Vol.5 No.1 2012

Research paper : Research and development of a monopivot centrifugal blood pump for clinical use (T. Yamane et al.)−18−Synthesiology - English edition Vol.5 No.1 (2012) though the size is a little larger than axial flow types. An axial flow pump with hydrodynamic bearings has also been developed by the National Cerebral and Cardiovascular Center (NCVC)/the National Institute of Advanced Industrial Science and Technology (AIST)/Mitsubishi Heavy Industries, Ltd./Nipro Corporation.The second and the third generation VADs enabled patients to go out of the hospital. The controllers are portable and the batteries can be used for 8-10 hours, and the patients can use showers at home. The recent implantations of VADs are almost all rotary pumps in the US. The patients can return to their factories or campuses even in Japan.[1]At present a necessary device for patients is a bridge-to-bridge pump applicable up to the next diagnosis such as the eligibility for implantable VADs or the sufficient recovery of lung function. However, the presently available product is a pneumatic ventricular assist device whose price is more than 30,000 US dollars. A circulatory support pump applicable up to four weeks is necessary whose price is less than 5,000 US dollars. We, at AIST, have been studying the second and the third generation VADs and, based on the research, have succeeded in developing a product for a circulatory support pump for four-week use. In the present paper we describe the scenario of the R&D process and the collaboration between the medical and the engineering teams (M/E collaboration).2 Research of a monopivot centrifugal blood pumpWhen we started the research of artificial heart in 1991, rotary pumps for open heart surgery were requested to eliminate shaft and seal structure. Among seal-less pumps we proposed the “monopivot” mechanism[2] (Fig. 1), which supports the impeller on a point contact, had it patented and started collaboration with the School of Medicine of University of Tsukuba. The pump made by former technology was such that the pump impeller was supported with a shaft and two ball bearings and, therefore, it easily induced hemolysis or thrombosis due to the leakage of blood from the seal. A double pivot pump was also proposed by other facilities. Then we proposed a one-point support mechanism because it was expected to reduce the contact area as well as the hemolysis.An important advice from the clinical side (Professor and Dr Tatsuo Tsutsui, University of Tsukuba) in the collaboration was that, saving animal experiments, engineering evaluation, or in vitro testing, should be conducted first to obtain scientific evidence and then we can proceed next to the animal experiment. It can be called a concept of evidence-based medicine. We joined the national project of NEDO totally implantable artificial heart which started in 1995 and set a tentative goal of developing an implantable VAD.First, we repeated redesign and verification alternatively at each stage of the design through flow visualization. A visualized model was made with a 3 times scale-up acrylic model and the circuit was filled with 64 wt% NaI water solution (specific gravity: 1.9) whose refractive index (1.49) matches with the acrylic model. As tracer particles silver-coated glass beads (average size: 10 m, specific gravity: 1.4) were used. The particle images were taken by a high-speed video system (Phantom), and were illuminated with Ar ion laser light sheet (output: 4 W). The images were analyzed with 4-frame particle tracking method for in-plane motion and with 3-frame particle tracking method for out-of-plane motion because the particle immediately disappeared. Centrifugal blood pumps are often provided with washout Fig. 1 Structure and picture of a disposable monopivot centrifugal blood pump as a product (MERA centrifugal pump HCF-MP23, Senko Medical Instruments Mfg. Co. Ltd.)(Made of mainly polycarbonate, an impeller of 50 mm in diameter, a washout hole of 8 mm in diameter, a spherical pivot of 3 mm in diameter of a combination of a stainless ball and ultra high molecular weight polyethylene)Table 1. Purpose of use, driving mechanism, mission life, and product information of artificial heart/circulatory assist deviceNot approved yet1-6 monthsCentrifugal pump (non-contact bearing)8) Bridge-to-decision (new category)RotaFlow by Maquet, etc.4 daysCentrifugal pump (mechanical bearing)7) Circulatory assist during/after operation BioPump by Medtronic, Capiox by Terumo, HPM15 by Senko Medical, etc.6 hoursRoller pump or Centrifugal pump6)Surgical extracorporeal pumpDuraHeart by Terumo, EVAHEART by Sun Medical Tech.Res., VentrAssist by VentraCor, HVAD by HeartWare7 years or more (on going)Motor-driven rotary pump (non-contact bearing)5)Implantable rotary VADDeBakeyVAD=HeartAssist5、 Jarvik 2000、 HeartMate II5 years or more (on going)Motor-driven rotary pump (mechanical bearing)4)Implantable rotary VADNovacor、 HeartMate XVE1 year(Endurance limit)Electro-magnetic pulsatile pump3)Implantable pulsatile VADToyobo VAD by Nipro1-12 months(Endurance limit)Pneumatic pulsatile pump2)Paracorporeal ventricular assist deviceJarvik 7 by Symbion1 year(Endurance limit)Pneumatic pulsatile pump1)Total replacementartificial heartProduct informationMission lifeDriving mechanismPurpose of useStraight-pathimpellerRadial Magnetic CouplingMonopivotSUS/UHMWPE


page 21