of ventricular suction conditions of the EVAHEART ventricular assist pump

Purpose: Mismatches between pump output and venous return in a continuous-flow ventricular assist device may elicit episodes of ventricular suction. This research describes a series of in vitro experiments to characterize the operating conditions under which the EVAHEART centrifugal blood pump (Sun Medical Technology Research Corp., Nagano, Japan) can be operated with minimal concern regarding left ventricular (LV) suction. Methods: The pump was interposed into a pneumatically driven pulsatile mock circulatory system (MCS) in the ventricular apex to aorta configuration. Under varying conditions of preload, afterload, and systolic pressure, the speed of the pump was increased step-wise until suction was observed. Identification of suction was based on pump inlet pressure. Results: In the case of reduced LV systolic pressure, reduced preload (=10 mmHg), and afterload (=60 mmHg), suction was observed for speeds =2,200 rpm. However, suction did not occur at any speed (up to a maximum speed of 2,400 rpm) when preload was kept within 10-14 mmHg and afterload =80 mmHg. Although in vitro experiments cannot replace in vivo models, the results indicated that ventricular suction can be avoided if sufficient preload and afterload are maintained. Conclusion: Conditions of hypovolemia and/or hypotension may increase the risk of suction at the highest speeds, irrespective of the native ventricular systolic pressure. However, in vitro guidelines are not directly transferrable to the clinical situation; therefore, patient-specific evaluation is recommended, which can be aided by ultrasonography at various points in the course of support

In vitro hemodynamic evaluation of ventricular suction conditions of the EVAHEART ventricular assist pump.

<p>Purpose: Mismatches between pump output and venous return in a continuous-flow ventricular assist device may elicit episodes of ventricular suction. This research describes a series of in vitro experiments to characterize the operating conditions under which the EVAHEART centrifugal blood pump (Sun Medical Technology Research Corp., Nagano, Japan) can be operated with minimal concern regarding left ventricular (LV) suction. Methods: The pump was interposed into a pneumatically driven pulsatile mock circulatory system (MCS) in the ventricular apex to aorta configuration. Under varying conditions of preload, afterload, and systolic pressure, the speed of the pump was increased step-wise until suction was observed. Identification of suction was based on pump inlet pressure. Results: In the case of reduced LV systolic pressure, reduced preload (=10 mmHg), and afterload (=60 mmHg), suction was observed for speeds =2,200 rpm. However, suction did not occur at any speed (up to a maximum speed of 2,400 rpm) when preload was kept within 10-14 mmHg and afterload =80 mmHg. Although in vitro experiments cannot replace in vivo models, the results indicated that ventricular suction can be avoided if sufficient preload and afterload are maintained. Conclusion: Conditions of hypovolemia and/or hypotension may increase the risk of suction at the highest speeds, irrespective of the native ventricular systolic pressure. However, in vitro guidelines are not directly transferrable to the clinical situation; therefore, patient-specific evaluation is recommended, which can be aided by ultrasonography at various points in the course of support.</p