In Vitro Mitral Valve Model with Unrestricted Ventricular Access: Using Vacuum to Close the Valve and Enable Static Trans-Mitral Pressure

Current in vitro models of the left heart establish the pressure difference required to close the mitral valve by sealing and pressurizing the ventricular side of the valve, limiting important access to the subvalvular apparatus. This paper describes and evaluates a system that establishes physiological pressure differences across the valve using vacuum on the atrial side. The subvalvular apparatus is open to atmospheric pressure and accessible by tools and sensors, establishing a novel technique for experimentation on atrioventricular valves. Porcine mitral valves were excised and closed by vacuum within the atrial chamber. Images were used to document and analyze closure of the leaflets. Papillary muscle force and regurgitant flow rate were measured to be 4.07 N at 120 mmHg and approximately 12.1 ml/s respectively, both of which are within clinically relevant ranges. The relative ease of these measurements demonstrates the usefulness of improved ventricular access at peak pressure/force closure. Graphical abstract

Computational Modeling of Aortic Stenosis with a Reduced Degree-Of-Freedom Fluid-Structure Interaction Valve Model

In this study, a novel reduced degree-of-freedom (rDOF) aortic valve model is employed to investigate the fluid-structure interaction and hemodynamics associated with aortic stenosis. The dynamics of the valve leaflets are determined by an ordinary differential equation with two parameters and this rDOF model is shown to reproduce key features of more complex valve models. The hemodynamics associated with aortic stenosis is studied for three cases: a healthy case and two stenosed cases. The focus of the study is to correlate the hemodynamic features with the source generation mechanism of systolic murmurs associated with aortic stenosis. In the healthy case, extremely weak flow fluctuations are observed. However, in the stenosed cases, simulations show significant turbulent fluctuations in the asending aorta, which are responsible for the generation of strong wall pressure fluctuations after the aortic root mostly during the deceleration phase of the systole. The intensity of the murmur generation increases with the severity of the stenosis, and the source locations for the two diseased cases studied here lies around 1.0 inlet duct diameters ($D_o$) downstream of the ascending aorta.

Novel full-flow valves, impact on early mitral post-replacement period: a non-randomised controlled cohort trial

Background. Among cardiovascular diseases, valve pathology of various aetiology comprises a primary factor of chronic heart failure. Mitral valve diseases afflict over half of all patients with acquired heart defects. Today’s long-term outcomes of mitral valve replacement are not quite satisfactory, which urges the invention of novel vales. Such a modern artificial valve is the nationally developed bivalve full-flow MedInzh-ST prothesis.Objectives. Assessment of advantages of the novel MedInzh-ST full-flow mechanical valve vs. MedInzh-2 model in analyses of short-term postoperative outcomes.Methods. Over a five-year period, 116 patients underwent indicated mitral replacement with MedInzh valves. The full-flow MedInzh-ST was implanted in 55 patients, and MedInzh-2 — in 61. All patients had transthoracic echocardiography for structural and functional heart and implant control prior to surgery and discharge from hospital. Clinical and echocardiographic analyses were performed in the early postoperative period.Results. The choice of valve model had no effect on the rates of postoperative complications and hospital mortality. All lethal cases were not associated with the valve malfunction. All patients with predominant mitral stenosis revealed the reliably lower peak and mean transmitral pressure gradient and pulmonary artery systolic pressure, irrespective of the valve model. The novel full-flow valve implantation significantly more often associated with a reduced right ventricle size. All patients with predominant insufficiency were observed to reduce mitral regurgitation and the left ventricular size upon defect correction. Patients with full-flow protheses significantly more often had a reduced end-systolic dimension.Conclusion. The MedInzh-ST full-flow mechanical valve satisfies the modern requirements for efficacy and safety. Mitral stenosis correction with full-flow valves is shown to exert a greater effect on reverse right ventricular remodelling compared to the classical model.

STABILITY ANALYSIS OF GLOBE VALVE USING CLASSICAL TECHNIQUES

The importance of globe valve in fluid handling and control cannot be overemphasized. It is useful in oil and gas applications. If globe valve is not properly modelled, its primary purpose of regulation of fluid flow may be defeated. In this work, model of globe valve is developed from basic mechanical principles. The resulting model is a second order system whose response to a step input signal gives no overshoot. Further stability analysis with bode plot, Nyquist plot and root locus plot give a stable system indicating that the developed globe valve model is suitable for relevant areas of application.

Investigation of Pressure Losses and Flow Fluctuations in an Intercept Valve Assembly of an Intermediate-Pressure Turbine Part

A new design of an intercept valve assembly of the intermediate-pressure turbine part of greater power output is investigated in terms of pressure losses and flow fluctuations by using measurement on an experimental valve model. In addition, numerical simulations are used to further clarify measured phenomena. For such valve assemblies, it is important to exactly predict pressure losses and avoid danger of vibrations, which are caused by undesirable flow fluctuations, in order to guarantee valve’s efficiency and operational reliability. For this type of valve, it is especially important for turbine operations in partial loads (off-design conditions). Measurements were carried out in the Aerodynamic laboratory of the Institute of Thermomechanics of the Czech Academy of Sciences (IT) in a modular aerodynamic tunnel. Numerical simulations were carried out in the Doosan Skoda Power Company (DSP) by using a package of ANSYS software tools. The experimental valve model is a scaled model of a real valve assembly. It consists of an inlet pipeline, a stop valve and a control valve including its diffuser and outlet pipeline. Measured regimes were defined by a mass flow rate and a control valve cone lift which can be precisely changed. In order to investigate pressure loses, total and static pressures at valve characteristic locations were measured by using Prandtl probes and wall static pressure taps. In order to measure pressure fluctuations, Kulite fast response pressure transducers were used. They were situated near the valve throat where the flow fluctuations, which are strongly related to a flow separation, are the most visible and influential. Measurement results are compared with numerical results and locations with a flow separation were found. In order to reduce this phenomenon, different valve seat angles were also tested. As a result, a valve design could be optimized and, for a pressure loss prediction, a pressure loss model for this new intercept valve assembly could be created. Therefore, pressure losses in similar valve assemblies can be predicted with required accuracy for each new turbine where modern intercept valves are used. This helps to increase steam turbine efficiency and reduce fuel consumption. Based on pressure fluctuations results, operating conditions at which dangerous flow instabilities occur were identified. It was concluded that there is an operating condition border where the flow field starts to be unstable. As a result, the areas of safe and dangerous operating conditions can be predicted so that the operational reliability of the valve can be guaranteed.

Real World Experience with an Optimized Control Scheme for a Ventricular Assist Device

A closed-loop control software for the new mobile Berlin Heart EXCORR driving unit was optimized to balance usability, durability, pump wash out, blood stress and power consumption. The piston of the electro-pneumatic cylinder is moved on a pump-cannula-specific trajectory. A friction and a valve model are adapted online. Verification and real world data show constant flow, low power consumption and the adherence of all limits.