Enhancement of hemocompatibility of the MERA monopivot centrifugal pump: toward medium-term use.

The MERA monopivot centrifugal pump has been developed for use in open-heart surgery, circulatory support, and bridge-to-decision for up to 4 weeks. The pump has a closed-type, 50-mm diameter impeller with four straight paths. The impeller is supported by a monopivot bearing and is driven by a radial-flux magnet-coupling motor.

Simple in vitro testing method for antithrombogenic evaluation of centrifugal blood pumps.

We developed a simple in vitro antithrombogenic testing method using a mock circulation system as used in the hemolysis tests to evaluate the antithrombogenicity of centrifugal blood pumps. This method was not designed to substitute for animal experiments but was intended to be a screening test method for selecting pumps robust enough to operate properly during animal experiments. In this study, we were able to maintain an almost constant activated clotting time for test blood for 10 hours by using both trisodium citrate and calcium chloride.

Hemocompatibility evaluation with experimental and computational fluid dynamic analyses for a monopivot circulatory assist pump.

The hemocompatibility of a newly developed monopivot circulatory assist pump was evaluated by the computational fluid dynamic (CFD) analyses with the particle tracking velocimetry measurement. Results were compared with those of the hemolysis test and in vitro antithrombogenic test to prevent hemolysis and thrombus formation inside the pump. The results of the CFD analysis and the particle tracking velocimetry had a good agreement with each other.

Pivot wear of a centrifugal blood pump developed for circulatory assist.

We are developing a monopivot centrifugal pump for circulatory assist for a period of more than 2 weeks. The impeller is supported by a pivot bearing at one end and by a passive magnetic bearing at the other. The pivot undergoes concentrated exposure to the phenomena of wear, hemolysis, and thrombus formation.

Development of failure detection system based on vibration signal for smart artificial heart: in vitro study.

To realize safe and effective medical treatment for patients with implantable artificial hearts, we have developed a smart artificial heart (SAH). The SAH can grasp the mechanical condition of the artificial heart and the physiological condition of the patient. The purpose of this study is to develop a failure detection system based on the vibration signal from artificial heart in order to enhance the ability of failure detection for the SAH.

Antithrombogenic properties of a monopivot magnetic suspension centrifugal pump for circulatory assist.

The National Institute of Advanced Industrial Science and Technology (AIST) monopivot magnetic suspension centrifugal pump (MC105) was developed for open-heart surgery and several weeks of circulatory assist. The monopivot centrifugal pump has a closed impeller of 50 mm in diameter, supported by a single pivot bearing, and is driven through a magnetic coupling to widen the fluid gap. Design parameters such as pivot length and tongue radius were determined through flow visualization experiments, and the effectiveness was verified in preliminary animal experiments.

Resonant frequency control method for total artificial heart: in vitro study.

In order to develop a therapeutic control method for an artificial heart that adapts to physiological behavior for more effective medical care, we applied a resonant frequency control method to a total artificial heart, and evaluated the effectiveness through an in vitro study. The proposed control method utilizes a resonant frequency that can effectively provide blood flow. This resonant frequency was estimated using the systemic circulation model with an online system identification method in real time from two measured physiological data: aortic pressure and blood flow.

Hemolytic evaluation using polyurethane microcapsule suspensions in circulatory support devices: normalized index of hemolysis comparisons of commercial centrifugal blood pumps.

We have been developing some types of microcapsule suspensions with polyurethane membranes to evaluate the absolute hemolytic characteristics of the centrifugal blood pumps used in circulatory support devices such as artificial hearts. In order to facilitate/realize hemolysis testing on centrifugal blood pumps that have hemolysis levels as low as those of commercial centrifugal blood pumps, we eliminated capsules with diameters less than 72.2 microm, amounting to 15.

Hemocompatibility of a hydrodynamic levitation centrifugal blood pump.

A noncontact type centrifugal pump without any complicated control or sensing modules has been developed as a long-term implantable artificial heart. Centrifugal pumps with impellers levitated by original hydrodynamic bearings were designed and have been modified through numerical analyses and in vitro tests. The hemolysis level was reduced by changing the pressure distribution around the impeller and subsequently expanding the bearing gap.

The hemolytic characteristics of monopivot magnetic suspension blood pumps with washout holes.

The hemolytic characteristics of monopivot magnetic suspension blood pumps as a function of impeller washout hole configuration and female pivot shape are observed. The pump impellers are designed with three washout hole configurations for blood circulation, and four female pivot shapes to reduce blood stagnation and to enhance antithrombogenicity. The hemolytic characteristics of the monopivot pumps were observed to be better than those of a currently available commercial centrifugal blood pump, BP-80, and changed to be nearly equal when the female pivot shape was changed.

Resonant frequency control for artificial heart using online parameter identification.

To develop effective medical care and therapeutic control using an artificial heart, a new control method has been developed. This new method can control the artificial heart effectively and can adapt to internal physiological behavior using measured physiological data; aortic pressure, aortic flow, and pump flow. This method consists of first, a second-order physiological model, which represents the internal physiological behavior by a mathematical equation; and second, an estimation method, which can identify the physiological parameters; aortic inertia, aortic resistance, aortic compliance, and peripheral resistance by a parameter identification method.

The most profitable use of flow visualization in the elimination of thrombus from a monopivot magnetic suspension blood pump.

The purpose of this study was to eliminate fluid dynamic causes of thrombus formation for the monopivot magnetic suspension centrifugal pump under development with the aid of flow visualization as an indirect measurement tool for animal experiments. The formation of thrombus observed in early animal experiments was successfully overcome by combining the multiple washout holes at the center into a single hole, optimizing the hole diameter, and eliminating the pivot gap. Flow visualization was used to optimize the washout hole diameter influencing the flow around the pivot.

Tsukuba remote monitoring system for continuous-flow artificial heart.

In order to make long-term medical treatment with the use of an artificial heart effective, we developed the Tsukuba remote monitoring system, which enables medical staff to manage the physiological condition of patients and the driving condition of the artificial heart at anytime from a remote place. This remote monitoring system has three functions: first, a remote monitoring function, which enables medical staff to monitor measured data from a remote place anytime by using not only a personal computer but also a cellular phone; second, an analyzing function, which estimates the unmeasured physiological behavior in the body based on a mathematical physiological model; and third, a warning function, which detects physiological problems and malfunction of the artificial heart by applying the if-then rule and sends a warning message to the medical staff. As a result of applying this system to animal experiments, we have confirmed the effectiveness of the proposed system.

Development of built-in type and noninvasive sensor systems for smart artificial heart.

It is very important to grasp the artificial heart condition and the physiologic conditions for the implantable artificial heart. In our laboratory, a smart artificial heart (SAH) has been proposed and developed. An SAH is an artificial heart with a noninvasive sensor; it is a sensorized and intelligent artificial heart for safe and effective treatment.

Online parameter identification of second-order systemic circulation model using the delta operator.

To develop effective medical care with the artificial heart, we proposed a new method that can calculate the time varying and unmeasured hemodynamics of the human body from measured physiological data: aortic pressure, aortic flow, and pump flow in real time. This method comprises first, the second order of systemic circulation model, which consists of aortic compliance (Ca), aortic resistance (Ra), aortic inertia (L), and total peripheral resistance (Rp); and second, system identification using the delta operator. In the computer simulation, we confirmed the effectiveness of this method.

Fractural characteristic evaluation of a microcapsule suspension using a rotational shear stressor.

We are developing microcapsule suspensions to evaluate the absolute hemolytic properties of centrifugal blood pumps. Four types of microcapsule suspensions, with maximum diameters of 100 microm or 10 microm, and membranes of polyurethane or melamine resin, were exposed to fluid dynamic shear up to 15,000 s(-1) with a rotating shear stressor developed in our laboratory. As a result, destruction was observed of only the 100 microm microcapsules.

On-line parameter identification of systemic circulation using the delta operator.

To develop effective medical care with the artificial heart, we propose a new method, on-line parameter identification of the systemic circulation using the delta operator which can calculate the time-varying and unmeasured hemodynamics of the internal human body from some measured data: aortic pressure and total flow in real time. This method consists of first, a dynamic physiological model which is configured with the physiological parameters Ca (aortic compliance) and Rp (total peripheral resistance); and second, a system identification method using the delta operator. In the computer simulation study, we could confirm the effectiveness to identify the physiological parameters.