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Model-Based Computation of Total Stressed Blood Volume from a Preload Reduction Experiment Pironet, Antoine ; Desaive, Thomas ; et al Conference (2014, August) Total 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 resuscitation therapy, which ... [more ▼] Total 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 resuscitation therapy, which is a treatment for cardiac failure. From an engineering point of view, this parameter dictates the cardiovascular system's dynamic behavior. Current methods to determine this parameter involve repeated phases of circulatory arrests followed by fluid administration. In this work, a method is developed to compute stressed blood volume from preload reduction experiments. 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 most sensitive parameters; and (3) adjust only these sensitive parameters. Stressed blood volume was determined sensitive for all datasets, which emphasizes the importance of this parameter. The model was able to track experimental trends with a maximal mean squared error of 11.77 %. Stressed blood volume has been computed to range between 450 and 963 ml, or 15 to 28 ml/kg, which matches previous independent experiments on pigs, dogs and humans. Consequently, the method proposed in this work provides a simple way to compute total stressed blood volume from usual hemodynamic data. [less ▲] Detailed reference viewed: 30 (7 ULg)Structural identifiability analysis of a cardiovascular system model Pironet, Antoine ; Dauby, Pierre ; et al Conference (2014, August) A simple experimentally validated cardiovascular system model has been shown to be able to track the evolution of various diseases. The model has previously been made patient-specific by adjustment of its ... [more ▼] A simple experimentally validated cardiovascular system model has been shown to be able to track the evolution of various diseases. The model has previously been made patient-specific by adjustment of its parameters on the basis of a minimal set of hemodynamic measurements. However, this model has not yet been shown to be structurally identifiable, which means that the adjusted model parameters may not be unique. The model equations were manipulated to show that, from a theoretical point of view, all of their parameters can be exactly retrieved from a restricted set of model outputs. However, this set of model outputs is still too large for a clinical application, because it includes left and right ventricular pressures. Consequently, further hypotheses that determine some model parameter values have to be made for the model to be clinically applicable. [less ▲] Detailed reference viewed: 42 (10 ULg)Structural Identifiability Analysis of a Cardiovascular System Model Pironet, Antoine ; Dauby, Pierre ; et al in Preprints of the 19th World Congress (2014, August) A simple experimentally validated cardiovascular system model has been shown to be able to track the evolution of various diseases. The model has previously been made patient-specific by adjustment of its ... [more ▼] A simple experimentally validated cardiovascular system model has been shown to be able to track the evolution of various diseases. The model has previously been made patient-specific by adjustment of its parameters on the basis of a minimal set of hemodynamic measurements. However, this model has not yet been shown to be structurally identifiable, which means that the adjusted model parameters may not be unique. The model equations were manipulated to show that, from a theoretical point of view, all of their parameters can be exactly retrieved from a restricted set of model outputs. However, this set of model outputs is still too large for a clinical application, because it includes left and right ventricular pressures. Consequently, further hypotheses that determine some model parameter values have to be made for the model to be clinically applicable. [less ▲] Detailed reference viewed: 31 (8 ULg)Model-Based Computation of Total Stressed Blood Volume from a Preload Reduction Experiment Pironet, Antoine ; Desaive, Thomas ; et al in Preprints of the 19th World Congress (2014, August) Total 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 resuscitation therapy, which ... [more ▼] Total 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 resuscitation therapy, which is a treatment for cardiac failure. From an engineering point of view, this parameter dictates the cardiovascular system’s dynamic behavior. Current methods to determine this parameter involve repeated phases of circulatory arrests followed by fluid administration. In this work, a method is developed to compute stressed blood volume from preload reduction experiments. 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 most sensitive parameters; and (3) adjust only these sensitive parameters. Stressed blood volume was determined sensitive for all datasets, which emphasizes the importance of this parameter. The model was able to track experimental trends with a maximal mean squared error of 11.77 %. Stressed blood volume has been computed to range between 450 and 963 ml, or 15 to 28 ml/kg, which matches previous independent experiments on pigs, dogs and humans. Consequently, the method proposed in this work provides a simple way to compute total stressed blood volume from usual hemodynamic data. [less ▲] Detailed reference viewed: 22 (12 ULg)Relation between convective thermal patterns and heat flux through an evaporating surface via 2D and 3D numerical simulations Machrafi, Hatim ; ; Dauby, Pierre in Interfacial Phenomena and Heat Transfer (2014), 2(3), 199-209 Detailed reference viewed: 15 (5 ULg)Multi-scale model of the cardiovascular system Kosta, Sarah ; Pironet, Antoine ; et al in 13th Belgian National Day on Biomedical Engineering (2014) Detailed reference viewed: 21 (2 ULg)Multi-scale model of the cardiovascular system Kosta, Sarah ; Pironet, Antoine ; et al Poster (2014) Detailed reference viewed: 15 (5 ULg)Computing the derivatives of the mean and amplitude of physiological variables with respect to the parameters of a mathematical model Pironet, Antoine ; Dauby, Pierre ; et al Conference (2013, September 06) Detailed reference viewed: 32 (6 ULg)Simulation of Left Atrial Function Using a Multi-Scale Model of the Cardiovascular System Pironet, Antoine ; Dauby, Pierre ; Paeme, Sabine et al in PLoS ONE (2013), 8(6), 65146 During a full cardiac cycle, the left atrium successively behaves as a reservoir, a conduit and a pump. This complex behavior makes it unrealistic to apply the time-varying elastance theory to ... [more ▼] During a full cardiac cycle, the left atrium successively behaves as a reservoir, a conduit and a pump. This complex behavior makes it unrealistic to apply the time-varying elastance theory to characterize the left atrium, first, because this theory has known limitations, and second, because it is still uncertain whether the load independence hypothesis holds. In this study, we aim to bypass this uncertainty by relying on another kind of mathematical model of the cardiac chambers. In the present work, we describe both the left atrium and the left ventricle with a multi-scale model. The multi-scale property of this model comes from the fact that pressure inside a cardiac chamber is derived from a model of the sarcomere behavior. Macroscopic model parameters are identified from reference dog hemodynamic data. The multi-scale model of the cardiovascular system including the left atrium is then simulated to show that the physiological roles of the left atrium are correctly reproduced. This include a biphasic pressure wave and an eight-shaped pressure-volume loop. We also test the validity of our model in non basal conditions by reproducing a preload reduction experiment by inferior vena cava occlusion with the model. We compute the variation of eight indices before and after this experiment and obtain the same variation as experimentally observed for seven out of the eight indices. In summary, the multi-scale mathematical model presented in this work is able to correctly account for the three roles of the left atrium and also exhibits a realistic left atrial pressure-volume loop. Furthermore, the model has been previously presented and validated for the left ventricle. This makes it a proper alternative to the time-varying elastance theory if the focus is set on precisely representing the left atrial and left ventricular behaviors. [less ▲] Detailed reference viewed: 74 (36 ULg)A Multi‐Scale Computer Model of the Cardiovascular System Can Account for the Three Roles of the Left Atrium Pironet, Antoine ; Dauby, Pierre ; Kosta, Sarah et al in Abstract Book GIGA-Day (2013, January 28) Detailed reference viewed: 62 (16 ULg)A Multi‐Scale Computer Model of the Cardiovascular System Can Account for the Three Roles of the Left Atrium Pironet, Antoine ; Dauby, Pierre ; Kosta, Sarah et al Poster (2013, January 28) Detailed reference viewed: 43 (23 ULg)Time-dependent Marangoni-Bénard instability of an evaporating binary-liquid layer including gas transients Machrafi, Hatim ; ; et al in Physics of Fluids (2013), 25 We are here concerned with Bénard instabilities in a horizontal layer of a binary liquid, considering as a working example the case of an aqueous solution of ethanol with a mass fraction of 0.1. Both the ... [more ▼] We are here concerned with Bénard instabilities in a horizontal layer of a binary liquid, considering as a working example the case of an aqueous solution of ethanol with a mass fraction of 0.1. Both the solvent and the solute evaporate into air (the latter being insoluble in the liquid). The system is externally constrained by imposing fixed "ambient" pressure, humidity, and temperature values at a certain effective transfer distance above the liquid-gas interface, while the ambient temperature is also imposed at the impermeable rigid bottom of the liquid layer. Fully transient and horizontally homogeneous solutions for the reference state, resulting from an instantaneous exposure of the liquid layer to ambient air, are first calculated. Then, the linear stability of these solutions is studied using the frozen-time approach, leading to critical (monotonic marginal stability) curves in the parameter plane spanned by the liquid layer thickness and the elapsed time after initial contact. This is achieved for different ratios of the liquid and gas thicknesses, and in particular yields critical times after which instability sets in (for given thicknesses of both phases). Conversely, the analysis also predicts a critical thickness of the liquid layer below which no instability ever occurs. The nature of such critical thickness is explained in detail in terms of mass fraction profiles in both phases, as it indeed appears that the most important mechanism for instability onset is the solutal Marangoni one. Importantly, as compared to the result obtained previously under the quasi-steady assumption in the gas phase [H. Machrafi, A. Rednikov, P. Colinet, and P. C. Dauby, Eur. Phys. J. Spec. Top.192, 71 (2011)]10.1140/epjst/e2011-01361-y, it is shown that relaxing this assumption may yield essentially lower values of the critical liquid thickness, especially for large gas-to-liquid thickness ratios. A good-working analytical model is developed for the description of such delicate transient effects in the gas. The analysis reveals that the system considered in this paper is generally highly unstable, the instability setting in even for very small times and liquid thicknesses. © 2013 AIP Publishing LLC. [less ▲] Detailed reference viewed: 37 (9 ULg)Assessment of ventricular contractility and ventricular-arterial coupling with a model-based sensor. Desaive, Thomas ; LAMBERMONT, Bernard ; JANSSEN, Nathalie et al in Computer Methods & Programs in Biomedicine (2013), 109(2), Estimation of ventricular contractility and ventricular arterial coupling is clinically important in diagnosing and treating cardiac dysfunction in the critically ill. However, experimental assessment of ... [more ▼] Estimation of ventricular contractility and ventricular arterial coupling is clinically important in diagnosing and treating cardiac dysfunction in the critically ill. However, experimental assessment of indexes of ventricular contractility, such as the end-systolic pressure-volume relationship, requires a highly invasive maneuver and measurements that are not typical in an intensive care unit (ICU). This research describes the use of a previously validated cardiovascular system model and parameter identification process to evaluate the right ventricular arterial coupling in septic shock. Model-based ventricular arterial coupling is defined by the ratio of the end systolic right ventricular elastance (E(esrvf)) over the pulmonary artery elastance (E(pa)) or the mean pulmonary inflow resistance (R(pulin)). Results are compared to the clinical gold-standard assessment (conductance catheter method). Six anesthetized healthy pigs weighing 20-30kg received a 0.5mgkg(-1) endotoxin infusion over a period of 30min from T0 to T30, to induce septic shock and veno-venous hemofiltration was used from T60 onward. The results show good agreement with the gold-standard experimental assessment. In particular, the model-based right ventricular elastance (E(esrvf)) correlates well with the clinical gold standard (R(2)=0.69) and the model-based non-invasive coupling (E(esrvf)/R(pulin)) follow the same trends and dynamics (R(2)=0.37). The overall results show the potential to develop a model-based sensor to monitor ventricular-arterial coupling in clinical real-time. [less ▲] Detailed reference viewed: 39 (12 ULg)A simplified model for mitral valve dynamics. ; Paeme, Sabine ; et al in Computer Methods & Programs in Biomedicine (2013), 109(2), Located between the left atrium and the left ventricle, the mitral valve controls flow between these two cardiac chambers. Mitral valve dysfunction is a major cause of cardiac dysfunction and its dynamics ... [more ▼] Located between the left atrium and the left ventricle, the mitral valve controls flow between these two cardiac chambers. Mitral valve dysfunction is a major cause of cardiac dysfunction and its dynamics are little known. A simple non-linear rotational spring model is developed and implemented to capture the dynamics of the mitral valve. A measured pressure difference curve was used as the input into the model, which represents an applied torque to the anatomical valve chords. A range of mechanical model hysteresis states were investigated to find a model that best matches reported animal data of chord movement during a heartbeat. The study is limited by the use of one dataset found in the literature due to the highly invasive nature of getting this data. However, results clearly highlight fundamental physiological issues, such as the damping and chord stiffness changing within one cardiac cycle, that would be directly represented in any mitral valve model and affect behaviour in dysfunction. Very good correlation was achieved between modeled and experimental valve angle with 1-10% absolute error in the best case, indicating good promise for future simulation of cardiac valvular dysfunction, such as mitral regurgitation or stenosis. In particular, the model provides a pathway to capturing these dysfunctions in terms of modeled stiffness or elastance that can be directly related to anatomical, structural defects and dysfunction. [less ▲] Detailed reference viewed: 45 (9 ULg)Evaporation Rates and Bénard-Marangoni Supercriticality Levels for Liquid Layers Under an Inert Gas Flow Machrafi, Hatim ; ; et al in Microgravity Science and Technology (2013) Detailed reference viewed: 16 (4 ULg)Effect of abrupt preload reduction on left atrial and ventricular pressures in a multi-scale mathematical model of the cardiovascular system Pironet, Antoine ; Dauby, Pierre ; Kosta, Sarah et al Poster (2013) Detailed reference viewed: 28 (8 ULg)Effect of abrupt preload reduction on left atrial and ventricular pressures in a multi-scale mathematical model of the cardiovascular system Pironet, Antoine ; Dauby, Pierre ; Kosta, Sarah et al in European Heart Journal Supplements : Journal of the European Society of Cardiology (2013), 34 Detailed reference viewed: 32 (11 ULg)A new method for computing the derivatives of the mean and amplitude of physiological variables with respect to the parameters of a cardiovascular system model Pironet, Antoine ; Dauby, Pierre ; et al in Minimally Invasive Therapy & Allied technologies : Official Journal of the Society for Minimally Invasive Therapy (2013), 22 Detailed reference viewed: 29 (8 ULg)A multi-scale cardiovascular system model can account for the load-dependence of the end-systolic pressure-volume relationship. Pironet, Antoine ; Desaive, Thomas ; Kosta, Sarah et al in BioMedical Engineering OnLine (2013), 12(1), 8 ABSTRACT: BACKGROUND: The end-systolic pressure-volume relationship is often considered as a load-independent property of the heart and, for this reason, is widely used as an index of ventricular ... [more ▼] ABSTRACT: BACKGROUND: The end-systolic pressure-volume relationship is often considered as a load-independent property of the heart and, for this reason, is widely used as an index of ventricular contractility. However, many criticisms have been expressed against this index and the underlying time-varying elastance theory: first, it does not consider the phenomena underlying contraction and second, the end-systolic pressure volume relationship has been experimentally shown to be load-dependent. METHODS: In place of the time-varying elastance theory, a microscopic model of sarcomere contraction is used to infer the pressure generated by the contraction of the left ventricle, considered as a spherical assembling of sarcomere units. The left ventricle model is inserted into a closed-loop model of the cardiovascular system. Finally, parameters of the modified cardiovascular system model are identified to reproduce the hemodynamics of a normal dog. RESULTS: Experiments that have proven the limitations of the time-varying elastance theory are reproduced with our model: (1) preload reductions, (2) afterload increases, (3) the same experiments with increased ventricular contractility, (4) isovolumic contractions and (5) flow-clamps. All experiments simulated with the model generate different end-systolic pressure-volume relationships, showing that this relationship is actually load-dependent. Furthermore, we show that the results of our simulations are in good agreement with experiments. CONCLUSIONS: We implemented a multi-scale model of the cardiovascular system, in which ventricular contraction is described by a detailed sarcomere model. Using this model, we successfully reproduced a number of experiments that have shown the failing points of the time-varying elastance theory. In particular, the developed multi-scale model of the cardiovascular system can capture the load-dependence of the end-systolic pressure-volume relationship. [less ▲] Detailed reference viewed: 97 (55 ULg)non invasive estimation of left atrial pressure and mitral valve area waveforms during an entire cardiac cycle Paeme, Sabine ; Pironet, Antoine ; Lancellotti, Patrizio et al Poster (2012, December 07) Detailed reference viewed: 15 (3 ULg) |
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