태아의 짧은 심박변이의 근사 엔트로피 : 효율적인 태아 이상 측정 지표

유철승,이상훈 인제대학교 2003 仁濟論叢 Vol.18 No.1

초음파 도플러 심박 측정기로 구한 태아의 R-R interval 데이터를 약 8-10분에 해당하는 길이가 1024인 segment로 나누어 approximate entropy(ApEn)를 계산하였다. 계산된 ApEn 값의 누적 histogram 분포를 이용해 자궁 비수축 검사(non-stress test : NST)로 구분된 distress 태아군이 정상 태아에 비해 통계적으로 낮은 ApEn값을 가지고, 0.6~0.7정도의 ApEn 분별치를 설정해서 구분 할 그 있음을 조사하였다. 그러나 distress 태아군의 acidemia 태아군과 non-acidemia 태아군은 ApEn값의 histogram 분포로서 통계적으로 유의성 있는 차이를 확인할 수 없었다. 본 연구에서는 approximate entropy가 fetal HRV 데이터에 대해 특별한 전처리과정 없이 짧은 길이(1024 R-R intervals)의 데이터를 이용해 태아의 건강상태를 정량화 할 수 있는 유용한 비선형지수임을 확인 했다. Using R-R interval data acquired from ultrasonic Doppler heartbeat gauge, we computed the ApEn(approximate entropy) of segments with length 1024 that have the duration of 8 ~ 10 minutes. An accumulated histogram of ApEn's shows that the fetal group who were identified as the distress in the uterus non-stress test has smaller ApEn than the normal group. The threshold in ApEn that is about 0.6 ~0.7 enables discriminating the distress fetus from the normal fetus. However, we can't find any statistically significant differences between acidemia and non-acidemia in distress fetal group. This study reports that approximate entropy is a useful nonlinear index quantifying states of fetus from the short(1024 R-R intervals) fetal heart rate variability(HRV) without any specific preprocessing of HRV

정신분열병 환자의 Clozapine 복용기간에 따른 심장 상태 변화의 정량적 분석 : Case Study of Clozapine-treated Schizophrenia Patients

유철승,이상훈 인제대학교 2004 仁濟論叢 Vol.19 No.1

본 연구의 목적은 심박변이(heart rate variability)를 이용하여 clozapine을 복용하고 있는 정신분열병 환자의 약물복용기간에 따른 선형 및 비선형지수들을 계산하여 약물이 심장에 미치는 효과를 조사하는 것이다. 심박변이 데이터는 12주 동안 4주 간격으로 정신분열병 환자 4명(반응군 2명과 비반응군 2명)으로부터 얻어졌다. Detrending은 심박변이 데이터의 전처리과정으로 수행되었다. 주파수분석의 경우 반응군의 HF 성분이 8주에서 증가하는 반면, 비반응군에서는 감소하였다. 프랙탈 상관성은 반응군과 비반응군 사이에 차이를 보이지 않았다. 반응군의 비선형 복잡도(non-linear complexity)는 4주에서 증가하는 반면 비반응군의 복잡도는 감소하였다. 이 결과들에서 임상지수와 분석지표들 사이의 뚜렷한 상관성을 알 수 있었다. 또한 심박변이의 detrending 과정이 분석지표에 어떤 영향을 주는지 검토하였다. The purpose of this study was to investigate the change in heart state in terms of the linear and nonlinear measures associated with periods of clozapine treatment for Schizophrenia subjects using hear rate variability (HRV). HRV data was obtained from 4 Schizophrenia subjects (2 responder and 2 non-responder) at intervals of 4-week during 12-week period. Detrending was carried out as a preprocessing for HRV data. For spectral power analysis, high frequency component of the responder increased at 8-week, while one of the non - responder decreased. Fractal correlation didn't show significance difference between responder and non responder. Nonlinear complexity of the responder increased at 4-week, while one of the non - responder decreased. From the above results, we found significant correlations between clinical indices and computational measures of analysis. We also discuss how detrending procedure of heart rate variability can have some effects on the computational measures of analysis.

태아의 짧은 심장박동 변이의 근사 엔트로피를 이용한 효율적인 태아 이상 측정 지표

유철승,이상훈,전계록 한국물리학회 2005 새물리 Vol.50 No.3

Using R-R interval data acquired from an ultrasonic Doppler heartbeat gauge, we computed the ApEn (approximate entropy) of segments with length 1024 that had a duration of 8 10 minutes. An accumulated histogram of ApEn's showed that the fetal group that had been identied as having distress by using the uterus non-stress test had a smaller ApEn than the normal group. We also found that the ApEn showed a higher specicity than any other linear measure by comparing the overlapping ratio of an accumulated histogram. The threshold in ApEn which is about 0.6 0.7, enables the distressed fetus to be distinguished from the normal fetus. However, we did not nd any statistically signicant dierences between acidemia and non-acidemia in the distressed fetal group. By using the short (1024 R-R intervals) fetal heart rate variability (HRV) without any specic preprocessing of the HRV data, this study showed the approximate entropy to be a useful nonlinear measure for quantifying the states of a fetus.

Association of Heart Rate Variability with the Framingham Risk Score in Healthy Adults

유철승,이가영,이상훈,김준수,김희철 대한가정의학회 2011 Korean Journal of Family Medicine Vol.32 No.6

Background: The aim of this study was to investigate the relationship between heart rate variability (HRV), the Framingham risk score (FRS), and the 10-year risk of coronary heart disease (CHD) development among Korean adults. Methods: The subjects were 85 healthy Korean adults recruited from a health check-up center. The FRS and 10-year risk of CHD development were calculated. Results: The FRS in men was inversely correlated with the standard deviation of all normal to normal RR-intervals (SDNN);the root mean square successive difference (RMSSD); the percentage of successive normal cardiac inter-beat intervals greater than 20 ms, 30 ms, and 50 ms (pNN20, pNN30, pNN50); the low frequency (LF); and the high frequency (HF) (P < 0.05). There was no signifi cant relationship between the FRS and HRV in women. Overall, in the receiver operating characteristic (ROC) analysis, the RMSSD, HF, SDNN, LF, LF/HF ratio, and pNN30 predicted an increased 10-year CHD risk. After adjusting for sex and body mass index, those with greater than one standard deviation in the RMSSD, HF, and LF had a 52-59% reduction in their 10-year risk of CHD development ≥ 10%. Conclusion: This study therefore indicates that the HRV indices, particularly SDNN, RMSSD, pNN30, LF, and HF may be useful parameters for the assessment of CHD risk. Most notably, the usefulness of these HRV measures as indicators for CHD risk evaluation may be greater among men than among women.

내·외부적 자극을 받고 있는 정상인의 다중채널 뇌파의 비선형동역학적 지수 계산

유철승,이상훈 인제대학교기초과학연구소 2002 자연과학 Vol.6 No.-

내·외부적으로 자극(시각, 수치계산)을 받는 정상인 뇌파(electroencephalogram:EEG)의 매립환경변수와 비선형지수를 계산하였다. 18채널 정상인 뇌파의 채널별 상관차원, 최대리야푸노프지수, 비선형예측오차의 분포를 통해 자극이 뇌파에 미치는 효과를 비선형적으로 정량화 하였다. 상관차원으로 시각자극에 민감한 채널은 후두엽의 p7, o1, o2이고, 내부적인 복잡한 계산에 민감한 채널은 우측 전두엽의 f4, f8임을 통계적으로 확인하였다. 최대리야푸노프지수는 주로 전두엽의 fp1,f3, fp2, f8채널에서 자극을 받지 않는 상태보다 시각자극 또는 복잡한 계산 상태에서 더 낮아짐을 알았다. 예측오차는 상관차원, 최대리야푸노프지수에 비해 각 상태에 대한 부위별 반응변화를 충분히 나타내지 못했다. 이 결과들로 부터 자극의 변화에 따른 비선형지수들의 유용성을 검토하였다. Embedding parameters and nonlinear indices were calculated for the electroencephalogram(EEG) of the normal person under the intrinsic or extrinsic stimuli(visual or numerical calculation). Using the inter-channel distribution in the correlation dimension, the primary Lyapunov exponent, and nonlinear predication error of 18 channel EEG obtained from the normal person, we could get the nonlinear dynamic quantification of effects on EEG induced from stimuli. Correlation dimension statistically showed that p7, o1, o2 channels in the occipital lobe are sensitive to a visual stimulus, and f4,f8 channels in the right frontal lobe are sensitive to an intrinsic stimulus such as complex calculation. In fp1, f3, fp2, f8 channels of frontal lobe, the primary Lyapunov exponent was found relatively lower in states of visual stimulus or complex calculation than in those with no stimuli. Nonlinear prediction error reflect less sufficiently the inter-channel reactions than the correlation dimension and the primary Lyapunov exponent. This study examines the usefulness of nonlinear indices in the presence of various stimuli.

정상인과 좌심실 기능부전환자에서 심박변동도의 비선형적 분석:심장혈관계 위험예측인자로서의 역할

신동구,유철승,박경태,이상훈,홍그루,박종선,김영조,심봉섭,김웅,이상희 대한심장학회 2006 Korean Circulation Journal Vol.36 No.8

고체상 켜쌓기법에 의해 형성된 GexSi1-x/Si(100)의 결정구조 특성

김현수,유철승,김건호,최치규,이정용,이정주,임태균 濟州大學校 基礎科學硏究所 1996 基礎科學硏究 Vol.9 No.2

고체상 켜쌓기법(solid phase epitaxy; SPE)으로 GexSi1-x/Si(100)이종접합을 형성하기 위하여 Si(100)기관위에 중착된 a-Ge(amorphous-Ge)/Au을 온도와 시간을 변화시키면서 열처리하였다. 300℃ 이상에서 열처리하는 동안 Ge이 Au층으로 확산되어 기관위에 켜쌓기 되면서 처음의 a-Ge/Au/Si(100)구조가 Au/GexSi1-x/Si(100) 구조로 변하였다. 형성된 GexSi1-x층을 X선 회절 및 투과 전자현미경으로 측정 분석한 결과, 조성이 Ge??Si0₂인 단결정 박막이 성장되었으며 Ge??Si0₂/Si(100)계면의 주요 결정결함으로 전위, 적층결함 미소쌍정구조 등이 관측되어졌다. For the solid-phase heteroepitaxial growth of GexSi1-x/Si(100), bilayers of a-Ge/Au deposited on a single crystal Si(100) substrate were annealed at 250℃, 300℃, and 350℃ for 5,15, and 30 min, respectively. The samples before and after thermal annealing were characterized using X-ray diffraction(XRD) and cross-sectional TEM(XTEM). During annealing above 300℃, the Ge transported through the Au layer and grew epitaxially to the substrate; the final structure was Au/GexSi1-x/Si(100) as opposed to the original structure of a-Ge/Au/Si(100). The composition x of the GexSi1-x film examined by XRD was 0.8, and the main defects in the epitaxial film observed by XTEM were Dislocations, Stacking faults, and microtwins.

의복형 생체신호 모니터링을 이용한 건강증진 시스템

김준수,이가영,유철승,김태웅,이상훈,김희철 대한임상건강증진학회 2011 Korean Journal of Health Promotion Vol.11 No.1

생체 신호센서 기술의 발전으로 의복형 생체 신호 모니터링 시스템은 U-헬스 영역에서 각광 받는 분야로 떠오르고 있다. 의복형 센서는 장시간의 생체신호 모니터링을 통하여 건강증진 및 여러 만성질환, 신경 정신 질환의 치료에도 도움을 주고 있다. 본 종설에서는 각국의 의복형 생체 신호 모니터링 시스템의 사례를 기술하고, 향후 전망과 표준화, 행정적 관점, 타당성 문제, 기술과 임상적 응용의 차이점 등에 대해서 논의한다. With the development of body sensor technology, wearable health monitoring systems have been an emerging information technology in the ‘ubiquitous health care’ system. Wearable sensors enable long-term continuous physiological monitoring important in health promotion and management of many chronic disorders. In this paper, we present several wearable health monitoring systems developed by different countries and discuss emerging opportunities, as well as, existing challenges such as standardization, administration, validation, and discrepancy issues between technology and clinical implication.

내·외적인 자극을 받는 뇌파의 비선형 동력학적 특징

정기영,김재문,유철승,이상훈 대한임상신경생리학회 2002 Annals of Clinical Neurophysiology Vol.4 No.1

Backgrounds and objective : EEG reflect dynamic changes of continuous neuronal activities by internal and external stimuli. The aim of this study is to quantify nonlinearly the local dynamic differences among EEG data corresponding to different states of brain. Methods : EEG was recorded from twelve healthy normal subjects(mean age, 29.7 years; 8 men and 4 women) using digital EEG machine. 18-channel EEG data were selected during eyes closed(EC), eyes open(EO), and mental arithmetic( MA) in each subject. Correlation dimension(D2) and largest Lyapunov exponent(LLE) were calculated from three states and average value was mapped 2 dimensionally and compared with each other. Results : The distribution of D2 was relatively symmetric and its value was higher in frontal than in parieto-occipital region during EC. These findings were reversed during EO. Bilateral centro-temporo-parietal region showed high D2 value in MA compared with those in EC, which was more prominent in left side. LLE was larger than zero in all state and showed significant differences among EC, EO and MA(p=0.000). Conclusion : These results suggest that nonlinear analysis of EEG can quantify dynamic state of brain.

측두엽성 간질에서 비선형 교차예측을 이용한 발작의 시공간 분포

정기영,김재문,손은희,홍승봉,유철승,이상훈 대한신경과학회 2002 대한신경과학회지 Vol.20 No.2