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1

A study on a newly designed aortofemoral prosthetic Y graft

Fujimoto T., Nakano S., Iwamura H., Shiraishi Y., Yambe T., Umezu M.

Biocybernetics and Biomedical Engineering

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2008

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Vol. 28, no. 1

59-63

EN

Aortofemoral prosthetic Y grafts are applied for treating abdominal aortic aneurysms. In this study, experiments were conducted in order to demonstrate the effects of an incremental increase in branch diameter in a newly designed aortofemoral Y graft under conditions of both steady and pulsatile flow conditions. It was revealed that in Y grafts, the incremental increase by only 4 mm in the branch diameter affects hydrodynamic characteristics drastically under conditions of both steady and pulsatile flow conditions.

2

Development of implantable probe for observation of microcirculation

Imachi K., Mochizuki S., Baba A., Isoyama T., Saito I., Takiura K., Chinzei T., Shiraishi Y., Yambe T., Abe Y.

Biocybernetics and Biomedical Engineering

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2007

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Vol. 27, no. 1-2

45-52

EN

It is a long-term controversial point between the circulatory physiologists and the artificial heart researchers whether the pulsatile flow is essential for the living body or not [1]. In particular, since the axial flow pump, a continuous flow pump, that could keep the patients alive for more than a few years was introduced into use in clinical setting in 2001, this problem has been regarded as a very important physiological and pathophysiological issue. The objective of this study was to develop an implantable probe to observe microcirculation in artificial circulation. The principle of the probe developed in this study is the following: a thin living tissue is put directly on a highly integrated CCD (charge coupled device), and it is illuminated from the backside of the tissue with LED(light emitting diode). The microvascular nets in the tissue will be projected on the CCD surface, like a contact photograph, which produces an image on the TV screen. The problems are how to magnify them to be able to observe the erythrocyte flow, how to control the focus, how to electrically insulate them and how to make them compact. After several attempts to magnify the image, a micro lens having 2 mm in diameter, 2 mm long and 6 times magnification, was designed and made of acrylic resin. The lens was installed into a CCD camera with 8 mm in diameter and it was 60 mm long. The camera could magnify the image about 650 times on the 14 inches TV screen. A distinct microcirculation image, including the capillary flow, could be observed when the camera was implanted into the connective tissue under the skin of the rabbit. Now the focus control system is being developed with the camera to be implanted in animals on the long-term base.

3

A newly-designed myocardial assist device using a sophisticated shape memory alloy fibre

Shiraishi Y., Yambe T., Sekine K., Ogawa D., Nagatoshi J., Itoh S., Park Y., Uematsu M., Sakata R., Wada Y., Saijo Y., Higa M., Hori Y., Liu H., Wang Q., Konno S., Kuwayama T., Olegario P., Tanaka A., Masumoto N., Ibuki R., Maruyama S., Okamoto E., Fujimoto T., Yoshizawa M., Umezu M., Imachi K., Nitta S.-I., Sasada H., Tabayashi K., Homma D.

Biocybernetics and Biomedical Engineering

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2007

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Vol. 27, no. 1-2

147-154

EN

Recently, the ventricular assist devices are widely applied for a surgical treatment of the final stage of severe heart failure as the bridge to heart transplantation or the destination therapy. However, it was anticipated that the artificial components in the ventricular assist devices might cause the problems concerning thrombosis and infection. As heart failure involves the decrease in myocardial contractile function, the mechanical assistance by using an artificial myocardium might be effective. In this study, the authors developed a mechano-electric artificial myocardial assist system (artificial myocardium), which is capable of supporting natural contractile function from the outside of the ventricle.

4

Biomedical engineering analysis of effectiveness of cardiovascular surgery: anastomosis methods for coronary artery bypass grafting

Umezu M., Kawai J., Suehiro J., Arita M., Shiraishi Y., Iwasaki K., Tanaka T., Akutsu T., Niinami H.

Biocybernetics and Biomedical Engineering

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2006

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Vol. 26, no. 1

61-67

EN

There are two types of coronary artery bypass grafting (CABG) anastomosis methods: the end-to-side anastomosis (ESAs) and the side-to-side anastomosis (SSAs). The choice of these methods is determined by the surgeon's favor because there is no evidence how to optimize. The ultimate objective of this study is to provide new methodology for the surgeons to enable them to choose the anastomosis methods through both in-vivo and invitro tests. The in-vivo tests were performed on pigs and the energy loss at the anastomosis ESAs and SSAs were compared. The in-vitro tests were conducted in the newly-developed system to evaluate CABG anastomosis methods. This system is composed of the mock circulatory system and the coronary simulator, which originally was designed to reproduce various types of the coronary hemodynamics. Both the in-vivo and the in-vitro tests showed a similar 'tendency of the energy loss: SSAs had a lower energy loss than ESAs under the same conditions. These effects were caused by the difference in the local flow at the anastomosis between ESAs and SSAs. Consequently, SSAs is believed to be an anastomosis method preferable to ESAs.

5

Evaluation of freestyle bioprosthesis behavior in mechanical circulatory system

Fujimoto T., Kawaguchi D., Shiraishi Y., Iwasaki K., Arita M., Umezu M.

Biocybernetics and Biomedical Engineering

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2003

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Vol. 23, no. 2

51-55

EN

A freestyle prosthetic heart valve using a porcine aortic root is expected to yield high performance. In this study, Subcoronary and Full-root techniques, that are mainly used for implanting the freestyle bioprosthesis into the aorta, were simulated under conditions in which the degree of elasticity around the bioprosthesis at the aortic root position was varied in a mechanical circulatory system. As a result, the forward flow at the bioprosthesis in the case of the Subcoronary was 11% greater than that of the Full-root. The variation in the elasticity around the bioprosthesis was suggested to influence the hydrodynamic characteristics.

6

Left ventricle simulator for surgeons' support

Umezu M., Arita M., Iwasaki K., Shiraishi Y., Tono S., Uchida K.

Biocybernetics and Biomedical Engineering

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2002

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Vol. 22, no. 4

47-53

EN

The authors have been developing various types of mock circulatory systems to evaluate a performance of artificial organs. Among several attempts, it was indicated that a simulation of the mitral valve region was very difficult due to a complicated shape and movement of the valve. In this paper, a new trial to install a porcine valve into the mock circulatory system is introduced. A fresh porcine valve with papillary muscles and chordae was fixed into the mitral position of the modified Windkessel-type mock circulatory system. To allow direct 3-D observation of the mitral annulus, a digital video camera and a laser displacement sensor were employed. A circulation was generated by a pneumatically-driven artificial ventricle. When a normal circulatory condition (pump rate: 70BPM, Flow: 3L/min) was selected, similar opening and closing motion to the natural mitral valve could be reproduced. Moreover, a diseased condition was made by shifting a position of papillary muscles. After this procedure, an abnormal movement, such as significant leakage, could also be reproduced.

7

In vitro evaluating system for prosthetic heart valves in a case of the Jyros valve

Fujimoto T., Tsutsumi Y., Shiraishi Y., Iwasaki K., Yoshida M., Umezu M., Begg J., Woodard J.

Biocybernetics and Biomedical Engineering

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2002

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Vol. 22, no. 4

41-46

EN

The Jyros valve has unique hydrodynamic characteristics comparing with other types of valves. In this study, precise hydrodynamic characteristics of the valve were examined using a mock circulatory system, which we have developed. Further, the influence of leaflet rotation is shown to reduce flow resistance under the rotational flow condition which was produced by a spiral vortex pump. However, hemolysis was not revealed to be reduced by the Jyros.