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Biomedical subjects

T Akutsu

Publications and source records attributed to T Akutsu.

At least 181 records · Page 10Linked to original sources
PubMedDate not supplied

Three-dimensional interface geometry of the human heart with the artificial heart.

The interface geometry of human and artificial hearts was defined. It included: 1) the approximate mitral orifice and mitral orifice planes; 2) the approximate tricuspid orifice and tricuspid orifice planes; 3) the long and short diameters of the aorta; 4) the long and short diameters of the pulmonary artery; and 5) the angles between the mitral orifice and tricuspid orifice planes, as well as the axes of the aorta and pulmonary artery. The orifice plane was defined as a plane such that the sum of the squared distances between the plane and points on the orifice contour was minimized. A standard coordinate system was also defined, whose origin was the centroid of the approximate mitral orifice. Its X-Y plane was the approximate mitral orifice plane. One set of interface parameters was determined using magnetic resonance images of a volunteer's heart. The angle between the approximate mitral orifice plane and tricuspid plane was found to be 19.9 degrees. The areas of the approximate mitral and tricuspid orifices were 1020 and 1655 mm2, respectively. The approximate mitral orifice was covered by a 44 x 40 mm rectangle and the approximate tricuspid orifice was covered by a 59 x 41 mm rectangle. This interface geometry is important, not only in the manufacture of artificial hearts of precise dimensions, but also in avoiding complications due to their long-term use.

Computer Graphics↗
PubMedDate not supplied

Chronic in vivo evaluation of a portable electrohydraulic ventricular assist system with a linear actuator.

Chronic experiments of the electrohydraulic ventricular assist system with a linear motor actuator were performed in two goats weighing 54 kg and 56 kg, and the system was used for more than 30 days. The actuator was designed to be fixed on the goat's back with a saddle. The pump was connected between the left atrium and descending aorta and placed paracorporeally on the chest wall. Linear action of an actuator bellows was delivered by silicone oil in a U-shaped polyvinylchloride tube to activate the pump. The maximum output in the 56 kg goat was 5.0 L/min. Goats could stand and sit freely. The first goat with a pusher-plate type pump died on the fifth day because of thromboembolism, but the second goat with a diaphragm type pump survived for 42 days. Blood chemistries remained within normal limits. Pump control was easy in both the duty-control mode and the stroke-control mode. With the automatic negative pressure control (ANPC) to prevent atrial wall sucking, the left atrial pressure was kept within +/- 10 mmHg, although left atrial pressure sometimes went below -80 mmHg without ANPC. Considering reliability, automaticity, and portability, the electrohydraulic ventricular assist system has become another choice for a practical, electrically driven ventricular assist system.

Animals↗
PubMedDate not supplied

Bioenergetic recovery processes of injured myocardium.

We employed cervically transplanted nonworking myocardium to simulate the condition of a heart supported by a ventricular assist device, and to investigate the bioenergetic recovery processes of injured myocardium with 31P nuclear magnetic resonance (NMR) techniques. A heterotopic graft was placed in the cervical portion of a recipient rat. One week later, a control 31P NMR spectrum was obtained from the graft. On the same day, the aorta of the graft was clamped for 30 minutes at room temperature. After this procedure, 31P NMR measurements of the graft were performed for 1 week. The phosphocreatine (PCr)/Inorganic phosphate (Pi) ratio, and beta-phosphate from adenosine triphosphate (beta-ATP)/Pi ratio on the first and second day after injury were significantly lower than control (p less than 0.05). However, these ratios recovered to a significant extent on the third and fourth day. These results suggest that 3 or 4 days are required for bioenergetic recovery of reversibly injured myocardium, even under nonworking conditions.

Adenosine Triphosphate↗
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Endothelial injury during extracorporeal circulation. Role of the complement system.

This study attempted to elucidate in vitro, endothelial cell (EC) injury induced by complement activation in extracorporeal devices. The in vitro injury model using cultured bovine ECs showed the following: 1) a dose-dependent transmembrane injury, determined by monitoring intracellular calcium mobilization, occurred spontaneously upon addition of complement-activated serum. 2) The respiratory rate of adherent ECs, monitored by an oxygen electrode, was reduced with increases in activated complement serum levels, and increased further with time. 3) Whole cell activity, measured by the rate of cellular proliferation, was reduced with an increase in activated serum complement levels. 4) These cellular responses were almost completely absent in the presence of C3 antiserum, strongly indicating that activated C3 fragments are responsible for EC injury. Thus, complement activation during extracorporeal circulation may injure endothelium at the transmembranous, mitochondrial, and/or proliferative levels, depending upon contact time and concentration of activated complement.

Animals↗
PubMedDate not supplied

Development of hybrid compliant graft: rapid preparative method for reconstruction of a vascular wall.

This paper presents a rapid preparative method of vascular wall reconstruction using a compliant artificial graft. The architecture of a hierarchically structured vessel wall composed of a "biomimic" intima, a basement membrane, and media was produced using step-by-step reconstruction. Electron microscopic observation of transverse sections of the reconstructed vessel wall showed a four-layered structure: monolayered endothelial cells as an intima; an artificial basement membrane composed of a collagen fiber matrix complexed with dermatan sulfate; a medial composed of smooth muscle cells embedded in collagen fiber nets; and an open-cell structured microporous compliant artificial graft as a structural matrix. The tissue-engineered structure, with a complete and morphologically intact lumen covered with endothelial cells, imparts biologic function. Thus, the tissue engineering approach promises to provide rapid construction of a viable bioartificial vessel.

Animals↗
PubMedDate not supplied

Altered humoral control of circulating volume during artificial circulation.

UNLABELLED: Plasma atrial natriuretic polypeptide (ANP) levels and plasma renin activity (PRA) were measured in six left ventricular assist device (LVAD) goats, four single artificial heart (SAH) goats, i.e., LVAD animals with fibrillated hearts, and 3 total artificial heart (TAH) calves. During the 4 week experiment, the ANP levels in the SAH goats increased to 516 pg/ml from the control value of 61.8 pg/ml because of an elevated CVP of 13-21 mmHg, while those of the LVAD goats were near the lower limit of the control values. The TAH calves had slightly decreased ANP levels at 23-46 pg/ml after the third postoperative week, which did not increase after the steep increase in CVP induced by the changes in the driving conditions. The PRA levels were 10-50 times higher than control in the SAH goats and a TAH calf whose CVP rose to 19 mmHg, although the cardiac output was within normal limits. IN CONCLUSION: 1) The secretion of ANP secondary to alteration in CVP was preserved in the LVAD recipients and enhanced diuresis, while it was compromised in the TAH cases. 2) The PRA levels in cases with elevated CVPs were high enough to suppress diuresis.

Animals↗
PubMedDate not supplied

Cardiac disuse atrophy during LVAD pumping.

The authors investigated morphologic changes of myocardial tissue of goats supported with a long-duration left ventricular assist device (LVAD). The bypass flow rates of the LVAD were kept at maximum levels (about 80% of total cardiac output) in four goats for 30 days, and at a limited flow rate (around 60%) in one goat each for 30 and 90 days. Morphometric studies using light and electron microscopy were performed on the left ventricles, comparing them to those in the four control studies. The results disclosed: 1) relative volume densities of the myocytes and interstitial tissue in the myocardium were unchanged; 2) cross-sectional areas of the myocytes in the maximum bypass cases were significantly reduced in comparison with pre-experimental data; 3) relative myocyte volumes, calculated by myocytes and nuclear volume densities, were reduced in three goats in the maximum bypass group; and 4) relative volume density of myofibrils was reduced in the maximum and 90 day bypass groups, whereas that of mitochondria was reduced only in the 90 day bypass case. These results indicate that LVADs cause cardiac atrophy which correlates with bypass flow rate and duration of assistance.

Animals↗
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Myocardial free fatty acid metabolism of the ischemic heart treated by left ventricular assist device.

Three-beta-methyl-iodophenyl-pentadecanoic acid (BMIPP), a newly developed radiographic probe of metabolic processes in tissue free fatty acid (FFA), was applied to a study analyzing the effect of a left ventricular assist device (LVAD) on impaired dog hearts. The radiographic image obtained with BMIPP was compared with 201thallium chloride (TL) imaging, which indicates tissue perfusion. In the myocardial infarction (MI) model, the BMIPP and TL uptake were equally increased with the use of LVAD in the marginal area of the MI. In another model using the reperfused myocardium after ischemia, the BMIPP and TL uptake were increased in the reperfused area by LVAD pumping. On the other hand, BMIPP uptake in the residual myocardium of both models was decreased by LVAD pumping when compared with TL uptake. This discrepancy between these radiographic tracers in the residual myocardium suggests that tissue metabolic processes may be suppressed as result of a decrease in the energy demand by the myocardium caused by LVAD pumping. The results of this study showed that use of LVADs for the impaired heart improved cell function of "stunned" myocardium and also unloaded the excess work from the residual myocardium as judged by FFA metabolism.

Animals↗
PubMedDate not supplied

Development of an anaphylatoxin scavenging device. Principle, surface molecular design, and selective adsorption.

The anaphylatoxins (C3a and C5a) generated upon extracorporeal circulation often cause adverse reactions at local and systemic levels. In this paper, the principle surface molecular design and highly selective adsorptional behaviors of anaphyatoxin-scavenging materials were demonstrated. Both C3a and C5a are highly basic proteins, whereas most plasma proteins are negatively charged in blood. This indicates that negatively charged surfaces could preferentially adsorb these basic proteins from plasma. Based on the above working hypothesis, surface molecular designs aiming at incorporation of negatively charged groups such as carboxylate and sulfonate groups on surfaces were attempted. The control of surface density at the outermost layer was assessed by x-ray photoelectron spectroscopy. The designed surfaces preferentially adsorbed C3a and C5a from activated serum. This provides a rational basis for the extracorporeal anaphylatoxin-scavenging device under development.

Adsorption↗
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A hybrid artificial vascular graft based upon an organ reconstruction model. Significance and design criteria of an artificial basement membrane.

The design of an artificial basement membrane is one of the central concerns in a hybrid artificial vascular graft. The design criteria defined here include 1) structural matrix, 2) enhanced adhesion and growth of endothelial cells, and 3) ensured antithrombogenicity. The designed artificial basement membrane is a complex gel of type I collagen with dermatan sulfate that drastically alters the cellular responses for both endothelial cells and platelets. The incorporation of a very small amount of dermatan sulfate was sufficient to enhance adhesion and growth of endothelial cells and to suppress platelet adhesion and activation.

Animals↗
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Chronic effect of left ventricular assist pumping on right ventricular function.

We evaluated right ventricular (RV) function during left ventricular assist device (LVAD) pumping during acute and chronic experiments in both normal hearts and hearts with left ventricular failure. An LVAD was implanted between the left atrium and the descending aorta of goats. The LVAD was pumped in a counterpulsation mode and at maximum bypass flow for 4-6 weeks in chronic experiments. The following results were obtained: 1) LVAD pumping itself did not affect RV function, even after 6 weeks of pumping, 2) the dimensions of the RV free-wall segments measured by sonomicrometers showed a gradual and small increase during the early postoperative days, which was due to an increase in volume returned to the RV and the deformity of the RV cavity derived from reduction in LV volume, and 3) the same tendencies were seen even with LV failure hearts. These results suggested that 1) LVADs can assist not only the LV but also the RV by reducing RV afterload, 2) excessive and prolonged assistance by an LVAD seems to dilate the RV free-wall, and 3) preexisting RV dysfunction is the main cause of signs of RV failure during LV pumping.

Animals↗
PubMedDate not supplied

Optical sensor for hemoglobin content and oxygen saturation. Application to artificial heart research.

A hybrid optical sensor that can measure both hemoglobin content ([ Hb]) and oxygen saturation (OS) of whole blood has been developed. The measurement errors in [Hb] and OS are 0.5 g% and 1.2%, respectively, over an hematocrit range of 25 to 45%. The oxygen content derived from the optical sensor yielded a standard error of 0.1 to 0.2 vol%. The sensors were mounted in the outflow ports of left and right artificial hearts that maintained the entire circulation and were used to chronically monitor arterial and mixed venous [Hb] and OS. In combination with pump output and pressure measurements, oxygen delivery and oxygen consumption of the animal was derived on-line using a microprocessor. In the experiment that lasted 40 days, both sensors functioned well, with stable measurements, and no thrombus formation around the sensor at the time of autopsy. The optical sensors are useful for monitoring cardiopulmonary function and metabolic status of patients without requiring blood samples. In addition, the pump output may be controlled through the level of mixed venous OS or in combination with the arterial OS.

Animals↗
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A synthetic tetrapeptide as a novel platelet-preserving agent during cardiopulmonary bypass.

The possibility of using the synthetic tetrapeptide arginine-glycine-aspartic acid-serine (Arg-Gly-Asp-Ser, RGDS), which was recently identified as the common cell attachment site of adhesive plasma proteins, for platelet preservation during cardiopulmonary bypass (CPB) was investigated. The synthetic RGDS inhibited platelet aggregation and adhesion and secretion of thromboxane A2 in a dose-dependent manner, due to antagonistic inhibition via ligand-receptor interaction. Platelet consumption during CPB was drastically reduced by the administration of RGDS with no remarkable change in hemodynamics and a fairly rapid recovery of platelet functions. Electron microscopic observation revealed that this platelet-preserving effect of RGDS resulted from the inhibition of adhesion and aggregation on the artificial surface. These strongly indicate that the cell attachment site of adhesive plasma proteins plays an important role in platelet consumption during CPB. The synthetic RGDS acting as an antagonist of the platelet membrane receptor, is a novel platelet-preserving agent, especially useful when using an extracorporeal circuit with a large blood-material contact area, such as CPB.

Animals↗
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Fundamental dose distribution for interstitial irradiation with Au grains.

A principle of radiation therapy is to determine a proper dose distribution for tumor localization. In this paper we present several models of arranging Au grains for interstitial irradiation and discuss characteristics of their dose distributions. Au grains were arranged in a lattice of three by three for evaluation of isodose curves on a source plane and several planes parallel to it. Intersource distances were varied to determine adequate distances for ideal dose distributions for tumor control. Through this study, we concluded that the most favorable intersource distance for effective dose distribution was 1.0-1.25 cm. We also found that interstitial irradiation with Au grains was hard to apply to deeply spreading tumors.

Brachytherapy↗