Yasunori Taira

An implantable artificial esophagus to propel food simulating natural anatomical esophageal function

We have been developing implantable esophagus devices to achieve dynamic assistance in food-taking function for the patients suffering from esophageal cancer. Promotion of the quality of life as well as the activity of daily lives of the patients with severe esophageal cancer so that the esophageal tubular restoration by stenting or gastroesophagotomy are often carried out in order to ameliorate self-digestive function. Some patients with those severe cancer have difficulty to make food deliver smoothly due to the lack of peristaltic motions in the lesion. In this study, we presented a new structure of an artificial esophagus which was capable of delivering foods from a mouth to stomach with a distributed mechanism. We examined the natural esophageal specimens in order to obtain a relationship between volume and pressure. Prior to the measurement of mechanical characteristics of the natural specimen, the portions of esophagus were freshly extracted from goats after the experiments. Then we modeled the characteristics of natural esophageal functions through a digestive process from the anatomical, biomechanical point of view and confirmed the functional distribution in the artificial esophagus that could drive the contents from proximal to distal. A new structural design for the proximal esophageal portion was also developed to achieve squeezing motion by using a shape memory alloy fiber as an actuator and its dynamic characteristics were tested.

Recent Progress in the Study of the Cardio-Ankle Vascular Index (CAVI)

To measure the stiffness of the aorta, femoral artery and tibial artery noninvasively, cardio-ankle vascular index (CAVI) which was independent of blood pressure had been developed in cooperation of the Tohoku University and Fukuda denshi Co. The reproducibility had been studied, and the Independence from blood pressure has been studied till now. The results suggested that CAVI could reflect arteriosclerosis of the aorta, femoral artery and tibial artery. Furthermore we can evaluate the baroreflex sensitivity of an artery by the use of arterial tone. International cooperation study is ongoing now. So various scientific reports are easily found in pubmed. Medical device maker is now gathering these international papers for the presentation to the every doctor in the world for the achievements of better medical care. If the evaluation by this methodology in not so good, all doctors have a chance to use another devices. So, it is not necessary to use this method when the scientific papers showed another device had been good. Every doctor in all over the world must check recent progress in medical device in the scientific fields. By the use of the scientific, physical, quantitative methodology, evaluation of the atherosclerosis will be embodied in near future based on the normal value of every people in every country.

Design of a Right Ventricular Simulator for the Evaluation of Artificial Pulmonary Valve

Prosthetic materials are used for right ventricular outflow tract (RVOT) reconstruction in cases of congenital heart defects with right ventricular outflow hypoplasia or atresia and for pulmonary valve replacement in the Ross procedure. This procedure is to replace the stenotic pulmonary heart valve such as hypoplastic RVOT by the artificial valved conduit in infants. The authors have been developing a mechanical mock circulatory system for the evaluation of RVOT reconstruction. Improving the inflow characteristics of the right ventricular function and pulmonary circulatory hemodynamics was essentially necessary for more precise evaluation of newly designed heart valves. We developed an original pediatric pulmonary mechanical circulatory system, which was capable of simulating normal pulmonary hemodynamics in children. The system consists of a pneumatic-driven silicone right ventricle, a pneumatic-driven right atrium with a bileaflet polymer valve, a pulmonary valve chamber with a visualization port, a pulmonary arterial compliance tubing, a pulmonary peripheral resistance unit, and a venous reservoir. The mechanical interaction between the right atrium and ventricle was pneumatically controlled by the originally developed microcomputer. Transvalvular pressure waveforms were measured by the pressure transducers and the pulmonary flow was obtained at the outflow portion of right ventricle by the electromagnetic blood flow probe. As a result, hemodynamic waveforms of either the right ventricle or atrium were obtained at the revised pulmonary mock circulatory system. The characteristics with atrial kick were well simulated as the natural hemodynamics. Moreover we could examine the effects of the bulging sinus structure on the valve leaflet motion in the vicinity of the leaflet as well as the atrial contraction. In this study, we simulated natural hemodynamics in our pulmonary circulatory system. We concluded that the simulation of right atrial contraction was inevitable in the quantitative examination of right heart prosthetic valves for congenital heart failure.

Achievement of Peristaltic Design in the Artificial Esophagus Based on Esophageal Characteristic Analysis of Goats’ Specimen

In order to promote activity of daily life of patients with severe esophageal diseases, supporting peristalsis motion at the esophagus might be efficient. So we have been developing an artificial esophagus (AE) which has peristalsis motion function, and we have achieved the AE by using Ni-Ti shape memory alloy fibers. We extracted the esophagus from the epiglottis to the cardia potion from goats, which weighed 48.6±16.3 kg (n=4), after the animal experiment procedures. Prior to the measurement of characteristics of natural esophagus, we defined 5 segments in each extracted esophagus. Then we set the specimen in the static characteristic test apparatus in which we could measure segmental pressure-volume relations. Pressure and volume were measured simultaneously. All these measurement were performed within 3 hours from the extraction. Average length of each esophagus was 63±7cm. Because of the proximal segment of the specimen exhibited that the steeper increase of pressure than the distal portion near the cardia, we characterized that the distal esophagus is firmer than proximal. The proximal segment exhibited 55% bigger increase in pressure than the distal portion near the gastric cardiac part. Therefore it was suggested that compliance at the proximal portion could be lower at the small amount of internal volume. On the other hands, the extensibility of distal esophagus might be bigger than that at proximal segment. Consequently it was indicated that a new mechanical structure could be applied for the development of AE which could reproduce peristaltic motions.

Modeling of Signal Transmissions in Nerves in Vitro for the Development of a Renal Nerve Cooling Device for Hypertension Control

Hyperactivity of the central nervous system may increase feedback gains in the hemodynamic system. We have been developing a totally implantable renal nerve cooling system which is capable of changing the hyperactive renal nerve function; in particular, those that reversibly eliminate excess signal-gains by using Peltier effects. In this study, we examined the effect of cooling on neurotransmission in vivo and in vitro. Then we evaluated functional characteristics of signal transmission by the change in thermal implication on the nerve to perform thermal sedation of nervous activity. After the animal experimental procedures, we examined the electrical signal transmission in the nerves extracted from the goats. Using the neurogram amplifier and the functional signal generator, we tested the signal transmission characteristics through the nerves and evaluated their filtering functions by regional nerve cooling. In order to examine of natural renal neurotransmission, the renal nerves were dissected from the left kidney in goats under the normal anesthesia using 2.5% of isoflurane. Aortic pressure and the neurogram were measured, and we applied the low-temperature exposure of the nerve. The electric signals exhibited filtered-transmission through the nerve by the cooling in vitro. In the goat’s experiment, the amplitude of the signal which was obtained at the renal nerve decreased when we decreased the nerve surface temperature by -15 degrees. Then we could evaluate these transmission functions of the renal nerve with the interactive changes of the temperature which was to be controlled by the cooling device. We examined characteristics of the signal transmission in the renal nerve in goats by cooling. And we could evaluate these changes in the functional transmission model with the thermal interactions.