Search PubMed⌕ Search

Biomedical subjects

Y Niimi

Publications and source records attributed to Y Niimi.

At least 91 records · Page 5Linked to original sources
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

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

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

Strategy of leukocyte filtration for immunomodulation: development of stainless steel leukocyte filter.

Commercially available leukocyte filters are frequently used to prepare leukocyte depleted blood products for prevention of transfusion reactions. Recently, immunomodulation by using leukocyte filtration was evaluated. At this time, a new leukocyte filter was fabricated with a 4 microm diameter stainless steel fiber. The goal of this study was to assess the efficiency of the stainless steel filter for leukocyte and platelet removal by comparison with the polyester filter that is commercially available. The production of humoral factors, including interleukin-1 beta, tumor necrosis factor-alpha, and interleukin-1 receptor antagonist (IL-1 Ra), was also evaluated. The results show that the stainless steel filter has more than 2 times greater efficiency in leukocyte removal than the polyester filter. Furthermore, the cytokine studies indicate good biocompatibility of the filter, and the stainless steel filter has a possibility of inhibiting inflammatory cytokines by inducing interleukin-1 receptor.

Antibody Formation↗
PubMed1997

In vitro thrombogenic evaluation of centrifugal pumps.

One of the major considerations in the development of a circulatory assist device is its antithrombogenecity. Although the precise evaluation should be accomplished by in vivo tests, these tests are costly and require a relatively long period. In this study, we established a simple in vitro test and assessed feasibility using 2 clinically available centrifugal pumps, the BioMedicus and Nikkiso pumps. Two identical mock loops were fabricated, and fresh heparinized human blood (activated clotting time of 150-250 s) was circulated at 5 L/min against a total pressure head of 100 mm Hg. After 3 h of pumping, only the BioMedicus pumps had thrombi while the Nikkiso pumps were thrombus free. Following 6 h of pumping, thrombi were observed in both pumps. Clotting patterns and locations were reproducible in each pump and similar to the results of clinical or ex vivo studies. This simple in vitro test was considered to be feasible as a pilot study, particularly to predict thrombogenic sites.

Centrifugation↗
PubMed1996

Effects of nitroglycerin infusion on segmental wall motion abnormalities after anesthetic induction.

OBJECTIVES: To assess the effect of intravenous nitroglycerin (NTG) on segmental wall motion abnormalities (SWMAs) and global ventricular function after anesthetic induction in patients undergoing coronary artery bypass grafting (CABG). DESIGN: Prospective study. SETTING: University hospital. PARTICIPANTS: Twenty patients scheduled for elective CABG. INTERVENTIONS: Patients demonstrating SWMAs in at least two myocardial segments after induction received intravenous NTG at 2 micrograms/kg/min. MEASUREMENT AND MAIN RESULTS: Transesophageal echocardiography (TEE) was performed before and after the NTG infusion for analysis of segmental wall motion abnormalities. Mean arterial pressure (MAP), central venous pressure, and pulmonary capillary wedge pressure decreased significantly after NTG infusion, whereas cardiac index and heart rate remained unchanged. End-diastolic area and end-systolic area decreased, and consequently fractional area change increased significantly. Two of 20 patients (10%) showed electrocardiogram evidence of ischemia after induction. After NTG infusion, 15 of 20 patients (75%) showed an increase in a wall motion score more than two points. In these 15 patients with NTG-responsive wall motion abnormalities, the mean ratio of peak early diastolic filling velocity (E) to peak late diastolic filling velocity (A) increased from 0.89 +/- 0.20 to 1.04 +/- 0.25 (p < 0.01) after NTG infusion despite a decrease in filling pressure. Systolic wall thickening improved in segments with poor preoperative function from a pre-NTG value (mean +/- SD) of -1.0% +/- 7.4% to a post-NTG value of 31.4% +/- 24.9% (p < 0.01). CONCLUSIONS: Intravenous NTG improved postinduction SWMAs in 75% of patients with known coronary artery disease. TEE-guided NTG infusion after induction may provide an optimal baseline echocardiogram for monitoring intraoperative myocardial ischemia by improving the reversible portion of postinduction SWMAs.

Aged↗
PubMed1995

Heterogeneity in the expression of Ro and La antigens in human skin.

OBJECTIVE: To determine whether there are variations in the expression of Ro and La antigens in human skin. METHODS: Levels of expression of Ro and/or La antigens in 26 specimens of normal human skin (11 sun-exposed, 15 sun-protected) were measured by indirect immunofluorescence with monospecific antisera. RESULTS: Levels of expression of both antigens varied by more than 2,000-fold in the skin of different individuals. There usually was a correlation between the levels of expression of Ro and La antigens in the same skin specimen. There was no correlation found between the levels of Ro or La antigen expression and sun exposure, nor was there a correlation found between levels of antigen expression and location of the skin on the body. CONCLUSION: There is a marked heterogeneity in the expression of both Ro and La antigens in the skin of different individuals. The present study findings suggest that the levels of expression of these antigens may play a role in the propensity of some individuals to develop anti-Ro or anti-La antibodies and/or skin lesions associated with the presence of these antibodies.

Autoantigens↗
PubMed1995

The detection of coronary ostial lesions by intraoperative transesophageal echocardiography: report of a case.

Transesophageal echocardiography (TEE) is a valuable diagnostic tool for providing clear images of the proximal coronary arteries. We describe herein the case of an elderly man in whom dissection and an atherosclerotic plaque in the proximal coronary arteries were demonstrated by TEE during combined coronary artery bypass grafting and aortic valve replacement. Thus, retrograde cardioplegia was employed, whereby trauma to the coronary ostia was avoided.

Aged↗
PubMed1995

Accelerated endothelial regeneration and intimal hyperplasia following a repeated denudation of rabbit carotid arteries: morphological and immunohistochemical studies.

1. We compared endothelial regeneration and intimal thickening after endothelial denudation between normal and sclerotic carotid arteries (CA). Endothelial denudation of the right CA of rabbits formed intimal thickening covered with regenerated endothelial cells (EC) in 6 weeks, which was considered as the sclerosis model. Both CA were then denuded. Morphological and immunohistochemical studies using antibodies for proliferating cell nuclear antigen (PCNA), von Willebrand factor and macrophages were performed. 2. Regeneration of EC were observed 24 h after denudation on both CA, but completed earlier in the double-denuded right CA. The density of EC in both CA increased after regeneration and gradually decreased afterwards. 3. After a single denudation on the left CA, PCNA-positive cells clearly appeared in 24 h, markedly increased in 72 h both in the intima and media, then greatly decreased in 4 and 6 weeks. 4. After a double denudation of the right CA, enhancement of the intimal hyperplasia was observed. PCNA-positive cells markedly increased in 1 week and remained significantly increased in 6 weeks both in the intima and the media. 5. We concluded from these results that the repeated endothelial denudation caused more sustained proliferation of smooth muscle cells which led to an enhancement of the intimal hyperplasia.

Analysis of Variance↗
PubMed1995

Late-onset renal dysfunction in a patient with non-Hodgkin's lymphoma following an autologous bone marrow transplantation.

Various types of glomerulonephropathy have been reported in patients with malignant lymphoma. The present report describes a 21-year-old man with non-Hodgkin's lymphoma who developed renal insufficiency 4 months after undergoing autologous bone marrow transplantation without combined total body irradiation treatment. At the presentation of renal dysfunction, the malignant lymphoma had been in complete remission. A renal biopsy specimen revealed glomerular changes resembling those seen in patients with hemolytic uremic syndrome. However, hematologic examinations exhibited no evidence of thrombocytopenia or thrombotic microangiopathy, such as red cell fragmentations on the peripheral blood smear. Although the etiology of this nephropathy remains unclear, the chemotherapeutic agents administered in conditioning regimens for bone marrow transplantation were suspected of contributing to the renal insufficiency. Methylprednisolone pulse therapy appeared to be effective in arresting progression of the nephropathy. This case indicates that renal function should be monitored carefully in patients with malignant lymphoma after bone marrow transplantation, even if such patients lack the signs or symptoms of thrombotic microangiopathy.

Adult↗
PubMed1995

[Measurements of ventilatory parameters during closed circuit anesthesia--comparisons with semiclosed circuit, high-flow anesthesia].

Since induction of anesthesia using a closed-circuit technique is difficult with most modern anesthesia machines, it is a common clinical practice to convert semiclosed, high-flow anesthesia (SCA) to closed circuit anesthesia (CCA) during the maintenance phase by decreasing the fresh gas flow. The purpose of the current studies was to determine if such changes in the fresh gas flow influence parameters of ventilatory dynamics. The tidal volume, airway pressure, and a ratio of expiratory volume in one second to a tidal volume (EV1.0/VT) were measured in six patients and in a lung simulator during CCA with a fresh gas flow of 200 ml.min-1 and SCA with a flow of 6 l.min-1. The ventilator settings were constant throughout the experiments. Dynamic compliance was calculated as (measured VT)/(peak airway pressure-positive end-expiratory pressure). Both in patients and in a lung simulator, dynamic compliance and EV1.0/VT were higher during CCA as compared to SCA while the tidal volume and airway pressure were lower. It was also suggested that these differences were secondary to differences in the fresh gas flow and not to the circuit situation (closed vs. semiclosed) per se. The results emphasize that the fresh gas flow should be taken into consideration in interpreting the data of ventilatory dynamics during anesthesia. This is especially so during CCA because CCA employs a minimum fresh gas flow.

Adult↗
PubMed1994

Repeated endothelial removal augments intimal thickening and attenuates EDRF release.

To evaluate the significance of repeated denudation injury in progression of atherosclerosis, we performed a single and then a second balloon denudation on the rabbit carotid arteries. Morphological examinations and organ chamber experiments were performed, and the results were compared. On morphological examinations, reendothelialization was almost completed in 2 wk after redenudation, whereas it required 6 wk after a single denudation. Intimal thickening progressed after redenudation. Organ chamber experiments showed that contractile responses and endothelium-independent relaxation remained unchanged after redenudation. Endothelium-dependent relaxations to acetylcholine, ADP, and substance P decreased progressively by repeating denudation. These relaxation responses were inhibited by NG-nitro-L-arginine, hemoglobin, and methylene blue and were considered to be associated with the production and/or release of endothelium-derived relaxing factor-nitric oxide (EDRF-NO). The diffusion barrier mechanism for the decreased endothelium-dependent relaxations was ruled out using sandwich experiments. In conclusion, repeated endothelial denudation caused progression of intimal thickening and acceleration of endothelial regeneration, and repeated endothelial regeneration resulted in progressively less production and/or release of EDRF-NO.

Acetylcholine↗
PubMed1994

Role of endothelin-1 in neointima formation after endothelial removal in rabbit carotid arteries.

To investigate the role of local endothelin (ET)-1 in neointima formation, we performed a balloon denudation in the rabbit carotid artery. Four weeks after denudation, regeneration of endothelial cells was almost complete, and a marked intimal hyperplasia was observed. The tissue level of ET-1-like immunoreactivity was significantly increased even at 24 and 72 h after denudation and was 9.3 times higher than the control group in 4 wk. On the same time course, the proliferating cell nuclear antigen (PCNA)-positive cells clearly appeared. Receptor density values for 125I-ET-1 and 125I-IRL-1620 [ET-receptor subtype B (ETB)-selective ligand] bindings were significantly greater in the hyperplastic artery without changes in dissociation equilibrium constant values. The 125I-ET-1 binding sites not inhibited with BQ-123 [ET-receptor subtype A (ETA)-selective antagonist] were significantly increased in hyperplastic arteries. ETB receptors were more densely localized in the neointima. The chronic intravenous administration of BQ-123 at plasma concentrations sufficient to antagonize the ETA receptors had no effect on neointima formation and the appearance of PCNA-positive cells. We concluded from all results that ET-1 would be involved in neointima formation after endothelial removal and that the ETA receptors would not play a role in this process.

Animals↗
PubMed1994

Popliteal venous aneurysm with pulmonary embolism.

A 29-year-old female was admitted to the hospital because of increasing exertional dyspnea, chest oppressive feeling and palpitation. Lung perfusion scan, pulmonary angiography, and venography of the lower extremities revealed multiple pulmonary embolism and a right popliteal venous aneurysm as the probable source of emboli. B-mode/Doppler echography and magnetic resonance imaging were useful for the preoperative evaluation. Following anticoagulant therapy and thrombolytic therapy using intravenous heparin and urokinase, respectively, the popliteal venous aneurysm was surgically excised; the walls contained organized thrombus. She delivered a baby without any complication 2 years after the surgery.

Adult↗