Levels of agreement for RR intervals and short-term heart rate variability obtained from the Polar S810 and an alternative system

The aim of this study was to assess the agreement between HRV measures derived from a time series of RR intervals recorded by a standard 12-lead ECG (CP) and a commercially available RR interval recorder (S810). Thirty-three participants (19 males) (median age 36, range 20-63) underwent simultaneous, 5-min, supine RR-interval recordings. Each RR interval time series was analysed using the software supplied with the recording equipment. Two comparisons were then made. First, a comparison of RR interval data recording and editing only was made. Second, comparisons were made for measures of HRV derived from edited RR interval data. Agreement between RR intervals and standard HRV measures were assessed using intraclass correlation coefficient and limits of agreement. Agreement of HRV measures derived from RR intervals recorded and edited by individual systems was not acceptable. Agreement analyses for the number of RR intervals recorded and edited by each systems software showed excellent intraclass correlation coefficients (ICC lower 95% CI > 0.75) and acceptably narrow limits of agreement (LoA). These data indicate that the number of RR intervals recorded by S810 can agree well those recorded from a standard 12-lead ECG. This is true even after application of system specific data editing procedures. Commercial RR-interval recorders may offer a simple, inexpensive alternative to full 12-lead ECG in the recording and editing of RR intervals for subsequent HRV analysis in healthy populations.     

Heart rate and heart rate variability in chicken embryos at the end of incubation

Our immediate goal was to study heart rate variability (HRV) in chicken embryos in the egg. Instantaneous heart rate data were needed for this purpose, and accordingly an ECG recording method in the egg was developed. The aim of this work was to test the hypothesis that autonomic nervous cardiac modulation, as shown from HRV parameters, is present at the end of development and that it reaches a constant value during the last days of incubation. Embryonic chicken heart rate was obtained at the final incubation period (days 19 and 20) from ECG recordings. Tachograms were computed and time- and frequency-domain indices of HRV were determined. No significant differences were found between HRV indices from day 19 and day 20. The power spectra extended in two frequency bands with centre frequency around 0.6-0.7 Hz (low frequency (LF) component), and another around 1.2-1.5 Hz (high frequency (HF) component); the latter was shown to reflect respiratory sinus arrhythmia. A relation between mean RR interval and some HRV parameters (rMSSD, pNN5 and HF power) was shown. HRV results obtained from embryonic chickens, showed the presence of modulation of cardiovascular function by the autonomic nervous system. The results suggested that sympathetic and parasympathetic activities have already reached a constant level at day 19 of incubation. High frequency oscillations (0.78-2.5 Hz) were detected and are considered to reflect respiratory sinus arrhythmia.     

Beta-adrenergic control and inter-relationships between heart rate and blood pressure in neonatal lambs

Our aim was to develop a signal analysis method for revealing interrelationships between heart rate and blood pressure and for displaying the influence of autonomic nervous control on these signals in a chronic lamb model. A chronically instrumented neonatal lamb model was made to record ECG and direct arterial blood pressure (N=15). Continuous two-minute recordings of blood pressure (BP) and ECG were digitised. The instantaneous heart rate signal (IHR) was derived from the ECG. The IHR and BP signals were bandpass filtered. Autospectra, cross-spectra, coherence spectra and phase spectra for the signals were computed to study the relative magnitudes and inter-relationships of the cardiovascular signals under normal conditions and during beta-adrenergic blockade. It was noted that both in the BP and IHR there were oscillations at the frequency of <0·1 Hz and also at the respiratory rate around 0·6 Hz. Beta-blockade reduced the oscillations of the IHR in <30-day-old lambs. It did not affect the coherence spectra or the phase lag between the signals. During quiet sleep the variability of blood pressure was decreased. In over-30-day-old-lambs the beta-blockade did not affect the variabilities of the cardiovascular parameters. These findings indicate that in neonatal lambs the sympathetic control system is a major regulator of cardiovascular interactions.     

A simple method for the routine assessment of heart-rate variation in autonomic neuropathy

A simple method is described for the rapid assessment of respiratory heart-rate variation (HRV) by making use of an EMG machine to record the RR-interval of the electrocardiogram. The built-in software for single-fibre EMG usually incorporated in modern EMG equipment is sufficient for a rapid data analysis based on the difference between the shortest and longest RR-intervals recorded over a period of 60 to 100 s. Measurements of HRV obtained by our new method correlate well with those obtained by the more tedious conventional manual measurement of an ECG recording (r = 0.88).     

心率变异和RT变异频域分析的方法学研究

心率变异作为检测自主神经系统功能平衡状态的无创性指标，日益受到重视，已成为心电信号处理中的研究热点之一。ＱＴ是心室肌复极化时间，从另一方面来反映自主神经系统的平衡状态。ＱＴ变异分析在临床应用上与心率变异分析是否有互补作用，目前这方面研究工作开展得不多。由于ＱＴ间期检测困难，一般以ＲＴ间期代替ＱＴ间期。建立了心率变异和ＱＴ变异测定方法。在采集２４ｈ心电信号后，首先要完成标志点的检测。较好地实现了心电Ｒ波标志点的检测和异位心跳的剔除，并采用以相关系数为条件的模板匹配方法检测出Ｔ波标志点。频域分析方法分别通过快速傅里叶变换法（ＦＦＴ）和自回归谱估计法（ＡＲ）实现了２４ｈ三维频谱显示图以及２４ｈＨＦ／ＬＦ和高频能量变化趋势图。以不同的频率控制受试者的呼吸，采集其心电数据，从ＲＲ间期和ＲＴ间期谱分析的结果可以看到，高频峰受到呼吸频率的调制，高频峰可能与迷走神经活动有关。这一过程也检验了心电信号采集、检测和谱分析方法的可靠性。建立的方法为今后进一步深入研究打下了基础。随着心率变异和ＱＴ变异的检测和分析技术的日趋成熟，一定会在一些疾病的早期诊断、监护及预后评估等方面发挥更大的作用     

A comparison of photoplethysmography and ECG recording to analyse heart rate variability in healthy subjects

Measures of heart rate variability (HRV) are widely used to assess autonomic nervous system (ANS) function. The signal from which they are derived requires accurate determination of the interval between successive heartbeats; it can be recorded via electrocardiography (ECG), which is both non-invasive and widely available. However, methodological problems inherent in the recording and analysis of ECG traces have motivated a search for alternatives. Photoplethysmography (PPG) constitutes another means of determining the timing of cardiac cycles via continuous monitoring of changes in blood volume in a portion of the peripheral microvasculature. This technique measures pulse waveforms, which in some instances may prove a practical basis for HRV analysis. We investigated the feasibility of using earlobe PPG to analyse HRV by applying the same analytic process to PPG and ECG recordings made simultaneously. Comparison of 5-minute recordings demonstrated a very high degree of correlation in the temporal and frequency domains and in nonlinear dynamic analyses between HRV measures derived from PPG and ECG. Our results confirm that PPG provides accurate interpulse intervals from which HRV measures can be accurately derived in healthy subjects under ideal conditions, suggesting this technique may prove a practical alternative to ECG for HRV analysis. This finding is of particular relevance to the care of patients suffering from peripheral hyperkinesia or tremor, which make fingertip PPG recording impractical, and following clinical interventions known to introduce electrical artefacts into the electrocardiogram.     

Assessment of autonomic nervous system with analysis of heart rate variability in children with spastic cerebral palsy

The purpose of this study was to investigate the function of the autonomic nervous system in children with spastic cerebral palsy (CP) through an analysis of heart rate variability (HRV) occurring with orthostatic stress. Twelve children with spastic CP and twelve normal children participated in this study. The echocardiogram (ECG) signals were recorded for 3 minutes in both the supine and 70 degrees C head-up tilt positions, and then the HRV signals underwent power spectrum analysis at each position. Two components were measured; a low- frequency (LF) component (0.05 - 0.15 Hz) primarily reflecting sympathetic activity during orthostatic stress and a high-frequency (HF) component (0.15 - 0.4 Hz) reflecting parasympathetic activity. In the supine position, there was no significant difference between any of the HRV components of the two groups. In the head-up tilt position, absolute and normalized LF were significantly increased and absolute HF was significantly decreased in the normal children (p < 0.05), but not in the children with spastic CP. The results of this study suggest that cardiac autonomic functions, such as vagal withdrawal and sympathetic activation which occur during head-up tilt position, are not sufficient to overcome the orthostatic stress arising in spastic CP children.     

Study of time reversibility/irreversibility of cardiovascular data: theoretical results and application to laser Doppler flowmetry and heart rate variability signals

Time irreversibility can be qualitatively defined as the degree of a signal for temporal asymmetry. Recently, a time irreversibility characterization method based on entropies of positive and negative increments has been proposed for experimental signals and applied to heart rate variability (HRV) data (central cardiovascular system (CVS)). The results led to interesting information as a time asymmetry index was found different for young subjects and elderly people or heart disease patients. Nevertheless, similar analyses have not yet been conducted on laser Doppler flowmetry (LDF) signals (peripheral CVS). We first propose to further investigate the above-mentioned characterization method. Then, LDF signals, LDF signals reduced to samples acquired during ECG R peaks (LDF_R(ECG) signals) and HRV recorded simultaneously in healthy subjects are processed. Entropies of positive and negative increments for LDF signals show a nonmonotonic pattern: oscillations--more or less pronounced, depending on subjects--are found with a period matching the one of cardiac activity. However, such oscillations are not found with LDF_R(ECG) nor with HRV. Moreover, the asymmetry index for LDF is markedly different from the ones of LDF_R(ECG) and HRV. The cardiac activity may therefore play a dominant role in the time irreversibility properties of LDF signals.     

Clinical evaluation of a wireless ECG sensor system for arrhythmia diagnostic purposes

In a clinical study, a novel wireless electrocardiogram (ECG) recorder has been evaluated with regard to its ability to perform arrhythmia diagnostics. As the ECG recorder will detect a “non-standard” ECG signal, it has been necessary to compare those signals to “standard” ECG recording signals in order to evaluate the arrhythmia detection ability of the new system. Simultaneous recording of ECG signals from both the new wireless ECG recorder and a conventional Holter recorder was compared by two independent cardiology specialists with regard to signal quality for performing arrhythmia diagnosis. In addition, calculated R–R intervals from the two systems were correlated. A total number of 16 patients participated in the study. It can be considered that recorded ECG signals obtained from the wireless ECG system had an acceptable quality for arrhythmia diagnosis. Some of the patients used the wireless sensor while doing physical sport activities, and the quality of the recorded ECG signals made it possible to perform arrhythmia diagnostics even under such conditions. Consequently, this makes possible improvements in correlating arrhythmias to physical activities.     

Sampling frequency of the RR interval time series for spectral analysis of heart rate variability

Spectral analysis of heart rate variability (HRV) is an accepted method for assessment of cardiac autonomic function and its relationship to numerous disorders and diseases. Various non-parametric methods for HRV estimation have been developed and extensive literature on their respective properties is available. The RR interval time series can be seen as a series of non-uniformly spaced samples. To analyse the power spectra of this series using the discrete Fourier transform (DFT), we need to interpolate the series for obtaining uniformly spaced intervals. The selection of sampling period plays a critical role in obtaining the power spectra in terms of computational efficiency and accuracy. In this paper, we shall analyse the RR interval time series from selected subjects for different sampling frequencies to compare the error introduced in selected frequency-domain measures of HRV at a constant frequency resolution for a specific duration of electrocardiogram (ECG) data. It should be pointed out that, although many other error causes are possible in the frequency-domain measures, our attention will be confined only to the performance comparison due to the different sampling frequencies. While the choice of RR interval sampling frequency (f(s)) is arbitrary, the sampling rate of RR interval series must be selected with due consideration to mean and minimum RR interval; f(s = )4 Hz was proposed for a majority of cases. This is an appropriate sampling rate for the study of autonomic regulation, since it enables us to compute reliable spectral estimates between dc and 1 Hz, which represents the frequency band within which the autonomic nervous system has significant response. Furthermore, resampled RR intervals are evenly spaced in time and are synchronized with the samples of the other physiologic signals, enabling cross-spectral estimates with these signals.     

心率波动信号的谱分析及其应用

本文从颇域角度对心率波动(HRN)信号进行分析、处理。为此,首先利用ECG经峰值检测、内插得到3HRN信号,然后对此信号施以基于AR模型的谱估计法。在正常生理情况下说明了呼吸对心率波动的作用,给出了几种不同呼吸状态下,呼吸对心率波动影响的变化。为说明正常生理状态下,心率波动的神经生理机制提供了依据,同时也为此方法的临床使用打下了一定的基础。     

Quantification of error between the heartbeat intervals measured form photoplethysmogram and electrocardiogram by synchronisation

Abstract

Currently, heartbeat intervals required for the analysis of heart rate variability (HRV) are derived from electrocardiogram (ECG). Many investigators have explored the possibility of using photoplethysmography (PPG), for the analysis of HRV. However, all these studies are based on statistical approach and have used the correlation coefficient for the comparison of HRV data obtained using ECG and PPG, which is inappropriate as the causal relationship between the R-peaks in ECG and the systolic peaks in PPG is well known in physiology. In this study, the heart beat intervals measured from PPG, are compared, beat by beat, with the corresponding beat intervals of same cardiac cycle obtained from the synchronously recorded ECG and the differences between them are taken as errors. These errors are verified to exactly match with the variations in the pulse transit times (PTTs), beat by beat. The error in the measurement of heartbeat intervals using PPG is quantified by obtaining the root mean square of the errors associated with each beat interval for a subject. The rms error, which is found to vary between 0.17 and 1.81% across the study group of 42 subjects, can be treated as insignificant, considering the nonstationary character of physiological signals. The errors are compared and interpreted with the variations in PTT. In view of these findings, PPG can be considered as a low cost, safe and more convenient alternative to ECG, as a wearable sensor outside hospital environment, for the analysis of HRV, without compromising on accuracy.     

A multichannel telemetry system for recording cardiovascular neural signals.

A multichannel telemetry system was developed for use with chronically instrumented unrestrained cats. This system can simultaneously record efferent and afferent cardiovascular neural signals, bioelectrical noise arising near the electrode recording the neural signals, EEG, ECG, and a standard calibration signal. The miniature (18 cm3), lightweight (24 g), telemeter is a five-channel, time-multiplexed, pulse width modulation (PWM)/FM device employing a high frequency subcarrier (60 kHz) and two sampling frequencies (30 kHz and 6 kHz). The device is powered by two small 120 mA . h silver oxide cells; it has an indoor transmission range of 10 m and can operate for 48 h. One channel transmits a standard signal (a square wave of 100 Hz and 200 mVp-p) used to monitor and regulate the system's performance. When the variation in either the amplitude or frequency of the standard signal is greater than 10% of the control value, the transmitted bioelectrical signals are automatically discarded.     

Comparison of pulse rate variability with heart rate variability during obstructive sleep apnea

We investigate whether pulse rate variability (PRV) extracted from finger photo-plethysmography (Pleth) waveforms can be the substitute of heart rate variability (HRV) from RR intervals of ECG signals during obstructive sleep apnea (OSA). Simultaneous measurements (ECG and Pleth) were taken from 29 healthy subjects during normal (undisturbed sleep) breathing and 22 patients with OSA during OSA events. Highly significant (p<0.01) correlations (1.0>r>0.95) were found between heart rate (HR) and pulse rate (PR). Bland-Altman plot of HR and PR shows good agreement (<5% difference). Comparison of 2 min recording epochs demonstrated significant differences (p<0.01) in time, frequency domains and complexity analysis, between normal and OSA events using PRV as well as HRV measures. Results suggest that both HRV and PRV indices could be used to distinguish OSA events from normal breathing during sleep. However, several variability measures (SDNN, RMSSD, HF power, LF/HF and sample entropy) of PR and HR were found to be significantly (p<0.01) different during OSA events. Therefore, we conclude that PRV provides accurate inter-pulse variability to measure heart rate variability under normal breathing in sleep but does not precisely reflect HRV in sleep disordered breathing.     

时频分析在心率变异性研究中的应用

心率变异(HRV)包含着心血管神经体液调节的大量信息,由于信号提取的无创性,心率变异性分析是近年生理信号分析研究的热点。鉴于动态变化或病理状态下心电信号的非平稳特性,传统的时域和频域HRV分析有一定的局限性,而时频分析法在这方面显示出其明显的优越性。目前较常用的时频分析法有短时傅里叶变换(STFT)、Wigner-Ville分布(WVD)、小波变换等。本研究系统阐述了这3种时频分析方法在HRV分析中的应用,并提出了今后的研究方向和发展前景。     

The effect of ventilation on spectral analysis of heart rate and blood pressure variability during exercise

Heart rate variability (HRV) and systolic blood pressure variability (BPV) during incremental exercise at 50, 75, and 100% of previously determined ventilatory threshold (VT) were compared to that of resting controlled breathing (CB) in 12 healthy subjects. CB was matched with exercise-associated respiratory rate, tidal volume, and end-tidal CO(2) for all stages of exercise. Power in the low frequency (LF, 0.04-0.15 Hz) and high frequency (HF, >0.15-0.4 Hz) for HRV and BPV were calculated, using time-frequency domain analysis, from beat-to-beat ECG and non-invasive radial artery blood pressure, respectively. During CB absolute and normalized power in the LF and HF of HRV and BPV were not significantly changed from baseline to maximal breathing. Conversely, during exercise HRV, LF and HF power significantly decreased from baseline to 100% VT while BPV, LF and HF power significantly increased for the same period. These findings suggest that the increases in ventilation associated with incremental exercise do not significantly affect spectral analysis of cardiovascular autonomic modulation in healthy subjects.     

Sampling frequency of the RR interval time series for spectral analysis of heart rate variability

Spectral analysis of heart rate variability (HRV) is an accepted method for assessment of cardiac autonomic function and its relationship to numerous disorders and diseases. Various non-parametric methods for HRV estimation have been developed and extensive literature on their respective properties is available. The RR interval time series can be seen as a series of non-uniformly spaced samples. To analyse the power spectra of this series using the discrete Fourier transform (DFT), we need to interpolate the series for obtaining uniformly spaced intervals. The selection of sampling period plays a critical role in obtaining the power spectra in terms of computational efficiency and accuracy. In this paper, we shall analyse the RR interval time series from selected subjects for different sampling frequencies to compare the error introduced in selected frequency-domain measures of HRV at a constant frequency resolution for a specific duration of electrocardiogram (ECG) data. It should be pointed out that, although many other error causes are possible in the frequency-domain measures, our attention will be confined only to the performance comparison due to the different sampling frequencies. While the choice of RR interval sampling frequency (f_s) is arbitrary, the sampling rate of RR interval series must be selected with due consideration to mean and minimum RR interval; f_s?=?4 Hz was proposed for a majority of cases. This is an appropriate sampling rate for the study of autonomic regulation, since it enables us to compute reliable spectral estimates between dc and 1 Hz, which represents the frequency band within which the autonomic nervous system has significant response. Furthermore, resampled RR intervals are evenly spaced in time and are synchronized with the samples of the other physiologic signals, enabling cross-spectral estimates with these signals.     

基于连续小波变换的心电信号特征提取及其仪器实现

介绍了一种用于心电信号的记录和识别的虚拟式测量和分析仪器系统，目的是要构建一种基于PC的虚拟仪器．能够实现十二导联心电信号的同步记录、同步整体观察及测量12导联同一心动周期的波形，从而提高心电参数测量的准确性。同时，由于Mexican hat小波特有的时域特性，对QRS波群具有很好的定位特性和分析精度，因此在本仪器中利用连续小波变换，选用Mexicanhat作为小波基，对心电信号中的特征信息进行精确检测，并给出准确的心电信号特征描述参数。对临床实测心电信号的分析表明，即使在有严重噪声干扰的情况下，本方法也很容易实现对心电信号特征信息的精确描述，并且具有很高的实时性，从而在本仪器中获得了实际和有效的应用。