Hiroyuki Hayashi

Formation of Diamond-Like Carbon Films by Photoemission-Assisted Plasma-Enhanced Chemical Vapor Deposition

Diamond-like carbon (DLC) films, which are an amorphous carbonaceous allotrope composed of sp2 carbon, sp3 carbon, and hydrogen, were prepared by photoemission-assisted plasma-enhanced chemical vapor deposition (PA-PECVD). The electrical behavior during film growth monotonically depended on the methane source gas concentration. Raman analysis of the films suggests that a DLC film grown at a high methane concentration condition contains a small number of graphitic domains, decreasing amorphicity of the film. In contrast, at a low concentration, the methane molecules were transformed into sufficiently fragmented radicals, forming a lot of graphitic nuclei and increasing the amorphicity. However, the variations of the relative dielectric constant, breakdown strength, and optical bandgap exhibited extreme values at an intermediate methane concentration. Thus, the two growth modes give different DLC films with varying combinations of electrical and optical characteristics.

Cardiac-related sympathetic nerve activity during circulation with only the left ventricular assist device.

Circulatory maintenance with a left ventricular assist device (LVAD) alone during cardiac arrest until heart transplantation has been evaluated. To assess the effect on the autonomic nervous system, the sympathetic neurogram was analyzed by power spectrum and coherence function. LVAD were inserted between the left atrium and the descending aorta in seven adult mongrel dogs and ventricular fibrillation was induced electrically. Renal sympathetic nerve activity (RSNA) was detected by bipolar electrodes attached to the left renal sympathetic nerve. Values of squared coherence between the arterial pulse wave and RSNA were calculated. Under the condition of circulatory maintenance with only LVAD, coherence at the cardiac rhythm frequency was decreased, and coherence at the LVAD pumping rhythm frequency was increased. These results indicate that the arterial pulse wave observed during maintenance of the circulation with only LVAD contributed to the sympathetic neurogram.

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.

Towards Computational Biomechanics Based Cardiovascular Medical Practice

Some of our recent fundamental computational biomechanical studies of the cardiovascular system, from modeling aortic flow to the microscale dynamics of the platelet, are discussed. It is emphasized that a living system inherently needs multi-scale, multi-physics analysis, and the rapid advancement of the biological sciences must also be incorporated in computational biomechanics studies. Based on these efforts, it is now expected that a computational biomechanics-based software system that can be applied to real clinical situations will be developed for the cardiovascular system. This will help medical practitioners to accumulate the fundamental data and clinical experience that they obtain from real patients, and use it to make quantitative predictions.

The prospective control of a total artificial heart using sympathetic tone and hemodynamic parameters

In order to develop the real-time control system of a total artificial heart (TAH), we use the sympathetic tone and the hemodynamic parameters. Moving averages of the mean left atrial pressure and mean aortic pressure were used as the parameters of the preload and the afterload in the circulatory system. Also, renal sympathetic nerve activity (RSNA) was utilized as the parameter of the sympathetic tone. A functional formula which prospectively indicated cardiac output, was calculated using the multiple regression analysis of the time series data in the acute animal experiments using adult mongrel dogs. Also, a functional formula which prospectively indicated heart rate was determined through the time series data of the RSNA.