Search PubMed⌕ Search

Biomedical subjects

I Yamada

Publications and source records attributed to I Yamada.

At least 91 records · Page 5Linked to original sources
PubMed1996

Evaluation of aortic regurgitation with digitally determined color Doppler-imaged flow convergence acceleration: a quantitative study in sheep.

OBJECTIVES: The aim of the present study was to validate a digital color Doppler-based centerline velocity/distance acceleration profile method for evaluating the severity of aortic regurgitation. BACKGROUND: Clinical and in vivo experimental applications of the flow convergence axial centerline velocity/distance profile method have recently been used to estimate regurgitant flow rates and regurgitant volumes in the presence of mitral regurgitation. METHODS: In six sheep, a total of 19 hemodynamic states were obtained pharmacologically 14 weeks after the original operation in which a portion of the aortic noncoronary (n = 3) or right coronary (n = 3) leaflet was excised to produce aortic regurgitation. Echocardiographic studies were performed to obtain complete proximal axial flow acceleration velocity/distance profiles during the time of peak regurgitant flow (usually early in diastole) for each hemodynamic state. For each steady state, the severity of aortic regurgitation was assessed by measurement of the magnitude of the regurgitant flow volume/beat, regurgitant fraction and instantaneous regurgitant flow rates determined by using both aortic and pulmonary artery electromagnetic flow probes. RESULTS: Grade I regurgitation (regurgitant volume/beat < 15 ml, six conditions), grade II regurgitation (regurgitant volume/beat between 16 ml and 30 ml, five conditions) and grade III-IV regurgitation (regurgitant volume/beat > 30 ml, eight conditions) were clearly separated by using the color Doppler centerline velocity/distance profile domain technique. Additionally, an equation for correlating "a" (the coefficient from the multiplicative curve fit for the velocity/distance relation) with the peak regurgitant flow rates (Q [liters/min]) was derived showing a high correlation between calculated peak flow rates by the color Doppler method and the actual peak flow rates (Q = 13a + 1.0, r = 0.95, p < 0.0001, SEE = 0.76 liters/min). CONCLUSIONS: This study, using quantified aortic regurgitation, demonstrates that the flow convergence axial centerline velocity/distance acceleration profile method can be used to evaluate the severity of aortic regurgitation.

Animals↗
PubMed1996

Evaluation of eccentric aortic regurgitation by color Doppler jet and color Doppler-imaged vena contracta measurements: an animal study of quantified aortic regurgitation.

To evaluate the utility of measurements of the color Doppler jet area, jet length, and width of the color Doppler-imaged vena contracta (the smallest flow diameter in any part of the flow acceleration field) as methods for quantifying aortic regurgitation (AR), eight sheep with surgically induced AR were studied. AR was quantified as peak and mean regurgitant flow rates, regurgitant stroke volumes, and regurgitant fractions as determined with pulmonary and aortic electromagnetic flow probes and flowmeters balanced against each other. Simple linear regression analysis between the maximal color jet areas, jet length, and flowmeter data showed only moderately good correlation (jet area: 0.42 < or = r < or = 0.57, SEE = 2.85 cm2; jet length: 0.42 < or = r < or = 0.59, SEE = 1.23 cm). In contrast, the width of color Doppler-imaged vena contracta was a better indicator of the severity of AR on the basis of the electromagnetic flowmeter methods (0.73 < or = r < or = 0.90, SEE = 0.15 cm). Therefore the color Doppler jet length and jet area methods have limited use for determining AR, whereas the width of the color Doppler-imaged vena contracta can be used for quantifying the severity of AR.

Animals↗
PubMed1996

Antibacterial activity of silver ions implanted in SiO2 filler on oral streptococci.

OBJECTIVE: To evaluate the role of silver ions in composite resin dental materials, an in vivo investigation was conducted into the antibacterial effect of SiO2 filler implanted with silver ions on oral streptococci. METHODS. SiO2 filler samples (0.1g) were implanted with silver ions. The effect of the filler with silver ions (Ag+ filler) was tested on oral streptococci bacteria. These bacterial strains had been isolated predominantly from composite resin surfaces. The organisms tested were anaerobically cultured in 5 mL Trypticase Soy Broth containing 0.5 per cent yeast extract at 37 degrees C for 10-12 h. Each bacterial strain was adjusted to a concentration of 1 x 10(6) cells per mL with reduced transport fluid (RTF). Ag+ filler was immersed in 1 mL of RTF and anaerobically incubated 2, 6 and 12 h to study the antibacterial effect. The survival of bacteria was then estimated by culturing on TSBY agar plates. A plate with approximately 100 discrete colonies was chosen from the serial agar cultures, and the number of colonies was counted at each sampling time. RESULTS: The Ag+ filler showed significantly more antibacterial activity than the control filler without silver ions. SIGNIFICANCE: These results indicate that the antibacterial effect found in this study was due to the silver ions released by the Ag+ filler and that it may be useful to add this filler to composite resin dental materials for secondary caries protection.

Anti-Infective Agents, Local↗
PubMed1996

Angiographic findings in Buerger disease.

To clarify the angiographic findings in patients with Buerger disease and to elucidate the relationship between the angiographic findings and the clinical prognosis, 144 angiographic images of the lower extremities of 119 patients with Buerger disease have been studied. The present study has included patient data in our previous report. Results of this study revealed that in lower extremities showing a femoropopliteal arterial occlusion (n = 57), the frequency of gangrene was significantly lower statistically in limbs in which the main arteries of the lower leg and foot were well visualized (2 (12%) of 17 limbs) than in limbs in which the main arteries did not visualize (25 (63%) of 40 limbs) (P < 0.001). Further, in lower extremities showing a crural arterial occlusion (n = 59), the incidence of pedal gangrene increased as the extent of pedal arterial occlusion increased, though this rise was not statistically significant. Also, the collateral vessels had a 'corkscrew' appearance in 39 (27%) of 144 limbs affected by Buerger disease, whereas this appearance was seen in only 2 (3%) of 63 limbs of patients with arteriosclerosis obliterans (P < 0.001). Another finding of this study is that corkscrew-shaped vessels that extend from the sites of the arterial occlusion to the periphery of the feet without opacification of the main pedal arteries indicate a poor prognosis. Based on the above findings, we thus believe that the appearance of corkscrew-shaped vessels is the most characteristic feature of Buerger disease and that each represents a dilated vasa vasorum of the occluded main arteries.

Adult↗
PubMed1996

Gastrointestinal physiology-regulated dogs for bioavailability evaluation of an oral controlled-release dosage form composed of pulsatile release granules.

Gastrointestinal (GI) physiology-regulated beagle dogs (regulated dogs) were regulated by a combined treatment using intramuscular pentagastrin and intravenous atropine sulfate. In the regulated dogs, the gastric pH was shifted to around 2, and the GI transit time was prolonged to approximate that in humans. Pranoprofen, an acidic anti-inflammatory agent, was granulated around sucrose seeds, and then coated with low substituted hydroxypropyl cellulose used as a swelling agent to afford plain granules (A-granule). Then, A-granule was coated stepwise with ethyl cellulose used as an outer shell material to afford two kinds of pulsatile release granules (B- and C-granules). In the dissolution study using pH 1.2 and 6.8 media, A-, B- and C-granules exhibited lag times of 0, 1 and 2h, respectively. Even in intact beagle dogs, the absorption profiles for A- and B-granules corresponded with those expected from the dissolution profiles. In contrast, the bioavailability of C-granule was only 35% in the intact dogs, but was 55% in the regulated dogs. Thus, the absorption of pranoprofen from pulsatile release granules after a longer lag time should be influenced by the location in the GI tract. Next, a controlled-release (CR) dosage form of pranoprofen was tentatively prepared by combining A-, B- and C-granules at the ratio of 3:4:3 (w/w in contents of pranoprofen). The bioavailability of the CR dosage form was significantly diminished in the intact dogs, being about 70% as much as that in the regulated dogs. Therefore, the regulated dogs would be superior to the intact dogs in avoiding the underestimation of the bioavailability of a CR dosage form with a pulsatile release property.

Animals↗
PubMed1996

SPECT and MRI evaluations of the posterior circulation in moyamoya disease.

UNLABELLED: We evaluated the posterior circulation in patients with moyamoya disease by SPECT and MRI. METHODS: Six patients with idiopathic moyamoya disease were studied by SPECT, MRI and angiography. Patients received an injection of 555-740 MBq of 99mTc-HMPAO, after which SPECT images were taken. The cerebral-to-cerebellar activity ratio in five cerebral regions was calculated to assess the regional cerebral blood flow (rCBF). The SPECT and MRI findings were then compared with angiographic. RESULTS: Of the 12 posterior cerebral arteries (PCAs) in the six patients studied, seven PCAs (58%) in five patients had a stenotic or occluded lesion. Furthermore, rCBF in all five regions significantly decreased as the degree of steno-occlusive lesions of the PCA progressed. No significant correlation, however, was found between the steno-occlusive lesions of the internal carotid artery bifurcation and the rCBF. The rCBF significantly decreased in the absence of leptomeningeal collateral vessels from the PCA to the anterior circulation. On the basis of the MR images, the frequency of cerebral infractions significantly increased in patients with steno-occulasive PCA lesions. CONCLUSION: The rCBF in moyamoya disease decreases proportionally with the degree of steno-occlusive lesions of the PCA. The steno-occlusive PCA lesions decrease the number of leptomeningeal collateral vessels to the anterior circulation, thereby causing severe cerebral ischemia that is likely to result in infractions.

Adolescent↗
PubMed1996

Safety and efficacy of in vivo gene transfer into the porcine heart with replication-deficient, recombinant adenovirus vectors.

Gene transfer with replication-deficient recombinant adenovirus (Ad) vectors may provide a novel approach to the treatment of some cardiac disorders. The relative efficiency of intramyocardial vs intracoronary Ad vector injection in transducing myocardial cells remains to be determined. Further, Ad vectors are associated with localized inflammation, and this could be associated with clinically significant side-effects. Female minipigs underwent open chest surgery and the Ad vector AdCMV.NLS beta-gal was injected into the circumflex coronary artery (IC; 2 x 10(10) p.f.u.; n = 5) or the posterobasal wall of the left ventricle (i.m.; 5 x 10(9) p.f.u., n = 4; 2 x 10(10) p.f.u., n = 18). The minipigs were killed after 2-31 days and the hearts examined for evidence of beta-galactosidase activity. Minipigs underwent epicardial echocardiography immediately before, within 15 min following the i.m. injection of AdCMV.NLS beta-gal and again at the time of death. Blood samples for white blood cell count, alkaline phosphatase, total bilirubin, blood urea nitrogen, creatinine and electrolytes were obtained before i.m. and i.c. injection of the Ad vector and before death. Intramuscular injection of the Ad vector was more efficient than i.c. infusion in infecting cells in a localized area of the heart. Myocardial beta-gal activity peaked at 3-6 days after i.m. injection and returned to its control value within 1 month. Although inflammatory cells were present at the injection site, echocardiograms did not show any evidence of either segmental or global left ventricular dysfunction. No minipigs died and all blood tests remained within normal limits following either i.m. or i.c. exposure to the Ad vector. In summary, direct i.m. administration of replication-deficient, recombinant Ad vectors provides a safe and effective approach for short-term gene transfer into the heart of large mammals.

Adenoviruses, Human↗
PubMed1995

Moyamoya disease: diagnostic accuracy of MRI.

Our purpose was to evaluate the diagnostic accuracy of MRI in moyamoya disease. We studied 30 patients with this disease, comparing MRI and angiographic findings. The diagnostic value of MRI was evaluated for occlusive lesions, collateral vessels, and parenchymal lesions. In all patients bilateral occlusion or stenosis of the supraclinoid internal carotid artery and proximal anterior and middle cerebral arteries was clearly shown by MRI, and staging of the extent of occlusion agreed with angiographic staging in 44 (73%) of 60 arteries. MRI, particularly coronal images, clearly showed basal cerebral moyamoya vessels in 54 hemispheres, and 45 of a total of 71 large leptomeningeal and transdural collateral vessels were identified. MRI also showed parenchymal lesions in 48 (80%) hemispheres, and the extent of occlusion in the anterior and posterior circulations respectively correlated with white matter and cortical and/or subcortical infarcts.

Adolescent↗
PubMed1995

MRI in spontaneous cerebrospinal fluid rhinorrhoea.

We studied two patients with spontaneous cerebrospinal fluid (CSF) rhinorrhoea with MRI and other imaging modalities. T2-weighted images proved most useful for the detection and localisation of the CSF leakage. MRI appeared to provide an accurate and noninvasive method for preoperative investigation of spontaneous CSF rhinorrhoea.

Aged↗
PubMed1995

Relation of left atrial V-wave/left ventricular systolic pressure ratio to mitral regurgitant volume.

Evaluation of mitral regurgitation is difficult whether invasive or noninvasive methods are used. The determination of the regurgitant volume itself cannot be done in clinical practice with reasonable accuracy. In six sheep with chronic mitral regurgitation, left ventricular and left atrial pressures were recorded with high-fidelity catheters. The regurgitant volume was measured directly with electromagnetic flow probes positioned at the mitral annulus and around the ascending aorta, balanced against each other. A total of 24 hemodynamic states were obtained varying preload and afterload by fluid expansion and angiotensin infusion. On the basis of these studies, the pressure ratio of the V wave divided by the left ventricular systolic pressure is proposed as an index of regurgitant volume. A good correlation was found between this ratio and the regurgitant volume (r = 0.75). The ratio is easily recorded during routine heart catheterization.

Animals↗
PubMed1995

Color flow Doppler determination of transmitral flow and orifice area in mitral stenosis: experimental evaluation of the proximal flow-convergence method.

To evaluate the in vivo accuracy of color Doppler flow-convergence methods for determining transmitral flow volumes and effective orifice areas in mitral stenosis, we studied two models for flow-convergence surface geometry, a hemispheric (HS) model and an oblate hemispheroid (OH) model in a chronic animal model with quantifiable mitral flows. Color Doppler flow mapping of the proximal flow-convergence region has been reported to be useful for evaluation of intracardiac flows. Flow-convergence methods in patients with mitral stenosis that use HS assumption for the isovelocity surface have resulted in underestimation of actual flows. Chronic mitral stenosis was created surgically in six sheep with annuloplasty rings (group 1) and 11 sheep with bioprosthetic porcine valves (group 2). Hemodynamic and echocardiographic/Doppler studies (n = 18 in group 1; n = 21 in group 2) were performed 20 to 34 weeks later. Left ventricular inflow obstruction was of varied severity, with mean transmitral valve gradients in group 1 ranging from 1.3 to 18 mm Hg and in group 2 ranging from 6.3 to 25.6 mm Hg. Although transmitral flows derived by both geometric flow convergence models showed significant correlations with reference cardiac outputs, the correlations for the OH model were better than those for the HS model (group 1, r = 0.86 for the OH model vs r = 0.72 for the HS model; group 2; r = 0.84 for the OH model vs r = 0.62 for the HS model). The OH model was also superior to the HS model in determining effective orifice areas compared to reference orifice areas determined by postmortem planimetry of anatomic orifices (group 1 only, r = 0.64 for OH vs 0.58 for HS), by the Gorlin and Gorlin formula (group 1, r = 0.63 for OH vs 0.72 for HS; group 2, r = 0.82 for OH vs 0.76 for HS), and by the Doppler pressure half-time method (group 1, r = 0.76 for OH vs 0.69 for HS; group 2, r = 0.84 for OH vs 0.62 for HS).(ABSTRACT TRUNCATED AT 400 WORDS)

Analysis of Variance↗
PubMed1995

Doppler evaluation of severity of mitral regurgitation: relation to pulmonary venous blood flow patterns in an animal study.

OBJECTIVES: This study examined the influence of regurgitant volume on pulmonary venous blood flow patterns in an animal model with quantifiable mitral regurgitation. BACKGROUND: Systolic pulmonary venous blood flow is influenced by atrial filling and compliance and ventricular output and by the presence of mitral regurgitation. The quantitative severity of the regurgitant volume itself is difficult to judge in clinical examinations. METHODS: Six sheep with chronic mitral regurgitation produced by previous operation to create chordal damage were examined. At reoperation the heart was exposed and epicardial echocardiography performed. Pulmonary venous blood flow waveforms were recorded by pulsed Doppler under color flow Doppler guidance using a Vingmed 750 scanner. The pulmonary venous systolic inflow to the left atrium was expressed as a fraction of the total inflow velocity time integral. Flows across the aortic and mitral valves were recorded by electromagnetic flowmeters balanced against each other. Pressures in the left ventricle and left atrium were measured directly with high fidelity manometer-tipped catheters. Preload and afterload were systematically manipulated, resulting in 24 stable hemodynamic states. RESULTS: Simple logarithmic correlation between the regurgitant volume and size of a positive or negative pulmonary venous inflow velocity time integral during systole was good (r = -0.841). By stepwise linear regression analysis with pulmonary venous negative systolic velocity time integral as a dependent variable compared with the regurgitant volume, fractional shortening, left atrial v wave size, systemic vascular resistance and left ventricular systolic pressure, only contributions from v wave size and regurgitant volume (r = 0.80) reached statistical significance in determining pulmonary venous negative systolic flow. CONCLUSIONS: Evaluation of systolic pulmonary venous blood flow velocity time integral can give valuable information helpful for estimating the regurgitant volume secondary to mitral regurgitation.

Animals↗
PubMed1995

Dynamic change in mitral regurgitant orifice area: comparison of color Doppler echocardiographic and electromagnetic flowmeter-based methods in a chronic animal model.

OBJECTIVES: The aim of the present study was to investigate dynamic changes in the mitral regurgitant orifice using electromagnetic flow probes and flowmeters and the color Doppler flow convergence method. BACKGROUND: Methods for determining mitral regurgitant orifice areas have been described using flow convergence imaging with a hemispheric isovelocity surface assumption. However, the shape of flow convergence isovelocity surfaces depends on many factors that change during regurgitation. METHODS: In seven sheep with surgically created mitral regurgitation, 18 hemodynamic states were studied. The aliasing distances of flow convergence were measured at 10 sequential points using two ranges of aliasing velocities (0.20 to 0.32 and 0.56 to 0.72 m/s), and instantaneous flow rates were calculated using the hemispheric assumption. Instantaneous regurgitant areas were determined from the regurgitant flow rates obtained from both electromagnetic flowmeters and flow convergence divided by the corresponding continuous wave velocities. RESULTS: The regurgitant orifice sizes obtained using the electromagnetic flow method usually increased to maximal size in early to midsystole and then decreased in late systole. Patterns of dynamic changes in orifice area obtained by flow convergence were not the same as those delineated by the electromagnetic flow method. Time-averaged regurgitant orifice areas obtained by flow convergence using lower aliasing velocities overestimated the areas obtained by the electromagnetic flow method ([mean +/- SD] 0.27 +/- 0.14 vs. 0.12 +/- 0.06 cm2, p < 0.001), whereas flow convergence, using higher aliasing velocities, estimated the reference areas more reliably (0.15 +/- 0.06 cm2). CONCLUSIONS: The electromagnetic flow method studies uniformly demonstrated dynamic change in mitral regurgitant orifice area and suggested limitations of the flow convergence method.

Animals↗
PubMed1995

A comparison of failure modes of glutaraldehyde-treated versus antibiotic-preserved mitral valve allografts implanted in sheep.

Morphologic studies and calcium analyses were made on mitral valve allografts from 12 juvenile sheep surviving 12 to 24 weeks after mitral valve replacement. Before implantation, the allografts were treated with 0.625% glutaraldehyde (group I, n = 4) or with cold antibiotic solution (group II, n = 8). Three group I animals died 12 to 19 weeks after implantation because of dysfunction of calcified valves; the surviving animal also had extensive allograft calcification. One group II animal died of mitral regurgitation; the valves of the other seven (including five with regurgitation shown by Doppler and ventriculographic studies) were explanted at 19 to 24 weeks. Chordal rupture related to calcific deposits was found in all group I valves. Leaflet perforations (n = 4) and ruptured chordae (n = 4), each caused by connective tissue deterioration, were found in group II valves. Inflammatory reaction was absent or minimal in group I valves but moderate or severe in group II valves. Fibrous sheaths were thicker in group II than in group I valves. Calcium levels were much higher in group I than in group II valves. Calcification in group I valves was diffuse and involved collagen, elastic fibers, and connective tissue cells and matrix; in group II valves, it was localized in connective tissue cells. Thus glutaraldehyde-treated allografts failed because of extensive calcification, whereas antibiotic-preserved allografts underwent deterioration of connective tissue and infiltration by inflammatory cells.

Animals↗
PubMed1995

Photofrin photosensitization. Correlation of Photofrin:erythrocyte binding processes with photolysis.

Unilamellar suspensions of dimyristoylphosphatidylcholine (DMPC) can be utilized to remove Photofrin from the erythrocyte. This enables correlation of the Photofrin membrane-binding processes with Photofrin-sensitized photolysis. The observed rates of erythrocyte biding as well as the observed rates of removal of PHotofrin from the erythrocyte membrane suggest the existence of two Photofrin species that differ in their rates of exchange between the erythrocyte and buffer phases. Selective depletion and readdition of these Photofrin species to the erythrocyte membrane permits evaluation of their separate and joint photolytic efficiencies. These rapidly and slowly exchanging membrane-bound Photofrin species are separately much less efficient photosensitizers than the two species together. The two Photofrin species exhibit essentially identical fluorescence emission spectra in the presence of DMPC. Nevertheless, models consistent with the results involve partitioning by chemically distinct Photofrin components or partitioning of chemically similar Photofrin components into distinct membrane environments, or a combination of these.

Dihematoporphyrin Ether↗
PubMed1995

Long-term change of anti-acetylcholine receptor antibody in patients with myasthenia gravis after thymectomy.

Anti-acetylcholine receptor antibody (AChR Ab) plays an important role in the pathogenesis of myasthenia gravis (MG). We investigated the change of anti-AChR Ab titer after thymectomy of 10 MG patients including five patients whose age at onset was younger than 16 years. Anti-AChR Ab titer was increased in four of six patients with remission and three of four patients without remission. Change of anti-AChR Ab titer in individual patients showed an increase occurred 1-4 years after thymectomy. It is likely that thymectomy influences immune response and induces autoreactive lymphocytes and autoantibodies.

Adolescent↗
PubMed1995

Moyamoya disease: comparison of assessment with MR angiography and MR imaging versus conventional angiography.

PURPOSE: To evaluate magnetic resonance (MR) angiography and MR imaging in assessment of moyamoya disease. MATERIALS AND METHODS: The cases of 26 patients with moyamoya disease were evaluated prospectively. After three-dimensional time-of-flight 1.5-T MR angiography and MR imaging, images were evaluated in blinded separate interpretation. RESULTS: MR angiography and MR imaging accurately depicted 217 (82%) and 184 (70%) of 264 arteries, respectively, but the degree of stenosis was overestimated in the other arteries. Basal cerebral moyamoya vessels were depicted in all 52 hemispheres with conventional angiography and in 42 (81%) and 48 (92%) hemispheres with MR angiography and MR imaging, respectively. The respective sensitivity and specificity for diagnosis of moyamoya disease were 73% and 100% for MR angiography, 92% and 100% for MR imaging, and 92% and 100% for MR angiography plus MR imaging. CONCLUSION: Assessment of moyamoya disease is most thorough with MR angiography and MR imaging.

Adolescent↗