Fuzzy Control Concept for a Total Artificial Heart

Abstract: 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.     

Constructional and Functional Characteristics of Recent Total Artificial Heart Models TNS Brno VII, VIII, and IX

Abstract: Twelve total artificial heart (TAH) models have been developed at the Brno Research Center. Devices VII, VIII, and IX were constructed on the principle of asymmetry. Three main objectives had to be fulfilled by this construction. First, contact of the flap inflow valve with the diaphragm during the pumping cycle had to be avoided. Second, the evacuation regimen of the blood chamber needed to be improved. Third, the danger of thrombi formation due to the lesser incidence of the dead corners had to be decreased or eliminated. The type VII heart has a roof-shaped polyurethane valve in the outflow tract whereas the type VIII heart has a flap valve. The decrease of thrombi incidence around the outflow valve was thus secured, and the driving pressure was decreased as well. In the type IX heart, the small additional flap valve is attached to the outflow valve. In one Brno VII device, Imachi's jellyfish valve has been mounted. Altogether, 62 long-term experiments with survival times of 30–314 days have been performed. To this number, 4 comparative experiments using the Rostock artificial heart were added.     

In Vitro and In Vivo Validation Tests for Total Artificial Heart

Abstract: Properly planned in vitro and in vivo studies are mandatory to validate blood pump performance. However, standard procedures for in vitro and in vivo tests of total artificial heart (TAH) performance still do not exist. At Baylor College of Medicine, standard tests procedures for performance validation of the totally implantable TAH have been established. In this paper, these in vitro tests protocols (performance mapping tests, accelerated endurance test, hemolysis test, flow visualization tests, etc.) are described as well as in vivo test procedures (TAH implantation procedure, including surgical technique, postoperative management and tests, etc.). In addition, pathological protocols are presented. In our experience, these procedures are very simple, easy to perform, and inexpensive. These protocols are proposed as standard in vitro and in vivo tests for a TAH.     

Separation of the Natural Atria in Experimental Implantation of Total Artificial Heart

Abstract: Atrial connections in a single-unit total artificial heart (TAH) may be difficult to make because of the rigidity of the device and the fixed position of the atrial inlets. We developed a technique to separate the natural atrial borders in an experimental implantation of a unitary TAH. In this technique, the interatrial groove was dissected to separate the posterior wall of the right atrium from the roof of the left atrium before cardiopulmonary bypass (CPB) was initiated. After initiation of CPB and cardiectomy, the atrial septum was separated completely, and the right atrial wall was reconstructed with glutaral-dehyde-treated autopericardium. We believe that this simple adjunctive technique provides increased mobility of the atrial cuffs and allows for an easier connection of the unitary TAH.     

Left and Right Pump Output Control in One-Piece Electromechanical Total Artificial Heart

Abstract: Left master alternate (LMA) ejection control based on the left pump fill method was implemented for a one-piece electromechanical total artificial heart (TAH). The TAH consists of left and right pusher-plate-type blood pumps sandwiching a compact electromechanical actuator comprising a direct current (DC) brushless motor and a planetary roller screw. The motor rotation is controlled on the basis of the roller-screw position as detected by a Hall effect sensor and a commutation pulse-counting method. Since the pusher-plate shaft and roller screw are decoupled during filling, both pumps fill passively with the right and left atrial pressure. To obtain response to the right atrial pressure change in the LMA mode, the left fill trigger level as detected by a Hall effect position sensor is adjusted to operate the pump at a higher rate and to drive the right pump at 85–90% of the full stroke level. The invitro evaluation demonstrated that this method can respond to right atrial pressure changes provided that the right pump is operated at less than the full stroke level. When the preload is high and the right pump goes into full stroke operation, the left eject level can be decreased to run the pump at a higher rate and to transfer more blood from the right to the left. In the in vivo evaluation, which lasted 1 week in a 95 kg calf, the left and right atrial pressures were kept within physiological ranges. The LMA mode triggered by the left pump fill can protect the lungs and can also respond to venous return change and therefore is a reliable control method for a one-piece to-tally implantable TAH system.     

The Italian Artificial Heart Program

Abstract: 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 mediumterm bench and in vivo testing by early 1994.     

Electron Microscopic Study of Driving Diaphragms in Long-Term Survival with a Total Artificial Heart

Abstract: A driving diaphragm in the long-term working total artificial heart (TAH) is under serious mechanical stress, and the long steady contact with blood causes changes to the diaphragm's surface. These changes can be influenced either by local or systemic interventions. In our study, we tried to follow the development of changes to the diaphragm's surface comparing the samples of diaphragms of long (over 30 days) and short (under 30 days) surviving calves and the effect of some preventive measures as well. We could confirm the presence of two types of calcification: a dystrophic calcification affecting primarily formed thrombi and necrotic tissue, and a primary type of calcification that begins in the form of calcifying nuclei on the protein layer of the polyurethane surface that is later on extensively covered with a fibrin network and blood cells. The calcified deposits caused mechanical damage or were the source of microembolization to the vital organs. A clotting mechanism occurs at the same time as the calcifying process from the beginning, often forming a fibrin network in and over the calcified deposits. An attempt at prevention was made by systemic administration of colloidal iron solution, Ferrum Lek (fern saccharate in a stable colloidal form), based on the concept of the so-called reversed calciphylaxis.     

150-Day Survival of a Calf with a Polymethylmethacrylate Total Artificial Heart: TNS-BRNO-II

A 150-day experiment in a calf with an implanted total artificial heart, TNS-BRNO-II, is described. The Czechoslovak TAH-BRNO-II device is a hybrid; the outer housing is made of polymethylmethacrylate, the moving parts of segmented polyurethane. The blood flow through the device after the surgery gradually increased from 7 L/min to 12 L/min by the end of the experiment. Atrial pressures were automatically maintained at the same level, about one kPa on both sides. The left systolic time was automatically derived from the pump emptying phase; the right systolic time was maintained between 40% and 50%. After the surgery, normal values of blood gases, stabilization of respiratory activity, and normalization of gastrointestinal functions were reached very soon. Anticoagulant therapy was performed during the whole experiment, with several periods of increased bleeding tendency. The clinical state of the calf was essentially physiological until the 94th day of the experiment, when acute bronchopneumonia, with a high fever, over 41°C, initiated a series of complications (pseudomembranous enterocolitis, followed by sepsis lenta). The fatal complication was sudden impairment of the coagulation mechanisms on the 149th to 150th day of the experiment. This was the basic reason for the subsequent death of the animal, caused by acute cerebral anemic anoxia, which could not be prevented by immediate therapeutic procedures. In spite of these complications, the clinical state of this calf was relatively good until the end of the experiment. Autopsy revealed minimal thromboembolization at the valves. The outer surface of the diaphragm was covered with pseudoneointimal deposits and the inlet orifices were free of pannus or other connective tissue crescents. Macroscopic signs of infection were not seen, but bacteriological cultivation from internal organs confirmed Klebsiella infection. The state of the device at the time of autopsy, with simultaneous undisturbed function of the control and driving unit, showed the possibility of still longer survival.     

Control of the Total Artificial Heart: New Aspects in Human versus Animal Experience

Control strategies for total artificial heart application have generally been based on experience with healthy animals. Human patients in a bad state of health who have impaired organ functions and who are subjected to intensive care procedures can develop atypical hemodynamic behavior. In these patients, both unstable and hyperstable behavior of the vascular resistance were observed. Therefore, regulation of cardiac output (CO) by pressure parameters only was avoided and CO was adjusted to obtain an appropriate O2-utilization (O2U). Intending to keep the O2U within ranges of 20-25%, we obtained cardiac indexes between 3.3 and 4.4 L/m2/min (CO 6-8 L/min), which is higher than other cardiac indexes reported. A CO of 10.5 L/min was even necessary to obtain an O2U of 30% in a septic patient. This strategy caused a stable driving management and led to a rapid hemodynamic stabilization and general improvement of the patients' condition. Results indicate that it is also very important to monitor metabolic parameters for appropriate driver adjustment as well, especially in the early postoperative phase, and that O2-U is a sensitive and useful parameter for this purpose.     

In Vitro Evaluation of Linear Motor-Driven Total Artificial Heart

Abstract: This paper deals with the in vitro evaluation of a newly developed linear motor-driven total artificial heart (linear TAH). The linear TAHs have been developed and evaluated in mock testing and acute animal experiments. The new linear TAH was made based on experience with acute animal experiments. The maximum static thrust of the new linear pulse motor is 146 N with exciting current of 1.69 A. The weight and the volume of this linear TAH are 1.9 kg and 560 ml, respectively. The linear TAH has a kinetic thrust of 85 to 43 N and provides the maximum flow rate of 6.8 L/min in mock circulatory testing.     

Dynamic In Vitro and In Vivo Performance of a Permanent Total Artificial Heart

In vivo characterization studies were performed to compare the dynamic in vivo performance of the Penn State/3M Health Care electric total artificial heart to existing in vitro data. Fully implanted systems were utilized including the artificial heart, controller, backup batteries, compliance chamber, and transcutaneous energy transmission. Catheters were implanted to measure central venous pressure (CVP), left atrial pressure (LAP), right atrial pressure (RAP), pulmonary artery pressure (PAP), and aortic pressure (AoP). Cardiac output (CO) was determined from the implanted controller, and systemic vascular resistance (SVR) was calculated. Steady state data were collected for each animal along with data regarding the transient responses to changes in preload and afterload. Preload was manipulated through volume changes. Afterload changes were accomplished through vasoactive agents. Increased preload caused little change in cardiac output because the pump output was nearly maximum at baseline. LAP, AoP, and SVR increased with increasing RAP. Decreased preload caused a reduction in CO, LAP, and SVR. Afterload increase resulted in a slight decrease in flow and an increase in system power and SVR. Afterload reduction was accompanied by a decrease in preload and a concomitant reduction in flow. Overall, the system response was similar to the response observed in vitro.     

Control System Modification of an Electromechanical Pulsatile Total Artifical Heart

Abstract: A reliable control system is one of the most important characteristics of the electromechanical pulsatile total artificial heart (TAH). Obtaining an error-free procedure is essential for a successful in vivo implantation. To avoid any malfunction of the electrical control system, a modification of the previously designed controller was made to ensure stable pumping without the Hall effect sensor missensing. The installation position of the Hall effect sensor was changed from the top of the housing to the central piece with small magnets being installed in the stabilizer rods. The usage of the Hall effect sensor was chosen as an electrical switch. An in vitro one month running test of the TAH demonstrated adequate hydro-dynamic performance with a completely error-free pumping characteristic. The total efficiency of the TAH was 12.6 ± 1.4% at an 8 L/min outflow and 10.7 ± 1.0% at a 6 L/min outflow condition.     

Investigation of the Durability of a Diaphragm for a Total Artificial Heart

One of the most critical components regarding the durability of the ReinHeart total artificial heart (TAH) is its biocompatible diaphragm, which separates the drive unit from the ventricles. Hence, a durability tester was designed to investigate its required 5‐year lifetime. The aim of this study was to prove the validity of accelerated testing of the polyurethane diaphragm. The durability tester allows simultaneous testing of 12 diaphragms and mimics physiological conditions. To accelerate the time of testing, it operates with an increased speed at a frequency of 8 Hz. To prove the correctness of this acceleration, a servo‐hydraulic testing machine was used to study the effect of different frequencies and their corresponding loads. Thereby the viscoelastic behavior of the polyurethane was investigated. Additionally, high‐speed video measurements were performed. The force against frequency and the high‐speed video measurements showed constant behavior. In the range of 1–10 Hz, the maximum resulting forces varied by 3%, and the diaphragm movement was identical. Frequencies below 10 Hz allow a valid statement of the diaphragm's mechanical durability. Viscoelasticity of the polyurethane in the considered frequency‐range is negligible. The accelerated durability test is applicable to polyurethane diaphragms, and the results are applicable to TAH use. The reliability of the diaphragm for a lifetime of 5 years was found to be 80% with a confidence of 62%.     

A New Total Implantable Artificial Heart

A new kind of total implantable artificial heart (TIAH), developed by the author, offers miniaturization with good hemodynamic and physiologic properties. The heart has two units of function, and each has two blood sacs, compressed and expanded by twos, that are filled from one circulation and push out the blood in the other circulation, one after the other. Therefore, the blood flow is continuous and modulated, regulated by pneumatic controlled membrane valves. Shaped plates mechanically synchronized by a pushing rod control compression and expansion of the blood sacs. Starling, atrium, Windkessel, and Anrep effects are guaranteed by construction. The heart can be used for bridging toward transplantation, for definitive substitution of the heart, and for a new kind of therapy--"extracorporeal regeneration of organs."     

The Total Artificial Heart: Indications and Preliminary Results

The development of the total artificial heart (TAH) has reached a level where it is now available for clinical applications. The TAH has demonstrated distinct advantages over other forms of mechanical circulatory assistance. As of December 1, 50 TAHs have been implanted: 5 as permanent devices, and 45 as a temporary mechanical bridge to cardiac transplantation. The use of the TAH has increased in the last several months, leading to a growing interest in defining the indications and contraindications to its use. End-stage cardiomyopathy (either idiopathic, ischemic, viral, or postpartum) has been the underlying disease in 80% of the TAH procedures to date. The TAH has also been applied in 5 cases of acute cardiac graft rejection, 2 cases of congenital heart diseases, and in one case after acute myocardial infarction. The indications for the use of the TAH in these and other potential patient groups is discussed in light of the current clinical results.     

Heart Substitution: Transplantation and Total Artificial Heart. The Texas Heart Institute Experience

Two methods of heart substitution have been used at the Texas Heart Institute: cardiac transplantation and the total artificial heart (TAH). Cardiac transplantation is an effective means of saving patients with endstage heart disease and, since the introduction of the immunosuppressive agent cyclosporine, survival has increased significantly. In a recent series from July 1982 to May 1984, 25 patients underwent cardiac transplantation at the Texas Heart Institute. Nineteen of these patients are alive, in Functional Class I, and leading normal lives. A major disadvantage of cardiac transplantation is that it cannot be used on an emergency basis for postcardiotomy patients. In this situation, TAH has been used twice (1969 and 1981) as the first stage to maintain circulation prior to subsequent cardiac transplantation. In both instances, the TAH functioned well until a satisfactory donor was found. This demonstrates the feasibility of the two-staged concept and encourages further development of cardiac prostheses.