8 results on '"Keisuke Muto"'
Search Results
2. Mechanisms of cage noise generation in machine tool bearings
- Author
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Kazuho Takeshima, Keisuke Mutoh, Kenji Imanishi, and Shunichi Oshima
- Subjects
cage instability ,cage noise ,visualization ,high-speed camera system ,dynamic analysis ,ball bearing ,Mechanical engineering and machinery ,TJ1-1570 - Abstract
Cage instability in ball bearings can lead to torque fluctuations and significant noise. In machine tool spindles, which require high rotational precision, outer ring-guided cages are often preferred over common ball-guided cages. While outer ring-guided cages suppress instability modes caused by sliding friction between the cage and balls, increased interaction between the cage and outer ring can introduce other instability modes, leading to noise. Despite the critical implications of these findings, prior research into this specific type of cage instability, incorporating both experimental and analytical perspectives, remains limited. Therefore, in this study, we utilized a high-speed camera system to conduct visualization tests on cage behavior in grease-lubricated angular contact ball bearings used in machine tools. Through detailed image-processing of the results, we identified specific behaviors associated with cage noise. To facilitate the optimal design of the cage to stabilize these behaviors, we developed a dynamic analysis model focusing on the friction between the cage and the outer ring under grease lubrication, considering fluid pressure effects. The validity of this model was confirmed through experiments at various rotational speeds. This analytical model enabled us to elucidate the underlying mechanisms driving cage instability. The insights gained from this research are expected to significantly enhance the fundamental understanding of cage design principles aimed at eliminating cage noise.
- Published
- 2025
- Full Text
- View/download PDF
3. Verification of Echocardiographic Assessment of Left Ventricular Diastolic Dysfunction in Patients With Preserved Left Ventricular Ejection Fraction Using the American Society of Echocardiography and European Association of Cardiovascular Imaging 2016 Recommendations
- Author
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Shohei Kikuchi, Nobuyuki Ohte, Hidekatsu Fukuta, Toshihiko Goto, Junki Yamamoto, Kazuaki Wakami, Keisuke Muto, and Yoshihiro Seo
- Subjects
medicine.medical_specialty ,Ejection fraction ,Diastolic function ,business.industry ,Diastole ,Original article ,General Medicine ,Guideline ,Left ventricle ,medicine.disease ,Predictive value ,Imaging ,Heart failure ,Internal medicine ,medicine ,Cardiology ,Left ventricular diastolic dysfunction ,Clinical significance ,In patient ,Non-invasive ,business ,Normal range - Abstract
Background: Non-invasive evaluation of left ventricular (LV) diastolic dysfunction (DD) and elevated LV filling pressure are crucial for diagnosing heart failure. The 2016 American Society of Echocardiography/European Association of Cardiovascular Imaging (ASE/EACVI) recommendations for evaluating elevated LV filling pressure (algorithm B) have acceptable diagnostic accuracy, including in patients with reduced LV ejection fraction (EF). No prior study, however, has assessed the diagnostic accuracy of algorithm A of the ASE/EACVI recommendations for evaluating LVDD in patients with normal LVEF. Methods and Results: We evaluated the clinical relevance of algorithm A in 94 patients who underwent invasive LV pressure measurement. Algorithm A identified invasively defined LVDD (time constant τ≥48 ms and/or LV end-diastolic pressure ≥16 mmHg) with low sensitivity (22.4%) but high specificity (90.7%). Algorithm A also identified elevated LV filling pressure with low sensitivity (41.7%) but high specificity (87.5%), and with a high negative predictive value (90.9%). Conclusions: Algorithm A may not be useful for screening LVDD in patients with normal LVEF. Negative findings using algorithm A, however, may identify a patient with normal LVDD with high specificity, and most of such patients will have LV pre-A pressure in the normal range.
- Published
- 2019
4. A successful case of percutaneous fistula closure in a patient with high output heart failure and extracardiac arteriovenous fistula
- Author
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Shuichi Kitada, Hisao Suda, Junki Yamamoto, Takafumi Nakayama, Nobuyuki Ohte, Yukiko Kato, Keisuke Muto, Shinji Kamiya, Kazushi Suzuki, and Masashi Shimohira
- Subjects
Cardiac output ,medicine.medical_specialty ,business.industry ,Fistula ,Arteriovenous fistula ,Dilated cardiomyopathy ,030204 cardiovascular system & hematology ,medicine.disease ,Article ,Shunt (medical) ,03 medical and health sciences ,0302 clinical medicine ,Heart failure ,Internal medicine ,cardiovascular system ,medicine ,Cardiology ,030212 general & internal medicine ,Cardiology and Cardiovascular Medicine ,business ,Venous return curve ,High-output heart failure - Abstract
Intra-cardiac shunt diseases may cause chronic ventricular volume overload, but extra-cardiac fistula could also cause high-output heart failure (HF). A patient presented with high-output HF and significant extra-cardiac shunt flow. Although the size and shape of the patient’s left ventricle suggested dilated cardiomyopathy, considerable origins were not identified except for a high-flow fistula between the right subclavian artery and right internal jugular vein. Right heart catheter examination revealed inappropriately high cardiac output. Left-to-right shunt ratio was calculated at 40.3% from an oximetry run, under the assumption that the left anonymous vein which was not contaminated with any shunt flow could be substituted for venous return from the upper body. We could determine the indication of fistula closure according to the estimated high left-to-right shunt ratio, reducing cardiac output by 42.7% which was similar to the pre-estimated left-to-right shunt ratio. Two months later, the patient’s serum B-type natriuretic peptide level and left ventricular end-diastolic and end-systolic diameters were decreased. The proposed method to estimate the left-to-right shunt ratio was useful in determining the indication for fistula closure in a patient with HF and a significant shunt fistula. Learning objective: A significant extracardiac left-to-right shunt more than 30–35% could cause heart failure with left ventricular dilatation similar to dilated cardiomyopathy. One can decide fistula closure with the finding of left-to-right shunt ratio calculated using a transcatheter oximetry run. It is mandatory that the venous oxygen saturation at the upper stream of fistula is determined precisely without the contamination of arterial blood. In this case, the oxygen saturation at the left anonymous vein substituted for it.>
- Published
- 2019
- Full Text
- View/download PDF
5. Correlation Between Longitudinal Strain in the Apical Segments of the Left Ventricle at End-Systole Obtained by 2-Dimensional Speckle-Tracking Echocardiography and Left Ventricular Relaxation
- Author
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Kazuaki Wakami, Yoshihiro Seo, Junki Yamamoto, Shohei Kikuchi, Keisuke Muto, Nobuyuki Ohte, Tomoyuki Banno, Toshihiko Goto, and Hidekatsu Fukuta
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medicine.medical_specialty ,Systole ,medicine.medical_treatment ,Heart Ventricles ,Speckle tracking echocardiography ,030204 cardiovascular system & hematology ,Ventricular Function, Left ,030218 nuclear medicine & medical imaging ,Elastic recoil ,Coronary artery disease ,03 medical and health sciences ,0302 clinical medicine ,Internal medicine ,Medicine ,Humans ,Isovolumetric contraction ,Cardiac catheterization ,Ejection fraction ,Receiver operating characteristic ,business.industry ,Stroke Volume ,General Medicine ,medicine.disease ,medicine.anatomical_structure ,Ventricle ,Echocardiography ,Cardiology ,Cardiology and Cardiovascular Medicine ,business - Abstract
BACKGROUND It is well acknowledged that left ventricular (LV) contractile performance affects LV relaxation via LV elastic recoil. Accordingly, we aimed to investigate whether global longitudinal strain (GLS), particularly longitudinal strain at LV apical segments at end-systole (ALS), obtained by 2-dimensional speckle-tracking echocardiography could be used to assess LV relaxation.Methods and Results:We enrolled 121 patients with suspected or definite coronary artery disease in whom echocardiography and diagnostic cardiac catheterization were performed on the same day. We obtained conventional echo-Doppler parameters and GLS, as well as ALS prior to catheterization. LV functional parameters were obtained from the LV pressure recorded using a catheter-tipped micromanometer. In all patients, GLS and ALS were significantly correlated with the time constant τ of LV pressure decay during isovolumetric relaxation (r=0.63 [P
- Published
- 2021
6. 2次元スペックルトラッキング心エコー図法による収縮末期の左室心尖部長軸方向のストレイン値と左室弛緩の関係性<要約>
- Author
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Keisuke, Muto
- Abstract
令和2年度
- Published
- 2021
7. Compensatory Increase in Heart Rate Is Responsible for Exercise Tolerance among Male Patients with Permanent Atrial Fibrillation
- Author
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Shohei Kikuchi, Nobuyuki Ohte, Toshihiko Goto, Keisuke Muto, Kento Mori, Kazuaki Wakami, Junki Yamamoto, and Hidekatsu Fukuta
- Subjects
Male ,medicine.medical_specialty ,Cardiac output ,030204 cardiovascular system & hematology ,Asymptomatic ,General Biochemistry, Genetics and Molecular Biology ,03 medical and health sciences ,0302 clinical medicine ,Oxygen Consumption ,Heart Rate ,Internal medicine ,Heart rate ,Atrial Fibrillation ,medicine ,Humans ,Sinus rhythm ,030212 general & internal medicine ,Peak exercise ,Aged ,Ejection fraction ,Exercise Tolerance ,business.industry ,Atrial fibrillation ,General Medicine ,medicine.disease ,Male patient ,Echocardiography ,Multivariate Analysis ,Cardiology ,Exercise Test ,Regression Analysis ,medicine.symptom ,business - Abstract
Atrial fibrillation (AF) is an exacerbating factor for exercise tolerance due to the loss of atrial kick. However, many patients with permanent AF, which lasts for at least a year without interruption, and preserved left ventricular ejection fraction (LVEF ≥ 50%) are asymptomatic and have good exercise tolerance. In such cases, the possible mechanism that compensates for the decrease in cardiac output accompanying the loss of atrial kick is a sufficient increase in heart rate (HR) during exercise. We investigated the relationship between exercise tolerance and peak HR during exercise using cardiopulmonary exercise testing in 242 male patients with preserved LVEF, 214 with sinus rhythm (SR) and 28 with permanent AF. Peak HR was significantly higher in the AF group than the SR group (148.9 ± 41.9 vs. 132.0 ± 22.0 beats/min, p = 0.001). However, oxygen uptake at peak exercise did not differ between the AF and SR groups (19.4 ± 5.7 vs. 21.6 ± 6.0 mL/kg/min, p = 0.17). In multiple regression analysis, peak HR (β, 0.091; p < 0.001) and the interaction term constructed by peak HR and presence of permanent AF (β, 0.05; p = 0.04) were selected as determinants for peak VO2; however, presence of permanent AF was not selected (β, -0.38; p = 0.31). Therefore, the impact of peak HR on exercise tolerance differed between the AF and SR groups, suggesting that a sufficient increase in HR during exercise is an important factor to preserve exercise tolerance among patients with AF.
- Published
- 2018
8. Compensatory Increase in Heart Rate Is Responsible for Exercise Tolerance among Male Patients with Permanent Atrial Fibrillation.
- Author
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Kento Mori, Toshihiko Goto, Junki Yamamoto, Keisuke Muto, Shohei Kikuchi, Kazuaki Wakami, Hidekatsu Fukuta, and Nobuyuki Ohte
- Abstract
Atrial fibrillation (AF) is an exacerbating factor for exercise tolerance due to the loss of atrial kick. However, many patients with permanent AF, which lasts for at least a year without interruption, and preserved left ventricular ejection fraction (LVEF ≥ 50%) are asymptomatic and have good exercise tolerance. In such cases, the possible mechanism that compensates for the decrease in cardiac output accompanying the loss of atrial kick is a sufficient increase in heart rate (HR) during exercise. We investigated the relationship between exercise tolerance and peak HR during exercise using cardiopulmonary exercise testing in 242 male patients with preserved LVEF, 214 with sinus rhythm (SR) and 28 with permanent AF. Peak HR was significantly higher in the AF group than the SR group (148.9 ± 41.9 vs. 132.0 ± 22.0 beats/min, p = 0.001). However, oxygen uptake at peak exercise did not differ between the AF and SR groups (19.4 ± 5.7 vs. 21.6 ± 6.0 mL/kg/min, p = 0.17). In multiple regression analysis, peak HR (β , 0.091; p < 0.001) and the interaction term constructed by peak HR and presence of permanent AF (β , 0.05; p = 0.04) were selected as determinants for peak VO
2 ; however, presence of permanent AF was not selected (β , -0.38; p = 0.31). Therefore, the impact of peak HR on exercise tolerance differed between the AF and SR groups, suggesting that a sufficient increase in HR during exercise is an important factor to preserve exercise tolerance among patients with AF. [ABSTRACT FROM AUTHOR]- Published
- 2018
- Full Text
- View/download PDF
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