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Biomedical subjects

H Nakahara

Publications and source records attributed to H Nakahara.

At least 19 recordsLinked to original sources
PubMed2003

Autologous blood storage before hepatectomy for hepatocellular carcinoma with underlying liver disease.

BACKGROUND: Preoperative autologous blood donation has been suggested for patients with liver disease who are to undergo liver resection. The aim of this retrospective study was to clarify the risk factors for increased blood loss and the need for blood transfusion during hepatectomy for hepatocellular carcinoma (HCC). METHODS: From January 1996 to December 2000, 206 consecutive patients, 98.5 per cent of whom had underlying liver disease, underwent elective hepatectomy for HCC. RESULTS: Major hepatectomy was performed in 34 patients (16.5 per cent) and minor hepatectomy in 172 patients (83.5 per cent). The mean blood loss was 410 (median 260) ml. Eleven (5.3 per cent) of the 206 patients received blood transfusion during or after the operation. Operation time (P = 0.004) and central venous pressure (CVP) (P = 0.041) were independently correlated with blood loss of more than 1000 ml. Only preoperative haemoglobin level (P = 0.001) was independently correlated with the need for blood transfusion. CONCLUSION: In patients with underlying liver disease, maintaining CVP at a level below 5 cm H2O during parenchymal transection to reduce blood loss is more important than reserving autologous blood before the operation.

Adult↗
PubMed2003

Resection of hepatocellular carcinoma in a patient with congenital anomaly of the portal system.

Hepatic resection in a patient with an anomalous portal vein system is presented. A 53-year-old man was referred to our hospital for hepatic resection. Preoperative computed tomography (CT) and angiography demonstrated that the umbilical portion of the portal vein gave off major branches to the right anterior segment, and the hepatic tumor was located on the dorsal side of one of the right anterior portal branches near the umbilical portion. Partial hepatic resection was performed using the indocyanine green staining technique under operative echo guidance. Limited hepatic resection was indicated due to the patient's poor hepatic reserve function. His postoperative course was uneventful. This case emphasizes the importance of delineating the hepatic vascular anatomy before and during operation, especially in the case of an anomalous portal vein system.

Carcinoma, Hepatocellular↗
PubMed2003

[Traumatic aortic regurgitation with an ascending aortic aneurysm: report of a case].

We reported a case of an aortic regurgitation due to nonpenetrating chest trauma with an ascending aortic aneurysm. A 58-year-old man was admitted to our hospital with an acute left cardiac failure. Severe aortic regurgitation and ascending aortic aneurysm were diagnosed on ultrasonic echocardiography (UCG) and computed tomography (CT) scan. On the 13th day after the injury, semi-emergency operation was done. The commissure between the right coronary and non-coronary cups was torn, and modified Bentall operation was performed. The patient recovered well and discharged uneventfully.

Aortic Aneurysm↗
PubMed2002

Attention modulation of neural tuning through peak and base rate in correlated firing.

The present study investigates the influence of attention modulation on neural tuning functions under a Gaussian correlation structure. Recent experiments have shown that attention modulates the tuning curve via its height and base rate. Inspired by this experimental finding, we previously showed the effective size of attention modulation (i.e. the critical length) on the neural population that enhances encoding accuracy. The previous result, however, was obtained under the assumption of uncorrelated firing, i.e. stimulus-conditional independence of neural responses. A question still remains whether the above findings can be applied to correlated firing. It is important to investigate this issue partly because neural firings are usually correlated but even more so because common attentional inputs may cause correlated firings. The present study first provides the general framework of attention modulation in relation to an attended stimulus and an actual stimulus and then shows the existence of a critical length under a Gaussian correlation structure. In order to improve encoding accuracy, measured by the Fisher information, the height and the base rate should be increased when the attended stimulus is in the critical length from the peak of the tuning curve and decreased otherwise. Furthermore, we confirm that a similar nature of the critical length also holds even when the neural decoder uses an uncorrelated unfaithful model. Thus, the existence of the critical length seems to be a ubiquitous phenomenon in attention modulation, and so its implications are discussed.

Attention↗
PubMed2002

[A case of mitral regurgitation with a giant thrombus thought to be caused by anti-phospholipid syndrome].

A 58-year-old woman suffered from mitral valve regurgitation with a giant thrombus in right atrium was thought to be complicated by anti-phospholipid syndrome (APS). Positive anti-loops anti-coagulant and histories of cerebral infarction and miscarriage strongly indicated the diagnosis of APS. She underwent mitral valve replacement using bileaflet mechanical prosthetic value and removal of thrombus. She recovered uneventfully and strict anti-coagulation therapy has been continuing.

Antiphospholipid Syndrome↗
PubMed2002

[Angina pectoris with a left atrial myxoma; report of a case].

A 78-year-old woman who had been diagnosed as left atrial myxoma and angina pectoris underwent simultaneous coronary artery bypass grafting (CABG) and resection of the left atrial myxoma. CABG was preceded by resection of myxoma to avoid systemic embolism of fragment of myxoma. Myocardial protection was secured by combination of antegrade and retrograde infusion of cardioplegia. The patient recovered well and discharged uneventfully.

Aged↗
PubMed2001

Parallel cortico-basal ganglia mechanisms for acquisition and execution of visuomotor sequences - a computational approach.

Experimental studies have suggested that many brain areas, including the basal ganglia (BG), contribute to procedural learning. Focusing on the basal ganglia-thalamocortical (BG-TC) system, we propose a computational model to explain how different brain areas work together in procedural learning. The BG-TC system is composed of multiple separate loop circuits. According to our model, two separate BG-TC loops learn a visuomotor sequence concurrently but using different coordinates, one visual, and the other motor. The visual loop includes the dorsolateral prefrontal (DLPF) cortex and the anterior part of the BG, while the motor loop includes the supplementary motor area (SMA) and the posterior BG. The concurrent learning in these loops is based on reinforcement signals carried by dopaminergic (DA) neurons that project divergently to the anterior ("visual") and posterior ("motor") parts of the striatum. It is expected, however, that the visual loop learns a sequence faster than the motor loop due to their different coordinates. The difference in learning speed may lead to inconsistent outputs from the visual and motor loops, and this problem is solved by a mechanism called a "coordinator," which adjusts the contribution of the visual and motor loops to a final motor output. The coordinator is assumed to be in the presupplementary motor area (pre-SMA). We hypothesize that the visual and motor loops, with the help of the coordinator, achieve both the quick acquisition of novel sequences and the robust execution of well-learned sequences. A computational model based on the hypothesis is examined in a series of computer simulations, referring to the results of the 2 x 5 task experiments that have been used on both monkeys and humans. We found that the dual mechanism with the coordinator was superior to the single (visual or motor) mechanism. The model replicated the following essential features of the experimental results: (1) the time course of learning, (2) the effect of opposite hand use, (3) the effect of sequence reversal, and (4) the effects of localized brain inactivations. Our model may account for a common feature of procedural learning: A spatial sequence of discrete actions (subserved by the visual loop) is gradually replaced by a robust motor skill (subserved by the motor loop).

Basal Ganglia↗
PubMed2001

Movement-related magnetic fields to tongue protrusion.

Movement-related magnetic fields (MRFs) associated with tongue protrusion were measured in five normal subjects using a helmet-shaped magnetoencephalography system. Bihemispherical two-dipolar patterns appeared from approximately -2000 or -1000 to 0 ms to the trigger signal indicating when protrusion of the tongue tip reached the frontal part of the palate. Equivalent current dipoles (ECDs) for the MRFs were localized on the central sulcus, 14.4 +/- 6.1 mm inferior (P < 0.0001) and 7.6 +/- 6.9 mm anterior (P < 0.01) to the ECD for the N20m in the somatosensory evoked fields for median nerve stimuli. The ECD orientations of MRFs were anterior and perpendicular to the central sulcus. These results correspond to the movement-related potentials for tongue protrusion previously recorded from subdural electrodes in patients with epilepsy. Magnetoencephalography can be applied to analyze cortical functions related to tongue movement with high resolution in time and space in normal subjects.

Adult↗
PubMed2001

Three-dimensional MR imaging of mammographically detected suspicious microcalcifications.

BACKGROUND: The purpose of this study was to evaluate the diagnostic value and clinical significance of three-dimensional MR imaging of the breast in patients with mammographically detected suspicious microcalcifications. METHODS: Forty patients with suspicious microcalcifications on mammography were evaluated with three-dimensional MR imaging. MR findings were grouped mainly by distribution of abnormal enhancement (linear, focal-clumped, segmental-clumped, segmental-stippled and diffuse-stippled). These findings were compared with the mammography findings according to the criteria of the Breast Imaging Reporting and Data System (BI-RADS) and histopathologic data. RESULTS: Twenty patients had proven malignancies, most frequently ductal carcinoma in situ. For all the cases, linear (100%) and segmental-clumped type (100%) enhancement on MR imaging showed a significantly higher risk for malignancy. Diffuse stippled type (7%) and no enhancement (0%) on MR imaging indicated the lowest possibility of malignancy. 3D-MR imaging showed a sensitivity of 90%, a specificity of 95% and an overall accuracy of 93% in this study. CONCLUSIONS: Three-dimensional MR imaging of the breast can more accurately diagnose ductal carcinoma in situ. Combined with mammography, this procedure is useful for reducing the number of false-positive biopsies and helpful for deciding the better management of patients with mammographically detected suspicious microcalcifications.

Adult↗
PubMed2001

Ethenesulfonamide and ethanesulfonamide derivatives, a novel class of orally active endothelin-A receptor antagonists.

In the previous paper, we described a series of 2-phenylethenesulfonamide derivatives, a novel class of ET(A)-selective endothelin (ET) receptor antagonists, including the 2-methoxyethoxy derivative 2a and the 2-fluoroethoxy derivative (2b). In this paper, we wish to report further details of structure-activity relationships (SARs) of the two regions of the molecule in compound 2b, which were the alkoxy region at the 6-position of the core pyrimidine ring and the 2-phenylethenesulfonamide region. In these modifications, replacement of the 2-fluoroethoxy group with a methoxy group (6e) and replacement of the 2-phenylethenesulfonamide group with a 2-(pyridin-3-yl)ethenesulfonamide group (6l) or 2-phenylethanesulfonamide group (6q) were well tolerated both in the ET(A) binding affinity and ET(A) selectivity. Among them, compound 6e showed further improvement in oral activity compared to 2b. After oral administration, compound 6e inhibited the big ET-1 induced pressor response in conscious rats at 0.3mg /kg with a duration of >6.5h. Compound 6e also exhibited a potent antagonistic activity in the pithed rats.

Administration, Oral↗
PubMed2001

Hearing changes and questionnaire responses in patients with paramedian suboccipital vestibular neurectomy.

In order to determine the effectiveness of paramedian suboccipital transmeatal vestibular neurectomy, pre- and postoperative neurotological studies were conducted and questionnaire responses of 30 patients who underwent surgery were evaluated. Hearing was maintained within 10 dB of the preoperative level or improved in 54% of patients 2 years after surgery. Questionnaire responses indicated that all patients suffering from intractable vertigo experienced no vertiginous symptoms after surgery. Based on this study, we conclude that paramedian suboccipital transmeatal vestibular neurectomy is a useful method for relieving ear-related vertigo.

Adult↗
PubMed2001

Population coding with correlation and an unfaithful model.

This study investigates a population decoding paradigm in which the maximum likelihood inference is based on an unfaithful decoding model (UMLI). This is usually the case for neural population decoding because the encoding process of the brain is not exactly known or because a simplified decoding model is preferred for saving computational cost. We consider an unfaithful decoding model that neglects the pair-wise correlation between neuronal activities and prove that UMLI is asymptotically efficient when the neuronal correlation is uniform or of limited range. The performance of UMLI is compared with that of the maximum likelihood inference based on the faithful model and that of the center-of-mass decoding method. It turns out that UMLI has advantages of decreasing the computational complexity remarkably and maintaining high-level decoding accuracy. Moreover, it can be implemented by a biologically feasible recurrent network (Pouget, Zhang, Deneve, & Latham, 1998). The effect of correlation on the decoding accuracy is also discussed.

Algorithms↗
PubMed2001

Attention modulation of neural tuning through peak and base rate.

This study investigates the influence of attention modulation on neural tuning functions. It has been shown in experiments that attention modulation alters neural tuning curves. Attention has been considered at least to serve to resolve limiting capacities and to increase the sensitivity to attended stimulus, while the exact functions of attention are still under debate. Inspired by recent experimental results on attention modulation, we investigate the influence of changes in the height and base rate of the tuning curve on the encoding accuracy, using the Fisher information. Under an assumption of stimulus-conditional independence of neural responses, we derive explicit conditions that determine when the height and base rate should be increased or decreased to improve encoding accuracy. Notably, a decrease in the tuning height and base rate can improve the encoding accuracy in some cases. Our theoretical results can predict the effective size of attention modulation on the neural population with respect to encoding accuracy. We discuss how our method can be used quantitatively to evaluate different aspects of attention function.

Animals↗
PubMed2001

High-resolution electron microscopy of the crystallites of fossil enamels obtained from various geological ages.

To elucidate the stability of the central dark line (CDL) in biologically induced hydroxyapatite crystals, we examined the diagenetic changes on the microstructures of the crystallites during the course of fossilization. Using transmission electron microscopy, we investigated the enamel crystallites of fossil animals of various geological ages ranging from Pleistocene to Cretaceous. Electron micrographs indicated that the microstructures and lattice images of each crystallite in fossil enamels were well-preserved regardless of the thickness of the enamel layer, and the presence of CDLs in fossil enamel crystals was also confirmed. The results indicated that the microstructure of hydroxyapatite crystals containing lattice images of CDLs appear stable during long geological periods. In addition, we conclude that the existence of lattice images in apatite with CDLs may be an indicator for the assessment of the evolution of dental enamel from fossil remains.

Animals↗
PubMed2001

[Two cases of left main trunk lesion treated with coronary artery bypass grafting the proximal circumflex coronary artery (# 11)].

Two cases are reported of coronary artery bypass graft (CABG) surgery to the proximal left circumflex artery (LCX) system and left anterior descending artery (LAD) system. Both patients suffered from unstable angina due to left main trunk (LMT) lesions and required semi-emergent coronary revascularization. In both cases, the obtuse marginal branch and postero-lateral branch were too small to be grafted, although there are the usual target branches in the LCX system. CABG to the proximal portion (# 11) of LCX in the atrioventricular groove using saphenous vein grafts was performed and good blood flow rates were seen intra-operatively. Both patients recovered uneventfully and had no recurrence of anginal attacks. Postoperative coronary angiography confirmed good graft patency and an adequate coronary blood supply. CABG to LCX (# 11) is feasible without special techniques or tools. This method seems to be useful in patients with LMT lesions or with proximal lesions of LCX in which the branches are too small to be grafted.

Aged↗
PubMed2000

Vascular permeability in allergic conjunctivitis in mice lacking histamine H1 receptors.

To clarify the role of histamine H1 receptors in allergic conjunctivitis, changes in vascular permeability of the conjunctiva were measured in histamine H1 receptor deficient mice. Wild-type mice showed a significant increase in vascular permeability of the conjunctiva induced by histamine. However, no such increase was found in histamine H1 receptor deficient mice. On the other hand, no differences were observed between wild-type and histamine H1 receptor deficient mice in response to serotonin. A significant increase in vascular permeability was observed in actively sensitized wild-type mice, whereas no increase was observed in histamine H1 receptor deficient mice. Similar findings were noted in passively sensitized animals. Histamine contents of the conjunctiva were significantly decreased by topical application of antigen in both wild-type and histamine H1 receptor deficient mice after active sensitization with antigen. These findings suggested that vascular permeability in the conjunctiva in allergic conjunctivitis is entirely regulated through histamine H1 receptor.

Animals↗
PubMed2000

Demonstration of the central dark line in crystals of dental calculus.

Using an electron microscope and Fourier transform infrared (FTIR) microspectroscopy, we studied the lattice images of crystallites of dental calculus to demonstrate the presence of the central dark line (CDL) in its crystallite and to compare this CDL with that of bone and synthetic hydroxyapatite crystals. Ultrastructural observations revealed clearly a number of crystallites, which displayed a proper lattice image and CDL similar to that of bone, in the dental calculus. FTIR microspectroscopy revealed that the dental calculus displayed a set of major spectra analogous to that of bone. These results suggest that the formation process of hydroxyapatite crystals with CDL in dental calculus, which is considered to be an unusual type of calcified structure in association with microorganisms, is basically similar to that of the ordinary calcifying hard tissues (bone, enamel, etc.).

Animals↗