Role and applications of circulatory models in cardiovascular pathophysiology.

Circulatory models are relevant for research, education and prosthetic devices/components testing. Independently of its structure that can be numerical, physical or hybrid, the models can be used in different areas of cardiovascular pathophysiology. However, the models are often used to reproduce specific circulatory conditions instead of being used as "systemic" tools. That is to say, the models are used to evaluate the global effects of external disturbances such as pathologies, therapies, special environments or surgery on the circulatory system. Aim of this paper is to illustrate a family of circulatory models developed to represent the whole circulatory system in pathophysiological conditions describing some of the possible applications

Parallel left ventricular assistance tests on the hybrid circulatory model.

Objectives: Evaluation of new control and measurement methods worked out for heart assist devices and artificial hearts need new laboratory tools making experiments more accurate, repeatable, easier and less time consuming. The proper answer to this demand seems to be a hybrid hydro-numerical model HHNM of the circulatory system. Its performance illustrates the exemplary laboratory application when the physical left ventricle assist device is connected in parallel to the numerical left ventricle

Development of a modelling platform. The circulatory model: a tool for research and education in cardiovascular patho-physiology.

Objectives: The aim of this work is the development of a modelling platform with hybrid capabilities: that is to say, its structure can be modified according to the experimental needs merging, if necessary, numerical models and physical devices or models that can be indifferently hydraulic or electrical. The numerical circulatory model is an important part of the platform. It can be applied as a fully numerical model or as a part of a hybrid system

A modular computational circulatory model applicable to vad testing and training

Aim of this work was to develop a modular computational model able to interact with ventricular assist devices (VAD) for research and educational applications. The lumped parameter model consists of five functional modules (left and right ventricles, systemic, pulmonary, and coronary circulation) that are easily replaceable if necessary. The possibility of interacting with VADs is achieved via interfaces acting as impedance transformers. This last feature was tested using an electrical VAD model. Tests were aimed at demonstrating the possibilities and verifying the behavior of interfaces when testing VADs connected in different ways to the circulatory system. For these reasons, experiments were performed in a purely numerical mode, simulating a caval occlusion, and with the model interfaced to an external left-VAD (LVAD) in two different ways: with atrioaortic and ventriculoaortic con- nection. The caval occlusion caused the leftward shift of the LV p-v loop, along with the drop in arterial and ven- tricular pressures. A narrower LV p-v loop and cardiac output and aortic pressure rise were the main effects of atrioaortic assistance. A wider LV p-v loop and a ven- tricular average volume drop were the main effects of ventricular-aortic assistance. Results coincided with clini- cal and experimental data attainable in the literature. The model will be a component of a hydronumerical model designed to be connected to different types of VADs. It will be completed with autonomic features, including the bar- oreflex and a more detailed coronary circulation model

Role and applications of circulatory models in cardiovascular pathophysiology.

Circulatory models are relevant for research, education and prosthetic devices/components testing. Independently of its structure that can be numerical, physical or hybrid, the models can be used in different areas of cardiovascular pathophysiology. However, the models are often used to reproduce specific circulatory conditions instead of being used as "systemic" tools. That is to say, the models are used to evaluate the global effects of external disturbances such as pathologies, therapies, special environments or surgery on the circulatory system. Aim of this paper is to illustrate a family of circulatory models developed to represent the whole circulatory system in pathophysiological conditions describing some of the possible applications

A new coronary circulation model for hybrid applications.

Aim: The Waterfall model of the coronary circulation in a whole computational circulatory model used in hybrid cardiovascular simulator (HCS) has several limitations. The aim of this study is to develop a new computational coronary circulation model (CCM) useful for HCS applications. Methods: The new CCM is based on a time-varying normalized impedance, whose resistive component is strongly nonlinear and depends on the phase of the cardiac cycle. The CCM was integrated in the HCS together with the base computational circulatory model, where the left and right ventricles are represented by time-varying elastance and systemic and pulmonary circulation are lumped Windkessel models. Starting from the HCS reproducing the same patho-physiological conditions, two groups of simulations were performed: one with the Waterfall and one with the new CCM. Then, a comparison between the two groups of results was performed. Results: Using the HCS in real-time modality, time courses of coronary flow, aortic, left ventricular and right atrial pressures were collected. Results show that in comparison to the simple CCM, the new CCM better reproduces nonlinear coronary flow pattern, according to the reference data from literature. Conclusions: The presented new CCM is able to reproduce the proper coronary flow pattern and is useful for HCS applications related especially to intraaortic balloon pump assistance investigations

Reproduction of continuous flow lvad experimental data by means of a hybrid cardiovascular model with baroreflex control.

Long-term mechanical circulatory assistance opened new problems in ventricular assist device-patient interaction, especially in relation to autonomic controls. Modeling studies, based on adequate models, could be a feasible approach of investigation. The aim of this work is the exploitation of a hybrid (hydronumerical) cardiovascular simulator to reproduce and analyze in vivo experimental data acquired during a continuous flow left ventricular assistance. The hybrid cardiovascular simulator embeds three submodels: a computational cardiovascular submodel, a computational baroreflex submodel, and a hydronumerical interface submodel. The last one comprises two impedance transformers playing the role of physical interfaces able to provide a hydraulic connection with specific cardiovascular sites (in this article, the left atrium and the ascending/descending aorta). The impedance transformers are used to connect a continuous flow pump for partial left ventricular support (Synergy Micropump, CircuLite, Inc., Saddlebrooke, NJ, USA) to the hybrid cardiovascular simulator. Data collected from five animals in physiological, pathological, and assisted conditions were reproduced using the hybrid cardiovascular simulator. All parameters useful to characterize and tune the hybrid cardiovascular simulator to a specific hemodynamic condition were extracted from experimental data. Results show that the simulator is able to reproduce animal-specific hemodynamic status both in physiological and pathological conditions, to reproduce cardiovascular left ventricular assist device (LVAD) interaction and the progressive unloading of the left ventricle for different pump speeds, and to investigate the effects of the LVAD on baroreflex activity. Results in chronic heart failure conditions show that an increment of LVAD speed from 20?000 to 22?000?rpm provokes a decrement of left ventricular flow of 35% (from 2 to 1.3?L/min). Thanks to its flexibility and modular structure, the simulator is a platform potentially useful to test different assist devices, thus providing clinicians additional information about LVAD therapy strategy