Itsuro Saito

A nonpulsatile total artificial heart with 1/R control.

A total artificial heart (TAH) using continuous flow pumps is promising for size reduction of the device; however, the role of pulsatility in TAHs has been a subject of great debate. Additionally, it is unclear whether, in a nonpulsatile TAH, a physiological control method such as 1/R control can keep the experimental animal in good condition. To realize a nonpulsatile TAH with 1/R control, the artificial valves were removed from undulation pump total artificial hearts (UPTAHs), which can produce both pulsatile and nonpulsatile flows using a single device. The UPTAHs were implanted into 18 goats, and 4 goats survived for more than 1 month. Three weeks of long-term nonpulsatile TAH operation could be tested in the goat that survived for 72 days, and it was proved that 1/R control is possible not only with a pulsatile TAH but also with a nonpulsatile TAH. The general condition of the goat and its organ function did not change on the application of nonpulsatile mode. Cardiac output and arterial pressure changed with the condition of the goat in pulsatile and also in nonpulsatile modes, and the changes seemed almost identical. However, the sucking effect of the atria was very significant in nonpulsatile mode, resulting in hemolysis. Therefore, nonpulsatile TAHs under 1/R control are considered to be inadequate unless some pulsatility can be introduced to avoid fatal sucking effects and to ensure sufficient inflow. During nonpulsatile operation, regular fluctuations were sometimes found in the aortic pressure, and these were caused by the periodic sucking effect in the left atrium that was possibly influenced by respiratory changes.

Implementation of the Natural Heartbeat Synchronize Control for the Undulation Pump Ventricular Assist Device Using the Inflow Pressure

The undulation pump ventricular assist device (UPVAD) is a small implantable ventricular assist device using an undulation pump. The UPVAD can produce not only continuous flow but also pulsatile flow by changing the motor rotational speed of the UPVAD. Because the undulation pump is a volume displacement type pump in which the inflow action and outflow action both start at the same phase, the inflow sucking occurs easily. The purpose of this study is to develop a suitable control method for the UPVAD. The UPVAD inflow cannula equipped with an implantable blood pressure sensor is inserted into the ventricular. Therefore, pressure fluctuation that synchronizes with the natural heartbeat is observed in the inflow cannula. By changing the motor rotational speed that responds to the inflow pressure, the UPVAD can synchronize with the natural heartbeat and the UPVAD can generate either aco-pulse assist flow or a counter pulse assist flow. The newly developed control method exhibited superior characteristics than existing ones due to high immunity against pressure sensor drift. The improved control method is implemented into the microcontroller. The UPVAD generated 5.3 l/min co-pulse assist flow without inflow cannula sucking using this control method. The assist flow can be increased more than 15% with this control method. This control was implemented one-chip microcontroller without extra peripheral device. It can reduce the UPVAD controller size. The UPVAD can generate the suitable assist flow with the developed control method.

Development of an Auto Calibration Method for the Implantable Blood Pressure Sensor in the Undulation pump ventricular assist device (UPVAD)

Development of an implantable artificial heart is very important to save cardiac disease patients. An undulation pump ventricular assist device (UPVAD) could be a good candidate because of the compact size. Although the implantation improves patient’s quality of life (QOL) considerably, several implications hamper the development of an implantable artificial heart. The difficulty in blood pressure measurement is the one of the implications to be solved. We have developed the im-plantable absolute pressure sensor to be integrated into a UPVAD and the algorithm to infer the blood pressure referred to gauge pressure. Noble feature of the algorithm is autonomous compensation of the offset drift with the pressure sensor in time. Thus the blood pressure could be controlled precisely with the implantable UPVAD even if the pressure sensor exhibited certain drift characteristics. Animal experiment demonstrated the effectiveness in compensating the offset drift

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.

Fundamental study to develop a fiber-optic gap sensor for a rotary undulation pump

The rotary undulation pump is believed to be a good candidate for the next-generation artificial heart. Due to its complex movement, it is desirable to magnetically levitate the rotor and dynamically control the gap. In this article, the applicability of a fiber-optic gap sensor to the dynamic position control of the rotor in the rotary undulation pump was investigated. The fiber-optic gap sensor consisted of two plastic-core fibers and a reflection plate. Two 1-mm-diameter optical fibers were aligned parallel: one for source light propagation and the other for reflected light transmission. The basic properties of gap sensors using four different light sources were explored in five media (air, physiologic saline, and blood samples with three different hematocrit levels). The influence of the oxygen saturation level in the blood on sensing was investigated with two types of light sources. It is desirable to use a light source the wavelength of which shows similar absorption coefficients for both oxygenated blood and deoxygenated blood. The effect of the distance between the two fibers on the sensing and range was also investigated. The results indicated that the fiber-optic gap sensor is quite promising for the active control of rotor positioning in the rotary undulation pump.

Development of an Implantable Observation System for Angiogenesis

A miniaturized video camera system integrated with a scaffold for blood vessels and tissue induction that is implantable into an animal body was developed. A small auto-focus camera with USB interface was used as an imaging device. A close-up lens was added to reduce the focusing point. Also 45-degree reflecting prism was added for the compact system design. A spongy polyglycolic acid sheet of 0.3 mm thickness was used as a scaffold. The observation area was about 8 x 6 mm and the tissue was induced from sideways. The camera was implanted into a muscular layer of a goat for more than 60 days to observe the skeletal muscle induction. Tissue induction to the scaffold started from second week and it took about 5 weeks to cover the entire area by the tissue, Vigorous angiogenesis was observed at the front region of tissue induction resulting dense distribution of capillary vessels and red blood cells. The density of capillary vessels reduced considerably behind the front region and arterioles and venules started to appear.

An Implantable Probe for Chronic Observation of Microcirculation

Whether the pulsatile flow is essential for living body or not is long-term controversial point between circulatory physiologist and artificial heart researchers. Especially, since an axial flow pump, continuous flow pump, has begun to use clinically in 2001, and could keep the patients alive for more than few years, this problem has become to be thought as very important physiological and pathophysiological problem. The objective of this study is to develop an implantable probe to observe microcirculation under artificial circulation.

Compact Ventricular Assist Device and Total Artificial Heart Using Undulation Pump

Fully implantable VAD and TAH are eager to be developed as destination therapy for the severe heart failure patients who do not be candidate of heart transplantation. We have been developing fully implantable VAD and TAH using undulation pump(UP) under multi-institutional cooperative project supported by the Program for Promotion of Fundamental Studies in Health Sciences of the Pharmaceuticals and Medical Device Agency(PMDA). The objective of this presentation is to introduce the present status of their development.