Noninvasive assessment method to determine the anatomic compatibility of an implantable artificial heart system

To assess the anatomic compatibility of an artificial heart (AH), we attempted to develop a computer environment that would facilitate a reliable simulation of an AH implanted in the human thorax. A three-dimensional thoracic computer model with a ventricle-resected heart was constructed, by using manually extracted contour points of the aorta, pulmonary artery, atria, atrioventricular valves, diaphragm, and thoracic wall from a set of consecutive CT images. Such a model enabled simulation of an AH implantation by orienting the AH model in it. Error evaluation on CT imaging and contour extraction with a Plexiglas cylindrical phantom showed that the diameter of the extracted phantom contour was approximately 2 mm smaller than its original with a standard deviation of <0.5 mm. Errors in contour and surface reconstruction could be reduced to far less than 1 mm under constrained conditions. A study on the influence of breathing revealed that variations in some thoracic dimensions between inspiration and expiration could reach 10 mm. In summary, computer simulation of AH implantation is a worthwhile approach with acceptable accuracy, although further considerations of extreme thoracic situations will be required.     

Right-left ventricular output balance in the totally implantable artificial heart

Pneumatically powered artificial hearts readily accommodated the higher net stroke volumes by the right ventricle than from the left ventricle. We published that this discrepancy was approximately 8% of the left ventricular cardiac output. A variety of methods have been used to achieve balance between the right and left atrial pressures. Relatively large volume-displacement chambers (VDC) present potential problems, but do provide balance. The VDC in volumetrically coupled right-left stroke volumes was eliminated by using a small-diameter interatrial shunt (IAS). Preliminary studies demonstrated excellent balance in contracted and expanded blood volume (preload) and by hypotension and hypertension created with vasoactive drugs (afterload). At a mean aortic pressure of 120 mmHg, heart rate of 120 BPM, cardiac output of 8 L/minute and right atrial pressure of 13 mmHg, the peak IAS flow was 3.2 ml/beat in a right to left direction and 8.0 ml/beat in a left to right direction. The net left to right flow was 4.8 ml/beat. Over a wide range of preload (2 to 20 mmHg) and afterload (45 to 180 mmHg), the left atrial pressure was routinely 5 mm Hg more than the right atrial pressure. Elimination of the VDC reduces the number of components, volume, and weight of the totally implantable artificial heart. The IAS offers a simple solution to a very complex problem and provides a device that is simpler to implant and is possible to explant.     

One piece ultracompact totally implantable electromechanical total artificial heart for permanent use

An ultracompact, one piece, totally implantable electromechanical total artificial heart (TAH) has been developed as a permanent replacement for failing hearts. It consists of left and right pusher plate blood pumps (stroke volume 55 ml) made of titanium alloy (Ti-6Al-7Nb) sandwiching a miniaturized electromechanical actuator between them. The diameter of the TAH is 90 mm, with a thickness of 70 mm, yielding an overall volume of 400 ml. It weighs 450 g. Although it is miniaturized, it provided a maximum pump output of 8 L/min against a left afterload of 100 mm Hg. It required approximately 12 watts to provide a pump output of 6.5 L/min with maximum efficiency of 13.5%. To balance left and right flow, the right stroke length was made 10% shorter than the left, and an auxiliary compliance chamber was used to compensate for additional flow differences between them. Motor commutation pulses and a Hall effect pusher plate sensor signal were used in the controller to implement the left master alternate variable rate mode. The calf fitting study revealed excellent anatomic compatibility, and the first successful survivor was obtained in December 2001. Studies of system endurance and biocompatibility are required to ensure long-term reliability. This TAH is promising for permanent replacement of the failing heart as well as for bridge to heart transplantation for the smaller size group of end-stage cardiac patients.     

Durability testing of a completely implantable electric total artificial heart

In vitro durability testing was conducted on the Penn State/3M electric total artificial heart (ETAH) to determine device durability and to evaluate device failures. A specialized mock circulatory loop was developed for this testing. Customized software continuously acquired data during the test period, and failures were analyzed using FMEA (failure modes and effects analysis) and FMECA (failure modes, effects, and criticality analysis) principles. Redesigns were implemented when appropriate. Reliability growth principles were then applied to calculate the 1 and 2 year reliability. The 1 and 2 year reliability of the Penn State/3M ETAH was shown to be 96.1% and 59.9%, respectively, at 80% confidence.     

Development of an implantable artificial anal sphincter by the use of the shape memory alloy

In this study, we developed and assessed an artificial anal sphincter driven by an shape memory alloy actuator (AS-SMA). The performance characteristics of the device were analyzed with a measurement system. Assessment showed that the AS-SMA could generate a pressure of 55 mm Hg at an atmospheric temperature of 36 degrees C, and displacement of the SMA actuator was 7.5 mm when the temperature of the SMA plate was 55 degrees C. To evaluate opening and closing, we studied a piglet colostomy model, in which the AS-SMA was implanted around the colostomy in the extraperitoneal space. Flow control tests using living porcine intestine revealed that the AS-SMA could maintain fecal continence against an intestinal pressure of 75 mm Hg. The high pressure zone corresponding to the location of the device was demonstrated in a manometric examination. For 6 days after surgery, we activated the AS-SMA twice a day and observed the bowel movements. The animal experiment indicated that the AS-SMA is able to control the bowel movements of patients with fecal incontinence if several problems, such as burning of tissue around the device and compression injury of the intestine, are resolved.     

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.     

Development of an implantable artificial lung: challenges and progress

Unlike dialysis, which functions as a bridge to renal transplantation, or a ventricular assist device, which serves as a bridge to cardiac transplantation, no suitable bridge to lung transplantation exists. Our goal is to design and build an ambulatory artificial lung that can be perfused entirely by the right ventricle and completely support the metabolic O2 and CO2 requirements of an adult. Such a device could realize a substantial clinical impact as a bridge to lung transplantation, as a support device immediately post-lung transplant, and as a rescue and/or supplement to mechanical ventilation during the treatment of severe respiratory failure. Research on the artificial lung has focused on the design, mode of attachment to the pulmonary circulation, and intracorporeal versus paracorporeal placement of the device.     

The MiniACcor: constructive redesign of an implantable total artificial heart, initial laboratory testing and further steps

The Aachen Total Artificial Heart (ACcor) has been under development at the Helmholtz Institute in Aachen over the last decade. It may serve as a bridge to transplant or as a long-term replacement of the natural heart. Based upon previous in vivo experiments with the ACcor total artificial heart, it was decided to optimize and redesign the pump unit. Smaller dimensions, passive filling and separability into three components were the three main design goals. The new design is called the MiniACcor, which is about 20% smaller than its predecessor, and weighs only 470 grams. Also its external driver/control unit was miniaturized and a new microcontroller was selected. To validate the design, it was extensively tested in laboratory mock loops. The MiniACcor was able to pump between 4.5 and 7 l/min at different pump rates against normal physiological pressures. Several requirements for the future compliance chamber and transcutaneous energy transmission (TET) system were also measured in the same mock loop. Further optimization and validation are being performed in cooperation with the Heart and Diabetes Centre North Rhine-Westphalia.     

植入式人工肛门括约肌系统的实现及动物实验***

背景：研制新型的符合人体生理需求的人工肛门括约肌系统具有十分重要的意义。 目的：设计一种新型植入式人工肛门括约肌系统。 方法：利用无线通讯模块和压力传感器重建排便控制机制,并由经皮能量传输模块供电,采用机电系统模拟人体自然器官的功能,最终实现人体肛门括约肌的控制效果。 结果与结论：设计并实现了一种新型的植入式人工肛门括约肌系统,在重建排便机制和模型的基础上,一定程度上恢复肛门失禁患者的生物反馈控制能力,并带有经皮能量传输模块,为体内系统长期无缆式供电提供可能。该系统实现了植入式动物实验,完成了系统植入可行性和基本功能验证。 关键词：人工肛门括约肌;生物反馈控制;经皮能量传输;植入式动物实验;数字化医学  doi:10.3969/j.issn.1673-8225.2012.13.013     

基于功率谱密度相似性的最佳心音信号选择

心音采集过程中混入的干扰噪声影响着心音诊断,目前多通过手动方式选择干扰较少的信号段做后续分析。为从采集信号中筛选出干扰最少、稳定性最强的最佳心音信号,提出一种最佳心音信号的自动选择方法。对采集的25例正常和119例患先天性心脏病儿童的心音信号,基于离散小波变换与哈达玛积相结合定位心动周期。根据心动周期信号的周期稳定性及功率谱密度相似性计算质量因子,将质量因子最大的连续3个心动周期信号作为最佳心音信号。由心脏病专家通过音频回放对信号选择的成功率和有效性进行评估。结果表明,最佳心音信号自动选择的成功率为95.83%,选择成功信号均包含对应疾病的典型听诊特点。该方法选择性能良好且自动执行,为心音信号的全自动分析提供参考。     

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.     

Improvement in magnetic field immunity of externally-coupled transcutaneous energy transmission system for a totally implantable artificial heart

Transcutaneous energy transmission (TET) that uses electromagnetic induction between the external and internal coils of a transformer is the most promising method to supply driving energy to a totally implantable artificial heart without invasion. Induction-heating (IH) cookers generate magnetic flux, and if a cooker is operated near a transcutaneous transformer, the magnetic flux generated will link with the external and internal coils of the transcutaneous transformer. This will affect the performance of the TET and the artificial heart system. Hence, it is necessary to improve the magnetic field immunity of the TET system. During operation of the system, if the transcutaneous transformer is in close proximity to an IH cooker, the electric power generated by the cooker and coupled to the transformer can drive the artificial heart system. To prevent this coupling, the external coil was shielded with a conductive shield that had a slit in it. This reduces the coupling between the transformer and the magnetic field generated by the induction cooker. However, the temperature of the shield increased due to heating by eddy currents. The temperature of the shield can be reduced by separating the IH cooker and the shield.     

An implantable pacemaker for the reduction of heart rate

Previous studies by one of the authors have demonstrated, using an external pulse source, that a regulated reduction in heart rate can be achieved by using approapriately time pairs of stimuli. However, these experiments were restricted to comparatively short periods of time. This paper describes an implantable pacemaker to study whether a long-term reduction can be achieved and, if so, to enable the resulting physiological and biochemical effects to be assessed. An initial experiment on a dog is described, in which the heart rate was reduced from 140 to 98 over a period of nine days.