K. J. Pałko

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 connection. The caval occlusion caused the leftward shift of the LV p–v loop, along with the drop in arterial and ventricular 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 ventricular average volume drop were the main effects of ventricular-aortic assistance. Results coincided with clinical 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 baroreflex and a more detailed coronary circulation model.

Reproduction of Continuous Flow Left Ventricular Assist Device 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.

A new hybrid electro-numerical model of the left ventricle

The paper presents a new project of a hybrid numerical-physical model of the left ventricle. A physical part of the model can be based on electrical or hydraulic structures. Four variants of the model with numerical and physical heart valves have been designed to investigate an effect of a heart assistance connected in series and in parallel to the natural heart. The LabVIEW real time environment has been used in the model to increase its accuracy and reliability. A prototype of the hybrid electro-numerical model of the left ventricle has been tested in an open loop and closed loop configuration.

Application of a user-friendly comprehensive circulatory model for estimation of hemodynamic and ventricular variables

Purpose Application of a comprehensive, user-friendly, digital computer circulatory model to estimate hemodynamic and ventricular variables. Methods The closed-loop lumped parameter circulatory model represents the circulation at the level of large vessels. A variable elastance model reproduces ventricular ejection. The circulatory model has been modified embedding an algorithm able to adjust the model parameters reproducing specific circulatory conditions. The algorithm reads input variables: heart rate, aortic pressure, cardiac output, and left atrial pressure. After a preliminary estimate of circulatory parameters and ventricular elastance, it adjusts the amount of circulating blood, the value of the systemic peripheral resistance, left ventricular elastance, and ventricular rest volume. Input variables and the corresponding calculated variables are recursively compared: the procedure is stopped if the difference between input and calculated variables is within the set tolerance. At the procedure end, the model produces an estimate of ventricular volumes and Emaxl along with systemic and pulmonary pressures (output variables). The procedure has been tested using 4 sets of experimental data including left ventricular assist device assistance. Results The algorithm allows the reproduction of the circulatory conditions defined by all input variable sets, giving as well an estimate of output variables. Conclusions The algorithm permits application of the model in environments where the simplicity of use and velocity of execution are of primary importance. Due to its modular structure, the model can be modified adding new circulatory districts or changing the existing ones. The model could also be applied in educational applications.

Development of an electronic manometer for intrapleural pressure monitoring.

Background: Measurement of intrapleural pressure is useful during various pleural procedures. However, a pleural manometer is rarely available. Objectives: The aim of this study was to (1) construct an electronic pleural manometer, (2) assess the accuracy of the measurements done with the new device, (3) calculate the costs of the manometer construction and (4) perform an initial evaluation of the device in a clinical setting. Methods: Only widely accessible elements were used to construct the device. A vascular pressure transducer was used to transform pressure into an electronic signal. Reliability of the measurements was evaluated in a laboratory setting in a prospective, single-blind manner by comparing the results with those measured by a water manometer. Functionality of the device was assessed during therapeutic thoracentesis. The cost of the new pleural manometer was calculated. Results: We built a small, portable device which can precisely measure intrapleural pressure. The measurement results showed very high agreement with those registered with a water manometer (r = 0.999; p < 0.001). The initial evaluation of the electronic manometer during therapeutic thoracentesis showed it was easy to use. The total time needed for 6 measurements after withdrawal of different volumes of pleural fluid in 1 patient did not exceed 6 min. The total cost of the device was calculated to be <2,000 EUR. Conclusions: In the face of very limited offer of commercially available pleural manometers, it is possible to successfully construct a self-made, reliable, electronic pleural manometer at modest costs. The device is easy to use and enables data display and storage in the personal computer.

Cough during therapeutic thoracentesis: friend or foe?

We report intriguing preliminary observations on the effect of cough on pleural pressure changes during therapeutic thoracentesis. We found that cough‐related elevation of pleural pressure persisted even when the cough had stopped. Thus, we hypothesize that cough during therapeutic thoracentesis may have a beneficial effect preventing the excessive drop in pleural pressure. The true role of cough‐related elevation of pleural pressure is unknown, but it seems to be an interesting subject for further research.

RC Model-based Comparison Tests of the Added Compliance Method with Computer Simulations and a Standard Method

RC Model-based Comparison Tests of the Added Compliance Method with Computer Simulations and a Standard Method Ventilation of the lungs involves the exchange of gases during inhalation and exhalation causing the movement of respiratory gases between alveolars and the atmosphere as a result of a pressure drop between alveolars and the atmosphere. During artificial ventilation what is most important is to keep specific mechanical parameters of the lungs such as total compliance of the respiratory system Cp (consisting of the lung and the thorax compliances) and the airway resistance Rp when the patient is ventilated. Therefore, as the main goal of this work and as the first step to use our earlier method of added lung compliance in clinical practice was: 1) to carry out computer simulations to compare the application of this method during different expiratory phases, and 2) to compare this method with the standard method for its accuracy. The primary tests of the added-compliance method of the main lung parameters measurement have been made using the RC mechanical model of the lungs.

Influence of Preterm Birth, BPD and Lung Inhomogeneity on Respiratory System Impedance – Model Studies

The influence of preterm birth, bronchopulmonary dysplasia (BPD) and lung inhomogeneity on respiratory system impedance (RSI) was studied. The simulation of spontaneous breathing in full term newborns (FT), very low birth weight (VLBW) and extremely low birth weight (ELBW) preterm infants was carried out using a developed linear RLC respiratory system model. Besides BPD, four types of lung inhomogeneity: (1) one-lung obstruction (OBSTR), (2) one-lung restriction (RESTR), (3) one-lung obstructive-restrictive disturbance (OBSTR-RESTR I), (4) bilateral obstructive-restrictive disturbance (OBSTR-RESTR II), with obstruction of one lung and restriction of the second, were studied.

The hybrid piston model of lungs

The novel hybrid (pneumo-electrical-numerical physical) model of lungs is presented. A general procedure of creating of this type of models is also described. It consists in application of proportional transformation of an electrical impedance of a lumped parameter electrical or numerical model of lungs into a pneumatic impedance obtained in an input pneumatic terminal of the model. The standard Dubois mathematical model of lungs has been applied in model examinations. That proved the assumed concept of hybrid modeling.