• Proceedings of the Korean Society for Emotion and Sensibility Conference
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• 2002.05a
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• pp.90-94
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• 2002

이전연구에서 가상현실에 몰입하는 동안 넓은 시야 (Field of view: 150$^{\circ}$)와 빠른 운행속도 (70 km/sec)가 사이버멀미를 심화시킨다는 결과를 얻었다: 피험자의 90%가 좁은 시야 (50$^{\circ}$)와 느린 운행속도 (30 km/sec)에서 사이버멀미 증상이 적었다. 본 실험에서는 피험자가 생리적인 동요를 경험할 때마다 바이오피드백 방법을 사용해서 사이버멀미 감소 가상환경 (cybersickness alleviating virtual environment, CAVE)을 제시한 후, 그 효과를 관찰하였다. 피부전도도, 말초체온, 말초혈류량, 심박률, 눈 깜박임, 뇌전위의 변수들을 입력으로 하는 인공신경망으로 구성된 실시간 멀미 탐지 시스템과 CAVE-제시 피드백 시스템을 구축하였다. 이 시스템은 생리적 측정치들이 사이버멀미의 출현을 신호할 때마다 피드백 출력으로 좁은 화면과 감소된 운행속도를 일시적으로 제공했다. 36명의 피험자를 대상으로 SSQ (simulator sickness questionnaires)와 자기보고를 이용하여 사이버멀미의 빈도와 심각도를 조사하였다. 모든 피험자는 한달 간격으로 CAVE 조건과 non-CAVE 조건에서 두 번 가상현실을 경험하였다. 사이버멀미의 빈도와 심각도는 non-CAVE 조건보다 CAVE 조건에서 유의미하게 감소하였다. 즉, 전기생리학적 특징들에 기반한 인공신경망에 의해 제공된 좁은 시야와 느린 운행의 가상환경은 사이버멀미 증상들을 의미있게 감소시켰다. 이러한 결과들은 생체신호 피드백 시스템을 이용하여 인간 친화적 가상환경을 구축할 수 있는 가능성을 보인 것이다.

• IE interfaces
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• v.18 no.2
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• pp.178-183
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• 2005

In this study, changes in memory performance, blood oxygen saturation and heart rate according to 30% concentration oxygen supply were observed. Ten healthy male and female college students (male:$25.8{\pm}0.8$ years, female: $24.2{\pm}1.9$ years) participated in the study. The experiment was performed as Rest (1min.), Control task (1min.), Word presentation (1min.), Reaction time task (1min.), Distractor (2min.), and Word recall (1min.) and the physiological signals such as blood oxygen saturation and heart rate were measured throughout the stages. Subjects who received 30% oxygen recalled more words than those who received 21% oxygen, which shows 30% oxygen supply has influenced positively on memory cognitive performance. When 30% concentration oxygen is supplied, the blood oxygen saturation in the task phases was increased and the heart rate decreased when comparing to 21%. It means that 30% oxygen can stimulate brain activation by increasing actual blood oxygen concentration in the process of cognitive performance, and the heart rate decreases because enough oxygen is supplied to process the cognitive performance.

• Journal of Chest Surgery
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• v.31 no.11
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• pp.1031-1036
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• 1998

Background: Medtronic-Hall mechanical valve is a world widely using prosthesis. But, in Korea, the clinical result from Medtronic-Hall valve replacement is not frequenthy available. Materials and methods: From March 1986 to May 1990, 50 patients underwent valve replacement surgery with Medtronic-Hall valve at Pusan National University Hospital. Seventeen were male and thirty three were female and ra nging in age from 16 to 70 years of age(mean=35 years). Results: The causes of valvular lesion were rheumatic in 43 patients, bicuspid aortic valve in 3 patients, degenerative lesion in three patients and bacterial endocarditis in one patient. The operative procedures were mitral valve replacement(MVR) in 38, aortic valve replacement(AVR) in 5 and double valve replacement(DVR) in 7. The most commonly used valve size was 21mm in AVR, 29mm in MVR. Concomitant surgical procedures were performed in 15 patients; left atrial thrombectomy in 9, left atrial auricle obliteration in 6 and tricuspid annuloplasty in 5(Kay: 2, DeVega: 3). New York Heart Association functional class was mostly Class Ⅲ or Ⅳ(91.5%) preoperatively and ClassⅠor Ⅱ(87.2%) after operation. The findings of postoperative echocardiogram of LAD, LVESD, LVEDD were reduced compared with preoperative period and ejection fraction was increased compared with preoperative period. Postoperative complications were massive bleeding in three, low cardiac output syndrome in two, thromboembolism in one and fulminant hepatitis in one patient. There were three hospital deaths and their causes were low cardiac output syndrome in two and rupture of left ventricle in one patient. The 5 year survival rate was 93.65±0.71% and 10 year actuarial survival rate was 88.27±6.42%. Conclusions: Medtronic-Hall mechanical valve has low valve related complication rate. It's durability and hemodynamic performance is comparable to other mechanical valves.

• Clinical and Experimental Pediatrics
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• v.46 no.10
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• pp.983-988
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• 2003

Purpose : Syncope appears to be common. However, the mechanism of syncope is not clear. Increased vagal activity and withdrawal of sympathetic stimulation cause hypotension, bradycardia and finally loss of consciousness. The purpose of this study was to evaluate changes of cerebral blood flow velocity, blood pressure, and heart rate during tilt test in children with vasovagal syncope. Methods : Sixty four children with a past history of syncope were evaluated. The stand up test was performed for 15 minutes after a rest at supine position for 10 minutes, followed by an $80^{\circ}$ tilt test lasting 45 minutes. If presyncope(lightheadedness, nausea, blurred vision, or sweating) or syncope occurred, the study was discontinued. 12-lead electrocardiography, echocardiography, and electroencephalography were performed. Transcranial Doppler study was performed at the middle cerebral artery with 2 MHz continuous Doppler probe in 10 children with positive tilt test. Systolic, diastolic, mean cerebral blood flow velocity, integral, and pulsatility index were measured with blood pressure, heart rate, and $O_2$ saturation. Results : The positive rate of tilt test was 31.3%(20/64). Systolic, diastolic, and mean cerebral blood flow velocity decreased significantly in absence of hypotension or bradycardia during presyncope. Time velocity integral of cerebral artery also decreased significantly. Conclusion : Decreased cerebral blood flow velocity can predict the presyncope manifestation. Impairment of autoregulation of cerebral blood flow might play an important role in the pathophysiology of vasovagal syncope.

• Science of Emotion and Sensibility
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• v.11 no.1
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• pp.105-112
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• 2008

This study investigated the effect of 40% oxygen administration on the addition task performance in three levels of difficulties and physiological signals. Ten male and female college students were selected as the subjects for this study. The experiment consisted of two runs: one was a addition task, with normal air (21% oxygen) administered and the other was with hyperoxic air (40% oxygen) administered. The experimental sequence in each run consisted of Rest1 (3 min), Task1 (1 min, one digit addition task), Task2 (1 min, two digit addition task), Task3 (1 min, three digit addition task), and Rest2 (4 min). Blood oxygen saturation and heart rate were measured throughout the five phases. The accuracy rates of the addition task were enhanced with 40% oxygen administration compared to 21% oxygen. Difference in the accuracy rates grew higher with the rise of difficulty. When 40% concentration oxygen is supplied, blood oxygen saturation increased and heart rate was decreased comparing to 21%. This study showed that the supply of high concentration oxygen increases blood oxygen saturation, which in turns accelerates brain activation resulting from cognitive process and enhances arithmetic abilities. Particularly when difficulty is high, demand for oxygen increases and, as a result, the effect of high concentration oxygen becomes more significant.

• Journal of Chest Surgery
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• v.31 no.9
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• pp.837-844
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• 1998

Background: Adenosine is secreted by myocardial cells during myocardial ischemia or hypoxia. It has many beneficial effects on arrhythmias, myocardial ischemia, and reperfusion ischemia. Although many investigators have demonstrated that cardioplegia that includes adenosine shows protective effects in myocardial ischemia or reperfusion injury, reports of the optimal dose of adenosine in cardioplegic solutions vary. We reported the results of beneficial effects of single dosage(0.75 mg/Kg/min) adenosine by use of self-made Langendorff system. But it is uncertain that dosage was optimal. The objective of this study is to determine the optimal dose of adenosine in cardioplegic solutions. Material and Method: We used a self-made Langendorff system to evaluate the myocardial protective effect. Isolated rat hearts were subjected to 90 minutes of deep hypothermic arrest(15$^{\circ}C$) with modified St. Thomas' Hospital cardioplegia including adenosine. Myocardial adenosine levels were augmented during ischemia by providing exogenous adenosine in the cardioplegia. Three groups of hearts were studied: (1) group 1 (n=10) : adenosine - 0.5 mg/Kg/min, (2) group 2(n=10): adenosine -0.75 mg/Kg/min, (3) group 3 (n=10) : adenosine -1 mg/Kg/min. Result: Group 3 resulted in a significantly rapid arrest time of the heart beat(p<0.05) but significantly slow recovery time of the heart beat after reperfusion(p<0.05) compared to groups 1 and 2. Group 2 showed a better percentage of recovery(p<0.05) in systolic aortic pressure, aortic overflow volume, coronary flow volume, and cardiac output compared to groups 1 and 3. Group 1 showed a a better percentage of recovery(p<0.05) in the heart rate compared to the others. In biochemical study of drained reperfusates, CPK and lactic acid levels did not show significant differences in all of the groups. Conclusion: We concluded that group 2 [adenosine(0.75 mg/Kg/min) added to cardioplegia] has better recovery effects after reperfusion in myocardial ischemia and is the most appropriate dosage compared to group 1 and 3.

• KIPS Transactions on Software and Data Engineering
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• v.9 no.10
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• pp.309-316
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• 2020

We predict the mortality of the elderly patients visiting the emergency department who are over 65 years old using Feed Forward Neural Network (FFNN) and Convolutional Neural Network (CNN) respectively. Medical data consist of 99 features including basic information such as sex, age, temperature, and heart rate as well as past history, various blood tests and culture tests, and etc. Among these, we used random forest to select features by measuring the importance of features in the prediction of mortality. As a result, using the top 80 features with high importance is best in the mortality prediction. The performance of the FFNN and CNN is compared by using the selected features for training each neural network. To train CNN with images, we convert medical data to fixed size images. We acquire better results with CNN than with FFNN. With CNN for mortality prediction, F1 score and the AUC for test data are 56.9 and 92.1 respectively.

• The KIPS Transactions:PartB
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• v.15B no.6
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• pp.507-516
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• 2008

Cardiac disease is the leading cause of death in the world. Quantification of cardiac function is performed by manually calculating blood volume and ejection fraction in routine clinical practice, but it requires high computational costs. In this study, an automatic left ventricle (LV) segmentation algorithm using short-axis cine cardiac MRI is presented. We compensate coil sensitivity of magnitude images depending on coil location, classify edge information after extracting edges, and segment LV by applying region-growing segmentation. We design a weighting function for intensity signal and calculate a blood volume of LV considering partial voxel effects. Using cardiac cine SSFP of 38 subjects with Cornell University IRB approval, we compared our algorithm to manual contour tracing and MASS software. Without partial volume effects, we achieved segmentation accuracy of $3.3mL{\pm}5.8$ (standard deviation) and $3.2mL{\pm}4.3$ in diastolic and systolic phases, respectively. With partial volume effects, the accuracy was $19.1mL{\pm}8.8$ and $10.3mL{\pm}6.1$ in diastolic and systolic phases, respectively. Also in ejection fraction, the accuracy was $-1.3%{\pm}2.6$ and $-2.1%{\pm}2.4$ without and with partial volume effects, respectively. Results support that the proposed algorithm is exact and useful for clinical practice.

• Journal of the Korean Applied Science and Technology
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• v.36 no.1
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• pp.142-152
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• 2019

This study aimed to explore the association between obesity index and heart rate variability (HRV) in college-aged male smokers. A total of 85 male college students (> 10 cigarettes per day for at least 3 years) were participated in this study. According to a standardized protocol, body mass index (BMI), percent body fat (%BF), waist circumference (WC), and waist-to-hip ratio (WHR) were taken as obesity indices. Resting r-r interval was monitored for HRV analysis as an indicator of cardiac autonomic regulation. Compared with low WHR subjects, high WHR subjects had significantly lower values of rMSSD, pNN50, HF, and SD1, suggesting decreased parasympathetic activity. No such differences in LF/HF ratio were found between the WHR-based subgroups. Bivariate correlation analysis showed that obesity indices of WC, WHR, and %BF were significantly associated with rMSSD, pNN50, HF, and SD1, with a tendency for correlation coefficient to be higher with WHR than with WC or %BF. No significant association was found between BMI and HRV parameters indicative of parasympathetic activity. This study suggest that central obesity is significantly associated with decrease in parasympathetic activation, independent of BMI as an indicator of obesity, in male college smokers.

• Proceedings of the Korea Information Processing Society Conference
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• 2017.04a
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• pp.680-682
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• 2017

최근 급성 질환으로 인한 사망률은 꾸준히 증가하고 있다. 이러한 급성 질환은 초기 증상 발생 시 올바른 인지와 신속한 대처가 요구된다. 그러나 유지 관리비용 면에서 모든 개인의 응급상황을 관리할 수 있는 의료시스템은 구축하기 어렵다. 본 논문에서는 언급한 문제점을 해결하기 위해 웨어러블 디바이스와 개인건강기록 시스템을 제안한다. 웨어러블 디바이스에서 측정한 심박 체온의 생체신호로 응급 상황을 판별해 지정된 보호자에게 알린다. 또한, 응급버튼을 통해 곧바로 응급상황을 알린다. 개인이나 가족과 관련된 건강정보를 관리할 수 있는 개인건강기록(Personal Health Record)을 제공한다. 본 시스템을 통해 사용자의 응급상황에 신속하게 대처하여 생명을 보호할 수 있을 것으로 기대한다.