Biomedical subjects

Atsushi Baba

Publications and source records attributed to Atsushi Baba.

26 records · Page 2Linked to original sources

PubMed2002

Different Ca2+ dynamics between isolated hippocampal pyramidal cells and dentate granule cells.

The hippocampal formation contains a variety of neuronal types. The principal neurons are granule cells in the dentate gyrus and pyramidal cells in Ammon's horn. These two neuron types show distinct cell morphology and display a different vulnerability to ischemic injury or various neurotoxins. In order to illustrate the difference in the pathophysiological properties of these neurons, we established a method for separately culturing granule cells and pyramidal cells. They were prepared from the dentate gyrus and Ammon's horn of 3-day-old Wistar rat pups and maintained for 7-9 days in culture. After transient exposure to N-methyl-D-aspartate or glutamate, both the cultured neuron populations displayed somatic Ca(2+) transients with similar amplitudes, but the subsequent recovery to baseline was about twice as fast in granule cells than in pyramidal cells. Similar results were obtained for K(+) depolarization-induced Ca(2+) elevation, suggesting that the relatively rapid Ca(2+) clearance in granule cells is independent of Ca(2+) influx pathways. The present study provides the first evidence for a difference in Ca(2+) dynamics and homeostasis between granule and pyramidal cells and may represent a cellular basis for the differential vulnerability of hippocampal neurons.

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↗

PubMed2002

Review of existing research on microgravity boiling and two-phase flow: future experiments on the international space station.

This paper describes research objectives on boiling and two-phase flow under microgravity conditions from both scientific and technological points of view. Existing research for various systems in flow boiling are briefly reviewed and problems indicated for research conducted by available facilities with short microgravity duration. A wide range of experimental subjects that become possible by using different types of test sections is clarified and the validity of long term experiments is emphasized. A first step outline is described for a test loop with interchangeable test sections, such as transparent heated tubes, transparent flat heating surfaces, and narrow channels optimized for individual objectives and restricted by specifications of the facility.

Journal Article↗

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

Advance in animal experiments with the undulation pump total artificial heart: 50 and 54 day survival periods with 1/R control.

The undulation pump total artificial heart (UPTAH) is a unique, implantable, total artificial heart (TAH) that uses undulation pumps. To achieve long-term survival in animals with physiologic hemodynamic conditions, a control method based on conductance and arterial pressure was applied to UPTAH. With this control method, called 1/R control, survival periods of 50 days (No. 0016, 49.6 kg) and 54 days (No. 0030, 42.5 kg) were obtained in adult female goats. In No. 0016, 1/R control was applied to the left pump, whereas in No. 0030, it was applied to the right pump. Another pump was used for left-right balance control. The control stability was better in No. 0030 than in No. 0016. The sucking effect of the left atrium was remarkable in No. 0016, possibly because of a time delay when left-right balance control was performed with the right pump. In No. 0016, the cause of death was probably a thrombus flown from a panus in the left atrium. It is possible that the left atrial suction effect influenced the thrombus and panus formation in the left atrium. In No. 0030, the cause of death was a small rupture of the membrane in the right pump. The rupture may have been caused by excessive negative pressure inside the pump. This pressure resulted from suction of the right atrium because of an unexpected control excursion, which was probably caused by a software bug. It will be necessary to redesign the undulation pump and improve the software to achieve longer survival periods for animals with physiologic hemodynamic conditions.

Animals↗

PubMedDate not supplied

Microcirculation of the bulbar conjunctiva in the goat implanted with a total artificial heart: effects of pulsatile and nonpulsatile flow.

A new system to observe the microcirculation on the bulbar conjunctiva was developed using a digital high definition microscope to investigate the influence of the flow patterns on the microcirculation in a goat with a total artificial heart (TAH). The undulation pump TAH was implanted into the goat. When the whole body condition became stable, the flow pattern was modulated between the pulsatile and the nonpulsatile mode, and the changes in the microcirculation were observed. When the flow pattern was changed from pulsatile to nonpulsatile mode, the erythrocyte velocity in capillaries dropped from 526+/-83 to 132+/-41 microm/s and remained at a low level. The number of perfused capillaries decreased as well. Then the nonpulsatile flow mode was maintained for 20 minutes. After the flow pattern was returned to the pulsatile mode again, the erythrocyte velocity recovered to the initial level (433+/-71 microm/s). In many cases, the flow of the nonperfused capillaries in the nonpulsatile mode recovered to the initial level after the flow pattern was changed to the pulsatile mode again. The perfused capillary density in the nonpulsatile mode (19.7+/-4.1 number of capillaries/mm) was significantly lower than that in the pulsatile mode (34.7+/-6.3 number of capillaries/mm). It is thought that the basal and flow stimulated endothelium derived nitric oxide release in the microvessels decreased because of the disappearance of pulsatility and that the nitric oxide induced the constriction of arterioles after the flow pattern was changed to the nonpulsatile mode. At the same time, the baroceptors might sense the decrease in the arterial peak pressure or dp/dt, and the sympathetic nerve increases activities and induce the constriction of arterioles. Then, the erythrocyte velocity in capillaries would decrease. Because of the flow pattern further in the chronic phase, it is important to follow the change in the microcirculation.

Animals↗

PubMedDate not supplied

Pathophysiologic study of goats with undulation pump total artificial heart: those that survived for more than 1 month.

The undulation pump total artificial heart is an implantable total artificial heart that is being developed at the University of Tokyo. Many advances in our system have been made by the adoption of hardware and software solutions that enabled the animals with the undulation pump total artificial hearts to survive more than 1 month. Pathophysiologic observations were performed for these goats that survived. In this article, the pathophysiologic findings are described in detail for three goats that survived for 46 (goat 9916), 54 (0030), and 63 (0107) days. The microscopic findings indicated that in goat 0107 the histologic changes in key organs occurred at the termination of the experiments. Therefore, the pathophysiologic changes in goats 9916 and 0030 were mainly investigated in this study to evaluate the chronic effect caused by our total artificial heart system. The signs of chronic ischemia and cell dystrophy were observed in both the liver and kidney. Until now, 13 goats had survived more than 1 week and 6 goats survived more than 1 month, including one that survived for 63 days, which is the longest in our experimental series. The pathophysiologic results of goats 9916 and 0030 showed that the undulation pump total artificial heart might still cause some damage to the liver and the kidney. To accomplish long-term survival with the undulation pump total artificial heart, further pathophysiologic studies are required, and the necessary modifications to the total artificial heart system will need to be made.

Animals↗

PubMedDate not supplied

Functions for detecting malposition of transcutaneous energy transmission coils.

A transcutaneous energy transmission system (TETS) for artificial hearts and ventricular assist devices uses electrical coupling of power between external and implanted coils. If the position of coils changes relative to each other, the TETS cannot feed the required power of the implanted device. During activity or sleep, the coils may move accidentally. TETS users and the people around them have to pay attention to this because the range of the position where the required power can be fed efficiently is not wide. Therefore, we added functions for the position changes of the coils to the TETS. Regular, cautious, and irregular positions were introduced, and the ranges of them were decided upon in our experiments. The cautious position was determined by the area where the change of the relative position of the coils was relatively small. When the coils were in the cautious position, the circuit was tuned by way of changing the resonant point. This modulation could give good power efficiency in the cautious position. When the coils were in the irregular position, an alarm switch was turned on. These functions ease the restriction of the coil position and give better quality of life (QOL) than do the conventional TETS.

Biomedical Engineering↗