ABSTRACT
Objective To investigate the gait stability of healthy old and young adult volunteers during walking using the nonlinear time series analysis method so as to comprehensively assess the dynamic balance of human and provide important references for the prediction of fall risk. Methods The Vicon motion capture system was used to collect three-dimensional kinematic data of healthy volunteers (seven old subjects and ten young subjects) at different walking speed (80%, 100%, 120% of the natural walking speed). The anterior-posterior and medio-lateral motions of the seventh cervical and tenth thoracic vertebrae, as well as the flexion-extension and abduction-adduction angles of the lower extremity joints, were obtained from 30 consecutive gait cycles to calculate the largest Lyapunov exponents and analyze the difference of gait stability between the old and young group and the influence of walking speed on gait stability. Results The gait stability in the young group was better than that in the old group, and there were significant differences in certain motion segments (P＜0.01). The gait stability in both groups were reduced with the increase of speed (P＜0.05). Conclusions The largest Lyapunov exponent based on nonlinear time series analysis method can be used to effectively and quantitatively analyze the gait stability of each motion segment in human during walking.
ABSTRACT
OBJECTIVE: This study was done to propose a new method of determining the cutoff frequency against measurement noise in fetal heart rate signal and to analyze the discriminating value for normal fetus (pH>7.15) and abnormal fetus (pH< or =7.15) by nonlinear method. METHODS: The patients were classified by umbilical artery pH (7.15) or base excess (-10 mEq/L). After removing the high frequency noise components at the cutoff frequency determined in this study, we calculated correlation dimension as a discriminating value for the normal and abnormal fetuses. RESULTS: After low pass filtering of fetal heart rate signal at the cutoff frequency, the numerical result of embedding dimension was 5.47+/-0.67 (normal), 4.43+/-0.60 (abnormal) (p<0.001), and correlation dimension was 2.51+/-0.43 (normal), 1.79+/-0.15 (abnormal). CONCLUSION: We could determine the cutoff frequency from the different fluctuation level between high frequency noise and principal signal according the cutoff frequency function. The detection of fetal distress was done objectively by this method. We could discriminate between normal fetus and abnormal fetus by correlation dimension as indicator for the nonlinear complexity.