Biomedical subjects

C De Lazzari

Publications and source records attributed to C De Lazzari.

27 records · Page 2Linked to original sources

PubMed1997

Technical standards for medical devices. Assisted circulation devices.

The steep rise in the clinical use of high technology biomedical devices and materials, involving multidisciplinary competencies, points out the problem of mutual standards defining, first of all, functional characteristic and tests able to characterise and qualify devices, materials and minimal safety requirements both for patients and operators. Standards defined by consent of the parties or by law are used to this aim. Fast technical development in specific sectors produces besides lack of rules, which must be quickly filled up. The aim of this paper is both the presentation of the approach to problems related to technical standards for biomedical devices and the presentation of the set up of a technical standard for mechanical heart assist devices.

Assisted Circulation↗

PubMed1996

In vitro testing of a left ventricular assist device. Study of the effect of its control strategy on energetic relationships inside the left ventricle.

In this study an original left ventricular assist device is tested on an open loop modular physical circuit reproducing Starling's law of the heart to set an optimal control strategy for heart recovery. It is assumed that the goals of the assistance are reduction of oxygen consumption, external work and improvement of cardiac mechanical efficiency. The assistance is evaluated by the position of a working point on the characteristic surfaces of the ventricle defined by peripheral resistance, atrial pressure and selected variables pertaining to energy (pressure-volume area, external work and cardiac mechanical efficiency). In this frame an optimal assistance for heart recovery is a compromise among different requirements corresponding to a restricted set of control parameters values: driving pressure PZB = 35 kPa and timing values T1 and T2 (systole beginning and systole ending in relation to QRS complex and cardiac cycle duration T) T1 = 0.55.T and T2 = 0.73.T.

Bioelectric Energy Sources↗

PubMed1994

A desk-top computer model of the circulatory system for heart assistance simulation: effect of an LVAD on energetic relationships inside the left ventricle.

The study of the interaction between a pneumatic left ventricle assist device (LVAD), driven with different control strategies, and the cardiovascular system is the subject of this paper. It is performed by a modular numerical model of the cardiovascular system connected to a numerical model of the LVAD. The circulatory system is simulated by a lumped parameter numerical model. The ventricle is represented by a time-varying elastance model to reproduce the Starling law of the heart. The effect of the LVAD on the cardiovascular system is evaluated, on the left ventricle alone, by an open-loop circuit consisting of the models of the ventricle, the LVAD and the arterial tree. The analysis is performed in terms of energy variables (such as external work and oxygen consumption and cardiac mechanical efficiency versus control strategy. The LVAD is driven by different control strategies: a fixed heart rate (with different delays from the onset of the natural ventricle contraction) and a variable heart rate.

Cardiovascular Physiological Phenomena↗

PubMed1992

A modular numerical model of the cardiovascular system for studying and training in the field of cardiovascular physiopathology.

A modular numerical model of the cardiovascular system has been developed to reproduce the most important circulatory phenomena in terms of pressure and volume relationships. It is an easy tool to use, designed to be used with a friendly approach on any IBM or compatible personal computer: it offers a wide selection of graphical and numerical outputs and can be rearranged easily for a particular experiment. A set of subroutines related to different circulatory phenomena has been developed; they can be assembled easily together and communicate with each other by two variables. A full description of the existing subroutines is presented in this paper with three different application examples resulting from the rearrangement of the existing software modules: the first concerns the behaviour of the natural ventricle model itself and can be regarded as a ventricle stand-alone characterization test in terms of preload and afterload sensitivities, the second is related to the use of a pneumatic ventricle instead of the model of the natural ventricle, and the third is a full model of the cardiocirculatory system.

Cardiology↗

PubMed1991

Effect of magnetic fluids on the efficiency of an electromagnetic actuator prototype.

An electromagnetic actuator to substitute ventricular function presents some advantages compared with different energy converters. The drastic reduction of the moving parts leads to greater reliability and an accurate control system can be set up. Its major limitations concern weight, heat dissipation and, finally, the overall pump efficiency which is usually rather low. We investigated the possibility of using magnetic fluids in an electromagnetic actuator. Limitations intrinsic to the magnetic fluids prevent their being used as pumping elements but they can be useful to increase the pump efficiency by reducing losses in the magnetic circuit. A remarkable increase in pump efficiency was attained. It is necessary to point out that in designing the electromagnetic actuator the focus was on the pump efficiency with and without the magnetic fluids more than on its performance.

Electromagnetic Phenomena↗

PubMedDate not supplied

A virtual instrument (VI) for haemodynamic management in ICU and during surgery.

Systolic pressure variations (SPV) during mechanical ventilation and its single components, related to short apnea, reflect changes of the volemic condition of the patient. To introduce their determination during clinical monitoring for different fluid states and for different tidal volumes, they must be computed on-line without introducing interference with standard activities. A system computing on-line systolic pressure variation during mechanical ventilation, connected to standard monitoring devices, has been proposed. It is based on a notebook PC implemented with graphical software comprising a user panel in the form of a virtual instrument and is able to acquire, process and present signals from different instruments utilized in ICU and during surgery. It can be used as a base to assess the ability of computed parameters helpful in clinical decision. The use of a notebook PC and open software allows operators, even if non-expert in computer science, to test and implement this, as well as other innovative tools in clinical practice.

Blood Pressure Determination↗

PubMedDate not supplied

Ventricular energetics during mechanical ventilation and intraaortic balloon pumping--computer simulation.

Computer simulation of a cardiovascular system enabled us to predict the effects of simultaneous application of mechanical ventilation (MV) and intraaortic ballon pumping (IABP) on ventricular energetics. External work (EW), pressure-volume area (PVA), potential energy (PE) and cardiac mechanical efficiency (CME) were calculated. Nummerical simulation showed that changes of positive intrathoracic pressure have a considerable effect on left and right ventricular EW, PE, PVA and CME, whether IABP is used or not. The right ventricular energetics was much less influenced by systemic resistance (Ras) changes than the left ventricular one. Simultaneous application of IABP and MV showed a remarkable effect on left ventricular EW. The net result was reversed sensitivity to pulmonary resistance (Rap) and reduced sensitivity to Ras. PVA was generally reduced, while CME is increased by simultaneous presence of IABP and MV. The sensitivity of CME to Rap and Ras variation was diminished in this situation.

Computer Simulation↗

PubMedDate not supplied

Energetic parameter changes with mechanical ventilation in conjunction with BVAD assistance.

The aim was to assess the influence of a biventricular assist device (BVAD) on ventricular energetics parameters (external work, oxygen consumption, cardiac mechanical efficiency) for both ventricles, when mechanical ventilation was applied. The experiments were performed using a computer simulator of cardiovascular system (CARDIOSIM) after modelling a pathological state of the left ventricle (E(v)Left = 0. 9 mmHg cm(-3) and increasing pulmonary resistance (Rap = 0.3 mmHg cm(-3 s). The effect of mechanical ventilation was mean intrathoracic pressure changes from 0 to +5 mmHg. This simulation showed that application of BVAD for both ventricles reduces external work and that this effect is stressed by positive intrathoracic pressure, reduces cardiac mechanical efficiency that is quite insensitive to intrathoracic pressure and increases oxygen consumption, which is reduced by positive intrathoracic pressure. The increase of potential energy at the onset of BVAD evidences a rightwards shift of ventricular work cycle (unloading of the ventricles). In general, positive intrathoracic pressure during BVAD assistance adversely affects ventricular energetics.

Biomedical Engineering↗

PubMedDate not supplied

Mock circulatory system for in vitro reproduction of the left ventricle, the arterial tree and their interaction with a left ventricular assist device.

A modular physical circuit for testing monoventricular and biventricular heart assist devices (HAD) is under development. The modules now available are assembled in an open-loop circuit and reproduce the function of the left ventricle and the systemic arterial tree. The left ventricle model reproduces Starling's law of the heart and can be easily controlled to modify other parameters such as contractility and timing (i.e. heart rate and systole/diastole ratio). This circuit, in connection with a left ventricular assist device (LVAD), can be used to evaluate the LVAD performance, its effect on the circulatory system and as a training system. This paper is devoted to a description of the circuit and of its interaction with a LVAD, which is analysed after the simulation of a low contractility pathology of the ventricle. Results obtained in these experiments are reported.

Heart-Assist Devices↗