Biomedical subjects

E Tayama

Publications and source records attributed to E Tayama.

At least 55 records · Page 3Linked to original sources

PubMed1998

In vivo evaluation of the miniaturized Gyro centrifugal pump as an implantable ventricular assist device.

A miniaturized Gyro centrifugal pump has been developed to be incorporated into a totally implantable artificial heart. The Gyro PI (permanently implantable) model is a pivot bearing supported centrifugal pump with a priming volume of 20 ml. With the miniaturized actuator, the pump-actuator package has a height of 53 mm, a diameter of 65 mm, and a displacement volume of 145 ml. To evaluate the hemocompatibility and efficiency of the Gyro PI pump system, a plastic prototype (Gyro PI-601) was implanted into a bovine model as a left or right ventricular assist device (LVAD or RVAD), bypassing from the left ventricular apex to the descending aorta or from the right ventricular infundibulum to the main pulmonary artery. The calves were anticoagulated with heparin to maintain activated clotting times from 150 to 200 s. Four calves were supported for 23, 24, and 50 days in the LVAD studies, and 40 days in the RVAD study. The first calf died due to intrathoracic bleeding associated with sepsis. The second calf was euthanized for a low flow rate less than 2 L/min due to an obstructed inflow with growing pannus. The third and fourth calves were euthanized as scheduled. Renal and hepatic functions remained normal, and plasma free hemoglobin values were less than 8 mg/dL throughout the experiments. The fourth case showed flow rates of 4.83 +/- 0.57 L/min, input power of 6.16 +/- 0.49 W, and the inside temperature of the actuator of 43.5 +/- 0.52 degrees C. The pumps implanted in the fourth calf demonstrated no thrombus formation at the autopsy. These in vivo experiments revealed that the Gyro PI pump can provide adequate flow as an easily implantable, efficient, antithrombogenic, and nonhemolytic centrifugal LVAD or RVAD with miniaturized actuators.

Animals↗

PubMed1998

Estimation of the native cardiac output from a rotary blood pump flow: in vitro study.

The rotary blood pump will be an implantable left ventricular assist device (LVAD) in the near future. However, the best control method and the interrelationship between the rotary blood pump and native heart functions are unclear. An estimation was made of the native heart cardiac output from the change of an LVAD's outflow waveform. The mock circulation loop was composed of an aortic compliance chamber, left arterial chamber, total artificial heart as a native heart, and a rotary blood pump that was placed as an LVAD with left ventricular drainage. The fast Fourier transform (FFT) technique was utilized to analyze the LVAD's outflow waveform and calculate the pulse power index (PPI) to examine a relation between the PPI and total artificial heart (TAH) output. The PPI increased with the increase of the TAH output; there was a positive correlation, and there was an inverse correlation between the PPI and the assist ratio. From this viewpoint, an estimation of the pulsatility change of the LVAD's outflow wave may indicate the native cardiac output.

Aorta↗

PubMed1998

Prosthetic valve thrombosis after abdominal surgical procedures: a case report.

A 63-year-old woman with a prosthetic mitral valve who developed valve thrombosis after abdominal surgical procedures is reported. She had undergone mitral valve replacement with a Sorin-Bicarbon valve 3 years previously, and was referred for an operation due to rectal cancer with anal bleeding. On admission, the patient was on oral anticoagulant therapy with warfarin, and the intensity of anticoagulation was around 40% of Thrombotest. Doppler echocardiography showed that the prosthetic mitral valve function was normal. Low anterior resection of the rectum was uneventful. Management of the perioperative anticoagulation was peformed with heparin, however, the postoperative anticoagulation using intravenous infusion of heparin was imperfectly achieved. Consequently, thrombosis of the prosthetic mitral valve occurred 8 days after the operation. Replacement of the thrombosed prosthetic valve was performed with successful results. The imperfect postoperative anticoagulation with heparin may have been the cause of the valve thrombosis. The management of perioperative anticoagulation during noncardiac operations is discussed.

Abdomen↗

PubMed1997

Flow characteristics and required control algorithm of an implantable centrifugal left ventricular assist device.

As the clinical application of LVADs has increased, attempts have been made to develop smaller, less expensive, more durable and efficient implantable devices using rotary blood pumps. Since chronic circulatory support with implantable continuous-flow LVADs will be established in the near future, we need to determine the flow characteristics through an implantable continuous-flow LVAD. This study describes the flow characteristics through an implantable centrifugal blood pump as a left ventricular assist device (LVAD) to obtain a simple non-invasive algorithm to control its assist flow rate adequately. A prototype of the completely seal-less and pivot bearing-supported centrifugal blood pump was implanted into two calves, bypassing from the left ventricle to the descending aorta. Device motor speed, voltage, current, flow rate, and aortic blood pressure were monitored continuously. The flow patterns revealed forward flow in ventricular systole and backward flow in diastole. As the pump speed increased, an end-diastolic notch became evident in the flow profile. Although the flow rate (Q [l/min]) and rotational speed (R [rpm]) had a linear correlation (Q = 0.0042R - 5.159; r = 0.96), this linearity was altered after the end-diastolic notch was evident. The end-diastolic notch is considered to be a sign of the sucking phenomenon of the centrifugal pump. Also, although the consumed current (I [A]) and flow rate had a linear correlation (I = 0.212Q + 0.29; r = 0.97), this linearity also changed after the end-diastolic notch was evident. Based upon the above findings, we propose a simple algorithm to maintain submaximal flow without inducing sucking. To maintain the submaximal flow rate without measuring flow rate, the sucking point is determined by monitoring consumed current according to gradual increases in voltage.

Algorithms↗

PubMed1997

Vibration assessment for thrombus formation in the centrifugal pump.

To clarify the correlation of vibration and thrombus formation inside a rotary blood pump, 40 preliminary vibration studies were performed on pivot bearing centrifugal pumps. No such studies were found in the literature. The primary data acquisition equipment included an accelerometer (Isotron PE accelerometer, ENDEVCO, San Juan Capistrano, CA, U.S.A.), digitizing oscilloscope (TDS 420, Tektronix Inc., Pittsfield, MA, U.S.A.), and pivot bearing centrifugal pumps. The pump impeller was coupled magnetically to the driver magnet. The accelerometer was mounted on the top of the pump casing to sense radial and axial accelerations. To simulate the 3 common areas of thrombus formation, a piece of silicone rubber was attached to each of the following 3 locations as described: a circular shape on the center bottom of the impeller (CI), an eccentric shape on the bottom of the impeller (EI), and a circular shape on the center bottom casing (CC). A fast Fourier transform (FFT) method at 5 L/min against 100 mm Hg, with a pump rotating speed of 1,600 rpm was used. The frequency response of the vibration sensors used spans of 40 Hz to 2 kHz. The frequency domain was already integrated into the oscilloscope, allowing for comparison of the vibration results. The area of frequency domain at a radial direction was 206 +/- 12.7 mVHz in CI, 239.5 +/- 12.1 mVHz in EI, 365 +/- 12.9 mVHz in CC, and 163 +/- 7.9 mVHz in the control (control vs. CI p = 0.07, control vs. EI p < 0.001, control vs. CC p < 0.001, EI vs. CC p < 0.001, CI vs. CC p < 0.001). Three types of imitation thrombus formations were roughly distinguishable. These results suggested the possibility of detecting thrombus formation using vibration signals, and these studies revealed the usefulness of vibration monitoring to detect thrombus formation in a centrifugal pump.

Analysis of Variance↗

PubMed1997

Effects of ultrathin silicone coating of porous membrane on gas transfer and hemolytic performance.

To assess the effect of an ultrathin (0.2 microm) silicone-coated microporous membrane oxygenator on gas transfer and hemolytic performance, a silicone-coated capillary membrane oxygenator (Mera HP Excelung-prime, HPO-20H-C, Senko Medical Instrument Mfg. Co., Ltd., Tokyo, Japan) was compared with a noncoated polypropylene microporous membrane oxygenator of the same model and manufacturer using an in vitro test circuit. The 2 oxygenators showed little difference in the oxygen (O2) transfer rate over a wide range of blood flow rates (1 L/min to 8 L/min). The carbon dioxide (CO2) transfer rate was almost the same in both devices at low blood flow rates, but the silicone-coated oxygenator showed a decrease of more than 20% in the CO2 transfer rate at higher blood flow rates. This loss in performance could be partly attenuated by increasing the gas/blood flow ratio from 0.5 or 1.0 to 2.0. In the hemolysis study, the silicone-coated membrane oxygenator showed a smaller increase in plasma free hemoglobin than the noncoated oxygenator. The pressure drop across both oxygenators was the same. These results suggest that the ultrathin silicone-coated porous membrane oxygenator may be a useful tool for long-term extracorporeal lung support while maintaining a sufficient gas transfer rate and causing less blood component damage.

Adult↗

PubMed1997

Effects of pulsatile flow on gas transfer of membrane oxygenator: MENOX EL-4000 and Gyro C1-E3 pulsatile mode.

It is acknowledged that pulsatile flow enhances the gas exchange performance of membrane oxygenators. However, the data for currently developed oxygenators are limited. In this study, the effect of pulsatile flow was assessed utilizing the MENOX EL-4000 oxygenator. The in vitro test was performed following the Association for the Advancement of Medical Instrumentation (AAMI) standards. Pulsatile flow was produced by the Gyro C1-E3 centrifugal pump with periodical changing of the impeller speed. In Study 1, the following 3 groups were created and examined: nonpulsatile flow, pulsatile flow of 40 bpm, and pulsatile flow of 60 bpm. The blood flow rate was maintained at 3 L/min, and the V/Q ratio was 1. In Study 2, four groups were examined, nonpulsatile flow with V/Q = 1, nonpulsatile with V/Q = 2, pulsatile with V/Q = 1, and pulsatile with V/Q = 2. The blood flow rate was maintained at 4 L/min, and the pulse frequency was set at 40 bpm. In study 1, although O2 transfer was not enhanced, CO2 transfer was significantly improved (40-50%) by pulsatile flow, regardless of pulse frequency. Study 2 demonstrated that pulsatile flow resulted in improved CO2 transfer as did higher ventilation (V/Q = 2). Furthermore, even after applying higher ventilation, the pulsatile mode enhanced CO2 transfer more than the nonpulsatile mode. It was considered that the pulsatile mode induced an active secondary flow and enhanced mixing effects, and consequently CO2 transfer was improved. In conclusion, the pulsatile flow significantly enhanced the CO2 transfer of the MENOX oxygenator. It is indicated that applying the pulsatile mode is a unique and effective method to improve the gas exchange performance for a current membrane oxygenator.

Analysis of Variance↗

PubMed1997

Anatomical consideration for an implantable centrifugal biventricular assist system.

A miniaturized pivot bearing-supported centrifugal blood pump (Gyro PI) has been developed as a long-term biventricular assist system (BiVAS). In this study we determined the anatomical configuration of this system using a bovine model. Under general anesthesia, a left lateral thoracotomy was performed to open the chest. Two Gyro PI-601 pumps for left and right assists were placed in the preperitoneal pocket by a subcostal abdominal incision. The left pump could be placed along the dome of the diaphragm just beneath the apex of the left ventricle. The right pump could be placed next to the left pump. The inlet and outlet ports of both pumps penetrated the diaphragm. The inlet port of the left pump, with a length of 55 mm, was inserted directly into the apex of the left ventricle. A woven Dacron graft (150 mm long, 11 mm inner diameter) was placed between the outlet port of the left pump and the descending aorta. As for the right pump, a 100 mm long and 120 degree angled inflow conduit was placed between the inlet port and the right ventricular infundibulum. The outlet port of the right pump was connected to the main trunk of the pulmonary artery using a 90 mm long, 11 mm inner diameter Dacron graft. We could perform biventricular assistance to confirm the anatomical feasibility of the Gyro implantable centrifugal BiVAS.

Animals↗

PubMed1997

Hemolysis test of a centrifugal pump in a pulsatile mode: the effect of pulse rate and RPM variance.

Centrifugal pumps are generally employed as nonpulsatile blood flow pumps; however, these pumps can produce pulsatile flow by periodically alternating the impeller rotation speed. This study investigates blood trauma due to the effect of pulse frequency and various ranges of pump speed. The hemolysis tests were conducted using the Gyro C1E3 pump. The study was divided into the following categories: Group 1 in a nonpulsatile mode; Group 2 operated at 40 bpm with 30% of speed variance; Group 3, 60 bpm with 30% of speed variance; Group 4, 40 bpm with 70% of speed variance; and Group 5, 60 bpm with 70% of speed variance. A flow rate of 3 L/min and a total pressure head of 200 mm Hg were employed in all groups to simulate a percutaneous cardiopulmonary support condition. There were no significant differences in the hemolysis levels among Groups 1, 2, and 3. However, Groups 4 and 5 exhibited a significantly higher hemolysis rate compared to the other groups. These results indicate that a high rate of speed variance increases hemolysis; however, a range of less than 30% does not affect hemolysis. The pulse rate has no significant effect on hemolysis. In conclusion, the higher speed variance increases the hemolysis level when a pulsatile mode is applied with a centrifugal pump at the given test conditions. However, a speed variance of less than 30% or a pulse rate of less than 60 bpm does not affect hemolysis.

Analysis of Variance↗

PubMed1997

Estimation of the minimum pump speed to prevent regurgitation in the continuous flow left ventricular assist device: left ventricular drainage versus left atrial drainage.

Due to the fact that centrifugal and axial pumps do not require valves, there is a possibility of back flow when the pump speed is low. To estimate the minimum required pump speed to prevent this regurgitation, an in vitro simulation test was conducted. A pulsatile pump simulated the natural heart while a centrifugal pump simulated the continuous flow left ventricular assist device (LVAD). The LVAD flow was attained from the left atrial (LA) drainage or left ventricular (LV) drainage. The minimum or regurgitate flow was observed in the systolic phase with LA drainage and in the diastolic phase with LV drainage. LV drainage always provided higher flow than LA drainage at the same pump speed. These differences are due to the various total pressure heads of the LVAD. To prevent the regurgitation, the LVAD should maintain a certain pump speed which can create positive flow against the aortic systolic pressure with LA drainage and against the aortic diastolic pressure with LV drainage. These required pump speeds can be identified by the LVAD flow-pressure curve.

Aortic Valve Insufficiency↗

PubMed1997

The simple in vitro thrombogenic test: modified methods for same priming pumps.

The improvement of antithrombogenicity is one of the major objectives for the development of blood pumps. Previously we reported that an in vitro thrombogenic test was useful as a pilot study, especially to predict thrombogenic areas. In this study we modified the method for testing pumps with identical priming volumes by eliminating the blood reservoir. Identical compact mock loops (priming volume of 53 ml, without pump) were constructed and tested with the same priming volume of Nikkiso centrifugal pumps, noncoated verus heparin-coated. Two pumps were run simultaneously using the same source of fresh heparinized human blood (activated clotting time [ACT] 150-250 s) for 4 or 6 h. Results indicated that the heparin-coated pump had a longer thrombus free period than the noncoated one. The thrombi location and forms were consistently in the same places the in vivo study had identified. It is suggested that this modified in vitro thrombogenic test is a feasible pilot study, as well as the one previously reported. The minimal priming volume will allow evaluation of multiple pumps simultaneously with the same source blood.

Anticoagulants↗

PubMed1997

Therapeutic and physiological artificial heart: future prospects.

Current left ventricular assist devices (LVADs) have demonstrated admirable results. However, approximately one-fourth of the patients who require LVADs suffer from right heart failure and require additional right ventricular (RV) assist devices (RVADs). The RV failure impairs the splanchnic circulation, subsequently developing into multiorgan failure (MOF). An aggressive application of a biventricular assist device (BVAD) is the best way to avoid and treat MOF because the BVAD reduces splanchnic congestion. Also, because the BVAD allows retention of the natural heart, recovery of the heart function can be expected after long-term assist. This benefit cannot be expected from conventional total artificial hearts. Although there are no implantable clinical BVAD systems in existence today, present advanced technologies in rotary blood pumps can enable these systems to be totally implantable. So, we should focus on developing a totally implantable BVAD system. The implantable BVAD will be a therapeutic and physiological total artificial heart, and it will be a common home health care device in the near future.

Cost-Benefit Analysis↗

PubMed1997

Development and initial testing of a permanently implantable centrifugal pump.

To be able to salvage heart failure patients, the need for an economical permanent ventricular assist device is increasing. To meet this increasing demand, a miniaturized centrifugal blood pump has been developed as a permanently implantable device. The Gyro permanently implantable model (PI-601) incorporates a sealless design with a blood stagnation free structure. The pump impeller is magnetically coupled to the driver magnet in a sealless manner. This pump is atraumatic and antithrombogenic and incorporates a double pivot bearing system. A miniaturized actuator was utilized in this system in collaboration with the University of Vienna. The priming volume of this pump is 20 ml. The overall size of the pump actuator package is 53 mm in height and 65 mm in diameter, 145 ml of displacement volume, and 305 g in weight. Testing to date has included in vitro hydraulic performance and hemolysis. This pump can provide 5 L/min against a 110 mm Hg total pressure head at 2,000 rpm and 8 L/min against 150 mm Hg at 2,500 rpm. The normalized index of hemolysis (NIH) value of this pump was 0.0028 g/100 L at 5 L/min against 100 mm Hg. A preliminary anatomical study revealed the possibility of the implantability of 2 such systems in biventricular bypass at a preperitoneal location. This system is feasible for use as a permanently implantable biventricular assist device.

Animals↗

PubMed1997

The hemolysis test of the Gyro C1E3 pump in pulsatile mode.

While a centrifugal pump is generally used for nonpulsatile blood flow, it can also produce a pulsatile flow by alternating the impeller rotational speed (rpm) periodically. However, there is a concern that this centrifugal pump pulsatile mode may induce added hemolysis as a result of the repeated acceleration and deceleration of rpm. Thus, a hemolysis study of the pulsatile modes of the Gyro C1E3 centrifugal pump (Gyro-P) was conducted. The results were then compared with the nonpulsatile mode of the same pump (Gyro-N) and the nonpulsatile BioMedicus BP-80 (Bio-N) pump. Three different conditions were simulated: left ventricular assist device (LVAD), cardiopulmonary bypass (CPB), and percutaneous cardiopulmonary support (PCPS). The beating rate of the Gyro-P was set at 40 bpm, with repetition of two different impeller speed (the lower being 70% of the higher speed). The 2 impeller speeds were set to obtain the same average flow as that of the nonpulsatile mode. The hemolysis results of the Gyro-P were comparable to or better than those of Bio-N, and no excessive hemolysis was observed, compared to the Gyro-N. In conclusion, The Gyro-P had an excellent hemolytic characteristic and generated no excessive hemolysis in most clinical usage conditions. With the concern of hemolysis eliminated, this pulsatile mode may have various possible mode advantages.

Analysis of Variance↗

PubMed1997

Hemolytic effect of surface roughness of an impeller in a centrifugal blood pump.

The present study investigates how the surface roughness of an impeller affects hemolysis in the pivot bearing supported Gyro C1E3 pump. This study focuses on particular areas of the impeller surface in the impeller type centrifugal pump. Seven Gyro C1E3 pumps were prepared with smooth surface housings and different impeller parts with different surface roughnesses. The vanes, top side, and backside of the impeller were independently subjected to vapor polishing, fine sand blasting, or coarse sand blasting to produce three different grades of surface roughness. These surfaces were then examined by a surface profile instrument. Using these pumps with different impellers, in vitro hemolysis tests were performed simulating cardiopulmonary bypass (5 L/min, 350 mm Hg). The findings of this study conclusively proved that surface roughness of the back side of the impeller has the greatest effect on hemolysis, followed by the top side and then the vanes. The following are reasons for these findings. First, the shear rate may be greater on the back side than on the top side because of the smaller gap between the back and the housing and the greater relative speed against the impeller. Second, the fluid beneath the impeller may have a longer exposure time because there is little chance for the fluid to mix beneath the impeller. Third, the shear rate may be greater on the top side of the impeller than on the vanes because a vortex formation occurs behind the vanes.

Analysis of Variance↗

PubMed1997

Reconsideration of total erythrocyte destruction phenomenon.

During a particular long-term in vitro hemolysis test, the plasma free hemoglobin suddenly increased even though the hemolysis level had risen linearly for the previous several hours. This phenomenon was dubbed the total destruction of erythrocytes (TDE) phenomenon, and it was hypothesized that this was the result of the accumulation of sublethal damage to erythrocytes. It was suggested that the TDE might demonstrate the hemolytic characteristics of a pump more sensitively than a conventional hemolysis test. However, the previous report did not consider the effects of temperature or contamination. To study these effects, 3 long-term hemolysis tests were concluded under the following conditions. For Study 1 blood temperature was maintained at 27 degrees C (n = 2); for Study 2, at 37 degrees C (n = 4); and for Study 3, at 37 degrees C with gentamicin (n = 4). The BioMedicus and Nikkiso pumps were used as they were in our previous report. Gas sterilization of all circuits and pumps preceded experimentation. In Studies 1 and 3, hemolysis increased linearly for 29 h. However, in Study 2 a sudden increase of hemolysis occurred for both pumps. Possible causes of this were the dramatic changes in environmental factors such as severe acidosis, high O2 and glucose consumption, and CO2 accumulation. In contrast, neither Study 1 nor Study 3 showed a sudden increase in hemolysis. The plasma free hemoglobin increased linearly in both groups until 29 h of pumping. The environmental changes resulting from contamination were considered to be the cause of the sudden increase in hemolysis. In conclusion, the TDE did not reflect mechanical blood cell damage, but rather different environment situations. Hemolysis increased linearly up to 29 h in either 27 degrees C or germ-free conditions.

Animals↗

PubMed1997

In vitro thrombogenesis study in the Gyro C1E3 for vibration assessment.

To clarify the correlation between vibration and thrombus formation in a centrifugal blood pump, a preliminary simulated thrombus study was conducted for possible detection of thrombus formation inside a pump. Additional in vitro thrombogenesis studies were performed to confirm the results of the preliminary study. The primary data acquisition equipment included an accelerometer (Isotron PE accelerometer, Endevco, San Juan Capistrano, CA, U.S.A.), digitizing oscilloscope (TDS 420, Tektronic, Inc., MA, U.S.A.), and pivot bearing centrifugal pumps. The accelerometer was mounted to the top of the pump casing to sense radial and axial accelerations. For the preliminary study, a piece of Silastic was adhered to each of the 3 common areas of thrombus formation inside the pump. The results provided baseline information to speculate on the possibility of detecting thrombus formation by vibration signal changes. For the next studies, fresh bovine blood was harvested under sterile conditions and with strict avoidance of air contact, adding 1.0 U/ml of heparin. The sterilized test circuit consisted of 3/8 inch tubing (Tygon) and a soft reservoir. During the operating time, the activated clotting time (ACT) was maintained between 150 to 300 s using protamin. A restrictor on the outflow tube maintained the flow rates at about 4.5 L/min. The pumps ran continuously for 6 h. Possible blood clot formation inside the pump was monitored by observing the vibration signal from the device for 6 h. These studies revealed that it was possible to distinguish between an impeller that did not form thrombus and ones that formed fibrogenous thrombus using vibration signal assessment. Vibration assessment is worthwhile as a thrombus monitoring tool for a centrifugal blood pump.

Analysis of Variance↗

PubMed1997

Comparison of the Gyro C1E3 and BioMedicus centrifugal pump performances during cardiopulmonary bypass.

The compact eccentric inlet port (C1E3) centrifugal blood pump was developed as a cardiopulmonary bypass (CPB) pump. The C1E3 pump incorporated a sealless design with a blood stagnation free structure. The pump impeller was magnetically coupled to the driver magnet in a sealless manner. To develop an atraumatic and antithrombogenic centrifugal pump without a shaft seal junction, a double pivot bearing system was introduced. Recently, a mass production model of the C1E3 was fabricated and evaluated. The ratio of the normalized index of hemolysis (NIH) of the C1E3 was 0.007 g/ 100 L, in comparison to the NIH of the BP-80, 0.018 g/ 100 L, each in a CPB condition of 5 L/min against 325 mm Hg. Both pumps were compared in identical in vitro circuits. To further evaluate the pumps during cardiopulmonary bypass for reliability and function, 6 h of CPB was performed on each of 8 bovines using either the C1E3 or BP-80 centrifugal pump. The BP-80 and C1E3 provided pump flows of 50-60 ml/kg/min without incident. The hemodynamics were stable, and the hematology and biochemistry data were within normal ranges. There were no statistically significant differences between the 2 groups. Concerning the plasma free hemoglobin values, a mass production model of the C1E3 pump had the same hemolysis levels as the BP-80. Our preliminary studies reveal that the C1E3 pump is reliable. Also, the C1E3 will satisfy clinical requirements as a cardiopulmonary bypass pump.

Alanine Transaminase↗