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Biomedical subjects

Y Takayama

Publications and source records attributed to Y Takayama.

At least 55 records · Page 3Linked to original sources
PubMed1998

Relationship between spatial coherence of synchrotron radiation and emittance.

Analytical calculation of the first-order spatial coherence for the Gaussian beam and the exact numerical calculation for synchrotron radiation are compared in this paper. The approximation of regarding synchrotron radiation as a Gaussian beam is often used to investigate the brightness, the flux and some qualitative properties. Calculations show that synchrotron radiation does not have as high coherence as the Gaussian beam because of the beam profile, the phases of the wave and the polarization. If one can measure the beam size and the spatial coherence of synchrotron radiation, it is possible to determine the total photon beam emittance without any knowledge of the Twiss parameters of the ring.

Journal Article↗
PubMed1998

Measurement of the coherence of synchrotron radiation.

The first-order spatial (transverse) coherence of synchrotron radiation has been measured using a Young's interferometer at BL28A (a helical-undulator beamline) of the Photon Factory, KEK. The range of the photon energy is about 70-180 eV. The visibility of the fringe was found to depend largely on the electron emittance and the intrinsic photon emittance. In principle, it is possible to gain knowledge of the very small electron emittance, of the order of 10(-10) m rad, without disturbing the electron beam in the storage ring.

Journal Article↗
PubMed1998

Human hippocampal long-term sustained response during word memory processing.

Temporal behavior of activation associated with the neural substrate of human memory function was investigated during and after an auditorily instructed word memory task using multislice functional magnetic resonance imaging. The hippocampal formation, which is involved in human memory function, displayed a long-term sustained response that persisted significantly (approximately 90 s) beyond the duration of the memory task. This sustained period was approximately two-fold longer than the duration of the post-task activation observed in auditory areas and Broca's area, which are involved in the phonological loop of the verbal working memory. These observations suggest that the hippocampal memory processing involves sustained activation in the transitional function for the long-term memory over the working memory period.

Adult↗
PubMed1998

Nondissection method for tibial bypass surgery using Esmarch's rubber bandage or an automatic sequential pneumatic tourniquet: long-term results.

It is suspected that operative injury to the native arteries during a vascular bypass procedure causes periarterial fibrosis contributing to late graft failure. A a nondissection method for tibial artery bypass has been developed using Esmarch's rubber bandage or an automatic sequential pneumatic tourniquet. This retrospective study examined patency and other late results in distal bypass operations using the nondissection method. Between June 1982 and July 1995, 78 tibial bypasses were performed using reversed autogenous saphenous vein grafts in 70 patients (57 men, 13 women; mean age 57.4 years). Graft patency was assessed angiographically. When a stenotic lesion was recognized, the graft was revised and considered an assisted primary patency. Primary patency rates at 1, 3, 5, and 10 years were 82.8%, 75.3%, 63.4% and 63.4%, respectively, by life-table analysis. Six grafts required revision for stenosis; one involved distal anastomotic stenosis. As a result, assisted primary patency rates resembled secondary patency rates of 87.7%, 84.3%, 80.3%, and 80.3% at the same respective intervals. In conclusion, the nondissection method improved long-term patency by preventing late distal anastomotic stenosis.

Arterial Occlusive Diseases↗
PubMed1998

Pancreatic surgery in Japan: historical review.

The advent of surgical techniques for the management of pancreatic cancer has had a long and varied history in the Western culture. The development of current surgical techniques and treatment modalities is based on (rooted in) techniques developed over time. Although the first written anecdotes of pancreatic resection--primarily from the 1600s through the late 1800s--did not alter the mortality of pancreatic cancer, they did pave the way for advances in surgical techniques that subsequently attained lower morbidity and mortality rates. Although there were some meager attempts at pancreatic resection in Japanese institutions before and during World War II, it was not until after the war, and particularly after the mid-1950s, that pancreatic surgery developed tremendously. The development of more radical approaches to pancreatic surgery developed tremendously. The development of more radical approaches to pancreatic resection as well as other surgical developments resulted in lower morbidity and mortality rates.

General Surgery↗
PubMed1998

Role of platelet-activating factor on extravascular lung water after coronary reperfusion in dogs.

Platelet-activating factor (PAF), one of the harmful substances released after coronary reperfusion, has been reported to increase pulmonary vascular permeability and induce pulmonary edema. In this study, we sought to examine the possible role of PAF in the genesis of pulmonary edema after coronary reperfusion. Extravascular lung water (EVLW) was measured by the thermal-dye double indicator dilution method during coronary ligation and after reperfusion in situ in dogs. The proximal left anterior descending coronary artery was occluded for 15 min and reperfused in 5 dogs (group 1), while five other dogs (group 2) were treated with PAF-antagonist (TCV-309, 1 mg/kg) before coronary artery occlusion. EVLW and hemodynamic indices were measured at baseline, 15 min of coronary occlusion, and 15 and 30 min after coronary reperfusion. EVLW increased at 15 min of coronary occlusion in both groups, but there was no significant difference between the two groups (6.4 to 10.3 ml/kg and 5.4 to 7.1 ml/kg in groups 1 and 2, respectively). After coronary reperfusion, EVLW increased further in group 1 (6.4 to 16.5 ml/kg, p < 0.01), but no further increase was observed in group 2 at 30 min after coronary reperfusion. There were no significant differences in hemodynamic indices between the two groups throughout the test. Thus, PAF-antagonist attenuated the increase in EVLW after coronary reperfusion independent of hemodynamic indices, and hence, PAF may play an important role in the genesis of pulmonary edema caused by coronary reperfusion.

Animals↗
PubMed1997

Role of Csk in neural differentiation of the embryonic carcinoma cell line P19.

To examine the neural function of Csk (C-terminal Src kinase), a membrane-targeted form of Csk (Src/Csk) and its kinase-defective variant (DK-Src/Csk) were expressed in the embryonic carcinoma cell line P19. Expression of Src/Csk, but not DK-Src/Csk, caused reduction of the specific activities of Src and Fyn in the differentiated P19 cells. During neural differentiation, the specific activity of Src was elevated in the control P19 cells, whereas the activation was completely eliminated in the Src/Csk transfectant. In normally differentiated P19 cells, cross-linking of a cell adhesion molecule, L1, induced a short-term activation of Src and Fyn. In the Src/Csk transfectant, L1 stimulation induced delayed activation of Src and Fyn peaking at much lower levels than in the control cells. Src/Csk transfectants developed normally in the initial stages of neural differentiation, but exhibited an apparent defect in cell-to-cell interaction, i.e. neurite fasciculation and aggregation of cell bodies, in the latter stages. These findings imply that Csk is involved in the regulation of Src family kinases that play roles in cell-to-cell interaction mediated by cell adhesion molecules.

Animals↗
PubMed1997

Comparative hypocholesterolemic effects of capybara (Hydrochoerus hydrochaeris dabbenei) oil, horse oil, and sardine oil in cholesterol-fed rats.

The hypocholesterolemic efficacy of various polyunsaturated fatty acids was compared in rats given cholesterol-enriched diets. Capybara oil (CO, linoleic + alpha-linolenic acids), horse oil (HO, alpha-linolenic acid), and sardine oil (SO, eicosapentaenoic + docosahexaenoic acids) were added to diets at 50 g/kg. The weight gain, food intake, and liver weight in the CO-fed group were significantly higher than those in other groups during the 6-wk experimental period. The serum total and very low density lipoprotein (VLDL) + intermediate density lipoprotein (IDL) + low density lipoprotein (LDL) cholesterol concentrations of the CO-fed and SO-fed groups were significantly lower than in the HO-fed group after 6 wk. The serum high density lipoprotein cholesterol concentration in the SO-fed group was significantly higher than that in the CO-fed and HO-fed groups. The fecal neutral sterol concentration in the CO-fed group was reduced significantly compared with the other groups, and the fecal bile acid concentration in the HO-fed group was significantly higher than that in the SO-fed group. The results of this study demonstrate that CO lowers the serum total cholesterol and VLDL + IDL + LDL-cholesterol concentrations in the presence of excess cholesterol in the diet as well as SO.

Animals↗
PubMed1997

Effects of platelet-activating factor on left ventricular performance in dogs.

To elucidate the mechanism by which platelet-activating factor (PAF) decreases cardiac output (CO), its effects on left ventricular (LV) performance were studied using a LV pressure-volume model in 9 anesthetized dogs. LV volume was measured with a conductance catheter and LV pressure with a manometer-tipped catheter. The slopes of the end-systolic pressure-volume (Ees), stroke work-end-diastolic volume (Mw), and arterial end-systolic pressure-stroke volume relations (Ea), and of end-diastolic pressure-volume relations (EDPVRs), were obtained to evaluate changes in LV performance. The time constant of isovolumetric relaxation (T) was computed by a logarithmic and a derivative method. After intravenous administration of PAF (1 microgram/kg), LV end-diastolic volume and pressure, end-systolic pressure, maximum dP/dt and CO decreased. Ees and Mw decreased significantly, minimum dP/dt decreased, and T increased. The arterial end-systolic pressure-stroke volume relation shifted leftward with an increase in the slope (Ea), whereas EDPVRs were shifted to the left and superimposed on their potential passive diastolic properties. These findings indicate the PAF decreases CO by reducing preload and contractility and by increasing arterial load. However, despite a prolongation of relaxation, PAF may not affect passive diastolic chamber stiffness.

Animals↗
PubMed1997

Acute myocardial infarction due to vasospasm in a 13-year-old-boy.

We describe an unusual case of acute myocardial infarction due to vasospasm in a 13-year-old boy. He was admitted to our hospital with severe congestive heart failure and shock. He had experienced a feeling of chest oppression with dyspnea while running, which grew worse. He then lost consciousness and was brought by ambulance to our intensive care unit. He had had similar but milder episodes of chest oppression months earlier. The family history revealed that his father had died suddenly from hypertrophic cardiomyopathy and that his grandmother also had hypertrophic cardiomyopathy. On admission, the patient was bathed in a cold sweat, his pulse was weak, and his blood pressure was too low to measure. Coarse crackling and wheezing were audible in both lung fields. Administration of catecholamine and intra-aortic balloon pumping failed to stabilize the hemodynamic variables, but percutaneous cardiopulmonary support proved to be lifesaving. Coronary arteriography performed during his convalescence showed on evidence of atherosclerosis. The acetylcholine provocation test ultimately revealed a diagnosis of acute myocardial infarction due to vasospasm.

Acetylcholine↗
PubMed1997

Pheochromocytoma in a long-term hemodialysis patient, discovered as an adrenal incidentaloma.

A case of pheochromocytoma was discovered incidentally during long-term hemodialysis for chronic renal failure due to acquired cystic kidney disease. A 52-year-old male patient was examined for weight loss of 3 kg during over a period of 3 months. Abdominal computed tomography (CT) revealed a left adrenal mass (3.0 cm in size). Plasma adrenaline and noradrenaline were increased to 521 pg/ml and 1,341 pg/ml, respectively, and the metoclopramide provocative test was positive. Further, in the scintiscan using 123I-metaiodobenzylguanidine (MIBG), an accumulation of the radionuclide in the left adrenal tumor region was confirmed. The patient is currently under observation and conservative treatment due to the possible occurrence of arterial hypotension after resection of the tumor and to lesser possibility of the malignancy.

3-Iodobenzylguanidine↗
PubMed1996

Functional magnetic resonance imaging (fMRI) during mental writing with phonograms.

Functional magnetic resonance imaging (fMRI) at 1.5 T using a gradient echo echo-planar sequence was employed to identify brain regions activated during the performance of a mental writing task using phonograms. Four regions were activated in all six subjects; the region surrounding the left intraparietal sulcus, the region surrounding the middle part of the left precentral sulcus and the posterior part of the left superior frontal sulcus, the region surrounding the right intraparietal sulcus, and the region surrounding either or both of the left and right cingulate sulci. The left intraparietal region was usually the most extensively activated. The results suggest that these four regions particularly the left intraparietal region, are essential in writing with phonograms. Since the left hemisphere was more extensively activated than the right, fMRI during the mental writing task is a good candidate for determining non-invasively which hemisphere is dominant for language.

Adult↗
PubMed1996

Functional anatomy on perception of position and motion in depth.

To investigate the neural substrates for the perception of motion and of position in depth, we examined the changes in regional cerebral blood flow during positional and motion stereopsis in humans by positron emission tomography. During positional stereopsis, the right striate and peristriate cortices (areas V1/V2 and V3) and the inferior parietal lobule were significantly activated. During motion stereopsis, the right striate and peristriate cortices (V1/V2) and the ventrolateral occipital cortex (V5) were significantly activated. These results suggest that brain regions active during stereopsis may be dependent, despite their considerable overlap, on the properties of stereopsis, i.e. positional or motion stereopsis.

Adolescent↗
PubMed1996

Enhanced regional deformation at the anterior papillary muscle insertion site after chordal transsection.

BACKGROUND: Clinical and experimental studies of mitral valve replacement have shown a depression of ventricular function after chordal transsection; most recent studies have proposed that this is secondary to a depression of local function near the papillary muscle insertion site. However, there is no direct experimental evidence for changes in local fiber shortening in the wall of the left ventricle overlying the papillary muscle. Accordingly, we investigated the effect of chordal transsection on left ventricular shape and on three-dimensional regional deformation of the myocardium near the insertion of the anterior papillary muscle. METHODS AND RESULTS: In six open-chest dogs, two sets of three transmural columns of radiopaque markers were implanted in the anterior wall, one set at the tip of the papillary muscle (basal) and one at the site of papillary muscle fiber insertion (apical). A Björk-Shiley mitral valve was placed in the left atrium adjacent to the native valve. Markers were then tracked with biplane cineradiography, and deformation was quantified with the use of finite strain analysis. Chordal transection resulted in reduced left ventricular end-systolic pressure and slowed relaxation. After chordal transsection, outward displacement of the ventricular wall and transverse shearing deformation were observed in the area of the papillary muscle during isovolumic contraction. Circumferential and radial strains during ejection were maintained at our basal site and enhanced on our apical site. CONCLUSIONS: Chordal transsection led to enhanced local shortening and wall thickening and regional strain nonuniformity. These results indicate that chordal transsection induces an unloading of myocardium at the papillary muscle insertion site and that the resulting heterogeneity of regional function is the mechanism for the reduced global function and slowed ventricular relaxation.

Animals↗
PubMed1996

Use of a nondissection method in lower extremity revascularization: a report on our 12-year experience of autogenous vein bypass surgery.

We report herein on our 12-year experience of performing autogenous vein grafting in the lower extremity using a nondissection method. This method involves limiting preparation for the distal anastomosis to exposure of the anterior surface of the vascular sheath, and substituting an Esmarch's rubber bandage or a pneumatic tourniquet for vascular clamps. A series of 86 consecutive patients who received 101 autogenous vein grafts employing this method were retrospectively analyzed. The causes of arterial occlusion were atherosclerosis in 55 patients, Buerger's disease in 23, and other causes in 9. There was one operative death, and 12 late deaths were recorded within a follow-up period extending to 12 years. Of four early occlusions and two stenoses, three were successfully revised within 30 days of surgery. A total of 11 revision operations were required for 10 grafts during the follow-up period, and late graft closure occurred in 9 bypasses. The primary, primary revised, and secondary patency rates at 5 years for the entire series (n = 101) were 65%, 85%, and 86%, respectively, with 42 bypasses to the tibial or peroneal artery having 84% primary revised and 86% secondary patency rates. These findings led us to conclude that minimization of the surgical injury at the distal anastomosis contributed to the long-term patency of the distal bypass.

Adult↗
PubMed1996

Surgical treatment of abdominal aortic aneurysms in octogenarians.

Due to the increase in life span and the decrease in mortality associated with aortic surgery, many geriatric patients now undergo surgery for abdominal aortic aneurysms (AAAs). Therefore, we studied our surgical results for AAAs in an elderly population to assess the value of such operations. Twenty-six patients aged 80 years or older underwent surgery during an 11-year period from 1984 to 1994 at our institutions, and their outcomes were compared with those of 212 younger patients. The ratio of ruptured to non-ruptured AAAs was significantly higher in the older patients (aged 80 years or older) than in the younger patients (aged 79 years or younger), and aneurysm size in cases of non-rupture was greater in older patients than in younger patients. For octogenarians with non-ruptured AAAs, the survival rate was 85.7% at 5 years, compared with 43.6% at 3 years for those with ruptured AAAs, and these figures were not significantly different from those in younger patients. The present findings support the value of our active surgical approach for octogenarians with AAAs. We believe that an aggressive approach for octogenarians will decrease the incidence of ruptured AAAs and contribute to better patient survival.

Adult↗
PubMed1995

Epiregulin. A novel epidermal growth factor with mitogenic activity for rat primary hepatocytes.

Epiregulin, a novel epidermal growth factor (EGF)-related growth regulating peptide, was purified from conditioned medium of the mouse fibroblast-derived tumor cell line NIH3T3/clone T7. It was a 46-amino-acid single chain polypeptide, and its amino acid sequence exhibited 24-50% amino acid sequence identity with sequences of other EGF-related growth factors. Epiregulin exhibited bifunctional regulatory properties: it inhibited the growth of several epithelial tumor cells and stimulated the growth of fibroblasts and various other types of cells. Epiregulin bound to the EGF receptors of epidermoid carcinoma A431 cells much more weakly than did EGF, but was nevertheless much more potent than EGF as a mitogen for rat primary hepatocytes and Balb/c 3T3 A31 fibroblasts. These findings suggest that epiregulin plays important roles in regulating the growth of epithelial cells and fibroblasts by binding to receptors for EGF-related ligands.

3T3 Cells↗