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Y Taenaka

Publications and source records attributed to Y Taenaka.

161 records · Page 9Linked to original sources
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↗
PubMedDate not supplied

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

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

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↗
PubMedDate not supplied

Replacement of the left ventricle with a single-chambered artificial pump.

Early clinical experience with total artificial hearts has stimulated further research and interest in this field. The concept of total heart replacement with a permanent mechanical device has been reevaluated, and its application as a bridge to heart transplantation is becoming more widely accepted. The size of total artificial hearts, however, limits the number of cases in which they can be used. In an effort to solve this problem, we evaluated a single-ventricle artificial pump in six Hereford calves. During surgery, the left ventricle was excised and replaced with a pneumatically actuated polyurethane pump connected to the mitral and aortic valve anulus. The right ventricle provided flow through the pulmonary vasculature, which eliminated the necessity of maintaining elevated right-sided filling pressures. The single-ventricle pump required less space than a biventricular device and was capable of maintaining adequate hemodynamic parameters in experimental animals. In comparison with the biventricular pump, this device offered the advantages of less extensive dissection requirements, ease of anastomosis, and a better anatomic fit. Patients whose pericardial cavities are too small for a biventricular artificial heart may benefit from the single-ventricle pump if they require hemodynamic support while awaiting heart transplantation.

Animals↗
PubMedDate not supplied

An implantable left ventricular assist system with an electrical impedance monitoring and control system.

The authors developed an implantable left ventricular assist system (LVAS) for bridge to transplant of rather small sized adults. The pump was made of segmented polyether polyurethane and was 86 mm in diameter, 50 mm in height, with a 70 ml nominal stroke volume. A percutaneous drive line was connected with an external pneumatic control drive unit (CDU). In chronic animal experiments using 11 adult goats, the pump was installed between the LV apex and the descending aorta and was placed in the abdominal wall. Five goats were killed after 4 to 14 weeks while in good physical condition, and one is ongoing. There were no prominent thromboembolic symptoms despite no anti-thrombogenic agent being used. The new electrical impedance-based monitoring and control system (Z system) was installed in the CDU. In this Z system, automatic calibration was performed periodically for several seconds while the drive condition was changed to ensure full-fill of the blood pump. The full-fill to full-empty drive was well controlled by this Z system. In conclusion, the new Z system is practical and useful for monitoring and control of an implantable pump, giving this LVAS a promising place in clinical use.

Adult↗
PubMedDate not supplied

A two stage axial flow pump. New approach to reduction of hemolysis.

From an engineering point of view, the suitable revolution number for high efficiency operation of an axial flow pump is known. A multistage axial flow pump is a useful tool for reducing revolution number with a high efficiency axial flow pump. A two stage (25) axial flow pump designed at a 5 L/min flow rate and a 100 mmHg pressure head was evaluated in three kinds of in vitro hemolysis tests. Each stage design point of the 2s pump was tested at a 5 L/min flow rate and a 50 mmHg pressure head. Specific speed and revolution number of the 2S pump were 1400 rpm, m3/min, m, and 15500 rpm, respectively. In the first test the 2S pump was compared with two single stage axial flow pumps (1S-A and 1S-B100) designed by the same method. The specific speed of the 1A was the same as that of the 2S pump, which was driven at 26000 rpm. The impeller of the 1S-B100 was the same as that of the 2S pump, which was driven at a 22000 rpm RN and a 1100 specific speed. The 2S pump was separated into two single stage axial flow pumps and the effect of series operation on hemolysis was evaluated in the second test. In the third test the 2S pump was compared with the 1S-B100 by using diluted goat blood samples with three different hematocrit values. The results showed that the hemolysis index of the 2S pump, regarded as a total hemolysis index of both stage axial flow pumps, was less than those of the single stage axial flow pumps at all hematocrit values.

Animals↗
PubMedDate not supplied

Hemodynamic and humoral conditions in stepwise reduction of pulmonary blood flow during venoarterial bypass in awake goats.

The effects of reduced pulmonary arterial blood flow (PAF) during venoarterial bypass (VAB) on hemodynamic and humoral conditions were investigated in a series of experiments in a chronic animal model. A biventricular bypass system was installed in five adult goats weighing 49.8 +/- 1.1 kg. Two weeks later, the extracorporeal circuitry was changed to VAB without anesthesia. The PAF was reduced stepwise from 100% to 50, 25, 10, and 0% of total systemic flow. The mean aortic pressure and systemic vascular resistance decreased from 110 +/- 14 to 66 +/- 3 mmHg and from 1,288 +/- 77 to 740 +/- 73 dyne.sec/cm5, respectively, in proportion to the decrease in PAF from 100 to 0%. The prostaglandin E2 concentration increased from 1.5 +/- 0.6 to 8.8 +/- 0.6 pg/ml following the decrease in PAF from 100 to 0%. The renin-angiotensin system increased in proportion to the decrease in PAF. In contrast, the epinephrine and norepinephrine concentrations (60 +/- 10 and 227 +/- 80 pg/ml, respectively, at 100% PAF) did not change appreciably even at 10% PAF, but were markedly elevated to 335 +/- 117 and 2,088 +/- 1,503 pg/ml at 0% PAF. The antidiuretic hormone level similarly changed. In conclusion, decrease in PAF during VAB exerts significant effects on hemodynamics in a proportional manner and on vasoactive humoral factors in a diverse manner.

Animals↗
PubMedDate not supplied

In vitro and in vivo heat dissipation of an electrohydraulic totally implantable artificial heart.

The authors evaluated the heat transfer characteristics of an electrohydraulic totally implantable artificial heart (EH-TAH) developed at our institute. In three in vitro experiments, the heat dissipation of the EH-TAH was investigated. First, the EH-TAH was connected to a closed mock circuit filled with 1 L of saline, and driven at an input power of 20 W. The estimated heat conducted to the blood was approximately 10.3 W, which was almost half of the input power. Second, we simulated heat transfer with the circulation of a calf by using a heat exchanger. The amount of heat dissipating directly from the EH-TAH surface was calculated to be 10 W. Third, the temperature of the actuator examined with thermography was found to be almost uniform, and no prominent high temperature area was observed. In an in vivo study, the EH-TAH was implanted for 10 days in a calf weighing 62 kg. The input power was 18 +/- 2 W, the temperature of the actuator-tissue contacting surface was 39.4 +/- 0.8 degrees C, and that of the pump blood chamber was 39.8 +/- 0.4 degrees C. This slight temperature elevation was thought to be attributable to heat dissipation to the blood. On histologic study of the chest wall and the lung in contact with the actuator, vascularized connective tissue envelopes were observed, but unfavorable side effects, such as tissue necrosis, were not observed. These results suggest that the thermal effect of this system is acceptable at the input power used.

Animals↗
PubMedDate not supplied

Development of an implantable centrifugal blood pump for circulatory assist.

An implantable centrifugal pump (ICP) for prolonged circulatory assist has been developed, at 320 ml and 830 g. A central balancing hole was made in its impeller for better antithrombogenicity. Waterproofing and histocompatibility were supported by a silicone seal and a casing made of titanium and acrylic resin. Overall efficiency was 30% and normalized index of homolysis was 0.003 mg/dl, the same value as the BP-80, at a flow rate of 5 L/min and a head of 100 mmHg. Antithrombogenicity and hemolytic properties of the ICP were investigated in paracorporeal implantation in three goats (61-71 kg). Exothermicity, anatomic fit, and water tightness of the ICP were evaluated in intrathoracic implantation in an adult goat (66 kg). The ICP could run paracorporeally for 50, 200, and 381 days. There was no thrombus in the ICP after 381 days' pumping, and the ICP could run in the chest cavity for 40 days. The temperature of the motor rose 1.8 +/- 0.3 degrees C from that of the pleura. Moisture content of the seal remained normal. The ICP was completely covered with smooth fibrous tissue. Although a small area of atelectasis was found in the lingula, neither lung adhesion nor necrosis of the chest wall was observed. The ICP has satisfactory antithrombogenicity, hemolytic property, water tightness, anatomic fit, and exothermicity for use as an implantable circulatory assist device.

Animals↗
PubMedDate not supplied

In vitro and in vivo evaluation of a left-right balancing capacity of an interatrial shunt in an electrohydraulic total artificial heart system.

The authors evaluated the basic performance of an interatrial shunt (IAS) made by punching a hole in the atrial septum, in accommodating the left-right imbalance in our electrohydraulic total artificial heart (EHTAH) system. In an in vitro study conducted in a closed mock circuit connected with the EHTAH, the interatrial pressure gradient changed in compliance with the amount of bronchial flow and the size of the IAS. The IAS of 4.4 mm diameter or larger maintained the interatrial pressure gradient within physiologically permissible limits when the amount of bronchial flow was 5% of cardiac output or less. A left-to-right one-way valve made of a piece of pericardium, a possible option in this IAS method, successfully prevented right-to-left reverse shunt flow through the IAS. In a chronic in vivo study using a calf implanted with the EHTAH for 10 days, a 4.5 mm IAS without the one-way valve demonstrated satisfactory dynamic left-right balancing capacity with a stable interatrial pressure gradient of 4 +/- 1 mmHg over a wide range of atrial pressures. No thrombus was found in or around the IAS at autopsy. The authors conclude that the IAS is a simple and promising means of left-right balancing in the EHTAH system.

Animals↗
PubMedDate not supplied

Establishment of flow estimation for an implantable centrifugal blood pump.

A less invasive and non thrombogenic flow estimation of an implantable centrifugal blood pump (ICBP) has been developed, which was derived from electric power consumption, the rotating speed of a motor, and blood viscosity presumed by hematocrit and body temperature. The power consumption and the rotating speed of the motor were measured by a wattmeter every 0.2 sec. Accuracy and stability of the estimated flow (EF) were investigated during in vitro and in vivo experiments. The EF was compared with a measured flow rate (MF) monitored by an electromagnetic flowmeter. During in vitro experiments, the EF and MF were measured at 79 operating points. The ICBP was driven in a closed mock loop filled with goat blood with hematocrit values of 21.5, 28, 34, and 42%. During in vivo experiments, the ICBP was implanted in the chest cavity of a goat and driven for 40 days with continuous estimation of the bypass flow rate. Blood was taken to determine hematocrit value several times a week. The temperature of the pleura away from the ICBP was measured every 15 min. A linear correlation between the EF and MF was observed, and the correlation coefficient between the EF and MF was 0.99 during in vitro examinations. An averaged error of the EF was 0.5 L/min, with the MF ranging from 2.3 to 8.1 L/min during in vivo experiments. In conclusion, flow estimation was established with good stability and accuracy in both in vitro and in vivo experiments.

Animals↗
PubMedDate not supplied

Early changes in circulating blood volume and volume regulating humoral factors after implantation of an electrohydraulic total artificial heart.

The early changes in circulating blood volume (CBV) and volume regulating humoral factors after implantation of an electrohydraulic total artificial heart (EH-TAH) were investigated in a calf and compared with results in a sham operated control calf. CBV was measured by the dye dilution method using indocyanine green. CBV and humoral factors were periodically investigated. In the EH-TAH implanted calf, the cardiac output was estimated at 6-7 L/ min (94-109 ml/kg/min), and the aortic pressure and aerobic metabolic condition were favorable. Nevertheless, the CBV was increased to 132 and 168% of the pre-operative value (range in the control calf, 83-103%) on post operative days 4 and 8, respectively. The atrial natriuretic peptide level on days 2, 5, and 7 was 23, 170, and 240 (in the control calf, 19-61) pg/ml, respectively, and the antidiuretic hormone level was 7.3, 2.0, and 1.3 (0.5-1.3) pg/ ml, respectively. The plasma renin activity was 3.2, 3.7, and 3.1 (0.5-0.3) ng/ml/hr, respectively. The angiotensin-I and angiotensin-II levels were also increased in the EH-TAH implanted calf. It is concluded that significant water retention occurs even at sufficient cardiac output early after EH-TAH implantation. The changes in humoral factors are suggested to arise secondary to the increased CBV or other unknown factors.

Angiotensin I↗
PubMedDate not supplied

Characteristics of mixed venous oxygen saturation and physical activity as parameters for artificial heart control.

Mixed venous oxygen saturation (SvO2) and physical activity (PhyAc) are practical candidates as parameters of total artificial heart (TAH) control because SvO2 can be measured through a transparent blood pump housing with infrared rays and PhyAc can be calculated from signals of an accelerometer used for rate response pacemakers. Although the methods for measurement of the parameters have already been developed, characteristics of these parameters for TAH control, such as during exercise, are still unclear and were examined in this study. SvO2, cardiac output (CO), and PhyAc were measured as parameters. Multi-stage treadmill exercise tests were performed. Difference values (DVs) from the value at the start of exercise showed better correlation than did absolute values. Correlation coefficients between DV in CO and DV in SvO2 and between DV in CO and PhyAc were high at -0.82 and 0.72, while the time constants for the change of SvO2 and CO to the PhyAc change were 26 and 32 sec. Although the correlation coefficient between the CO and SvO2 was higher than that between CO and PhyAc, PhyAc responded more quickly to the speed change compared with the response of SvO2 and CO. It was concluded that SvO2 and PhyAc were useful parameters with different characteristics for TAH control during exercise.

Animals↗
PubMedDate not supplied

Morphologic changes of the aortic wall due to reduced systemic pulse pressure in prolonged non pulsatile left heart bypass.

The morphologic changes of the aortic wall due to reduced systemic pulse pressure in prolonged non pulsatile left heart bypass (LHB) were investigated. Sixteen adult goats were divided into three groups: the non pulsatile group in which non pulsatile LHB was conducted for 137 days on average, the pulsatile group in which pulsatile LHB was conducted for 79 days on average, and the control group used as the normal control. The average aortic pulse pressures were 12, 48, and 37 mmHg, respectively. At the end of the experiments, the descending aorta was excised and subjected to morphologic examination. The wall thickness of the aorta in the non pulsatile group (1.4 mm) was significantly thinner than that in the pulsatile group (2.2 mm) and the control group (2.0 mm), and the volume ratio of smooth muscle cells (SMC) in the non pulsatile group (37%) was lower than that in the pulsatile group (48%) and the control group (49%). In SMC classification, the proportion of SMC with low activity and low contractility in the non pulsatile group (57%) was high as compared with that in the pulsatile (2%) and control (5%) groups. These results strongly indicate that prolonged non pulsatile LHB causes substantial morphologic changes in the aorta.

Animals↗