Axial flow blood pumps are widely used for mechanical circulatory support including implantable left ventricular assist device and peripheral intra-aortic ventricular assist device. The ...miniaturization of the devices plays more and more important role in extending the treatable therapeutic options using these blood pumps. On the other hand, miniaturization will be accompanied with higher motor speed and lower energy efficiency, and blood compatibility of the devices must be taken special care in their developmental stage.
For the continued development of improved mechanical circulatory systems, longer term evaluation of new devices in animal model experiments may be critical. The effects of anticoagulants in adult ...goats have not been well studied. We assessed the effects of oral warfarin in three adult goats during fasting or after feeding. The goats weighing 57.8 ± 8.1 kg (53.0–67.2 kg) were administered warfarin orally beginning at a dose of 5 mg/day and then increasing to 10, 20, 40, and 60 mg every 2 weeks. One goat (receiving 10 mg/day warfarin) was killed on day 27 because of the inability to stand. After administration of 60 mg warfarin, the remaining goat received no warfarin for 4 days to return to coagulated state. The goats were then fasted and treated with 40 mg warfarin. During warfarin administration, both goats required a dose of 60 mg/day to achieve International Normalized Ratios (INRs) of approximately 2.5; however, when, the animals were in the fasted condition, precipitous extension of INR was observed in 5 days. After resuming feeding, the INR was reduced to the proper range. We showed the tendency that warfarin therapy in goats required higher doses than the doses administered to human patients and that the effects of therapy were related to the feeding state. The results of this study provide important information for development of anticoagulation protocols to assess mechanical circulatory support devices for long-term use in preclinical examination.
The flow field of the newly developed inflow cannula designed for a bridge-to-decision circulatory support was numerically analyzed by computational fluid dynamics. This new cannula has elastic ...struts at the tip that enable minimal invasive insertion into the left ventricle while maintaining a wide inflow area by its lantern-like tip. The cannula’s hydrodynamic loss, including change in pressure loss due to deformation, and its thrombus potential were numerically examined. Hydraulic resistance of the cannula with blood analog fluid was 31 mmHg at the flow rate of 5.0 L/min. There were regions on the inner surface of the struts where the shear rate was <100 s
−1
, and these regions can be a potential for thrombus formation, especially at low flow rates or under limited anticoagulant therapy.
In cardiopulmonary support systems with a membrane oxygenation such as a percutaneous cardiopulmonary support (PCPS) or an extracorporeal membrane oxygenation (ECMO), blood pumps need to generate the ...pressure rise of approximately 200mmHg or higher, due to the high hydraulic resistances of the membrane oxygenation and of the cannula tubing. In order to realize the blood pump with higher pressure rise, higher anti-hemolysis and thrombosis performances, the development of novel centrifugal blood pump composed of two-stage has been conducted by the authors. In the present paper, effective attempts to decrease the wall shear stress and to suppress the stagnation are introduced for the prevention of hemolysis and thrombosis in blood pumps. The hemolysis test was also carried out and it was clarified that the decrease of wall shear stress is effective as a guideline of design of blood pumps for improving the anti-hemolysis performance.
The “washout effect” inside a blood pump may depend in part on the configuration of the blood pump, including its “port angle.” The port angle, which is primarily decided based on anatomical ...considerations, may also be important from the rheological viewpoint. In our department, a next-generation diaphragm-type blood pump is being developed. In this study, we examined the influence of the port angle on flow conditions inside our new blood pump. Acrylic resin mock pumps with three different port angles (0°, 30°, and 45°) were prepared for flow visualization. Mechanical monoleaflet valves were mounted on the inlet and outlet ports of the mock pumps. Flow conditions within the mock pumps were visualized by means of particle image velocimetry during a half stroke. As a result, a high flow velocity region was seen along the main circular flow from the inlet to the outlet port. This circular flow was almost uniform and parallel to the plane of the diaphragm-housing junction (DhJ) when viewed from the inlet and outlet sides. Moreover, the proportion of high flow velocity vectors in the plane in the vicinity of the DhJ decreased as the degree of the port angle increased. In conclusion, we found that the flow behavior in the plane in the vicinity of the DhJ changed with the port angle, and that a port angle of 0° may be suitable for our diaphragm-type blood pump in view of the washout effect.
Aiming the ‘Bridge to Recovery’ course, we have developed a novel left ventricular assist device (LVAD) controlling system. It can change the rotational speed of the continuous flow LVAD, EVAHEART, ...synchronized with the cardiac beat. Employing this system, we have already demonstrated that myocardial oxygen consumption (MVO2), which is considered to be equivalent to native heart load, changes in the hearts of normal goats. Herein, we examined changes in goats with acute ischemic heart failure. We studied 14 goats (56.1 ± 6.9 kg) with acute ischemic heart failure due to coronary microsphere embolization. We installed the EVAHEART and drive in four modes: “circuit-clamp”, “continuous support”, “counter-pulse”, and “co-pulse”, with 50 and 100 % bypass. In comparison to the circuit-clamp mode, MVO2 was reduced to 70.4 ± 17.9 % in the counter-pulse mode and increased to 90.3 ± 14.5 % in the co-pulse mode, whereas it was 80.0 ± 14.5 % in the continuous mode, with 100 % bypass (
p
< 0.05). The same difference was confirmed with 50 % bypass. This means that we may have a chance to change the native heart load by controlling the LVAD rotation in synchrony with the cardiac rhythm, so we named our controller as the Native Heart Load Control System (NHLCS). Employing changeable MVO2 with NHLCS according to the patient’s condition may provide more opportunity for native heart recovery with LVAD, especially for patients with ischemic heart diseases.
Driveline infection is a serious complication in long-term therapy using a ventricular assist device (VAD). However, measures taken against this complication have not been sufficient. In this study, ...we evaluated our newly developed infection-resistant skin-button system against driveline infection of an implantable VAD in a chronic animal study. The skin button is made of two flanges using tissue-compatible segmented polyurethane. The exposed upper layer is made of a nonporous sheet with relative flexibility similar in texture to the skin. In addition, this shape was designed to defuse excessive stress at the edge of the skin caused by the external force put on the driveline. The lower layer, which is implanted subcutaneously, is made of a porous material with a three-dimensional reticular structure. The combination of these two flanges with different features enables the driveline to fix to the skin without epithelial downgrowth and peridriveline pocket formation and can prevent bacterial infection over a prolonged period. Results of 90 days of animal tests, the button maintained secure adhesion to the skin and did not exfoliate without special daily treatments, such as dressing or disinfection, and there were no infections or inflammations at the exit site. This study demonstrates that our newly developed skin-button system can be useful for preventing infections at the driveline exit site.
Coronary circulation is closely linked to myocardial oxygen consumption (MVO2), and previous reports have suggested decreased coronary flow (CoF) under left ventricular assist device support. ...Decreased CoF itself under support is not unfavorable because the native heart can be well unloaded and myocardial oxygen demand is also decreased. There should be an autoregulatory system that would maintain optimal CoF according to oxygen demand; however, the detailed mechanism is still unclear. The aim of the current study is to evaluate the effect of centrifugal pumps on CoF under varied bypass rates in relation to left ventricle workload. A centrifugal pump, EVAHEART (Sun Medical Technology Research Corporation, Nagano, Japan), was installed in an adult goat (n = 10, 61.3 ± 6.5 kg). We set up the following conditions, including Circuit‐Clamp (i.e., no pump support), 50% bypass, and 100% bypass. In these settings, CoF, MVO2, pressure–volume area (PVA), and coronary vascular resistance (CVR) were measured. In 100% bypass, CoF, MVO2, and PVA were all decreased significantly from clamp. While in 50% bypass, CoF and MVO2 decreased from clamp, but not PVA. There was a significant 40% increase in CVR in 100% bypass from clamp. This CVR increase in 100% bypass was possibly due to mechanical collapse of coronary vascular bed itself by pump support or increased vascular tone through autoregulatory system. In clinical settings, we should adjust optimal pump speed so as not to cause this vascular collapse. However, to clarify autoregulatory system of the coronary perfusion, further investigation is ongoing in ischemic and heart failure models.
In the cardiopulmonary support system with an ECMO (extracorporeal membrane oxygenation), ahigher pump head is demanded for a blood pump. In order to realize a blood pump with higher pump head, ...higher anti-hemolysis and thrombosis performances, astudy on the development of unprecedented multistage blood pump was conducted. In consideration of the applicationof the blood pump for pediatric patients, a miniature two-stage centrifugal blood pump with the impeller's diameter of40mm was designed and the performance was examined in experiments and computations. Some useful knowledge for a design of the blood pump with higher anti-hemolysis and thrombosis performances was obtained.
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