Modeling arthropod filiform hair motion using the penalty immersed boundary method

Crickets are able to sense their surrounding environment through about 2000 filiform hairs located on a pair of abdominal cerci. The mechanism by which the cricket is able to sense a wide range of input signals using these filiform hairs of different length and orientation is of great interest. Most of the previous filiform hair models have focused on a single, rigid hair in an idealized air field. Here, we present a model of the cercus and filiform hairs that are mechanically coupled to the surrounding air, and the model equations are based on the penalty immersed boundary method. The key difference between the penalty immersed boundary method and the traditional immersed boundary method is the addition of forces to account for density differences between the immersed solid (the filiform hairs) and the surrounding fluid (air). The model is validated by comparing the model predictions to experimental results, and then the model is used to examine the interactions between multiple hairs. With multiple hairs, there is little interaction when the hairs are separated by more than 1mm, and, as they move closer, they interact through viscous coupling, which reduces the deflection of the hairs due to the air movement. We also examine the computational scalability of the algorithm and show that the computational costs grow linearly with the number of hairs being modeled.     

A comparative computational study of blood flow through prosthetic heart valves using the finite element method

The steady flow of blood through three common types of prosthetic heart valves was simulated numerically using the finite element method. The velocity, pressure and stress fields were obtained for the disk-type, tilting-disk and ball-type prosthetic heart valves in aortic position, for increasing Reynolds numbers up to 900, 1500 and 2000 respectively. Computer graphics of calculated velocities are presented, showing in detail the accelerated flow, recirculation and stagnation areas developed in the prosthesis. Maximum wall shear stresses were found at 0.5, 1.4, and 1.2 diameters from the sewing ring downstream for the disk, tilting-disk and ball valves being the values of 55, 18 and 33 dyn cm-2 respectively. In the vicinity of the occluder, maximum shear stresses of 38, 30 and 47 dyn cm-2 respectively were computed. The flow characteristics and performance for each valve are compared, the results are presented in terms of energy loss and maximum shear stress. The velocity and stress fields are compared with in vitro evaluations found in the literature.     

Identification and quantification of prosthetic mitral regurgitation by flow convergence method using transthoracic approach

Ultrasound is the preferred imaging modality in diagnosis of vascular complications following cardiac catheterization and intervention. In some cases, however, bleeding surrounding the femoral vessels, may severely distort the color Doppler images, making detection of venous complications especially difficult. This report refers to such a case where post-catheterization haematoma was suspected to cause an obstruction of the femoral vein. Spectral Doppler recordings of blood flow in the common femoral vein, up-stream, distal to the hemorrhagic area, confirmed the diagnosis of obstruction by demonstrating changes in the venous flow pattern in the common femoral vein, consistent with venous hypertension. Due to the poor quality of the ultrasound images, the exact cause of the obstruction had to be established by another imaging modality, not affected by haemorrhages. CT showed that the common femoral vein was compressed at the puncture site by surrounding haemorrhages. Thus, when bleeding due to cardiac catheterization is associated with possible venous obstruction and findings by color Doppler are equivocal due to degradation of the color-Doppler image, detection of venous hypertension by spectral Doppler, performed distal to the bleeding area, strongly supports the presence of venous obstruction where the exact cause may be established by CT.     

Modeling technique of prosthetic heart valves

This paper demonstrates a modeling technique of prosthetic heart valves. In the modeling, a pumping cycle is divided into four phases, in which the state of the valve and flow is different. The pressure-flow relation across the valve is formulated separately in each phase. This technique is developed to build a mathematical model used in the real time estimation of the hemodynamic state under artificial heart pumping. The model built by this technique is simple enough for saving the computational time in the real time estimation. The model is described by the first-order ordinary differential equation with 12 parameters. These parameters can be uniquely determined beforehand from in-vitro experimental data. It is shown that the model can adapt, with sufficient accuracy, to a change in the practical pumping condition and the viscosity of the fluid in their practical range, and is also demonstrated that the estimated backflow volume by model agrees closely with the actual one.     

Velocity profiles in the wake of two prosthetic heart valves using a new cardiovascular simulator

In this paper we present a study of the post valvular flow field on a new cardiovascular simulator including an elastic model of the aortic arch. Transverse and vertical two-dimensional velocity measurements are performed with an ultrasonic velocimeter. Two prosthetic heart valves are tested in the aortic position. The behaviour of the velocity vectors patterns during one pulsatile cycle is one of the most striking features of the flow.     

Unravelling the proteome of degenerative human mitral valves

Degenerative mitral valve disease (DMVD), which includes the syndromes of mitral valve prolapse (MVP) and flail leaflet, is a common valvular condition which can be complicated by mitral regurgitation and adverse cardiovascular outcomes. Although several genetic and other studies of MVP in dog models have provided some information regarding the underlying disease mechanisms, the proteins and molecular events mediating human MVP pathogenesis have not been unraveled. In this study, we report the first large‐scale proteome profiling of mitral valve tissue resected from patients with MVP. A total of 1134 proteins were identified, some of which were validated using SWATH‐MS and western blotting. GO annotation of these proteins confirmed the validity of this proteome database in various cardiovascular processes. Among the list of proteins, we found several structural and extracellular matrix proteins, such as asporin, biglycan, decorin, lumican, mimecan, prolargin, versican, and vinculin, that have putative roles in the pathophysiology of MVP. These proteins could also be involved in the cardiac remodeling associated with mitral regurgitation. All MS data have been deposited in the ProteomeXchange with identifier PXD000774 ( http://proteomecentral.proteomexchange.org/dataset/PXD000774 ).     

An immersed boundary method for simulating a single axisymmetric cell growth and division

For an animal cell, cytokinesis is the process by which a cell divides its cytoplasm to produce two daughter cells. We propose a new mathematical model for simulating cytokinesis. The proposed model is robust and realistic in deciding the position of the cleavage furrow and in defining the contractile force leading to cell division. We use an immersed boundary method to track the morphology of cell membrane during cytokinesis. For accurate calculation, we adaptively add and delete the immersed boundary points. We perform numerical simulations on the axisymmetric domain to have sufficient resolution and to incorporate three-dimensional effects such as anisotropic surface tension. Finally, we investigate the effects of each model parameter and compare a numerical result with the experimental data to demonstrate the efficiency and accuracy of our proposed method.     

Structural simulations of prosthetic tri-leaflet aortic heart valves

This study presents a combined computational and experimental approach for the nonlinear structural simulations of polymeric tri-leaflet aortic valves (PAVs). Nonlinear shell-based and quasi-static finite-element (FE) structural models are generated for a prosthetic valve geometry that includes the leaflets, stents and root materials, such as the bottom base and outside walls. The PAV structural model is subject to an ensemble averaged transvalvular pressure waveform measured from repeated in vitro tests conducted with a left heart simulator. High-resolution optical measurements are used to measure the in vitro kinematics of the leaflets and the stents. Qualitative and quantitative deformation measures are defined in order to compare the predicted kinematics from the PAV models with the in vitro measurements. Six new quantitative deformation metrics are introduced. They include three distances measuring the current PAV geometric center to the leaflet edges while additional three distances define the stent post-to-stent post (SPTSP) distances. The structural model is able to predict the kinematic deformation metrics with maximum errors around 10% especially in systole where the displacements are larger in magnitude. The combined structural modeling with experimental simulations along with the new proposed deformation metrics provide an effective way to study the PAV structural behavior and a path for improving the structural design of prosthetic valves.     

Physiologically-based testing system for the mechanical characterization of prosthetic vein valves

Due to the relatively limited amount of work done to date on developing prosthetic vein (as opposed to cardiac) valves, advances in this topic require progress in three distinct areas: 1) improved device design, 2) relevant device testing conditions, and, 3) appropriate parameters for evaluation of results. It is the purpose of this paper to address two of these issues (#2 and #3) by: 1) performing a study of normal volunteers to quantify the anatomy and hemodynamic features of healthy venous valves, 2) construction of a 2-step, in vitro testing procedure, which simulates both physiologic and postural conditions seen in the lower extremity venous system, and, 3) defining several modified and new parameters which quantify dynamic valve characteristics.     

Incorporating an immersed boundary method to study thermal effects of vascular systems during tissue cryo-freezing

In this paper, the three-dimensional thermal effects of a clinically-extracted vascular tissue undergoing cryo-freezing are numerically investigated. Based on the measured experimental temperature field, the numerical results of the Pennes bioheat model combined with the boundary condition-enforced immersed boundary method (IBM) agreed well with experimental data with a maximum temperature discrepancy of 2.9 °C. For simulating the temperature profile of a tumor sited in a dominantly vascularized tissue, our model is able to capture with ease the thermal effects at specified junctions of the blood vessels. The vascular complexity and the ice-ball shape irregularity which cannot be easily quantified via clinical experiments are also analyzed and compared for both two-dimensional and three-dimensional settings with different vessel configurations and developments. For the three-dimensional numerical simulations, a n-furcated liver vessels model from a three-dimensional segmented volume using hole-making and subdivision methods is applied. A specific study revealed that the structure and complexity of the vascular network can markedly affect the tissue's freezing configuration with increasing ice-ball irregularity for greater blood vessel complexity.     

Compositional changes of human mitral valves with aging

To elucidate compositional changes of the mitral valve with aging, the authors investigated the relationships among element contents in the mitral valves. The subjects consisted of 10 men and 15 women, ranging in age from 65 to 102 yr. After the ordinary dissection, mitral valves, lower parts of the interventricular septa, and terminal crests containing the sinoatrial nodes were resected and the element contents were determined by inductively coupled plasma-atomic emission spectrometry. The interventricular septa and sinoatrial nodes were used to compare with the mitral valves. With regard to the mitral valve, it was found that extremely significant correlations were found among the contents of Ca, P, Mg, and Na, but no significant correlations were found between the contents of S and elements such as Ca, P, or Mg. Regarding the interventricular septum, it was found that an extremely significant correlation was found between P and S contents; very significant correlations were found between Ca and Mg contents and between Mg and S contents; and a significant correlation was found between P and Mg contents. However, no significant correlation was found between Ca and P contents in the interventricular septa. In the terminal crest containing the sinoatrial node, significant correlations were found among the contents of Ca, P, Mg, and S. The present study revealed that with regard to the relationships among element contents, the compositional change of the mitral valve was intermediate between those of the thoracic aorta and the interventricular septum.     

Laser assessment of leaflet closing motion in prosthetic heart valves

The dynamics of leaflet motion in heart valve prostheses (HVP), and in particular the closing velocity, is believed to be related to the valve sound and possibly to the phenomenon of valve cavitation. This paper describes a non-intrusive laser sweeping technique enabling the study of leaflet motion. The principle of measurement and the equipment involved are presented, together with the results of two commerially available, 29 mm bileaflet mitral valves, a St. Jude Medical, and an Edwards Duromedic valve. Experiments were carried out in a pulsatile mock flow testing loop designed to mimic physiological pressure waveforms and ventricular contraction. Measurements of heart rate were made in the range 70–120 beats min⁻¹, with a ventricular pressure slope range of 1800–5600 mm Hgs⁻¹ and a cardiac output range of 5.0–7.5 litres min⁻¹. Motion analysis of the measured data focuses on the velocity of the leaflet immediately before closure.     

Study of the velocity and strain fields in the flow through prosthetic heart valves

A comparative experimental study of the velocity field and the strain field produced down-stream of biological and mechanical artificial valves is presented. In order to determine the spatial and temporal distributions of these fields, a phase-locked stereoscopic particle image velocimetry (or 3D-PIV) technique was implemented. Emphasis was placed on the identification of the fundamental differences between the extensional and the shear components of the strain tensor. The analysis of the characteristic flows reveal that the strains in every direction may reach high values at different times during the cardiac cycle. It was found that elevated strain levels persist throughout the cardiac cycle as a result of all these contributions. Finally, it is suggested that the frequency with which the strain variations occur at particular instants and locations could be associated to the cumulative damage process of the blood constituents and should be taken into account in the overall assessment of existing valve types, as well as in future design efforts.     

Design of a new pulse duplicator system for prosthetic heart valves

This paper discusses results of a computer simulation for designing a new pulse duplicator system for mechanical heart valves. The design objective of the system is to obtain a compact, efficient pulse duplicator system capable of accurately measuring the volume flow rate across a valve. The volume flow rate is determined as the derivative of the volume displacement of an actuator piston which directly drives the fluid. The system does not need any circulatory loop, since the piston is controlled on-line to follow command signals representing an aortic impedance. The results of the computer simulation show: the designed PI-controllers of the actuator can precisely control valve motion to follow given command signals, the eigenvalues of the controllers have to be carefully chosen to prevent unstable behaviors of a valve in diastole, and the dimensions of the actuator is optimized by minimizing a cost function of the total efficiency of the system.     

Total hip arthroplasty wear simulation using the boundary element method

In this paper an application of the boundary element method for simulating wear in total hip prosthesis is presented. Several examples including different update periods of the worn acetabular cup, various femoral head sizes and various materials for both the femoral head and the acetabular cup are simulated under the same variable loading conditions for up to 20 years of service. Moreover, two different femoral models are considered in order to investigate the influence of the femoral modelling. The analysis demonstrates that due to the boundary only modelling requirement, the computational time and storage remains low, allowing large service periods to be simulated. Generally, the results obtained are in good agreement with other researchers findings. Moreover, ignoring the bending of the femoral neck in the model, results in a small overestimation of the maximum wear depth, while the volumetric wear is slightly underestimated. However, these differences are trivial considering the reduction of the computational effort.     

Collagen composition of normal and myxomatous human mitral heart valves.

The collagens were studied in 13 normal and 19 myxomatous human mitral valves. The collagens of the valve were completely solubilized by using a method consisting of guanidinium chloride extraction, limited pepsin digestions and CNBr cleavage of the residue. The normal valves contained 74% type I, 24% type III and 2% type V collagen. The type I and type III collagens had similar solubility patterns, although only type I collagen was detected in the guanidinium chloride extract. Type V collagen was only detected in the first pepsin extract. The type I and III collagens had higher contents of hydroxylysine than did the same collagens from age-matched dermis. The two-dimensional electrophoretic 'maps' of CNBr-cleavage peptides showed low recoveries of the C-terminal alpha 1(I) CB6 and alpha 1(III) CB9 peptides, which are involved in forming intermolecular cross-linkages. Most of the reducible cross-linkages were present in large-Mr peptide complexes, and these complexes were shown by labelling with 125I to include the tyrosine-containing alpha 1(I) CB6 peptide. The myxomatous valves contained 67% type I, 31% type III and 2% type V collagens. There was a significant increase in the concentration of each type of collagen, which consisted of a 9% increase of type I collagen, a 53% increase of type III collagen and a 25% increase of type V collagen. The contents of hydroxylysine in type I and III collagens and the electrophoretic 'maps' of the CNBr-cleavage peptides involved in cross-linkages did not differ significantly from the results obtained from the normal valves. The biochemical findings suggest that there is an increased production of collagen, in particular type III collagen, and glycosaminoglycan as well as a proliferation of cells as part of a repair process in the myxomatous valves.     

Age-related changes of element contents in human mitral and tricuspid valves

To examine age-related changes of human cardiac valves, mitral and tricuspid valves were analyzed by inductively coupled plasma-atomic emission spectrometry. The subjects for mitral valves consisted of 12 men and 8 women, ranging in age from 52 to 96 yr. The subjects for tricuspid valves consisted of 11 men and 6 women, ranging in age from 52 to 93 yr. Furthermore, 16 of the samples of the cardiac valves were derived from the same subjects. The contents of calcium, phosphorus, and magnesium in the mitral valves increased progressively with advancing age and reached maximum in the 80s in regard to calcium and phosphorus and maximum in the 90s in regard to magnesium. The maximum average amounts corresponded to about three times the average contents in the 60s. In contrast, the content of sulfur in the mitral valves remained constant between the 50s and 90s. Regarding tricuspid valve, the contents of calcium, phosphorus, and magnesium scarcely increased with advancing age, except for one subject who died of chronic renal failure. Histological observations of the mitral valves revealed that deposits of calcium were present in both the elastic fibers and its degenerative tissues of the mitral valve. The present study indicates that the accumulation of calcium, phosphorus, and magnesium occurs progressively in the mitral valve with aging, but does not occur in the tricuspid valve.