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Passive nonlinear elastic behaviour of skeletal muscle: Experimental results and model formulation

The goal of this study was to characterize the passive elastic behaviour of muscle and tendon tissues of rat tibialis anterior. For that purpose, tissue samples from 3 month old female Wistar rats (210+/-11g) were mechanically tested in vitro. Moreover, an in vivo device was developed to measure the muscle-tendon unit response to increasing load. Mechanical tests, consisting of uniaxial loading along the longitudinal axis of tendon and muscle strips, revealed the nonlinear mechanical behaviour of these tissues. A material model was formulated and its parameters fit to the experimental data using the Levenberg-Marquardt optimization algorithm. The fit goodness was assessed and R(2) values close to 1 and very low epsilon values were obtained. The passive behaviour of a future finite element model of a muscle-tendon unit will be validated against the in vivo passive extension tests by comparing the reaction force-extension curves.

A 3D active-passive numerical skeletal muscle model incorporating initial tissue strains. Validation with experimental results on rat tibialis anterior muscle

This paper presents a three-dimensional finite element model of skeletal muscle and its validation incorporating inital tissue strains. A constitutive relation was determined by using a convex free strain energy function (SEF) where active and passive response contributions were obtained fitting experimental data from the rat tibialis anterior (TA) muscle. The passive and active finite strains response was modelled within the framework of continuum mechanics by a quasi-incompressible transversely isotropic material formulation. Magnetic resonance images (MRI) were obtained to reconstruct the external geometry of the TA. This geometry includes initial strains also taken into account in the numerical model. The numerical results show excellent agreement with the experimental results when comparing reaction force-extension curves both in passive and active tests. The proposed constitutive model for the muscle is implemented in a subroutine in the commercial finite element software package ABAQUS.

Superoxide Anion and Nitric Oxide in High-Grade Esophagitis Induced by Acid and Pepsin in Rabbits

It has been proposed that free radicals are involved in the pathogenesis of esophageal mucosal damage induced by acid and pepsin. Recent data have suggested that nitric oxide (NO) is involved in the mucosal defense of the esophagus and that superoxide anion plays a minor role in low-grade esophagitis. To study the role and potential interaction of NO and superoxide anion in an experimental model of high-grade esophagitis, acidified pepsin was perfused (45 min/12 hr) for five days in rabbits with different agents to modulate the generation of these radicals. Measurements included both macroscopic and microscopic mucosal damage, superoxide anion generation, NO synthase mucosal activity, and peroxynitrite formation. High-grade esophagitis was associated with mucosal superoxide anion generation. Treatment with exogenous superoxide dismutase completely prevented mucosal damage. The perfusion of acidified pepsin in the lumen of the esophagus was initially associated with increased NO synthase mucosal activity but decreased with the progression of damage. Generation of peroxynitrites was present in those cases with severe damage. Treatment with NO-modifying agents did not induce consistent modification of mucosal damage. It is concluded that superoxide anion is involved in the induction of high-grade esophagitis and that it interacts with nitric oxide to generate peroxynitrite radicals in this model. Superoxide dismutase but not NO-donor-modifying agents might have a therapeutic role in preventing severe esophageal mucosal damage induced by acid and pepsin.

Nitric oxide and superoxide anion in low-grade esophagitis induced by acid and pepsin in rabbits.

It has been suggested that free radicals are involved in esophagitis. To study the role and potential interaction of superoxide anion and nitric oxide (NO) in low-grade esophagitis, we perfused acidified pepsin (30 min every 12 hr) for seven days in rabbits treated with different agents to modulate the generation of these radicals. Measurements included macroscopic and microscopic damage, superoxide anion generation, mucosal nitric oxide synthase activity, and peroxynitrite formation. Low-grade esophagitis was associated with increased nitric oxide synthase mucosal activity and mucosal damage was dose-dependently increased by treatment with the NO synthase inhibitor NG-nitro-l-arginine. Superoxide anion was scarcely generated in the mucosa, but this was not accompanied by any change in the activity of mucosal superoxide dismutase. Treatment with superoxide dismutase did not improve mucosal damage. Generation of peroxynitrites was not detected. In conclusion, nitric oxide is involved in the mucosal defense of the esophagus against acid- and pepsin-induced damage. Superoxide anion generation seems irrelevant in the induction of low-grade esophagitis and not sufficient to interact with nitric oxide to generate measurable mucosal peroxynitrite radicals.

Active response of skeletal muscle: in vivo experimental results and model formulation.

The contractile properties of the tibial anterior (TA) of Wistar rats were measured by means of a multipurpose testing machine. The muscle was isolated from the connective tissues, preserving the proximal insertion. The distal tendon was transected and fixed to the machine actuator. The leg was inmobilised using a pin drilled through the femoral condyle. In this way the force response was studied in vivo at different constant lengths for some voltages and frequencies. Mathematical functions are proposed for adjusting the force-length, force-frequency and force-time relations. The model includes a novel formulation for the depression response during muscle tetanisation.

A quantitative method for the detection of muscle functional active and passive behavior recovery in models of damage-regeneration

Unlike other organs, skeletal muscle is endowed with a remarkable potential for regeneration that depends on the presence of satellite cells. Histological and functional (force generation) recoveries after muscle damage are not parallel processes. The aim of this study is to examine the in vivo contractile properties and in vitro passive stress–stretch behavior of muscle during degeneration–regeneration processes. Notexin was injected into rat tibialis anterior muscle, and functional recovery and histological changes were compared. We found that histological improvement of damaged muscle is delayed in comparison with its capacity to generate force. The elastic properties of muscle were not altered in agreement with the unchanged cross-linking index, probably as a consequence of the unaltered deposition of total collagen during degeneration–regeneration processes together with the maintenance of the ratio of collagens type I and III.

Mirada a los clásicos. "Cine forum", nuevo enfoque interdisciplinar en el Grado de Óptica y Optometría - [A look back at the classics."Cinema forum", new interdisciplinary approach in the Optics and Optometry Degree]

Five academic years ago, an interdisciplinary collaboration started between two subjects belonging to different areas of knowledge in the first year of the Optics and Optometry Degree at the University of Zaragoza. This collaboration focuses on Problem-Based Learning (PbL) and Portfolios methodologies. With the purpose of exploring new educational strategies that allow us to approach both subjects comprehensively, and without abandoning those that we already have integrated in the teaching of our subjects, we have used, during the present academic year 2016-17, the cinema as a formative resource; obtaining clearly satisfactory results since the students, besides working purely technical aspects of the subjects, appreciated learning in terms of more emotional, affective or empathic aspects as future health professionals.

Valoración de la utilización de SOCRATIVE como herramienta didáctica interactiva en dos asignaturas del grado en Óptica-Optometría de la Universidad de Zaragoza

Se presenta el analisis de la herramienta digital docente SOCRATIVE en relacion a diversas modalidades y finalidades de utilizacion. La experiencia se ha realizado en el marco del trabajo interdisciplinar desarrollado en las asignaturas: “Anatomia e Histologia Ocular” y “Fisiologia Ocular y del Sistema Visual” del primer curso del Grado en Optica y Optometria de la Universidad de Zaragoza. Se ha utilizado SOCRATIVE para que en clase los estudiantes, por grupos, respondiesen a un cuestionario, en un caso con retroalimentacion inmediata, en otro con un caracter mas evaluativo y por ultimo como herramienta de Tutoria de grupo completo. Una de las ventajas de esta practica es la rapidez en la obtencion de informacion acerca del grado de comprension de la asignatura por los estudiantes, asi como en la retroalimentacion ofrecida. Para su utilizacion como herramienta de evaluacion se constata la necesidad de acotar adecuadamente las condiciones de la misma. En cuanto a la opinion de los estudiantes, lo consideran bastante o muy util como herramienta de aprendizaje, pero no asi para la evaluacion.