Yusuke Tsuboko

Peristaltic hemodynamics of a new pediatric circulatory assist system for Fontan circulation using shape memory alloy fibers

Fontan procedure is one of the common surgical treatments of congenital heart diseases. Patients with Fontan circulation have single ventricle in the systemic circulation with the total cavopulmonary connection. We have been developing a pulmonary circulatory assist device using shape memory alloy fibers for Fontan circulation with total cavopulmonary connection. It consisted of the shape memory alloy fibers, the diameter of which are 100 μm. The fibers could wrap the ePTFE conduit for Fontan TCPC connection from the outside. We designed the sequential motion control system for sophisticated pulmonary hemodynamics by the pulsatile flow generation. In order to achieve pulsatile flow assistance in pulmonary arterial system, we fabricated a mechanical structure by sequential contraction of shape memory alloy fibers. Then, we developed a sequential contraction controller for the assist system, which could reproduce the wall contractile velocity at 6.0 to 20.0 cm/sec. We examined hemodynamic characteristic of its function using a mock circulatory system, which consisted of two overflow tanks representing venous and pulmonary arterial pressures in Fontan circulation. As a result, the pulmonary circulation assist device with sequential contraction could achieve effective promotion of the pulsatility in pulmonary arterial flow.

Hemodynamic effects of pressure-volume relation in the atrial contraction model on the total artificial heart using centrifugal blood pumps

Hemodynamic effects of atrial contraction with centrifugal pump type total artificial heart is unknown. In this study, we simulated an atrial contraction in a mock model. By the driving condition with higher pressure in the mock atrial model, the load during atrial contraction increased. Based on these findings, we examined atrial contraction in the animal using adult goats. Prior to the measurement, we installed a centrifugal-type ventricular assist device (VADs), and then clamped both ventricles. We measured the hemodynamic data without ventricular contractile functions in order to obtain the effect of atrial contraction on hemodynamics under the condition of the total artificial heart (TAH) circulatory support model. We could estimate the heart rate by revolution number and voltage of pumps. There might be a possibility that we could regulate autonomic nervous response with the control of cardiac output.

Controlling methods of a newly developed extra aortic counter-pulsation device using shape memory alloy fibers

Diastolic counter-pulsation has been used to provide circulatory augmentation for short term cardiac support. The success of intra-aortic balloon pump (IABP) therapy has generated interest in long term counter-pulsation strategies to treat heart failure patients. The authors have been developing a totally implantable extra aortic pulsation device for the circulatory support of heart failure patients, using 150μm Ni-Ti anisotropic shape memory alloy (SMA) fibers. These fibers contract by Joule heating with an electric current supply. The special features of our design are as follow: non blood contacting, extra aortic pulsation function synchronizing with the native heart, a wrapping mechanical structure for the aorta in order to achieve its assistance as the aortomyoplsty and the extra aortic balloon pump. The device consisted of rubber silicone wall plates, serially connected for radial contraction. We examined the contractile function of the device, as well as it controlling methods; the phase delay parameter and the pulse width modulation, in a systemic mock circulatory system, with a pneumatically driven silicone left ventricle model, arterial rubber tubing, a peripheral resistance unit, and a venous reservoir. The device was secured around the aortic tubing with a counter-pulsation mode of 1-4 against the heartbeat. Pressure and flow waveforms were measured at the aortic outflow, as well as its driving condition of the contraction phase width and the phase delay. The device achieved its variable phase control for co-pulsation or counter-pulsation modes by changing the phase delay of the SMA fibers. Peak diastolic pressure significantly augmented, mean flow increased (p<;0.05) according to the pulse width modulation. Therefore the newly developed extra aortic counter-pulsation device using SMA fibers, through it controlling methods indicated its promising alternative extra aortic approach for non-blood contacting cardiovascular circulatory support.

Preliminary Design of the Mechanical Circulation Assist Device for Fontan Circulation using Shape Memory Alloy Fibers

Fontan procedure is one of the common surgical treatment of congenital heart diseases. Patients with Fontan circulation have single ventricle in the systemic circulation with the total cavopulmonary connection. Pulmonary blood flow in the Fontan circulation is lower than in healthy subjects, and the central venous pressure may elevate. In this study, we developed a mechanical circulatory assist device for the extracardiac conduit for Fontan circulation and examined its driving method in the mock pediatric pulmonary circulatory system. We used shape memory alloy (SMA) fiber as an actuator of the device. The SMA actuator wrapped the extracardiac conduit between inferior vena cava and pulmonary artery. We designed two different types of the circulatory assist devices. We drove these devices in two different modes by the synchronized and sequential motions. The flow volume was 10mL/min against a load of 10mmHg, and the maximum contractile force indicated 60mmHg in the mock test. These results suggested the effective mechanical assistance for Fontan pulmonary circulation.

Engineering based assessment for a shape design of a pediatric ePTFE pulmonary conduit valve

The authors examined the hemodynamic characteristics of expanded polytetrafluoroethylene (ePTFE) pulmonary valved conduits quantitatively by our originally developed pediatric pulmonary mechanical circulatory system, in order to suggest the optimal shape design. The system consisted of pneumatically driven right atrium and ventricle model, a pulmonary valve chamber, and elastic pulmonary compliance model with peripheral vascular resistance units, a venous reservoir. We employed two different types of ePTFE valve and evaluated the relationship between the leaflets motion and hemodynamic characteristics by using a high-speed video camera. As a result, we successfully reproduced hemodynamic simulations in our pediatric pulmonary mock system. We confirmed that the presence of bulging sinuses in the pulmonary valved conduit reduced the transvalvular energy loss and increased the valve opening area during systolic period. Our engineering-based in vitro analysis could be useful for proposing a shape design optimization of sophisticated pediatric ePTFE pulmonary valve.

Effect of valsalva in the pulmonary prosthetic conduit valve on hemodynamic function in a mock circulatory system.

Pulmonary conduit valves are used as one of the surgical treatment methods of congenital heart diseases. We have been designing a sophisticated pulmonary conduit valve for the right ventricular outflow tract reconstruction in pediatric patients. In this study, two types of polyester grafts with or without bulging structures for the conduit valves were used and evaluated from the hemodynamic point of view focusing on the application of these conduit valves in the grown-up congenital heart failure patients. We examined valvular function in the originally developed pulmonary mock circulatory system, which consisted of a pneumatic driven right ventricular model, a pulmonary valve chamber, and an elastic pulmonary compliance model with peripheral vascular resistance units. Prior to the measurement, a bileaflet valve was sutured in each conduit. Each conduit valve was installed in the mock right ventricular outflow portion, and its leaflet motion was obtained by using a high-speed camera synchronously with pressure and flow waveforms. As a result, we could obtain hemodynamic changes in two different types of conduits for pulmonary valves, and it was indicated that the presence of the Valsalva shape might be effective for promoting valvular response in the low cardiac output condition.

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.