Electrohydraulic Total Artificial Heart Research Articles

Closing behavior of the mechanical heart valve in a total artificial heart.

Recently, cavitation on the surface of mechanical heart valves has been studied as a cause of fractures occurring in implanted mechanical heart valves. The cause of cavitation in mechanical heart valve was investigated in both 25-mm Björk-Shiley and 25-mm Medtronic Hall valves. The closing events of these valves in the mitral position were simulated in an electrohydraulic total artificial heart with a stroke volume of 85 ml. The tests were conducted under physiologic pressures at heart rates of 60, 70, 80, and 90 beats/min with cardiac outputs of 4.5, 5.5, 6.4, and 7.5 l/min, respectively. The disk closing behavior was measured by a laser displacement sensor. The closing behaviors were investigated under various atrial and aortic pressures. In both valves, the duration of closing decreased with an increase in the cardiac output. The greater the amount of atrial pressure, the shorter the closing duration of both valves. The maximum closing velocity of the Medtronic Hall monostrut valve ranged from 0.8 to 0.9 m/s, and that of the Björk-Shiley monostrut valve ranged from 0.73 to 0.78 m/s. In both valves, the maximum closing velocities were less than the reported cavitation thresholds. This suggests that there should be no possibility of occurrence of cavitation in an electrohydraulic total artificial heart with mechanical heart valve.

PROGRESS IN THE DEVELOPMENT OF THE ELECTROHYDRAURIC TOTAL ARTIFICIAL HEART AT NATIONAL CARDIOVASCULAR CENTER

We have been developing an electrohydraulic total artificial heart (EHTAH) system. The system consists of polyurethane-made diaphragm-type blood pumps, an electrohydraulic energy converter, an internal control unit, a transcutaneous energy transfer (TET) system, a transcutaneous optical telemetry (TOT) system, and an internal battery. The energy converter, placed outside the pericardial space, reciprocates and delivers hydraulic silicone oil to the alternate blood pumps through flexible oil conduits. The external diameter, the thickness and the weight of the energy converter were 76 mm, 47 mm and 720 g, respectively. The performance of the pumping unit was examined by in vitro experiment. The maximum efficiency of the unit was 26.1%. The pumping unit with an external controller has been implanted in 22 calves of as small as 54 kg. Eleven of 23 calves survived for more than a week. One of these lived for 6 weeks (42 days) and the other lived for over 8 weeks (60 days). Two of these lived for over 12 weeks (86 and 87 days) in good general condition. In the case of longest surviving animal, the cardiac output ranged between 6–8 L/min, the power consumption was 14 +/−3 W, and the average values of the left and right atrial pressures throughout the experimental period were 2 +/− 5 and 1 +/− 7 mm Hg, respectively. These results indicate that our EHTAH system has the potential to be a totally implantable system.

405 電気油圧式全人工心臓における Bjork-Shiley 人工弁開閉運動の計測

405 電気油圧式全人工心臓における Bjork-Shiley 人工弁開閉運動の計測

Current status of development and in vivo evaluation of the National Cardiovascular Center electrohydraulic total artificial heart system

We have been developing an electrohydraulic total artificial heart system. The system has a pumping unit, consisting of diaphragm-type blood pumps and an energy converter, and an electronics unit, consisting of an internal controller, an internal battery, and transcutaneous energy transfer and optical telemetry subunits. The energy converter, designed to be placed outside the pericardial space, reciprocates and delivers hydraulic silicone oil to the alternate blood pumps through a pair of flexible oil conduits. The left-right output balance is achieved with an interatrial shunt made in the composite atrial cuff. In vivo performance of the pumping unit has been evaluated by chronic implantation of 16 calves weighing 54–88 kg. Five calves survived for more than a week, and the longest-surviving animal lived for over 12 weeks until its accidental death. In this animal, a cardiac output of 6–81/min was maintained by the device with power consumption of 13.5±0.9W and 9%–11% efficiency. The left and right atrial pressures were 16±4 and 14±4 mm Hg, respectively, and the left-right output difference was adequately balanced with the interatrial shunt. The mixed venous oxygen saturation was 65±6% and the serum lactate level was 5±1 mg/dl, representing favorable oxygen metabolic conditions. The temperatures of the energy converter and the blood pump surfaces were 39.4±0.7° and 38.8±1.5°C, respectively, indicating that heat generation and dissipation were acceptable. The serum and tissue silicon levels were within normal (<1 μg/ml or <1 μg/g), indicating that permeation of silicone oil through the blood pump diaphragm was inconsequential and unlikely to be detrimental. We conclude that the system has the potential to be a totally implantable cardiac replacement.

Challenges in control of balanced cardiac output of a new electrohydraulic total artificial heart

Challenges in control of balanced cardiac output of a new electrohydraulic total artificial heart

Progress of an electrohydraulic total artificial heart system with a separate energy converter.

We have been developing an electrohydraulic total artificial heart (EHTAH) system. The system consists of diaphragm blood pumps, an abdominally placed energy converter, an internal controller, a transcutaneous energy transfer (TET) system, a transcutaneous optical information transfer system, and internal and external lithium-ion (Li-ion) batteries. The energy converter was optimized to obtain better oil transfer. Maximum cardiac output and efficiency of the EHTAH were increased from 8 L/min to 10 L/min and from 10% to 12%, respectively. The volume of the energy converter was reduced from 280 to 210 ml. The pumping unit was successfully implanted in 68-85 kg calves without anatomic problems, and the calves survived up to 10 days with good circulatory results. The maximum temperature rise of the implanted energy converter was only 1 degrees C. Stable performance of the TET system was confirmed in goats for more than 1 month. DC-DC energy transfer efficiency with 20 W of energy transmission remained within the range of 80% to 85%, and no significant temperature rise was observed in the implanted circuit. The internal Li-ion battery was also evaluated in a goat, and the maximum temperature rise during the charging period was 1.5 degrees C, while the charging and discharging times were 72 and 58 min, respectively. We conclude that our system has progressed in its development as a practical implantable system.

In vivo evaluation of the national cardiovascular center electrohydraulic total artificial heart.

We have been developing an electrohydraulic total artificial heart system. The system comprises an intrathoracic pumping unit composed of diaphragm type ellipsoidal blood pumps and an energy converter in addition to an electronics unit. The in vivo performance of the pumping unit was evaluated in a series of animal implantations with 3 calves weighing 62-85 kg. An interatrial shunt 4.5 mm in diameter was made in the atrial septum to compensate left-right imbalance. Two calves died early postoperatively, one of external controller power failure and the other of interatrial shunt stenosis due to thrombus formation. One calf, however, survived over 10 days under stable circulatory conditions. No abnormality was found in the oxygen metabolic condition or in major organ functions. The generation and dissipation of heat from the device was acceptable. This animal died of device malfunction caused by energy converter bearing breakdown. The device demonstrated a good anatomic fit without compromising the great vessels and adjacent tissues. It is concluded that the pumping unit has a sufficient in vivo basic performance although appropriate countermeasures are to be implemented against the detected problems concerning mechanical durability and interatrial shunt patency.

History of the Kolff Laboratory turbine driven electrohydraulic artificial heart.

The concept of an electrically powered total artificial heart has been pursued by Dr. Kolff and his associates since the 1960s. Since the 1980s these efforts have been concentrated upon the development of the electrohydraulic total artificial heart, a turbine pump powered by a brushless DC motor. Dr. Kolff realized the benefits of pulsatile flow and device response to Starling's Law, and these concepts have formed the basis of subsequent design decisions. Design iterations have both solved existing problems and exposed new challenges. The current device design is greatly improved over early attempts due to the incorporation of technologies that have recently become available as the result of progress in the fields of materials and electronics and due to the lessons learned over many years of research under the guidance of Dr. Kolff. This article describes, from its inception, the last major research project of Dr. Kolff prior to his retirement. The discussion centers around development, problems and their solutions, and the reasoning for given solutions.

Characterization and optimization of the flow pattern inside a diaphragm blood pump based on flow visualization techniques.

We applied two different flow visualization techniques to obtain detailed information on the inside flow of the diaphragm blood pump of our electrohydraulic total artificial heart system to determine the optimum washout effect that would result in better antithrombogenicity. Major orifice directions of the inflow and outflow Bjork-Shiley valves of the left blood pump were independently changed to create 17 varied patterns. The character and velocity of the main flow at the diaphragm-housing junction were acquired using a laser light sheet method with polyethylene tracers. Wall shear flow, a major factor governing washout in the blood pump, was estimated by a newly developed paint erosion method. In this method, quantitative evaluation for an index of washout effect was made by calculating the residual ratio of the paint on the blood pump inner surface at 30 sec of pumping. When a single circular flow was consistently observed by the laser light sheet method, the paint residual ratio become low, indicating washout was relatively good. At the lowest paint residual ratio, the center of the circular flow observed by the laser light sheet method was located at the geometric center of the blood chamber. In conclusion, the flow pattern inside the blood pump could be characterized by combined use of these two flow visualization techniques, and the significant role of circular flow in better washout was clarified.

In Vitro and In Vivo Evaluation of a Left-Right Balancing Capacity of an Interatrial Shunt in an Electrohydraulic Total Artificial Heart System

The authors evaluated the basic performance of an interatrial shunt (IAS) made by punching a hole in the atrial septum, in accommodating the left-right imbalance in our electrohydraulic total artificial heart (EHTAH) system. In an in vitro study conducted in a closed mock circuit connected with the EHTAH, the interatrial pressure gradient changed in compliance with the amount of bronchial flow and the size of the IAS. The IAS of 4.4 mm diameter or larger maintained the interatrial pressure gradient within physiologically permissible limits when the amount of bronchial flow was 5% of cardiac output or less. A left-to-right one-way valve made of a piece of pericardium, a possible option in this IAS method, successfully prevented right-to-left reverse shunt flow through the IAS. In a chronic in vivo study using a calf implanted with the EHTAH for 10 days, a 4.5 mm IAS without the one-way valve demonstrated satisfactory dynamic left-right balancing capacity with a stable interatrial pressure gradient of 4 +/- 1 mmHg over a wide range of atrial pressures. No thrombus was found in or around the IAS at autopsy. The authors conclude that the IAS is a simple and promising means of left-right balancing in the EHTAH system.

Early Changes in Circulating Blood Volume and Volume Regulating Humoral Factors After Implantation of an Electrohydraulic Total Artificial Heart

The early changes in circulating blood volume (CBV) and volume regulating humoral factors after implantation of an electrohydraulic total artificial heart (EH-TAH) were investigated in a calf and compared with results in a sham operated control calf. CBV was measured by the dye dilution method using indocyanine green. CBV and humoral factors were periodically investigated. In the EH-TAH implanted calf, the cardiac output was estimated at 6-7 L/ min (94-109 ml/kg/min), and the aortic pressure and aerobic metabolic condition were favorable. Nevertheless, the CBV was increased to 132 and 168% of the pre-operative value (range in the control calf, 83-103%) on post operative days 4 and 8, respectively. The atrial natriuretic peptide level on days 2, 5, and 7 was 23, 170, and 240 (in the control calf, 19-61) pg/ml, respectively, and the antidiuretic hormone level was 7.3, 2.0, and 1.3 (0.5-1.3) pg/ ml, respectively. The plasma renin activity was 3.2, 3.7, and 3.1 (0.5-0.3) ng/ml/hr, respectively. The angiotensin-I and angiotensin-II levels were also increased in the EH-TAH implanted calf. It is concluded that significant water retention occurs even at sufficient cardiac output early after EH-TAH implantation. The changes in humoral factors are suggested to arise secondary to the increased CBV or other unknown factors.

Development of a microcontroller-based automatic control system for the electrohydraulic total artificial heart.

An automatic physiological control system for the actively filled, alternately pumped ventricles of the volumetrically coupled, electrohydraulic total artificial heart (EHTAH) was developed for long-term use. The automatic control system must ensure that the device: 1) maintains a physiological response of cardiac output, 2) compensates for an nonphysiological condition, and 3) is stable, reliable, and operates at a high power efficiency. The developed automatic control system met these requirements both in vitro, in week-long continuous mock circulation tests, and in vivo, in acute open-chested animals (calves). Satisfactory results were also obtained in a series of chronic animal experiments, including 21 days of continuous operation of the fully automatic control mode, and 138 days of operation in a manual mode, in a 159-day calf implant.

Set-up, improvement, and evaluation of an electrohydraulic total artificial heart with a separately placed energy converter.

The authors have been developing an electrohydraulic total artificial heart (TAH) system with a separately placed electrohydraulic energy converter to minimize anatomic constraints in the pericardial space. Improvements to the system and current status of the development are reported. The energy converter was miniaturized to improve implantability, and its thickness was reduced to 54 mm. System efficiency was increased by suppressing rush current at the time of motor reversal. Maximum cardiac output of the TAH system was 9 L/min, and maximum system efficiency increased to 10%. The blood pump system was implanted easily in the body of a 57 kg calf, and no significant temperature rise on the energy converter surface was observed. As the next step, main components were integrated into a total system. The transcutaneous energy transfer system could supply power to the TAH without a decline in pump performance, and the internal battery could support the system at 6.5 L/min of cardiac output for 1 hour without a decrease in cardiac output. The authors consider the TAH system with a separately placed energy converter the most promising approach to development of a TAH for smaller sized patients.

Development of an electrohydraulic total artificial heart at the National Cardiovascular Center, Osaka, Japan.

The authors have been developing an electrohydraulic total artificial heart with a basic concept placing the blood pumps and an electrohydraulic energy converter separately, in the thorax and the abdominal region, respectively, to minimize anatomic constraints. Major problems of the system were a high energy consumption of 56 W at 6 L/min output and an insufficient maximum output of 6.7 L/min. The energy converter was redesigned to overcome these problems. A three phase, 4 pole brushless DC motor, which has maximum efficiency of 79% at a motor rotation of 2500 rpm with a load of 0.1 Nm, was developed for the new energy converter. Flow-channel design of the regenerative oil pump was optimized, which resulted in increasing the maximum flow rate at one directional motor rotation from 18 to 29 L/min. In vitro performance of the electrohydraulic total artificial heart was evaluated in a mock circulation with physiologic pressure conditions. Maximum output was increased to 10.7 L/min at a pump rate of 120 bpm and energy consumption of the motor at 6 L/min output was reduced to 18 W. Based upon these favorable results, the system is now being assembled for chronic animal implantation.

Noninvasive diagnosis of mechanical failure of the implanted total artificial heart using neural network analysis of acoustic signals.

Acoustic signal measurement has been proposed as a noninvasive method of detecting mechanical failure of the implanted total artificial heart. However, differences in acoustic spectra obtained from undamaged and damaged devices may be difficult to distinguish using standard techniques, such as visual inspection or statistical analysis. A new technique, artificial neural network analysis, which has been used successfully on other problems of pattern recognition and classification, was applied to improve the detectability of the acoustic method. Acoustic signals were measured using two different devices in one damaged and one undamaged electrohydraulic total artificial heart, both in a mock circulation set-up and in animal experiments where they were implanted in eight post mortem sheep and the acoustic signal measured using a microphone placed at the skin surface. Spectra of the acoustic waveforms were calculated by discrete Fourier transformation and 400 values (representing the log magnitude in each 2.5 Hz band of the spectrum between 0 and 1 kHz) and used as input to the neural network. A three layer backpropagation neural network containing 400 input nodes, 20 intermediate nodes, and one output node was able to forms. The trained neural network then perfectly distinguished damaged waveforms from undamaged ones, with good separability. Because the neural network's output can take on a value between two extremes denoting damaged and undamaged states, it is possible to detect any progressive failure at relatively earlier stages. With multiple output node configuration, it could also classify the different types of damage using single acoustic signal waveforms.

The Cleveland Clinic-Nimbus total artificial heart

We describe the design and in vitro testing of the Cleveland Clinic-Nimbus electrohydraulic permanent total artificial heart as it nears completion of development. The total artificial heart uses an electric motor and hydraulic actuator to drive two diaphragm-type blood pumps. The interventricular space contains the pump control electronics and is vented to an air-filled compliance chamber. Pericardial tissue valves and biolized blood-contacting surfaces potentially eliminate the need for anticoagulation. In vitro studies on a mock circulatory circuit demonstrated preload-sensitive control of pump output over the operating range of the blood pump: 70 to 160 beats/min and 5 to 9.6 L/min at right and left atrial pressures of 1.0 to 7.0 mm Hg and 5.0 to 12.0 mm Hg, respectively. The pump output was found to be insensitive to afterload over a range of 15 to 40 mm Hg mean pulmonary artery pressure and 60 to 130 mm Hg mean systemic pressure. The left master alternate control mode balanced the ventricular outputs during simulated bronchial artery shunting of up to 20% of cardiac output. A 10% to 15% right-pump, stroke-volume limiter balanced ventricular outputs during maximum output of 9.6 L/min. In response to a sustained increase in systemic venous return, the pump increased output by 2 L/min (29%) in 35 seconds. Thus the Cleveland Clinic-Nimbus total artificial heart meets the National Heart, Lung, and Blood Institute hemodynamic performance goals for devices being developed for permanent heart replacement. The biolized blood-contacting surfaces should decrease the risk of thromboembolism associated with circulatory assist devices.

The Cleveland Clinic-Nimbus total artificial heart

In vitro function of the Cleveland Clinic-Nimbus electrohydraulic total artificial heart met National Heart, Lung, and Blood Institute hemodynamic guidelines for such devices. In a series of in vivo experiments, we implanted the total artificial heart in eight calves (mean weight 87 kg), one for a short-term experiment and seven for long-term experiments. The mean blood flow during support was 7.7 +/- 1.6 L/min with left atrial pressure 13 +/- 6 mm Hg, right atrial pressure 13 +/- 4 mm Hg, and aortic pressure 97 +/- 9 mm hg. Maximum pump flow (9.6 L/min) occurred after 4 days of support as a result of the high resting cardiac output of the animals. A 10% to 15% right pump stroke-volume limit effectively balanced atrial pressures, and afterload insensitivity was confirmed by the in vivo studies. Calves tolerated treadmill exercise studies well, with an average duration of 22 minutes and an average top speed of 2.1 mph. The experiments were terminated after 1 day to 120 days of support (mean 32 days). Most experiments were terminated as a result of correctable mechanical problems. In a separate study of six adult human patients undergoing orthotopic cardiac transplantation, five showed an excellent fit for the Cleveland Clinic-Nimbus total artificial heart. Further studies using chest roentgenograms, chest measurements, and transesophageal echocardiography should help predict fit of the total artificial heart in potential candidates. Initial candidates for a "vented-electric" version of the Cleveland Clinic-Nimbus total artificial heart are patients for whom univentricular (left ventricular assist device) support is not appropriate, but who require mechanical support as a bridge to cardiac transplantation.

Chronic in vivo evaluation of an electrohydraulic total artificial heart.

Development of the Abiomed total artificial heart (TAH) designed for human use is progressing. Implant durations of longer than 60 days have been achieved in calves. The device consists of blood pumps, valves, and a hydraulic atrial flow balancing chamber fabricated from polyetherurethane. The energy converter, a centrifugal hydraulic pump with a rotary fluid switching valve, is positioned between the blood pumps. In two consecutive chronic in vivo studies (47 days and longer than 60 days), cardiac output was maintained in excess of 8 l/min. The atrial flow balancing chamber maintained a mean right-to-left pressure gradient of 7.5 and -1.4 mmHg in each respective study. There were no pulmonary complications. Platelet counts, fibrinogen concentrations, and hematocrit values returned to baseline levels within 20 days, whereas bilirubin, serum glutamic-oxaloacetic transaminase, blood urea nitrogen, and creatinine levels returned to normal within 1 week of implant. After the first post-operative day, plasma free hemoglobin levels of less than 10 mg/dl indicated no device-related hemolysis throughout the duration of the studies. At explant (47 day study), pathologic analysis showed no renal infarcts, no tissue necrosis, and no thermal damage. The device was fully encapsulated by 2-4 mm thick fibrous connective tissue. A newly designed textured-to-smooth surface inflow showed no signs of pannus ingrowth or thrombotic complications. These studies demonstrate that this TAH is suitable for long-term implantation.

Adaptive Full-Ejection Point Detection for Automatic Control of the Electrohydraulic Total Artificial Heart

An adaptive algorithm to detect full ejection points was developed for the automatic control of the electrohydraulic total artificial heart (EHTAH). To automatically control the EHTAH, systole in each ventricle is completed when a hyper-pressurization spike is detected on the oil side of that ventricle. A problem associated with the method of determining ventricular full ejection under variable afterload pressure is that a fixed level comparison method could fail to provide a normal full ejection condition. To increase system stability, safety, and efficiency, there is a definite need to vary the full ejection trigger level with changes in afterload. In this study, the full ejection trigger level for the current beat was changed based on the estimated afterload derived from the previous beat's pressure waveform. To increase this estimate's accuracy, an adaptive averaging window was used to determine which part of the previous pressure waveform would be used for the afterload estimation. With this enhanced control scheme, mock circulation tests with the EHTAH device demonstrated that estimated afterload tracked actual afterload. This scheme was also used successfully to control the EHTAH device implanted in three chronic calves.

Adaptive Full-Ejection Point Detection for Automatic Control of the Electrohydraulic Total Artificial Heart

Adaptive Full-Ejection Point Detection for Automatic Control of the Electrohydraulic Total Artificial Heart