• International Journal of Aeronautical and Space Sciences
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• v.15 no.4
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• pp.434-443
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• 2014

A turbo fan engine performance analysis and the optimization using particle swarm optimization(PSO) algorithm have been conducted to investigate the effects of major performance design parameters of an aircraft gas turbine engine. The FJ44-2C turbofan engine, which is widely used in the small business jet, CJ2 has been selected as the basic model. The design parameters consists of the bypass ratio, burner exit temperature, HP compressor ratio, fan inlet mass flow, and nozzle cooling air ratio. The sensitivity analysis of the parameters has been evaluated and the optimization of the parameters has been performed to achieve high net thrust or low specific fuel consumption.

• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.1201-1206
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• 2008

Psychrometric chart displays graphically the thermophysical properties of moist air, so it is very conveniently used in air-conditioning and refrigeration. On general psychrometric chart, there are dry bulb temperature, web bulb temperature, absolute humidity ratio, relative humidity, specific enthalpy, specific volume, sensible heat factor, and enthalpy-humidity difference ratio. However, various state and process values besides aboves can be plotted on psychrometric chart. In this study, we developed the software drawing twenty kinds of lines, that is vapor pressure, mole fraction ratio of vapor, dew point temperature, degree of saturation, density, specific entropy, specific exergy, contact or bypass factor, uncomfort index, discomposition index, predicted mean vote index, predicted percent dissatisfied, and so on. We wish to this software is a help to design, analysis and education.

• Journal of Preventive Medicine and Public Health
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• v.34 no.3
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• pp.244-252
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• 2001

Objective : Health insurers and policy makers are increasingly examining the hospital mortality rate as an indicator of hospital quality and performance. To be meaningful, a risk-adjustment of the death rates must be implemented. This study reviewed 5 severity measurement methods and applied them to the same data set to determine whether judgments regarding the severity-adjusted hospital mortality rates were sensitive to the specific severity measure. Methods : The medical records of 584 patients who underwent coronary artery bypass graft surgery in 6 general hospitals during 1996 and 1997 were reviewed by trained nurses. The MedisGroups, Disease Staging, Computerized Severity Index, APACHE III and KDRG were used to quantify severity of the patients. The predictive probability of death was calculated for each patient in the sample from a multivariate logistic regression model including the severity score, age and sex to evaluate the hospitals' performance, the ratio of the observed number of deaths to the expected number for each hospital was calculated. Results : The overall in-hospital mortality rate was 7.0%, ranging from 2.7% to 15.7% depending on the particular hospital. After the severity adjustment, the mortality rates for each hospital showed little difference according to the severity measure. The 5 severity measurement methods varied in their statistical performance. All had a higher c statistic and $R^2$ than the model containing only age and sex. There was a little difference in the relative hospital performance evaluation by the severity measure. Conclusion : These results suggest that judgments regarding a hospital's performance based on severity adjusted mortality can be sensitive to the severity measurement method. Although the 5 severity measures regarding hospital performance concurred, more often than would be expected by chance, the assessment of an individual hospital mortality rates varied by the different severity measurement method used.

• Quality Improvement in Health Care
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• v.7 no.2
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• pp.218-228
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• 2000

Background : Among 'structure', 'process' and 'outcome' approaches, outcome evaluation is considered as the most direct and best approach to assess the quality of health care providers. Risk-adjustment is an essential method to compare outcome across providers. This study has aims to judge performance of hospitals by severity adjusted mortality rates of coronary artery bypass graft (CABG) surgery. Methods : Medical records of 584 patients who got the CABG surgery in 6 general hospitals during 1996 and 1997 were reviewed by trained nurses. The MedisGroups was used to quantify severity of patients. The predictive probability of death was calculated for each patient in the sample from a multivariate logistic regression model including the severity score, age and sex. For evaluation of hospital performance, we calculated ratio of observed number to expected number of deaths and z score [(observed number of deaths - expected number of deaths)/square root of the variance in the number of deaths], and compared observed mortality rate with confidence interval of adjusted mortality rate for each hospital. Results : The overall in-hospital mortality was 7.0%, ranged from 2.7% to 15.7% by hospital. After severity adjustment the mortality by hospital was from 2.7% to 10.7%. One hospital with poor performance was distinctly divided from others with good performance. Conclusion : In conclusion, severity-adjusted mortality rate of CABG surgery might be applied as an indicator for hospital performance evaluation in Korea. But more pilot studies and improvement of methodologies has to be done to use it as quality indicator.

• Journal of Chest Surgery
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• v.49 no.3
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• pp.171-176
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• 2016

Background: A previous percutaneous coronary intervention (PCI) may affect the outcomes of patients who undergo coronary artery bypass grafting (CABG). The objective of this study was to compare the early in-hospital postoperative outcomes between patients who underwent CABG with or without previous PCI. Methods: The present study included 160 patients who underwent isolated elective on-pump CABG at the department of cardiothoracic surgery, Minia University Hospital from January 2010 to December 2014. Patients who previously underwent PCI (n=38) were compared to patients who did not (n=122). Preoperative, operative, and early in-hospital postoperative data were analyzed. The end points of the study were in-hospital mortality and postoperative major adverse events. Results: Non-significant differences were found between the study groups regarding preoperative demographic data, risk factors, left ventricular ejection fraction, New York Heart Association class, EuroSCORE, the presence of left main disease, reoperation for bleeding, postoperative acute myocardial infarction, a neurological deficit, need for renal dialysis, hospital stay, and in-hospital mortality. The average time from PCI to CABG was $13.9{\pm}5.4$ years. The previous PCI group exhibited a significantly larger proportion of patients who experienced in-hospital major adverse events (15.8% vs. 2.5%, p=0.002). On multivariate analysis, only previous PCI was found to be a significant predictor of major adverse events (odds ratio, 0.16; 95% confidence interval, 0.03 to 0.71; p=0.01). Conclusion: Previous PCI was found to have a significant effect on the incidence of early major adverse events after CABG. Further large-scale and long-term studies are recommended.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.7
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• pp.435-440
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• 2016

Effects of the increase rate of Reynold number on near-wall turbulent structures are investigated by performing direct numerical simulations of transient turbulent channel flows. The simulations were started with the fully-developed turbulent channel flow at $Re_{\tau}=180$, then temporal accelerations were applied. During the acceleration, the Reynolds number, based on the channel width and the bulk mean velocity, increased almost linearly from 5600 to 13600. To elucidate the effects of flow acceleration rates on near-wall turbulence, a wide range of durations for acceleration were selected. Various turbulent statistics and instantaneous flow fields revealed that the rapid increase of flow rate invoked bypass-transition like phenomena in the transient flow. By contrast, the flow evolved progressively and the bypass transition did not clearly occur during mild flow acceleration. The present study suggests that the transition to the new turbulent regime in transient channel flow is mainly affected by the flow acceleration rate, not by the ratio of the final and initial Reynolds numbers.

• Journal of Chest Surgery
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• v.52 no.1
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• pp.16-24
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• 2019

Background: Optimal graft selection for coronary artery bypass grafting (CABG) in patients with severe left ventricular (LV) dysfunction remains debatable. We report an analysis of our experiences of isolated CABG in patients with severe LV dysfunction and the impact of graft strategy on long-term outcomes. Methods: We analyzed 209 patients with severe LV dysfunction (ejection fraction [EF] <30%) who underwent primary isolated CABG. Of these, 169 were revascularized with a bilateral internal thoracic arterial (ITA) graft (BITA group) and 40 were revascularized with a single ITA graft (SITA group). The mean follow-up duration was $22{\pm}32$ months. Results: There were 18 early deaths (8.6%). Overall survival at 5 years was 66.7%. The rate of freedom from cardiac-related death at 5 years was 74.1%, and was significantly higher in patients who underwent off-pump CABG (p=0.005) and in the BITA group (p=0.023). Multivariate analysis demonstrated that old age (hazard ratio [HR], 2.548; 95% confidence interval [CI], 1.134-5.762; p=0.024), off-pump CABG (HR, 0.245; 95% CI, 0.090-0.661; p=0.006), and BITA grafts (HR, 0.333; 95% CI, 0.146-0.757; p=0.009) were correlated with cardiac mortality. Conclusion: CABG in patients with severe LV dysfunction (EF <30%) showed reasonable long-term outcomes. The rate of freedom from cardiac-related death was significantly higher in patients who underwent off-pump CABG and in the BITA group. Off-pump BITA grafting strategies can be accepted as a viable primary option in patients with severe LV dysfunction if performed by an experienced surgeon.

• Journal of Chest Surgery
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• v.54 no.2
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• pp.117-126
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• 2021

Background: Several factors, such as the degree of target vessel stenosis, are known to be associated with radial artery (RA) graft patency in coronary artery bypass grafting (CABG). There is a lack of data regarding the effect of the RA proximal configuration (aortic anastomosis versus T-anastomosis). This study evaluated the effects of the RA proximal configuration on the patency rate and clinical outcomes after CABG. Methods: We conducted a retrospective study, analyzing 328 patients who had undergone CABG with an RA graft. We divided the patients into 2 groups. The primary endpoint was RA patency and the secondary endpoints were overall mortality and major adverse cardiac and cerebrovascular events (MACCE). We performed a propensity score-matched comparison. Results: Aorta-RA anastomosis was performed in 275 patients, whereas the rest of the 53 patients received T-RA anastomosis. The mean age was 67.3±8.7 years in the T-RA anastomosis group and 63.8±9.5 years in the aorta-RA anastomosis group (p=0.02). The mean follow-up duration was 5.13±3.07 years. Target vessel stenosis ≥70% (hazard ratio [HR], 0.42; 95% confidence interval [CI], 0.20-0.91; p=0.03) and T-RA anastomosis configuration (HR, 2.34; 95% CI, 1.01-5.19; p=0.04) were significantly associated with RA occlusion in the multivariable analysis. However, T-RA anastomosis was not associated with higher risks of overall mortality and MACCE following CABG (p=0.30 and p=0.07 in the matched group, respectively). Conclusion: Aorta-RA anastomosis showed a superior patency rate compared to T-RA anastomosis. However, the RA proximal anastomosis configuration was not associated with mortality or MACCE.

• Journal of Chest Surgery
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• v.55 no.6
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• pp.442-451
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• 2022

Background: This meta-analysis was conducted to evaluate the effect of fractional flow reserve (FFR) on clinical outcomes after coronary artery bypass grafting (CABG). Methods: Five online databases were searched for studies that (1) enrolled patients who underwent isolated CABG or CABG with aortic valve replacement and (2) demonstrated the effect of an FFR-guided strategy on major adverse cardiac events (MACE) after surgery based on a randomized controlled trial or adjusted analysis. MACE included cardiac death, acute myocardial infarction (MI), and repeated revascularization. The primary outcomes were all MACE outcomes and a composite of all-cause death and MI, and the secondary outcomes were the individual MACE outcomes. Publication bias was assessed using a funnel plot and the Egger test. Results: Six articles (3 randomized and 3 non-randomized studies: n=1,027) were selected. MACE data were extracted from 4 studies. The pooled analyses showed that the risk of MACE was not significantly different between patients who underwent FFR-guided CABG and those who underwent angiography-guided CABG (hazard ratio [HR], 0.80; 95% CI, 0.57-1.12). However, the risk of the composite of death or MI was significantly lower in patients undergoing FFR-guided CABG (HR, 0.62; 95% CI, 0.41-0.94). The individual MACE outcomes were not significantly different between FFR-guided and angiography-guided CABG. Conclusion: FFR-guided CABG might be beneficial in terms of the composite outcome of death or MI compared with angiography-guided CABG although data are limited.

• Journal of Chest Surgery
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• v.30 no.11
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• pp.1083-1091
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• 1997

This study was purposed to assess the result of coronary artery bypass graft surgery by analyzing and comparing the pre and postoperative myocardial perfusion state quantitatively by using myocardial SPECT. Twenty patients who received coronary artery bypass graft surgery since 1993 underwent both preoperative and postoperative myocardial SPECT and the result were analyzed. The mean age was 56.4$\pm$9.0 years, and the patients were composed of thirteen males and seven females. For quantitative analysis, we used polar maps of SPECT generated by Cedars-Sin i Medical Center program and we calculated perfusion scores, ischemic myocardial area ratios and reperfusion scores from polar maps. Preoperative mean stressfrest perfusion score was 7.3$\pm$ 1.117.7$\pm$ 1.0 and postoperative score was 8.1 $\pm$ 1 118.3$\pm$ 1.1. Preoperative mean stress ischemic myocardial area ratio was 0.32$\pm$0.2 and postoperative ratio was 0.15 $\pm$0.1. Postoperative mean perfusion score was significantly increased but, on the other hand, mean ischemic myocardial area ratio was significantly decreased as compared with preoperative values(p<0.01). Preoperative mean perfusion score of patients with postoperative roper(usion score more than 1.5 was significantly higher(p<0.01) than that of patients with postoperative reperfusion score less than 1.5. Preoperative perfusion scores of coronary artery territories that had fixed perfusion defect at myocardial SPECT were significantly low(4.3 $\pm$0.514.6$\pm$0.6, stresslrest), nevertheless it proved quantitatively that there was improvement in myocardial perfusion after surgery by showing improved perfusion scores postoperatively. In conclusion, myocardial SPECT is useful method for quantitative analysis of the myocardial perfusion state after coronary artery bypass grafting surgery.