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최의근(E. K. Choi),이상욱(S. W. Lee) 한국소성가공학회 2009 한국소성가공학회 학술대회 논문집 Vol.2009 No.5
In this study, the repetitive loading-unloading tensile tests with AZ31B magnesium sheet metal have been conducted under various elevated temperatures to check out how the Young’s moduli of the sheets evolve during the plastic deformation. The loading-unloading tests have been carried out at every 1% of strain increment. With the tested results, some damage parameters of magnesium sheets based on the Lemaitre’s continuum damage theory could be calculated at room temperature, 100℃, 150℃, and 250℃. It has been shown that the critical damage parameters obtained in all temperature conditions are within the range of 0.12 to 0.18.
이사민,최의근,장혁재,김지훈,서원우,박진주,최상일,전은주,장성아,김형관,김용진,구본권,최동주,오병희 대한심장학회 2010 Korean Circulation Journal Vol.40 No.9
Background and Objectives: Primary prevention of coronary artery disease (CAD) has become a public health issue, according to increasing awareness of the substantial risks posed by asymptomatic atherosclerosis. The aims of this study were to determine the prevalence and characteristics of subclinical CAD using coronary computed tomography angiography (CCTA), and to evaluate the role of this advanced technology in identifying subclinical CAD in asymptomatic Korean individuals,compared with conventional risk stratification. Subjects and Methods: We enrolled 4,320 consecutive asymptomatic individuals (61% males, aged 50±9 years), who underwent 64-slice CCTA during a routine health check. Results: Coronary artery plaques were present in 1,053 (24%) individuals. Significant stenosis (diameter stenosis ≥50%) was identified in 139(3%) subjects, and most of the significant lesions (87%) were located in the left anterior descending artery. CCTA revealed noncalcified plaques in 5% of subjects with a coronary calcium score of zero (n=801). Although 25% (n=10) of those with noncalcified plaque had significant stenosis, most of them (90%) were classified into low- or moderate-risk groups according to National Cholesterol Education Program risk stratification guidelines. In a young population (age ≤55 years for males, ≤65 years for females), 30% of subjects with significant stenosis were classified into a low-risk group and 60% had low (0 to 100) calcium scores. Conclusion: Subclinical CAD in asymptomatic individuals cannot be ignored for its considerable prevalence, CCTA may be helpful in identifying at-risk subclinical CAD in a noninvasive manner, especially in the young and traditionally lowrisk population.
Short-Term Autonomic Denervation of the Atria Using Botulinum Toxin
오세일,최의근,최윤식 대한심장학회 2010 Korean Circulation Journal Vol.40 No.8
Background and Objectives: Major epicardial fat pads contain cardiac ganglionated plexi (GP) of the autonomic nervous system. Autonomic denervation may improve the success rate of atrial fibrillation (AF) ablation. This study was designed to elucidate the acute effects of blocking the right atrium-pulmonary vein (RA-PV) and left atrium-inferior vena cava (LA-IVC)fat pads on the electrophysiologic characteristics of the atrium and AF inducibility with a botulinum toxin injection. Materials and Methods: Eight mongrel dogs were studied. The RA-PV and LA-IVC fat pads were exposed through a median thoracotomy. Botulinum toxin (BT, 50 U to each fat pad, n=6) or normal saline (NS, n=2) was injected in the entire area of two fat pads. The study protocol was applied before injection and repeated at 1, 2, 3, 4, and 5 hours thereafter. The sinus rate, ventricular rate during rapid atrial pacing with a cycle length of 50 ms, and AF inducibility were measured with and without vagal stimulation (VS). Bilateral cervical VS was applied (20 Hz, 0.2 ms, 5.6±2.0 V). AF inducibility was evaluated with burst pacing with 200 impulses at a 50-ms cycle length. Results: VS effects on the sinus node and AF inducibility were eliminated a few hours after injection of BT; these changes were not observed after injection of NS. Conclusion: Short-term autonomic denervation of the atria was achieved by blocking the major epicardial GP with BT.