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Heart Rate Variability: Standards of Measurements, Physiological Interpretation, And Clinical Use
... Heart rate variability (HRV) refers to continuous variations in the distances between consecutive beats [1,2]. Heart beats originate at the sinus node, whose activity is modulated by parasympathetic and sympathetic nerves. ...
... For each recording within each experimental group, several temporal HRV indices are computed, including SDNN, SDANN, SDNNIDX, pNN50, SDSD, rMSSD, IRRR, MADRR, TINN, and HRVi [1,2]. The width of the sliding window used for the computations of SDANN and SDNNIDX is set to 300 seconds by default, as recommended by [1]. ...
... For each recording within each experimental group, several temporal HRV indices are computed, including SDNN, SDANN, SDNNIDX, pNN50, SDSD, rMSSD, IRRR, MADRR, TINN, and HRVi [1,2]. The width of the sliding window used for the computations of SDANN and SDNNIDX is set to 300 seconds by default, as recommended by [1]. However, different values may be used, especially in animal experimentation, with values as low as 60 seconds [18] or even 10 seconds [19]. ...
Heart Rate Variability (HRV) analysis aims to characterize the physiological state affecting heart rate, and identify potential markers of underlying pathologies. This typically involves calculating various HRV indices for each recording of two or more populations. Then, statistical tests are used to find differences. The normality of the indices, the number of groups being compared, and the correction of the significance level should be considered in this step. Especially for large studies, this process is tedious and error-prone. This paper presents RHRVEasy, an R open-source package that automates all the steps of HRV analysis. RHRVEasy takes as input a list of folders, each containing all the recordings of the same population. The package loads and preprocesses heart rate data, and computes up to 31 HRV time, frequency, and non-linear indices. Notably, it automates the computation of non-linear indices, which typically demands manual intervention. It then conducts hypothesis tests to find differences between the populations, adjusting significance levels if necessary. It also performs a post-hoc analysis to identify the differing groups if there are more than two populations. RHRVEasy was validated using a database of healthy subjects, and another of congestive heart failure patients. Significant differences in many HRV indices are expected between these groups. Two additional groups were constructed by random sampling of the original databases. Each of these groups should present no statistically significant differences with the group from which it was sampled, and it should present differences with the other two groups. All tests produced the expected results, demonstrating the software’s capability in simplifying HRV analysis. Code is available on https://github.com/constantino-garcia/RHRVEasy.
... Patients with congenital heart disease/defects (CHDs) present cardiac autonomic dysfunction [1]. Heart rate variability (HRV) is a non-invasive method to evaluate cardiac autonomic responsiveness [2]. Nevertheless, pediatric cardiologists have rarely considered HRV analysis in the setting of CHDs [3]. ...
... Nevertheless, pediatric cardiologists have rarely considered HRV analysis in the setting of CHDs [3]. The gold standard for obtaining RR intervals (RRi) for HRV is electrocardiography (ECG) [2]. Over last decades, devices like heart rate monitors (HRM) or mobile applications have been used for measuring HRV [4][5][6]. ...
... The spectral analysis determined the spectral power of the interferogram (45 indicators), the arterial oscillogram itself using Fourier transformation (340 indicators), and the instantaneous frequency and phase using Hilbert-Huang transformation (90 indicators) [3]. The following indicators were used to analyze interferograms [28], [29]: ...
... It should be noted that the physiological value of the ULF electrocardiographic signal has been studied the least. However, there is an opinion that its power increases significantly when the body's regulatory systems are exhausted [28], [29]. Therefore, the study of the influence of the ultraslow oscillation index (ULF) on the value of the assessment of the patient's mental state based on the results of the arterial oscillogram analysis is of some interest and scientific novelty. ...
The presented study explores the clustering of arterial oscillogram (AO) data among a sample of patients, focusing on ultra-low-frequency (ULF) indicators and their relationship with depression levels. Through dimensionality reduction using UMAP, two distinct classes emerged, categorized as lighter and more severe cases. Utilizing machine learning methods, an automated classifier was developed based on correlated ULF indicators, which led to improved classification accuracy. By incorporating ULF parameters, products of correlated parameters, and additional measured factors, the classifier achieved high reliability in estimating depression levels. Specifically, the nearest neighbors method yielded accuracies up to 0.9792. This research supports the creation of an automated diagnostic classification AI service capable of reliably estimating at least four levels of depression based on AO analysis.
... For data analysis, short-term (5 min of each recording taken) HRV recordings were used, following the guidelines established by the Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology [64], at three different time points: pre-intervention, during intervention, and immediately post intervention. Subsequently, the recordings were processed using Kubios HRV Scientific Lite 4.1.0 ...
... It has been reported that HRV is highly sensitive to changes in position [30,77] and sex [78]. The lack of stability in HRV during rest questions the current methodologies and confirms the need for standardized protocols for comparison between studies following the recommendations of the Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology [64]. ...
Background: The modulation of the autonomic nervous system’s activity, particularly increasing its parasympathetic tone, is of significant interest in clinical physiotherapy due to its potential benefits for stress-related conditions and recovery processes. This study evaluated the effectiveness of the addition of neurodynamics in enhancing parasympathetic activation in subjects with chronic stress. Methods: A clinical trial randomly assigned participants to a group with neurodynamics (6 bpm breathing protocol + manual therapy + neurodynamic technique) or a group without neurodynamics (6 bpm breathing protocol + manual therapy only). Metrics of heart rate variability (HRV), including the Mean Heart Rate (Mean HR), standard deviation of intervals between consecutive heartbeats (SDNN), Heart Rate Difference (Diff. HR), Root Mean Square of Successive Differences (RMSSD), number of intervals differing by more than 50 ms (NN50), percentage of consecutive NN intervals that differed by more than 50 ms (pNN50), and the high-frequency component measured in standardized units (HF), were assessed before, during, and after the intervention. Results: During the intervention, the group with neurodynamics showed significant changes in all variables except in the pNN50 and HF while the group without neurodynamics only showed improvements in the Mean HR, SDNN, and RMSSD. In the post-intervention phase, the group with neurodynamics maintained an increase in HRV while the group without neurodynamics experienced a decrease, suggesting an increase in sympathetic activity. Conclusions: Vagal nerve neurodynamics appear to represent an effective method for enhancing parasympathetic activation in patients with chronic stress. The results highlight the importance of a more comprehensive analysis of HRV variables in order to obtain a correct picture of the impact of interventions on the complex and multifaceted functioning of the autonomic nervous system.
... However, standard measures of cardiac sympathetic activity do not successfully detect the physiological responses of OSA events, as compared with blood pressure or sympathetic nerve neurogram [2]. Indeed, the challenges of accurately estimating sympathetic dynamics through heart rate variability (HRV) has been long discussed [3] [4]. We recently developed a robust estimator of sympathetic tone called cardiac sympathetic index (CSI) [5]. ...
... The turning points in ECGs labeled with the letters P, Q, R, S, and T are shown in Figure 5. In the NTA of ECGs, the various intervals that can be defined within a heartbeat, like QRS and QT, as well as interbeat intervals like RR (see Figure 5) or NN (which are [208] intervals between adjacent QRS complexes resulting from sinus-node depolarizations), were considered [45,47,48,51,209-212] Q k . In these studies, the entropy, S, in the NTA, as well as its fluctuations, δS (defined as the standard deviation of the S time-series), were used to show the non-Markovianity of ECGs [45], as well as the distinction between healthy (H) humans and humans who experience sudden cardiac death (SCD) [45,48] based on either QT, RR, or QRS intervals. ...
A new concept of time, termed natural time, was introduced in 2001. This new concept reveals unique dynamic features hidden behind time-series originating from complex systems. In particular, it was shown that the analysis of natural time enables the study of the dynamical evolution of a complex system and identifies when the system enters a critical stage. Hence, natural time plays a key role in predicting impending catastrophic events in general. Several such examples were published in a monograph in 2011, while more recent applications were compiled in the chapters of a new monograph that appeared in 2023. Here, we summarize the application of natural time analysis in various complex systems, and we review the most recent findings of natural time analysis that were not included in the previously published monographs. Specifically, we present examples of data analysis in this new time domain across diverse fields, including condensed-matter physics, geophysics, earthquakes, volcanology, atmospheric sciences, cardiology, engineering, and economics.
... Some non-invasive measures of cardiovascular ANS tone include heart rate variability (HRV), blood pressure variability (BPV) and baroreflex sensitivity (BRS). HRV is defined as the fluctuations between consecutive R-R intervals (Electrophysiology TFotESoCtNASoP, 1996), and broad evidence supports that the root mean square of successive differences (RMSSD) and the high frequency (HF: 0.15-0.4 Hz) component of HRV (HF HRV) reflect changes in cardiovascular PNS activity (Cowan, 1995;Joyner, 2016;Malik & Camm, 1993;Stauss, 2003). ...
Sport‐related concussion (SRC) is associated with cardiovascular autonomic nervous system (ANS) dysfunction. This study examines resting cardiovascular ANS activity in adolescents with SRC compared to controls early post‐injury and after clinical recovery, analyzing its correlation with symptom severity and recovery outcomes. Cardiovascular ANS function was evaluated using heart rate variability (HRV), systolic blood pressure variability (SBPV) and baroreflex sensitivity (BRS). Symptoms were assessed via the Post‐Concussion Symptom Scale, and recovery outcomes were categorized by recovery duration. Following acute SRC, no significant differences in HRV, SBPV or BRS were found between SRC and control groups, nor between those with delayed or normal recovery. Post‐recovery, SRC participants had higher low frequency (LF) SBPV than controls and their initial assessment. When concussed participants were symptomatic, LF SBPV correlated directly with overall, cognitive, and fatigue symptom severity, while high frequency (HF) HRV inversely correlated with affective symptoms (Spearman's rho: 0.4–0.6). Resting cardiovascular ANS function remains unchanged in adolescent athletes acutely after SRC, suggesting it has limited diagnostic and prognostic potential. Although some correlations between individual symptom domains and ANS activity were observed, they were not significantly different from asymptomatic controls, limiting the ability to interpret these findings.
... Before the analysis, all records (continuous R-R intervals and blood pressure) were carefully checked and the artifacts were manually removed. The 5 min long time series were used for analysis according to recommendation for shortterm analysis [20]. Firstly, continuous R-R intervals were measured by Polar V800 (Polar Electro, Kempele, Finland) with a sampling frequency of 1000 Hz. ...
Background
Globus pharyngeus could be described as a benign sensation of lump or foreign object in the throat. The etiology of the globus as a solitary syndrome is still unknown, but it is proposed that stress could have an important role in symptom emergence.
Aims
To evaluate the autonomic nervous regulation in patients with globus compared to healthy controls in reaction to stress.
Methods
Patients included in the study were diagnosed based on ROME IV criteria for Disorders of Gut Brain Interaction. Besides globus, the patients did not suffer any other substantial medical condition. As a control group, measurement of healthy volunteers was performed. Both groups underwent the same stress protocol assessment in the same laboratory settings. The protocol consist of two types of stressors: cold pressor test and mental arithmetic test to test different types of autonomic reactivity.
Results
Baroreflex sensitivity was significantly decreased in patients compared to controls in all phases of the protocol. Low-frequency band of systolic blood pressure variability was significantly increased during both stress phases in patients compared to controls. High-frequency band of heart rate variability was significantly decreased in patients compared to controls during the both of the stress phases.
Conclusion
The results of this study shows discrete abnormalities in complex autonomic reflex control which are predominantly manifested in response to stressful stimuli indicating altered neurocardiac regulation as a reaction to stress associated with globus pharynegus. This fact could have an important role in the personalized management of globus patients such as biofeedback.
In clinical practice, heart rate variability (HRV) has not been considered an indicator for the preventive assessment of cardiovascular autonomic neuropathy (CAN). The paper studies HRV in a large, randomly selected group. A cross-sectional study included a representative sample of 5707 Kazakhs aged 20 years and older from a total population of 25,454 attached to an urban clinic in the capital of Kazakhstan. The sample was drawn from individuals who visited the clinic for a preventive examination. CAN diagnosis was confirmed using data from questionnaires, electronic medical records, HRV, and heart rate measurements. Mean values of the standard deviation of normal sinus RR intervals (SDNN) and the root mean square of successive RR interval differences (RMSSDs) from a 24 h electrocardiogram recording were assessed. CAN was identified in 17.19% of the study participants, with a ratio of the subclinical to clinical phase of 1:0.24. Diabetes mellitus was present in 30.99% of patients with CAN. The prevalence of CAN varied by sex and age, aligning with the prevalence trajectory of diabetes. It was concluded that the SDNN and RMSSD parameters in electrocardiographic studies can be used for preventive measures in the context of limited healthcare resources.
There are several mechanisms responsible for the dynamical link between heart period (HP) and respiration (R), usually referred to as cardiorespiratory coupling (CRC). Historically, diverse signal processing techniques have been employed to study CRC from the spontaneous fluctuations of HP and respiration (R). The proposed tools differ in terms of rationale and implementation, capturing diverse aspects of CRC. In this review, we classify the existing methods and stress differences with the aim of proposing a variability-based multi-method approach to CRC evaluation. Ten methodologies for CRC estimation, namely, power spectral decomposition, traditional and causal squared coherence,\;information transfer, cross-conditional entropy, mixed prediction, Shannon entropy of the latency between heartbeat and inspiratory/expiratory onset, conditional entropy of the phase dynamics, synchrogram-based analysis, pulse-respiration quotient, and joint symbolic dynamics, are considered. The ability of these techniques was exemplified over recordings acquired from patients suffering from postural orthostatic tachycardia syndrome (POTS) and healthy controls. Analyses were performed at rest in the supine position (REST) and during head-up tilt (HUT). Although most of the methods indicated that at REST, the CRC was lower in POTS patients and decreased more evidently during HUT in POTS, peculiar differences stressed the complementary value of the approaches. The multiple perspectives provided by the variability-based multi-method approach to CRC evaluation help the characterization of a pathological state and/or the quantification of the effect of a postural challenge. The present work stresses the need for the application of multiple methods to derive a more complete evaluation of the CRC in humans.
Creativity research can robustly predict creative ideation performance from brain physiological data assessed in laboratories. However, physiologically driven prediction models of creative ideation performance in the field are less advanced. The vagus nerve quantified via vagally mediated heart rate variability (vmHRV) signals a brain–heart interaction. In contrast to central nervous brain functioning, vmHRV can easily be assessed in everyday life situations, indicating body-mind interactions. We recorded the electrocardiogram signal of 157 participants 5 min prior to solving verbal and figural creative ideation tasks multiple times in everyday life. The creativity domain moderated the prediction effect of vmHRV. Decreased vmHRV was associated with higher verbal but lower originality of figural ideas, which increased with higher vmHRV. This indicates that different neurophysiological states are associated with the originality of verbal and figural ideas in everyday life situations, which mirrors neuroscientific research findings that link a specific brain activation pattern to verbal and figural creativity.
In this manuscript, the problem of assessing the heart rate variability (HRV) of a single subject using a colocated multiple-input multiple-output radar of frequency modulated continuous wave type is investigated. The proposed solution exploits beamforming to acquire multiple measurements from different points on the body of the monitored subject. These measurements are combined using a selection strategy that aims at reducing the impact of random body movements while enhancing the overall signal-to-noise ratio. The resulting signal is then filtered using a physiology-inspired filter. Our results demonstrate that the proposed estimation method can accurately identify the instants at which heartbeats occur and achieve accuracy similar to a regular electrocardiogram in terms of specific HRV metrics referring to interbeat intervals.
Earthquakes, as significant natural disasters, still cannot be accurately predicted today. Although current earthquake early warning systems can provide alerts several seconds in advance, acute stress responses (ASR) in emergency situations can waste these precious escape seconds. To investigate the correlation between personality and ASR, this study collected the temperament and character of all participants using the Chen Huichang‐60 Temperament Scale and the DISC Personality Inventory. In addition, this study simulated growing earthquakes in an earthquake experience hall, collecting heart rate variability and respiration signal variations throughout the process from subjects. Multivariate analysis of variance (MANOVA) and Toeplitz Inverse Covariance‐Based Clustering methods were used to analyse the differences and connections between them. Furthermore, this study employed a deep learning model that combines Convolutional Neural Networks (CNN) and Long Short‐Term Memory (LSTM) to predict ASR across personalities. This model used datasets from the majority dataset of a certain personality and a single participant, respectively, and showed different performance. The results are as follows. After categorising participants based on personality test results, MANOVA revealed significant differences between the personality groups Influence‐Choleric and Influence‐Sanguine ( p = 0.001), Influence‐Phlegmatic and Steadiness‐Sanguine ( p = 0.023), Influence‐Sanguine and Steadiness‐Sanguine ( p < 0.001) and Influence‐Sanguine and Steadiness‐Phlegmatic ( p < 0.001), as well as across different earthquake stages ( p < 0.01). The clustering method quantified stress responses over time for different personalities and labelled ASR levels for use in supervised learning. Ultimately, the CNN‐LSTM model performed predictions of ASR using both personality and individual datasets, achieving the AUC of 0.795 and 0.72, demonstrating better prediction and classification effectiveness with the former. This study provides a new personality‐based method for earthquake stress management, creating possibilities for longitudinal stress research and prediction. It aids the general public in comprehending their own acute stress and allows authorities and communities to make practical, efficient disaster evacuation plans based on the overall situation of public ASR.
Functional capacity is an important objective health metric, and relies on the maintenance of physiological homeostasis. Autonomic nervous system is known to coordinates the maintenance of multi-organ homeostasis. The objective of this study was to examine the association of autonomic nervous system function with functional capacity in adults aged 55 years and older. A cohort of 542 adults (mean age of 70.1 years) received repeated measurements of heart rate variability, an autonomic nervous system function marker, and chair rise time, a functional capacity measure. Linear mixed models analysis showed that 1 SD lower powers in low-frequency range at baseline was associated with a 0.11 (95% CI 0.01–0.21) s/year faster increase in chair rise time during the follow-up, whereas 1 SD increase in powers in high-frequency range and 1 SD decrease in the ratio of powers in low-frequency range to powers in high-frequency range during the follow-up were associated with a 0.22 (95% CI 0.06–0.39) s and 0.17 (95% CI 0.01–0.33) s increase in chair rise time. In conclusion, autonomic nervous system function and its changes were longitudinally associated with changes in functional capacity in older adults.
Purpose
To assess the effects of two different body positions on the cardiovascular autonomic profile during a single bout of exercise in patients with postural orthostatic tachycardia syndrome (POTS).
Methods
Thirteen patients with POTS and thirteen healthy controls (C) participated in the study. ECG, respiration, beat-by-beat arterial pressure and O2 consumption (VO2) were continuously recorded while on a cycle ergometer in supine and upright positions, before and during exercise (6 min, 50 Watts). Spectral analysis of RR intervals and systolic arterial pressure (SAP) variability provided indexes of cardiac sympathovagal interaction (LF/HF ratio), cardiac vagal modulation (HFRR, high-frequency component of RR variability, ~ 0.25 Hz), sympathetic vasomotor control (LFSAP, low-frequency component of SAP variability, 0.1 Hz) and baroreflex sensitivity (BRS, αLF).
Results
While supine, patients with POTS showed lower HFRR and αLF, greater heart rate (HR), LF/HF and LFSAP, compared with C, suggesting cardiovascular sympathetic over-activity and reduced BRS. While sitting upright, POTS showed greater HR and reduced HFRR and αLF compared with C. During supine exercise, SAP, HR, LF/HF increased and HFRR and αLF decreased similarly in POTS and C. In POTS, upright sitting exercise was associated with slightly higher , a greater increase in HR whereas LFSAP was lower than in C.
Conclusion
Upright exercise was associated with excessive enhancement of HR and a blunted increase of the sympathetic vasomotor control in POTS. Conversely, supine exercise-induced hemodynamic and autonomic changes similar in POTS and C, thus making supine exercise potentially more suitable for physical rehabilitation in POTS.
Research indicated that extremely low‐frequency (ELF) electric field (EF) treatment modifies autonomic activity in healthy subjects; however, the effects do not persist after the treatment. This study examined whether persistence of the effects is dependent on the baseline autonomic conditions. The depressed subjects are known to frequently exhibit autonomic dysregulation, and were enrolled in the present study to test this hypothesis. Autonomic activity was evaluated using heart rate variability (HRV) analysis. Heart rate (HR) was measured using R‐R intervals of the electrocardiogram in the resting state before and after the 20‐min ELF‐EF treatment (30 kV, 60 Hz) in the patients with major depressive disorder and in the control subjects, and HRV was analyzed using frequency‐domain power spectrum analysis of R‐R interval trend. Sham treatment was conducted in the control subjects but not in the patients due the ethical restriction. In the patients with depression, high‐frequency variation (HF) related to breathing‐dependent parasympathetic activity was low before the 60‐Hz EF treatment and increased to the control level after treatment. No effects of EF were found for low‐frequency variation (LF), LF/HF, and HR. The results indicated that acute 60‐Hz EF treatment increased parasympathetic activity in the depressed subjects, who showed a reduction in baseline parasympathetic activity. This study suggests that the effects of ELF‐EF treatment on autonomic activity are dependent on the baseline autonomic conditions. Future studies with larger sample sizes, incorporating sham treatment in the patients with depression, are needed to confirm these observations. © 2024 The Author(s). IEEJ Transactions on Electrical and Electronic Engineering published by Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.
Ubiquitous on-device heart rate sensing is vital for high-stress individuals and chronic patients. Non-contact sensing, compared to contact-based tools, allows for natural user monitoring, potentially enabling more accurate and holistic data collection. However, in open and uncontrolled mobile environments, user movement and lighting introduce noises. Existing methods, such as curve-based or short-range deep learning recognition based on adjacent frames, strike the optimal balance between real-time performance and accuracy, especially under limited device resources. In this paper, we present UbiHR, a ubiquitous device-based heart rate sensing system. Key to UbiHR is a real-time long-range spatio-temporal model enabling noise-independent heart rate recognition and display on commodity mobile devices, along with a set of mechanisms for prompt and energy-efficient sampling and preprocessing. Diverse experiments and user studies involving four devices, four tasks, and 80 participants demonstrate UbiHR's superior performance, enhancing accuracy by up to 74.2% and reducing latency by 51.2%.
Aim
Infants born very preterm spend their early postnatal life in a neonatal intensive care unit, where irregular and unpredictable sounds replace the structured and familiar intrauterine auditory environment. Music interventions may contribute to alleviate these deleterious effects by reducing stress and providing a form of environmental enrichment.
Material and Methods
This was an ancillary study as part of a blinded randomised controlled clinical trial entitled the effect of music on preterm infant's brain development. It measured the impact of music listening on the autonomic nervous system (ANS), we assessed heart rate variability (HRV) through high‐resolution recordings of heart rate monitoring, at three specific postmenstrual ages in premature infants.
Results
From 29 included subjects, 18 were assessed for complete HRV dataset, including nine assigned to the music intervention and nine to the control group. Postmenstrual age appeared to be the main factor influencing HRV from 33 weeks to term equivalent age. Further analyses did not reveal any detectable effect of music intervention on ANS response.
Conclusion
This study found that ANS responses were not modified by recorded music intervention in very preterm infants during wakefulness or sleep onset. Further research is warranted to explore other factors influencing ANS development in this population.
In the era of Industry 4.0, the study of Human-Robot Collaboration (HRC) in advancing modern manufacturing and automation is paramount. An operator approaching a collaborative robot (cobot) may have feelings of distrust, and experience discomfort and stress, especially during the early stages of training. Human factors cannot be neglected: for efficient implementation, the complex psycho-physiological state and responses of the operator must be taken into consideration. In this study, volunteers were asked to carry out a set of cobot programming tasks, while several physiological signals, such as electroencephalogram (EEG), electrocardiogram (ECG), Galvanic skin response (GSR), and facial expressions were recorded. In addition, a subjective questionnaire (NASA-TLX) was administered at the end, to assess if the derived physiological parameters are related to the subjective perception of stress. Parameters exhibiting a higher degree of alignment with subjective perception are mean Theta (76.67%), Alpha (70.53%) and Beta (67.65%) power extracted from EEG, recovery time (72.86%) and rise time (71.43%) extracted from GSR and heart rate variability (HRV) metrics PNN25 (71.58%), SDNN (70.53%), PNN50 (68.95%) and RMSSD (66.84%). Parameters extracted from raw RR Intervals appear to be more variable and less accurate (42.11%) so as recorded emotions (51.43%).
Objective: This study aims to evaluate the differences in heart rate variability (HRV), a biomarker of autonomic nervous system, between offspring of normotensive and hypertensive parents to understand the genetic predisposition of autonomic dysfunction. Methods: This study was a cross-sectional observational study.Two groups of healthy adults, offspring of parents with hypertension (n = 50) and offspring of parents with normal blood pressure (n = 50). Short-term HRV was measured using 5-minute electrocardiogram (ECG). HRV indices such as time and frequency domainwere measured. Data were compared by using independent t-tests, with p < 0.05 being considered as statistically significant. Results:The offspring of parents with hypertension showed significantly lower HRV, with SDNN (30.5 ± 8.2 ms) compared to offspring of parents with normal blood pressure (45.2 ± 7.1 ms, p < 0.001). RMSSD also was significantly lower in offspring of hypertensive group. Low-frequency (LF) power was higher in offspring of parents with hypertension,while high-frequency (HF) power was significantly reduced in them compared to the normotensive group. The LF:HF ratio was higher in offspring of parents with hypertension (2.80 ± 0.85) compared to the normotensive group (1.40 ± 0.60, p < 0.001), indicating sympathovagal imbalance. Conclusion: Offspring of parents with hypertension hadlower HRV, suggesting autonomic dysfunction even in the absence of clinical hypertension. These findings emphasize the potential role of genetic predisposition in the early onset of autonomic dysregulation Further studies are required to understand mechanisms contributing to these differences in HRV.
A BSTRACT
Context
PCOS is one of the most neglected noncommunicable diseases, and early detection would be of great value to primary care physicians. Sympathovagal imbalance detected using heart rate variability (HRV) can be used to detect early autonomic changes if any.
Aim
The present study aimed to evaluate QTc and Poincare plot (nonlinear analysis of HRV) in young adolescent PCOS patients.
Materials and Methods
It was a cross-sectional study involving 25 PCOS and 25 healthy individuals of age group 12–18 years. HRV was evaluated using the lead II ECG for 10 min from which QTc was calculated manually using the Bazett formula. Student’s t -test was used to assess differences between means. A P value < 0.05 was taken for statistical significance. The association between QTc and Poincare plot descriptors was assessed by Pearson’s correlation analysis.
Results
HRV linear analysis domain represented as the LF/HF ratio was reported to significantly increased among the PCOS group ( P = 0.04). Similarly, the nonlinear analysis of HRV by Poincare plot reported a significant decrease in SD1 ( P = 0.04) and SD2 ( P = 0.02). The heart rate was significantly increased among the PCOS group ( P < 0.001). QTc did not show any significant increase among the PCOS group ( P = 0.09). QTc was reported to be positively correlated with SD1 (r = 0.37, P < 0.01), SD2 (r-0.33, P = 0.02), LF HF ratio (r = 0.52, P < 0.001), and BMI (r = 0.92, P < 0.001), respectively.
Conclusion
The study suggests that HRV nonlinear analysis can be used as a simple noninvasive tool to evaluate cardiovascular autonomic changes.
Atrial fibrillation (AF) is a heart disease affecting millions of Americans. Clinicians evaluate AF-related risk by assessing the temporal pattern, variation, and severity of AF episodes through AF burden (AFB). However, existing prognostic tools based on these metrics are suboptimal, as they do not account for electrical complexity of AF signals. This study introduced Electrical Burden (EB) as a new marker to assess electrical instability and complexity of AF. We also developed a Complexity AF score that incorporates AFB, EB, and Poincaré analysis to assess the severity of AF. Electrocardiogram (ECG) from 50 AF patients in the Long-term AF database were analyzed. EB was calculated using four metrics and combined with AFB and Poincaré metrics to derive the Complexity AF score for each patient. Our results show that AFB, EB, and Poincaré metrics are independent markers, each describing different aspects of AF complexity. The Complexity AF score effectively distinguished between terminated (2.82 ± 1.29, 17 patients) and non-terminated AF groups (4 ± 1.46, 33 patients) (p-value < 0.05). This study emphasizes the importance of EB and Poincaré analysis as an indicator of electrical complexity of AF and highlights the utility of the Complexity AF score in accurately characterizing and stratifying AF to guide management.
Purpose
Acute exercise can transiently enhance cognitive flexibility. The cognitive demand of firefighters makes it relevant to understand if on-shift exercise could produce similar improvements in cognitive performance during subsequent occupational tasks. Metrics of heart rate variability (HRV), such as time- and frequency-domain outcomes, may shed light upon the influence exercise has on cognition, as they discern information related to cardiac autonomic (sympathetic/parasympathetic) function. We aimed to determine if acute resistance and aerobic exercise impact cognitive flexibility during occupational tasks and its relation to HRV.
Methods
32 participants completed a baseline Wisconsin Card Sorting Task (WCST) and three experimental trials: resistance exercise (RE), aerobic exercise (AE), or a rested control (CON). An occupational task assessment (OTA) including four rounds of 10 deadlifts and a 0.15-mile sandbag carry in an environmental chamber (35 °C/50% humidity) was completed after each trial. The second round was followed by the WCST. Repeated measures ANOVAs were used to analyze differences by condition.
Results
For the WCST, total, perseverative, and non-perseverative errors did not differ (ps > 0.39). Time-domain HRV metrics were not different (ps > 0.05). All frequency-domain metrics, other than low-frequency power, were not different (ps > 0.24). Low-frequency power was lower based on condition (p = 0.03). Post hoc analysis showed low-frequency power was lower following AE compared to RE and CON.
Conclusion
Results suggest an acute bout of on-shift aerobic or resistance exercise may not impact cognitive flexibility during subsequent simulated occupational tasks, despite depressed metrics of heart rate variability following aerobic exercise.
Introduction: Yoga practices emphasize spinal energy's role in physical, mental, and spiritual well-being,
suggesting specific techniques that can enhance energy flow along the spine. Modern research aims to
validate these claims and understand the mechanisms behind these effects, potentially integrating them
into contemporary healthcare models. This study explores the relationship between yoga breathing
techniques, spinal energy dynamics, and health based on yoga philosophy and bioenergetics.
Methodology: Thirty participants, averaging 44 years old with 10-20 years of yoga practice, underwent
sessions of slow deep breathing (SDB), alternate nostril breathing (ANB), kapalbhati pranayama, specific
nostril breathing exercises, and moderate exercise as a control. Spinal energy was measured using the
NeuralChek Spinal Energy system (BrainTap® INC, New Bern, NC), capturing baseline, session, and
postsession readings. Statistical analyses assessed changes in spinal energy levels across cervical, thoracic,
lumbar, sacral, and coccygeal regions.
Results: SDB and ANB significantly increased spinal energy levels across multiple spinal regions. Kapalbhati
pranayama showed variable effects, with significant decreases observed in some regions. Specific nostril
breathing exercises also demonstrated significant increases in spinal energy. In contrast, exercise resulted in
decreased spinal energy levels, particularly in cervical and lumbar regions.
Conclusion: The findings highlight the potential of yoga breathing techniques to influence spinal energy
dynamics, correlating with traditional yoga teachings on energy centers and modern concepts of
bioenergetics. These results suggest avenues for integrating yoga practices, particularly breathing
techniques, into holistic healthcare approaches aimed at enhancing physiological and psychological wellbeing. Further research could explore underlying mechanisms and clinical applications, bridging ancient
wisdom with contemporary scientific understanding for optimized health outcomes.
Categories: Public Health, Physical Medicine & Rehabilitation, Healthcare Technology
Keywords: bioenergetics, breathing exercises, physical fitness, spinal cord, yog
Objective
The aetiology of impairments in autonomic modulation of heart rate variability (HRV) in polycystic ovary syndrome (PCOS) remains unclear, as does the impact of aerobic physical training (APT) on controlling endocrine‐metabolic disorders and HRV. This is because these women often present excess body fat. Therefore, we assessed whether the dysregulation in autonomic modulation of HRV in women with PCOS is due to endocrine‐metabolic disorders and whether the combination of excess body fat with endocrine‐metabolic disorders amplifies cardiovascular autonomic deficits. We also investigated whether APT positively influences autonomic modulation of HRV in PCOS.
Design
Non‐randomised clinical trial.
Participants
Women with and without PCOS with different percentages of body fat.
Measurements
Participants were divided into four groups: women without PCOS with a body fat percentage between 22% and 29% (CONTROL group; 22%–29%); CONTROL (30%–37%) group; PCOS (22%–29%) group; and PCOS (30%–37%) group. Hemodynamic, metabolic, and hormonal characteristics and HRV parameters were obtained before and after 16 weeks of APT.
Results
The PCOS (22%–29%) group exhibited lower vagal modulation than the CONTROL (22%–29%) group. In contrast, no significant differences were observed between the CONTROL (30%–37%) and PCOS (30%–37%) groups. Furthermore, the PCOS (30%–37%) group demonstrated lower sympathetic modulation than the PCOS (22%–29%) group. After APT, the PCOS (22%–29%) group increased in vagal modulation, while the PCOS (30%–37%) group increased in sympathetic modulation.
Conclusion
PCOS affects vagal modulation; however, this effect may be masked at elevated levels of body fat. Additionally, the combination of excess body fat with endocrine‐metabolic dysregulation appears to reduce sympathetic modulation, possibly due to sympathetic drive hyperactivity. APT positively affected HRV in both PCOS groups.
Background Alterations of the autonomic nervous system (ANS) in the chronic stage of ischemic stroke (IS) are not well understood. Heart rate variability (HRV) provides a noninvasive approach to assess autonomic function.
Objective To compare the HRV parameters during the sleep-wake cycle between patients with IS in the chronic stage and healthy subjects.
Methods We conducted a retrospective transversal study based on clinical records and 24-hour electrocardiogram (EKG) monitoring registries of 179 patients with a confirmed IS diagnosis and 184 age- and sex-matched healthy subjects. Circadian variation was calculated according to the variation of the total autonomic activity (VTAI) and the parasympathetic activity (VPAI) indexes. Comparisons were performed using nonparametric tests. Multivariable analyses were performed with canonical discriminant analysis (CDA) and a three-way analysis of variance (ANOVA). Statistical significance was established with a confidence level of 95%.
Results During waking hours, the healthy group exhibited higher variability in the time domain and frequency domain parameters: standard deviation of NN intervals (SDNN, p < 0.001) and of the average NN intervals (SDANN, p < 0.001), as well as low-frequency (LF) band ( p < 0.001). During sleep, the difference was higher in the high-frequency (HF) band ( p < 0.001), and lower in the low-/high-frequency ratio (LF/HF, p < 0.001). Both VPAI and VTAI showed less significant difference in IS patients ( p < 0.001).
Conclusion There was diminished heart vagal activity among IS patients, as measured through HRV. During sleep, this is likely caused by an imbalance in the sympathetic and parasympathetic systems shifting through the sleep phases. These imbalances could persist over time in patients with IS, lasting months after the initial injury.
Background: Vitamin D deficiency is a global health problem and is highly prevalent among the Saudi population. A growing body of evidence indicates an association between vitamin D deficiency and risk of cardiovascular disease (CVD). Heart rate variability (HRV) is a non-invasive technique that evaluates cardiac autonomic function, which is a major determinant of cardiovascular health. Limiteddata is available on the relationship between vitamin D deficiency and HRV and none exists among the Saudi population. Therefore, this study was conducted to examine the association between vitamin D status and HRV in female medical students at King Abdulaziz University (KAU) in Jeddah, Saudi Arabia. Methods: This cross-sectional study was conducted from March to May, 2015 at the Faculty of Medicine, KAU. A total of 124 female students participated in the study. After completing a self-administered questionnaire, anthropometric measurements were taken for all subjects. HRV was recorded after five minutes rest in the supine position using ML870 power lab machine. Blood was obtained for the determination of serum levels of 25-hydroxyvitamin D3 (25[OH]D), parathyroid hormone (PTH), calcium, phosphate and magnesium. Informed consent was obtained from all participants and the study was approved by the ethics committee at KAU hospital. Results: The mean age of the study subjects was 21.7± SD 1.1 and the mean 25 (OH) D levels was 31.2 nmol/L ± SD 16.9. Almost 86 % of the participants were vitamin D deficient. Seventy-two (72%) of the participants with 25(OH) D< 30 nmol/L had RMSSD values (an index of parasympathetic activity) below the 25 th percentile compared to 28% with 25(OH) D ≥30 nmol/L (chi-square, P=0.049). Regression analysis showed that 25(OH) D level was independently and negatively associated with LFnu (an index of sympathetic activity) (B=-0.175, P<0.028). Conclusion: Our findings suggest that vitamin D deficiency is associated with low HRV, a predictor of CVD risk. Larger community based studies are needed to confirm these findings. Early identification of vitamin D deficiency coupled with appropriate treatment measures can prevent the risk of CVD in otherwise healthy subjects.
This study explored the relationship between cognitive function and the autonomic nervous system by categorizing participants into two groups based on their cognitive function scores in each domain of the SNSB-D: a High Cognitive Performance (HCP) group and a Low Cognitive Performance (LCP) group. We analyzed the Pulse Rate Variability (PRV) parameters for each group. Photoplethysmography (PPG) data were collected and processed to remove noise, and the PRV parameters in the time and frequency domains were extracted. To minimize the impact of age and years of education on the PRV parameters, we performed an adjusted analysis using a Generalized Linear Model (GLM). The analysis revealed that the autonomic nervous system, particularly the parasympathetic nervous system, was more activated in the LCP group compared to the HCP group. This finding suggests that in individuals with low cognitive function, the sympathetic nerves in the autonomic nervous system are less activated, so the parasympathetic nerves are relatively more activated. This study investigated the correlation between cognitive function and PRV parameters, highlighting the potential use of these parameters as indicators for the early diagnosis and classification of cognitive decline.
Internalizing psychopathology is associated with abnormalities in heart rate variability (HRV). Lower HRV that reflects reduced parasympathetic nervous system activity has been observed in depressive and anxiety disorders. Existing studies predominantly used categorical rather than dimensional approaches, the latter of which better addresses clinical comorbidity and heterogeneity. Moreover, there is little evidence on the role of HRV in longitudinal symptom trajectory in adolescents and young adults. The current study examined the association between HRV and internalizing symptom trajectory using a dimensional approach—the tri-level model of depression and anxiety. Adolescents and young adults (N = 362) were recruited in a 3-year longitudinal study, where they completed electrocardiogram recordings and self-report symptom questionnaires. Multilevel modeling was conducted with high-frequency power bands (HF power) of interbeat intervals at baseline as the predictor, and tri-level symptom factors over 3 years as the outcome. HF power significantly predicted the trajectory of the broad General Distress symptom factor, but not the intermediate Fears or Anhedonia-Apprehension symptom factors. Higher HF power was associated with a decline in General Distress over time. This association was held when neuroticism, other tri-level symptom factors, and demographic variables were covaried. That is, greater parasympathetic nervous system activity at baseline was significantly associated with a greater decline in the broad internalizing symptom factor, but not symptom factors that are more specific to depressive or anxiety disorders. Parasympathetic activity, therefore, may be a transdiagnostic biomarker for internalizing symptoms in adolescents and young adults.
There is substantial evidence regarding the positive influences of natural elements on patients’ health outcomes. However, research has predominantly focused on natural green elements rather than natural blue elements. While sky and water are significant components of what humans perceive as "nature" and both offer considerable restorative effects in various built environments, research about their role in healthcare facilities has been limited. Therefore, this study investigated influences of exposure to natural blue elements on patients in medical imaging environments, specifically in Positron Emission Tomography/Computed Tomography (PET/CT) rooms. Virtual reality (VR) was employed to develop several scenarios with design strategies based on natural blue elements. These scenarios were presented to twenty participants who were former patients of medical imaging settings. The study employed a mixed methods research approach, collecting both subjective (questions on visual perception, positive and negative affects, self-reported stress) and physiological responses (mean heart rate and vagally-mediated heart rate variability). The study supports the idea that virtual reality serves as an effective tool for prototyping PET/CT scan environments. Furthermore, the results show that certain design strategies incorporating all aspects of natural blue elements, such as flowing water and its sound, water motion, water reflection, light in the sky, clouds, and the presence of birds in flight, have the potential to evoke specific positive subjective and physiological responses in participants. The findings also highlight the significant benefits of incorporating motion with natural blue elements, which makes them more realistic and, consequently, brings more life to medical imaging environments.
Health disparities among African Americans have been reported for decades. This is especially true for cardiovascular disease (CVD) even when compared with other minority groups in America. Such disparities have been tied to perceived discrimination. A previous study found that perceived racism accounted for a substantial percentage of the variance in resting heart rate variability (HRV), an independent biomarker of cardiac health. The present study attempts to replicate such findings. This study includes 57 healthy African American individuals who met inclusion criteria. Participants were given the Perceived Ethnic Discrimination Questionnaire–Community Version (PEDQ-CV) and the Perceived Racism Scale (PRS) and had their resting HRV and blood pressure measured. After accounting for breathing rate and age, the lifetime score on the PRS uniquely accounted for up to 45% of the variability of HRV metrics. The PEDQ-CV was not found to be a statistically significant predictor of HRV. Within this sample, blood pressure was not significantly predicted by either scale. The findings suggest that lifetime perceived racism may directly affect HRV indices, which may indicate an increased risk for CVD. Further research should continue to investigate this association and potential avenues for related intervention.
Fuel dispensing at fuel stations is performed manually by unprotected male gas station attendants in Sri Lanka, who have long working hours. These workers are exposed to hydrocarbon fuels associated with multiple health effects by modulation of the autonomic nervous system. This study was performed to determine cardiovascular autonomic functions among fuel pump attendants in Sri Lanka. Fuel pump attendants (n = 50) aged between 19 and 65 years were identified for the study from seven fuel stations. They were compared with age‐ and gender‐matched controls (n = 46) without occupational exposure to fuel. A physical examination was performed before the autonomic function and heart rate variability (HRV) assessment. There were no significant differences in weight, height, or BMI between the study and the control populations (p > 0.05). Both the systolic blood pressure (SBP) (Mann Whitney U (MWU) = 743.5, p = 0.003) and diastolic blood pressure (DBP) (MWU = 686.5, p = 0.001) were significantly higher among the gas station attendants compared to controls. Valsalva ratio was significantly higher among the study group (MW U = 874.00, p = 0.043) compared to controls. The HRV analysis showed significantly higher SDNN and SD2 (MWU = 842.00, p = 0.034, and MWU = 843.50, p = 0.035 respectively) among the gas station attendants compared to controls. The changes to the cardiovascular autonomic parameters among those exposed to fuel vapor as a gas station attendant indicate an increase in sympathetic outflow to the vessels. In the occupational setting as fuel pump attendants need periodic monitoring.
The empirical and clinical literature emphasizes the importance of alliance ruptures, signaling therapeutic processes occurring within and between the partners of the therapeutic dyad. However, knowledge about the underlying regulatory processes that occur amid ruptures is scarce. Identifying the underlying physiological markers may shed light on these regulatory processes. The overarching goal of the present study was to explore physiological markers of withdrawal and confrontation ruptures, within the patient and the therapist. Given the little known on the subject, we used a single-case design (94 episodic segments) to explore biologically based regulatory processes in the face of a rupture, contrasting confrontation ruptures versus withdrawal ruptures versus control episodes (emotional and neutral episodes). Findings showed that the patient and the therapist had contrasting physiological responses to the ruptures, depending on the type. During withdrawal ruptures, the patient exhibited high regulation, while the therapist did not show a clear physiological reaction. During confrontation ruptures, the patient exhibited low regulation, while the therapist exhibited high regulation. The different physiological regulation processes at times of ruptures suggest that, in withdrawal, the patient relied on intrapersonal regulation, contrasting with the interpersonal regulation observed in confrontation ruptures. Findings remained robust after controlling for speech turns and 10,000 Monte Carlo permutations to assess chance-level results. These findings provide initial evidence for the link between arousal and behavior in ruptures, offering valuable psychoeducational material for therapists to improve their handling of these challenging moments.
Background and purpose
Critical illness polyneuropathy (CIP) has been linked to neurocardiac dysfunction mediated by autonomic nervous system dysregulation, which increases mortality. We aimed to assess if heart rate variability (HRV) biofeedback could improve neurocardiac function in CIP.
Methods
We randomly allocated (1:1) patients with electrophysiologically confirmed CIP undergoing early inpatient neurological rehabilitation to additional HRV or sham biofeedback over 14 days. We evaluated neurocardiac function via standard deviation of normal‐to‐normal intervals (SDNN) as the primary outcome, as well as HRV frequency domains, sympathetic cutaneous sudomotor and vasomotor functions and disability at baseline, post intervention and 4 weeks later. The study is registered on the German Clinical Trials Register (DRKS00028911).
Results
We included 30 patients with CIP (40% females, median [interquartile range] age 64.6 [56, 72] years). We observed an increase in SDNN and the predominantly parasympathetic high frequency domain post intervention (ß = 16.4, 95% confidence interval [CI] 0.2, 32.6 [p = 0.047] and ß = 1179.2, 95% CI 119.9, 2158.5 [p = 0.018]), which was sustained at the 4‐week follow‐up (ß = 25.7, 95% CI 6.0, 45.4 [p = 0.011] and ß = 25.7, 95% CI 6.0, 45.4 [p = 0.011]). Patients who underwent HRV biofeedback displayed a higher adjusted Barthel index, indicating less severe disability 4 weeks after the intervention compared to those in the sham group (ß = 23.3, 95% CI 5.5, 41.1 [p = 0.014]). Low frequency and sympathetic skin functions did not differ between groups (p = nonsignificant).
Conclusions
Our study provides pilot data suggesting that, in patients with CIP, HRV biofeedback can improve neurocardiac function with a predominant effect on the parasympathetic nervous system and has a beneficial effect on functional recovery.
(1) Background: Our previous studies indicated that low-intensity extremely low-frequency electric field (ELF-EF) treatment alters autonomic activities, as revealed through heart rate variability (HRV) analysis. However, the high-frequency (HF) component of HRV that reflects parasympathetic activity showed no changes either during or after the end of the treatment, suggesting the involvement of sympathetic nerves. (2) Methods: To examine this issue in the present study, the effect of ELF-EF on skin conductance (SC), which is controlled solely by sympathetic nerves, was analyzed. Twelve healthy subjects underwent a 20 min ELF-EF treatment (applied voltage: 9 kV, induced current density: below 6 mA/m2) and a sham treatment in a random order with an interval of more than 2 weeks. SC and HRV were recorded under the eyes-open condition during a 2 min period both before and after the treatment. (3) Results: The number of spontaneous fluctuations in skin conductance (SC-SFs) significantly decreased after the ELF-EF treatment, suggesting psychological changes, including relaxation. The skin conductance level, heart rate, and HRV indices did not change after the ELF-EF treatment. (4) Conclusion: The results support the idea that low-intensity ELF-EF affects autonomic nerves by reducing sympathetic activity, as reflected by SC-SFs.
Mitral valve prolapse (MVP) is a common valvular abnormality especially in young female subjects. Recently, Boudulas had classified the patients with MVP into two types: the 1st type is MVP-anatomic (MVPa) with valvular malfunction and the 2nd MVP-syndrome (MVPs) without valvular disease. In the 2nd type, several authors have reported the occurrence of functional abnormalities of neuroendocrine or autonomic systems. Also, the syncope called 'neuromediated' has been found and is probably associated with modification of the autonomic nervous system. To understand the role of the autonomic nervous system, 39 female patients with MVPs (group 1) and 24 normal females as control group (group 2) were evaluated by a spectral analysis of heart rate variability (HRV) in time and frequency domains. The analysis between the two groups showed a low vagal tone in group 1 resulting in a lower high-frequency normalized unit (HF-NU) in comparison with the control group 2 (p < 0.03). Group 1 was divided into two subgroups with and without syncope. The analysis of HRV by Anova indicated no differences for all parameters between the two subgroups of MVPs patients. These results demonstrate that (1) MVPs has a low vagal tone; (2) the syncope in MVPs could not be only in relation to the autonomic nervous system malfunction, but probably other causes underlined this phenomenon.
Objectives:
This study was designed to test the hypothesis that antiarrhythmic drugs that decrease RR variability will predict all-cause mortality during follow-up after myocardial infarction.
Background:
RR variability, a noninvasive indicator of autonomic nervous system activity, predicts death after acute myocardial infarction independently of other risk predictors and changes substantially in response to some drugs. A previous study in patients with chronic heart disease and frequent ventricular premature complexes reported that flecainide decreased vagal modulation of RR intervals but amiodarone did not. The investigators of that study speculated that changes in RR variability during antiarrhythmic drug therapy predict an increased mortality rate during long-term drug treatment. To explore this hypothesis further, we compared the effects of encainide and flecainide, which increase long-term mortality substantially, on RR variability with the effects of placebo and moricizine, which have no significant effect on mortality during long-term treatment of unsustained ventricular arrhythmias after myocardial infarction.
Methods:
The 24-h power spectral density was computed from the baseline electrocardiographic recordings and drug evaluation tapes, and six frequency domain measures of RR variability were calculated: ultra-low frequency (< 0.0033 Hz), very low frequency (0.0033 to < 0.04 Hz), low frequency (0.04 to < 0.15 Hz) and high frequency power (0.15 to < 0.40 Hz), plus total power (< 0.40 Hz) and the ratio of low to high frequency power. Changes in power spectral measures were related to drug treatment and to mortality.
Results:
In the placebo group, values for RR interval and RR variability increased because of recovery from the effects of acute myocardial infarction. Contrasting placebo treatment with all three active antiarrhythmic drug treatments taken together showed that of all the measures of RR variability, only NN50, pNN50 and low frequency power changed significantly during drug treatment (Bonferroni adjusted p value < 0.025); these variables all decreased during drug therapy. Contrasting encainide and flecainide with moricizine, we found that the encainide and flecainide groups taken together showed a larger decrease in dLF than moricizine, but the difference was of borderline significance (Bonferroni adjusted p value < 0.08). Survival was significantly worse in the groups treated with encainide and flecainide than in the groups treated with placebo or moricizine (relative risk > 2.0, adjusted p < 0.05). The antiarrhythmic drug-induced change in measures of RR variability was not a significant predictor of all-cause mortality during a year of follow-up after myocardial infarction.
Conclusions:
Encainide, flecainide and moricizine all caused a decrease in RR variability in patients studied approximately 1 month after acute myocardial infarction. Encainide and flecainide caused a significant increase in mortality rates; placebo and moricizine did not. Baseline measurements of RR variability also predicted all-cause mortality after myocardial infarction. The decrease in RR variability produced by the three antiarrhythmic drugs did not predict mortality during follow-up.
Activation of the sympathetic nervous system has been extensively studied in patients with chronic heart failure, but the parasympathetic nervous system has received relatively little attention. The objective in this study was to investigate cardiac parasympathetic activity in chronic heart failure and to explore its relation to left ventricular function.
Heart rate variability was measured from 24 hour ambulatory electrocardiograms by counting the number of times each RR interval exceeded the preceding RR interval by more than 50 ms (counts). This method provided a sensitive index of cardiac parasympathetic activity.
Mean (range) of counts were: waking 48 (1-275)/h, sleeping 62 (0-360)/h, and total 1310 (31-7278)/24 h. These were lower than expected, and in 26 (60%) of the 43 patients counts fell below the lower 95% confidence intervals (95% CI) for RR counts in normal subjects. A significant correlation between total 24 hour RR counts and left ventricular ejection fraction was present (r = 0.49, p less than 0.05).
These results indicate that most patients with chronic heart failure have reduced heart rate variability and therefore reduced cardiac parasympathetic activity. The degree of parasympathetic dysfunction is related to the severity of left ventricular dysfunction. This may be relevant to the high incidence of ventricular arrhythmias and poor prognosis of patients with chronic heart failure.
Heart rate variability was measured in 77 healthy controls and 343 diabetic patients by a count of the number of beat-to-beat differences greater than 50 ms in the RR interval during a 24 hour ambulatory electrocardiogram. In the healthy controls the lower 95% tolerance limits for total 24 hour RR interval counts were approximately 2000 at age 25, 1000 at 45, and 500 at 65 years. Six controls confined to bed after injury had normal 24 hour patterns of RR counts, while eight other controls showed loss of diurnal variation in both heart rate and RR counts during a period of sleep deprivation. RR counts in ten controls on and off night duty increased during sleep whenever it occurred. Nearly half (146) the 343 diabetic patients had abnormal 24 hour RR counts. The percentage of abnormal RR counts increased with increasing autonomic abnormality assessed by a standard battery of tests of cardiovascular autonomic function. A quarter of those with normal cardiovascular reflex tests had abnormal 24 hour RR counts. There were close correlations between 24 hour RR count results and the individual heart rate tests (r = 0.6). The assessment of cardiac parasympathetic activity by 24 hour RR counts was reliable. The diurnal variations in RR counts seen in the controls were probably related to sleep rather than either posture or time of day. The method was more sensitive than conventional tests of cardiovascular reflexes.
We have demonstrated previously that transfer function analysis can be used to precisely characterize the respiratory sinus arrhythmia (RSA) in normal humans. To further investigate the role of the autonomic nervous system in RSA and to understand the complex links between respiratory activity and arterial pressure, we determined the transfer functions between respiration, heart rate (HR), and phasic, systolic, diastolic, and pulse arterial pressures in 14 healthy subjects during 6-min periods in which the respiratory rate was controlled in a predetermined but erratic fashion. Pharmacological autonomic blockade with atropine, propranolol, and both, in combination with changes in posture, was used to characterize the sympathetic and vagal contributions to these relationships, as well as to dissect the direct mechanical links between respiration and arterial pressure from the effects of the RSA on arterial pressure. We found that 1) the pure sympathetic (standing + atropine) HR response is characterized by markedly reduced magnitude at frequencies greater than 0.1 Hz and a phase delay, whereas pure vagal (supine + propranolol) modulation of HR is characterized by higher magnitude at all frequencies and no phase delay; 2) both the mechanical links between respiration and arterial pressure and the RSA contribute significantly to the effects of respiration on arterial pressure; 3) the RSA contribution to arterial pressure fluctuations is significant for vagal but not for sympathetic modulation of HR; 4) the mechanical effects of respiration on arterial pressure are related to the negative rate of change of instantaneous lung volume; 5) the mechanical effects have a higher magnitude during systole than during diastole; and 6) the mechanical effects are larger in teh standing than the supine position. Most of these findings can be explained by a simple model of circulatory control based on previously published experimental transfer functions from our laboratory.
THE AUTHORS HAVE MEASURED RESPIRATORY SINUS ARRHYTHMIA (RSA) IN NORMAL SUBJECTS AND NEUROPATHS OVER A RANGE OF STEADY STATE BREATHING, ALTERING BOTH TIDAL VOLUME AND FREQUENCY OF BREATHING. THE PRIMARY PURPOSE OF THE STUDY WAS TO QUANTIFY THE WAY IN WHICH HRV (HEART RATE VARIABILITY) CHANGES IN BOTH GROUPS OF SUBJECTS FOR DIFFERENT BREATHING STATES. THE RESULTS OF THESE INVESTIGATIONS CONFIRM THE REDUCTION IN HRV FOUND IN THE PRESENCE OF DIABETIC AUTONOMIC NEUROPATHY. THE REDUCTION IN VARIABILITY NECESSITATES A HIGHER RATE OF DATA SAMPLING THAN REQUIRED FOR NORMAL SUBJECTS IF FREQUENCY SPECTRA ARE TO BE OBTAINED. THE RESULTS WOULD INDICATE THAT ANY INVESTIGATIONS WHERE THE SAMPLING WAS MADE AT LESS THAN 200 HZARE LIKELY TO BE IN ERROR. USE OF THE INTERBEAT FREQUENCY METHOD HAS ADVANTAGES IN TERMS OF COMPUTATION TIME AND SHOULDENABLE THESE STUDIES TO BE CARRIED OUT ON A MICROPROCESSOR-BASED DATA ANALYSIS SYSTEM WHICH WOULD BE SUITABLE FOR USE IN A CLINICAL ENVIRONMENT. THE SHIFT IN THE PEAK OF THE HRV FREQUENCY RESPONSE WHICH OCCURS IN NEUROPATHY APPEARS TO BE DUE TO AN INCREASE IN THE LOOP TIME DELAY OF THE REFLEX, AND MAY PROVIDE THE BASIS FOR A NONINVASIVE CLINICAL TEST TO ASSESS THE PROGRESS OF THE DISEASE.
The degree of parasympathetic control of heart rate was assessed by the abolition of respiratory sinus arrhythmia with atropine. Peak-to-peak variations in heart periods (VHP) before atropine injection correlated significantly (r = 0.90, P < 0.001) with parasympathetic control, indicating that VHP alone may be used as a noninvasive indicator of the parasympathetic control of heart rate. Pharmacologic blockade of β-adrenergic supply in a separate group of normal volunteers did not alter the relationship between VHP and parasympathetic control, indicating that the condition of the experiment (complete rest in a quiet atmosphere) allows the use of VHP alone without pharmacologic interventions to characterize the vagal control of heart rate in humans.
To determine the reproducibility of frequency domain measures of heart period variability in patients with previous myocardial infarction, 2 random samples of 40 patients each (1 from the Cardiac Arrhythmia Pilot Study [CAPS] [unsustained ventricular arrhythmias], and 1 from the Electrophysiologic Studies Versus Electrocardiographic Monitoring [ESVEM] [sustained ventricular arrhythmias] trial) were studied. For each patient, two 24-hour continuous electrocardiographic recordings were analyzed, and the average normal RR interval, total power and 4 components of total power were calculated. Group means and standard deviations for each sample were virtually identical for the pairs of 24-hour recordings. Furthermore, measurements for individual patients were stable from day to day, as measured by the intraclass correlation coefficients and the standard errors of measurement. Reproducibility of heart period variability measurements is excellent in patients with previous myocardial infarction and ventricular arrhythmias, and is comparable to the high stability previously found in a small group of normal subjects. The stability of measures of heart period variability facilitates distinguishing real changes due to progression or regression of cardiac disease or to drug effects from apparent changes due to random variation.
Spontaneous variability of heart-rate has been related to three major physiological originating factors: quasi-oscillatory fluctuations thought to arise in blood-pressure control, variable frequency oscillations due to thermal regulation, and respiration; frequency selective analysis of cardiac interbeat interval sequences allows the separate contributions to be isolated. Using this method, a laboratory and field study of the effects of mental work load on the cardiac interval sequence has been carried Out. Results suggest that mean heart rate and variance are unreliable measures, but that consistent changes in interval spectrum occur; these have been traced to alterations mainly in the 0·1 Hz region, perhaps originating with changes in the patterns of respiration which interact with the 0·1 Hz vasomotor activity,
Reduced heart rate variability (HRV) has been reported as a predictor of mortality in recent myocardial infarction patients.
However, its automated assessment in long-term ECG recordings is complicated by recording noise and beat-recognition errors
which necessitate filtering of the computer-established sequence of beat-to-beat intervals, and visual checking and manual
editing of the long-term recordings, making the whole method operator-dependent. To develop a fully automated method for analysis
of HRV from 24 h ECG recordings, five filtering algorithms were combined with three methods of expressing HRV numerically
and used to compare two groups of patients undergoing 24 h tape recordings of the ECG within the first two weeks after myocardial
infarction. One group comprised 15 patients who later suffered death or ventricular tachycardia, the other group comprised
15 randomly selected uncomplicated cases. Using the same two groups of patients, three different methods of expressing HRV
on a beat-to-beat basis were also compared empirically. The results show that alternative, operator-independent methods for
establishing HRV from continuous long-term ECG recordings of postmyocardial infarction patients seem to be as effective as
previously reported methods which rely on operator-dependent data post-processing techniques.
Objectives:
This study was designed to examine the relation of the Poincaré plot heart rate variability pattern to sympathetic nervous system activity as assessed by serum norepinephrine.
Background:
Poincaré plots demonstrate a complexity of beat to beat behavior not readily detected by other heart rate variability measures. Previous studies have described two abnormal Poincaré patterns in patients with heart failure: a torpedo pattern with reduced beat to beat variability and a complex pattern with clustering of points.
Methods:
To assess the relation of these plots to sympathetic activity, plasma norepinephrine at rest and a standard deviation measure of heart rate variability were analyzed in 21 patients with heart failure (mean left ventricular ejection fraction [+/- SD] 0.22 +/- 0.05).
Results:
Eleven subjects had a torpedo-shaped and 10 subjects had a complex Poincaré plot pattern. These two groups did not differ significantly in age, functional class, disease etiology, left ventricular ejection fraction, heart rate, ventricular ectopic activity or in a standard deviation measure of heart rate variability. However, patients with a complex Poincaré plot pattern had higher norepinephrine levels (722 +/- 373 pg/ml) than patients with torpedo-shaped plots (309 +/- 134 pg/ml) (p = 0.003). Patients with a complex pattern also had more severe hemodynamic decompensation, as evidenced by their higher levels of pulmonary capillary wedge and mean pulmonary artery pressures and lower values for cardiac index than those of patients with a torpedo-shaped plot.
Conclusions:
Complex Poincaré plots are associated with marked sympathetic activation and may provide additional prognostic information and insight into autonomic alterations and sudden cardiac death in patients with heart failure.
RR variability was analyzed in 15 patients with ventricular arrhythmias to evaluate whether the antiarrhythmic action of propafenone is associated with alteration of neural control mechanisms. Before drug administration, spectral analysis of RR variability was characterized by 2 major components at low and high frequency, which are considered to reflect sympathetic and parasympathetic modulation of the heart period. After propafenone (600 to 900 mg/day), there was a marked reduction in RR variance (826 ± 184 to 412 ± 77 ms2; p < 0.05), although the mean RR interval was unchanged. The drug significantly reduced the low-frequency component (52 ± 6 to 28 ± 4 nu) and augmented the high-frequency component (39 ± 6 to 55 ± 5 nu). As a result, the low-/high-frequency ratio (an index of sympathovagal balance) decreased from 2.0 ± 0.4 to 0.6 ± 0.1. A positive correlation between serum levels and drug-induced changes in the low-frequency component was also observed. Furthermore, the increase in the low-frequency component induced by tilt (53 ±5 to 79 ± 3 nu) was markedly attenuated after drug administration (27 ± 5 to 54 ± 7 nu). Thus, propafenone administration is associated with changes in spectral components that are consistent with a β-blocking effect of the drug.
Four components of the heart period power spectrum—ultra low frequency (<0.0033 Hz), very low frequency (0.0033 to <0.04 Hz), low frequency (0.04 to <0.15 Hz) and high frequency power (0.15 to 0.40 Hz)—plus total power (1.157 × 10−5 to 0.4 Hz for a 24-h electrocardiographs [ECG] recording) all predict mortality after myocardial infarction. To determine the time course and magnitude of recovery for these measures of heart period variability, 68 patients in the Cardiac Arrhythmia Pilot Study (CAPS) placebo group who had 24-h ECG recordings at baseline, 3, 6 and 12 months after myocardial infarction were studied. The 24-h power spectral density was computed with use of fast Fourier transforms and divided into the four components listed previously. The values for the five frequency domain measures of heart period variability in the CAPS patients were similar to those found in 715 patients who participated in the Multicenter Post Infarction Program (MPIP), indicating that the CAPS sample is generally representative of postinfarction patients with respect to these measures. The values for the five measures were one third to one half of those found in 95 normal persons of similar age and gender. There was a substantial increase in all measures of heart period variability between the baseline 24-h ECG recording and the 3-month recording (p < 0.001). Between 3 and 12 months, the values were quite stable for the group as a whole, as well as for individual patients (intraclass correlation coefficients ≥ 0.66). However, even at 12 months after infarction, values for the five measures of heart period variability were one half to two thirds the values found in the sample of 95 normal persons.
Objectives:
To determine whether spectral measures of heart period (RR) variability predict death when measured late after infarction, we studied patients in the Cardiac Arrhythmia Pilot Study (CAPS) who survived for 1 year and had a 24-h electrocardiographic (ECG) recording made after the CAPS drug was washed out.
Background:
Four components of the heart period power spectrum--ultra low frequency (< 0.0033 Hz), very low frequency (0.0033 to < 0.04 Hz), low frequency (0.04 to < 0.15 Hz) and high frequency power (0.15 to < 0.40 Hz)--plus total power (1.157 x 10(-5) to < 0.40 Hz) and the ratio of low to high frequency power predict mortality when measured < 30 days after myocardial infarction. However, these variables increase to steady state values by 3 months after infarction and the prognostic significance of recovery values is unknown.
Methods:
The 24-h power spectral density was computed from ECG recordings made 1 year after infarction using fast Fourier transforms and the six measures listed were calculated. The values were dichotomized at cut points that maximized the association with mortality.
Results:
Each measure of RR variability had a strong and significant univariate association with mortality; the relative risks for these variables ranged from 2.5 to 5.6. After adjustment for age, New York Heart Association functional class, rales in the coronary care unit, left ventricular ejection fraction and ventricular arrhythmias, some measures of heart period variability still had a strong and significant independent association with all-cause mortality.
Conclusions:
Spectral measures of heart period variability, measured late after infarction, predict death.
Objectives:
The purpose of this report was to study heart rate variability in Holter recordings of patients who experienced ventricular fibrillation during the recording.
Background:
Decreased heart rate variability is recognized as a long-term predictor of overall and arrhythmic death after myocardial infarction. It was therefore postulated that heart rate variability would be lowest when measured immediately before ventricular fibrillation.
Methods:
Conventional indexes of heart rate variability were calculated from Holter recordings of 24 patients with structural heart disease who had ventricular fibrillation during monitoring. The control group consisted of 19 patients with coronary artery disease, of comparable age and left ventricular ejection fraction, who had nonsustained ventricular tachycardia but no ventricular fibrillation.
Results:
Heart rate variability did not differ between the two groups, and no consistent trends in heart rate variability were observed before ventricular fibrillation occurred.
Conclusions:
Although conventional heart rate variability is an independent long-term predictor of adverse outcome after myocardial infarction, its clinical utility as a short-term predictor of life-threatening arrhythmias remains to be elucidated.
The heart and vasculature have been viewed for too long as a self contained system. Arrhythmias have been treated by suppression of one or another property of myocardial excitability, but extracardiac factors also have a role in the genesis of sporadic, paroxysmal ventricular arrhythmias as well as ventricular fibrillation. In animal models, manipulation of the sympathetic neural input affects cardiac vulnerability; in the ischemic myocardium, such manipulation may be a sufficient stimulus to induce fibrillation. Psychologic stresses, even of brief duration, profoundly reduce the threshold for ventricular fibrillation and result in major ventricular rhythm disorders. In man, the occurrence of ventricular arrhythmias is likewise correlated with the activity of the sympathetic nervous system. Especially relevant are three recent studies suggesting that in patients who have recovered from acute myocardial infarction, the incidence of sudden death is markedly reduced by beta adrenergic blocking drugs. It may be that pharmacologic treatments for prevention of sudden death should be focused on restraining neurophysiologic triggers rather than protecting the cardiac target.
THE way in which adrenaline acts on the sinoatrial (SA) node to
accelerate the heart rate has hitherto been obscure. However, in various
other parts of the heart adrenaline increases the slow inward
(Ca2+/Na+) current1-4, and
voltage-recording experiments have indicated that adrenaline also has
this action in the sinus region5-7. In the voltage-clamp
experiments reported here, we find that adrenaline does indeed increase
the slow inward current in the SA node of the rabbit, but that it also
augments the outward current which would tend to decelerate pacemaker
depolarisation. We find that an additional current, if, is
activated within the range of voltage where the pacemaker depolarisation
occurs: this could be important both in normal pacemaking and in
adrenaline-induced acceleration.
Voltage clamp experiments were carried out in order to study the mechanism of the ACh action in the rabbit S-A node cell. The following results were obtained: 1. The reversal potential of the ACh-induced current behaved like a potassium electrode, confirming that the ACh-operated channels pass potassium ions selectively. 2. On depolarizing voltage jumps the ACh-induced current showed an instantaneous peak from which the current decayed to a new steady level (relaxation). On hyperpolarizing voltage jumps the initial step change in current was followed by a gradual increase. 3. The time course of the current change on voltage jumps was well fitted by a single exponential and the time constant became longer as the membrane potential was increased. 4. The instantaneous I-V curve was linear while in the steady state the curve became flatter at low negative membrane potentials and steeper at high negative membrane potentials. The results suggest that ACh opens a specific potassium channel when the drug is bound to the muscarinic receptor. The opening and closing rate constants for this potassium channel depend on the membrane potential in such a way that on depolarizing voltage jumps the fraction of open channels gradually decreases and on hyperpolarization the fraction increases.
Sinus arrhythmia, defined by means of a calculation of variance of the R-R interval on admission to hospital, was present in 73 of 176 patients admitted to a coronary care unit with acute myocardial infarction. These patients had a lower hospital mortality. They tended to have a higher incidence of inferior infarction, and a lower incidence of anterior infarction, and to have smaller infarcts as measured by the Norris index. The main difference between patients with sinus arrhythmia and without sinus arrhythmia related to heart rates on admission to hospital, the patients with the former having slower heart rates at that time.
Spectral analysis was used to investigate variations of heart period in 13 decerebrate cats under different conditions of neural input to the heart. Spectral density plots in intact animals showed three well-defined peaks: P1 (1.5-2.5 cycles/min), P2 (6-10 cycles/min), and P2 (respiratory frequency). In the presence of sympathetic input only the amplitudes of all peaks were decreased; when only vagal input was present the amplitudes of P1 and P2 were increased and there was no change in P3; when neither sympathetic nor vagal input was present the amplitudes of all peaks were decreased. In addition, the amplitudes of P1 and P2 were increased and there was no change in P3; when neither sympathetic nor vagal input was present the amplitudes of all peaks were decreased. In addition, the amplitudes of P1 and P2 were found to be significantly correlated with the mean heart period under the condition of vagal control only. It is concluded that P3 is related to sinus arrhythmia and that P1 and P2 may be related to spontaneous rhythms that are an intrinsic feature of the dynamic regulation of heart period by the vagus system. Sympathetic activity plays no role in the genesis of these rhythms.
The degree of parasympathetic heart rate control, PC, was defined as the decrease in average heart period (RR interval) caused by the elimination of parasympathetically mediated influences on the heart while keeping sympathetic activity unchanged. By reviewing published results on the interaction of sympathetic and parasympathetic heart rate control, the prediction was made that PC should be directly proportional to VHP, the peak-to-peak variations in heart period caused by spontaneous respiration. In sevel chloralose/urethan-anesthetized dogs the vagi were reversibly blocked by cooling, and PC (the difference between average heart period before and after cooling) and VHP (without cooling) were determined under a variety of conditions that included a) increasing vagal activity by elevating the blood pressure b) sympathetic blockade, and c) parasympathetic blockade. The relationship between VHP and PC was linear with an average correlation coefficient of 0.969 +/- 0.024 (SD) and a PC-axis intercept of 15.2 +/- 25.9 ms. In each dog the correlation coefficient between VHP and PC was higher than between VHP and the average heart period (avg correlation coef: 0.914 +/- 0.044). These results suggest that the degree of respiratory sinus arrhythmia may be used as a noninvasive indicator of the degree of parasympathetic cardiac control.
Ambulatory ECG is an evolutionary cardiovascular discipline with regard to both its clinical applications and technology. With the technologic advances of the past decade, powerful personal computers have expanded the traditional clinical role of ambulatory ECG examination for cardiac arrhythmias to detection of ST-segment changes, heart-rate variability, QT interval measurement, and the signal-averaged ECG. These expanded clinical applications increase the practicality of a 24-hour ambulatory ECG on an individual cardiac disease patient and make the 24-hour ambulatory ECG one of the most cost-effective cardiovascular diagnostic tests when used properly. The current clinical developments make valid ST-segment detection and quantitation readily available and heart-rate variability an easily applied investigative tool to a wide spectrum of diseases. Automatic QT interval measurements and signal averaging of ambulatory ECG are just technologically emerging and can be expected to develop more in the near future.
Reduced heart rate (HR) variability is associated with increased risk of cardiac arrest in patients with coronary artery disease. In this study, the power spectral components of HR variability and their circadian pattern in 22 survivors of out-of-hospital cardiac arrest not associated with acute myocardial infarction were compared with those of 22 control patients matched with respect to age, sex, previous myocardial infarction, ejection fraction and number of diseased coronary arteries. Survivors of cardiac arrest had significantly lower 24-hour average standard deviation of RR intervals than control patients (29 +/- 10 vs 51 +/- 15 ms, p less than 0.001), and the 24-hour mean high frequency spectral area was also lower in survivors of cardiac arrest than in control patients (13 +/- 7 ms2 x 10 vs 28 +/- 14 ms2 x 10, p less than 0.01). In a single cosinor analysis, a significant circadian rhythm of HR variability was observed in both groups with the acrophase of standard deviation of RR intervals and high-frequency spectral area occurring between 3 and 6 A.M. which was followed by an abrupt decrease in HR variability after arousal. The amplitude of the circadian rhythm of HR variability did not differ between the groups. Thus, HR variability is reduced in survivors of cardiac arrest but its circadian rhythm is maintained so that a very low HR variability is observed in the morning after awakening, corresponding to the time period at which the incidence of sudden cardiac death is highest.
Signs of sympathetic hyperactivity and low parasympathetic activity have been found during the acute and recovery phases of myocardial infarction and have been associated with an increased risk of cardiac mortality. Beneficial effects of physical training have been recently reported in post-myocardial infarction patients. We tested the hypothesis that physical training would be effective in improving the autonomic balance by studying 22 patients with a first and recent myocardial infarction who were randomly assigned to enter or not enter a 4-week in-hospital physical training program. Spectral indices of heart rate variability were analyzed at rest and during 70 degrees head-up tilt before and after the index training, not training period. As expected, physical training induced a significant increase in exercise duration (13.7 +/- 0.8 vs 17.1 +/- 0.1 min, p less than 0.001) and in the anaerobic threshold (9.5 +/- 0.7 vs 12.0 +/- 1.0 min, p less than 0.02) in trained patients, while no changes were observed in the untrained group. At entry, in both groups, spectral profile of heart rate variability was characterized by a predominant LF component and a smaller HF component with no further modification after head-up tilt. After 4 weeks, in resting conditions, no significant changes in spectral components were observed in both trained and untrained patients. After physical training, head-up tilt produced significant modifications in spectral profile with an increase in the LF component (84 +/- 3 vs 69 +/- 5 nu, p less than 0.01) and a decrease in the HF component (7 +/- 1 vs 19 +/- 4 nu, p less than 0.05) in trained patients, while no changes were observed in the untrained patients. Our data suggest that in postmyocardial infarction patients, 4 weeks of physical training may induce an improvement in the autonomic balance with a restoration toward normal in the reflex activity of the system.
The circadian variations of spectral indices of heart rate variability were analyzed in 20 patients 4 weeks after a first and uncomplicated myocardial infarction (MI) and in 20 control subjects. R-R interval and variance showed a characteristic day-night pattern with a significant reduction of the latter parameter in patients after MI (10,967 +/- 1109 msec2 vs 16,860 +/- 2132 msec2). Control subjects were characterized by a predominance of low-frequency (approximately 0.1 Hz) component during the day and of high-frequency (approximately 0.25 Hz) component during the night, which reflected the expected 24-hour pattern of variation of sympatho-vagal balance. A 24-hour elevation (64 +/- 3 normalized units [nu] vs 56 +/- 2 nu; p less than 0.05) of the low-frequency component and a smaller (23 +/- 2 nu vs 32 +/- 2 nu; p less than 0.05) high-frequency component during the night differentiated patients after MI from subjects. The difference between the two groups was even more evident when the 24-hour sympatho-vagal balance was assessed with the low frequency/high frequency ratio. Thus spectral analysis of heart rate variability indicates that in patients after MI there is an alteration of neural control mechanisms as indicated by the presence of signs of sympathetic activation and by the attenuation of the nocturnal increase in vagal tone.
The effect of quinapril on blood pressure (BP), heart rate (HR) and their variabilities in 12 patients with severe congestive heart failure (New York Heart Association class III and IV) was assessed using ambulatory electrocardiographic and intraarterial monitoring. Mean +/- standard deviation daytime BP was 122/75 +/- 20/15 mm Hg at baseline and 113/70 +/- 13/16 mm Hg after 16 weeks of therapy with quinapril (p greater than 0.05 for systolic and diastolic BP); mean nighttime BP was 114/69 +/- 19/14 mm Hg at baseline and 107/69 +/- 15/14 mm Hg with quinapril (p greater than 0.05 for systolic and diastolic BP). Mean daytime HR was unchanged but nighttime HR was reduced from 77 +/- 11 to 71 +/- 10 beats/min, p = 0.02. HR variability (difference between the 75th and 25th percentiles of the frequency distribution of RR intervals) increased from 91 +/- 34 to 134 +/- 47 ms, p = 0.008. The variability of successive differences between RR intervals also increased significantly (75th to 25th percentile = 17 +/- 4 ms at baseline and 31 +/- 26 ms with quinapril, p = 0.02). Long-term quinapril caused clinically unimportant decreases in BP in patients with severe congestive heart failure. An increase in vagal activity caused by the reduction in circulating angiotensin II may account for the effect of converting enzyme inhibition on HR and its variability.
Imbalances in autonomic nervous system function have been posed as a possible mechanism that produces ventricular fibrillation and sudden cardiac arrest in patients with cardiovascular disease. Heart rate (HR) variability is described in survivors and nonsurvivors of sudden cardiac arrest within 48 hours after resuscitation using time and frequency domain analytic approaches. HR data were collected using 24-hour ambulatory electro-cardiograms in 16 survivors and 5 nonsurvivors of sudden cardiac arrest, and 5 control subjects. Survivors of sudden cardiac arrest were followed for 1 year, with recurrent cardiac events occurring in 4 patients who died within that year. Analysis of 24-hour electrocardiograms demonstrated that control subjects had the highest HR variability (standard deviation of all RR intervals = 155.2 +/- 54 ms), with nonsurvivors demonstrating the lowest HR variability (standard deviation of all RR intervals = 52.3 +/- 6.1 ms) and survivors of sudden cardiac arrest falling between the other 2 groups (standard deviation of all RR intervals = 78 +/- 25.5 ms, p less than or equal to 0.0000). Two other indexes of HR variability (mean number of beat to beat differences in RR intervals greater than 50 ms/hour and root-mean-square of successive differences in RR intervals) did not demonstrate the expected pattern in this sample, indicating that perhaps patterns of HR variability differ between groups of patients with cardiovascular disorders. Spectral analytic methods demonstrated that survivors of sudden cardiac arrest had reduced low- and high-frequency spectral power, whereas nonsurvivors demonstrated a loss of both low- and high-frequency spectral power.(ABSTRACT TRUNCATED AT 250 WORDS)
We addressed the problem of the circadian changes in neural control of heart period in ambulant hypertensive subjects. A running spectral analysis of R-R variability from Holter tapes provided markers of sympathetic, i.e. low-frequency component (LF) almost equal to 0.10 Hz, and vagal, i.e. high-frequency component (HF) almost equal to 0.25 Hz, controlling activities for the 24-h period of the recording. Significant circadian differences were observed in LF between the two groups of subjects: during night-time rest (0300-0400 h), LF was greater in hypertensives than in normotensives (56 +/- 2 and 48 +/- 2 nu, respectively; P less than 0.05). Furthermore, the difference between daytime and night-time LF values was progressively reduced with increasing severity of the hypertensive state, as assessed by resting arterial pressure levels. Spectral analysis of R-R variability suggests that essential hypertension may be characterized by a reduced day-night oscillation in sympathetic activity than can be quantified non-invasively using this approach.
To determine the diurnal pattern of cardiac autonomic tone in acute myocardial infarction (AMI), this study examined the power spectrum of heart rate (HR) variability in 24 patients during a single 24-hour segment within 4 days of AMI. Patients were nonrandomly allocated to a group (n = 14) without autonomic drugs and to a group (n = 10) already receiving beta blockers at the time of AMI. With use of autoregressive modeling, the power spectrum of HR variability was computed from continuous 1-hour electrocardiographic segments recorded at equally spaced intervals; 7 to 8 A.M., 3 to 4 P.M., and 11 to 12 P.M. All patients were supine, awake and pain free during recordings. There were no differences in HR, HR variance or the low-frequency peak power (0.06 to 0.1 Hz) from one temporal sequence to another. For the patients not taking beta blockers, the high-frequency peak power (0.2 to 0.36 Hz) or vagal component increased significantly from 3 P.M. to 11 P.M. (28 +/- 11 to 45 +/- 20 beats/min2.Hz-1, p less than 0.01). There was a significant decrease in the low- to high-frequency peak power and area ratios from 3 P.M. to 11 P.M. All power spectral parameters in the patients taking beta blockers remained unchanged over 24 hours. There was significantly heightened vagal modulation of sinus node activity in those receiving beta blockers, especially at 7 A.M. and 3 P.M. The data suggest that under steady-state wakeful conditions in the early recovery phase after an AMI, vagal tone is more pronounced during the late evening hours with a possible shift to relative sympathetic dominance during early morning and midafternoon hours.(ABSTRACT TRUNCATED AT 250 WORDS)
The dipyridamole stress test is used with thallium-201 to detect areas of inhomogeneity of blood flow that point to coronary artery disease (CAD). It is unclear whether dipyridamole produces inhomogeneous perfusion only or whether it actually decreases net flow in the obstructed vessels and produces true ischemia. It is also unclear what effect dipyridamole has on global and segmental left ventricular function. Therefore, ejection fraction, segmental wall motion and ventricular volume equivalents were measured before and after dipyridamole in 113 patients and 32 normal subjects. Ejection fraction responded in an abnormal fashion in 98 patients (87%), decreasing from 49 +/- 11% to 43 +/- 13% (p less than 0.0001), whereas it increased in 29 normal subjects (90%) from 57 +/- 6% to 64 +/- 10% (p less than 0.0001). Wall motion worsened distinctly in 75 patients (66%), and pressure/volume ratio deteriorated in 72%. The effect of dipyridamole lasted between 10 and 25 minutes, but was promptly reversed by aminophylline. These findings indicate that dipyridamole generally induces true ischemia in CAD. Furthermore, the degree of dysfunction is related to the angiographically assessed severity of CAD. The shortness of breath (seen in 10% of patients) may be partially explained by the findings, and it seems advisable to give aminophylline to every patient in order to promptly correct left ventricular dysfunction.
Before heart rate (HR) variability can be used for predictive purposes in the clinical setting, day-to-day variation and reproducibility need to be defined as do relations to mean HR. HR variability and mean HR were therefore determined in 2 successive 24-hour ambulatory electrocardiograms obtained from 33 normal subjects (age 34 +/- 7 years, group I), and 22 patients with coronary disease and stable congestive heart failure (CHF) (age 59 +/- 7 years, group II). Three measures were used: (1) SDANN (standard deviation of all mean 5-minute normal sinus RR intervals in successive 5-minute recording periods over 24 hours); (2) SD (the mean of the standard deviation of all normal sinus RR intervals in successive 5-minute recording periods over 24 hours); and (3) CV (coefficient of variation of the SD measure), a new measure that compensates for HR effects. Group mean HR was higher and HR variability lower in group II than in group I (80 +/- 10 vs 74 +/- 9 beats/min, p less than 0.04). Mean group values for HR and HR variability showed good correlations between days 1 and 2 (mean RR, r = 0.89, 0.97; SDANN, r = 0.87, 0.87; SD, r = 0.93, 0.97; CV, r = 0.95, 0.97 in groups I and II, respectively). In contrast, considerable individual day-to-day variation occurred (group I, 0 to 46%; group II, 0 to 51%). Low HR variability values were more consistent than high values. SDANN and SD correlated moderately with HR in both groups (r = 0.50 to 0.64). The CV measure minimizes HR effects on HR variability.(ABSTRACT TRUNCATED AT 250 WORDS)
Heart rate variability (HRV) spectra are typically analyzed for the components related to low- (less than 0.15 Hz) and high- (greater than 0.15 Hz) frequency variations. However, there are very-low-frequency components with periods up to hours in HRV signals, which might smear short-term spectra. We developed a method of spectral analysis suitable for selectively extracting very-low-frequency components, leaving intact the low- and high-frequency components of interest in HRV spectral analysis. Computer simulations showed that those low-frequency components were well characterized by fractional Brownian motions (FBMs). If the scale invariant, or self-similar, property of FBMs is considered a new time series (x') was constructed by sampling only every other point (course graining) of the original time series (x). Evaluation of the cross-power spectra between these two (Sxx') showed that the power of the FBM components was preserved, whereas that of the harmonic components vanished. Subtraction of magnitude of Sxx from the autopower spectra of the original sequence emphasized only the harmonic components. Application of this method to HRV spectral analyses indicated that it might enable one to observe more clearly the low- and high-frequency components characteristic of autonomic control of heart rate.
An analysis of heart rate (HR) variability (HRV) was based on quantifying the number and amplitude of HR fluctuations over long (8–30 cycles) and short (2–4 cycles) sequences of acceleration and deceleration-forming oscillations. The ‘product’ (number times amplitude) is an equivalent of the power spectrum in the frequency domain. In the time domain, positive correlations with HR were found for the number of long (L) sympathetic-mediated oscillations, whereas they were negative for short (S) vagally-mediated oscillations. The L/S ratio, an index of the autonomic nervous system (ANS) balance, closely paralleled the circadian HR values.
HRV was studied in the ambulatory ECG of three groups of 15 normal adults (group I), 13 patients with left ventricular hypertrophy (LVH, group II) and 13 patients-with heart failure (HF, group III). In basic conditions the mean HR was 77.1 ±l.9 beats min⁻¹ (mean±SEM) in group 1, 76.8±3.3 in II, 79.5±3.5 in III (P = NS). The different types of oscillations had smaller 24-h average values of the product in groups II and III than in group I, but the trends did not reach significance. However, the pooled 24 hourly values of the L/S ratio in group I (1.17 ± 0.09) were lower than in group II (1.33 ±0.06, P<0.05 at Ancova) and higher than in group III (1.06 ±0.09, P<0.001). A 3-day treatment with acebutolol non-uniformly slowed the mean HR: -9.5% in group I, -18.1% in II and -19.1% in III (P<0.001), and uniformly diminished the L/S ratio by 17% to 20% (P<0.01).
In conclusion, the sympathetic predominance of the ANS balance in LVH and HF is reflected by the beta-blockade induced HR decrease that is twice as marked in patients as in controls. In basic conditions HRV tends to be depressed in LVH and even more in HF. The ANS imbalance, however, has different modalities depending on the presence of HF, probably because of the different status of beta-adrenergic receptors in this condition.
Although enhanced sympathetic tone is a well recognized component of the autonomic profile characteristic of congestive heart failure, the contribution of parasympathetic withdrawal to this autonomic imbalance is less well described. The technique of spectral analysis of heart rate variability provides a dynamic map of sympathetic and parasympathetic tone and was thus used to define the nature of sympathetic-parasympathetic interactions in humans with idiopathic dilated cardiomyopathy and in a paced canine model of congestive heart failure. Humans with cardiomyopathy were found to have an augmentation of the sympathetically mediated low frequency area of the power density spectrum. Parasympathetic withdrawal was demonstrated by significant reductions in the parasympathetically mediated high frequency area (p less than 0.05) and the ratio of high to low frequency areas (p less than 0.01). Administration of atropine to normal subjects resulted in a significant reduction in the high frequency area (p less than 0.05) and the high/low frequency area ratio, both of which decreased within the range noted in patients with congestive heart failure. Administration of isoproterenol in normal subjects led to an augmentation of the low frequency area but to only a small decrease in the high/low frequency area ratio. Induction of congestive heart failure in a paced canine model resulted in alterations in the autonomic profile that resembled those seen in humans with ventricular failure. The prominent high frequency region of the spectrum at baseline, indicating a predominance of parasympathetic tone, was absent after the evolution of congestive heart failure, and there was a marked augmentation of the low frequency region of the spectrum.(ABSTRACT TRUNCATED AT 250 WORDS)
A consistent link appears to exist between predominance of vagal or sympathetic activity and predominance of HF or LF oscillations, respectively: RR variability contains both of these rhythms, and their relative powers appear to subserve a reciprocal relation like that commonly found in sympathovagal balance. In this respect, it is our opinion that rhythms and neural components always interact, just like flexor and extensor tones or excitatory and inhibitory cardiovascular reflexes, and that it is misleading to separately consider vagal and sympathetic modulations of heart rate. In humans and experimental animals, functional states likely to be accompanied by an increased sympathetic activity are characterized by a shift of the LF-HF balance in favor of the LF component; the opposite occurs during presumed increases in vagal activity. In addition, LF oscillation evaluated from SAP variability appears to be a convenient marker of the sympathetic modulation of vasomotor activity. Although based on indirect markers, the exploration in the frequency domain of cardiovascular neural regulation might disclose a unitary vision hard to reach through the assemblage of more specific but fragmented pieces of information.
Heart rate (HR) variability index and left ventricular ejection fraction (EF) were compared for the prediction of all-cause mortality, arrhythmic events and sudden death in 385 survivors of acute myocardial infarction. For arrhythmic events, where, for a sensitivity of 75%, HR variability index had a specificity of 76%, EF had a specificity of only 45%. An EF of less than or equal to 40% had a sensitivity of 42% and a specificity of 75% for arrhythmic events; for the same sensitivity an HR variability index of 20 U had a specificity of 92%. An EF less than or equal to 40% had a sensitivity of 40% and a specificity of 73% for sudden death; HR variability index had a specificity of 83% for the same sensitivity. For all cause mortality, where, for a sensitivity of 75%, HR variability index had a specificity of 52%, EF had a specificity of 40%. It is concluded that HR variability index appears a better predictor of important postinfarction arrhythmic complications than left ventricular EF, but both indexes perform equally well in predicting all-cause mortality.
Both time and frequency domain measures of heart rate (HR) variability have been used to assess autonomic tone in a variety of clinical conditions. Few studies in normal subjects have been performed to determine the stability of HR variability over time, or the correlation between and within time and frequency domain measures of HR variability. Fourteen normal subjects aged 20 to 55 years were studied with baseline and placebo 24-hour ambulatory electrocardiograms performed 3 to 65 days apart to assess the reproducibility of the following time domain measures of cycle length variability: the standard deviation of all normal cycle intervals; mean normal cycle interval; mean day normal cycle interval; night/day difference in mean normal cycle interval; root-mean-square successive cycle interval difference; percentage of differences between adjacent normal cycle length intervals that are greater than 50 ms computed over the entire 24-hour electrocardiographic recording (proportion of adjacent intervals greater than 50 ms); and the frequency domain measures of high (0.15 to 40 Hz), low (0.003 to 0.15) and total (0.003 to 0.40) power. The mean and standard deviations of these measures were virtually identical between placebo and baseline measurements and within the studied time range. Variables strongly dependent on vagal tone (high-frequency, low-frequency and total power, root-mean-square successive difference, and percentage of differences between adjacent normal cycle intervals greater than 50 ms computed over the entire 24-hour electrocardiographic recording) were highly correlated (r greater than 0.8). It is concluded that measures of HR variability are stable over short periods of time.(ABSTRACT TRUNCATED AT 250 WORDS)
The purpose of this study was to investigate whether heart rate variability could be reliably assessed in patients with ventricular arrhythmias and to evaluate whether it is affected by antiarrhythmic drugs. The study was based on an analysis of 239 ambulatory electrocardiographic (ECG) recordings obtained from 67 patients with frequent and complex ventricular arrhythmias enrolled in the Antiarrhythmic Drug Evaluation Group (ADEG) study. In each recording, after exclusion of premature ventricular complexes, the number of times during a 24 h period in which two consecutive sinus RR intervals differed by more than 50 ms was calculated. The total 24 h count from each recording was then used as an index of heart rate variability. This method is a reliable marker of cardiac parasympathetic activity. Recordings were analyzed at baseline (n = 56), during long-term treatment with amiodarone (n = 17), flecainide (n = 22) or propafenone (n = 17) and after washout in selected patients (n = 5). Despite the presence of a different number of arrhythmias, total 24 h counts in the same patient appeared reproducible over time (r = 0.83 between two different recordings, n = 49, p less than 0.0001). Baseline counts (median 1,698, range 26 to 13,648) were not correlated (r = 0.15) with the number of arrhythmias. The three antiarrhythmic drugs had a disparate effect on total 24 h counts: no change was observed in patients treated with amiodarone (median percent change [delta %]-8, p = NS), whereas a significant (p less than 0.025) decrease occurred in patients treated with flecainide (median delta % -56%) or propafenone (median delta % -64%).(ABSTRACT TRUNCATED AT 250 WORDS)