Nonlinear multivariable modeling and analysis of sleep apnea time series.

This paper investigates the modeling and analysis of physiological data recorded from a 49-year-old male and are composed of three time series: blood oxygen saturation, heart rate and respiration. In particular, it is desired to verify if the models estimated from data can distinguish between the dynamics underlying two different breathing patterns (normal breathing and apnea). The estimated models are nonlinear autoregressive, moving average with exogenous inputs (NARMAX) and the regressors used to compose such models are carefully chosen, among hundreds of candidates, by an automatic procedure. The results discussed in this paper suggest that the dynamics underlying the data are nonlinear and basically deterministic. Using estimated models it seems to be possible to quantify the stability of the fixed point in phase space reconstructed using the blood oxygen time series. This, as discussed, could be the basis of an algorithmic monitoring system.     

心率信号非线性动力结构的确定

在Silvio等提出的压力反射控制心脏活动的短期压力模型的基础上,推导出关于心率信号的一种四参量的非线性结构,通过实际的心率信号降维分析,表明心率信号存在非线性动力结构,为心率信号是确定性低维混沌的诊断提供了依据。     

Non-uniform multivariate embedding to assess the information transfer in cardiovascular and cardiorespiratory variability series

The complexity of the short-term cardiovascular control prompts for the introduction of multivariate (MV) nonlinear time series analysis methods to assess directional interactions reflecting the underlying regulatory mechanisms. This study introduces a new approach for the detection of nonlinear Granger causality in MV time series, based on embedding the series by a sequential, non-uniform procedure, and on estimating the information flow from one series to another by means of the corrected conditional entropy. The approach is validated on short realizations of linear stochastic and nonlinear deterministic processes, and then evaluated on heart period, systolic arterial pressure and respiration variability series measured from healthy humans in the resting supine position and in the upright position after head-up tilt.     

Music,perceived arousal,and intensity: Psychophysiological reactions to Chopin's “Tristesse”

The present study investigates the relation of perceived arousal (continuous self‐rating), autonomic nervous system activity (heart rate, heart rate variability) and musical characteristics (sound intensity, musical rhythm) upon listening to a complex musical piece. Twenty amateur musicians listened to two performances of Chopin's “Tristesse” with different rhythmic shapes. Besides conventional statistical methods for analyzing psychophysiological reactions (heart rate, respiration rate) and musical variables, semblance analysis was used. Perceived arousal correlated strongly with sound intensity; heart rate showed only a partial response to changes in sound intensity. Larger changes in heart rate were caused by the version with more rhythmic tension. The low‐/high‐frequency ratio of heart rate variability increased—whereas the high frequency component decreased—during music listening. We conclude that autonomic nervous system activity can be modulated not only by sound intensity but also by the interpreter's use of rhythmic tension. Semblance analysis enables us to track the subtle correlations between musical and physiological variables.     

多目标优化方法检测随机受迫系统的混沌现象以及在心率变异信号分析中的应用

心率变异信号往往很不规则 ,确定它是混沌还是噪声是目前研究的焦点。从非线性动力学的角度 ,虽然已进行了大量的工作 ,但迄今还没有明确的证据表明心率变异信号是混沌的。本文假设心率变异信号是其内在动力学机制和外部环境影响混合的产物 ,并提出一种多目标优化方法 ,以此获得一组既与心率变异信号尽可能接近又对于某种非线性动力学系统为确定的序列 ,然后计算依赖于初始值敏感的特征指数 ,定量刻划系统中确定性因素的动力学特性。在成功地检验了两类受迫混沌模型后 ,应用于心率变异信号分析 ,结果表明 :心脏动力学系统的确定性部分是混沌的     

Assessment of Granger Causality by Nonlinear Model Identification: Application to Short-term Cardiovascular Variability

A method for assessing Granger causal relationships in bivariate time series, based on nonlinear autoregressive (NAR) and nonlinear autoregressive exogenous (NARX) models is presented. The method evaluates bilateral interactions between two time series by quantifying the predictability improvement (PI) of the output time series when the dynamics associated with the input time series are included, i.e., moving from NAR to NARX prediction. The NARX model identification was performed by the optimal parameter search (OPS) algorithm, and its results were compared to the least-squares method to determine the most appropriate method to be used for experimental data. The statistical significance of the PI was assessed using a surrogate data technique. The proposed method was tested with simulation examples involving short realizations of linear stochastic processes and nonlinear deterministic signals in which either unidirectional or bidirectional coupling and varying strengths of interactions were imposed. It was found that the OPS-based NARX model was accurate and sensitive in detecting imposed Granger causality conditions. In addition, the OPS-based NARX model was more accurate than the least squares method. Application to the systolic blood pressure and heart rate variability signals demonstrated the feasibility of the method. In particular, we found a bilateral causal relationship between the two signals as evidenced by the significant reduction in the PI values with the NARX model prediction compared to the NAR model prediction, which was also confirmed by the surrogate data analysis. Furthermore, we found significant reduction in the complexity of the dynamics of the two causal pathways of the two signals as the body position was changed from the supine to upright. The proposed is a general method, thus, it can be applied to a wide variety of physiological signals to better understand causality and coupling that may be different between normal and diseased conditions.     

Nonlinear Coupling Among Heart Rate,Blood Pressure,and Respiration in Patients Susceptible to Neuromediated Syncope

The aim of this study is to evaluate the degree of coupling between the cardiovascular variability series and the respiration in subjects susceptible to neurally mediated syncope. Twenty-one informed patients susceptible to syncope and ten sex- and age-matched control subjects were enrolled in the study. ECG, respiration activity, and arterial blood pressure were simultaneously recorded at rest (controlled and free breathing) and during the 70° head-up TILT test (free breathing). The degree of nonlinear coupling among heart rate variability (HRV), blood pressure variability (BPV), and respiration was quantified by means of two indices according to a multivariate embedding-based approach. Eleven patients developed syncope during the TILT test. We found that during the late TILT phase, the TILT-positive group experienced a significant increase in nonlinear coupling respect to the mid TILT phase (p < 0.01, Wilcoxon nonparametric test for pair data) while the TILT-negative group did not (p < 0.01, Mann-Whitney U-test). If the proposed nonlinear coupling indexes can be considered expression of the coupling mechanisms involved in the vagal regulation of the cardiovascular system, an increase in vagal tone accompanied by a decrease in sympathetic activity seem to occur before a vasovagal event. © 2003 Biomedical Engineering Society. PAC2003: 8719Hh, 8719Uv, 8719La     

用联合熵分析短时心率变异信号的非线性动力学复杂性

用联合熵方法来分析短时心率变异性信号,该方法可以有效地从短时心跳间期信号中提取出动力学信息,从而反映心率变异性的强弱,为临床应用提供了方便。我们首先介绍联合熵基本理论,用低维的混沌序列进行了检验,证明该方法有效。然后将其应用于人体短时的心跳间期时间序列,该方法可以揭示复杂生理信号所具有的动力学特征以及衰老和疾病所伴随的非线性动力学复杂性的丢失和降低的个体自适应能力。最后,用联合熵方法来考察短时心率变异性信号的非随机性程度,该方法可以有效的揭示心室对心室纤维性颤动响应的非随机模式。     

Does preprocessing change nonlinear measures of heart rate variability?

This work investigated if methods used to produce a uniformly sampled heart rate variability (HRV) time series significantly change the deterministic signature underlying the dynamics of such signals and some nonlinear measures of HRV. Two methods of preprocessing were used: the convolution of inverse interval function values with a rectangular window and the cubic polynomial interpolation. The HRV time series were obtained from 33 Wistar rats submitted to autonomic blockade protocols and from 17 healthy adults. The analysis of determinism was carried out by the method of surrogate data sets and nonlinear autoregressive moving average modelling and prediction. The scaling exponents , ₁ and ₂ derived from the detrended fluctuation analysis were calculated from raw HRV time series and respective preprocessed signals. It was shown that the technique of cubic interpolation of HRV time series did not significantly change any nonlinear characteristic studied in this work, while the method of convolution only affected the ₁ index. The results suggested that preprocessed time series may be used to study HRV in the field of nonlinear dynamics.     

Compiled profile of respiration,heart beat and motility in newborn infants: A methodological approach

The inter-relationships between respiration, heart beat and motility are investigated in newborn infants. Motility seems to be a determinant for changes in respiratory and heart rates. In contrast to the more usual epoch analysis of polygraphic recordings, a moving-window method is described in which the positions of the peaks in the three cross-correlation functions between both rates and motility (peak height and time lag when this peak occurs) are displayed as a function of recording time. Heart rate and motility are positively correlated; respiratory rate is negatively correlated with these two variables. There is no time lag between the minima in respiratory rate and the maxima in motility. The heart rate maxima lag approximately 10 s behind the motility maxima and respiratory rate minima.     

Two-electrode telemetric instrument for infant heart rate and apnea monitoring

Infants may be at risk of life threatening episodes caused by still unknown factors. The Sudden Infant Death Syndrome (SIDS) is believed to be connected with respiration problems due to immature and developing brain breathing control, and many other factors. Currently heart rate and respiration monitoring is considered of major importance to be applied in the hospital and eventually at home. The objective is accurate detection of bradycardia (heart rate below a selected limit, usually between 80 and 100 beats/min) and apnea (cessation of breathing for more than 20 s). A telemetric instrument was developed for monitoring the heart rate and respiration by extraction of the respiration signal from the electrocardiogram QRS complex peak-to-peak amplitude. It makes use of two electrodes integrated in a transmitter module, thus avoiding use of leads and also reducing artifacts to an acceptable minimum. The receiver station can be a simple detector with apnea and bradycardia alarms, a more complicated recorder or a fully developed signal analyser.     

Two-electrode telemetric instrument for infant heart rate and apnea monitoring

Infants may be at risk of life threatening episodes caused by still unknown factors. The Sudden Infant Death Syndrome (SIDS) is believed to be connected with respiration problems due to immature and developing brain breathing control, and many other factors. Currently heart rate and respiration monitoring is considered of major importance to be applied in the hospital and eventually at hoinc. The objective is accurate detection of bradycardia (heart rate below a selected limit, usually between 80 and 100 beats/min) and apnea (cessation of breathing for more than 20 s). A telemetric instrument was developed for monitoring the heart rate and respiration by extraction of the respiration signal from the electrocardiogram QRS complex peak-to-peak amplitude. It makes use of two electrodes integrated in a transmitter module, thus avoiding use of leads and also reducing artifacts to an acceptable minimum. The receiver station can be a simple detector with apnea and bradycardia alarms, a more complicated recorder or a fully developed signal analyser.     

Does synchronization reflect a true interaction in the cardiorespiratory system?

Cardiorespiratory synchronization, studied within the framework of phase synchronization, has recently raised interest as one of the interactions in the cardiorespiratory system. In this work, we present a quantitative approach to the analysis of this nonlinear phenomenon. Our primary aim is to determine whether synchronization between HR and respiration rate is a real phenomenon or a random one. First, we developed an algorithm, which detects epochs of synchronization automatically and objectively. The algorithm was applied to recordings of respiration and HR obtained from 13 normal subjects and 13 heart transplant patients. Surrogate data sets were constructed from the original recordings, specifically lacking the coupling between HR and respiration. The statistical properties of synchronization in the two data sets and in their surrogates were compared. Synchronization was observed in all groups: in normal subjects, in the heart transplant patients and in the surrogates. Interestingly, synchronization was less abundant in normal subjects than in the transplant patients, indicating that the unique physiological condition of the latter promote cardiorespiratory synchronization. The duration of synchronization epochs was significantly shorter in the surrogate data of both data sets, suggesting that at least some of the synchronization epochs are real. In view of those results, cardiorespiratory synchronization, although not a major feature of cardiorespiratory interaction, seems to be a real phenomenon rather than an artifact.     

New method for the assessment of neonatal respiratory sinus arrhythmia

Respiratory sinus arrhythmia (RSA) is sometimes hard to identify in neonates, in particular when the respiratory rate approaches half the mean heart rate. It is shown that the analysis of the cardiac event series may reveal RSA in cases where traditional heart rate variability analysis methods fail. A signal analysis approach to event series processing is reviewed. The validation of the spectral analysis of event series is illustrated with the help of simulation results. In accordance with this approach, the event series spectrum of a neonate shows a RSA component at 0·9 Hz, which was in agreement with the frequency of the simultaneously measured respiration. The possible implications for research into the causes of sudden infant death syndrome (SIDS) are discussed.     

心脏节律蕴涵的确定性动力学机制重构

本研究以受迫非线性动力学系统为分析模型，以Volterra级数方法为基础，研究了心脏节律的确定性动力学机制重构问题。首先，采用最优变换方法充分表征相应级数项蕴涵的确定性动力学机制；其次，利用EM算法对观测和动力噪声强度、确定性动力学行为、模型结构和参数进行迭代采样，实现从多种生理过程的影响中准确重构心脏节律的确定性动力学机制。应用实验数据表明：重构模型具有与心脏节律非常相似的动力学行为和统计特性；心脏节律内在机制具有初始值敏感性质。     

Heart Rate and Respiratory Responses as a Function of Task Difficulty: The Use of Discriminant Analysis in the Selection of Psychologically Sensitive Physiological Responses

The relationship between physiological response patterns.and task difficulty was investigated by evaluating heart rate and respiratory responses during a choice reaction lime tusk with three levels of task difficulty. The data fit a two-component model or attention containing reactive and sustained responses. There were two reactive responses: An immediate deceleration which was independent of task manipulation; and a short latency response, monotonically paralleling task difficulty, which was characterized by acceleration and an increase in heart rate variability. The sustained component exhibited task dependent deceleration and u generalized reduction in heart rate variability and respiration amplitude variability. A stepwise discriminant analysis was performed on the task conditions using physiological responses to determine responses sensitive to task demands. Physiological response patterns were monotonically ordered as a function of task difficulty, suggesting that this technique may have advantages for determining physiological responses most sensitive to psychological manipulation.     

A genetic analysis of ambulatory cardiorespiratory coupling

This study assessed the heritability of ambulatory heart period, respiratory sinus arrhythmia (RSA), and respiration rate and tested the hypothesis that the well-established correlation between these variables is determined by common genetic factors. In 780 healthy twins and siblings, 24-h ambulatory recordings of ECG and thorax impedance were made. Genetic analyses showed considerable heritability for heart period (37%-48%), RSA (40%-55%), and respiration rate (27%-81%) at all daily periods. Significant genetic correlations were found throughout. Common genes explained large portions of the covariance between heart period and RSA and between respiration rate and RSA. During the afternoon and night, the covariance between respiration rate and RSA was completely determined by common genes. This overlap in genes can be exploited to increase the power of linkage studies to detect genetic variation influencing cardiovascular disease risk.     

Automatic assessment of the interaction between respiration and heart rate variability signal

The present paper introduces an original method of processing heart rate variability (HRV) and respiration signals as detected respectively through chest electrodes and thoracic belt in dogs under different experimental conditions. Signals are processed as time series synchronous with the occurrence of QRS complexes on ECG signal and auto and cross spectra are accordingly calculated. Two particular bands appear mainly of interest on the spectrum of HRV signal: one in correspondence with the respiration rate and another one at a lower frequency value. Values of power at these frequency bands together with coherence and phase between HRV signal and respiration complete the parameters which try to quantify a few aspects of the complex dynamic relationships between the original signals. In particular, controlled respiration in dogs was studied through the connection with an automatic ventilator, as well as the effects of drugs which interact with the neural regulatory systems (i.e. sympathetic and parasympathetic nervous system). Gain and phase relationships between heart rate variability and respiration, obtained with spectral analysis, could be used to provide a better understanding of the neural control mechanisms linking heart rate and respiration in various experimental conditions. The method described in this study is to be used both in physiological and clinical research.     

Effects of Isometric Muscle Tension on Vasomotor Activity and Heart Rate

Twenty-four adults each performed two isometric exercises at three levels of exertion while finger pulse amplitude, skin temperature, heart rate, and respiration rate and amplitude were monitored. Due to exercise, pulse amplitude and skin temperature were significantly reduced while heart rate was significantly increased. The magnitude of cardiovascular (CV) effect varied in proportion to the magnitude of exercise. Further evidence for the close association between exercise and CV effects was implied by the rapid recovery of pulse amplitude and heart rate at the termination of exercise. This evidence in addition to a detailed analysis of respiration data led to the conclusion that CV reactions to isometric exercise were not mediated by respiratory variations. The implications of these, findings for studies of operant conditioning of CV and other autonomic responses are discussed.     

Heart rate variability in diabetic patients during orthostatic load — A spectral analytic approach

Summary Spectral analysis of heart rate variability (HRV) was used to assess the autonomic nervous control of cardiac function during orthostatic load in insulin-dependent diabetic patients and healthy subjects. The diabetic patients were divided into three groups: diabetics without neuropathy (group 1), diabetics with peripheral neuropathy (group 2), and diabetics with peripheral and autonomic neuropathy (group 3). Resting mid-frequency (MF, 0.05–0.15 Hz) and respiration-related (RF, power around respiration rate) HRV were significantly lower in group 2 and 3 diabetics than in controls, indicating a reduced parasympathetic nervous system influence on the heart. Standing MF and RF spectral power data were significantly lower in all diabetic groups than in controls, suggesting marked alterations in the autonomic cardiovascular control during a mild physical load not only in symptomatic diabetics but also in patients with no signs and symptoms of neuropathy. The difference between supine and standing MF power, an estimate of-adrenergic influence on the heart, was significantly lower in all diabetic subject groups studied than in controls. This suggests a reduced sympathetic nervous system influence on the heart in diabetic patients. Our data suggest that computerized spectral analysis of HRV during orthostatic load seems to be a very sensitive method of evaluating of the autonomie nervous systems influence on the heart in patients suffering from diabetes niellitus.Abbreviations dB decibel - HRV heart rate variability - LF low-frequency component - MF mid-frequency component - RF respiration related frequency component