Modelling mitral valvular dynamics–current trend and future directions

Dysfunction of mitral valve causes morbidity and premature mortality and remains a leading medical problem worldwide. Computational modelling aims to understand the biomechanics of human mitral valve and could lead to the development of new treatment, prevention and diagnosis of mitral valve diseases. Compared with the aortic valve, the mitral valve has been much less studied owing to its highly complex structure and strong interaction with the blood flow and the ventricles. However, the interest in mitral valve modelling is growing, and the sophistication level is increasing with the advanced development of computational technology and imaging tools. This review summarises the state-of-the-art modelling of the mitral valve, including static and dynamics models, models with fluid-structure interaction, and models with the left ventricle interaction. Challenges and future directions are also discussed

Global Data Computation in a Dedicated Chordal Ring

Existing Global Data Computation (GDC) protocols for asynchronous systems are designed for fully connected networks. In this paper, we discuss GDC in a dedicated asynchronous chordal ring, a type of un-fully connected networks. The virtual links approach, which constructs t+1 (t<n) process-disjoint paths for each pair of processes without direct connection to tolerate failures (where t is the maximum number of processes that may crash and n is the total number of processes), can be applied to solve the GDC problem in the chordal but the virtual links approach incurs high message complexity. To reduce the high communication cost, we propose a non round-based GDC protocol for the asynchronous chordal ring with perfect failure detectors. The main advantage of our approach is that there is no notion of round, processes only send messages via direct connections and the implementation of failure detectors does not require process-disjoint paths. Analysis and comparison with the virtual links approach shows that our protocol reduces the message complexity significantly.Singapore-MIT Alliance (SMA

Gossiping in chordal rings under the line model

The line model assumes long distance calls between non neighboring processors. In this sense, the line model is strongly related to circuit-switched networks, wormhole routing, optical networks supporting wavelength division multiplexing, ATM switching, and networks supporting connected mode routing protocols. Since the chordal rings are competitors of networks as meshes or tori because of theirs short diameter and bounded degree, it is of interest to ask whether they can support intensive communications (typically all-to-all) as efficiently as these networks. We propose polynomial algorithms to derive optimal or near optimal gossip protocols in the chordal ring

Calculation of the longitudinal aerodynamic characteristics of STOL aircraft with externally-blown jet-augmented flaps

A theoretical investigation was made to develop methods for predicting the longitudinal aerodynamic characteristics of externally-blown, jet-augmented wing-flap combinations. A potential flow analysis was used to develop two models: a wing-flap lifting surface model and a high-bypass-ratio turbofan engine wake model. Use of these two models in sequence provides for calculation of the wing-flap load distribution including the influence of the engine wake. The method can accommodate multiple engines per wing panel and part-span flaps but is limited to the case where the flow and geometry of the configuration are symmetric about a vertical plane containing the wing root chord. Comparisons of predicted and measured lift and pitching moment on unswept and swept wings with one and two engines per panel and with various flap deflection angles indicate satisfactory prediction of lift and moment for flap deflections up to 30 to 40 degrees. At higher flap angles with and without power, the method begins to overpredict lift, due probably to the appearance of flow separation on the flaps

High Resolution Imaging of the Mitral Valve in the Natural State with 7 Tesla MRI

Imaging techniques of the mitral valve have improved tremendously during the last decade, but challenges persist. The delicate changes in annulus shape and papillary muscle position throughout the cardiac cycle have significant impact on the stress distribution in the leaflets and chords, thus preservation of anatomically accurate positioning is critical. The aim of this study was to develop an in vitro method and apparatus for obtaining high-resolution 3D MRI images of porcine mitral valves in both the diastolic and systolic configurations with physiologically appropriate annular shape, papillary muscle positions and orientations, specific to the heart from which the valve was harvested. Positioning and mounting was achieved through novel, customized mounting hardware consisting of papillary muscle and annulus holders with geometries determined via pre-mortem ultrasonic intra-valve measurements. A semi-automatic process was developed and employed to tailor Computer Aided Design models of the holders used to mount the valve. All valve mounting hardware was 3D printed using a stereolithographic printer, and the material of all fasteners used were brass for MRI compatibility. The mounted valves were placed within a clear acrylic case, capable of holding a zero-pressure and pressurized liquid bath of a MRI-compatible fluid. Obtaining images from the valve submerged in liquid fluid mimics the natural environment surrounding the valve, avoiding artefacts due to tissue surface tension mismatch and gravitational impact on tissue shape when not neutrally buoyant. Fluid pressure was supplied by reservoirs held at differing elevations and monitored and controlled to within ±1mmHg to ensure that the valves remained steady. The valves were scanned in a 7 Tesla MRI system providing a voxel resolution of at least 80μm. The systematic approach produced 3D datasets of high quality which, when combined with physiologically accurate positioning by the apparatus, can serve as an important input for validated computational models

Mitral Valve Imaging and Biomechanics: A Workflow Towards Computational Modeling and Validation

The mitral valve serves a critical role in healthy cardiac function by ensuring the unidirectional flow of oxygenated blood from the left atrium into the left ventricle. It experiences the highest pressures found within the heart and its closure is the result of a complex interaction of several different structures that, furthermore, are unique to each individual. Despite the valve’s vital role however, the specific function of these constituent structures is not fully understood. This, confounded by its asymmetric, personalized nature, make surgical interventions for the mitral valve far less effective than for its neighboring aortic valve. Efforts to overcome this have been made through the lens of computational simulation, in which the valve is studied virtually and procedures may be planned. The quality and reliability of these simulation results are only as good as the inputs that the simulation model receives. This study proposes and evaluates a workflow by which high-quality biomechanical inputs are obtained for computational input and validation. To account for individual variation, all steps are performed on the same valve such that a direct correspondence is made between geometry, stress/load distribution and the resulting coaptation. Ultrasound in vivo measurements are made so that custom tailored mounting hardware can be manufactured. This hardware is used to support the valve in a physiologically appropriate manner for µCT imaging in both the open and closed configurations. Scanning within a fluid medium, to prevent tissue desiccation and other detrimental effects, is made possible through a DiceCT tissue staining procedure. High resolution, 3D imagery is obtained for the open valve whereas only a relatively quick set of projection images is obtained for the closed configuration. Registration between open and closed imagery is accomplished by localizing aluminum oxide fiducial markers that are bound to the leaflet surface. Subsequent image analysis is performed to isolate the tissue and place the data in the proper format for computational use. The valve is then closed under known pressure while chordal forces/strains are simultaneously recorded to provide loading conditions. The effectiveness of the workflow is illustrated through two animal experiments. Incomplete results were obtained from the first experiment as the tissue degraded significantly during a prolonged period of µCT downtime. The second experiment resulted in good quality ultrasound imagery, leading to the creation of customized mounting hardware, yet the remainder of the process was still in progress at the final stages of this document. Computational modeling is still ongoing, yet some preliminary results are presented which show the geometry from the first animal experiment tending towards closure