Circulatory assist with centrifugal pump as a bridge to recovery: mathematical analysis.

Mechanical circulatory support is an essential issue in the management of patients with end-stage cardiac failure. The aim of this study is to evaluate the efficacy of temporary support with a centrifugal blood pump as bridge to heart function recovery or bridge to transplantation. Heart recovery is achieved by improving ventricular mechanical working conditions with proper modifications of preload and afterload. This article assesses the advantages of a novel 'cardiac chambers' cannulation setting versus the traditional one, in the case of biventricular or isolated right ventricular failure. The study was conducted using a numerical computer model based on the work by Guyton, Sagawa, Westerhof, and Noordergraaf. Simulation of the planned trials was achieved by changing the model parameters, the pump angular velocity, and the inflow and outflow settings.

Modeling, analysis, and validation of a pneumatically driven left ventricle for use in mock circulatory systems.

In this work a pneumatically driven mock left ventricle and a native left ventricle are modeled and alternatively connected to the numerical model of a closed circulatory system comprising the systemic circulation, the left atrium, and inlet and outlet ventricular valves. By simulating physiological changes of the system working conditions, behavior and preload sensitivity of the pneumatic ventricle have been compared to those of a native ventricle. Results show that a pneumatic ventricle, when used as a fluid actuator in mock circulations, has low flexibility in reproducing different scenarios, its interaction with peripheral circulatory districts is characterized by non-physiological values, and its preload sensitivity is in poor agreement with physiological data. Results' analysis also shows that present mock circulatory systems for testing cardiovascular prostheses are inadequate, if a careful attention is not paid to the pumping action of the pneumatic ventricle. The presented computer model, validated by comparing numerical results with in vitro measurements available in the literature, can be used for designing in vitro experiments, while choosing the best control strategy for pneumatic systems.

Hybrid test bench for evaluation of any device related to mechanical cardiac assistance.

Hydraulic mock circulatory systems have low flexibility to allow tests of different cardiovascular devices and low precision when a reference model must be reproduced. In this paper a new bench is described. It combines the computer model of the environment in which the device will operate and the electro-hydraulic interfaces by which device and computer are connected. A models library provided with basic functions allows implementing many layouts of the bench, which in turn depend both on the device properties and the desired experiment. In case of an apical LVAD evaluation, the bench can reproduce right and left ventricles, pulmonary and systemic circulations, inlet and outlet LVAD cannulas. An interface forces the instantaneous calculated flow at the VAD input and feeds back the measured pressure to the computer; another interface works in a similar -but complementary- way at the VAD output. The paper focuses on the operating principle of the electro hydraulic interfaces which represent a relevant component of the bench, on the RT-Linux-based software architecture, on the models of the basic elements of the bench. A patent is under preparation. At the moment, only a portion of the bench has been developed. It consists of a piston-cylinder mechanism, which mimics the elastance-based mechanism of a natural ventricle, and a hydraulic circuit representing the arterial load according to a modified windkessel model and the venous return according to the Guyton's model. The pump is driven by a real-time simulation of the cardiovascular system. This preliminary layout allowed testing the piston-cylinder mechanism, its control, and the software. This electro-hydraulic interface has been used to reproduce a pulsatile pump working in different modes. The hybrid model approach can support the development of new cardiac assist devices from their computer model to their manufacture.

Application of a mechanical filter to an artificial heart.

A mechanical filter developed to improved the performances of an artificial heart whose electrical motor has a reciprocating motion is presented. The filter phases the mechanical load strongly reducing its inertial component (which is of the same order of magnitude as the useful load). The analysis reported for a prototype developed by us shows that when its rate is equal to the first resonant frequency of the filter, a reduction of about 50 percent for the maximum value of the torque due to inertial and friction forces is obtained.

The Italian Artificial Heart Program.

In Italy, artificial heart development was promoted by virtue of a special program on technological and industrial development in areas related to cardiology and cardiosurgery. A first prototype series of electromechanical total artificial hearts (TAHs) and ventricular assist devices (VADs), with ball-screw-based actuation technology, has been developed, and preliminary bench tests and short-term animal implant experiments were performed. The project started with analysis and development of existing TAH and VAD models, and it included a fill-sensor-free control scheme and anatomical fitting studies using a three-dimensional computer model of the chest cavity. Second-generation prototypes are currently being developed, and they are scheduled for medium-term bench and in vivo testing by early 1994.

A new test circulatory system for research in cardiovascular engineering.

A new test circulatory system (TCS) has been developed for the in vitro testing of artificial hearts (AH) and for research in cardiovascular engineering, when connected to an AH that mimics the natural heart. The TCS is controlled by five variables whereby the slopes of the systemic and pulmonary venous return curves and the mean circulatory pressure can be fixed. It allows us to observe the mutual influence between TCS and AH characteristics and particularly the blood volume distribution, the pressure distribution, and the flowrates in steady-state conditions and (in the near future) also in dynamic conditions. A steady-state mathematical analysis describing the TCS is reported. Numerical results for the human circulatory system at different levels of activity and in physiologic conditions are shown. A first prototype of the TCS has been working for more than one year. The experimental results are in agreement with the mathematical analysis.

A new automatically controlled electric TAH.

Cardiovascular regulatory mechanisms are implemented by means of a very complex control system involving neural, humoral, and mechanical agents. The state of the art in TAH today reveals that we have passed a stage where we can be satisfied with a 6 or 9 mo survival. Development and implementation of a versatile control theory must be another milestone before a TAH can really serve the prospective patient population requiring such a device. This study reveals the vital role and merits as well as the feasibility of incorporating such a control theory into the device.