Development of a totally implantable electromechanical total artificial heart: Baylor TAH

A totally implantable, one-piece, electrome-chanical total artificial heart (TAH) intended for permanent human use has been developed. It consists of left and right pusher-plate pumps (63 cc design stroke volume) sandwiching a thin center piece with a compact electromechanical actuator. The pusher-plates are shaped conically to accommodate an actuator in the space between them. The actuator consists of an efficient and durable planetary roller screw and direct current brushless motor. The left master alternate pumping mode was implemented utilizing the left pump pusher-plate position signal. The blood-contacting surface was coated with a dry gelatin to yield long-term clot-free performance. Trileaflet tissue valves of 27 and 23 mm are used in the inflow and outflow ports. The diameter and thickness of the TAH are 97 and 82 mm. the overall volume is 510 cc, and the weight is 620 g. Anatomic fit was confirmed in 26 heart transplant recipients (body weight 78 kg and surface area 2 m2) without compressing adjacent organs. The pump performance study revealed that the TAH can yield outputs of 3-8 L/min against the 100 mm Hg afterload with 1-10 mm Hg filling pressure. The input power to the motor ranged from 7 to 12 W, with an efficiency of 18% to 14%. A one-week in vivo calf study demonstrated adequate performance of the TAH, particularly the regulation of atrial pressures. Good anatomic fit and good biocompatibility were also demonstrated.     

Totally Implantable Total Artificial Heart and Ventricular Assist Device with Multipurpose Miniature Electromechanical Energy System

Abstract: A multipurpose miniature electromechanical energy system has been developed to yield a compact, efficient, durable, and biocompatible total artificial heart (TAH) and ventricular assist device (VAD). Associated controller-driver electronics were recently miniaturized and converted into hybrid circuits. The hybrid controller consists of a microprocessor and controller, motor driver, Hall sensor, and commutation circuit hybrids. The sizing study demonstrated that all these components can be incorporated in the pumping unit of the TAH and VAD, particularly in the centerpiece of the TAH and the motor housing of the VAD. Both TAH and VAD pumping units will start when their power line is connected to either the internal power pack or the external battery unit. As a redundant driving and diagnostic port, an emergency port was newly added and will be placed in subcutaneous location. In case of system failure, the skin will be cut down, and an external motor drive or a pneumatic driver will be connected to this port to run the TAH. This will minimize the circulatory arrest time. Overall efficiency of the TAH without the transcutaneous energy transmission system was 14–18% to deliver pump outputs of 4–9 L/min against the right and left afterload pressures of 25 and 100 mm Hg. The internal power requirement ranged from 6 to 13 W. The rechargeable batteries such as NiCd or NiMH with 1 AH capacity can run the TAH for 30–45 min. The external power requirement, when TETS efficiency of 75% was assumed, ranged from 8 to 18 W. The accelerated endurance test in the 42°C saline bath demonstrated stable performance over 4 months. Long-term endurance and chronic animal studies will continue toward a system with 5 years durability by the year 2000.     

Ultracompact, completely implantable permanent use electromechanical ventricular assist device and total artificial heart

An ultracompact, completely implantable permanent use electromechanical ventricular assist device (VAD) and total artificial heart (TAH) intended for 50-60 kg size patients have been developed. The TAH and VAD share a miniature electromechanical actuator that comprises a DC brushless motor and a planetary roller screw. The rotational force of the motor is converted into the rectilinear force of the roller screw to actuate the blood pump. The TAH is a one piece design with left and right pusher plate type blood pumps sandwiching an electromechanical actuator. The VAD is one half of the TAH with the same actuator but a different pump housing and a backplate. The blood contacting surfaces, including those of the flexing diaphragm and pump housing, of both the VAD and TAH were made of biocompatible polyurethane. The diameter, thickness, volume, and weight of the VAD are 90 mm, 56 mm, 285 cc, and 380 g, respectively, while those of the TAH are 90 mm, 73 mm, 400 cc, and 440 g, respectively. The design stroke volume of both the VAD and TAH is 60 cc with the stroke length being 12 mm. The stroke length and motor speed are controlled solely based on the commutation signals of the motor. An in vitro study revealed that a maximum pump flow of 7.5 L/min can be obtained with a pump rate of 140 bpm against a mean afterload of 100 mm Hg. The power requirement ranged from 4 to 6 W to deliver a 4-5 L/min flow against a 100 mm Hg afterload with the electrical-to-hydraulic efficiency being 19-20%. Our VAD and TAH are the smallest of the currently available devices and suitable for bridge to transplant application as well as for permanent circulatory support of 50-60 kg size patients.     

Augmented destruction test with an electromechanical pulsatile total artificial heart

The total artificial heart (TAH) being developed by these authors successfully completed hydrodynamic and hemolysis studies followed by two acute implantations. Before commencing preclinical studies on any device, documentation of the reliability and durability of each component has to be done. This TAH was submitted to a 4 month destruction test under the most severe driving conditions to detect any weak mechanical components of the system. The maximum dP-dt in the left pumping chamber was chosen of more than 15,000 mm Hg/s, which is almost 6 times higher than that of the normal driving condition. The pump was submersed into a water bath that was maintained at 37 degrees C. The TAH was driven in a left master alternative (LMA) variable rate mode at 8 L/min output flow, 15 mm Hg reload, 100 mm Hg left afterload, and 25 mm Hg right afterload. The outflow, pressures, and temperature inside the TAH were monitored. Several stress concentration areas were detected. The connection between the roller nut and support plate proved to be one of the most stressed regions, and a more reliable fixing procedure was required. This portion was redesigned to offer a durable connection. No malfunctions of the actuator or controller were detected throughout the testing duration. No temperature elevation more than 1 degree C on the center piece of the TAH was demonstrated.     

The E4T Electric Powered Total Artificial Heart (TAH)

The E4T is a totally implantable total artificial heart (TAH) resulting from many years of research work at the Cleveland Clinic Foundation (CCF) and Nimbus, Inc. It consists of four implanted subsystems: the pumping unit, the variable volume device, the transcutaneous transformer, and the internal battery. The pumping unit consists of two CCF biolized pusher plate pumps, and a Nimbus electrohydraulic energy converter. The control logic is based on a left master, alternating beating scheme. The timing difference between end right eject and end left fill determines the actuator speed adjustment. The pumps free fill, so left-right flow differences are easily accommodated. A prototype system has been built and begun testing to validate and refine the design details.     

The New Small Viennese Total Artificial Heart: Experimental and First Clinical Experiences

For bridging to transplantation, a new small total artificial heart (TAH) design has been developed. Function of the two membrane pumps (filling volume left: 87 ml, and right: 75 ml; four mechanical disc valves and screwed connectors) for orthotopic implantation were studied in calf experiments. A calf survival up to 180 days was achieved without problems by pumping with a rate of 117 +/- 2.4 beats/min and a cardiac output of 7.4 +/- 0.7 L/min. For bridging to transplantation, the New Small Viennese TAH was implanted into a small 45-year-old patient (height 160 cm, weight 75 kg) with end-stage coronary heart disease. The patient deteriorated suddenly [mean aortic pressure: 38 mm Hg; cardiac output (CO): 1.8-2.1 L/min; anuria and multiple organ failure] while waiting for a donor heart. Even though his pericardial space was not enlarged, no fitting problems appeared. By using pumping rates of 104.3 +/- 8.7 beats/min, a cardiac output of 5.8 +/- 0.63 L/min was achieved (free hemoglobin was 4.1 +/- 0.48 mg/dl). Even though blood circulation was reestablished, after a TAH duration of 12 days, multiple organ failure persisted, and TAH bridging had to be stopped. In November 1989, a 50-year-old deteriorating transplant candidate with idiopathic cardiomyopathy was bridged for 6 days. Adjusting the heart rate to 86.5 +/- 11.2 beats/min, a CO of 6.84 +/- 0.46 L/min was achieved (free hemoglobin was 5.9 +/- 1.7 mg/dl). Because of chronic liver dysfunction, the patient developed severe icterus while on the TAH, and it took 2 months after heart transplantation to achieve physiological bilirubin concentrations. The patient recovered fully and remains in excellent condition.     

The OregonHeart Total Artificial Heart: Design and Performance on a Mock Circulatory Loop

Widespread use of heart transplantation is limited by the scarcity of donor organs. Total artificial heart (TAH) development has been pursued to address this shortage, especially to treat patients who require biventricular support. We have developed a novel TAH that utilizes a continuously spinning rotor that shuttles between two positions to provide pulsatile, alternating blood flow to the systemic and pulmonary circulations without artificial valves. Flow rates and pressures generated by the TAH are controlled by adjusting rotor speed, cycle frequency, and the proportion of each cycle spent pumping to either circulation. To validate the design, a TAH prototype was placed in a mock circulatory loop that simulates vascular resistance, pressure, and compliance in normal and pathophysiologic conditions. At a systemic blood pressure of 120/80 mm Hg, nominal TAH output was 7.4 L/min with instantaneous flows reaching 17 L/min. Pulmonary artery, and left and right atrial pressures were all maintained within normal ranges. To simulate implant into a patient with severe pulmonary hypertension, the pulmonary vascular resistance of the mock loop was increased to 7.5 Wood units. By increasing pump speed to the pulmonary circulation, cardiac output could be maintained at 7.4 L/min as mean pulmonary artery pressure increased to 56 mm Hg while systemic blood pressures remained normal. This in vitro testing of a novel, shuttling TAH demonstrated that cardiac output could be maintained across a range of pathophysiologic conditions including pulmonary hypertension. These experiments serve as a proof‐of‐concept for the design, which has proceeded to in vivo testing.     

The Artificial Heart: Pursuit of a Noninvasive Method for Determining Atrial Pressures

The use of conventional open-port catheters in total artificial heart (TAH) research shortens the survival time of recipients owing to sepsis and embolism caused from the catheters. Valuable data are lost when an open-port catheter clots off, and transducer position must be keyed to the level of the atria for accuracy. The need for an accurate, easily obtainable, noninvasive method for measuring atrial pressure is of obvious value. Such a method has been developed in vitro using a device that measures the stroke volume of a pneumatic ventricle. The stroke volume is obtained by quantifying the amount of air exiting a pneumatic TAH in diastole. Using this information ventricular filling rates can be calculated by the stroke volume measurement device, and these rates are correlated to measured atrial pressures. There is no need to continually adjust transducer levels in relation to the atria with this system. The data show an average percentage error of 2.4 of full scale (25 mm Hg) or 0.6 mm Hg. The method of measurement is accurate, without limitations on driving parameters. The information is available without any additional prosthetic fabrication or surgical intervention than that already needed for basic TAH implantation. This method of measuring atrial pressures now needs to be proved effective in vivo.     

Hemolysis in an electromechanical driven pulsatile total artificial heart

A motor rotation in an electromechanically-driven pulsatile total artificial heart (TAH) may influence hemolysis. This study is designed to evaluate motor rotational conditions of the TAH and choose a suitable condition to obtain the least hemolytic characteristics. The TAH was driven in two motor rotational conditions: a constant motor rotational speed (rpm) mode (mode A) and a gradually increasing rpm mode (mode B). In these two modes, a maximum dP/dt value and a degree of hemolysis were measured and compared. The TAH was connected to an in vitro testing loop. In each mode, the TAH was driven with a fixed pumping rate of 100 bpm. A preload and an afterload were held at 15 and 100 mm Hg, respectively. The outflow of the TAH was maintained at 4.0 L/min. The maximum dP/dt in mode A and mode B was 5914 +/- 405 mm Hg/s and 2953 +/- 191 mm Hg/s, respectively. The NIH value obtained from mode A and mode B was 0.063 +/- 0.005 g/100 L and 0.026 +/- 0.003 g/100 L, respectively. The results demonstrated that the TAH driven in a gradually increasing rpm mode reduces both a maximum dP/dt value and a degree of hemolysis. The gradually increasing rpm mode is a suitable driving condition to obtain the least hemolytic characteristics.     

Prototype Development of an Implantable Compliance Chamber for a Total Artificial Heart

At our institute a total artificial heart is being developed. It is directly actuated by a linear drive in between two ventricles, which comprise membranes to separate the drive and blood flow. A compliance chamber (CC) is needed to reduce pressure peaks in the ventricles and to increase the pump capacity. Therefore, the movement of the membrane is supported by applying a negative pressure to the air volume inside the drive unit. This study presents the development of the implantable CC which is connected to the drive unit of the total artificial hearts (TAH). The anatomical fit of the CC is optimized by analyzing CT data and adapting the outer shape to ensure a proper fit. The pressure peaks are reduced by the additional volume and the flexible membrane of the CC. The validation measurements of change in pressure peaks and flow are performed using the complete TAH system connected to a custom mock circulation loop. Using the CC, the pressure peaks could be damped below 5 mm Hg in the operational range. The flow output was increased by up to 14.8% on the systemic side and 18.2% on the pulmonary side. The described implantable device can be used for upcoming chronic animal trials.     

Development of a Closed Air Loop Electropneumatic Actuator for Driving a Pneumatic Blood Pump

In this study, we developed a small pneumatic actuator that can be used as an extracorporeal biventricular assist device. It incorporated a bellows-transforming mechanism to generate blood-pumping pressure. The cylindrical unit is 88 ± 0.1 mm high, has a diameter of 150 ±  0.1 mm, and weighs 2.4 ± 0.01 kg. In vitro, maximal outflow at the highest pumping rate (PR) exceeded 8 L/min when two 55 mL blood sacs were used under an afterload pressure of 100 mm Hg. At a pumping rate of 100 beats per minute (bpm), maximal hydraulic efficiency was 9.34% when the unit supported a single ventricle and 13.8% when it supported both ventricles. Moreover, pneumatic efficiencies of the actuator were 17.3% and 33.1% for LVAD and BVAD applications, respectively. The energy equivalent pressure was 62.78∼208.10 mm Hg at a PR of 60∼100 bpm, and the maximal value of dP/dt during systole was 1269 mm Hg/s at a PR of 60 bpm and 979 mm Hg/s at a PR of 100 bpm. When the unit was applied to 15 calves, it stably pumped 3∼4 L/min of blood at 60 bpm, and no mechanical malfunction was experienced over 125 days of operation. We conclude that the presently developed pneumatic actuator can be utilized as an extracorporeal biventricular assist device.     

Is A Totally Implantable Artificial Heart Realistic?

Abstract: The incidence of local infection that occurred after the implantation of the intrathoracic Jarvik 7 total artificial heart (5–7 TAH) in patients was a major problem of this cardiac prosthesis. Infection rates increased when the 5–7 TAH was implanted for longer periods of time, which was contrary to the results that were obtained by the implantation of the left ventricular assist devices (LVAD) either in the abdominal cavity or in the abdominal wall. Currently, the general belief is that the implantation of a cardiac prosthesis inside of the chest cavity is not safe, due to higher rates of infection. Thus, Part I of this paper deals with the question: “Is a total artificial heart physiologically acceptable?” We believe structural differences of the J-7 TAHs and other LVADs are an important part of the problem. The J-7 TAH is a volumetrically dynamic pump, and the other LVADs are a volumetrically fixed stationary pump. Based upon experiences of this investigator, intrathoracic implantation of a smooth surface pulsating device (or a volumetrically dynamic pump) generated persistent local inflammatory reactive tissues directly adjacent to the device. These tissue capsules were nonadherent to the device, and therefore may produce an ideal environment for allowing bacteria to grow. The findings were opposite to those for a non-pulsating surface pump inside the chest cavity. Part II of this paper discusses the question: “Is a totally implantable artificial heart technically achievable?” Many technical probiems for the totally implantable TAH were already resolved during the development program of the totally implantable LVAD. However, there are three TAH specific problems that remain to be solved before achieving a clinically useful totally implantable TAH system. They are (a) antonical compatibilities of the TAH system; (b) reliable control of the TAH system, (c) reliable and effective long-term operation of the TAH system. We have resolved the anatomical problem by the integral design of the pump-actuator system. Overall size of the hard shell Baylor TAH system is 510 cm³ with a diameter of 97 mm and a width of 82 mm. Its stoke volume was reduced to 63 cm³. The stable and reliable control of TAH performances was established by the three sets of Hall effect sensors with left master alternate mode of pumping. No physiological parameter was used as a feedback signal. Reliable long-term operation of the TAH system was established by the electromechanical actuation system. A simple drive mechanism with commercially available components and subsystems was used. Components are chosen from those already of proven reliability and long life. Blood compatible features was established by dry biolized coating for the blood contacting surface of the pump. The preceding features of the totally implantable TAH make this author believe that a totally implantable artificial heart is realistic and achievable within the not too far distant future.     

Auxiliary Total Artificial Heart: A Compact Electromechanical Artificial Heart Working Simultaneously with the Natural Heart

Leading international institutions are designing and developing various types of ventricular assist devices (VAD) and total artificial hearts (TAH). Some of the commercially available pulsatile VADs are not readily implantable into the thoracic cavity of smaller size patients because of size limitation. The majority of the TAH dimensions requires the removal of the patients' native heart. A miniaturized artificial heart, the auxiliary total artificial heart (ATAH), is being developed in these authors' laboratories. This device is an electromechanically driven ATAH using a brushless direct current (DC) motor fixed in a center metallic piece. This pusher plate-type ATAH control is based on Frank-Starling's law. The beating frequency is regulated through the change of the left preload, assisting the native heart in obtaining adequate blood flow. With the miniaturization of this pump, the average sized patient can have the surgical implantation procedure in the right thoracic cavity without removing the native heart. The left and right stroke volumes are 35 and 32 ml, respectively. In vitro tests were conducted, and the performance curves demonstrate that the ATAH produces 5 L/min of cardiac output at 180 bpm (10 mmHg of left inlet mean pressure and 100 mm Hg of left outlet mean pressure). Taking into account that this ATAH is working along with the native heart, this output is more than satisfactory for such a device.     

Development of the Undulation Pump Total Artificial Heart

Abstract: The undulation pump is a small size continuous flow displacement type blood pump that has been developed for an artificial heart. Using undulation pumps. 2 types of implantable total artificial hearts (TAHs), the undulation pump TAH (UPTAH) type 1 (UPTAH 1) and UPTAH type 2 (UPTAH 2) were developed. Both UP-TAHs were designed to be small enough to implant into the chest of a goat, the experimental animal. UPTAH 1 could be reduced in size to 75 mm in diameter and 78 mm in length. The weight was 520 g. UPTAH 2 could be reduced in size to 75 mm in diameter and 80 mm in length. The weight was 650 g. UPTAH 2 could be tested in an animal experiment using an adult female goat weighing 52.3 kg. The UPTAH 2 could be implanted successfully into the goat's chest with a good fit. The goat stood after the surgery and extubation and survived for 3 h and 40 min; thus, the potential of the UPTAH for a practical implantable TAH was demonstrated.     

The Significance and Prevention of Air Emboli with the Total Artificial Heart

Abstract: Embolism remains a significant complication of the total artificial heart (TAH). The ineffectual deairing of the TAH can allow embolization of the retained air. The standard needle aspiration of TAH air (Group A) was compared with a new protocol (Group B) that included standard needle TAH aspiration plus simultaneous pumping of the TAH against an occluded ascending aorta and main pulmonary artery with vacuum applied to a needle in the proximal aorta and pulmonary artery. There were 4 calves in each group. There was no premortem evidence of systemic or pulmonary emboli. Both groups of animals were electively terminated less than 2 weeks postoperatively. Postoperative mean aortic and pulmonary artery pressures were recorded for each animal. Animals in Group B had a significant decline in pulmonary artery pressures (43 ± 12 vs. 33 ± 8 mm Hg) 1 h after TAH implantation when compared with Group A. All other aortic and pulmonary artery pressure differences between Groups A and B were not statistically significant within 24 h of the operation. Group A animals had a 75% incidence, and Group B animals had 100% incidence of TAH thrombus. This very small thrombus was found exclusively at the inflow valve-TAH housing interface. Evaluation of the kidneys postmortem was used to identify embolic injury. All animals in Group A had evidence of acute, hemorrhagic injury, but none of the Group B animals had similar injury. Half of the animals in each group had small, fibrotic chronic renal cortical injury, which did not develop during TAH implantation. The more vigorous deairing protocol (Group B) significantly decreased early postoperative pulmonary hypertension. The absence of acute hemorrhagic renal injuries appeared to be associated with improved TAH deairing. Chronic renal injuries were not associated with the TAH, which makes them poor indicators of TAH emboli. Improved TAH deairing can provide beneficial effects for the recipient.     

Implantable Control, Telemetry, and Solar Energy System in the Moving Actuator Type Total Artificial Heart

The moving actuator type total artificial heart (TAH) developed in the Seoul National University has numerous design improvements based upon the digital signal processor (DSP). These improvements include the implantability of all electronics, an automatic control algorithm, and extension of the battery run-time in connection with an amorphous silicon solar system (SS). The implantable electronics consist of the motor drive, main processor, intelligent Li ion battery management (LIBM) based upon the DSP, telemetry system, and transcutaneous energy transmission (TET) system. Major changes in the implantable electronics include decreasing the temperature rise by over 21°C on the motor drive, volume reduction (40 × 55 × 33 mm, 7 cell assembly) of the battery pack using a Li ion (3.6 V/cell, 900 mA · h), and improvement of the battery run-time (over 40 min) while providing the cardiac output (CO) of 5 L/min at 100 mm Hg afterload when the external battery for testing is connected with the SS (2.5 W, 192 · 192, 1 kg) for the external battery recharge or the partial TAH drive. The phase locked loop (PLL) based telemetry system was implemented to improve stability and the error correction DSP algorithm programmed to achieve high accuracy. A field focused light emitting diode (LED) was used to obtain low light scattering along the propagation path, similar to the optical property of the laser and miniature sized, mounted on the pancake type TET coils. The TET operating resonance frequency was self tuned in a range of 360 to 410 kHz to provide enough power even at high afterloads. An automatic cardiac output regulation algorithm was developed based on interventricular pressure analysis and carried out in several animal experiments successfully. All electronics have been evaluated in vitro and in vivo and prepared for implantation of the TAH. Substantial progress has been made in designing a completely implantable TAH at the preclinical stage.     

Mock Circulation Loop to Investigate Hemolysis in a Pulsatile Total Artificial Heart

Hemocompatibility of blood pumps is a crucial parameter that has to be ensured prior to in vivo testing. In contrast to rotary blood pumps, a standard for testing a pulsatile total artificial heart (TAH) has not yet been established. Therefore, a new mock circulation loop was designed to investigate hemolysis in the left ventricle of the ReinHeart TAH. Its main features are a high hemocompatibility, physiological conditions, a low priming volume, and the conduction of blood through a closed tubing system. The mock circulation loop consists of a noninvasive pressure chamber, an aortic compliance chamber, and an atrium directly connected to the ventricle. As a control pump, the clinically approved Medos‐HIA ventricular assist device (VAD) was used. The pumps were operated at 120 beats per minute with an aortic pressure of 120 to 80 mm Hg and a mean atrial pressure of 10 mm Hg, generating an output flow of about 5 L/min. Heparinized porcine blood was used. A series of six identical tests were performed. A test method was established that is comparable to ASTM F 1841, which is standard practice for the assessment of hemolysis in continuous‐flow blood pumps. The average normalized index of hemolysis (NIH) values of the VAD and the ReinHeart TAH were 0.018 g/100 L and 0.03 g/100 L, respectively. The standard deviation of the NIH was 0.0033 for the VAD and 0.0034 for the TAH. Furthermore, a single test with a BPX‐80 Bio‐Pump was performed to verify that the hemolysis induced by the mock circulation loop was negligible. The performed tests showed a good reproducibility and statistical significance. The mock circulation loop and test protocol developed in this study are valid methods to investigate the hemolysis induced by a pulsatile blood pump.     

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.     

A ferrofluidic actuator for an implantable artificial heart

The feasibility of using a ferrofluidic actuator for an artificial heart was studied. A ferrofluidic actuator directly drives magnetic fluids simply by applying a magnetic field to the ferrofluids and does not require a bearing. Magnetic fluid in a U-shaped glass cylinder was placed in an air gap of a solenoid. When a magnetic flux of 0.32 T was applied to the interface of the ferrofluid and air, the ferrofluid was displaced and a pressure of 7.58 kPa (57 mm Hg) was obtained. An array of three poles of solenoids was mounted near the U-shaped glass cylinder. The solenoids were sequentially activated and deactivated. A pressure of 9.98 kPa (75 mm Hg)/-1.33 kPa (-10 mm Hg) was obtained. Calculations indicate that a magnetic flux of 0.49 T is enough to obtain a pressure of 13.3 kPa (100 mm Hg). A ferrofluidic actuator is promising for use with an implantable artificial heart.     

Implantation of the Total Artificial Heart by Lateral Thoracotomy

Progress in the techniques for surgical implantation of the artificial heart has progressed in parallel with the technology and design of the prosthesis. In the author's first experience with total artificial heart (TAH) implantation (1968) a trans-sternal split was used opening the sixth intercostal space on the right side across the sternum to the left space. This obviously was not the optimum approach but the complexity, design and size of the prosthesis required maximum exposure of the atria and great vessels. Subsequently the mid-sternal split incision was used. The Dacron fibril coated silicone rubber 8 cm Kwan-Gett ventricles implanted by the mid-sternal split sustained a calf for 14 days in 1972. A calf with the improved Jarvik 3 ventricles fabricated with the same material and implanted via mid-sternal split survived 19 days in early 1973. The surgical techniques for lateral (right) thoracotomy were adopted in this laboratory in 1973. These techniques were applicable only when the prosthesis fit better in the chest. This procedure has been adopted by other laboratories replacing the natural heart of the calf with a TAH. This report describes in detail the stepwise procedure for implantation of the total artificial heart by a lateral thoracotomy in the calf.