Kenkichi Ohba

Development of a Completely Autologous Valved Conduit With the Sinus of Valsalva Using In-Body Tissue Architecture Technology A Pilot Study in Pulmonary Valve Replacement in a Beagle Model

Background— We developed autologous prosthetic implants by simple and safe in-body tissue architecture technology. We present the first report on the development of autologous valved conduit with the sinus of Valsalva (BIOVALVE) by using this unique technology and its subsequent implantation in the pulmonary valves in a beagle model. Methods and Results— A mold of BIOVALVE organization was assembled using 2 types of specially designed silicone rods with a small aperture in a trileaflet shape between them. The concave rods had 3 projections that resembled the protrusions of the sinus of Valsalva. The molds were placed in the dorsal subcutaneous spaces of beagle dogs for 4 weeks. The molds were covered with autologous connective tissues. BIOVALVEs with 3 leaflets in the inner side of the conduit with the sinus of Valsalva were obtained after removing the molds. These valves had adequate burst strength, similar to that of native valves. Tight valvular coaptation and sufficient open orifice area were observed in vitro. These BIOVALVEs were implanted to the main pulmonary arteries as allogenic conduit valves (n=3). Postoperative echocardiography demonstrated smooth movement of the leaflets with trivial regurgitation. Histological examination of specimens obtained at 84 days showed that the surface of the leaflet was covered by endothelial cells and neointima, including an elastin fiber network, and was formed at the anastomosis sides on the luminal surface of the conduit. Conclusion— We developed the first completely autologous BIOVALVE and successfully implanted these BIOVALVEs in a beagle model in a pilot study.

Characterization and optimization of the flow pattern inside a diaphragm blood pump based on flow visualization techniques.

We applied two different flow visualization techniques to obtain detailed information on the inside flow of the diaphragm blood pump of our electrohydraulic total artificial heart system to determine the optimum washout effect that would result in better antithrombogenicity. Major orifice directions of the inflow and outflow Bjork-Shiley valves of the left blood pump were independently changed to create 17 varied patterns. The character and velocity of the main flow at the diaphragm-housing junction were acquired using a laser light sheet method with polyethylene tracers. Wall shear flow, a major factor governing washout in the blood pump, was estimated by a newly developed paint erosion method. In this method, quantitative evaluation for an index of washout effect was made by calculating the residual ratio of the paint on the blood pump inner surface at 30 sec of pumping. When a single circular flow was consistently observed by the laser light sheet method, the paint residual ratio become low, indicating washout was relatively good. At the lowest paint residual ratio, the center of the circular flow observed by the laser light sheet method was located at the geometric center of the blood chamber. In conclusion, the flow pattern inside the blood pump could be characterized by combined use of these two flow visualization techniques, and the significant role of circular flow in better washout was clarified.

Characteristics and behavior of the interfacial wave on the liquid film in a vertically upward air-water two-phase annular flow

Abstract The behavior of individual interfacial waves on liquid film in vertically upward air-water annular flows has been visualized, observed and analyzed by a pigment luminance method(PLM) which was calibrated with a fiber-optic liquid film sensor. By means of this technique, we distinguished three different types of interfacial waves, i.e. the ripple wave, the ring wave and the disturbance wave. Furthermore we measured the characteristics of these three different kinds of waves, and in particular those of the disturbance wave: i.e. its propagation velocity, its frequency in passing and the distance between two adjacent waves, and then obtained the dependency of these characteristics on the air and water volumetric fluxes j g and j l . These results agreed well with the results obtained by other investigators, using an electric needle contact method. A probable mechanism of the occurrence of the ring and the disturbance waves was posited.

Preparation of a completely autologous trileaflet valve-shaped construct by in-body tissue architecture technology

The aim of this study was to prepare completely autologous heart-valve-shaped constructs without using any artificial scaffold materials by in-body tissue architecture technology, which is a practical concept of regenerative medicine based on the biological defense mechanism against foreign bodies. Silicone rods were used as molds to achieve the tubular shape of the arteries, which were implanted in the subcutaneous spaces of rabbits. After 2 weeks of primary in-body tissue incubation, the silicone rods were completely encapsulated within a thin membranous connective tissue mainly consisting of collagen and having a thickness of approximately 100 microm. To achieve the trileaflet shape of the valve, the cylindrical tissues obtained were rolled up with polyurethane belts cut in the shape of three semi-ovals. The assembled tissues were reimplanted for 2 weeks for secondary incubation. The resulting tissues were over-encapsulated with the newly developed membranous connective tissue having a thickness of approximately 200-400 microm. The newly formed membranes were completely fused to the previously developed inner membrane. After the removal of the two artificial materials, tubular constructs with trileaflet-shaped internal surface were obtained. By controlling the formation of the encapsulating tissue in the two-step in-body tissue incubation process, we were able to develop completely autologous trileaflet valve-shaped constructs.

A completely autologous valved conduit prepared in the open form of trileaflets (type VI biovalve): Mold design and valve function in vitro†

In-body tissue, architecture technology represents a promising approach for the development of living heart valve replacements and preparation of a series of biovalves. To reduce the degree of regurgitation and increase the orifice ratio, we designed a novel mold for a type VI biovalve. The mold had an outer diameter of 14 mm for implantation in beagles, and it was prepared by assembling two silicone rods with a small aperture (1 mm) between them. One rod had three protrusions of the sinus of Valsalva, whereas the other was almost cylindrical. When the molds were embedded in the subcutaneous pouches of beagles for 1 month, the native connective tissues that subsequently developed covered the entire outer surface of the molds and migrated into the aperture between the rods. The mold from both sides of the harvested cylindrical implant was removed, and homogenous well-balanced trileaflets were found to be separately formed in the open form with a small aperture at the three commissure parts inside the developed conduit, which had a thick homogenous wall even in the sinus of Valsalva. Exposure of the obtained biovalves to physiological aortic valve flow in beagles revealed proper opening motion with a wide orifice area. The closure dynamics were suboptimal, probably due to the reduction in the size of the sinus of Valsalva. The mechanical behavior of this biovalve might allow its use as a living aortic valve replacement.

Experimental and clinical trial of measuring urinary velocity with the pitot tube and a transrectal ultrasound guided video urodynamic system

Background : The pitot tube is a common device to measure flow velocity. If the pitot tube is used as an urodynamic catheter, urinary velocity and urethral pressure may be measured simultaneously. However, to our knowledge, urodynamic studies with the pitot tube have not been reported. We experimentally and clinically evaluated the feasibility of the pitot tube to measure urinary velocity with a transrectal ultrasound guided video urodynamic system.

Instability of a perfectly conducting liquid jet in electrohydrodynamic spraying : Perturbation analysis and experimental verification

A linear theory of electrohydrodynamic instability of a perfectly conducting liquid jet injected from a capillary tube which is raised to a high DC voltage is presented. The effects of electric field strength and its configuration, jet velocity and physical properties of fluids are considered in the derived equation for disturbance growth rate. It is shown that the jet instability is sensitive to the electric field strength. The axisymmetric mode of instability is dominant at low electric field strength. With increasing electric field strength the nonaxisymmetric mode of instability is intensified. Moreover, as the electric field strength is increased, the breakup wavelength is decreased, which means the decrease in droplet size. Good agreements are obtained between the theoretical and experimental breakup wavelengths for the axisymmetric mode at low electric field strength. However, the breakup wavelengths for the nonaxisymmetric mode in practice are larger than those predicted by the theoretical analysis.

Development of Miniaturized Fiber-Optic Laser Doppler Velocimetry Sensor for Measuring Local Blood Velocity: Measurement of Whole Blood Velocity in Model Blood Vessel Using a Fiber-Optic Sensor with a Convex Lens-Like Tip

A miniaturized fiber-optic laser Doppler velocimetry sensor has been developed to measure the local blood velocity in vivo. The laser beam emitted from the sensor tip can be focused at any distance between 0.1 and 0.5 mm from the tip. Consequently, the sensor has a sufficiently high signal-to-noise ratio to measure the local velocity in almost any opaque fluid, including blood. The sensor head is inserted in an injection needle or a catheter tube. In the former case, it is inserted at an angle to the wall of a vessel and is scanned across the vessel to measure the velocity distribution. In the latter case, it is aligned parallel with the flow in a vessel. For all flows of whole human blood, whole caprine blood, and 69% hematocrit of bovine blood, the velocity distribution across the vessel could be measured very accurately. The insertion angle of the fiber into the flow significantly affects the measurement accuracy; an angle of about 50° is suitable when an injection needle is used. When a catheter is employed, an insertion direction opposite to the flow direction is better than parallel to the flow due to the generation of a wake behind the fiber.

Development of a Miniaturized Fiber-optic LDV Sensor for Local Blood Velocity Measurement

131 DOI: 10.5963/BER0203002 Development of a Miniaturized Fiber-optic LDV Sensor for Local Blood Velocity Measurement Local Velocity and Flow Profile Measurement of Pulsatile Blood Flow Modeled in Humans Shimpei Kohri, Tsutomu Tajikawa, Kenkichi Ohba Department of Medical Engineering, Aino University 4-5-4, Higashiohda, Ibaraki city, Osaka 567-0012 Japan Department of Mechanical Engineering, Kansai University, 3-3-35 Yamate-cho, Suita-shi, Osaka 564-8680 Japan s-kohri@me-u.aino.ac.jp

Influence of Valsalva Sinus on Flow Field around the Aortic Valve and the Valve Characteristics (Quantitative Evaluation by Experiments in vitro Using a Realistic Model)

One of the well known cures for the annuloaortic ectasia is a vascular grafting surgery using a composite graft as an artificial ascending aorta and an artificial valve. Although, almost all conventional grafts do not have Valsalva sinus at the aortic root, the influence of omitting the Valsalva sinus have not yet been clarified. In order to understand the effect of the Valsalva sinuses at aortic root on the valve characteristics and flow field around the valve and furthermore the coronary blood flow, the authors have fabricated some realistic models of aortic valve using three-dimensional modeling machine, and have investigated the effect of the sinus existence by particle image velocimetry (PIV). As the result, the fluctuation of flow rate at coronary artery in the case of the straight wall model was larger than the Valsalva sinus model. The valve leaflets were pulled to the left ventricle, which could cause a diastolic regurgitant flow from the aorta into the left ventricle. The leaflet suction in the Valsalva sinus model was weaker than the straight wall model. Flow visualization results showed that vortex flow occurred in the Valsalva sinus due to jet flow through the valve leaflets during systole. At early diastole, flow into coronary artery around the Valsalva sinus was smoothly than the straight wall model. Consequently it was concluded from a standpoint of flow and valve characteristics that the Valsalva sinus had an important role for the aortic valve and the inlet of the coronary circulation.