Heart Rate Variability Spectrum Research Articles

Stable Isotope Ratios in Hair and Teeth Reflect Biologic Rhythms

Biologic rhythms give insight into normal physiology and disease. They can be used as biomarkers for neuronal degenerations. We present a diverse data set to show that hair and teeth contain an extended record of biologic rhythms, and that analysis of these tissues could yield signals of neurodegenerations. We examined hair from mummified humans from South America, extinct mammals and modern animals and people, both healthy and diseased, and teeth of hominins. We also monitored heart-rate variability, a measure of a biologic rhythm, in some living subjects and analyzed it using power spectra. The samples were examined to determine variations in stable isotope ratios along the length of the hair and across growth-lines of the enamel in teeth. We found recurring circa-annual periods of slow and fast rhythms in hydrogen isotope ratios in hair and carbon and oxygen isotope ratios in teeth. The power spectra contained slow and fast frequency power, matching, in terms of normalized frequency, the spectra of heart rate variability found in our living subjects. Analysis of the power spectra of hydrogen isotope ratios in hair from a patient with neurodegeneration revealed the same spectral features seen in the patient's heart-rate variability. Our study shows that spectral analysis of stable isotope ratios in readily available tissues such as hair could become a powerful diagnostic tool when effective treatments and neuroprotective drugs for neurodegenerative diseases become available. It also suggests that similar analyses of archaeological specimens could give insight into the physiology of ancient people and animals.

The Significance of the Sympathetic Nervous System in the Pathophysiology of Periodic Leg Movements in Sleep

Periodic leg movements in sleep (PLMS) are frequently accompanied by arousals and autonomic activation, but the pathophysiologic significance of these manifestations is unclear. Changes in heart rate variability (HRV), HRV spectra, and electroencephalogram (EEG) spectra associated with idiopathic PLMS were compared with changes associated with isolated leg movements and respiratory-related leg movements during sleep. Furthermore, correlations between electromyographic activity, HRV changes, and EEG changes were assessed. Sleep laboratory. Whole-night polysomnographic studies of 24 subjects fulfilling the criteria of either periodic leg movements disorder (n = 8), obstructive sleep apnea syndrome (n = 7), or normal polysomnography (n = 9) were used. Spectral HRV changes started before all EEG changes and up to 6 seconds before the onset of all types of leg movements. An initial weak autonomic activation was followed by a sympathetic activation, an increase of EEG delta activity, and finally a progression to increased higher-frequency EEG rhythms. After movement onset, HRV indicated a vagal activation, and, the EEG, a decrease in spindle activity. Sympathetic activation, as measured by HRV spectra, was greater for PLMS than for all other movement types. In EEG, gamma synchronization began 1 to 2 seconds earlier for isolated leg movements and respiratory-related leg movements than for PLMS. Significant correlations were found between autonomic activations and electromyographic activity, as well as between autonomic activations and EEG delta activity, but not between higher-frequency EEG rhythms and EMG activity or HRV changes. These results suggest a primary role of the sympathetic nervous system in the generation of PLMS.

Change of the heart rate variability components in stroke patients when falling asleep

It is well known that stroke patients often have cardiovascular accidents during sleep. The aim of this study is to investigate the change of the autonomic nervous system function of stroke patients in the transition period from wakefulness to sleep. We studied three different groups, normal young subjects (21.3 ± 0.6 years; n = 20), normal elderly subjects (69.9 ± 1.3 years; n = 16) and stroke patients (72.8 ± 2.5 years; n = 10). An Actiwatch (Mini-mitter Co.) was used to distinguish sleep from wakefulness. An Activetracer AC-301 (ARM electronics) was used to record the R-R interval of an electrocardiogram at a sampling rate of 1 kHz. By applying maximum entropy methods (MemCalc/CHIRAM) to these data, the power spectrum of heart rate variability (HRV) was quantified in the area of two frequency bands: the high frequency (HF) power density component (0.15–0.40 Hz) and the low frequency (LF) power density component (0.04–0.15 Hz). In normal young and elderly subjects, the HF power density component increased significantly from wakefulness to sleep. However, in the stroke patients, there was no such increment. We also found that stroke patients showed no decrease in the LF/HF ratio after falling asleep, which was seen both in the normal young and elderly subjects. The abolishment of parasympathetic dominance during sleep may underlie cardiovascular accidents in stroke patients, such as arrhythmia and sudden death.

Altered autonomic nervous system activity as a potential etiological factor of premenstrual syndrome and premenstrual dysphoric disorder

BackgroundPremenstrual syndrome (PMS) encompasses a wide variety of cyclic and recurrent physical, emotional, and behavioral symptoms occurring during the late luteal phase of the menstrual cycle and abating shortly following the beginning of menses. Although PMS is widely recognized, its etiopathogenesis is not yet understood. The present study investigates whether the activity of the autonomic nervous system, which plays a vital role in orchestrating physiological homeostasis within the human body, is altered during the menstrual cycle of women with different degrees of premenstrual symptomatology.MethodsSixty-two women in their 20s to 40s with regular menstrual cycles participated in this study. All subjects were examined during the follicular and late luteal phases. Cycle phase was determined by the onset of menstruation and oral temperature and was verified by concentrations of ovarian hormones, estrone, and pregnanediol in a urine sample taken early in the morning. Autonomic nervous system activity was assessed by means of heart-rate variability (HRV) power spectral analysis during supine rest. The Menstrual Distress Questionnaire was used to evaluate physical, emotional, and behavioral symptoms accompanying the menstrual cycle of the subjects. The subjects were categorized in three groups, Control, PMS, and premenstrual dysphoric disorder (PMDD) groups, depending on the severity of premenstrual symptomatology.ResultsNo intramenstrual cycle difference in any of the parameters of HRV was found in the Control group, which had no or a small increase in premenstrual symptoms. In contrast, Total power and high frequency power, which reflect overall autonomic and parasympathetic nerve activity, respectively, significantly decreased in the late luteal phase from the follicular phase in the PMS group. As for the PMDD group, which had more severe symptoms premenstrually, heart-rate fluctuation as well as all components of the power spectrum of HRV were markedly decreased regardless of the menstrual cycle compared to those of the other two groups.ConclusionSeveral theories have been proposed to explain the underlying mechanisms of PMS with its complex web of bio-psycho-social factors. Although causes and consequences continue to elude, the present study provides intriguing and novel findings that the altered functioning of the autonomic nervous system in the late luteal phase could be associated with diverse psychosomatic and behavioral symptoms appearing premenstrually. In addition, when symptoms become more severe (as seen in women with PMDD), the sympathovagal function might be more depressed regardless of the menstrual cycle.

Psychological and physiological responses to the rustling sounds of Korean traditional silk fabrics

The objectives of this study were to investigate physiological and psychological responses to the rustling sound of Korean traditional silk fabrics and to figure out objective measurements such as sound parameters and mechanical properties determining the human responses. Five different traditional silk fabrics were selected by cluster analysis and their sound characteristics were observed in terms of FFT spectra and some calculated sound parameters including level pressure of total sound (LPT), Zwicker’s psychoacoustic parameters — loudness(Z), sharpness(Z), roughness(Z), and fluctuation strength(Z), and sound color factors such as ΔL and Δf. As physiological signals, the ratio of low frequency to high frequency (LF/HF) from the power spectrum of heart rate variability, pulse volume (PV), heart rate (HR), and skin conductance level (SCL) evoked by the fabric sounds were measured from thirty participants. Also, seven aspects of psychological state including softness, loudness, sharpness, roughness, clearness, highness, and pleasantness were evaluated when each sound was presented. The traditional silk fabric sounds were likely to be felt as soft and pleasant rather than clear and high, which seemed to evoke less change of both LF/HF and SCL indicating a negative sensation than other fabrics previously reported. As fluctuation strength(Z) were higher and bending rigidity (B) values lower, the fabrics tended to be perceived as sounding softer, which resulted in increase of PV changes. The higher LPT was concerned with higher rating for subjective loudness so that HR was more increased. Also, compression linearity (LC) affected subjective pleasantness positively, which caused less changes of HR. Therefore, we concluded that such objective measurements as LPT, fluctuation strength(Z), bending rigidity (B), and compression linearity (LC) were significant factors affecting physiological and psychological responses to the sounds of Korean traditional silk fabrics.

Hypotension, Heart Rate Variability, and Altered Autonomic Function

Dallas, Texas. latsont@charter.netThe elegant studies by Hanss et al. 1,2demonstrate that alterations in heart rate variability (HRV) may predict hypotension after spinal anesthesia. The authors found a significant association between an increased ratio of low-frequency HRV (LF) to high-frequency HRV (HF) (i.e. , LF/HF) and subsequent hypotension. A less predictive but still significant relation was found between decreased HF and subsequent hypotension.1In their discussion, the authors briefly compare their results with our previous results3investigating altered autonomic function and hypotension after induction of general anesthesia. Both of these studies demonstrated an association between decreased HF and subsequent hypotension. Although the stronger relation that we found with decreased HF and subsequent hypotension may simply reflect obvious differences in the study conditions (e.g. , general anesthesia vs. spinal anesthesia, different patient populations), it might also relate to the different methods used to quantitate HF.Heart rate variability measurements in the study by Hanss et al. 1are presented using normalized units, where the power in a specific frequency band (e.g. , HF) is normalized by the total power in the HRV spectrum (total HRV) for that patient (i.e. , HF in normalized units =[HF in absolute units]/[total HRV in absolute units]). A patient with decreased HF expressed in absolute units might have a normal value of HF when expressed in normalized units if the total HRV in his or her HRV power spectrum is also reduced (which is often the case in patients with autonomic dysfunction from multiple causes). For this reason, we used absolute measurements of HRV in our study. We found both a significant predictive value of decreased HF for postinduction hypotension and a strong correlation between HF and other measures of autonomic dysfunction. Historically, both absolute and normalized measurements of HRV have been used by different investigators.4Normalized units have advantages when HRV is used to examine “sympathovagal balance” (a major focus of the study of Hanss et al. 1), whereas absolute units have advantages when reflex integrity or “gain” (a major focus of our study) is examined.Did the authors of the current study1examine any possible relation between absolute measurements of HF and subsequent hypotension (or is such an analysis possible with their data)? The relation that they observed with postspinal hypotension and normalized measurements of HF might be even stronger using absolute measurements of HF. A stronger relation, if it exists, would argue that preexisting alterations in reflex integrity or gain might also play a role in hypotension after spinal anesthesia (similar to previous findings with general anesthesia3,5). Furthermore, if a significant predictive relation between absolute measurements of HF and postspinal hypotension does exist, fairly simple clinical tests of autonomic function (e.g. , the change in heart rate with six vital capacity breaths, which is highly correlated with absolute measures of HF3) might also have significant predictive value.Dallas, Texas. latsont@charter.net

Influence of external periodic stimuli on heart rate variability in healthy subjects and in coronary heart disease patients

Frequency estimates of the heart rate variability (HRV) spectrum influenced by external periodic stimuli were studied in healthy subjects and patients with coronary heart disease (CHD). Sensory stimulation by periodic eye opening at a rate of 15, 10, 8, 6, or 5 times per minute, as well as spontaneous and controlled breathing at a rate of 15, 10, 8, 6, or 5 times per minute, was used. It was found that the spectral response to external periodic oscillations was determined by a frequency-dependent phenomenon, the maximal amplitude of heart rate variations being observed in the case of external stimuli at a frequency of 0.1 Hz. A resonance frequency in the 0.1-Hz range may be suggested to exist in the cardiovascular controls. Significant differences in the HRV frequency characteristics between CHD patients and healthy subjects were shown. CHD patients had a characteristic decline in HRV responses to external oscillations; the power of these responses did not depend on the frequency of external stimuli.

Frequency modulation between low- and high-frequency components of the heart rate variability spectrum

Interactions among physiological mechanisms are abundant in biomedical signals, and they may exist to maintain efficient homeostasis. For example, sympathetic and parasympathetic neural activities interact to either elevate or depress the heart rate to maintain homeostasis. There has been considerable effort devoted to developing algorithms that can detect interactions between various physiological mechanisms. However, methods used to detect the presence of interactions between the sympathetic and parasympathetic nervous systems, to take one example, have had limited success. This may be because interactions in physiological systems are non-linear and non-stationary. The goal of this work was to identify non-linear interactions between the sympathetic and parasympathetic nervous systems in the form of frequency and amplitude modulations in human heart-rate data (n=6). To this end, wavelet analysis was performed, followed by frequency analysis of the resultant wavelet decomposed signals in several frequency brackets we define as: very low frequency (f<0.04 Hz), low frequency (0.04-0.15 Hz) and high frequency (0.15-0.4 Hz). Our analysis suggests that the high-frequency bracket is modulated by the low-frequency bracket in the heart rate data obtained in both upright and sitting positions. However, there was no evidence of amplitude modulation among these frequencies.

A modified Zeeman model for producing HRV signals and its application to ECG signal generation

Developing a mathematical model for the artificial generation of electrocardiogram (ECG) signals is a subject that has been widely investigated. One of the challenges is to generate ECG signals with a wide range of waveforms, power spectra and variations in heart rate variability (HRV)—all of which are important indexes of human heart functions. In this paper we present a comprehensive model for generating such artificial ECG signals. We incorporate into our model the effects of respiratory sinus arrhythmia, Mayer waves and the important very low-frequency component in the power spectrum of HRV. We use a new modified Zeeman model for generating the time series for HRV, and a single cycle of ECG is produced by using a simple neural network. The importance of the work is the model's ability to produce artificial ECG signals that resemble experimental recordings under various physiological conditions. As such the model provides a useful tool to simulate and analyse the main characteristics of ECG, such as its power spectrum and HRV under different conditions. Potential applications of this model include using the generated ECG as a flexible signal source to assess the effectiveness of a diagnostic ECG signal-processing device.

Scaling graphs of heart rate time series in athletes demonstrating the VLF, LF and HF regions

Scaling analysis of heart rate time series has emerged as a useful tool for the assessment of autonomic cardiac control. We investigate the heart rate time series of ten athletes (five males and five females), by applying detrended fluctuation analysis (DFA). High resolution ECGs are recorded under standardized resting conditions over 30 min and subsequently heart rate time series are extracted and artifacts filtered. We find three distinct regions of scale invariance, which correspond to the well-known VLF, LF and HF bands in the power spectra of heart rate variability. The scaling exponents α are αHF: 1.15 [0.96–1.22], αLF: 0.68 [0.57–0.84], αVLF: 0.83[0.82–0.99], p < 10−5). In conclusion, DFA scaling exponents of heart rate time series should be fitted to the VLF, LF and HF ranges, respectively.

Heart rate dynamics in iNOS knockout mice

Nitric oxide has both an inhibitory and excitatory role in the regulation of pre-ganglionic sympathetic neurons, involving the iNOS and nNOS systems respectively. The aim of the present study was to examine cardiovascular autonomic activity in iNOS knockout mice using spectral analysis of heart rate variability (HRV), and to determine the role of iNOS in altered HRV in endotoxaemia. Electrocardiograms were recorded in anaesthetised mice, and the R–R intervals digitized for spectral analysis of HRV and cardiac rhythm regularity using sample entropy analysis. The basal heart rate was higher in iNOS knockout mice compared with controls (465 ± 8 vs 415 ± 13 beat/min P < 0.05), with a significant increase in the low frequency power of HRV spectra in iNOS knockout mice compared with controls (49.4 ± 4.3 vs 33.8 ± 5.6 normalized units, P < 0.05), consistent with increased cardiac sympathetic activity. Endotoxaemia is known to decrease HRV, but the role of iNOS is unknown. LPS (20 mg/kg i.p) increased basal heart rate in both wild type and iNOS knockout mice, but caused a depression of HRV and sample entropy in both groups. Studies in isolated beating atria showed that the changes of HRV under basal or post-LPS conditions disappeared in vitro, suggesting that the autonomic system is responsible for altered HRV. We conclude that disruption of iNOS gene leads to an increase in the low frequency power of HRV consistent with increased cardiac sympathetic activity. These data also demonstrate that LPS-induced decrease of HRV is independent of iNOS.

Spectral analysis and interpretation of spectral components of heart rate variability

Requirements for a fragment of a random process taken for spectral analysis are formulated. It has been demonstrated that both the random process and its periodic components should be stationary within the fragment selected. Only in this case will the results of spectral analysis reflect the actual characteristics of the process studied. Variations in the depth of breathing and other factors have been shown to cause modulatory fluctuations of the HF and LF waves of the cardiac rhythm. The modulatory fluctuations are expressed as the VLF peak in the heart rate variability spectrum, the position of the peak on the frequency axis and its amplitude being determined by the frequency and depth of modulation, respectively. Depending on the modulation depth and the ratio between the modulation period and the length of the sample studied, spectral analysis of the same process may yield considerably different results. The ambiguity of the results of spectral analysis is the cause of discrepancy about the nature of individual spectral components of heart rate variability.

Heart rate variability in conscious neonatal swine: spectral features and responses to short-term intermittent hypoxia

BackgroundSpectral analysis of the cardiac time series has been used as a tool for assessing levels of parasympathetic and sympathetic modulation of the sinoatrial node. In the present investigation we evaluated daily changes in heart rate variability spectra in conscious neonatal piglets that were either neurally intact (n = 5) or had undergone right stellate ganglionectomy (n = 5). The partial stellectomized animals and their intact litter mates were exposed to four days of intermittent hypoxia, each day comprising nine episodes of hypoxia alternating with nine episodes of normoxia. A time control group (n = 7) comprised animals from different litters that were not exposed to intermittent hypoxia. We hypothesized that exposure to intermittent hypoxia would increase sympathetic efferent neuronal modulation of heart rate variability spectra in neurally intact animals and in those with right stellate ganglionectomy, and that his effect would be observed in heart rate variability spectra computed from baseline recordings.ResultsOverall, heart rate variability spectra during baseline conditions were dominated by high frequency activity, a reflection of parasympathetic efferent neuronal innervation and linkage to the ventilatory cycle manifested as respiratory sinus arrhythmia. Exposure to intermittent hypoxia did not alter daily baseline spectral features that would indicate an increase of sympathetic cardiac activity: low frequency (0.05 – 0.15 Hz) activity was unaffected and the ratio of low- to -high frequency activity remained less than unity indicating a predominance of high frequency activity. The resultant spectra were remarkably similar despite differences in cardiac sympathetic efferent neuronal innervation and experimental treatment. When spectra were computed from cardiac time series during representative hypoxic episodes, significant increases in activity across the low frequency region (0.05 – 0.15 Hz) of heart rate variability spectra were noted and were comparable in neurally intact animals and in those with right stellate ganglionectomy.ConclusionThe findings of this investigation provided important information regarding sympathetic efferent neuronal innervation of the heart during the neonatal period. Both neurally intact animals and those with right stellate ganglionectomy had equivalent increases of activity in the low frequency region of heart rate variability spectra during hypoxic stimulation. Such a finding demonstrated the capability of residual cardiac sympathetic neuronal innervation to affect functionally appropriate changes in cardiac chronotropy.

B105 心拍変動解析による1/fゆらぎ音楽の生体波及効果の検討

In this study, we examined the effect of the 1/f fluctuation element in sound by analyzing the power spectrum of Heart Rate Variability (HRV) when listening to music. The 1/f fluctuation means the inclination degree of the power spectrum in music. The following four tunes were used in experiment. Sample A dose not contain 1/f fluctuation. Sample C is the reversal play of "Sample A". Sample B contains 1/f fluctuation. Sample D is the reversal play of "Sample B". We measured the HRV of each subject, in the following state. In State 1, the subjects seated with eyes closed under resting condition for 2 minutes without music. In State 2, the subject heard a sample tune for 2 minutes while keeping the condition of "State 1". In State 3, he recovered to condition of "State 1" again for 2 minutes after stopping the sample tune. As a result, The LF/HF values of the reverse-reproduction music were greater than the values of the regular-reproduction music. We confirmed that personal preference (acquired by experience, environment and familiarity) strongly influenced the subject's comfort level more than the 1/f fluctuation element for music.

Assessment of Heart Autonomic Control on the Basis of Spectral Analysis of Heart Rate Variability

An orthostatic test with frequency-controlled breathing (with a respiration period of 10 s) or spontaneous breathing was used to analyze frequency estimates of the heart rate variability (HRV) in the low-frequency (LF) and high-frequency (HF) ranges in young men and women. It was demonstrated that the spectral components of HRV bear no signs of sex differentiation, suggesting a uniform structural organization of the system of autonomic nervous control of the heart (SANCH) in humans. The LF component of the HRV spectrum is a marker of the functional state of the SANCH; it should be studied under conditions of controlled breathing at a frequency of 0.1 Hz. The HF and LF components of the HRV characterize the state of the SANCH at a given moment and do not reflect directly its adaptation reserve. The HF component of the HRV is interesting as a parameter that may be used for estimating the changes in the adaptation reserve of heart autonomic control. It is preferable to analyze this component in the absence of external disturbances in the LF range of the spectrum.

Cardiac vagal tone, exercise performance and the effect of respiratory training

Heart rate variability (HRV) at rest and heart rate recovery after exercise reflect cardiac vagal activity. The aim of this study was to determine whether increasing HRV during involuntary respiratory training induced by rebreathing air using a Hepburn heart and lung exerciser (HHALE) could, like exercise, improve vagal tone. Eighteen subjects (36-88 years) underwent a 6-week control period, then a 6-week training period with the HHALE following which half continued training for 6 weeks and half ceased training. Measurements were made of HRV, work at 60% predicted heart rate max for 15 min, heart rate recovery after exercise, resting blood pressure, heart rate, vital capacity and forced expiratory volume. After the first 6-week HHALE training, there was a significant increase of 13.2 +/- 5.7 nu in the high frequency peak of the power spectrum of HRV at rest, whereas, the low frequency peak decreased. Similarly, exercise performance showed a significant improvement of 0.031 +/- 0.012 J per heartbeat from a pre-training 0.128 +/- 0.022. Also, heart rate recovery after exercise significantly faster (drop in the first 20 s improving by 3.3 +/- 1.5 beats from a pre-training 12.9 +/- 1.6). The subgroup that continued training maintained or slightly improved these values. In those that ceased training the speed of heart rate recovery at the end of the exercise test returned to pre-trained levels, whereas, other responses were either maintained or decreased slightly. We conclude that training with the HHALE can, without additional exercise, increase cardiac vagal tone and exercise performance.

Mechanisms of Periodic Heart Rate Oscillations: A Study Using Controlled Breathing Tests

An orthostatic test with frequency-controlled breathing (with periods of 4, 6, 8, 10, and 12 s) was used to analyze frequency estimates of the heart rate variability (HRV) spectrum in the low frequency (LF) and high frequency (HF) ranges in 36 volunteers (26 men and 10 women) aged 19-21 years without signs of heart or respiratory pathology. The subjects took a breath at the moment of an auditory signal. There were no other requirements for the respiration rhythm. Variables were compared using Wilcoxon's test for pairwise compar- isons; correlations were estimated by Spearman's rank correlation R test. The sensitivities of the LF and HF ranges of the HRV spectrum to periodic respiratory perturbations at different frequencies were demonstrated to differ from each other. Autonomous 0.10- and 0.25-Hz circuits of oscillatory processes were found in HRV. The transition zone of influence of these circuits was located in the region around 0.125 Hz. The characteristics of the 0.10- and 0.25-Hz oscillations in HRV were studied. It was demonstrated that the 0.10-Hz oscillatory pro- cess is a potent mechanism of heart rate control, is affected by external factors, and determines the dynamics of the autonomic nervous state of the body, while the 0.25-Hz process is a regulatory mechanism of medium strength, is resistant to external factors, and characterizes the adaptation reserve of the autonomic nervous con- trol of the heart rate, as well as the autonomic nervous state of the body. Resonance responses in the HRV spec- trum can be used for studying the characteristics of the 0.10- and 0.25-Hz oscillations.

Chronic but Not Acute Hydrocortisone Treatment Shifts the Response to an Orthostatic Challenge towards Parasympathetic Activity

Adrenocortical steroid hormones play a major role in the regulation of both action and metabolism of catecholamines. However, there is limited information on the effect of prolonged increase in plasma steroid hormone concentration on the sympathetic nervous system, which is the main source of norepinephrine. Using a double-blind, placebo-controlled cross-over design, we examined 20 male healthy volunteers after acute administration of 40 mg hydrocortisone or matching placebo as well as after a 1-week treatment with this steroid (daily dose, 40 mg) or placebo. Sympathetic nervous system activity was assessed by determination of overnight urinary norepinephrine and epinephrine secretion and by analysis of short-time heart rate variability (HRV) measures in the frequency domain. The low-frequency (LF) component of the HRV spectrum was considered to reflect both sympathetic and parasympathetic modulation and the high-frequency (HF) band vagal activity. HRV testing included the response to a mild cardiovascular challenge, orthostasis. After 1 subject had been excluded because of incompliance with the study medication, the data of 19 subjects were used for further analyses. Prolonged hydrocortisone treatment was associated with a significant shift of relative power from the LF to the HF band in the upright position, resulting in a significant decrease in the LF/HF ratio (placebo 6.77 ± 3.35 and hydrocortisone 4.72 ± 3.27; p < 0.05). No differences between groups were observed after acute steroid administration or after prolonged treatment in the supine position. Neither acute nor chronic hydrocortisone treatment resulted in significant changes in the overnight urinary catecholamine secretion. Our data suggest that prolonged but not acute hydrocortisone administration shifts the autonomic response to an orthostatic challenge towards parasympathetic activity.

Heart rate variability measurements and the prediction of ventricular arrhythmias

Heart rate variability (HRV) is the temporal variation between sequences of consecutive heartbeats. On a standard electrocardiogram (ECG), the maximum upwards deflection of a normal QRS complex is at the peak of the R wave (Figure 1), and the duration between two adjacent R wave peaks is termed the R-R interval. The ECG signal requires editing before HRV analysis can be performed, a process requiring the removal of all non-sinus-node-originating beats. The resulting period between adjacent QRS complexes resulting from sinus node depolarizations is termed the N-N (normal-normal) interval.1 HRV is the measurement of the variability of the N-N intervals. Figure 1. The normal electrocardiogram with component waves labelled. Although counter-intuitive, it is possible that HRV confers a survival advantage. Any system exhibiting intrinsic variability is primed to respond rapidly and appropriately to demands placed upon it. HRV is a measure of the balance between sympathetic mediators of heart rate (HR) (i.e. the effect of epinephrine and norepinephrine, released from sympathetic nerve fibres, acting on the sino-atrial and atrio-ventricular nodes), which increase the rate of cardiac contraction and facilitate conduction at the atrio-ventricular node, and parasympathetic mediators of HR (i.e. the influence of acetylcholine, released by the parasympathetic nerve fibres, acting on the sino-atrial and atrio-ventricular nodes), leading to a decrease in the HR and a slowing of conduction at the atrio-ventricular node. Sympathetic mediators appear to exert their influence over longer time periods and are reflected in the low frequency power (LFP) of the HRV spectrum (between 0.04 Hz and 0.15 Hz.2,,3 Vagal mediators exert their influence more quickly on the heart, and principally affect the high frequency power (HFP) of the HRV spectrum (between 0.15 Hz and 0.4 Hz).4 Thus, at any point in time, the LFP:HFP ratio is a proxy for the sympatho-vagal balance. Physiological and pathological process … Address correspondence to Dr M.J. Reed, Emergency Department, Royal Infirmary of Edinburgh, 51 Little France Crescent, Edinburgh EH16 4SA. e-mail: mattreed1{at}hotmail.com

Different methods of heart rate variability analysis reveal different correlations of heart rate variability spectrum with average heart rate

Heart rate variability (HRV) spectrum can be calculated from the R-R or the sequence of instantaneous heart rates (IHRs). Because these signals are reciprocal, their use in the determination of the correlation of HRV with average HR may yield opposite results. Aim The aim of this study is to reveal how HRV parameters correlate with HR depending on the kind of signal used and whether the normalization procedure or use of corrected signals affect the correlations. Methods Electrocardiographic recordings (512 beats) of 55 patients were considered in the analysis. RR and IHRs were calculated. Both signals were divided by their average values yielding the corrected RR and IHR. Heart rate variability spectra were estimated from these 4 kinds of signals. Total power (TP), low frequency (LF) and high frequency (HF) components, LF/HF ratio, and normalized values (ie, nLF, nHF) were calculated. Results Total power and LF estimated from RR correlated negatively with HR, but those calculated from IHR revealed a trend toward a positive correlation (respective correlation coefficients significantly differed, P < .01). The sign of correlation between HF and HR was the same regardless of the type of signal applied. The application of corrected signals made the results almost identical despite different signal origins (RR or IHR). The correlations of LF/HF, nLF, and nHF with HR were similar in all cases. Conclusions The type of signal determines the sign of correlation among TP, LF, and HR. The parameters obtained from corrected signals, normalized quantities, and LF/HF reveal a consistent relationship with HR.