Biomedical subjects

Yoshiyuki Taenaka

Publications and source records attributed to Yoshiyuki Taenaka.

At least 19 recordsLinked to original sources

PubMed2006

Mechanism for cavitation of monoleaflet and bileaflet valves in an artificial heart.

It is possible that mechanical heart valves mounted in an artificial heart close much faster than those used for clinical valve replacement, resulting in the formation of cavitation bubbles. In this study, the mechanism for mechanical heart cavitation was investigated using the Medtronic Hall monoleaflet valve and the Sorin Bicarbon bileaflet valve mounted at the mitral position in an electrohydraulic total artificial heart. The valve-closing velocity was measured with a charge-coupled device (CCD) laser displacement sensor, and images of mechanical heart valve cavitation were recorded using a high-speed video camera. The valve-closing velocity of the Sorin Bicarbon bileaflet valve was lower than that of the Medtronic Hall monoleaflet valve. Most of the cavitation bubbles generated by the monoleaflet valve were observed near the valve stop; with the Sorin Bicarbon bileaflet valve, cavitation bubbles were concentrated along the leaflet tip. The cavitation density increased as the valve-closing velocity and the valve stop area increased. These results strongly indicate that squeeze flow holds the key to cavitation in the mechanical heart valve. From the perspective of squeeze flow, bileaflet valves with a low valve-closing velocity and a small valve stop area may cause less blood cell damage than monoleaflet valves.

Heart Valves↗

PubMed2006

Estimation of mechanical heart valve cavitation in an electro-hydraulic total artificial heart.

The purpose of this study was to establish a method for estimating mechanical in vitro heart valve cavitation in an electro-hydraulic total artificial heart (EHTAH). The variations in the left driving pressure (LDP) slope of the EHTAH were used as an index of the cavitation intensity. The LDP slope was controlled by changing the stroke volume of the EHTAH. The stroke volume was changed from full-filling and full-eject to partial-filling and partial-eject conditions. A 25-mm Medtronic Hall valve was installed in the mitral position of the EHTAH. Cavitation bubbles were concentrated on the valve stop; the major cause of these cavitation bubbles was determined to be squeeze flow. The valve-closing velocity was found to be proportional to increases in the LDP slope and the stroke volume of the left blood pump. The cavitation intensity and the cavitation event rate increased with increases in the stroke volume of the EHTAH. A consistent correlation was observed between the valve-closing velocity and the cavitation intensity. The LDP slope of the EHTAH may play an important role in estimating the mechanical heart valve cavitation intensity.

Equipment Failure Analysis↗

PubMed2005

Gene transfection with human hepatocyte growth factor complementary DNA plasmids attenuates cardiac remodeling after acute myocardial infarction in goat hearts implanted with ventricular assist devices.

BACKGROUND: Although a left ventricular assist device is often used to provide circulatory support until transplantation in severe heart failure, the mortality of long-term use of left ventricular assist devices remains high. We have shown that hepatocyte growth factor causes angiogenesis, antifibrosis, and antiapoptosis in the myocardium. Therefore, gene therapy with hepatocyte growth factor-complementary DNA plasmids may enhance the chance of "bridge to recovery." In this study, we performed gene therapy with hepatocyte growth factor in the impaired goat heart with a left ventricular assist device. METHODS: Cardiac impairment was induced in 6 adult goats (56-65 kg) by ligation of the coronary artery, and ventricular assist devices were installed. The hepatocyte growth factor group (HGF; n = 3) was administered human hepatocyte growth factor-complementary DNA plasmid (2.0 mg) in the myocardium. The control group (n = 3) was similarly administered beta-galactosidase plasmid. Four weeks after gene transfection, we attempted to wean all goats from the ventricular assist device. RESULTS: The myocardia transfected with human hepatocyte growth factor-complementary DNA contained human hepatocyte growth factor protein at levels as high as 1.0 +/- 0.3 ng/g tissue 3 days after transfection. After weaning from the ventricular assist device, the HGF group showed good hemodynamics, whereas the control group showed deterioration. The percentage of fractional shortening was significantly higher in the HGF group than the control group (HGF vs control, 37.9% +/- 1.7% vs 26.4% +/- 0.3%, respectively; P < .01). Left ventricular dilatation associated with myocyte hypertrophy and fibrotic changes was detected in the control group but not in the HGF group. Vascular density was markedly increased in the HGF group. CONCLUSIONS: These results suggest that gene therapy with human hepatocyte growth factor may enhance the chance of bridge to recovery in the impaired heart supported with a ventricular assist device.

Animals↗

PubMed2005

Mechanism for cavitation in the mechanical heart valve with an artificial heart: nuclei and viscosity dependence.

Until now, we have estimated cavitation for mechanical heart valves (MHV) mounted in an electrohydraulic total artificial heart (EHTAH) with tap water. However, tap water at room temperature is not a proper substitute for blood at 37 degrees C. We therefore investigated fluid characterization in studies of MHV cavitation associated with the viscosity and nuclei content of a testing fluid. We used the Medtronic Hall valve mounted in the mitral position of the EHTAH. As testing fluids, tap water, distilled water, and glycerin solution were used. The valve-closing velocity, pressure-drop measurements, and a high-speed video camera were employed to determine the cavitation intensity in MHV. Most of the cavitation bubbles were observed at the edge of the valve stop. Our analysis of the results indicates that squeeze flow is the major cause of cavitation in the Medtronic Hall valve. The cavitation intensity increased with increases in the fluid viscosity and the valve-closing velocity. Even if cavitation intensity in glycerin solution was greater, the cavitation occurrence probability was less in glycerin solution than in tap water. Our results suggest that tap water contains particles that cause an increase in the cavitation occurrence probability. We conclude that cavitation intensity is greatly affected by the nuclei concentration in the fluid and the fluid viscosity.

Cardiac Output↗

PubMed2004

Observation of alveolar fibrosis in a goat following venoarterial bypass for up to 5 months using extracorporeal membrane oxygenation.

Prolonged cardiopulmonary bypass such as venoarterial bypass with extracorporeal membrane oxygenation (VA-ECMO) is becoming a potent therapeutic option in treating patients with severe respiratory and circulatory failure. However the chronic effects of this bypass modality have not yet been fully clarified. Recently, we developed an extremely durable thrombo-resistant ECMO system, and were successful with more than 5 months of continuous heparinless VA-ECMO in an animal experiment. This article presents the pathological findings on the lungs of the animal.A goat underwent VA-ECMO for a scheduled period of 151 days. This animal demonstrated a good general condition during the course of the experiment. On autopsy, however, the lungs of the animal showed severe alveolar fibrosis with topical atelectasis. von Willebrand factor levels on the endothelial cells in the alveolar capillaries were increased compared with those of normal goats. The ultrastructure of these cells showed ischemia-induced endothelial swelling. The pathological findings indicated that the vascular endothelial phenotypes had changed from respiratory type to nutrient type. The results of this study indicated that prolonged VA-ECMO may cause pulmonary alveolar fibrosis as a result of ischemia of the lungs accompanying reduced pulmonary blood flow.

Animals↗

PubMed2004

Observation of cavitation bubbles in monoleaflet mechanical heart valves.

Recently, cavitation on the surface of mechanical heart valves (MHVs) has been studied as a cause of fractures occurring in implanted MHVs. In the present study, we investigated the mechanism of MHV cavitation associated with the Björk-Shiley valve and the Medtronic Hall valve in an electrohydraulic total artificial heart (EHTAH). The valves were mounted in the mitral position in the EHTAH. The valve closing motion, pressure drop measurements, and cavitation capture were employed to investigate the mechanisms for cavitation in the MHV. There are no differences in valve closing velocity between the two valves, and its value ranged from 0.53 to 1.96 m/s. The magnitude of negative pressure increased with an increase in the heart rate, and the negative pressure in the Medtronic Hall valve was greater than that in the Björk-Shiley valve. Cavitation bubbles were concentrated at the edge of the valve stop; the major cause of these cavitation bubbles was determined to be the squeeze flow. The formation of cavitation bubbles depended on the valve closing velocity and the valve leaflet geometry. From the viewpoint of squeeze flow, the Björk-Shiley valve was less likely to cause blood cell damage than the Medtronic Hall valve in our EHTAH.

Equipment Failure Analysis↗

PubMed2003

Closing behavior of the mechanical heart valve in a total artificial heart.

Recently, cavitation on the surface of mechanical heart valves has been studied as a cause of fractures occurring in implanted mechanical heart valves. The cause of cavitation in mechanical heart valve was investigated in both 25-mm Björk-Shiley and 25-mm Medtronic Hall valves. The closing events of these valves in the mitral position were simulated in an electrohydraulic total artificial heart with a stroke volume of 85 ml. The tests were conducted under physiologic pressures at heart rates of 60, 70, 80, and 90 beats/min with cardiac outputs of 4.5, 5.5, 6.4, and 7.5 l/min, respectively. The disk closing behavior was measured by a laser displacement sensor. The closing behaviors were investigated under various atrial and aortic pressures. In both valves, the duration of closing decreased with an increase in the cardiac output. The greater the amount of atrial pressure, the shorter the closing duration of both valves. The maximum closing velocity of the Medtronic Hall monostrut valve ranged from 0.8 to 0.9 m/s, and that of the Björk-Shiley monostrut valve ranged from 0.73 to 0.78 m/s. In both valves, the maximum closing velocities were less than the reported cavitation thresholds. This suggests that there should be no possibility of occurrence of cavitation in an electrohydraulic total artificial heart with mechanical heart valve.

Biomechanical Phenomena↗

PubMed2003

The roles of vascular smooth muscle cells in the aortic wall thinness under prolonged continuous flow left heart bypass.

Aortic wall thinness was one of the most characteristic changes observed in experimental animals under prolonged continuous flow left heart bypass. The goal of this study was to determine the roles of smooth muscle cells in the vascular remodeling process in cases demonstrating aortic wall thinness under prolonged continuous flow left heart bypass. The aortic samples from three goats in which continuous flow left heart bypass was performed were subjected to histological and immunohistochemical analyses. After 4 weeks of observation, the pulse pressure in the goats under the continuous flow left heart bypass was clearly lower than that in the normal healthy goats. The aortic walls of these goats became thinner, an effect caused by the dilation of their internal diameter. These aortic smooth muscle cells maintained contractile formation due to the fact that they contained abundant alpha-smooth muscle actin (SMA) and smooth muscle myosin heavy chain (SMMS). These cells also synthesized redundant matrix metalloproteinase-2 and -9, and the ratio of the SMMS-positive to the SMA-positive area was significantly lower (0.76) than that observed in the control goat (1.00; P < 0.05). The smooth muscle cells demonstrated synthetic-dedifferentiated formation, which is one of the phenotypes of smooth muscle cell function. In conclusion, aortic wall thinness under prolonged continuous flow left heart bypass is caused by over-synthesis of matrix metalloproteinase in smooth muscle cells, and this refers the vascular remodeling process of the extracellular matrix.

Animals↗

PubMed2003

Design progress of the ultracompact integrated heart lung assist device--part 2: optimization of the diffuser vane profile.

The configuration of the vaned diffuser of the integrated heart lung assist device (IHLAD) has been revised to reduce mechanical blood trauma caused by the device. The flow visualization study of the flow near the diffuser vanes revealed the existence of a rotating stall which deteriorates the hydrodynamic performance of the device and augments the chance for blood cells to pass through the regions with intense shearing forces. Design changes of the diffuser included decrease in vane number from 7 to 5 and decrease in passage width from 3 mm to 2 mm. This design change was effective to suppress initiation of a rotating stall. Improvement of hydrodynamic performance and antihemolytic properties was confirmed with the newly designed configuration based on the flow visualization study.

Centrifugation↗

PubMed2003

Design progress of the ultracompact integrated heart lung assist device--part 1: effect of vaned diffusers on gas-transfer performances.

The integrated heart lung assist device (IHLAD) has been developed to overcome the problems of currently available extracorporeal membrane oxygenation devices. The integrated structure of a centrifugal blood pump and cylindrical bundle of polyolefin hollow-fibers has allowed a remarkably compact size for the device. This study deals with the design change of the IHLAD that added to the vaned diffuser between the impeller of the centrifugal pump and the hollow-fiber bundle with a view to enhancing the gas-transfer performance. Ex vivo gas-transfer performance tests were carried out, as well as hydrodynamic characteristics and hemolysis test using fresh goat blood. The oxygen transfer rate was generally improved, and the carbon dioxide removal rate was slightly improved. Intolerable amount of hemolysis (index of hemolysis= 0.177) was caused by the IHLAD, which must be resolved by improving the design in the future.

Animals↗

PubMed2003

Measurement of the closing behavior of the björk-shiley monoleaflet mechanical heart valve with an electrohydraulic total artificial heart.

When cavitation occurs near a material surface of a mechanical heart valve (MHV), pits on the surface of the MHV and hemolysis are caused. Therefore, it is very important to investigate the possibility of the occurrence of cavitation in an MHV. To study the possibility of cavitation occurrence in a 25 mm Björk-Shiley monoleaflet, we analyzed the closing behavior of these valves. The closing event of these valves in the mitral and aortic positions was simulated in an electrohydraulic total artificial heart with a stroke volume of 100 ml. Tests were conducted under physiologic pressures at heart rates of 50, 60, 70, and 80 beats/min with cardiac outputs of 4.8, 5.9, 7.0, and 8.1 l/min, respectively. The disk-closing behavior was measured by a laser displacement sensor. The closing behaviors were investigated with various cardiac outputs and gravity direction. The maximum velocities of the aortic valve ranged from 0.8 to 0.9 m/s, and for the mitral valve ranged from 1.48 to 1.6 m/s. In aortic position valves, the maximum closing velocities were less than the reported cavitation thresholds, but the maximum closing velocities of the mitral valve were similar to the cavitation threshold. Therefore, we suggest that there should be the possibility of cavitation occurrence in the mitral valve of an electrohydraulic total artificial heart.

Heart Valve Prosthesis↗

PubMed2002

At least thirty-four days of animal continuous perfusion by a newly developed extracorporeal membrane oxygenation system without systemic anticoagulants.

We developed an extracorporeal membrane oxygenation (ECMO) system with high antithrombogenicity and durability characteristics for prolonged continuous cardiopulmonary support. The oxygenator consists of a special hollow-fiber-type polyolefin gas-exchange membrane, which has an ultrathin dense layer in contact with the blood, in order to prevent plasma leakage during protracted use (Platinum Cube NCVC). The centrifugal pump (RotaFlow) is free of seals. The entire blood-contacting surface of the system is coated with a newly developed heparin material (Toyobo-NCVC coating). We performed a venoarterial bypass in a goat, and the ECMO system was driven for 34 days without systemic anticoagulants. Plasma leakage from the oxygenator did not occur, and sufficient gas exchange performance was maintained. Thrombus formation was hardly observed in the ECMO system except in the casing margins of the oxygenator. This ECMO system showed potential for long-term cardiopulmonary support with minimal or no use of systemic anticoagulants.

Animals↗

PubMed2002

Prostaglandin synthesis inhibitor affects humoral conditions and oxygen metabolism during normothermic cardiopulmonary bypass.

We have reported that infusion of prostaglandin synthesis inhibitor (PGSI) reduced the severity of hypotension during normothermic cardiopulmonary bypass (CPB). In the present study, we investigated the effects of PGSI on humoral conditions and whole body oxygen metabolism during normothermic CPB conducted for 60 min in 8 adult goats. The PGSI group (n = 4) was administered 100 to 150 mg of flurbiprofen, a potent PGSI, before and during CPB, and the control group (n = 4) was administered noradrenaline (NA) to restore hypotension. The prostaglandin E2 (PGE2) and NA concentrations in the PGSI group were significantly lower than those of the control group (PGE2 8.8 +/- 1.0 versus 30.3 +/- 11.5 pg/ml, NA 431 +/- 197 versus 3847 +/- 2,153 pg/ml). The adrenaline concentration was not significantly different between the groups. The oxygen consumption and the oxygen extraction rate were not significantly different between the groups, but the blood lactate level in the PGSI group was lower than that of the control group (34.3 +/- 7.6 versus 43.7 +/- 3.8 mg/dl). In conclusion, PGSI improves humoral disorder and thus prevents inadequate tissue oxygen delivery.

Analysis of Variance↗

PubMed2002

Morphological changes of the arterial systems in the kidney under prolonged continuous flow left heart bypass.

We investigated morphological changes of the arterial systems in the kidneys under prolonged continuous flow left heart bypass. Twelve goats were subjected to 2 weeks of pulsatile left heart bypass followed by 4 weeks of continuous flow left heart bypass (group CF). After autopsy, the kidneys underwent pathological evaluation. Six normal healthy goats were used as controls. The media of the afferent arterioles of group CF were frequently thickened by an increase in the number of the mature smooth muscle cells (SMCs). The juxtaglomerular areas (JGA) were expanded because of an increase in the number and size of SMCs and/or SMC-like cells. Furthermore, the percentage of anti-proliferating cell nuclear antigen antibody-positive cells in the JGA of group CF (9.9 +/- 1.9%) was significantly higher (p = 0.025) than that of the control group (4.6 +/- 3.4%), indicating active proliferation in group CF. We concluded that prolonged continuous flow left heart bypass causes proliferation of SMCs and/or SMC-like cells in the afferent arterioles and their perivascular tissue.

Animals↗

PubMed2002

[Totally implantable artificial heart systems].

Total artificial hearts have been used as bridging devices before cardiac transplantation. The donor heart shortage is still a major problem, and the advent of a totally implantable artificial heart system is eagerly awaited. The results of animal experiments have improved in the USA and Japan, and clinical application of the AbioCor artificial heart system has been initiated in the USA. The initial results were successful, and there is now a long-term survivor.

Animals↗

PubMedDate not supplied

Improvement of washout flow in a centrifugal blood pump by a semi-open impeller.

To reduce the possible thrombogenicity of the pump studied, pump characteristics and washout conditions were compared between a pump with a semi-open and a pump with a full-open impeller. A difference in hydrodynamic performance was observed between the semi-open impeller and the full-open impeller; the pressure in the former was less by approximately 10%, and the maximum attainable efficiency decreased from 0.41 to 0.34. The flow pattern, as visualized by the oil film method, showed that the washout condition was enhanced by addition of the shroud, especially at the bottom region of the pump where the blood flow tended to be stagnant. The stagnant area was observed in the suction side of the impeller in both models, where the vortices shed from the impeller tip contributed to the washout. It was also shown that the flow entering the bottom region was circumferentially uniform in the full-open impeller, whereas in the semi-open impeller the flow was not uniform and entered primarily from the vicinity of the outlet port. The semi-open impeller, thus, was demonstrated to have better washout conditions than the full-open impeller regardless of a slight decrease in hydrodynamic efficiency.

Blood Flow Velocity↗

PubMedDate not supplied

Visualization study of the transient flow in the centrifugal blood pump impeller.

Rotary blood pumps as a left ventricular assist device have several advantages over the use of existing pulsatile devices used for this purpose. The relative velocity distribution to the rotating impeller was observed by high-speed videography and particle image velocimetry (PIV) with the purpose of characterizing the unsteady fluid motion in the impeller and assessing antithrombogenicity based on the fluid dynamic properties within the flow path. Flow visualization in the present study has clearly shown the existence of drastic transient motion of flows in the impeller. The secondary flows developed in the passage, which are adverse in terms of hydrodynamic efficiency, contributed to the washout conditions on the blood contacting surface.

Blood Flow Velocity↗

PubMedDate not supplied

Prostaglandin synthesis inhibitor prevents hypotension without impairing gut perfusion during normothermic cardiopulmonary bypass.

Aortic pressure declines during cardiopulmonary bypass (CPB), particularly at normothermia. It has been reported that administering vasoconstrictors during normothermic CPB (NCPB) to restore perfusion pressure might induce hypoperfusion of splanchnic organs. We have reported that prostaglandin (PG), metabolized in the lung but increased during CPB, might have played a substantial role in hypotension, and that a PG synthesis inhibitor (PGSI) could improve hypotension during CPB. This study was designed to examine whether regional perfusion of splanchnic organs was reduced when PGSI restored systemic perfusion pressure during NCPB. NCPB was performed in eight adult goats for 60 minutes (body weight 57.0 +/- 5.9 kg). PGSI was administered in group P (n = 4), while norepinephrine was administered in group C (n = 4), to keep aortic pressure in the range of 50 to 80 mm Hg. The total systemic flow was maintained at approximately 70 ml/kg/min. Tissue blood flow was measured by means of the colored microsphere method before and 30 and 60 minutes after the start of CPB. In group P, gut blood flows after the start of CPB were higher than those before CPB, significantly in the stomach and jejunum at 30 minutes (p < 0.05), whereas gut blood flows in group C were decreased or not changed. In conclusion, PGSI prevents hypotension without impairing gut perfusion during NCPB.

Animals↗