Naoshi Sato

Deterministic chaos in the hemodynamics of an artificial heart

To analyze the hemodynamic parameters during prosthetic circulation as an entity, non linear mathematical techniques were used. To compare natural and prosthetic circulation, two pneumatically actuated ventricular assist devices were implanted as biventricular bypasses in chronic animal experiments using adult goats to consitute the biventricular bypass complete prosthetic circulation model with ventricular fibrillation. After implantation, these goats were placed in a cage and extubated after waking. All hemodynamic parameters with the natural circulation without biventricular bypass pumping, and the artificial circulation with biventricular bypass pumping under ventricular fibrillation were recorded under awake conditions. By the use of a non linear mathematical technique, the arterial blood pressure waveform was embedded into a four dimensional phase space and projected into three dimensional phase space. The Lyapunov numeric method is used as an adjunct to the graphic analysis of the state space. A phase portrait of the attractor showed a high dimension complex structure, with three dimensional solid torus suggesting deterministic chaos during natural circulation. However, a simple attractor, such as a limit cycle attractor, was observed during artificial circulation. Positive Lyapunov exponents during artificial circulation suggest the lower dimensional chaotic system. Thus, hemodynamic parameters during prosthetic circulation must be carefully controlled when unexpected stimuli are fed from outside.

Fundamental Rhythm of Sympathetic Nerve Discharges in Animals with Total Artificial Hearts

To evaluate the effect of total artificial heart replacement on the autonomie nervous system, sympathetic neurograms were analyzed by power spectrum and coherence function. Two pneumatically driven, sac type ventricular assist devices were implanted as biventricular bypasses (BVB) in adult, mongrel dogs. After initiation of BVB pumping, the natural heart was electrically fibrillated to form a BVB TAH model. Renal sympathetic nerve activity (RSNA) was recorded using a bipolar electrode attached to the left renal sympathetic nerve. RSNA was amplified and integrated by use of an R-C integrator. Power spectra of the RSNA and values of squared coherence between the arterial pressure wave form and the RSNA were calculated by computer. In animals with total artificial hearts (TAHs), coherence at the cardiac rhythm frequency was decreased, and coherence at the TAH pumping rhythm frequency was increased. These results indicate that the arterial pulse wave observed in TAH animals contributed to the sympathetic neurogram.

Experimental and clinical evaluation of a sack-type ventricular assist device and drive system

A newly designed ventricular assist device and driving system, including an automatic control system, is presented. The blood-contacting surfaces of the blood pump are coated with either Cardiothane or Cardiomat. The system was tested in experiments on goats, whereby only one of fifteen animals showed sudden thrombus formation after 34 pumping days. The system was also applied in three clinical cases for durations of 18 h, 2 days, and 5 days. In two of the cases, weaning could not be performed because of continued bleeding, and the other patient is still alive. No gross findings of thrombus formation were observed in any of the cases, except for a thin circular thrombus at the junction of the connectors and the sack of the blood pump.

Permanent pacemaker implantation in premature infants less than 2,000 grams of body weight

Pacemaker implantation in premature infants presents technical problems because of the relatively larger size of the pulse generator compared with their bodies. A new technique with which successful generator implantation was performed in 2 premature infants less than 2,000 g of body weight is described. The generator is wrapped in a Gore-Tex surgical membrane. A piece of membrane overlying the electrical contact surface of the generator is removed, and the generator is fixed to the abdominal wall in the peritoneal cavity. The technique is simple to perform and would give relative ease in generator exchange.

An electromagnetically driven univalved artificial heart

A wide variety of clinical blood pumps including powering systems have been developed and evaluated for totally implantable support systems [1–6]. However, there are still several serious problems, such as thromboembolic episodes, size, and weight, affecting prolonged survival of a total system inside the body.

Micro-Pressure Sensor for Continuous Monitoring of a Ventricular Assist Device

We have been involved in the development of a clinical ventricular assist device (VAD) system. Here, we report our investigation of in vitro and in vivo stability and sensibility of pressure microsensors. The sensors were mounted in the inflow and outflow cannulae wall to measure the left atrial and aortic pressures during VAD pumping. The pressure sensitive surface of the piezoresistive effect absolute pressure sensor was coated with a thromboresistant polymer, as was the inner surface of the cannulae of the VAD. In the in vitro and chronic animal experiments which were of more than a month duration, reliable stability and sensitivity, without any thrombus formation on the blood contacting surface of the sensors, and high sensitivity were observed. After chronic experiments, the sensitivity of sensors was reevaluated in the mock circulatory system as compared to reference values. The relationship between the output of the micro-sensors and the reference value was linear and correlated well.

Double‐Chambered Right Ventricle Associated with Infective Endocarditis Complication of the Pulmonary Valve: Surgical Management

Abstract  Double‐chambered right ventricle (DCRV) is a rare congenital heart disease characterized by the presence of anomalous muscle bundles, which divide the right ventricle into two chambers: a high‐pressure proximal chamber and a low‐pressure distal chamber. Most DCRV patients are diagnosed and treated during childhood, and presentation in adulthood is not common. Many congenital heart diseases are often associated with other complications such as infective endocarditis (IE). Right‐side endocarditis, which usually involves infection of the tricuspid valve, is uncommon, and endocarditis of the pulmonary valve is extremely rare. We report a 51‐year‐old woman with undiagnosed DCRV and ventricular septal defect associated with pulmonary valve endocarditis. The diagnostic evaluation and the surgical management are discussed.

Mayer waves in dogs with total artificial heart.

To assess the effect of a total artificial heart (TAH) on the autonomic nervous system a power spectral analysis of the hemodynamics in a TAH animal was done by the maximum entropy method. Two pneumatically driven sac-type ventricular assist devices were implanted as total biventricular bypass (BVB) in adult mongrel dogs to compare the differences between natural heart and TAH. Once the BVB was pumping, the natural heart was electrically fibrillated to constitute the BVB-type TAH model. In the arterial pressure waveform in animals with TAH, respiratory waves were not changed (97.7±24.6%) though Mayer waves were significantly decreased (47.5 ± 22.6%) compared with the animal with a natural heart. These results suggest that prosthetic hemodynamics in the TAH animal affect fluctuations in the cardiovascular system.

Clinical experience with ventricular

Since November 1984, eight postcardiotomy patients with ages ranging from 13 to 65 years, have received ventricular assist devices (VADs) at our institute. All the cases fulfilled the criteria for acute profound ventricular failure despite the administration of a large amount of catecholamines and application of intra-aortic balloon pumping (IABP). The original diseases were acute myocardial infarction (AMI) in two, left ventricular (LV) aneurysm in one, severe acquired valvular disease in three, and congenital cardiac anomaly in two cases. Of the eight cases, three with critical preoperative hemodynamic conditions underwent surgery with VAD on standby. The reasons for applying the VAD were difficulty in weaning from extracorporeal circulation (ECC) in five and low cardiac output syndrome after weaning from ECC in three cases. Two types of VAD system were used in this series. VAD systems developed at the University of Tokyo were used in the initial six cases and a blood pump (TH-7), and multipurpose driving system, which were newly developed at our institute, in the most recent two cases. The duration of assistance varied from 18 h to 70 days. Three cases were not weaned from VAD—two because of incomplete surgical repair and one because of multiple organ failure (MOF) after prolonged assistance for 70 days. Of the five patients who were weaned from VAD, two are alive. The remaining three patients were weaned from VAD and died on the 21st, 97th, and 123rd postoperative days. The cause of death was mainly MOF, originating from various complications such as acute renal failure, sepsis, respiratory failure, and cerebral embolism.

Fractal Dimension Analysis of Chaos in Hemodynamics with Artificial Heart

To analyze the hemodynamic parameters in prosthetic circulation as a complete entity, not as a decomposed entity, non-linear mathematical techniques, including chaos and fractal theory, were utilized. Two pneumatically actuated ventricular assist devices were implanted as biventricular bypasses (BVB) in chronic animal experiments in four healthy adult goats. For the comparison between the natural and prosthetic circulation, the BVB type complete prosthetic circulation model with ventricular fibrillation was adopted. All hemodynamic parameters with natural circulation without BVB pumping and artificial circulation were recorded under awake conditions, and calculated with a computer system. By the use of a non-linear mathematical technique, arterial blood pressure waveform was embedded into the return map by the beat-to-beat variability, and fractal dimension analysis was performed to analyze the reconstructed attractor. By the use of the box-counting method, fractal dimension analysis of the hemodynamics was performed. The return map of the hemodynamics during natural and artificial circulation showed the characteristics of lower dimensional fractal. The fractal time series data were suggested to have robusticity and error resistance. Thus, our results suggest that the circulatory regulatory system with the artificial heart may have these desirable characteristics.