Analysis Of Heart Rate Fluctuations Research Articles

Symbolic analysis of heart rate fluctuations identifies cardiac autonomic modifications during LPS-induced endotoxemia.

The present study aimed to compare linear and symbolic dynamics (SD) indices for detecting the autonomic cardiac changes produced by endotoxemia in freely-moving rats. In this context, we analyzed ECG-derived R-R time series in freely moving Dark Agouti rats, which received lipopolysaccharide (LPS, n = 9), or vehicle (V, n = 7). Five minutes R-R time series were assessed every hour up to +12 h and + 24 h post-LPS injection. We found that SD indices showed significant differences at +7 h between V vs. LPS groups and at +9 h between basal levels of LPS (-3 h) and post-LPS injection (pre-LPS vs. post-LPS). In general, SD seems more appropriate than linear indices to evaluate the autonomic changes of endotoxemic rats. Overall, the symbolic parameters detected decreased R-R variability and complexity, which indicate a modification of the autonomic regulation during LPS-induced endotoxemia. This modification is probably related to a reduced activity of the cholinergic anti-inflammatory pathway at the long term.

Spectrum Analysis of Heart Rate Fluctuations in Hatched and Unhatched Prenatal Chick Embryos

Instantaneous heart rate (IHR) was continuously measured in six hatched embryos and three unhatched embryos. Spectrum analysis of IHR was performed to determine indices of the sympathetic and parasympathetic nervous system activity and a spectrum gradient α (1/f α ). Developmental patterns of HR and HR fluctuations (HRFs) in successfully hatched embryos were elucidated. Developmental patterns and/or HRFs of unhatched embryos were different compared with those of normally hatched embryos. Although baseline HR and cyclic mean HR changes in unhatched embryos were similar to those in normally hatched embryos, indices of the autonomic nervous system and the spectrum gradient were distinctly different. These results imply abnormal physiological development of embryos could be speculated using time-series and spectrum analyses. In addition, characteristic HR changes occurred before embryonic death. Such HRFs may be a distinctive phenomenon of hypoxia. However, whether distinctive HRFs exist in hypoxia should be assessed in further research.

Comprehensive multilevel in vivo and in vitro analysis of heart rate fluctuations in mice by ECG telemetry and electrophysiology.

The normal heartbeat slightly fluctuates around a mean value; this phenomenon is called physiological heart rate variability (HRV). It is well known that altered HRV is a risk factor for sudden cardiac death. The availability of genetic mouse models makes it possible to experimentally dissect the mechanism of pathological changes in HRV and its relation to sudden cardiac death. Here we provide a protocol that allows for a comprehensive multilevel analysis of heart rate (HR) fluctuations. The protocol comprises a set of techniques that include in vivo telemetry and in vitro electrophysiology of intact sinoatrial network preparations or isolated single sinoatrial node (SAN) cells. In vitro preparations can be completed within a few hours, with data acquisition within 1 d. In vivo telemetric ECG requires 1 h for surgery and several weeks for data acquisition and analysis. This protocol is of interest to researchers investigating cardiovascular physiology and the pathophysiology of sudden cardiac death.

Cerebral correlates of heart rate variations during a spontaneous panic attack in the fMRI scanner

We report the first published case study of a suddenly occurring panic attack in a patient with no prior history of panic disorder during combined functional magnetic resonance imaging (fMRI, 1.5 Tesla) and electrocardiogram (ECG) recording. The single case was a 46-year-old woman who developed a panic attack near the planned end of the fMRI acquisition session, which therefore had to be aborted. Correlational analysis of heart rate fluctuations and fMRI data revealed a significant negative association in the left middle temporal gyrus. Additionally, regions-of-interest (ROI) analyses indicated significant positive associations in the left amygdala, and trends towards significance in the right amygdala and left insula.

Repeatability of heart rate variability in congenital hypothyroidism as analysed by detrended fluctuation analysis

The analysis of heart rate fluctuations, or heart rate variability (HRV), may be applied to explore children's neurodevelopment. However, previous studies have reported poor reliability (repeatability) of HRV measures in children at rest and during light exercise. Whether the reliability can be improved by controlling variables such as physical activity, breathing rate and tidal volume, or by selecting non-conventional techniques for analysing the data remains as an open question. We evaluated the short-term repeatability of RR-interval data from medicated children with congenital hypothyroidism (CH). The α1 exponents, obtained by detrended fluctuation analysis (DFA), from the data of 21 children collected at two different sessions were compared. Elapsed days between sessions were 59 ± 33, and data were obtained during 10 min, trying to restrict the children's activity while being seated. We found statistical agreement between the means of α1 exponents for each session (p = 0.94) and no bias with a low-coefficient variation (9.1%); an intraclass correlation coefficient ri = 0.48 ([0.14 0.72], 95% confidence interval) was also estimated. These findings, which were compared with results obtained by conventional time and frequency techniques, indicate the existence of agreement between the α1 exponents obtained at each session, thereby providing support concerning the repeatability of HRV data as analysed by DFA in children with congenital hypothyroidism. Of particular interest was also the agreement found by using the central frequency of the high-frequency band and the parameter pNN20, both showing better or similar ri than α1 (0.77 [0.57 0.89] and 0.51 [0.17 0.74], respectively), yet considerably better repeatability than other conventional time and frequency parameters.

Postural sway and diabetic peripheral neuropathy

The focus of this paper is to evaluate the relationship between postural sway assessed by a gravicorder and peripheral neuropathy in patients with type 2 diabetes. Posturography (GRAVICHART), electrophysiological tests, and power spectrum analysis of heart rate fluctuations were performed in the following age-matched subjects: 123 type 2 diabetic patients without peripheral neuropathy, 32 type 2 diabetic patients with peripheral neuropathy, and 55 healthy control subjects. All diabetic patients with a history of clinical neurological dysfunction were excluded from the study. Significant correlations were found between parameters of GRAVICHART and some parameters of the electrophysiological tests as well as the parameters of heart rate variability. The envelope area and the length per time were larger in type 2 diabetic patients with peripheral neuropathy than in patients without peripheral neuropathy and the control subjects. There were no significant differences in the GRAVICHART parameters between diabetic patients without neuropathy and the healthy control subjects. Type 2 diabetic patients with peripheral neuropathy exhibited an inability to maintain an upright posture. The GRAVICHART can indicate the early stage of postural balance impairment.

Capsaicin increases modulation of sympathetic nerve activity in rats: measurement using power spectral analysis of heart rate fluctuations.

We assessed the sympatho-vagal activities of the heart after administration of capsaicin by measuring the power spectral analysis in rats. There were major two frequency components of heart rate variability, which we defined as high (1.0 Hz <, HF) and low (LF, < 1.0 Hz) frequency components. Vagal blockade by atropine abolished the high frequency component, and lowered the amplitude of the low frequency component. On the other hand, under conditions of sympathetic blockade by propranolol, the low frequency component was reduced. Combined vagal and sympathetic blockade abolished all heart rate fluctuations. We analyzed the low and high frequency components by integrating the spectrum for the respective band width. The rats administered capsaicin had a higher heart rate and sympathetic nervous system index (LF/HF) than the control group of rats. These results suggest that power spectral analysis is an effective and noninvasive method for detecting subtle changes in autonomic activity in response to the intake of foods or drugs.

Prediction of the outcome of electrophysiologic study using nonlinear dynamic analysis of heart rate fluctuations

It has been reported that nonlinear deterministic methods can be used as diagnostic and prognostic tools to determine the state of health of cardiac arrhythmia. The accuracy of the methods and consequently the application to cardiac arrhythmia is in doubt because the current methods for detecting deterministic chaos in a time series require long and stationary data records. In addition, most of these methods assume that the observed dynamics arise only from the internal, deterministic workings of the system, and the stochastic portion of the signal (the noise component) is assumed to be negligible. As a consequence, many of the existing methods for detecting and quantifying chaotic dynamics will give erroneous results when applied to actual clinical data. To explicitly account for the stochastic part of the data we have recently developed a method based on the Stochastic Nonlinear Autoregressive (SNAR) algorithm (9). The method iteratively estimates NAR models for both the deterministic and stochastic portions of the signal. Subsequently, Lyapunov exponents (LE) are calculated for the estimated models to examine if chaotic determinism (i.e., sensitivity to initial conditions) is present in the time series. Due to specific modeling of the stochastic portion of the contaminated signal, the SNAR algorithm has been shown to be more accurate than most other methods in detecting nonlinear dynamics even in conditions of short and noisy time series. We show several computer simulation examples to demonstrate the efficacy of the SNAR method. To determine if nonlinear dynamic analysis of heart rate fluctuations can be used to assess arrhythmia susceptibility by predicting the outcome of invasive cardiac electrophysiologic study (EPS), we applied the SNAR algorithm to non-invasively measured resting sinus-rhythm heart-rate signals obtained from 16 patients. Our analysis revealed that a positive LE was correlated to a patient with a positive outcome of EPS. We found that the statistical accuracy of the SNAR algorithm in predicting the outcome of EPS was 83% (sensitivity=100%, specificity=75%, positive predictive value=80%, negative predictive value=100%, p=0.0019). Our results suggest that the SNAR algorithm may serve as a non-invasive probe for screening high-risk populations for malignant cardiac arrhythmias.

Spectral analysis of heart rate fluctuations and optimum thermal management for low birth weight infants.

Spectral analysis of heart rate variability is studied in 10 healthy growing premature infants to investigate the changes in autonomic balance achieved as a function of changes in skin temperature. Heart rate is obtained from ECG recordings and the power spectrum of beat-to-beat heart rate fluctuations is computed. The infants maintain mean rectal temperature within 36.3-37.2 degrees C, while skin temperature changes. The respiratory rate does not change at the different servocontrol set points. Heart rate is found to increase slightly, but consistently. The low-frequency band (0.02-0.2 Hz), reflecting the interplay of the sympathetic and parasympathetic tone and known to be maximum at the thermoneutral zone, is maximum at 35.5 and 36 degrees C and decreases gradually to a lower level at a servocontrol temperature of 36.5-37 degrees C. The high-frequency band (0.2-2.0 Hz), coinciding with the respiratory peak and reflecting parasympathetic activity, is significantly elevated at 36 degrees C (p < 0.01). The minimum low: high ratio, indicating the minimum sympathetic-parasympathetic balance and possibly reflecting the most comfortable conditions, occurs at 36 degrees C, although the differences are not statistically significant. Servocontrol skin temperature may thus be adapted, and possibly selected at 36 degrees C for growing premature infants in an attempt to achieve thermal comfort and more balanced autonomic activity.

Time-Frequency Analysis of Heart Rate Fluctuations during Carotid Surgery Using the Short Term Fourier and Fast Wavelet Transforms

Time-Frequency Analysis of Heart Rate Fluctuations during Carotid Surgery Using the Short Term Fourier and Fast Wavelet Transforms

The effects of lidocaine on cardiac parasympathetic control in normal subjects and in subjects after myocardial infarction.

It has been widely accepted that lidocaine has little or no effect on the autonomic nervous system. However, we have previously shown that in dogs with vagally induced atrial fibrillation, lidocaine has a pronounced parasympatholytic effect. To study the possible effect of lidocaine on autonomic cardiac control in humans, we performed spectral analysis of heart rate fluctuations in 19 healthy volunteers, who received an i.v. bolus of lidocaine (1.4 mg/kg), as well as in 13 patients suffering from acute inferior myocardial infarction (IMI) and 13 patients suffering from acute anterior myocardial infarction (AMI), who received therapeutic doses of i.v. lidocaine infusion (4 mg/min). Heart rate variability and respiratory pattern were monitored according to a predetermined protocol, with and without lidocaine. Computing the heart rate power spectrum and integrating over predetermined frequency bands, we focused mainly on the respiratory frequency band, known to predominantly reflect parasympathetic control. The administration of lidocaine resulted in a significant overall increase in mean heart rate: for the healthy control group an increase of 5.5 +/- 2.2% (mean +/- SE), for the IMI group an increase of 9.4 +/- 3.5%, and for the AMI group an increase of 8.1 +/- 2.9% (p < 0.01 for all). Simultaneously, following the administration of lidocaine, there was a decrease in the power of respiratory fluctuations: for the healthy control group a decrease of 38.4 +/- 12.5%, for the IMI group a decrease of 46.3 +/- 32.9%, and for the AMI group a decrease of 33.9 +/- 16.2% (p < 0.01 for all). These findings indicate that lidocaine has a consistent and significant parasympatholytic effect on the human heart, in healthy volunteers as well as in patients in the acute phase of myocardial infarction.

Sympathetic-Parasympathetic Activation During Spontaneous Attacks of Cluster Headache: Evaluation by Spectral Analysis of Heart-Rate Fluctuations

Twenty-four hour ECG Holter and blood-pressure monitorings were performed in eight patients suffering from cluster headache. Spectral analysis of heart-rate fluctuation was used to assess the autonomic balance under basal conditions, after head-up tilt, and during a spontaneous attack. Normal autonomic balance was found at rest and during sympathetic activation obtained with head-up tilt in the interparoxysmal period. Before the onset of headache, an increase in the low-frequency (LF) component of the power spectrum was apparent in all patients. This sign of sympathetic activation was followed by an increase in the high-frequency (HF) component that developed about 2000 beats after the onset of headache and rapidly overcame the LF component until the end of pain. Significant differences were found when comparing the spectral parameters [total spectral values (TP), power of the LF and HF components and LF/HF ratio] obtained before, during and after headache. During the attack, blood pressure increased and heart rate decreased in all subjects. There appears to be a primary activation of both sympathetic and parasympathetic functions in cluster headache attacks. The sympathetic component seems to be involved mostly in the development of the attack, whereas the parasympathetic activation seems to occur, following the onset of the attack, independently of the pain.

Sympathetic-Parasympathetic Activation during Spontaneous Attacks of Cluster Headache: Evaluation By Spectral Analysis of Heart-Rate Fluctuations

Sympathetic-Parasympathetic Activation during Spontaneous Attacks of Cluster Headache: Evaluation By Spectral Analysis of Heart-Rate Fluctuations

Development and Maturation of the Autonomic Nervous System in Premature and Full-Term Infants Using Spectral Analysis of Heart Rate Fluctuations

The changes in the power spectra of heart rate (HR) fluctuations, in particular the total power (within 0.02-2.0 Hz) and the power in the low- (0.02-0.2 Hz) and high- (0.2-2.0 Hz) frequency ranges, were computed from the ECG and respiratory signals of 59 premature and full-term infants. The objective of the study was to investigate the development and maturation of the autonomic nervous system from the first day of extrauterine life to several weeks of postnatal age. The study population was divided into four age groups. Group A: seven 1-d-old premature infants with gestational age of 34-35 wk. Group B: 28 premature infants 7-49 d old with a conceptional age of 34-35 wk. Group C: seven 1-d-old full-term infants of 39-41 wk gestation. Group D: six premature infants 35-97 d old with a conceptional age of 39-40 wk. Mean HR (+/- SEM) of groups C and D combined, i.e. 135 +/- 2 bpm, was significantly lower compared with groups A and B, i.e. 152 +/- 2 (p < 0.01). The mean (+/- SEM) of the low- to high-frequency power ratio obtained from the HR power spectrum decreased progressively from 71 +/- 31 in group A to 34 +/- 8 in group B, 16 +/- 3 in group C, and 17 +/- 2 in group D. The mean low to high ratio for the combined groups C and D, 17 +/- 1, was significantly lower compared with the combined group A and B, i.e. 44 +/- 9 (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of power spectral analysis of heart rate fluctuations. Effects of postural changes and respiration

Assessment of power spectral analysis of heart rate fluctuations. Effects of postural changes and respiration

Evaluation of a portable prototype to analyze heart rate variability.

Power spectrum analysis of heart rate fluctuations provide a quantitative noninvasive means of assessing the functioning of the cardiovascular control system. Until now the equipment used to study heart rate variability (HRV) have been complicated systems utilized mostly in research centers. Simpler systems are needed for routine clinical application. We have evaluated, through clinical practice, the usefulness of prototype equipment which allows acquisition and analysis of ECG signals by a portable electrocardiograph and a personal computer in which sophisticated software is installed. We performed one hundred forty-five recordings in twenty-two patients admitted to ICU. With this technique two different predictive patterns were detected: one concerning survivors, the other concerning nonsurvivors. Reliability, portability, simplicity and quality results are the main advantages of the system. The disadvantage is that it is difficult to perform HRV analysis in patients with ECG arrhythmia. This is because the program does not allow the choice of an arrhythmia-free section of the tachogram to analyze.

Spectral analysis of heart rate in vasovagal syncope: the autonomic nervous system in vasovagal syncope.

Spectral analysis of heart rate fluctuations was used to investigate the role of the autonomic nervous system in the pathogenesis of vasovagal syncope. Nine adolescents with a history of at least three episodes of vasovagal syncope and nine age-matched healthy controls were studied. All subjects were tested in supine position and at a 60 degrees inclination for 60 min or less if syncope developed. Blood pressure and heart rate were measured, while the ECG and respiration traces were recorded on magnetic tape for later spectral analysis. Baseline heart rate was lower in control subjects than in patients, increased with tilt in both groups, and remained lower in the control subjects throughout the experiment. Baseline systolic and diastolic blood pressure was similar in both groups. Diastolic blood pressure initially increased with tilt in all subjects and decreased significantly thereafter in patients. Pulse pressure was lower in patients throughout the experiment. The heart rate power spectra displayed a higher baseline level of low frequency fluctuations in the control group. The high frequency fluctuations component was similar in all subjects. The results of the test, regarding haemodynamic parameters and autonomic control of the heart rate, as expressed by low and high frequency fluctuations, are consistent with a reduced sympathetic reserve in the individuals with previous episodes of syncope.

Propranolol in the Prophylaxis of Migraine ‐ Evaluation by Spectral Analysis of Beat‐to‐Beat Heart Rate Fluctuations

Migraine patients seem to suffer from a continuous autonomic imbalance. Sympathetic instability, expressed by enhanced low frequency fluctuations, which exists during the headache free intervals, was observed in our previous study by spectral analysis of heart rate (HR) fluctuations. Propranolol--a beta adrenoceptor antagonist, is widely used in migraine prophylaxis. In order to specify and quantitate propranolol efficacy in migraine, spectral analysis of heart rate fluctuations was performed on 10 migraine patients before and during the treatment with propranolol. They were compared to 10 healthy control patients and 6 migraine patients who were treated for several months with propranolol and then discontinued the medication. The analysis was carried out on a 24h Holter ECG recording, which was performed for each subject during a headache free interval. Short 256 sec subtraces, taken every 30 min from the 24h ECG signal, were submitted to A/D conversion, R wave detection and computation of heart rate power spectrum. Propranolol achieved a marked effect, when comparing the power spectra of HR fluctuations in treated versus untreated migraine patients. A strong reduction (to normal level) in the low frequency HR fluctuations in the range below 0.1 Hz., was apparent in patients treated with propranolol. Subjects who had received propranolol in the past and discontinued the drug, displayed a carry-over effect of reduced fluctuations even 2-3 months after its discontinuation. It seems that the propranolol efficacy in migraine is associated with the mechanism of stabilizing the fluctuations within the frequency band related to sympathetic activity, hereby moderating the vascular instability in migraine.

Power spectrum analysis of heart rate fluctuations and respiratory movements associated with cooling the human skin

A length of respiratory movement and instantaneous heart rate was divided into 32 segments to adopt computerized power spectrum analysis. An array of frequency spectrum across all the segments was then constructed to demonstrate sequential changes in the respiratory rhythm (0.4 Hz), low (less than 0.1 Hz) and high (0.2–0.4 Hz)-frequency components of heart rate fluctuations associated with lowering the skin temperature. A significant increase in the power for the low and high frequency components of heart rate fluctuations accompanying bradycardia occurred by cooling the face to 0 and 10°C, while cooling the foot to 0°C yielded a significant increase and decrease in the power for the former and latter component, respectively, without change in heart rate. The spectral power for respiratory movements was not altered by these stimuli. The maximal change in the power for low- and high-frequency components as well as in the heart rate during cooling the face and foot to 0°C was found to correlate negatively with the relative resting magnitude of the respective parameter in the pre-stimulus period. Similar relationship existed only with the power for low-frequency component of heart rate fluctuations when lowering the temperature of foot to 10°C. The power spectrum array employed in this study thus enabled us to estimate the effectiveness of skin cooling on the three hemodynamic parameters.

Evidence for instability of the autonomic nervous system in patients with migraine headache.

Autonomic impairment in migraine is well documented. In order to evaluate the autonomic control in migraine, spectral analysis of heart rate fluctuations was performed on ten migraine patients, drug-free and during the inter-headache phase. They were compared to nine healthy controls and eight tension headache patients. A 24h Holter recording of ECG was performed for each subject. Every half hour, a short ECG subtrace was digitized and submitted to R wave detection, followed by computation of heart rate power spectrum. The spectral analysis of heart rate fluctuations disclosed significant differences between control subjects and patients with migraine. The migraine patients displayed markedly enhanced low frequency fluctuations (below 0.1 sec-1), during day hours (p less than 0.01) and especially at night (p less than 0.0006). In the respiratory frequency band (between 0.2 and 0.4 sec-1) no significant change was observed. Tension headache patients however, resembled the controls in that they did not display enhanced low frequency fluctuations. The enhancement at low frequencies fluctuations only, a frequency range known to be related to vasomotor control, suggests that the migraine patients are characterized by a clear sympathetic instability. This finding supports the hypothesis that migraine is of neural origin and is consistent with the observation of large variations in regional cerebral flow. Spectral analysis of heart rate fluctuations allows us to specify and quantitate this autonomic imbalance and may provide a useful tool for the evaluation of drug therapy in migraine.