Development of an implantable high-energy and compact battery system for artificial heart

The purpose of this study was to demonstrate the feasibility of the use of an implantable, high-energy, and compact battery system for an undulation pump total artificial heart (UPTAH). The implantable battery system tested consists of six lithium-ion batteries in series, a charge unit, and a charge/discharge control unit. A lithium-ion battery is currently the best energy-storage device because it has more energy density, a better life cycle, and a smaller temperature rise than those of other secondary batteries. The performance of the implantable battery system was evaluated in an in vitro experiment using an electric load that simulated the UPTAH. Also, sufficiently reliable operation of a system for supplying energy to a UPTAH consisting of a transcutaneous energy transmission system (TETS) and an implantable battery system was confirmed in three experiments using goats. The results of the in vitro and in vivo experiments showed that the implantable battery system supplied sufficient current to the UPTAH for maintenance of physiological conditions in the goat with maximum rise in temperature to less than 43 degrees C.     

A New Transcutaneous Energy Transmission System With Hybrid Energy Coils for Driving an Implantable Biventricular Assist Device

Abstract:  We have developed a new transcutaneous energy transmission (TET) system for a totally implantable biventricular assist device (BVAD) system in the New Energy and Industrial Development Organization (NEDO) artificial heart project. The TET system mainly consists of an energy transmitter, a hybrid energy coil unit, an energy receiver, an internal battery system, and an optical telemetry system. The hybrid energy coil unit consists of an air-core energy transmission coil and an energy-receiving coil having a ferrite core. Internal units of the TET system are encapsulated in a titanium alloy casing, which has a size of 111 mm in width, 73 mm in length, and 25 mm in height. In in vitro experiments, the TET system can transmit a maximum electric energy of 60 Watts, and it has a maximum transmission efficiency of 87.3%. A maximum surface temperature of 46.1°C was measured at the ferrite core of the energy-receiving coil during an energy transmission of 20 Watts in air. The long-term performance test shows that the TET system has been able to operate stably for over 4 years with a decrease of energy-transmission efficiency from 85% to 80%. In conclusion, the TET system with the hybrid energy coil can overcome the drawback of previously reported TET systems, and it promises to be the highest performance TET system in the world.     

A Remotely Controlled and Powered Artificial Heart Pump

Abstract: An intrathoracic pulsatile artificial heart pump has been developed. Transcutaneous energy transfer and biotelemetry systems provide continuous power and remote monitoring and control, with no percutaneous connections required. The electrohydraulic system can be used either as a ventricular assist device or with modifications as a total artificial heart. The device uses a unidirectional axial flow pump coupled with a pressure activated one-way valve to allow hydraulic fluid to passively return to the volume displacement chamber during diastole. The transcutaneous energy transfer system provides power to the device and recharges the implantable battery pack. A wearable external controller and external battery pack provide the patient enhanced mobility and thus an improved quality of life. The biotelemetry system allows control and monitoring of the device after implantation, as well as an added capability to monitor and control the device remotely over public communication lines. Early prototypes have functioned failure free for up to 3 years in vitro. The device has sustained circulation in vivo for up to 4 days. Design optimization is continuing, and chronic in vivo evaluation is planned.     

Development of a ventricular assist device for out-of-hospital use.

BACKGROUND: Success with temporary ventricular assist devices, has prompted interest in devices developed for long term use outside of the hospital setting. METHODS: A totally implantable intrathoracic electro-hydraulic ventricular assist device has been developed. Design focused on providing the recipient with a near normal quality of life. To meet this goal the system utilizes transcutaneous energy transfer and biotelemetry to eliminate percutaneous drive-lines/cables as well as a displacement chamber capable of pressure equalization to atmospheric pressures, so as to eliminate the need for percutaneous venting. An implanted battery provides backup power to allow the recipient the ability to bathe, shower, or swim without connection to an external power source. An integrated telemedicine capability allows the device to be monitored/controlled remotely, using telephone lines. RESULTS: The system has been tested in vitro with early prototypes running for up to 5 1/2 years. The system was studied in calves (n = 25) with durations of support of up to 30 days, demonstrating the ability of the device to function as a totally implantable device without percutaneous connections. CONCLUSIONS: The various in vitro and in vivo studies have demonstrated the feasibility of the totally implantable device. Chronic in vivo experiments will follow in preparation for regulatory submissions for human use.     

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.     

Excitability changes in peripheral nerve fibers after repetitive electrical stimulation. Implications in pain modulation.

The Melzack-Wall gate control theory has been invoked to explain the peripheral analgesia resulting from repetitive electrical stimulation of peripheral nerve. This model emphasizes presynaptic inhibitory interactions among afferent fiber terminals in the spinal cord. An alternative explanation, that of velocity change in peripheral nerve fiber conduction, has been suggested by compound action potential studies from our laboratory. The present study was designed to extend this work, and to investigate the single fiber changes subsequent to brief (5- to 20-minute) periods of repetitive, high frequency (180 to 200/sec) electrical stimulation through an implantable peripheral nerve cuff device of the type used clinically for pain relief. Most fibers, regardless of their diameter (estimated from conduction velocity), show one or more of the following characteristics: a transient slowing of conduction velocity, an increase in electrical threshold and/or a decrease in response probability following a period of repetitive electrical stimulation. This supports the hypothesis that there are changes in direct peripheral nerve fiber excitability occurring under conditions simulating clinical electroanalgesia.     

An electric artificial heart for clinical use.

Advances in microelectronics, high-strength magnets, and control system design now make replacement of the heart using an implantable, electrically powered pump feasible. The device described herein is a compact, dual pusher plate unit with valved polyurethane sac-type ventricles positioned at either end. The power unit consists of a small, brushless direct current motor and a motion translator. A microprocessor control system is used to regulate heart beat rate and provide left-right output balance. Bench studies lasting for as long as 1 year have been performed. Heart replacement with the electric heart has been performed in 18 calves since 1984. The longest survivor lived for more than 7 months. Among the causes of termination were component failure, thromboembolic complications, and bleeding. No major problem has been identified that precludes prolonged use of the electric heart. In the future the patient with end-stage heart disease will have an electric artificial heart as one therapeutic option.     

Left Heart Bypass Using the Oscillated Blood Flow with Totally Implantable Vibrating Flow Pump

Abstract Aiming at a totally implantable ventricular assist device (VAD), a vibrating flow pump (VFP) was developed in Tohoku University. A transcutaneous energy transmission system (TETS) using an amorphous fiber was developed for the totally implantable VAD system. The VFP works with a higher frequency than the natural heart of a biological system, a frequency of 10–50 Hz. In this research, animal experiments on left heart bypass were performed with healthy goats. Blood from the apex of the left ventricle was received and was sent to the aorta so that an adequate supporting effect of the left heart was provided. In particular, the depression effect of the left ventricle was obvious. As a result, sufficient artificial heart flow was provided. For a totally implantable type VAD, left heart bypass of almost 100% may become necessary in some situations. Therefore, apex approaches of left heart bypass may be desirable. From an anatomical consideration, an apex of the heart is suitable for the VFP of this totally implantable type. In the left heart bypass for which the apex of the heart was used, an almost 100% bypass was possible. This is a requirement that is important when waiting for recovery of sufficient cardiac function. It is also important that left heart circulation is maintained fully by an artificial heart of the complete implantation type. The VFP was considered to be useful as a totally implantable type artificial heart from the results.     

Renewable energy management of an hybrid water pumping system (photovoltaic/wind/battery) based on Takagi–Sugeno fuzzy model

This research work presents an optimal energy management for a hybrid water pumping system driven by a photovoltaic generator (PVG) and a wind turbine. These two renewable energies are used as power generation sources, whereas a battery is added as an energy-storing system, for the purpose of controlling the power flow and providing a constant load supply. The proposed management system, serve to guarantee the pumping system autonomy in a rural region where's no access to the electrical network. As a result, a maximum power point tracking (MPPT) controller is created based on the fuzzy Takagi–Sugeno (TS) model, ensuring maximum power transfer to the moto-pump in spite of wind speed and insolation changes. The synthesis of MPPT control law involves TS fuzzy reference models which generate the desired trajectories to track. A supervisor has been developed for energy management and its major purpose is to effectively use the battery to satisfy the power load requirements, and that is by maintaining the state of charge (SOC) to extend the battery's life. Finally, simulation results have been done based on Matlab/Simulink with the aim of validating the efficiency of the proposed energy management supervisor.     

Evaluation of a laser Doppler flowmetry implantable fiber system for determination of threshold thickness for flow detection in bone

Laser Doppler flowmetry (LDF) with the use of a standard metal shafted probe, has been successfully used to study bone blood flow in a wide variety of settings. The use of the standard probe is limited by the requirement that the probe be replaced onto the bone surface or driven into the bone with a trocar. In response to this, a system of implantable, detachable fibers was developed. This system allows repeated measurement over time without repeated surgical manipulation of the area of interest. This study was performed to evaluate the implantable fiber system by determining threshold thickness for flow detection in bone. A flow chamber with perpendicular and end-on flow was designed to collect results under controlled conditions for flow detection. Threshold thickness for bovine cortical and cancellous bone samples was determined after sequentially grinding the specimens and placing them in the flow chamber. A 2% solution of latex circulated in the chamber and each specimen was exposed to both flow directions and both types of probe. The laser Doppler probe was able to detect flow by resting on top of the sample, with the latex on the other side of the sample. The results showed a significantly greater threshold thickness for the standard probes than for the implantable probes, and a significantly greater threshold thickness for trabecular bone than for cortical bone. Despite the reduced threshold thickness with the implantable fiber, this new system was able to consistently detect depth of perfusion of 80–90% of the values for the standard probe. The minimum value for threshold thickness in cortical bone with the implantable fiber was 2.43 mm. This was well within a clinically relevant range for flow detection. Threshold thickness and the LDF output were not affected by the flow direction. The study provides baseline information on the utility of this technique and demonstrates the potential usefulness of the implantable fiber system.     

Development of an implantable hearing aid using a piezoelectric vibrator of bimorph design: state of the art

A new, implantable hearing aid has been developed. An ultraminiature electric microphone placed under the skin of the external ear canal transduces sound waves into electrical impulses that are amplified with battery power. The amplified electrical impulses are fed into a piezoelectric vibrator directly in contact with the stapes. The vibrator transduces the electrical impulses into mechanical vibration with minimal consumption of electrical energy. Direct coupling of the vibrator to the stapes allows a high degree of fidelity in the perception of sound. The developmental process and the structure and function of each component are described together with clinical problems. Preliminary and tentative implantation of this new device during middle ear surgery indicated that it would be beneficial to patients who have suffered hearing loss from middle ear disease and whose condition does not lend itself to surgical correction.     

Application of focal cerebral cooling for the treatment of intractable epilepsy

Epilepsy is usually treated with medication, but adequate seizure control is still not achieved in over 30% of epilepsy patients, even with the best available agents. Surgical treatment is also performed for such patients, but is not always successful. Focal cooling of the brain using a thermoelectric device has recently been evaluated as an alternative to epilepsy surgery. Brain cooling was first proposed approximately 50 years ago as an effective method for suppressing epileptic discharges (EDs). Recent studies indicate that focal cooling of the brain to a cortical surface temperature of 20°C to 25°C terminates EDs without inducing irreversible neurophysiological dysfunctions or neuronal damage in the brain tissue. Several mechanisms have been proposed for the antiepileptic effects of focal cooling, including reduction in neurotransmitter release, alternation of activation-inactivation kinetics in voltage-gated ion channels, and the slowing of catabolic processes. Developments in the implantable cooling device with closed-loop cooling systems for seizure detection and focal cooling have been promoted in the field of neuromodulation, but several aspects remain uncharacterized concerning the hardware. Recent advances in precision devices have enabled the optimization of the implantable local cooling system, which may become clinically applicable in the near future.     

A novel method to reduce device-related infections in patients supported with the HeartMate device

Improved implantable left ventricular assist device technology has made survival to heart transplantation a near certainty. Nevertheless, infection remains a major risk to recipients of current percutaneous systems. We developed a modified implantation technique applied to the last 9 of 30 patients who received the HeartMate vented electric left ventricular assist system (LVAS). Covering the upper surface of the pump with a patch of knitted graft material was followed by a decline in the incidence of pocket infections from 33.3% to 11.1%. This modification compares favorably to that of a lengthened percutaneous driveline tunnel in reducing device-related infection.     

A study on an energy supply method for a transcutaneous energy transmission system

This study proposes a new type of a transcutaneous energy transmission system (TETS) that can supply electrical power for an implanted device without an external battery. In this system, the power is supplied from the floor to the shoes of the patients through coils that are set beneath the floor and the bottom of the shoes. If the patients wear the special shoes, they will be able to move freely on the specially designed floor without an external battery. Direct current (DC)-DC power efficiency was measured in the experiments, and the results showed that it varies with relative positions between the shoe and the floor coils. The results suggested that three-layered floor coils would enable the system to meet the demand for providing the required power anywhere on the floor without intermission. DC-DC power efficiency could be kept over 60% under the practical condition. It can then be concluded that the proposed system has a potential to provide better quality of life for the patients using a TETS.     

The artificial heart: present status and future prospects

Artificial heart (AH) and heart transplantation (HTx) are complementary means of cardiac assistance and replacement. Temporary use AH including ventricular assist systems (VASs) and total artificial hearts (TAHs) have been put into clinical use. VASs applied to 848 patients in the world and 187 in Japan with acute profound heart failure. The short-term survival rates are 23.3% and 27.3%, respectively. HTx has become an accepted therapeutic procedures. To date, 255 patients received VAS and 182 received TAH as a bridge to HTx, because the number of candidates exceeds the supply of donor hearts. Long-term implantable AH is the future alternatives for cardiac replacement. It is recognized that several key components will be necessary for development of an AH with high performance including biomaterial with antithrombogenecity and durability, an implantable actuator, a noninvasive monitoring system and sensors, a miniature auto-control system, and an energy converter. Another types of devices are on the horizon. These are a muscle-powered biomechanical AH, an AH powered by artificial muscle, and an integrated artificial heart-lung device. With remarkable progress in medicine and engineering, we can expect to see totally implantable permanent use cardiac assist and replacement devices as an alternative for HTx in the near future.     

Evaluation of an implantable motor-driven left ventricular assist device

A console based implantable motor-driven left ventricular assist device (LVAD) was developed and tested. Ten sheep weighing 42-73 kg (mean, 54.4 kg) were used as the experimental animals. Four animals survived 5-12 h (mean, 9.5 h). The mean pump flow was 1.63 L/min, ranging from 0.8 to 2.5 L/min. The cause of termination was respiratory failure in 3 animals, bleeding in 2, ventricular fibrillation in 2, vent tube obstruction in 1, thrombus formation in 1, and mechanical failure of the driving console in 1. Following the in vivo studies, the computer regulated controller was tested in a mock circulatory system. The LVAD provided 5.34 L/min of maximum output against a mean afterload of 80 mm Hg with a filling pressure of 15 mm Hg when the pump rate was 80 bpm in the fixed rate mode. With an increase in the pump afterload from 80 to 140 mm Hg, the total system efficiency varied from 7.81 to 8.34% when the pump preload was 15 mm Hg. An ultracompact, completely implantable electromechanical VAD has been under development. This device should fit in a 60 kg adult. As the next step, we are preparing to implant this ultracompact implantable VAD with an electronic controller in an animal model with better results being expected.     

Development of an Intravenous Membrane Oxygenator: Enhanced Intravenous Gas Exchange Through Convective Mixing of Blood around Hollow Fiber Membranes

Abstract: In vitro testing of a new prototype intravenous membrane oxygenator (IMO) is reported. The new IMO design consists of matted hollow fiber membranes arranged around a centrally positioned tripartite balloon. Short gas flow paths and consistent, reproducible fiber geometry after insertion of the device result in an augmented oxygen flux of up to 800% with balloon activation compared with the static mode (balloon off). Operation of the new IMO device with the balloon on versus the balloon off results in a 400% increase in carbon dioxide flux. Gas flow rates of up to 9. 5 L/min through the 14–cm–long hollow fibers have been achieved with vacuum pressures of 250 mm Hg. Gas exchange efficiency for intravenous membrane oxygenators can be increased by emphasizing the following design features: short gas flow paths, consistent and reproducible fiber geometry, and most importantly, an active means of enhancing convective mixing of blood around the hollow fiber membranes     

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.     

Technique for placement of an implantable venous access system

Increasingly complex programs of cancer chemotherapy have necessitated a system of reliable venous access that is relatively free of infectious complications. These criteria are met by the Porta-Cath, a totally implantable system consisting of an injection port and Silastic catheter. A technique for implantation of this device has been presented. It focuses on patient safety and comfort, ease of placement, and minimization of time and expense in the operating room.     

Design, development, and first in vivo results of an implantable ventricular assist device, MicroVad

The design concept and first in vitro and in vivo results of a long-term implantable ventricular assist device system based on a microaxial blood pump are presented. The blood-immersed parts of the pump consist of a single-stage impeller and a proximally integrated microelectric motor. Both parts are surrounded by a pump housing currently made of polycarbonate to allow visible access to the blood-exposed parts. A titanium inflow cage attached to the tip of the housing is directly implanted into the left ventricular apex. The outflow of the pump is connected to the descending aorta by means of an e-PTFE graft. The overall dimensions of the device are 12 mm in outer diameter and about 50 mm in length. The calculated lifetime of the device is up to 2 years. The system underwent long-term durability tests, hydraulic performance tests, dynamic stability tests, and in vitro hemolysis and thrombogenicity tests. Furthermore, animal tests have been performed in adult Dorset sheep. In a first series, the pump has been placed extracorporeally; in a second series, the pump was completely implanted. Mean duration of the animal experiments of the second series was 31 days (range 8-110 days, n=14); no anticoagulation was administered over the whole test period. Blood data revealed no significant changes in blood cell counts, ionogram, or any other value. No end-organ dysfunction induced by long-term support could be observed, nor did the pathology reveal any evidence of thromboembolic complications.