One-dimensional time-dependent model of the cardiac pacemaker activity induced by the mechano-electric feedback in a thermo-electro-mechanical background

peer reviewedBut de l’étude : Dans un cœur sain, le mécanisme de feedback mécano-électrique (FME) agit comme un régulateur intrinsèque du myocarde, en atténuant les perturbations mécaniques, permettant une contraction cardiaque normale et une situation électromécanique saine. Cependant, dans certaines circonstances, le FME peut être un générateur d’arythmies cardiaques importantes en induisant localement des dépolarisations électriques dues à des déformations anormales du tissu myocardique, via des canaux mécano-sensibles activés par l’étirement des fibres musculaires cardiaques. Ces perturbations peuvent ensuite se propager à l’ensemble du cœur et mener à un dysfonctionnement global du myocarde. Dans cette étude, nous examinons qualitativement l’influence de la température sur l’activité électrique autonome induite par le FME. Méthode : Nous présentons un modèle unidimensionnel instationnaire contenant tous les éléments majeurs permettant de prendre en compte le couplage excitation-contraction, le FME et le couplage thermoélectrique. Résultats : Nos simulations numériques montrent qu’une activité électrique autonome peut être induite par les déformations mécaniques cardiaques mais seulement pour un intervalle donné de température. Par ailleurs, dans certains cas, l’activité électrique autonome est périodique tel un pacemaker. De plus, nous montrons que certaines propriétés des potentiels d’action, générés par le FME, sont significativement influencées par la température. En outre, lorsque l’activité électrique prend la forme d’un pacemaker, nous mettons en évidence que la période est fortement dépendante de la température. Conclusions : Notre modèle qualitatif montre que la température est un facteur influençant fortement le comportement électromécanique du cœur et plus particulièrement, l’activité électrique autonome induite par les déformations du tissu myocardique.Aim of the study: In a healthy heart, the mechano-electric feedback (MEF) process acts as an intrinsic regulatory mechanism of the myocardium which allows the normal cardiac contraction by damping mechanical perturbations in order to generate a new healthy electromechanical situation. However, under certain conditions, the MEF can be a generator of dramatic arrhythmias by inducing local electrical depolarizations as a result of abnormal cardiac tissue deformations, via stretch-activated channels (SACs). Then, these perturbations can propagate in the whole heart and lead to global cardiac dysfunctions. In the present study, we qualitatively investigate the influence of temperature on autonomous electrical activity generated by the MEF. Method: We introduce a one-dimensional time-dependent model containing all the key ingredients that allow accounting for the excitation-contraction coupling, the MEF and the thermoelectric coupling. Results: Our simulations show that an autonomous electrical activity can be induced by cardiac deformations, but only inside a certain temperature interval. In addition, in some cases, the autonomous electrical activity takes place in a periodic way like a pacemaker. We also highlight that some properties of action potentials, generated by the mechano-electric feedback, are significantly influenced by temperature. Moreover, in the situation where a pacemaker activity occurs, we also show that the period is heavily temperature-dependent. Conclusions: Our qualitative model shows that the temperature is a significant factor with regards to the electromechanical behavior of the heart and more specifically, with regards to the autonomous electrical activity induced by the cardiac tissue deformations

Influence of thermoelectric coupling on pacemaker activity generated by mechano-electric feedback in a one-dimensional ring-shaped model of cardiac fiber

Peer reviewe

Amplitude equations for Rayleigh-Benard convective rolls far from threshold

An extension of the amplitude method is proposed. An iterative algorithm is developed to build an amplitude equation model that is shown to provide precise quantitative results even far from the linear instability threshold. The method is applied to the study of stationary Rayleigh-Benard thermoconvective rolls in the nonlinear regime. In particular, the generation of second and third spatial harmonics is analyzed. Comparison with experimental results and direct numerical calculations is also made and a very good agreement is found.Peer reviewe

Model-based computation of total stressed blood volume from a preload reduction manoeuvre

peer reviewedTotal stressed blood volume is an important parameter for both doctors and engineers. From a medical point of view, it has been associated with the success or failure of fluid therapy, a primary treatment to manage acute circulatory failure. From an engineering point of view, it dictates the cardiovascular system’s behavior in changing physiological situations. Current methods to determine this parameter involve repeated phases of circulatory arrests followed by fluid administration. In this work, a more straightforward method is developed using data from a preload reduction manoeuvre. A simple six-chamber cardiovascular system model is used and its parameters are adjusted to pig experimental data. The parameter adjustment process has three steps: (1) compute nominal values for all model parameters; (2) determine the five most sensitive parameters; and (3) adjust only these five parameters. Stressed blood volume was selected by the algorithm, which emphasizes the importance of this parameter. The model was able to track experimental trends with a maximal root mean squared error of 29.2%. Computed stressed blood volume equals 486 ± 117 ml or 15.7 ± 3.6 ml/kg, which matches previous independent experiments on pigs, dogs and humans. The method proposed in this work thus provides a simple way to compute total stressed blood volume from usual hemodynamic data