Nonstationarity and duration of the cardiac interval time series in assessing the functional state of operator personnel

The influence of nonstationarity in the time series of cardiac intervals on the assessment of the functional state (FS) of operator personnel was analyzed with a three-factor model of heart rhythm variability (HRV). ECG recordings were made in supine position at rest and in the sedentary position before and after important operator testing. In all three cases, the FS assessments were not influenced by nonstationarity of the input data. The effect of nonstationarity was also negligible for some particular HRV indices. Reliable assessments could be obtained from relatively short samples (256 down to 32 RR intervals) with prior norming of the factor indices for the corresponding segment length. The influence of the time series duration on the HRV indices was examined in various FSs; stable indices and proper recording conditions were determined.     

Heart rate and heart rate variability in pregnant warmblood and Shetland mares as well as their fetuses

Heart rate (HR) is an important parameter of fetal well-being. In horses, HR and heart rate variability (HRV) can be determined by fetomaternal electrocardiography (ECG) from mid-pregnancy to foaling. Normal values for physiological parameters in larger breeds are often used as reference values in ponies. However, HR increases with decreasing size of the animal and in ponies is higher than in warmblood horses. It is not known if fetal HR is affected by breed and if values obtained in larger breeds can be used to assess Shetland fetuses. We have determined fetomaternal beat-to-beat (RR) interval (inversely correlated to HR) and HRV in warmblood (n=6) and Shetland pregnancies (n=7) at days 280 and 300 of gestation by ECG. Maternal RR interval was lower in pony than in warmblood mares (day 280: Shetland: 958±110, warmblood: 1489±126ms, p<0.01) The SDRR (standard deviation of RR interval) and the RMSSD (root mean square of successive RR differences) did not differ between breeds at any time. Also RR interval as well as HRV did not differ between warmblood and pony fetuses (RR interval day 280: Shetland: 606±39, warmblood: 589±38ms). In conclusion, although maternal RR interval is clearly higher in Shetland than in warmblood mares, fetal RR interval in the two breeds is on the same level.     

Automatic filtering of outliers in RR intervals before analysis of heart rate variability in Holter recordings: a comparison with carefully edited data

Background  

Undetected arrhythmic beats seriously affect the power spectrum of the heart rate variability (HRV). Therefore, the series of RR intervals are normally carefully edited before HRV is analysed, but this is a time consuming procedure when 24-hours recordings are analysed. Alternatively, different methods can be used for automatic removal of arrhythmic beats and artefacts. This study compared common frequency domain indices of HRV when determined from manually edited and automatically filtered RR intervals.     

Comparison of three methods for beat-to-beat-interval extraction from continuous blood pressure and electrocardiogram with respect to heart rate variability analysis.

In recent years the analysis of heart rate variability (HRV) has become a suitable method for characterizing autonomous cardiovascular regulation. The aim of this study was to investigate the differences in HRV estimated from continuous blood pressure (BP) measurement by different methods in comparison to electrocardiogram (ECG) signals. The beat-to-beat intervals (BBI) were simultaneously extracted from the ECG and blood pressure of 9 cardiac patients (10 min, Colin system, 1000-Hz sampling frequency). For both data types, slope, peak, and correlation detection algorithms were applied. The short-term variability was calculated using concurrent 10-min BP and ECG segments. The root mean square errors in comparison to ECG slope detection were: 1.74 ms for ECG correlation detection; 5.42 ms for ECG peak detection; 5.45 ms for BP slope detection; 5.75 ms for BP correlation detection; and 11.96 ms for BP peak detection. Our results show that the variability obtained with ECG is the most reliable. Moreover, slope detection is superior to peak detection and slightly superior to correlation detection. In particular, for ECG signals with higher frequency characteristics, peak detection often exhibits more artificial variability. Besides measurement noise, respiratory modulation and pulse transit time play an important role in determining BBI. The slope detection method applied to ECG should be preferred, because it is more robust as regards morphological changes in the signals, as well as physiological properties. As the ECG is not recorded in most animal studies, distal pulse wave measurement in combination with correlation or slope detection may be considered an acceptable alternative.     

SNPs Identified as Modulators of ECG Traits in the General Population Do Not Markedly Affect ECG Traits during Acute Myocardial Infarction nor Ventricular Fibrillation Risk in This Condition

Background

Ventricular fibrillation (VF) in the setting of acute ST elevation myocardial infarction (STEMI) is a leading cause of mortality. Although the risk of VF has a genetic component, the underlying genetic factors are largely unknown. Since heart rate and ECG intervals of conduction and repolarization during acute STEMI differ between patients who do and patients who do not develop VF, we investigated whether SNPs known to modulate these ECG indices in the general population also impact on the respective ECG indices during STEMI and on the risk of VF.

Methods and Results

The study population consisted of participants of the Arrhythmia Genetics in the NEtherlandS (AGNES) study, which enrols patients with a first STEMI that develop VF (cases) and patients that do not develop VF (controls). SNPs known to impact on RR interval, PR interval, QRS duration or QTc interval in the general population were tested for effects on the respective STEMI ECG indices (stage 1). Only those showing a (suggestive) significant association were tested for association with VF (stage 2). On average, VF cases had a shorter RR and a longer QTc interval compared to non-VF controls. Eight SNPs showed a trend for association with the respective STEMI ECG indices. Of these, three were also suggestively associated with VF.

Conclusions

RR interval and ECG indices of conduction and repolarization during acute STEMI differ between patients who develop VF and patients who do not. Although the effects of the SNPs on ECG indices during an acute STEMI seem to be similar in magnitude and direction as those found in the general population, the effects, at least in isolation, are too small to explain the differences in ECGs between cases and controls and to determine risk of VF.     

Inheritance of heart rate variability: the kibbutzim family study

Heart rate variability (HRV) measures are associated with coronary heart disease incidence and mortality. Therefore insight into the genetic and environmental determinants of these measures may have clinical relevance. We assessed the role of genetic and environmental factors of time domain and frequency domain HRV indices. Participants were 451 kibbutz members, aged 15 and up, belonging to 80 families. HRV indices were calculated from Holter recordings measured over 5 min. Our data indicate that for the two time- and four frequency domain indices, a mixture of two normal distributions fit the data significantly better than a single normal distribution (P<0.05). We used complex segregation analysis to infer the modes of inheritance of these HRV measures. We found evidence for possible involvement of a recessive major gene in the inheritance of the root mean square of successive differences in RR intervals (RMSSD), which is predominantly vagally mediated. A putative major gene explains 28%-34% of the adjusted inter-individual variability. The SD, determined by a mixture of mechanisms, is influenced by environmental and polygenic effects, but not by a major gene. The findings regarding the heritability of the frequency domain indices were not conclusive. However, the involvement of genetic factors was not rejected. Additional studies in extended families are needed to confirm the involvement of major genes in the determination of the autonomic activity.     

Breathing cardiovascular variability and baroreflex in mechanically ventilated patients

Heart rate and blood pressure variations during spontaneous ventilation are related to the negative airway pressure during inspiration. Inspiratory airway pressure is positive during mechanical ventilation, suggesting that reversal of the normal baroreflex-mediated pattern of variability may occur. We investigated heart rate and blood pressure variability and baroreflex sensitivity in 17 mechanically ventilated patients. ECG (RR intervals), invasive systolic blood pressure (SBP), and respiratory flow signals were recorded. High-frequency (HF) amplitude of RR and SBP time series and HF phase differences between RR, SBP, and ventilatory signals were continuously computed by Complex DeModulation (CDM). Cross-spectral analysis was used to assess the coherence and the gain functions between RR and SBP, yielding baroreflex sensitivity indices. The HF phase difference between SBP and ventilatory signals was nearly constant in all patients with inversion of SBP variability during the ventilator cycle compared with cycling with negative inspiratory pressure to replicate spontaneous breathing. In 12 patients (group 1), the phase difference between RR and ventilatory signals changed over time and the HF-RR amplitude varied. In the remaining five patients (group 2), RR-ventilatory signal phase and HF-RR amplitude showed little change; however, only one of these patients exhibited a RR-ventilatory signal phase difference mimicking the normal pattern of respiratory sinus arrhythmia. Spectral coherence between RR and SBP was lower in the group with phase difference changes. Positive pressure ventilation exerts mainly a mechanical effect on SBP, whereas its influence on HR variability seems more complex, suggesting a role for neural influences.     

Influence of recognition errors of computerised analysis of 24-hour electrocardiograms on the measurement of spectral components of heart rate variability

Spectral methods for the assessment of heart rate variability (HRV) in 24-h electrocardiogram (ECG) are believed to require visual verification and manual editing of the computerised recognition of the ECG. This study investigated the effect of the recognition errors of computerised ECG recognition on two methods providing spectral HRV indices: (a) Fast Fourier Transformation (FFT); and (b) peak-to-trough analysis (PTA). Both methods were used to measure HRV spectra in 24-h ECGs recorded in 557 survivors of acute myocardial infarction. Each ECG was analysed using the Marquette 8000 Holter system and spectral HRV analyses were performed both prior to and after manual verification of the automatic ECG analysis. The FFT and PTA methods were used to calculate the low (0.04-0.15 Hz), medium (0.15-0.40 Hz) and high (0.40-1.00 Hz) HRV spectral components. For each method and for each spectral component, the rank correlations between the results obtained from unedited and edited ECG recognition were calculated. The correlations between the corresponding spectral components provided by the FFT and PTA methods applied to the edited recognitions were also calculated. Both methods were substantially affected by recognition errors. The FFT method was more sensitive to the misrecognition than the PTA method. The inter-method correlations were higher for the high and medium spectral components than for the low spectral component. The study suggests that spectral HRV analysis should be performed only on carefully verified and manually corrected recognitions of long-term electrocardiograms.     

呼吸模式对心血管变异性非线性特性的影响

目的研究不同呼吸模式对心血管调节系统的影响。方法对16名健康的大学生采集心电、血压和呼吸信号,采用频谱分析方法和基于Volterra—Wiener级数的非线性方法分析自主呼吸、控制呼吸和屏气对心血管调节的影响。结果与自主呼吸模式相比,10次／分钟的控制呼吸使心率变异性的非线性特性定性和定量上均显著降低,而自主呼吸节律的控制呼吸的非线性特性定性上无显著差异,但定量上仍然显著降低。这些结果提示自主呼吸是保持心肺耦合的最优呼吸模式。     

Significance of the statistical characteristics of the sinus rhythm of the heart

Statistical analysis of prolonged continuous recordings of the ECG RR intervals was carried out in 64 patients with purulent surgical infection. The following indices were considered: the mean value of the RR intervals, the mean quadratic deviation (delta), the variation amplitude, the 1st and the 3rd correlation coefficients, the excess, asymmetry, the RR/delta ratio. Besides, the size and the shape of the autoregression could was analyzed. Statistically significant differences of the RR/delta ratio, of the mean quadratic deviation, and of the variation amplitude were revealed in 3 groups of patients differing by the severity of condition. These differences were reflected in the size and shape of the autoregression cloud. The results obtained suggest that statistical characteristics of prolonged recordings of the cardiac rhythm could be used for objective assessment of the severity of the patient's condition and of the therapeutic effect in the patients with a purulent surgical infection.     

Identifying physiological measurements for medical monitoring: implications for autonomous health care in austere environments

In a patient who has lost a significant amount of blood, avoiding cardiovascular collapse and impending circulatory shock depends on the ability to maintain adequate arterial blood pressure in the presence of significant central hypovolemia. Our analysis of hemodynamic, autonomic, and metabolic data obtained from healthy human subjects exposed to progressive reduction in central blood volume and supported by data from trauma patients provide evidence to support the following conclusions: 1. Because of autonomically-mediated compensatory mechanisms, standard vital signs can remain unchanged or change too late, when cardiovascular collapse is imminent. 2. Currently proposed closed-loop resuscitation and oxygen delivery systems controlled by arterial blood pressure and SpO2 may prove inadequate for early intervention decision-support. 3. Continuous capture of PP, ECG R-wave amplitude, indices of HRV, cardiac BRS, and/or muscle PO2 could improve the sensitivity of closed-loop resuscitation and oxygen delivery by providing earlier indications of clinical status.     

Natural environmental associations in a 50-day human electrocardiogram

Meteorotropic associations of heart rate (HR) and HR variability (HRV) were investigated in a clinically healthy 48-year-old man in Kiev. His electrocardiogram (ECG) was determined over 50 days by fitting him with an ambulatorily wearable device; various natural physical environmental variables were also monitored. The mean inter-beat interval, the standard deviation of these intervals, the spectral power in several frequency ranges, the power ratio of the approx. 10.5-s/approx. 3.6-s spectral components and other aspects of HRV were computed over consecutive 14.4-min intervals. Together with ordinary meteorological variables, geomagnetic disturbances (GMD) and fluctuations of atmospheric pressure (FAP) in the range 0.01–0.10 Hz (10–100 s) were measured. The assessable infradian spectra (with frequencies lower than 1 cycle/28 hours) of all HRV parameters showed two major components with periods of about 3.5 and 10 days. Two environmental variables, FAP and wind speed (with which FAP is closely related), revealed both of these rhythms and showed the greatest cross-spectral coherence (0.70–0.98) with corresponding oscillations of HRV. Less specific but statistically significant product-moment correlations with major HRV indices were also found; most of these were with FAP, but correlations with air temperature, humidity, wind speed and geomagnetic disturbances were also found. Long-term ECG recording, essential in the detection of infradian rhythms, proved to be sensitive to physical environmental variables, notably meteorological ones. FAP, usually neglected since its role has not been considered in previous biometeorological studies, or some factor closely related to FAP is probably involved in synchronizing or influencing the approximately 3.5-day HR and HRV rhythms in humans. Received: 27 July 2000 / Revised: 13 November 2000 / Accepted: 28 November 2000     

Dysregulation of Autonomic Control of Cardiac Function in Workers at am Broadcasting Stations (0.738–1.503 MHz)

Ninety-three adult males working at AM broadcasting stations (0.738–1.503 MHz) or radio line stations volunteered for cardiological examinations. The examinations included routine electrocardiogram (ECG) at rest, analysis of heart rate variability (HRV), Holter 24-h ECG, and 24-h ambulatory blood pressure (ABP). Results of cardiological examinations were correlated with individual exposure to EM fields (maximum exposure levels during working shift, daily exposure dose, and cumulative lifetime exposure). Of the 93 subjects qualified for the study, 71 (76.3%) experienced occupational RF exposure, while the remaining 22 (23.7%) had no history of regular EM exposure. ECG abnormalities or pathological changes were recorded quite frequently (50–70%) in both exposed and control populations. There was no correlation with exposure levels. We found measurable effects in the HRV and ABP parameters in the EM-exposed population, but none could be assigned clinical significance. The results suggest that exposure of workers to EM fields can cause slight disturbances in autonomic cardiac regulation and slight dysregulation of circadian rhythms in workers exposed to EM fields exceeding 100–150 V/m.     

Cortisol and progestin release, heart rate and heart rate variability in the pregnant and postpartum mare, fetus and newborn foal

The mechanisms leading to parturition in the horse in many aspects differ from those in other species. Pregnancy is maintained not by progesterone but by 5α-pregnanes and the progestin precursor pregnenolone originates from the fetus. As parturition approaches, the fetal adrenal switches from pregnenolone to cortisol synthesis but it is not known whether cortisol crosses the placenta. We hypothesized that in parallel to fetal cortisol release, cortisol in the maternal circulation increases before foaling and this increase can be determined in both saliva and plasma. In addition, maternal, fetal and neonatal heart rate and heart rate variability were measured. In 25 pregnant mares, saliva for cortisol analysis was collected 4 times daily from 15 days before to 5 days after foaling. In 13 mares, in addition, fetomaternal electrocardiogram (ECG) recordings were made and blood samples for progestin and cortisol analysis were collected once daily. Heart rate (HR) was recorded until 5 days after foaling. The heart rate variability (HRV) variables standard deviation of the beat-to-beat (RR) interval (SDRR) and root mean square of successive RR differences (RMSSD) were calculated. From Days 15 to 4 before parturition, progestin concentration increased (peak 267 ± 42 ng/mL) and decreased thereafter (P < 0.05, day of foaling 113 ± 18 ng/mL). A prepartum increase in maternal cortisol concentrations was evident in blood (P < 0.05) and saliva (P < 0.05) and paralleled the decrease in progestin concentrations. In mares, HR remained constant during the last days of pregnancy but decreased within one day after parturition (P < 0.05) while maternal HRV did not change. In the fetus and neonate, HR increased from before to after birth (P < 0.05) indicating increasing demands on the cardiovascular system with adaptation to extrauterine life.     

Assessment of autonomic cardiovascular indices in non-stationary data in rats

The analysis of heart rate in the frequency domain has become increasingly important in physiological studies, and supports the use of heart rate variability as an index of autonomic cardiovascular control. A new index, the instant centre frequency (ICF) has been proposed as a global index of the instantaneous relationship between sympathetic and vagal modulation. The aim of this study was to assess ICF, RR intervals, and heart rate variability measures as indices of sympathovagal balance during a pharmacological blockade of the autonomic nervous system in normotensive rats. RR intervals and arterial blood pressure of 10 conscious Wistar rats equipped with telemetry probes, were evaluated before, during, and after injection of: (1) saline (100 microl kg(-1) i.v.); (2) phentolamine (5 mg kg(-1) i.v.); (3) atropine methyl nitrate (0.5 mg kg(-1) i.v.); and (4) atenolol (1 mg kg(-1) i.v.). RR interval series were analysed by the smoothed pseudo-Wigner-Ville distribution. A general linearised model was used to evaluate the parameters. ICF was calculated in the same way as the peak power frequency by use of the first moment of instant spectrum. We calculated the ICF of the whole spectrum (ICF(T)), ICF in high frequency (ICF(H)) and ICF in low frequency (ICF(L)). The RR intervals and ICF indexes varied similarly and presented the lowest coefficient of variation among animals exposed to the same autonomic conditions. ICF(T)-ICF(L) and ICF(H)-ICF(T) were strongly correlated with normalised HF and normalised LF. In normotensive rats, RR intervals and ICF indices may reliably capture the effects of the sympathetic and parasympathetic nervous system on the sinus node.     

The circadian rhythm of selected parameters of heart rate variability

At present, two main circadian oscillators are known, responsible for the rhythm of body temperature (BT) and body activity. Their independence has been demonstrated by the dissociation of these two rhythms in people during long-term isolation. In order to ascertain the circadian rhythm (CR) of heart rate variability (HRV), the ECG was recorded in 24 healthy awake men every two hours in the sitting position, from Friday 5 p.m. to Monday 6 a.m., who were maintained on a standard regime. One hundred consecutive RR intervals in every ECG were measured and from these 11 selected indicators of HRV were computed. Chronograms from the means of BT, respiratory rate, and electrical skin resistance showed pronounced CR with acrophases at 6 to 8 p.m. "Frequency" parameters of HRV, especially the frequency of reversal points, behaved similarly. CR in the remaining 7 "amplitude" parameters was also detected in individual persons, but their acrophases were different, and averaged chronograms mostly exhibited a flat course. The study has shown that there are at least two circadian components of HRV: the first phase has the CR synchronized with BT and is interindividually more homogeneous; the second phase is synchronized with body activity rhythm and is interindividually heterogeneous. On this basis, three equal subgroups of subjects arose, tentatively called afternoon, night, and forenoon types, respectively, in accordance with information about their preference for working and sleeping.     

Estimation of spontaneous baroreflex sensitivity using transfer function analysis: effects of positive pressure ventilation.

To determine the short-term effects of non-invasive positive pressure ventilation (PPV) on spontaneous baroreflex sensitivity, we acquired time series of RR interval and beat-to-beat blood pressure in 55 healthy volunteers (mean age 46.5+/-10.5 years), who performed breathing tests on four occasions at frequencies of 12 and 15/min, with application of PPV of 5 mbar, and without positive pressure (control). Using spectral and transfer function analysis, we estimated RR interval variability (HRV) and systolic blood pressure variability (SBPV), as well as the gain (alpha-index) and phase shift (Phi) of the baroreceptor reflex for low- (LF) and high-frequency (HF) bands. Compared to control breathing, PPV at 12 and 15/min led to an increase in mean RR (p<0.001) and blood pressure (p<0.05). The alpha-index in the HF band increased significantly due to PPV for both respiratory frequencies (p<0.05). Phase shifts did not show significant changes in response to pressure ventilation. These results indicate that short-term administration of PPV in normal subjects elicits significant enhancement in the HF index of baroreflex gain. These findings may contribute to understanding the mechanisms, indications, and effectiveness of positive pressure breathing strategies in treating cardiorespiratory and other disease conditions.     

An Efficient Automated Algorithm for Distinguishing Normal and Abnormal ECG Signal

ObjectiveThe present study aims to simulate an alarm system for online detecting normal electrocardiogram (ECG) signals from abnormal ECG so that an individual's heart condition can be accurately and quickly monitored at any moment, and any possible serious dangers can be prevented.Materials and methodsFirst, the data from Physionet database were used to analyze the ECG signal. The data were collected equally from both males and females, and the data length varied between several seconds to several minutes. The heart rate variability (HRV) signal, which reflects heart fluctuations in different time intervals, was used due to the low spatial accuracy of ECG signal and its time constraint, as well as the similarity of this signal with the normal signal in some diseases. In this study, the proposed algorithm provided a return map as well as extracted nonlinear features of the HRV signal, in addition to the application of the statistical characteristics of the signal. Then, artificial neural networks were used in the field of ECG signal processing such as multilayer perceptron (MLP) and support vector machine (SVM), as well as optimal features, to categorize normal signals from abnormal ones.ResultsIn this paper, the area under the curve (AUC) of the ROC was used to determine the performance level of introduced classifiers. The results of simulation in MATLAB medium showed that AUC for MLP and SVM neural networks was 89.3% and 94.7%, respectively. Also, the results of the proposed method indicated that the more nonlinear features extracted from the ECG signal could classify normal signals from the patient.ConclusionThe ECG signal representing the electrical activity of the heart at different time intervals involves some important information. The signal is considered as one of the common tools used by physicians to diagnose various cardiovascular diseases, but unfortunately the proper diagnosis of disease in many cases is accompanied by an error due to limited time accuracy and hiding some important information related to this signal from the physicians' vision leading to the risks of irreparable harm for patients. Based on the results, designing the proposed alarm system can help physicians with higher speed and accuracy in the field of diagnosing normal people from patients and can be used as a complementary system in hospitals.     

Non-linear dynamic analysis of the cardiac rhythm during transient myocardial ischemia.

Coronary artery occlusions related to myocardial ischemia drive cardiac control system reactions that may lead to heart failure. The purpose of this study was to assess the autonomic nervous system (ANS) response during prolonged percutaneous transluminal coronary angioplasty (PTCA). Continuous ECG data were acquired from 50 patients before and during PTCA, with occlusions in the left anterior descending, left circumflex or right coronary artery. Heart rate variability (HRV) was analyzed for 3-min segments of the R-R interval signal obtained from ECG data. The ANS behavior was evaluated by HRV analysis using fractal-like indices. The fractal scalar exponent alpha(1) and power-law slope beta decreased considerably during PTCA. This indicates that significant reactions of autonomic control of the heart rate occurred during coronary artery occlusions, with a reduction in complexity of the ANS.