Automatic Control Systems for the Artificial Heart and Ventricular Assist Device

Automatic control systems for the artificial heart (AH) and ventricular assist device were developed using selected criteria of effectiveness, a mathematical model of regulation, and noninvasive measures of the hemodynamic parameters. The Sinus IS2 system was developed for control of the AH; its main component is a high-speed servomechanism that provides for the generation of pneumatic pulses. The servomechanism is controlled by automatic regulation with pressure feedback. Mean aortic pressure was used as the primary regulated hemodynamic parameter. The systems were tested using both a physical model and a physiologic experiment. Contractile insufficiency of the left ventricle was simulated in testing the control system for circulatory assistance. The studies demonstrate that automatic control systems function effectively by providing normal blood circulation in both the resting state and in certain transient processes occurring in a real, dynamic circulatory system.     

Development of a Direct Mechanical Left Ventricular Assist Device for Left Ventricular Failure

Abstract: We have developed a direct mechanical left ventricular assist device (DMLVAD) for severe left ventricular failure. The DMLVAD was attached to the left ventricle and compressed the heart by a pneumatic driving unit. In a mock circulation model with an extracted non-beating heart, a cardiac output (CO) of 1.93 L/min was obtained at a driving pressure of 200 mm Hg. In a canine left ventricular failure model induced by injection of sodium hydroxide into the myocardium, the systolic arterial pressure, systolic left ventricular pressure, maximum LV dP/dt, peak flow, and CO increased by 21, 24, 58, 144, and 37%, respectively. The mean left atrial pressure also decreased by 15% when the DMLVAD was driven. These effects were most prominent when the mean left atrial pressure was over 15 mm Hg, and the driving pressure was over 100 mm Hg. Compression at late systole was more effective in obtaining greater CO. We suggest that the DMLVAD could be an optional circulatory assist device for patients with left ventricular failure awaiting heart transplantation.     

Implantable Ventricular Assist Systems

A major goal of the Circulatory Support Program of the National Heart, Lung, and Blood Institute (NHLBI) is the development of a tether-free implantable ventricular assist system (VAS) to rehabilitate patients with advanced heart disease. In 1980, the NHLBI initiated a targeted program to develop and integrate implantable electromechanically powered VASs capable of operating for at least 2 years. The objectives of the program are to complete the development of the VAS and perform in vitro and in vivo evaluation studies. This article summarizes the research status of this NHLBI-sponsored program. It defines the VAS system requirements, describes the systems under development, identifies progress achieved to date, and identifies research challenges.     

A Novel Electromechanical Drive for a Tether-Free Implantable Ventricular Assist Device

Abstract: A tether-free ventricular assist device (VAD) based on a novel electromechanical drive was prototyped and evaluated. The unit can be adapted for implantation. The device utilizes a bladder-type ventricle taken from a pneumatically driven VAD. In mock loop testing, the unit has met the design capacity of 6 L/min against a pressure head of 150 mm Hg. The efficiency of the device allows it to operate at design flow and pressure for periods of up to 8 h when powered by a single rechargeable battery pack weighing less than 5 kg. The mechanism consists of a seamless sac-type bladder situated between hinged plates actuated by a motor-driven bell-and-crank linkage. Cycle parameters are controlled by a microprocessor-based servomotor drive.     

Characterization of a Magnetic Bearing System and Fluid Properties for a Continuous Flow Ventricular Assist Device

This article presents the performance test results of the CFVAD3 continuous flow blood pump in an artificial human circulation system. The CFVAD3 utilizes magnetic bearings that support a thin pancake impeller, the shape of which allows for a very compact pump whose total axial length is less than 5 cm with a radial length of about 10 cm. This gives a total volume of about 275 cc. The impeller itself has 4 vanes with a designed operating point of 6 L/min at 100 mm Hg of differential pressure and 2,000 rpm. The advantages of magnetic bearings, such as large clearance spaces and no mechanical wear, are elaborated upon. Furthermore, bearing model parameters such as load capacity and current gains are described. These parameters in conjunction with the operating conditions during testing are then used to estimate the fluid forces, stiffness, and damping properties while pumping. Knowledge of these parameters is desirable because of their effects on pump behavior. In addition, a better plant model will allow more robust control algorithms to be devised that can boost pump performance and reliability.     

Use of a Paracorporeal Pneumatic Ventricular Assist Device for Postoperative Cardiogenic Shock in Two Children with Complex Cardiac Lesions

Pneumatic ventricular assist device (VAD) was utilized for cardiogenic shock after intracardiac operation in two children with complex cardiac anomalies based with single ventricle. In the first case (a 10-year-old), after a modified Fontan operation, VAD was placed between the functional left atrium and ascending aorta, serving as a "artificial single ventricle" with neither pumping chamber nor artificial support in the right side of the heart. The systemic circulation was maintained by keeping relatively high central venous pressure. In another child (a 3-year-old) who underwent repair of incompetent atrioventricular valve leaving intracardiac lesions, VAD was placed between the common atrium and ascending aorta, serving as a pump for both pulmonary and systemic circulation with regulation of pulmonary blood flow through an aortopulmonary Gore-Tex shunt. The circulatory assist with VAD was utilized for 5 and 6 days, respectively. Although weaning from the device was not feasible in both patients because of the pulmonary dysfunction, these experience showed the possible use of VAD for cardiogenic shock after surgery in patients with complex cardiac anomalies.     

Chronic Survival of Calves Implanted with the DeBakey Ventricular Assist Device

The DeBakey ventricular assist device (VAD) is a miniaturized, electromagnetically driven axial flow pump capable of generating in excess of 10 L/min output. The VAD was evaluated in 19 calves during experiments designed to test iterative modifications in the system and to determine the safety of the DeBakey VAD for intermediate to long-term implant. Five of the animals died or were euthanized during the perioperative period (i.e., Days 1-5) due to complications associated with bleeding (n = 3), sudden cardiac arrest (n = 1), or pump occlusion due to a muscle remnant associated with coring (n = 1). The remaining 14 animals survived from 7-145 days. Ten of the 14 animals survived 30 or more days, and 2 animals survived 93 and 145 days before elective euthanasia. Pump function was evaluated in the 14 calves that survived beyond the perioperative period. Pump output at implantation averaged 3 L/min while output at 100 days (n = 2) averaged 4.22 L/min. The electrical current did not change across time during the study, indicating normal operation of the bearings. Pumps consumed less than 10.5 W of power for all support durations. Hemolysis did not occur; the average daily plasma free hemoglobin varied from 2.0 to 8.0 mg/dl. Evaluation of serum biochemical data showed that implantation of the DeBakey VAD in calves with normal hearts did not impair end organ function; BUN, creatinine, and total bilirubin varied minimally within the normal range. The white blood cell count of implanted animals remained within the normal range throughout the study.     

Motor Feedback Physiological Control for a Continuous Flow Ventricular Assist Device

The response of a continuous flow magnetic bearing supported ventricular assist device, the CFVAD3 (CF3) to human physiologic pressure and flow needs is varied by adjustment of the motor speed. This paper discusses a model of the automatic feedback controller designed to develop the required pump performance. The major human circulatory, mechanical, and electrical systems were evaluated using experimental data from the CF3 and linearized models developed. An open-loop model of the human circulatory system was constructed with a human heart and a VAD included. A feedback loop was then closed to maintain a desired reference differential pressure across the system. A proportional-integral (PI) controller was developed to adjust the motor speed and maintain the system reference differential pressure when changes occur in the natural heart. The effects of natural heart pulsatility on the control system show that the reference blood differential pressure is maintained without requiring CF3 motor pulsatility.     

A Treatment System for Implementing an Extracorporeal Liver Assist Device

Abstract: Biologically active devices are receiving increasing attention, especially in the management of endocrine pancreatic failure (diabetes) and acute liver failure. In both instances, mechanical devices have been unable to replace the function of the original organ, and consequences range from inconvenient (e.g., regular insulin shots, diabetic vasculopathy) to fatal (e.g., fulminant hepatic failure). In developing a cell-based liver assist device, we concluded that currently available extracorporeal blood treatment systems are not suited to the delivery of high molecular weight substances and that they do not adequately address the metabolic needs of the device. We therefore developed a system that provides safe, continuous perfusion of an extracorporeal organ. We detail the design and first clinical use of the system.     

Test Controller Design, Implementation, and Performance for a Magnetic Suspension Continuous Flow Ventricular Assist Device

A new continuous flow ventricular assist device using full magnetic suspension has been designed, constructed, and tested. The magnetic suspension centers the centrifugal pump impeller within the clearance passages in the pump, thus avoiding any form of contact. The noncontact operation is designed to give very high expected mechanical reliability, large clearances, low hemolysis, and a relatively small size compared to current pulsatile devices. A unique configuration of magnetic actuators on the inlet side and exit sides of the impeller provides full 5 axis control and suspension of the impeller. The bearing system is divided into segments which allow for 3 displacement axes and 2 angular control axes. The controller chosen for the first suspension tests consists of a decentralized set of 5 proportional integral derivative (PID) controllers. This document describes both the controller and an overview of some results pertaining to the magnetic bearing performance. The pump has been successfully operated in both water and blood under design conditions suitable for use as a ventricular assist device.     

The Short-term Pulsatile Ventricular Assist Device for Postcardiotomy Cardiogenic Shock: A Clinical Trial in China

Abstract:  Despite the recent advances in myocardial protection, surgical techniques, intra-aortic balloon therapy, and maximal pharmacological support, postoperative ventricular dysfunction continues to occur in 0.5–1.0% of all patients undergoing cardiac surgery. Ventricular assist device (VAD) is an important therapeutic adjunct in treating patients with profound ventricular dysfunction with postcardiotomy cardiogenic shock. The purpose of this report was to describe the clinical results with the China-made Luo-Ye VAD as a short-term circulatory support. From May 1998 to December 2006, 17 patients with postcardiotomy cardiogenic shock were supported by the Luo-Ye VAD. Of these patients, 10 were males and seven were females with a mean age of 49.6 years (range 36–68 years). All cases were supported by left VAD (LVAD). Mean duration of support was 46.3 h (range 13–113 h). A criteria of insertion was established to standardize implantation criteria. Among the 17 patients treated with LVAD, eight (47.1%) patients were weaned from support and seven (41.2%) patients were discharged from hospital. Ten (58.8%) patients died while on LVAD support (nine cases) or shortly after weaning (one case). The causes of death in the entire group were cardiac (40%), renal failure (20%), neurologic (10%), sepsis (10%), and multiple organ system failure (20%). The complications were represented by bleeding, renal failure, neurologic event, infection, ventricular arrhythmias, etc. The Luo-Ye VAD functioned well and proved to be useful in patients with postcardiotomy cardiogenic shock. It carries a less-postoperative anticoagulant and a low incidence of VAD-related complications. The survival rate was encouraging in our small cohort of patients.     

A New Mock Circulatory Loop and Its Application to the Study of Chemical Additive and Aortic Pressure Effects on Hemolysis in the Penn State Electric Ventricular Assist Device

Abstract: A new mock circulatory loop was developed for hemolysis studies associated with the Penn State electric ventricular assist device (EVAD). This flow loop has several advantages over previously designed loops. It is small enough to accommodate experiments in which only single units of blood are available, it is made out of biocompatible materials, it incorporates good geometry, and it provides normal physiological pressures and flows to both the aortic outlet and the venous inlet of the pumping device. Experiments with reduced aortic pressure but normal cardiac output showed that hemolysis in a loop with normal aortic blood pressure was significantly higher than that in a loop with lowered aortic pressure, thereby illustrating the importance of maintaining loop pressures as close as possible to those found in vivo. This data also imply that blood traveling through the left ventricle in an artificial heart may be subject to higher hemolysis rates than that traversing the right ventricle. Another set of experiments to determine the effects of 4 hemolysis or drag-reducing agents (Pluronic F-68, Dextran-40, Polyox WSR-301, and Praestol 2273TR) on blood trauma due to the EVAD and associated valves was performed. Results indicated that none of the additives significantly reduced hemolysis under the conditions found in the mock loop. Finally, a compilation of data gathered in these experiments showed that the index of hemolysis (IH) is dependent on hematocrit (HCT), which suggests that another parameter, IH/HCT, may be more suited to the quantification of hemolysis.     

Implantation of the Left Ventricular Assist Device

Development of mechanical devices for support of the failing heart is a major goal in cardiac surgery. The application of left ventricular assist device (LVAD) is a promising approach in the case of severe and otherwise untreatable cardiac failure. In our experience we have used two external centrifugal pumps for the extracorporeal biventricular cardiac support in a post-transplantation patient who experienced severe rejection six months after heart transplantation. Our own series includes a total of ten implantations of LVAD's with six patients who could be weaned from the device but only one long-term survivor. The clinical results are not encouraging which suggests that the heart of the patient who needs an LVAD has been damaged beyond any chance for later recovery. Obviously timing is the most crucial aspect of the decision to implant the device. It would appear that orthotopic implantation of the transplanted heart remains the method of definitive treatment.     

Analysis of Flow Patterns in a Ventricular Assist Device: A Comparative Study of Particle Image Velocimetry and Computational Fluid Dynamics

Abstract:  In order to develop a diaphragm-type ventricular assist device (VAD), we studied the flow field change following structural modifications. We devised a center flow-type pump by putting a small projection on the center of the housing and/or diaphragm to provide a center in the flow field, and examined the following four types of VADs: N type without a projection, D type with a projection on the diaphragm, H type with a projection on the housing, and DH type with projections on both the diaphragm and housing. Computational fluid dynamics (CFD) was used for flow simulation. Particle image velocimetry (PIV) was also used to verify the reliability of the CFD method and to determine how the flow field changes in the presence of a projection. The results of the PIV and CFD analyses were comparable. The placement of a projection on the housing was most effective in rectifying the flow field.     

A Pediatric Ventricular Assist Device: Its Development and Experimental Evaluation of Hemodynamic Effects on Postoperative Heart Failure of Congenital Heart Diseases

To evaluate the effectiveness of a pediatric ventricular assist device (VAD), hemodynamic effects of the VAD were investigated experimentally in two types of postoperative profound heart failure models of congenital heart disease. In the model I Fontan or modified Fontan operation model, right ventricular pump function was excluded surgically and a shunt between the right atrium and the pulmonary artery was constructed in four dogs. With a VAD between the left atrium and the aorta, pressure gradient across the lung and the cardiac output increased. Right ventricular failure was induced surgically and high pulmonary vascular resistance was made by injection of glass beads in five dogs in model II. Cardiac output increased and the right atrial pressure decreased when a VAD between the right atrium and the pulmonary arterial trunk was activated. In conclusion, the VAD will become a promising modality to manage pediatric profound heart failure cases.     

Feasibility of a Tiny Gyro Centrifugal Pump as an Implantable Ventricular Assist Device

The Gyro pumps were developed for long-term circulatory support. The first generation Gyro pump (C1E3) achieved 1 month paracorporeal circulatory support in chronic animal experiments; the second generation (PI702) implantable ventricular assist device (VAD) was successful for over 6 months. The objective of the next generation Gyro pump is for use as a long-term totally implantable VAD and for pediatric circulatory support. This tiny Gyro pump (KP101) was fabricated with the same design concept as the other Gyro pumps. The possibility of an implantable VAD was determined after performance and hemolysis test results were compared to those of the other Gyro pumps. The pump housing and impeller were fabricated from polycarbonate with an impeller diameter of 35 mm. The diameter and height of the pump housings are 52.3 mm and 29.9 mm, respectively. At this time, a DC brushless motor drives the KP101, which is the same as that for the C1E3. The pump performance was measured in 37% glycerin water at 37 degrees C. Hemolysis tests were performed utilizing a compact mock loop filled with fresh bovine blood in a left ventricular assist device (LVAD) condition at 37 degrees C. The KP101 achieved the LVAD conditions of 5 L/min and 100 mm Hg at 2,900 rpm; generated 10 L/min against 100 mm Hg at 3,200 rpm; 3 L/min against 90 mm Hg at 2,600 rpm; and 2 L/min against 80 mm Hg at 2,400 rpm. In addition, the pump efficiency during this experiment was 12.5%. The other Gyro pumps. that is, the C1E3, PI601, and PI701, in an LVAD condition require 1,600, 2,000, and 2,000 rpm, respectively. The KP101 produced a normalized index of hemolysis (NIH) value of 0.005 g/100 L. With regard to the NIH, the other Gyro pumps, namely the C1E3, PI601, and PI701 demonstrated 0.0007, 0.0028, and 0.004 g/100 L, respectively. The KP101 produced an acceptable pressure flow curve for a VAD. The NIH value was higher than that of other Gyro pumps, but is in an acceptable range.     

An Ultimate, Compact, Seal-less Centrifugal Ventricular Assist Device: Baylor C-Gyro Pump

Abstract: We have developed a compact, seal-less, allpurpose centrifugal pump, the Baylor C-Gyro pump, which is intended as a long-term ventricular assist device (VAD) as well as a cardiopulmonary bypass pump. In attaining this goal, we began with eliminating the shaft seals by adopting a pivot bearing system at the impeller shaft. In addition, a ring magnet encased in the bottom of the impeller was coupled magnetically to a driver magnet placed outside the pump housing (Cl Prototype). This first model yielded satisfactory performance in vitro with a flow rate of 8 L/min against 250 mm Hg at 2,400 rpm, and an index of hemolysis (IH) of 0.0083 g/100 L using bovine blood. In the second model, the C1 Eccentric Inlet Port Model, the inlet bearing support bar in the prototype were eliminated without reducing the prototype's performance. These designs for antithrombogenicity are being tested by the first in vivo experiment, which has lasted for more than 2 weeks.     

In Vitro and In Vivo Testing of an Implantable Motor-Driven Left Ventricular Assist Device

Abstract: A totally implantable motor-driven left ventricular assist device (LVAD) has been developed and tested. The performance of this LVAD was tested in a mock circulatory system. This pump provided 8 L/min of output against a mean afterload of 120 mm Hg with a filling pressure of 20 mm Hg when the pump was operated in the fill/empty mode. The right and left pumps were tested in a mock loop. The right pump afterload was kept in the range from 23–32 mm Hg. With increase in the left pump afterload, the pump power output varied from 1.64 to 2.37 W. The instantaneous motor power input varied from 22.6 to 30.6 W with the total system efficiency ranging from 6.7 to 9.4%. To date, 4 in vivo studies have been conducted for up to 12 h. Two animals survived 12 and 10 h, respectively. Termination was due to bleeding in 1 animal, vent tube obstruction in 1, and respiratory failure in 2. All animals died of technical failure. Another experiment is to be undertaken, and a newly designed cannula is now being manufactured.     

Ex Vivo Phase 1 Evaluation of the DeBakey/NASA Axial Flow Ventricular Assist Device

Abstract: A small ventricular assist device intended for long-term implantation has been developed by a cooperative effort between the Baylor College of Medicine and the NASA/Johnson Space Center. To date, in vitro tests have been performed to address hemolysis and pump performance issues. In this Phase 1 study, we assessed the durability and atraumatic features aiming for 2 day implantation. Eight pumps were implanted in 2 calves as paracorporeal left ventricular assist devices. The pump running times ranged from 18 to 203 h (78.1 ± 23.7; mean ± SEM). All the pump implantations were terminated because of thrombus formation. Plasma-free hemoglobin levels were below 13.7 mg/dl, except for 1 case complicated by inflow cannula obstruction. The pump speed was maintained between 10,100 and 11,400 rpm. Pump outputs were from 3.6 to 5.2 L/min. The electrical power required by the system ranged between 9 and 12 W. Clinically there was no detectable organ dysfunction noted, and postmortem evaluation demonstrated no pump related adverse effects in either calf except for small kidney infarctions. Thrombus deposition was observed mainly at the hub portions and the flow straightener.     

A Percutaneously Accessible Pulsatile Left Ventricular Assist Device: Modified Assist Device Type 5

Abstract: To provide percutaneous access, a new circulatory assist system was developed. We call this newly developed system the modified assist device (MAD). The system is composed of a sac-type blood pump and cannula. Inflow and outflow valves are mounted in the apex and at the side wall 10 cm from the apex of the cannula, respectively. During systole, the blood is sucked from the left ventricle through the inflow valve of the cannula connected to the blood pump, and during diastole, the blood is ejected to the root of the aorta through the outflow valve. In vitro and in vivo evaluations of the pump performance were performed. The maximum flow rate of 1.9 L/min was obtained in the mock circulatory system. In our animal experiment, effective systolic unloading and diastolic augmentation were observed by activation of this system during regular sinus rhythm. In conclusion, the MAD-5 is thought to be percutaneously accessible and increases systemic and coronary flow.