脊髓损伤患者心率变异性的局部尺度指数特征

Characteristics of local scale exponent of heat rate variability in people with spinal cord injury

心率变异性(heart rate variability,HRV)是目前评估脊髓损伤(spinal cord injury,SCI)患者残余自主神经功能的主要依据。分析HRV的一般方法是计算心电信号R-R序列的时域、频域或非线性指标,其中去趋势波动分析(detrended fluctuation analysis,DFA)是最常用的非线性方法之一,对于R-R序列,通常由DFA可得两个尺度指数α1(尺度<11)和α2(尺度>11)。本研究关注局部尺度指数α(t)(t为时间尺度)揭示谱分析和尺度指数不能表征的HRV动态特性,采集12例SCI患者和15名健康者在坐姿(10min)和俯卧姿(10min)时的心电信号,计算R-R序列的α(t)。由于α(t)在小尺度时容易被高估,本文采用一种新的校正方法计算α(t)并用仿真信号验证其有效性。将此方法应用于采集的数据,结果显示,健康者在坐姿和俯卧姿时R-R序列的α(t)在4s<t<12s(频率0.083~0.25 Hz)时单调下降,而SCI患者的α(t)在几乎所有的尺度上缓慢下降。另一方面,坐姿时SCI患者的α(t)在4s<t<7s(0.143~0.25 Hz)时显著低于健康者的α(t)值;俯卧姿时,SCI患者的α(t)值在t=12s(0.083Hz)附近显著大于健康者的α(t)值。然而,用谱分析和DFA所得结果显示,两组无显著差异这表明,局部尺度指数α(t)可揭示谱分析和传统的尺度指数不能表征的HRV动态特性。

Heart rate variability （HRV） is a fundamental basis for evaluating the residual autonomic nerve function in pa- tients with spinal cord injury （SCI）. The commonly used methods for analyzing HRV involve calculation of time- and fre- quency-domain or nonlinear indices of R-R interval series derived from ECG signals, and the detrended fluctuation analy- sis （DFA） is one of the most commonly used nonlinear methods. Typically, DFA of HRV can yield two scaling expo- nents： α1 （〈 11 beats） and α2 （〉 11 beats）. The present study was aimed to investigate whether the local scaling exponent α（t） （t is the time scale） could reveal the dynamics of HRV that cannot be characterized by spectral analysis and scaling exponents. ECG signals were collected from 12 SCI patients and 15 healthy subjects during upright sitting and prone pos- ture. A new method was used to calculate α（t） involving correcting the α（t） values at small scales. The results showed that, for both sitting and prone postures, α（t） in healthy subjects monotonically decreased in the range of 4 s〈t〈12 s （0. 083-0. 25 Hz）, whereas a（t） in SCI patients descended slowly on almost all scales. In the sitting posture, a（t） values in the scale range of 4 s〈t〈12 s （0. 143-0. 25 Hz） were significantly lower in SCI patients than in healthy subjects; in the prone posture, a（t） values around t= 12 s （0. 083 Hz） were significantly higher in SCI patients than in healthy subjects. However, the results obtained by spectrum analysis and DFA did not show significant difference, which indicates that the dynamics of HRV cannot be characterized fully by spectral analysis and traditional scaling exponents.