Numerical estimation of heat distribution from the implantable battery system of an undulation pump LVAD

We have been developing an implantable battery system using three series-connected lithium ion batteries having an energy capacity of 1800 mAh to drive an undulation pump left ventricular assist device. However, the lithium ion battery undergoes an exothermic reaction during the discharge phase, and the temperature rise of the lithium ion battery is a critical issue for implantation usage. Heat generation in the lithium ion battery depends on the intensity of the discharge current, and we obtained a relationship between the heat flow from the lithium ion battery q_c(I) and the intensity of the discharge current I as q_c(I) = 0.63 × I (W) in in vitro experiments. The temperature distribution of the implantable battery system was estimated by means of three-dimentional finite-element method (FEM) heat transfer analysis using the heat flow function q_c(I), and we also measured the temperature rise of the implantable battery system in in vitro experiments to conduct verification of the estimation. The maximum temperatures of the lithium ion battery and the implantable battery case were measured as 52.2°C and 41.1°C, respectively. The estimated result of temperature distribution of the implantable battery system agreed well with the measured results using thermography. In conclusion, FEM heat transfer analysis is promising as a tool to estimate the temperature of the implantable lithium ion battery system under any pump current without the need for animal experiments, and it is a convenient tool for optimization of heat transfer characteristics of the implantable battery system.     

Implantable total artificial heart: history and present status at the University of Tokyo

The University of Tokyo has been involved in research and development of the artificial heart since 1959. This paper is a brief review of 40 years of total artificial heart research in the University of Tokyo. Many types of artificial heart and various kinds of materials, blood pumps, valves, drive units, control methods, and pathophysiology have been investigated in our original fashion. The longest survival was 532 days for a goat with a total artificial heart (TAH) placed on the chest wall. These results made us take a step toward the development of an implantable TAH. Two kinds of implantable TAH are now being developed: FTPTAH (flow-transformed pulsatile total artificial heart) and UPTAH (undulation pump total artificial heart). Recently, a goat survived for 31 days with an UPTAH.     

Design of the solar cell system for recharging the external battery of the totally-implantable artificial heart

The solar cell as the advanced alternative energy resource was found to be acceptable for increasing battery running time of the totally-implantable artificial heart. A sample of the wireless charging system with solar cell base gives a maximum battery running time around 9 hours and some physical and psychological freedom to the patient. This improvement will assist the application of the implantable artificial heart for a longer period of time and with added convenience to the recipient.     

Mechanical circulatory support devices for bridge to heart transplantation, bridge to recovery, or destination therapy

Both the ventricular assist device (VAD) and the total artificial heart (TAH) have been effective in supporting circulation of end-stage cardiac patients and in bridging to heart transplantation. However, because of a shortage of donor hearts and age limitations, destination therapy with the completely implantable VAD has also been started. The totally implantable TAH in the United States is in the final stage of development and will go into preclinical trials in 2004. In Japan, heart transplantation has been re-instituted since last year, but because of shortages of donor hearts the waiting time prior to transplantation is fairly long. To date, six heart transplantations have been carried out, of which four have been bridged transplantations, using extracorporeal or implantable VADs. With the extracorporeal VADs, patients cannot be discharge home, which increases the hospital expenses. With the implantable VADs such as Novacor and HeartMate imported from the USA, patients can be discharged home, but major threats with these devices are thromboembolic, complications and infection. These devices are also fairly large, being designed for 80-kg patients, and are thus difficult to implant in patients of 50 to 60 kg, including women. Because of these limitations, there is a strong clinical demand for a compact, high-performance, implantable, permanent-use VAD. This paper addresses the current status of the artificial heart research and development program at the Tokyo Medical and Dental University, which was started in May 1999.     

A tester for nickel cadmium defibrillator batteries

A microprocessor-controlled tester for nickel cadmium batteries is described. This versatile instrument allows up to three cycles of charge and discharge to be performed automatically, with results presented in hard-copy form. The tester determines whether defective cells are present in a battery by comparing the discharge characteristics with previously established values. Batteries can also be discharged in a way which simulates their use in defibrillators.     

Recording vagal nerve activity for the control of an artificial heart system

Monitoring cardiovascular control system information is important in considering the quality of life (QOL) of patients with artificial hearts. Natural heart circulation is controlled by an autonomic nervous system. Therefore, it is desirable to record autonomic nerve activity for the control of artificial heart systems. We directly recorded vagal nerve activity in long-term animal experiments. Six healthy adult goats were anesthetized with halothane inhalation, and thoracotomy was performed with the fourth rib resection during mechanical ventilation. Arterial blood pressure and right and left atrial pressures were continuously monitored with an inserted catheter. Cardiac output was measured by an electromagnetic flow meter attached to the ascending aorta. After the chest was closed, an incision was made in the left neck, and the left vagal nerve was separated. Stainless steel electrodes were inserted into the vagal nerve and fixed by a plasticizer. After the incision was closed, the goats were transferred to a cage and extubated after waking. Vagal nerve activity was measured using hemodynamic parameters when the animals were awake. Our results show that clear observation of autonomic nerve discharge was made through this experimental system for over 1 month. The tonus of the vagal nerve was significantly altered before body motion with hemodynamic changes, suggesting the possibility of prediction. These results suggest that information from autonomic nerves may help to control implantable artificial hearts or ventricular assist devices.     

Optimizing the tensile properties of polyvinyl alcohol hydrogel for the construction of a bioprosthetic heart valve stent

Although bioprosthetic heart valves offer the benefits of a natural opening and closing, better hemodynamics, and avoidance of life-long anticoagulant therapy, they nevertheless tend to fail in 10-15 years from tears and calcification. Several authors, including the present ones, have identified the rigid stent as a factor contributing to these failures. The ultimate solution is an artificial heart valve that has mechanical properties that allow it to move in conformity with the aortic root during the cardiac cycle, has superior hemodynamics, is nonthrombogenic, will last more than 20 years, and mitigates the need for anticoagulants. We have identified a polymer, polyvinyl alcohol (PVA) hydrogel, that has mechanical properties similar to soft tissue. The purpose of this research is to match the tensile properties of PVA to the porcine aortic root and to fabricate a stent prototype for a bioprosthetic heart valve with the use of the PVA hydrogel. Specimens of 15% w/w PVA were prepared by processing through 1-6 cycles of freezing (-20 degrees C) at 0.2 degrees C/min freeze rate and thawing (+20 degrees C) at different thawing rates (0.2 degrees C/min and 1 degrees C/min), for different holding times (1 and 6 h) at -20 degrees C. Subsequently tensile tests and stress-relaxation tests were conducted on the specimens. The different holding times at -20 degrees C demonstrated no difference in the result. The slower thawing rate improved the tensile properties but did not produce significant changes on the stress-relaxation properties. The nonlinear stress-strain curve for the PVA after the fourth freeze-thaw cycle matched the porcine aortic root within the physiological pressure range. The stress-relaxation curve for PVA also approximated the shape of the aortic root. The complex geometry of an artificial heart valve stent was successfully injection molded. These results, in combination with other preliminary findings for biocompatibility and fatigue behavior, suggest that PVA hydrogel is a promising biomaterial for implants, catheters, and artificial skin.     

Differential pattern of sympathetic outflow during upper airway stimulation with smoke

This study investigates directly the possibility that sympathetic discharge to the heart is decreased while it is increased to other organs during upper respiratory perfusion with cigarette smoke. Blood pressure (BP), heart rate, ECG, and respiratory movements were monitored in urethane-anesthetized rabbits. Insertion of two cannulas allowed respiration of room air while passing smoke across the upper respiratory irritant receptors and out through the nares. Through a retroplural incision, the left stellate ganglion was exposed and a cardiac branch isolated. Similarly, a left renal nerve was isolated. Multiunit nerve recordings were obtained from both nerves. In four control animals, cigarette smoke (50 ml) caused apnea, bradycardia (-116 beats/min) and increased BP (33 mmHg). Activity in the renal nerve increased (248% of control [C]) and activity in the cardiac nerve was reduced (62% C). In these animals after Flaxedil and artificial respiration, nerve activity responses were still pronounced (renal, 178% C; cardiac, 66% C). In four other barodenervated animals neural responses to smoke were similar to those observed with baroreceptors intact (renal, 211% C; cardiac, 51% C). In these animals after artificial ventilation and Flaxedil, responses were not significantly changed. These results indicate that smoke stimulation causes a differential pattern of sympathetic discharge. The responses observed cannot be accounted for by secondary adjustments through arterial baroreceptors, chemoreceptors, or pulmonary stretch receptors.     

A portable pneumatic driving unit for a left ventricular assist device

The authors developed a portable air driving unit for an artificial heart. As the portable energy source of the driver, a commercially available Ni-Cd battery was used. A linear compressor was selected as a portable size compressor. To reduce the number of parts to be assembled, a new type of pneumatic system was employed. In this system, the pressure level was regulated by varying the output flow rate of the compressor instead of using a pressure regulator and large air reservoirs. A one-board microcomputer and pressure sensors were used to control the pressure level. The total weight of the unit is 9.5 Kg. After assembling the components into the portable unit, a blood pump was connected to examine the output characteristics of the system. It was confirmed that the unit could drive the blood pump continuously for more than 2 hours under the following conditions: output flow rate of the blood pump = 5 L/min and output pressure = 100 mmHg.     

Nickel‐Salen Type Polymers as Cathode Materials for Rechargeable Lithium Batteries

The nickel salen‐type redox polymers represent an interesting class of organometallic polymers frequently used in hybrid supercapacitor electrodes as thin films and carbon material composites. However, the suitability of these compounds for application as electrode materials for rechargeable batteries has not yet been tested. In this study, redox processes in monocomponent electrodes based on a series of nickel salen‐type redox polymers are investigated in 1 m LiPF₆ in 1:1 ethylene carbonate (EC)/diethyl carbonate (DEC) electrolyte in a Li‐ion battery. The oxidation potentials for polymer complexes of nickel exceed 3.5 V versus Li/Li⁺, which enhances specific energy. It is found that introduction of a proper substituent in the phenyl ring of the ligand allows to fabricate additive‐free electrodes which demonstrate high charge/discharge rate performance with the capacity on discharge at 10C being up to 73% of the capacity obtained at discharge at 1C , which corresponds to maximum power of 2.6 kW kg⁻¹.     

TEMPO‐Contained Polymer Grafted onto Graphene Oxide via Click Chemistry as Cathode Materials for Organic Battery

Poly(2,2,6,6‐tetramethylpiperidin‐1‐oxyl‐4‐yl methacrylate) (PTMA) is a typical organic battery material containing nitrogen and oxygen radicals. The grafting of PTMA onto graphene oxide to obtain composite cathode material poly(2,2,6,6‐tetramethylpiperidin‐1‐oxyl‐4‐yl methacrylate)‐Graphene Oxide (PTMA‐GO) via click chemistry is reported. The method of preparing PTMA‐GO is completed at room temperature, which can retain the oxygen‐containing functional groups on the surface of graphene oxide, and the process is simple and easy to conduct. The composite materials are characterized by infrared, X‐ray diffraction, thermogravimetry, and electron paramagnetic resonance. The cathode material is assembled in a button battery to measure its cyclic voltammogram, electrochemical impedance spectroscopy, and charge and discharge capacity cycles. It is found that the PTMA‐GO electrode is twice as conductive as the PTMA electrode alone. The specific capacity of the PTMA‐GO electrode is nearly 2.3 times higher than that of the PTMA electrode after 300 charge–discharge cycles. This represents an important reference value for the development of organic batteries, especially for the research of nitroxide radical polymer electrode materials.     

A case of conversion of a NIPRO ventricular assist system to an EVAHEART left ventricular assist system

Bridge to bridge (BTB) is a promising strategy for the treatment of end-stage heart failure that involves the left ventricular assist system (LVAS). We describe our experience with the conversion of an extracorporeal ventricular assist system (VAS), the NIPRO VAS, to an implantable LVAS, the EVAHEART LVAS. A 32-year-old man underwent a NIPRO VAS implantation as a bridge to decision for a condition consistent with Interagency Registry for Mechanically Assisted Circulatory Support profile 1. He was later diagnosed with secondary cardiomyopathy due to cardiac sarcoidosis. During the period in which he had NIPRO VAS support, no significant bacterial cultures were obtained from the cannula-piercing site, and no systemic infection occurred. Approximately 5 months after the NIPRO VAS implantation, he underwent an EVAHEART LVAS implantation as a BTB. The procedure required technical modifications, including the anastomosis of outflow grafts, trimming of the apical cuff, and creation of a pump pocket. The operation was completed uneventfully. The patient completed the discharge program for awaiting heart transplantation at home. Approximately 6 months after the EVAHEART LVAS implantation, he continues to do well without any complications, including infection, and visits our hospital as an outpatient. Conversion to an implantable LVAS can be beneficial in carefully selected patients after ascertaining the operative indications and operation timing.     

Development of an intracorporeal Thoratec ventricular assist device for univentricular or biventricular support

There is a need for a small, simple, and versatile intracorporeal ventricular assist device (IVAD) as an alternative to the large implantable electromechanical LVAD systems in current use. Because the basic design of the Thoratec paracorporeal VAD has been demonstrated in over 1,000 patients, weighing from 17 to 144 kg, and for durations up to 515 days including patient discharge (by using the portable driver), we are developing a new intracorporeal version of our VAD. This IVAD has a smooth contoured, polished titanium housing, and maintains the same blood flow path and Thoralon polyurethane blood pumping sac as the paracorporeal VAD. The IVAD is controlled with the Thoratec TLC-II Portable VAD Driver, which is a small briefcase sized, battery powered, pneumatic control unit. Intracorporeal LVADs and/or RVADs are implanted in a preperitoneal position, with a single small (9 mm OD) percutaneous pneumatic driveline for each VAD. The major advantages of the new IVAD design are size and simplicity. The IVAD weight (339 g) and implanted volume (252 ml) are substantially smaller than current implantable electromechanical LVAD systems. Only the small blood pump is implanted, leaving the more complex control unit external, where it can be serviced and replaced. The versatile design is intended for left and/or right heart support in large or small patients. The IVAD in combination with the TLC-II portable driver will be a viable and attractive alternative to large, implanted electromechanical systems.     

Bipolar implantable stimulator for long-term denervated-muscle experiments

A micropower bipolar implantable stimulator has been developed and tested for long-term (four weeks-six months) use in experiments involving the stimulation of denervated skeletal muscle. Implantable stimulators are typically operated from a single lithium battery at 3 V. After the first week of denervation, stimulation of denervated muscles of rats requires voltages in the range of 6–12 V. The stimulator described can deliver voltages up to 15 V, with variable pulsewidth, frequency and duty cycle. All stimulation parameters are set prior to implantation by selection of appropriate resistors and capacitors. Each primary failure mode for implantable stimulators is addressed. Long-term reliability rates in excess of 95% are achievable if the construction details are followed closely. Methods for battery power management, circuit component selection, electrode construction and encapsulation are described in detail. This device is not intended for use in humans.     

Biventricular Assist Devices: A Technical Review

The optimal treatment option for end stage heart failure is transplantation; however, the shortage of donor organs necessitates alternative treatment strategies such as mechanical circulatory assistance. Ventricular assist devices (VADs) are employed to support these cases while awaiting cardiac recovery or transplantation, or in some cases as destination therapy. While left ventricular assist device (LVAD) therapy alone is effective in many instances, up to 50% of LVAD recipients demonstrate clinically significant postoperative right ventricular failure and potentially need a biventricular assist device (BiVAD). In these cases, the BiVAD can effectively support both sides of the failing heart. This article presents a technical review of BiVADs, both clinically applied and under development. The BiVADs which have been used clinically are predominantly first generation, pulsatile, and paracorporeal systems that are bulky and prone to device failure, thrombus formation, and infection. While they have saved many lives, they generally necessitate a large external pneumatic driver which inhibits normal movement and quality of life for many patients. In an attempt to alleviate these issues, several smaller, implantable second and third generation devices that use either immersed mechanical blood bearings or hydrodynamic/magnetic levitation systems to support a rotating impeller are under development or in the early stages of clinical use. Although these rotary devices may offer a longer term, completely implantable option for patients with biventricular failure, their control strategies need to be refined to compete with the inherent volume balancing ability of the first generation devices. The BiVAD systems potentially offer an improved quality of life to patients with total heart failure, and thus a viable alternative to heart transplantation is anticipated with continued development.     

Auxiliary blood circulation and the artificial heart: forty years of development

The article summarizes forty-year experience in working over the problem of the artificial heart and auxiliary blood circulation in Laboratory and later Research Institute of Transplantology and Artificial Organs. This work has resulted in the development of balloon pumps for intraaortic contrapulsation, the technique of balloon installation, and indications to its application. The results of the clinical application of the method in patients with various pathologies have been estimated. Preclinically, left ventricular bypass techniques have been tested on more than twenty models of membrane type artificial ventricles. The results of the clinical application of left ventricular bypass have been analyzed. The authors adduce data on the development of the thermomechanical implantable bypass system "Micron-M". After achieving 100-day survival of calves with an artificial heart, an artificial heart with external power supply was used as a "bridge" to heart transplantation, but there was only one patient in whom transplantation was performed. The authors consider development of implantable auxiliary blood circulation devices and the artificial heart to be of great prospective value.     

Methods of energy generation from the human body: a literature review

Abstract

The purpose of this study is to review available methods of utilising the human body to obtain energy during the course of daily life activities, without interference with an individual’s lifestyle. The number of individuals with health issues requiring assistance from external or internal health-aiding devices is rapidly increasing. Battery life associated with these devices is currently a major limitation. Currently, medical devices that depend on batteries (i.e., implantable devices) require constant battery monitoring. Development of implantable devices with rechargeable batteries is, therefore, essential. Technologies that can capture energy from the human body can be developed, with different organs, systems, and activities having the potential to be utilised to generate energy. This energy source can act as an alternative to conventional batteries. This study provides an overview of various methods for obtaining energy from the human body. These methods are summarised, compared and analysed. The best results achieved (in terms of power output) are compared and listed.     

Blood flow pulsatility effects upon oxygen transfer in artificial lungs

This report discusses theoretical effects of blood flow pulsatility upon the rate of oxygen transfer in artificial lungs, demonstrates the effects with in vitro tests upon commercial oxygenators, and applies the theory to these oxygenators and to a thoracic artificial lung. Steady flow gas transfer theory is applied to pulsatile flow by using the instantaneous value of flow rate at each instant of time, that is, quasi-steady gas transfer. The theory suggests that the local rate of oxygen transfer for a given device and blood composition is proportional to the flow rate to a power less than unity and to the hemoglobin saturation level. It predicts, for some cases, overall reduced rates of gas transfer for pulsatile flow relative to those at steady flow for the same mean blood flow rates. In vitro bovine blood tests, using pediatric oxygenators, a pulsatile pump, and an adjustable compliance chamber, indicate a significant average 10% reduction of oxygen transfer for pulsatile flow relative to steady flow. The application of the theory to the oxygenators predicts gas transfer values that are in agreement with those measured during the experiments. The results have implications in the design of implantable thoracic artificial lungs, which should include a compliant section to dampen the cardiac pulse. A relatively small compliance (0.2 ml/mm Hg) at the thoracic artificial lung inlet is sufficient to obtain approximately 95% of steady flow oxygen transfer.     

Pulsatile release of parathyroid hormone from an implantable delivery system

Intermittent (pulsatile) administration of parathyroid hormone (PTH) is known to improve bone micro-architecture, mineral density and strength. Therefore, daily injection of PTH has been clinically used for the treatment of osteoporosis. However, this regimen of administration is not convenient and is not a favorable choice of patients. In this study, an implantable delivery system has been developed to achieve pulsatile release of PTH. A well-defined cylindrical device was first fabricated with a biodegradable polymer, poly(l-lactic acid) (PLLA), using a reverse solid-free form fabrication technique. Three-component polyanhydrides composed of sebacic acid, 1,3-bis(p-carboxyphenoxy) propane and poly(ethylene glycol) were synthesized and used as isolation layers. The polyanhydride isolation layers and PTH-loaded alginate layers were then stacked alternately within the delivery device. The gap between the stacked PTH-releasing core and the device frame was filled with PLLA to seal. Multi-pulse PTH release was achieved using the implantable device. The lag time between two adjacent pulses were modulated by the composition and the film thickness of the polyanhydride. The released PTH was demonstrated to be biologically active using an in vitro assay. Timed sequential release of multiple drugs has also been demonstrated. The implantable device holds promise for both systemic and local therapies.     

Observation and quantification of cavitation on a mechanical heart valve with an electro-hydraulic total artificial heart

In previous studies, we investigated the cavitation phenomenon in a mechanical heart valve using an electro-hydraulic total artificial heart. With this system, a 50% glycerin solution kept at 37 degrees C was used as the working fluid. We reported that most of the cavitation bubbles were observed near the valve stop and were caused by the squeeze flow. However, in these studies, the effect of the partial pressure of CO(2) on the mechanical heart valve cavitation was neglected. In this study, in order to investigate the effect of the partial pressure of CO(2) on mechanical heart valve cavitation using an electro-hydraulic total artificial heart, we controlled the partial pressure of the CO(2) in vitro. A 25-mm Medtronic Hall valve was installed in the mitral position of an electro-hydraulic total artificial heart. In order to quantify the mechanical heart valve cavitation, we used a high-speed camera. Even though cavitation intensity slightly increased with increases in the PCO(2) at heart rates of 60, 70 and 100 bpm, throughout the experiment, there was no significant difference between the PCO(2) and cavitation intensity.