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Biomedical subjects

M Umezu

Publications and source records attributed to M Umezu.

At least 37 records · Page 2Linked to original sources
PubMed1999

Preliminary study on the new self-closing mechanical mitral valve.

Anatural mitral valve starts closing before systole. Conventional mechanical mitral valves start their closing motion after systole. In order to let the mechanical mitral valves start closing before systole, we propose a new self-closing valve by adjusting the center of gravity of the leaflet. As a first step, we adjusted the center of gravity by attaching a block of lead to the leaflet of a CarboMedics bileaflet valve and evaluated it using a pulse duplicator and an x-ray high-speed video camera. Comparative study was conducted under 60 bpm and 4 L/min as the mean flow rate. It was clarified that the self-closing valve started closing before systole, no influence on inflow volume was found, the final closing speed of the self-closing valve just before complete closure was slower than the conventional valve (1.9-0.34 m/s), a design strategy of a self-closing valve (sewing ring diameter 29 mm) was obtained from the experiment that momentum of inertia of the leaflet should be less than 14.9 x 10-9 kg.m2 and the torque caused by gravity should be more than 4.2 x 10-6 N. m, and only one leaflet should be designed as self-closing, and surgeons need to pay attention to the positioning of the two leaflets. In conclusion, the preliminary study showed the ability of starting to close before systole and the design strategy for future prototyping.

Biocompatible Materials↗
PubMed1999

Rotary blood pump flow spontaneously increases during exercise under constant pump speed: results of a chronic study.

Many types of rotary blood pumps and pump control methods have recently been developed with the goal of clinical use. From experiments, we know that pump flow spontaneously increases during exercise without changing pump control parameters. The purpose of this study was to determine the hemodynamics associated with the long-term observation of calves implanted with centrifugal blood pumps (EVAHEART, Sun Medical Technology Research Corporation, Nagano, Japan). Two healthy female Jersey calves were implanted with devices in the left thoracic cavity. A total of 22 treadmill exercise tests were performed after the 50th postoperative day. During exercise, the following parameters were compared with conditions at rest: heart rate, blood pressure, central venous oxygen saturation (SvO2), pump speed, and pump flow. The pump flow in a cardiac cycle was analyzed by separating the systole and diastole. Compared to the base data, statistically significant differences were found in the following interrelated parameters: the heart rate (66.8 +/- 5.2 vs. 106 +/- 9.7 bpm), mean pump flow (4.8 +/- 0.2 vs. 7.0 +/- 0.3 L/min), and volume of pump flow in diastole (26.0 +/- 1.8 vs. 13.5 +/- 2.5 ml). During exercise, the volume of pump flow in systole was 3 times larger than that measured in diastole. Blood pressure, SvO2, and pump speed did not change significantly from rest to exercise. These results suggested that the mean pump flow depends on the systolic pump flow. Therefore, the increase in the mean pump flow during exercise under constant pump speed was caused by an increase in the heart rate.

Animals↗
PubMed1999

Superovulation of immature hypothyroid rdw rats by thyroxine therapy and the development of eggs after in vitro fertilization.

The aim of this study was to examine the effect of thyroxine on ovulation in immature rdw rats and the fertilization and development of the eggs. Serum thyroxine concentrations at 30 days of age were significantly lower in rdw rats than in normal rats (P < 0.001), and greatly increased after thyroxine replacement therapy (P < 0.001). Although few eggs (1-5 +/- 1-2) were obtained from immature rdw rats treated with gonadotrophins alone, females treated with gonadotrophins and thyroxine ovulated significantly more eggs (85 +/- 5). As a control, normal littermates ovulated 21-45 eggs when treated with gonadotrophins alone, and 68 eggs when administered with gonadotrophins and thyroxine. Of the eggs collected from rdw rats treated with gonadotrophins and thyroxine, and inseminated with spermatozoa from mature F1 males, 98% were penetrated and in almost all (99%) of these eggs, male and female pronuclei formed. Forty-seven per cent of the pronuclear eggs developed to the blastocyst stage in vitro. After transfer to recipients, 21% (14/66) of one-cell and 22% (8/37) of two-cell embryos developed to offspring, and 62% (8/13) of pups were of rdw/rdw genotype. The average body weight (6.9 versus 7.8 g) of offspring derived from one-cell embryos was lower than that for two-cell embryos. The morulae and blastocysts did not develop to term, although 41% implanted in the uterine horns of recipients. In conclusion, in immature rdw rats, superovulation was induced by gonadotrophins combined with thyroxine therapy and the superovulated oocytes were fertilized and developed in vitro and developed to term after embryo transfer.

Analysis of Variance↗
PubMed1998

Microtubule and microfilament dynamics in rat embryos during the two-cell block in vitro.

Developmental block of rat embryo is induced by phosphate at the late two-cell stage. The present study uses immunocytochemistry and laser scanning confocal microscopy to examine microtubule and microfilament dynamics in blocked and nonblocked two-cell-stage rat embryos. Thin fibrous microtubules were distributed homogeneously in the cytoplasm in nonblocked embryos during the interphase of the two-cell stage and then translocated into mitotic spindles at the M-phase. In embryos blocked at the two-cell stage, much thicker fibrous microtubules were formed and distributed as rude meshwork structures in the cytoplasm. Microfilaments were distributed adjacent to nuclei and along the inside of the plasma membrane in nonblocked embryos during the two-cell stage, at M-phase, and at cleavage to the four-cell stage. In embryos blocked at the two-cell stage, however, microfilaments formed granules and dispersed in the cytoplasm. The distribution of microtubules and microfilaments changed relative to the occurrence of two-cell block. In summary, these results indicate that both microtubules and microfilaments are closely involved in the developmental block in two-cell rat embryos.

Actin Cytoskeleton↗
PubMed1998

Rapid detection of male-specific DNA sequence in bovine embryos using fluorescence in situ hybridization.

An accurate, reliable, and quick (less than an hour) method for determining the sex of bovine embryos was developed using a fluorescence in situ hybridization (FISH), with a probe designed from a bovine Y chromosome specific DNA (BC1.2). First, to improve a protocol of FISH and evaluate an accuracy of the method, lymphocyte nuclei prepared from three bulls, two cows, and one freemartin were tested. We found that 5 min was enough for hybridization. The washing solution adequate for posthybridization was 0.5x SSC at 72 degrees C for 5 min. The whole procedure for FISH can be accomplished in less than an hour. A male-specific signal was detected, on average, as 97, 0.5, and 83%, respectively, of lymphocytes in males, females, and a freemartin. Using the rapid FISH protocol developed, 28 embryos were divided. According to the presence of the digoxigenin signal, 16 embryos (57.1%) were predicted as male, and 12 embryos (42.9%), predicted as female.

Animals↗
PubMed1998

An implantable centrifugal blood pump with a recirculating purge system (Cool-Seal system).

A compact centrifugal blood pump has been developed as an implantable left ventricular assist system. The impeller diameter is 40 mm, and pump dimensions are 55 x 64 mm. This first prototype, fabricated from titanium alloy, resulted in a pump weight of 400 g including a brushless DC motor. The weight of a second prototype pump was reduced to 280 g. The entire blood contacting surface is coated with diamond like carbon (DLC) to improve blood compatibility. Flow rates of over 7 L/min against 100 mm Hg pressure at 2,500 rpm with 9 W total power consumption have been measured. A newly designed mechanical seal with a recirculating purge system (Cool-Seal) is used for the shaft seal. In this seal system, the seal temperature is kept under 40 degrees C to prevent heat denaturation of blood proteins. Purge fluid also cools the pump motor coil and journal bearing. Purge fluid is continuously purified and sterilized by an ultrafiltration unit which is incorporated in the paracorporeal drive console. In vitro experiments with bovine blood demonstrated an acceptably low hemolysis rate (normalized index of hemolysis = 0.005 +/- 0.002 g/100 L). In vivo experiments are currently ongoing using calves. Via left thoracotomy, left ventricular (LV) apex descending aorta bypass was performed utilizing an expanded polytetrafluoroethylene (ePTFE) vascular graft with the pump placed in the left thoracic cavity. In 2 in vivo experiments, the pump flow rate was maintained at 5-9 L/min, and pump power consumption remained stable at 9-10 W. All plasma free Hb levels were measured at less than 15 mg/dl. The seal system has demonstrated good seal capability with negligible purge fluid consumption (<0.5 ml/day). In both calves, the pumps demonstrated trouble free continuous function over 6 month (200 days and 222 days).

Alloys↗
PubMed1998

Microscopic analysis of enzyme activity, mitochondrial distribution and hydrogen peroxide in two-cell rat embryos.

A developmental block is induced by phosphate in rat embryos at the late two-cell stage. The present study was designed to examine the energy metabolism of rat two-cell blocked and non-blocked embryos. Enzyme activity was measured in individual embryos by histochemical techniques. The activities of malate dehydrogenase, isocitrate dehydrogenase, lactate dehydrogenase, pyruvate dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, glutamate dehydrogenase, glucose-6-phosphate dehydrogenase, glucose-6-phosphatase, and phosphorylase did not differ among non-blocked and blocked embryos. However, the activity of succinate dehydrogenase was significantly decreased in blocked embryos compared with non-blocked embryos. In blocked embryos, cytochrome oxidase activity was distributed homogeneously, but was located at the perinuclear region in non-blocked embryos. Active mitochondrial organization was visualized using the fluorescent probe rhodamine 123 and laser scanning confocal microscopy. In both non-blocked and blocked embryos, mitochondria were distributed homogeneously. The concentration of H2O2 measured fluorometrically in embryos cultured without phosphate did not change significantly during the culture period, but decreased in embryos cultured with phosphate. The timing corresponded to the occurrence of the two-cell block. In summary, these results suggest that the developmental block in rat two-cell embryos is induced by disturbance of mitochondrial energy metabolism.

Animals↗
PubMed1998

Evaluation and characterization of congenital hypothyroidism in rdw dwarf rats.

The rdw rat is a new strain of dwarf mutant that has decreased blood thyroxine (T4) and growth hormone (GH) concentrations and testicular enlargement during development and aging. To confirm whether this strain can be used as a new hypothyroid model, the experiments reported here were carried out, using adult rdw rats, rdw rats treated with thyroxine, and clinically normal (N) Wistar-Imamichi rats. Clinical parameters of deficient thyroid function in rdw rats were chosen for evaluation and characterization. Body weight, hemoglobin (Hb) concentration, hematocrit (Hct), glucose (GLU), and systolic blood pressure were significantly lower, and serum values for aspartate transaminase (AST), total cholesterol (TC), total protein (TP), and blood urea nitrogen (BUN) were higher in rdw than in N rats. Serum concentrations of total T4 and free triiodothyronine (FT3) were significantly lower, and serum thyroid-stimulation hormone (TSH) concentration was markedly higher in rdw than in N rats. Serum GH concentration was significantly lower in rdw than in N rats. Results of histologic examination indicated that the thyroid gland of rdw rats was markedly atrophied, compared with that of N rats. Results of clinical examination of organs and hematologic and biochemical values in rdw rats corresponded to those of the hypothyroid state in humans. Most organ weights (heart, kidney, spleen, and adrenal gland), hematologic and biochemical values (Hb, Hct TC, TP, BUN), blood pressure, and serum hormone (TSH and GH) values underwent substantial restoration (partial or complete) toward normal in response to replacement therapy. In conclusion, the rdw rat is a useful model of congenital hypothyroidism.

Animals↗
PubMed1997

Study of the effect of atrial contraction on mitral prosthetic valve by high speed video camera.

To clarify the effect of atrial contraction on the dynamic behavior of mitral prosthetic valves, a mechanical mock circulatory system has been developed. It is able to simulate the inflow characteristics during diastole. The disc motions of Björk-Shiley Monostrut (BSM29) and CarboMedics (CM29) valves (both with an annulus diameter of 29 mm) were measured and compared with a high speed video camera. After contraction of the artificial atrium (100 ms), there was a delay of 75 ms before the onset of the ventricular contraction. Mitral flow similar to physiological conditions could be achieved. The BSM29 was tested in the anterior position (a) and the posterior position (p). Under the condition of active atrial contraction (AC), we confirmed that the closing motion was initiated and the period during closing motion (PDCM) was prolonged (BSM29[a]: 22.4 +/- 3.4-->63 +/- 3.2; BSM29[p]: 71.2 +/- 38-->94.2 +/- 11; and CM29: 14 +/- 0.0-->28.4 +/- 2.3 [unit: ms]), the prolongation of the PDCM of the CM29 due to the AC being smaller than that of the BSM29. We also confirmed that the closing volume (CV) increased slightly (BSM29 [a]: 7.8 +/- 0.4-->8.5 +/- 0.8; BSM29[p]: 6.9 +/- 0.6-->7.0 +/- 0.5; and CM29: 3.6 +/- 0.6-->4.1 +/- 0.6 [unit: ml]). The CM29 had a shorter PDCM, less prolongation of the PDCM due to the AC, and less CV than the BSM29. Thus, we confirmed that the CM29 produced better response at valve closure than the BSM29.

Atrial Function↗
PubMed1997

Physiologic remodeling annuloplasty to retain the shape of the anterior leaflet: a new concept in mitral valve repair.

BACKGROUND AND AIMS OF THE STUDY: The Carpentier-Edwards (CE) ring was developed to restore the normal 3:4 ratio between the anteroposterior and transverse diameters of the mitral valve orifice during systole. It is difficult to use in patients in whom the ratio is more than 3:4. To overcome this problem, we developed an adjustable obturator, the ratio of which may be changed by sliding apart its two components. METHODS: Remodeling annuloplasty was performed using part of a flexible Duran ring or autologous pericardium and the adjustable obturator in 17 patients with severe MR, including two with high anterior leaflet. RESULTS: Physiologic remodeling annuloplasty was easily accomplished in all cases. Intraoperative echocardiography was performed in 14 patients, and it showed no regurgitant jet in 11 cases and only trivial jet in three. CONCLUSION: Physiologic remodeling annuloplasty to retain the natural shape of the anterior leaflet by using an adjustable obturator is a very useful technique that enables annuloplasty to be performed in all cases, irrespective of the shape of the anterior leaflet.

Adult↗
PubMed1996

High-resolution fluorescent particle-tracking flow visualization within an intraventricular axial flow left ventricular assist device.

Flow visualization is typically applied in blood pump development to both confirm the design expectations and identify regions that may be predisposed to blood element deposition and trauma. Rotary pumps, in particular, place high demands on the technique chosen to visualize the flow given the limited visual accessibility of the flow path and the high impeller speeds. Fluorescent image-tracking velocimetry currently is used at the University of Pittsburgh Medical Center to visualize flow accurately inside of these pumps both qualitatively and quantitatively. Flow patterns under steady conditions within an intraventricular axial flow, left ventricular assist pump (prototype No. 7, SUN Medical Technology Research Corporation, Nagano, Japan) were investigated using this technique. The flow fields at the impeller-stator interface and at the pump outlet were given specific attention. This allowed the assessment of the fluid dynamics throughout the hydrodynamic design limits of the pump.

Biomechanical Phenomena↗
PubMed1996

Effects of surface roughness on mechanical hemolysis.

Previous in vitro hemolysis test results showed that an inlet taper or a round corner in the leading edge of a stenotic connector played an important role in the reduction of hemolysis. However, computational fluid dynamics (CFD) analysis of these results indicated that the shear rate and hemolysis level were not always related to each other. Then, further research was performed, focusing on the effects of surface roughness on hemolysis. The results thus far can be summarized as threefold. First, the rate of hemolysis occurring at an abrupt change in the stenotic section was different if the longitudinal length of the stenosis was changed. The level of plasma-free hemoglobin after 6 h of circulation was decreased from 280 mg/dl to 70 mg/dl when the longitudinal length was shortened from 15 mm to 1 mm. Second, a comparison of hemolysis rates in identical stenotic connectors with differing surface roughness (Ra = 0.45 and 1.35 micrograms) revealed that a smooth surface achieved as much as an 80% reduction in the rate of hemolysis. Third, the in vitro hemolysis results obtained were further defined through CFD analysis.

Animals↗
PubMed1996

Basic performance of a miniature intraventricular axial pump.

A miniature intraventricular axial pump for left ventricular (LV) support is under development. This pump was designed for placement in the LV cavity by insertion through the LV apex with the outlet located at the ascending aorta via the aortic valve. The basic hydrodynamic characteristics represented as a relationship between pump head (H) and flow (Q) showed a negative linear relationship under a constant head. This characteristic was generally the same as that obtained by other axial rotation pumps. However, the actual H-Q relationship was represented as anticlockwise "loops" caused by the contraction of the natural LV. The comparative in vitro data on these H-Q loops showed that the shape of the loops was changed drastically by the connecting condition between the pump and natural cardiovascular system.

Animals↗
PubMed1994

Increase in testis weight of hereditary dwarf rats (rdw/rdw) with advancing age.

Testis weight and seminal vesicle weight (relative to total body weight) in rdw rats and N rats were compared with advancing age. The results obtained were as follows 1) The increase in testis weight became remarkable at 15-16 weeks of age. The weight remained constant up to 23-30 weeks of age and decreased thereafter with age. 2) Seminal vesicle weight increased rapidly in rdw rat at 15-16 weeks of age, reflecting elevated androgen secretion and sexual maturation. 3) From the viewpoint of histology, one of causes of the increase in testis weight may be edema. The increase in testis weight coincided with the increase in androgen secretion at 15-16 weeks of age as suggested by the relative increase in seminal vesicle weight.

Aging↗
PubMed1994

[A case of Crow-Fukase syndrome associated with membranoproliferative glomerulonephritis].

Crow-Fukase syndrome is a rare multiorgan disorder. Although renal disorders, such as proteinuria, and renal impairment, have been observed in half the cases of this syndrome, there have been few reports describing the renal lesions. We report here a case of this syndrome associated with membranoproliferative glomerulonephritis. A 43-year-old woman was referred to our hospital because of hyperglycemia. She had also been suffering from hyperpigmentation, hepatosplenomegaly, lymphadenopathy, polyneuropathy and endocrine dysfunction, including diabetes mellitus and amenorrhea. Serum electrophoresis showed M protein and immunoelectrophoresis revealed IgA (lambda). Bone marrow aspiration showed a slight increase in the number of plasma cells. Urine protein was 30 mg/dl, BUN was 17 mg/dl and creatinine 0.8 mg/dl. Light microscopic examinations showed enlargement of glomeruli with proliferation of mesangial cells and matrix, a lobular pattern of the glomeruli and thickening of the glomerular basement membrane and associated double contour. Electron microscopic examinations showed thickened capillary walls, associated mesangial interposition and subendothelial dense deposits. Moreover, fine granular deposits of IgM, C3, and fibrinogen along the basement membrane were observed on immunofluorescent studies.

Adult↗
PubMed1994

[A case of sporadic acute type A hepatitis associated with acute renal failure].

We report a case of sporadic acute type A hepatitis associated with acute renal failure, due to mesangioproliferative glomerulonephritis and interstitial nephritis. A 42 year-old-man was admitted to Mitsui Memorial Hospital because of jaundice and oliguria with fever in February, 1989. His serum creatinine was 12.2 mg/dl, BUN 87 mg/dl, GOT 57 U/l and GPT 358 U/l. The serum IgM antibody to hepatitis A virus was positive, which indicated recent infection with hepatitis A virus. Hemodialysis and steroidal therapy were started, and the patient's acute renal failure and liver dysfunction ameliorated within one month. Light microscopic examinations showed an increased number of mesangial cells and an increased amount of mesangial matrix, and also showed inflammatory cell invasion in the interstitium. Electron microscopic examinations showed proliferation of mesangial cells and matrix, and a dense deposit along the basement membrane. On immunofluoresent studies, fine granular deposits of IgA and Clq were observed in the mesangium.

Acute Disease↗
PubMed1993

Pituitary and serum levels of prolactin (PRL), thyroid stimulating hormone (TSH) and serum thyroxine (T4) in hereditary dwarf rats (rdw/rdw).

Female and male hereditary dwarf mutation rats (rdw), offspring of those found by Koto et al. in a breeding colony of Wistar-Imamichi rats, were decapitated to collect blood and pituitary glands at 10 weeks of age. Levels of pituitary prolactin (PRL), thyroid stimulating hormone (TSH) and serum PRL, TSH and thyroxine (T4) in rdw rats were measured and compared with levels in normal rats (N). The hormone levels were measured with radioimmunoassay (RIA). It was found that the levels of pituitary and serum PRL were considerably lower in rdw rats and that the level of serum T4 was also significantly lower than that in normal rats. TSH per pituitary was significantly lower in rdw rats but TSH per mg pituitary was not different between rdw and normal rats. The levels of serum TSH in rdw was not different from that in normal rats, but was rather higher in female rdw rats than in normal female rats. When the results of previous research were combined with the present results, it was clear that rdw rats are characterized by hypoplasia of GH and PRL synthetic cells of the pituitary and that rdw rat is possibly useful as a model animal with endocrinological defects in pituitary PRL and GH.

Animals↗