生物医学信号时间属性及其分析研究的进展

Time Property and Its Research Progress on Biomedical Signal Time Series

与宇宙随着时间膨胀和大自然随着时间演化一样,表征生命体征的生物医学信号同样有很强的时效性,它随着时间不断地在变化着。因此,常用具有时间概念的时间序列信号来描述与分析。很久以来,借助各种传感器和电子测量仪器获取各种类型的生理时间序列信号,对其进行传统的方法分析与处理,同时认为生理系统为平稳的线性系统,进行时域、频域、时频变换分析以及统计学处理。人体(或高级动物)的生理系统是自然界中最复杂的系统。在对人体生物医学信号进行非线性动力学分析时,对时间属性的研究即是对时间复杂度参数(如熵值等)的研究。熵在增大,所有活体系都在耗散,现在研究的是远离平衡、非线性耗散系统中,时间上不可逆的动态演化。显然,在人们熟知的"生物钟"周期中,机体的生理状态每时每刻都不同,不同周期里的状态也各不相同,则通过非线性动力学分析表征生命体征的复杂度参数也各不相同。生物医学信号时间序列的非性线分析除了混沌分析、幂律分析、多重分形、熵分析等方法外,近期有学者对时间序列进行时间不可逆性分析,以期进一步揭示生命活动的非线性动力学系统本质。自然变更、生物进化、社会发展等都是无序的、不可逆的过程,研究其不可逆性正在引起空间、时间和动力学概念上的巨大变化。因此,序列的时间不可逆性分析提供了一种分析非线性动力学系统的新思路。

As the cosmic expansion and natural evolution over time,the biomedical signal that represents vital signs also has a strong timeliness,while it is changing itself over time.Therefore,time series with implied time concept are usually used to describe and analyze them.Various physiological time series signals are obtained with sensors and electronic measuring instruments for a long time.Then the physiological systems are considered as stationary linear systems and they are analyzed and processed by traditional methods,such as the time domain analysis,the frequency domain analysis,the time-frequency transform analysis and the statistical analysis.Human beings or advanced animals are the most complex physiological systems in nature.It has been proved for more than half a century that scientists cannot reveal the motion law of the material world only by linear approximation and the corresponding analysis method as a result of their nonlinear nature.Nonlinear methods should be applied to explore the nonlinear phenomenon during the vital movement.When applying nonlinear dynamic methods into biomedical signals,their time complexity parameters can be studied equally,i.e.entropy.As the entropy increases,all living systems are in dissipation.The issue under study is the irreversible dynamic time evolution in nonlinear dissipation systems that is far from equilibrium.Obviously,in the well-known bioclock period,the physiological statuses in an organism vary in every moment and every period,thus resulting in the fact that complexity parameters which represent vital signs and are characterized by nonlinear dynamic analysis are different from each other.In addition to chaos,power law,multifractals and entropy analysis as the nonlinear analysis methods in biomedical time series signals,newly-proposed time irreversibility has been adopted to further reveal the nonlinear dynamic nature in vital movements.Apparently,disordered and irreversible processes exist in natural changes,biological evolution and social development,whose irreversibility research causes great changes in the concepts of space,time and dynamics.In conclusion,the time irreversibility method on time series provides us a new idea for analyzing nonlinear dynamic systems.