Controlling the flow balance: In vitro characterization of a pulsatile total artificial heart in preload and afterload sensitivity

The objective of this study is to identify the preload and afterload sensitivity of the ReinHeart TAH 2.0. For adequate left-right flow balance, the concept of a reduced right stroke volume (by about 10%) and active adaption of the right diastole duration are evaluated concerning the controllability of the flow balance. This study used an active mock circulation loop to test a wide range of preload and afterload conditions. Preload sensitivity was tested at atrial pressures (APs) between 4 and 20 mm Hg. Left afterload was varied in a range of 60-140 mm Hg mean aortic pressure (MAP), right afterload was simulated between 15 and 40 mm Hg. Four scenarios were developed to verify that the flow difference fully covers the defined target range of 0-1.5 L/min. Although a positive correlation between inlet pressure and flow is identified for the right pump chamber, the left pump chamber already fills completely at an inlet pressure of 8-10 mm Hg. With increasing afterload, both the left and right flow decrease. A positive flow balance (left flow exceeds right flow) is achieved over the full range of tested afterloads. At high APs, the flow difference is limited to a maximum of 0.7 L/min. The controllability of flow balance was successfully evaluated in four scenarios, revealing that a positive flow difference can be achieved over the full range of MAPs. Under physiological test conditions, the linear relationship between flow and heart rate was confirmed, ensuring good controllability of the TAH.

The MiniACcor: Constructive Redesign of an Implantable Total Artificial Heart, Initial Laboratory Testing and Further Steps

The Aachen Total Artificial Heart (ACcor) has been under development at the Helmholtz Institute in Aachen over the last decade. It may serve as a bridge to transplant or as a long-term replacement of the natural heart. Based upon previous in vivo experiments with the ACcor total artificial heart, it was decided to optimize and redesign the pump unit. Smaller dimensions, passive filling and separability into three components were the three main design goals. The new design is called the MiniACcor, which is about 20% smaller than its predecessor, and weighs only 470 grams. Also its external driver/control unit was miniaturized and a new microcontroller was selected. To validate the design, it was extensively tested in laboratory mock loops. The MiniACcor was able to pump between 4.5 and 7 l/min at different pump rates against normal physiological pressures. Several requirements for the future compliance chamber and transcutaneous energy transmission (TET) system were also measured in the same mock loop. Further optimization and validation are being performed in cooperation with the Heart and Diabetes Centre North Rhine-Westphalia.

Proposal of a new electromechanical total artificial heart: the TAH Serpentina

A new type of energy converter for an electro-mechanical total artificial heart (TAH) based on the principle of a unidirectional moving motor is described. Named the TAH Serpentina, the concept consists of 2 major parts, a pendulum shaped movable element fixed on one side using a joint bearing and a special shaped drum cam. Pusher plates are mounted flexibly to the crossbar of the pendulum. A motor drives the special shaped drum cam linked to the pendulum through a ball bearing. The circular motion of the unidirectional moving brushless DC motor is transferred into the linear motion of the pendulum to drive the pusher plates. Using a crossbar with a variable length, the stroke of the pendulum and therefore the displaced blood volume is alterable. To achieve a variable length, an electric driven screw thread or a hydraulic system is possible. Comparable to the natural heart, cardiac output would be determined by frequency and stroke volume.

Fuzzy control concept for a total artificial heart

The development of an electromechanically driven total artificial heart (Helmholtz-TAH) was initiated in 1990. Anatomical fitting, biocompatibility, and automatic physiologic adaptation of pump output are the basic requirements that characterize the overall TAH concept. For evaluation of these features, a TAH labtype was developed. It provides most features of the conceptual artificial heart and supports in vitro testing of energy conversion, pump behavior, structural parts, sensors, and control concepts. A fuzzy controller has been implemented for adaptation of the pump rate to body perfusion demand by left pump chamber filling detection. This controller will be an important element of a future extensive TAH control system. The implementation is supported by a professional fuzzy control development tool that allows on-line and real time optimization of control strategies for dynamic processes. The first experiments proved the feasibility and the advantages of this fuzzy control concept. The first in vitro test results are presented.

Fuzzy logic and control: principal approach and potential applications in medicine

During the last few years intelligent machines appeared in nearly all technical areas, such as consumer electronics, robotics, and industrial control systems. There are for example washing machines that work very effectively, need comparably less power than in the past, and have short execution times because they adjust their washing cycles to each set of clothes and change their washing strategies as the clothes become clean. These intelligent systems are based on fuzzy control strategies, i.e., common sense rules are used to describe a system's behavior instead of complex mathematical models. We have applied this new technology to control problems as well as to reasoning problems in biomedical engineering where appropriate mathematical models could not be built due to the complexity of the problem. After a short introduction to the concepts of fuzzy logic two approaches in the field are described: a fuzzy control strategy for the pump rate adjustment of a novel total artificial heart and an intelligent alarm system based on fuzzy inference which supports the anesthetist in monitoring and evaluating the hemodynamic state of a patient undergoing cardiac surgery. These examples indicate the inherent reliability and stability of this technique in the field of complex dynamic systems. Such properties are highly significant especially in medical applications.

The Helmholtz Total Artificial Heart Labtype

To perform the first experimental tests for validation of a new gear unit concept, the pump chamber, diaphragm, and pusher plate design of an orthotopic electromechanical total artificial heart (TAH) (Helmholtz Labtype) was manufactured. In its early stage of development, it provides some of the most important features of the conceptual final artificial heart. The new gear unit transforms a uniform unidirectional rotational motor movement into translatory pusher plate movements, with resting phase in the end-diastolic position, and the angled pump chamber orientation determines the available space for the motor and gear unit. Furthermore, this labtype provides flexibility with regard to use of different types of structural parts for experimental investigations. The first in vitro test results, obtained with specially designed circulatory mockloops that simulate physiological preload and afterload conditions, are presented. They comprise pressure and flow generation, motor performance, efficiency, and energy consumption. The results prove the feasibility of the new gear unit concept for an electromechanical artificial heart and allow a reliable determination of the necessary performance of the future brushless DC motor for the first in vivo TAH model.

A new electrohydraulic energy converter for a left ventricular assist device

An energy converting system that can function for years without maintenance is required for the drive of a left ventricular assist device (LVAD). To meet the requirements of safety, the energy converter should have a simple design with few moving elements. The design applied herein has only one moving part and thus has greater inherent safety than competing systems. The only moving part is the rotor unit, comprised of the impeller of a centrifugal pump, the rotor of an electric motor, and the rotor of an electric axial actuator. A reversal of flow of the transmitter fluid can be achieved with an axial shift of this rotor unit. This fluid acts on the outer surface of a blood chamber and enables it to draw in blood and to expel it. Valves direct the flow of blood. The energy converter performs a flow of 12 L/min at a motor speed of 6,000 rpm against a pressure head of 115 mm Hg according to an output of the pulsatile blood pump of 5 L/min.