Gerard Fortuny

Simulation and study of the behaviour of the transversalis fascia in protecting against the genesis of inguinal hernias

Simulating the muscular system has many applications in biomechanics, biomedicine and the study of movement in general. We are interested in studying the genesis of a very common pathology: human inguinal hernia. We study the effects that some biomechanical parameters have on the dynamic simulation of the region, and their involvement in the genesis of inguinal hernias. We use the finite element method (FEM) and current models for the muscular contraction to determine the deformed fascia transversalis for the estimation of the maximum strain. We analysed the effect of muscular tissue density, Youngs modulus, Poissons coefficient and calcium concentration in the genesis of human inguinal hernia. The results are the estimated maximum strain in our simulations, has a close correlation with experimental data and the accepted commonly models by the medical community. Our model is the first study of the effect of various biological parameters with repercussions on the genesis of the inguinal hernias.

Effect of anticoagulant treatment in deep vein thrombosis: A patient-specific computational fluid dynamics study

A methodology that might help physicians to establish a diagnostic and treatment tailored for each specific patient with a pathological thrombus is presented. A realistic model for the geometry of a popliteal vein with a thrombus just above the knee was reconstructed from in vivo computed tomography images acquired from one specific patient and then it was used to perform computational fluid dynamics (CFD) simulations. The wall shear stress (WSS) response to the administration of anticoagulant drugs and the influence of viscosity on the shape of the velocity distribution were investigated. Both a Newtonian and a non-Newtonian viscosity model were implemented for different blood flow rates in the range 3-7 cm(3)/s. The effect of anticoagulants on the blood was simulated by setting three different levels of viscosity in the Newtonian model (μ/μ∞=0.60, 0.80 and 1 with μ∞=3.45×10(-3) Pas). A reduction of μ by a given amount always led to a more modest reduction, typically by a factor of two, of the resulting WSS levels. Moreover, for a given flow rate the calculation with the non-Newtonian viscosity model yielded WSS levels between 20% and 40% larger than those obtained in the corresponding Newtonian fluid simulation. It was also found that blood moves slowly in the region between the thrombus and the vein wall, a fact that will favor the growth of the thrombotic mass. Both the mean WSS levels and the degree of sluggishness of the blood flow can be described by functions of the Reynolds number.

Computational modeling of electromechanical propagation in the helical ventricular anatomy of the heart

The classical interpretation of myocardial activation assumes that the myocardium is homogeneous and that the electrical propagation is radial. However, anatomical studies have described a layered anatomical structure resulting from a continuous anatomical helical disposition of the myocardial fibers. To further investigate the sequence of electromechanical propagation based on the helical architecture of the heart, a simplified computational model was designed. This model was then used to test four activation patterns, which were generated by propagating the action potential along the myocardial band from different activation sites.

A CONTINUUM MODEL FOR THE WHOLE MUSCLE

The constitutive modelling of skeletal muscles is still poorly developed compared to passive tissues. However,, the recent software and hardware related to magnetic resonance techniques allowed improving significantly the knowledge in muscle simulation. The mathematical modelling of the muscular structure has its principal origin in the work of Hill (1922) who proposed the first approximation of the relation between force and contraction velocity in a muscle. The first mechanistic approximation for muscle contraction was presented by Huxley (1969) who incorporated the cross-bridge and sliding filament theories. He explained the muscular contraction at microscopic level, from the smallest muscular unit, the sarcomere. However, muscle mechanistic models at the tissue level are still lacking. The present work focussed, therefore, to fill the gap between mechanistic modelling and muscle description at the tissue level.. The mechanistic approach chosen aimed to define a unique strain energy function that separates both muscle and tendon material responses into fibre stretch.

Calculation of human femoral vein wall parameters in vivo from clinical data for specific patient.

A common problem in the elaboration of biomechanical models is determining the properties and characteristics (measures) of the physical behavior of in vivo tissues in the human body. Correct estimates must be made of the tissues physical properties and its surroundings. We suggest a method to compute the constitutive modeling of venous tissue, for every specific patient, from clinically registered ultrasounds images. The vein is modeled as a hyperelastic, incompressible, thin-walled cylinder and the membrane stresses are computed using strain energy. The approach is based on a strain-energy function suggested by Holzapfel capturing the characteristic nonlinear anisotropic responses of femoral veins with its collagen fibers.

Simulation and study of the geometric parameters in the inguinal area and the genesis of inguinal hernias

We are interested in studying the genesis of a very common pathology: the human inguinal hernia. How the human inguinal hernia appears is not definitively clear, but it is accepted that it is caused by a combination of mechanical and biochemical alterations, and that muscular simulation plays an important role in this. This study proposes a model to explain how some physical parameters affect the ability to simulate the region dynamically and how these parameters are involved in generating inguinal hernias. We are particularly interested in understanding the mechanical alterations in the inguinal region because little is known about them or how they behave dynamically. Our model corroborates the most important theories regarding the generation of inguinal hernias and is an initial approach to numerically evaluating this affection.

Effects of walking in deep venous thrombosis: a new integrated solid and fluid mechanics model.

Deep venous thrombosis (DVT) is a common disease. Large thrombi in venous vessels cause bad blood circulation and pain; and when a blood clot detaches from a vein wall, it causes an embolism whose consequences range from mild to fatal. Walking is recommended to DVT patients as a therapeutical complement. In this study the mechanical effects of walking on a specific patient of DVT were simulated by means of an unprecedented integration of 3 elements: a real geometry, a biomechanical model of body tissues, and a computational fluid dynamics study. A set of computed tomography images of a patients leg with a thrombus in the popliteal vein was employed to reconstruct a geometry model. Then a biomechanical model was used to compute the new deformed geometry of the vein as a function of the fiber stretch level of the semimembranosus muscle. Finally, a computational fluid dynamics study was performed to compute the blood flow and the wall shear stress (WSS) at the vein and thrombus walls. Calculations showed that either a lengthening or shortening of the semimembranosus muscle led to a decrease of WSS levels up to 10%. Notwithstanding, changes in blood viscosity properties or blood flow rate may easily have a greater impact in WSS.

ON THE CONSTITUTIVE MODELLING OF LUMBAR SPINE MUSCLES

Introduction Mechanical factors have a significant influence on the degenerative progression of spine tissues. Numerical models are particularly suitable to assess the specific contribution of these factors, but require the simulation of reliable boundary loads which remains unsolved. Since the spine musculature transfers most of the kinematical forces to the tissues, the careful constitutive modelling of muscle activity would stand for a significant improvement of spine models. As such, this study proposes a parametric study of an active muscle model to simulate the lumbar spine musculature.

Analysis of the Electro-Mechanical Activation Sequence of the Myocardium Following the Path Described by the HVMB

In order to contribute in the study of the HVMB, a computational model to simulate the behaviour of the myocardial tissue, mainly based in the fibre, is presented in a computational simplified model of the HVMB. The results obtained are compared with others works in the literature to conclude that if the electro-mechanical activation sequence in the myocardium coincides with the path described by the HVMB the path and the delay observed in the shortening of the fibres are according with the expected and observed behaviour in real hearts.

Computational Analysis of the Electro-Mechanical Activation Sequence of the Myocardium

In 1975 the valencian cardiologist F. Torrent-Guasp described the heart as a Helical Ventricular Myocardial Band (HVMB) in which “The ventricular myocardium is presented when it is unrolled under the form of a single big muscular band that, due to its special disposition, describes two cavities in the intact heart” [1]. It gives a different perspective of the morphology of the heart than the current and it could explain better and most coherently the propagation of the electrical stimulus which activates the shortening of the fibres, the complex deformation movement of the heart and maybe an explanation about understanding the cardiac contraction.Copyright