Biomedical subjects

Shuichi Mochizuki

Publications and source records attributed to Shuichi Mochizuki.

8 recordsLinked to original sources

PubMed2006

Estimation of early-stage malfunction using implantable artificial heart sound in animal experiments.

We have developed an automatic diagnosis system of an artificial heart in order to ensure the safety of the patient implanted with the artificial heart. The automatic diagnosis system is composed of an electro-stethoscope system, adaptive noise canceller (ANC), and artificial neural network (ANN). The ANC effectively eliminates ambient noise from the sound signal of the artificial heart detected by the electro-stethoscope, and a filtered sound signal is separated into each frequency components by fast Fourier transformation. Each frequency component of an artificial heart's acoustic signal is fed into the ANN in order to make a diagnosis of pump condition. The automatic diagnosis system was evaluated in mock circulatory tests and a long-term animal experiment using a goat implanted with an undulation pump ventricular assist device (UPVAD). In mock circulatory tests, the ANN was able to detect pump failing conditions, which were occlusion of inflow and outflow cannula and deterioration of the ball bearing. In a long-term animal experiment, after training the ANN using UPVAD's sound signal in normal condition, the diagnosis system continuously monitored UPVAD's sound signal detected by the electro-stethoscope placed on the surface of the left thoracic cavity of the goat. The UPVAD was stopped by rupture of a diaphragm in the pump on the ninth day of operation. We were able to identify initial signs of malfunction of the pump on the eighth day, while the UPVAD was able to operate normally. In conclusion, the automatic diagnosis system for malfunction of the artificial heart has enough performance to detect early stages of malfunction of the artificial heart, and it contributes to ensure the patient's safety.

Animals↗

PubMed2003

Evaluation of pulsatile and nonpulsatile flow in microvessels of the bulbar conjunctiva in the goat with an undulation pump artificial heart.

This study has three purposes, as follows. The first is to develop a microscopic system to observe the microcirculation of animals implanted with an artificial heart. The second is to investigate the influence of flow pattern change from pulsatile to nonpulsatile on the microcirculation. The third is to study the effects of pulsatility in blood flow on endothelium-derived nitric oxide release in the microvasculature. When the flow pattern was changed from pulsatile to nonpulsatile, the velocity of erythrocytes in many capillaries dropped and remained at a low level, and the number of perfused capillaries decreased. After the flow pattern was returned to pulsatile, the velocity of erythrocytes recovered to the initial level. In many cases, the flow of nonperfused capillaries recovered to the initial level as well. Also, the pulsatile flow enhances the basal and flow-stimulated endothelium-derived nitric oxide release in microvessels.

Animals↗

PubMed2003

Basic study to develop an electromagnetic drive method for the rotary undulation pump.

The rotary undulation pump, which is composed of a disk with a convex shape on both sides and a pump housing with one narrow side and one wide side, is a unique continuous flow pump with a new principle. The concept of the levitation drive method for this pump was proposed. The electromagnetic driver model and drive circuit were developed to examine the possibility and the difference among the delta wired, Y wired, and repulsion methods. In the repulsion method, the disk was driven by magnetic repulsion. The model could be driven with either method, and the repulsion method was demonstrated to also be possible. With either method, owing to the wide gap between the permanent magnets and coils, the output was not enough when the load was high. The efficiency was almost the same in the delta wired and Y wired methods. In the repulsion method, however, it was less than 50% of that in the other two methods. From the results, the delta wired and Y wired methods with an active control of the gap distance were considered to be better than the repulsion method, which required no active gap control.

Centrifugation↗

PubMed2003

Progress in the control system of the undulation pump total artificial heart.

The undulation pump total artificial heart (UPTAH) is a small implantable total artificial heart. As the UPTAH generates outflow and inflow at the same time, control of the UPTAH is very difficult. Therefore suitable control methods specifically for the UPTAH should be established. Various motor control, left-right flow balance control, and physiological control methods were examined and tried for the UPTAH control in this study. The control system is divided into seven categories. It has a hierarchical structure and all control modes work at the same time. The UPTAH with the newly developed control method has been implanted into the chest cavities of 48 goats. Until now, six goats survived for more than one month, including 63 days in the longest case. The good condition of the UPTAH implanted animal could be maintained with the newly developed control scheme, consisting of the 1/R control and several other additional controls.

Animals↗

PubMed2002

Ripple reduction control of the undulation pump total artificial heart.

An undulation pump total artificial heart (UPTAH) in which the revolutions of the motor are converted to undulation motion of a disk has been developed. In an experiment, a goat using the UPTAH survived for 54 days. However, a large ripple was observed in the device's output pressure and flow waveform. In calculating the spectrum of the ripple, we found that the ripple mainly comprised 2 frequency sine waves: 1 having the same frequency as and 1 having double the frequency of the motor revolutions. To reduce the ripple, 2 sine waves, 1 having the same frequency as and 1 having double the frequency of the motor revolutions, were provided to the motor current to modulate the pulse width of the pulse width modulation controlling the motor revolutions. This ripple control method reduced the pressure ripple by 90% in a mock circulation and by 70% in animal experiments. These results revealed that the ripple generated in the UPTAH could be controlled through the use of motor control software.

Animals↗

PubMedDate not supplied

Third model of the undulation pump total artificial heart.

The undulation pump is a small, continuous flow displacement type blood pump, and the undulation pump total artificial heart (UPTAH) is a unique, implantable total artificial heart based on this pump. To improve the durability of the UPTAH for investigating long-term pathophysiology with UPTAH, a third model (UPTAH3) has been developed. UPTAH3 was designed to separate the left and right undulation shafts and to be more durable. The undulation pumps were also redesigned. UPTAH3 was implemented with a diameter of 76 mm, width of 78 or 79 mm, total volume of 292 ml, and weight of 620 g. The priming volumes of the left and right pumps are 26 and 21 ml, respectively. The atrial cuffs and outflow cannulae were also redesigned for UPTAH3. The maximum output against an arterial pressure load of 100 mm Hg is about 11 L/min. The maximum pump efficiency is about 15% in the left pump and 18% in the right pump, giving a maximum total efficiency for both of about 11%. To date, UPTAH3 has been tested in 17 goats, and the longest survival period was 46 days. This third model will be useful for investigating pathophysiology with UPTAH.

Animals↗

PubMedDate not supplied

A temporal and spatial analysis of cavitation on mechanical heart valves by observing faint light emission.

Cavitation on mechanical heart valves (MHVs) could cause the mechanical failure of the occluder. A simple and reliable in vitro test method to evaluate cavitation potential must be developed. The bubble implosion damages the MHV material; thus, observing the behavior of the bubble implosion is essential. According to sonoluminescence, the collapsing cavity emits faint light. Therefore, in this study, the bubble collapse was analyzed both temporally and spatially by observing faint light emission. A photon counting system has been developed using a photomultiplier tube (H7360-01, Hamamatsu Photonics, Japan). The highest time resolution of this system is 5 microsec. A quartz optical fiber bundle of 2 mm diameter can be connected to this photomultiplier tube and traversed two-dimensionally over the MHV. The closure of the MHV triggers the photon counter, and the photons through 500 beats are recorded and integrated. A 20 mm Björk-Shiley valve was submerged in a water tank containing 10 L deionized water, and the pressure difference of 120 mm Hg was exerted on the valve at a rate of 60 bpm with a pulse duplicator. Approximately 700 microsec after the valve closure, light emission was detected along the edge of the occluder on the inflow side in the major orifice. Then, approximately 1,000 microsec after the closure, light along the occluder's edge in the minor orifice was recorded as well. Compared with the analysis, using a stroboscope and a high-speed camera, faint light was emitted from the collapsing cavities. In conclusion, sonoluminescnece was successfully observed around the MHV, and the photon counting technique and the traversing mechanism of the optical fiber bundle revealed the temporal and spatial distribution of the cavity collapse on the MHV.

Biomedical Engineering↗

PubMedDate not supplied

Development of a novel intrafascicular nerve electrode.

Artificial organs could be controlled using autonomic neural signals, because they exhibit rapid responses to physical needs similar to those of natural organs. A nerve electrode must satisfy many requirements to measure autonomous neural signals such as a long lifetime, high signal-to-noise ratio, multichannel recording, simple installation into a nerve fascicle, and good manufacturing productivity. The purpose of our study is to propose and evaluate a novel nerve electrode that satisfies these conditions, which to date has not been developed. A novel intrafascicular nerve electrode was designed, fabricated, and evaluated on autonomic nerves. Conventional extrafascicular and intrafascicular nerve electrodes were fabricated and tested for comparison to our novel intrafascicular nerve electrode. The novel intrafascicular nerve electrode had a 3-week lifetime, whereas the conventional extrafascicular nerve electrode had a 2-week lifetime. The signal-to-noise ratio was improved from 1.6 to 2.0 compared with the conventional extrafascicular nerve electrode. The novel intrafascicular nerve electrode was easier to install into a nerve fascicle and had better manufacturing productivity than the conventional intrafascicular nerve electrode. We succeeded in demonstrating the feasibility of our novel intrafascicular nerve electrode.

Animals↗