Amplitude Of Respiratory Sinus Arrhythmia Research Articles

Autonomic and vascular function testing in collegiate athletes following SARS-CoV-2 infection: an exploratory study.

Introduction: Recent studies suggest that SARS-CoV-2 infection alters autonomic and vascular function in young, otherwise healthy, adults. However, whether these alterations exist in young competitive athletes remains unknown. This study aimed to assess the effects of COVID-19 on cardiac autonomic control and vascular function in collegiate athletes who tested positive for COVID-19, acknowledging the limitations imposed by the early stages of the pandemic. Methods: Sixteen collegiate athletes from various sports underwent a battery of commonly used autonomic and vascular function tests (23 ± 9, range: 12-44days post-infection). Additionally, data from 26 healthy control participants were included. Results: In response to the Valsalva maneuver, nine athletes had a reduced early phase II blood pressure response and/or reduced Valsalva ratio. A depressed respiratory sinus arrhythmia amplitude was observed in three athletes. Three athletes became presyncopal during standing and did not complete the 10-min orthostatic challenge. Brachial artery flow-mediated dilation, when allometrically scaled to account for differences in baseline diameter, was not different between athletes and controls (10.0% ± 3.5% vs. 7.1% ± 2.4%, p = 0.058). Additionally, no differences were observed between groups when FMD responses were normalized by shear rate (athletes: 0.055% ± 0.026%/s-1, controls: 0.068% ± 0.049%/s-1, p = 0.40). Discussion: Few atypical and borderline responses to autonomic function tests were observed in athletes following an acute SARS-CoV-2 infection. The most meaningful autonomic abnormality being the failure of three athletes to complete a 10-min orthostatic challenge. These findings suggest that some athletes may develop mild alterations in autonomic function in the weeks after developing COVID-19, while vascular function is not significantly impaired.

Autonomic Testing in Collegiate Athletes Following SARS‐Cov‐2 Infection

To date, more than 46 million people in the United States have contracted the severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2), which causes COVID‐19. Over 700 thousand total cases have been linked to American colleges and universities. Post‐acute sequelae of SARS‐CoV‐2 infection may affect varied systems. It was reported that sympathetic nerve activity following SARS‐CoV‐2 infection was elevated in young individuals. Cardiovascular autonomic function post‐acute SARS‐CoV‐2 infection in other populations such as athletes, however, has not been thoroughly investigated. Collegiate athletes are a unique population given that they might have a high level of physical fitness before the infection. The present study examined 16 collegiate athletes (12 men and 4 women, age: 20±1 yrs, height: 181±10 cm, weight: 81±18 kg) who were evaluated ~2 weeks after testing positive for SARS‐CoV‐2 by polymerase chain reaction assay. These subjects were asymptomatic or with mild/moderate symptoms during infection. None of the subjects had been hospitalized for COVID‐19 and all subjects were asymptomatic at the time of the study. Beat‐by‐beat blood pressure (BP) with Finometer, and heart rate (HR) from ECG were recorded during 10 minutes of supine rest, Valsalva maneuver, slow breathing (6 breaths/min), handgrip exercise, and 10 minutes of standing. BP, HR, heart rate variability (HRV), and cardiac baroreflex sensitivity (CBRS), and venous blood aldosterone and renin levels were analyzed. The vagal tone index from HRV in 3 of 16 athletes was lower than normative values. The responses in BP to Valsalva maneuver during phases IIa (i.e., “early”) and IIb (i.e., “late”) were mildly abnormal in 4 athletes and moderately abnormal in one athlete. The Valsalva ratio was below the normal range in 6 athletes. In response to slow breathing, the respiratory sinus arrhythmia amplitude was below the normal range in 3 athletes. In response to handgrip exercise, one athlete had an atypical response where BP decreased while HR was increased from baseline. Three of the subjects were unable to tolerate an orthostatic challenge for 10 minutes. Four out of 16 athletes had abnormally elevated renin activity and 1 out 16 elevated aldosterone levels. It is important to note that while several athletes had abnormal responses to the various autonomic tests, these abnormalities did not correlate with symptoms seen during the infection. Our data suggest that SARS‐CoV‐2 infection may reduce parasympathetic and increase sympathetic tone and may contribute to the autonomic disfunction associated in a subset of collegiate athletes even after recovering from COVID‐19. This study provides further evidence for potential long‐term cardiovascular autonomic effects of Covid‐19 infection even in healthy young trained athletes. Further studies with a larger patient population as well as suitable healthy control subjects are warranted.

Short-term usage of three non-invasive ventilation interfaces causes progressive discomfort in healthy adults

PurposeTo evaluate the effect of three different non-invasive ventilation (NIV) interfaces on the subjective discomfort of healthy individuals, and on a set of physiological parameters hypothesized to change in correspondence to discomfort.MethodsContinuous pressure NIV was applied to 20 subjects using Total Face, Nasal, and Face masks for 10 min each. Tidal volume (VT) and respiratory period (RP) were estimated from respiratory inductance plethysmography. Electrodermal activity was estimated from conductance signals. Heart rate variability was measured using the time-domain indices SDNN and RMSSD, and the respiratory sinus arrhythmia amplitude (RSAp). Parameters were referenced to 5-min rest periods at beginning and end of protocol. A Likert-like scale of subjective discomfort with the masks and the ventilation was applied after 1, 5, and 9 min using each mask.ResultsRP and VT increased with the three mask models. Whereas the mean heart rate and RSAp did not change, both SDNN and RMSSD increased during NIV with Nasal and Face masks. Spontaneous electrodermal activity fluctuations were less frequent during NIV than at rest, with significant differences for Total Face and Nasal masks. Discomfort with all masks increased from minutes 1 to 9, markedly in the Total Face mask, considered most uncomfortable by 11 subjects.ConclusionIn healthy subjects, the three masks resulted in similar respiratory responses to NIV. Correspondence between changes in physiological parameters and discomfort with NIV interface could not be detected, whereas self-report with the Likert-like scale identified progressive discomfort and the Total Face mask as the most uncomfortable interface.Supplementary InformationThe online version contains supplementary material available at 10.1007/s42600-020-00114-3.

The critical role of respiratory sinus arrhythmia on temporal cardiac dynamics.

Temporal cardiac properties provide alternative information in analyzing heart rate variability (HRV), which may be disregarded by the standard HRV analyses. Patients with congestive heart failure (CHF) are known to have distinct temporal features from the healthy individuals. However, the underlying mechanism leading to the variation remains unclear. Whether or not these parameters can finely classify the severity for CHF patients is uncertain as well. In this work, an electrocardiogram was monitored in advanced CHF patients using 24-h Holter in four conditions, including baseline, one and three months after atenolol therapy, and healthy individuals. Slope and area under the curve (AUC) of multiscale entropy (MSE) curve over short (scales 1-5) and long (scales 6-20) scales, and detrended fluctuation analysis (DFA) scaling exponents at short (4-11 beats) and intermediate (>11 beats) window sizes were calculated. The results show that short-time scale MSE-derived parameters (slope: -0.08 ± 0.10, -0.03 ± 0.10, 0.02 ± 0.06, 0.08 ± 0.06; AUC: 4.03 ± 2.11, 4.69 ± 1.28, 4.73 ± 0.94, and 6.17 ± 1.23) and short-time scale DFA exponent (0.79 ± 0.16, 0.95 ± 0.22, 1.11 ± 0.19, and 1.35 ± 0.20) can hierarchically classify all four conditions. More importantly, simulated R-R intervals with different fractions and amplitude of respiratory sinus arrhythmia (RSA) components were examined to validate our hypothesis regarding the essentiality of RSA in the improvement of cardiovascular function, and its tight association with unpredictability and fractal property of HRV, which is in line with our hypothesis that RSA contributes significantly to the generation of the unpredictability and fractal behavior of HR dynamics.NEW & NOTEWORTHY Temporal cardiac properties provide useful diagnostic parameters for patients with congestive heart failure (CHF). Our study hierarchically classified CHF patients with β-blocker treatment by using multiscale entropy and detrended fluctuation analysis. Also, we provided the evidence to validate the critical role of respiratory sinus arrhythmia in the fractal properties of heart rate variability.

Influence of nasal CPAP on cardiorespiratory control in healthy neonate.

The present study aimed to further unravel the effects of nasal continuous positive airway pressure (nCPAP) on the cardiovascular and respiratory systems in the neonatal period. Six-hour polysomnographic recordings were first performed in seven healthy newborn lambs, aged 2-3 days, without and with nCPAP application at 6 cmH2O (nCPAP-6), in randomized order. The effects of nCPAP-6 on heart rate variability, respiratory rate variability, and cardiorespiratory interrelations were analyzed using a semiautomatic signal processing approach applied to ECG and respiration recordings. Thereafter, a cardiorespiratory mathematical model was adapted to the experimental conditions to gain further physiological interpretation and to simulate higher nCPAP levels (8 and 10 cmH2O). Results from the signal processing approach suggest that nCPAP-6 applied in newborns with healthy lungs: 1) increases heart rate and decreases the time and frequency domain indices of heart rate variability, especially those representing parasympathetic activity, while increasing the complexity of the RR-interval time series; 2) prolongs the respiratory cycle and expiration duration and decreases respiratory rate variability; and 3) slightly impairs cardiorespiratory interrelations. Model-based analysis revealed that nCPAP-6 increases the heart rate and decreases respiratory sinus arrhythmia amplitude, in association with a reduced parasympathetic efferent activity. These results were accentuated when simulating an increased CPAP level. Overall, our results provide a further understanding of the effects of nCPAP in neonates, in the absence of lung disease.NEW & NOTEWORTHY Application of nasal continuous positive airway pressure (CPAP) at 6 cmH2O, a level very frequently used in newborns, alters heart and respiratory rate variability, as well as cardiorespiratory interrelations in a full-term newborn model without lung disease. Moreover, whereas nasal CPAP at 6 cmH2O decreases parasympathetic efferent activity, there is no change in sympathetic efferent activity.

Association Between Phase Coupling of Respiratory Sinus Arrhythmia and Slow Wave Brain Activity During Sleep.

Phase coupling of respiratory sinus arrhythmia (RSA) has been proposed to be an alternative measure for evaluating autonomic nervous system (ANS) activity. The aim of this study was to analyze how phase coupling of RSA is altered during sleep, in order to explore whether this measure is a predictor of slow wave sleep (SWS). Overnight electroencephalograms (EEG), electrocardiograms (ECG), and breathing using inductance plethysmography were recorded from 30 healthy volunteers (six females, age range 21–64, 31.6 ± 14.7 years). Slow wave activity was evaluated by the envelope of the amplitude of the EEG δ-wave (0.5–4 Hz). The RSA was extracted from the change in the R-R interval (RRI) by band-pass filter, where pass band frequencies were determined from the profile of the power spectral density for respiration. The analytic signals of RSA and respiration were obtained by Hilbert transform, after which the amplitude of RSA (ARSA) and the degree of phase coupling (λ) were quantified. Additionally, the normalized high-frequency component (HFn) of the frequency-domain heart rate variability (HRV) was calculated. Using auto- and cross-correlation analyses, we found that overnight profiles of λ and δ-wave were correlated, with significant cross-correlation coefficients (0.461 ± 0.107). The δ-wave and HFn were also correlated (0.426 ± 0.115). These correlations were higher than that for the relationship between δ-wave and ARSA (0.212 ± 0.161). The variation of λ precedes the onset of the δ-wave by ~3 min, suggesting a vagal enhancement prior to the onset of SWS. Auto correlation analysis revealed that the periodicity of λ was quite similar to that of the δ-wave (88.3 ± 15.7 min vs. 88.6 ± 16.3 min, λ-cycle = 0.938 × δ-cycle + 5.77 min, r = 0.902). These results suggest that phase coupling analysis of RSA appears to be a marker for predicting SWS intervals, thereby complementing other noninvasive tools and diagnostic efforts.

Cardiac and behavioral effects of social isolation and experimental manipulation of autonomic balance.

Improved understanding of how depression and social isolation interact to increase cardiac morbidity and mortality will improve public health. This experiment evaluated the effect of pharmacological autonomic blockade on cardiac and behavioral reactivity following social isolation in prairie voles. Experiment 1 validated the dose and time course of pharmacological autonomic antagonism of peripheral β-adrenergic (atenolol) and muscarinic cholinergic receptors (atropine methyl nitrate), and Experiment 2 used a novel protocol to investigate behavioral responses in the tail suspension test during pharmacological autonomic blockade as a function of social isolation (vs. paired control). Prairie voles isolated for 4 weeks (vs. paired) displayed significantly elevated heart rate and reduced heart rate variability. Autonomic receptor antagonism by atenolol led to exaggerated reductions in heart rate and standard deviation of normal-to-normal intervals, and lower amplitude of respiratory sinus arrhythmia in the isolated group (vs. paired). Administration of atropine led to an attenuated increase in heart rate in the isolated group (vs. paired), and similar near-zero levels of respiratory sinus arrhythmia amplitude in both groups. During the tail suspension test, isolated animals (vs. paired) displayed significantly greater immobility. In paired animals, atenolol administration did not influence immobility; atropine administration increased the duration of immobility (vs. vehicle). In isolated animals, atenolol administration increased the duration of immobility; atropine did not influence immobility duration (vs. vehicle). The current study contributes to our understanding of differential effects of social isolation and autonomic imbalance on cardiac and behavioral reactivity.

Can Daytime Measures of Respiratory Sinus Arrhythmia and Breathing Stability Serve as Biomarkers for OSA?

Obstructive sleep apnea (OSA) is by definition a disorder of nighttime breathing however, there is good evidence that impairments in cognitive and cardiovascular function persist in the day and that adults with OSA exhibit daytime CO2 retention and hypoxemia. Although a diagnosis of OSA requires in‐home or in‐laboratory overnight polysomnography, these types of tests are expensive and, due to health insurance quotas, may be limited in availability. Here, we outline simple methods for assessing daytime respiratory sinus arrhythmia (RSA) and respiratory stability that show promise as potential diagnostic tools to identify adults at risk for OSA. We recorded heart rate (finger oxy‐photoplethysmography) and respiration (inductance plethysmography) in adults with obstructive sleep apnea (N=6) and age and BMI matched healthy adults (N=8). Subjects completed five minutes of eupneic breathing, five minutes of paced breathing (7.5 breaths/minute) and after equilibration, five minutes of hyperoxic, hypercapnia (5% FICO2). Using de‐identified data, we obtained estimates of RSA amplitude, RSA stability, and respiratory stability for each subject in each condition and performed a regression analysis to determine the relationship between each of these variables and subjects' apnea hypopnea index (0–25 AHI). Our preliminary results indicate that daytime measures of respiratory stability and RSA can differentiate healthy adults from adults diagnosed with OSA (p<0.006). Importantly, the analysis requires minimal instrumentation and short sampling periods (~5 minutes). Summary schematics arising from the analysis may prove useful as preliminary clinical/diagnostic biomarkers of RSA and cardio‐respiratory coupling in adults at risk for OSA.Support or Funding InformationThis work was supported by start‐up monies (Department of Physiology, University of Arizona) awarded to EFB and by The Finley and Florence Brown Predoctoral Fellowship (Sarver Heart Center, University of Arizona) awarded to JRV.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Vagal modulation of 1‐month‐old infants to auditory stimuli is associated with self‐regulatory behavior

AbstractDuring infancy, cardiac vagal modulation has been associated with attentional and social engagement behaviors. While studies have shown that infants display a behavioral repertoire that enables them to interact with others by being able to regulate themselves in order to attend to and to discriminate emotional and social cues, vagal modulation to sensory stimuli and its association with behavioral outcomes at early ages remains to be addressed. In this study, we analyzed the cardiac vagal response of 1‐month‐old infants to two auditory stimuli intensities and whether vagal response was associated with social interactive and self‐regulatory abilities. Therefore, we recorded cardiac and respiratory physiological responses in 28 infants using a Biopac System. Neurobehavioral assessment was performed using the Neonatal Behavioral Assessment Scale. We observed increased respiratory sinus arrhythmia (RSA) amplitude to both auditory stimuli intensities when compared to baseline. No intensity effect was found for the RSA response. Additionally, we observed that higher RSA amplitude to both auditory stimuli was positively correlated with adjusted self‐regulatory behaviors, suggesting a convergence between multiple measures assessing infants' state regulation. Results are discussed in light of 1‐month‐old infants' auditory stimuli processing and its implications for regulatory behaviors and the emergent social‐like behaviors.

The Autonomic Repercussions of Fetal and Maternal Interaction in Pre-eclampsia

Abstract Pre-eclampsia (PE) is one of the severe complications of pregnancy that leads to fetal deterioration. The aim of the investigation was to determine the role of maternal respiratory sinus arrhythmia (RSA) in regulation of fetal circulatory system in case of healthy pregnancy and in PE. The investigation of maternal and fetal HRV and umbilical venous blood flow velocity spectral analysis in 106 patients at 34-40 weeks of gestation was performed. 30 of them had healthy pregnancy and were involved in the Group I. In Group II 44 pregnant women with mild-moderate PE were observed. 32 patients with severe PE were monitored in Group III. The maternal sympathetic overactivity modulated HRV in PE. The suppression of RSA was explored in preeclamptic patients. The Doppler spectrograms of the umbilical veinous blod flow had the oscillatory peak with a frequency about 0.5 Hz. The above peak characterized the participation of the maternal RSA in fetal hemodynamics. Strong relationship between maternal RMSSD and amplitude of RSA associated peak, maternal and fetal RMSSDs was found in healthy pregnancy. No considerable relationship was revealed between the maternal RMSSD and the amplitude of 0.5 Hz frequency peak, the maternal and fetal RMSSDs in the patients with severe PE. The maternal RSA propagated its influence on the fetal umbilical venous blood flow and the fetal autonomic nervous regulation in normal gestation. The control of fetal hemodynamics diminished in the mild-moderate PE and even disappeared in severe PE.

Respiratory sinus arrhythmia as a non-invasive index of 'brain-heart' interaction in stress.

Respiratory sinus arrhythmia (RSA) is accepted as a peripheral marker of cardiac-linked parasympathetic regulation. According to polyvagal theory, the RSA is also considered as the index of emotion regulation. The neurovisceral integration model posits that parasympathetic modulation of the heart marked by RSA is related to complex nervous regulation associated with emotional and cognitive processing. From this perspective, high resting RSA amplitude associated with a greater withdrawal during stressors and subsequent recovery could represent a flexible and adaptive physiological response system to a challenge. Conversely, low resting RSA accompanied by an inadequate reactivity to stress might reflect maladaptive regulatory mechanisms. The RSA reactivity is different with various types of stressors: while the RSA decreases to cognitive tasks indicating a vagal withdrawal, the RSA magnitude increases to emotional challenge indicating an effective cognitive processing of emotional stimuli. The RSA reactivity to stress could have important implications for several mental disorders, e.g. depressive or anxiety disorder. It seems that the study of the RSA, as a non-invasive index of ‘brain-heart’ communication, could provide important information on the pathway linked to mental and physical health.

Cardiac output is improved in rats with myocardial infarction by enhancement of respiratory sinus arrhythmia

Respiratory sinus arrhythmia (RSA) is the physiological modulation of heart rate during respiration. Whilst its physiological function is debated, recent mathematical modelling predicts that RSA saves cardiac energy. Heart failure is associated with a loss of RSA. We aimed to test whether RSA would improve cardiac function in rats 3 days after left ascending coronary artery ligation (post‐MI). Cardiac dysfunction was indicated by infarct size (43±7% of left ventricle) and prolonged systole duration accompanied by reduced peak aortic flow compared to SHAM rats. We built and used a novel central pattern generator (CPG) that, utilizing real‐time diaphragm electromyogram input, generated RSA via respiratory phase‐locked stimulus output to the right cervical vagus nerve. In post‐MI rats, RSA enhancement caused a 12±3% increase in stroke volume, irrespective of the RSA amplitude. Tonic VNS at matched average heart rate increased stroke volume to a similar degree (8±1%, P =0.25 compared to RSA) (n = 7). Despite the increase in stroke volume, myocardial lactate concentrations were unchanged after 45 min of RSA (29±7bpm) or tonic VNS treatment (P = 0.35, One‐way ANOVA). Using a novel CPG device we have demonstrated that, in an acute setting, RSA increases stroke volume in post‐MI rats.British Heart Foundation and Fundação de Amparo à Pesquisa do Estado de São Paulo

Central regulation of heart rate and the appearance of respiratory sinus arrhythmia: New insights from mathematical modeling

A minimal model for the neural control of heart rate (HR) has been developed with the aim of better understanding respiratory sinus arrhythmia (RSA) – a modulation of HR at the frequency of breathing. This model consists of two differential equations and is integrated into a previously-published model of gas exchange. The heart period is assumed to be affected primarily by the parasympathetic signal, with the sympathetic signal taken as a parameter in the model. We include the baroreflex, mechanical stretch-receptor feedback from the lungs, and central modulation of the cardiac vagal tone by the respiratory drive. Our model mimics a range of experimental observations and provides several new insights. Most notably, the model mimics the growth in the amplitude of RSA with decreasing respiratory frequency up to 7 breaths per minute (for humans). Our model then mimics the decrease in the amplitude of RSA at frequencies below 7 breaths per minute and predicts that this decrease is due to the baroreflex (we show this both numerically and analytically with a linear baroreflex). Another new prediction of the model is that the gating of the baroreflex leads to the dependency of RSA on mean vagal tone. The new model was also used to test two previously-suggested hypotheses regarding the physiological function of RSA and supports the hypothesis that RSA minimizes the work done by the heart while maintaining physiological levels of arterial CO2. These and other new insights the model provides extend our understanding of the integrative nature of vagal control of the heart.

High‐Accuracy Extraction of Respiratory Sinus Arrhythmia with Statistical Processing Using Normal Distribution

SUMMARYThe autonomic nervous system is important in maintaining homeostasis by mediating the opposing effects of sympathetic and parasympathetic nervous activity on organs. Although it is known that the amplitude of RSA (respiratory sinus arrhythmia) is an index of parasympathetic nervous activity, it is difficult to estimate that activity in real time in everyday situations. This is in part because of body motion and extrasystole. Further, automatic recognition of the R wave on an electrocardiogram is required for a real‐time analysis of the RSA amplitude, and there is an unresolved problem of false recognition of the R wave. In this paper we propose a method of evaluating the amplitude of RSA accurately by statistical processing with probabilistic models. We then estimate parasympathetic nervous activity during body motion and isometric exercise to examine the validity of the method. As a result, using the proposed method we demonstrate that the amplitude of RSA can be extracted in the presence of false recognition of the R wave. An appropriate threshold for the estimate is 1 or 5% because the waveforms of the RSA amplitude do not follow the abrupt changes of parasympathetic nervous activity induced by isometric exercise with the threshold at 10%. Furthermore, the method using the normal distribution is found to be more appropriate than that of the chi‐square distribution for statistical processing. Therefore, we expect that the proposed method can be used to evaluate parasympathetic nervous activity with high accuracy in everyday situations. © 2013 Wiley Periodicals, Inc. Electron Comm Jpn, 96(9): 23–32, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.11441

Pain modulation induced by respiration: Phase and frequency effects

The voluntary control of respiration is used as a common means to regulate pain and emotions and is fundamental to various relaxation and meditation techniques. The aim of the present study was to examine how breathing frequency and phase affect pain perception, spinal nociceptive activity (RIII-reflex) and brain activity (scalp somatosensory-evoked potentials – SEP’s). In 20 healthy volunteers, painful electric shocks individually adjusted to 120% of the RIII-reflex threshold were delivered to the sural nerve near the end of inspiration or expiration phases, during three cued-breathing conditions: (1) slow breathing (0.1Hz) with slow (4s) inspiration (0.1Hz-SlowIns), (2) slow breathing (0.1Hz) with fast (2s) inspiration (0.1Hz-FastIns), and (3) normal breathing (0.2Hz) with fast (2s) inspiration (0.2Hz). Pain ratings were not affected by breathing patterns (p=0.3), but were significantly lower during inspiration compared with expiration (p=0.02). This phase effect was also observed on the N100 component of SEP’s, but only in the 0.1-Hz-FastIns condition (p=0.03). In contrast, RIII-reflex amplitude was greater during inspiration compared with expiration (p=0.02). It was also decreased in the 0.1-Hz-SlowIns compared with the 0.2-Hz condition (p=0.01). Slow breathing also increased the amplitude of respiratory sinus arrhythmia (RSA), although these changes were not significantly associated with changes in pain responses. In conclusion, this study shows that pain and pain-related brain activity may be reduced during inspiration but these changes are dissociated from spinal nociceptive transmission. The small amplitude of these effects suggests that factors other than respiration contribute to the analgesic effects of relaxation and meditation techniques.

Respiratory sinus arrhythmia during sleep in children with upper airway obstruction

Upper airway obstruction during adulthood is associated with cardiovascular morbidity; cardiovascular consequences of childhood upper airway obstruction are less well established. This study aimed at investigating the effect of childhood upper airway obstruction on respiratory sinus arrhythmia as a measure of cardiac vagal modulation during night-time sleep. Overnight polysomnography was conducted in 40 healthy children (20M; age: 7.5±2.6years; body mass index percentile: 60.7±26.4%) and 40 children with upper airway obstruction (24M; age: 7.5±2.7years; body mass index percentile: 65.8±31.9%). We used the phase-averaging technique to compute respiratory sinus arrhythmia amplitude and phase delay. To study sleep stage effects and the effect of upper airway obstruction, respiratory sinus arrhythmia was measured during all artefact-free sleep episodes, and after exclusion of respiratory events. A significant increase in respiratory sinus arrhythmia amplitude and phase delay was observed during stage 4 sleep as compared with rapid eye movement sleep in both groups (amplitude: controls=0.10±0.03 versus 0.07±0.02s, P<0.01, respectively, and upper airway obstruction=0.07±0.03 versus 0.05±0.03s, P<0.05, respectively; phase delay: controls=3.1±0.1 versus 3.0±0.1rad, P<0.05, respectively, and upper airway obstruction=3.13±0.04 versus 3.04±0.08rad, P<0.01, respectively). A significant association between respiratory sinus arrhythmia and apnea/hypopnea index was observed during stage 2 sleep in children with upper airway obstruction. Compared with healthy controls, a significant decrease in respiratory sinus arrhythmia amplitude during stage 2 sleep was observed in children with upper airway obstruction (0.09±0.03 versus 0.06±0.03s, P<0.05). However, this difference was not apparent when respiratory events were excluded from analysis. Importantly, respiratory sinus arrhythmia showed a strong negative correlation with body mass index. In conclusion, night-time respiratory sinus arrhythmia in children is sleep stage dependent and normal during quiet sleep in children with relatively mild upper airway obstruction.

Respiratory Sinus Arrhythmia as an Index of Vagal Activity during Stress in Infants: Respiratory Influences and Their Control

Respiratory sinus arrhythmia (RSA) is related to cardiac vagal outflow and the respiratory pattern. Prior infant studies have not systematically examined respiration rate and tidal volume influences on infant RSA or the extent to which infants' breathing is too fast to extract a valid RSA. We therefore monitored cardiac activity, respiration, and physical activity in 23 six-month old infants during a standardized laboratory stressor protocol. On average, 12.6% (range 0–58.2%) of analyzed breaths were too short for RSA extraction. Higher respiration rate was associated with lower RSA amplitude in most infants, and lower tidal volume was associated with lower RSA amplitude in some infants. RSA amplitude corrected for respiration rate and tidal volume influences showed theoretically expected strong reductions during stress, whereas performance of uncorrected RSA was less consistent. We conclude that stress-induced changes of peak-valley RSA and effects of variations in breathing patterns on RSA can be determined for a representative percentage of infant breaths. As expected, breathing substantially affects infant RSA and needs to be considered in studies of infant psychophysiology.

Analysis of heart rate variability and skin blood flow oscillations under deep controlled breathing

The effect of deep breathing controlled in both rate (0.25, 0.16, 0.1, 0.07, 0.05 and 0.03Hz) and amplitude on the heart rate variability (HRV) and respiration-dependent oscillations of forearm/finger skin blood flow (SBF) has been studied in 29 young healthy volunteers. The influence of sympathovagal balance on the respiratory sinus arrhythmia (RSA) amplitude and respiratory SBF oscillations has been studied. The subjects with predominant parasympathetic tonus had statistically significant higher RSA amplitudes in the breathing rate region of 0.03–0.07Hz than the subjects with predominant sympathetic tonus. In the finger-cushion zone, having a well-developed sympathetic vascular innervations, the amplitudes of respiratory SBF oscillations at breathing rates 0.05 and 0.07Hz were higher in the group of subjects with predominant parasympathetic tonus. In the forearm skin, where the density of sympathetic innervations is low comparatively to that in the finger skin, no statistically significant differences in the amplitude of respiratory SBF oscillations were found concerning the two groups of subjects.

Effects of assisted and variable mechanical ventilation on cardiorespiratory interactions in anesthetized pigs

The physiological importance of respiratory sinus arrhythmia (RSA) and cardioventilatory coupling (CVC) has not yet been fully elucidated, but these phenomena might contribute to improve ventilation/perfusion matching, with beneficial effects on gas exchange. Furthermore, decreased RSA amplitude has been suggested as an indicator of impaired autonomic control and poor clinical outcome, also during positive-pressure mechanical ventilation (MV). However, it is currently unknown how different modes of MV, including variable tidal volumes (VT), affect RSA and CVC during anesthesia. We compared the effects of pressure controlled (PCV) versus pressure assisted (PSV) ventilation, and of random variable versus constant VT, on RSA and CVC in eight anesthetized pigs. At comparable depth of anesthesia, global hemodynamics, and ventilation, RSA amplitude increased from 20 ms in PCV to 50 ms in PSV (p < 0.05). CVC was detected (using proportional Shannon entropy of the interval between each inspiration onset and the previous R-peak in ECG) in two animals in PCV and seven animals in PSV. Variable VT did not significantly influence these phenomena. Furthermore, heart period and systolic arterial pressure oscillations were in phase during PCV but in counter-phase during PSV. At the same depth of anesthesia in pigs, PSV increases RSA amplitude and CVC compared to PCV. Our data suggest that the central respiratory drive, but not the baroreflex or the mechano-electric feedback in the heart, is the main mechanism behind the RSA increase. Hence, differences in RSA and CVC between mechanically ventilated patients might reflect the difference in ventilation mode rather than autonomic impairment. Also, since gas exchange did not increase from PCV to PSV, it is questionable whether RSA has any significance in improving ventilation/perfusion matching during MV.

正規分布を用いた統計処理による呼吸性洞性不整脈の抽出精度向上

SUMMARY The autonomic nervous system is important in maintaining homeostasis by mediating the opposing effects of sympathetic and parasympathetic nervous activity on organs. Although it is known that the amplitude of RSA (respiratory sinus arrhythmia) is an index of parasympathetic nervous activity, it is difficult to estimate that activity in real time in everyday situations. This is in part because of body motion and extrasystole. Further, automatic recognition of the R wave on an electrocardiogram is required for a real-time analysis of the RSA amplitude, and there is an unresolved problem of false recognition of the R wave. In this paper we propose a method of evaluating the amplitude of RSA accurately by statistical processing with probabilistic models. We then estimate parasympathetic nervous activity during body motion and isometric exercise to examine the validity of the method. As a result, using the proposed method we demonstrate that the amplitude of RSA can be extracted in the presence of false recognition of the R wave. An appropriate threshold for the estimate is 1 or 5% because the waveforms of the RSA amplitude do not follow the abrupt changes of parasympathetic nervous activity induced by isometric exercise with the threshold at 10%. Furthermore, the method using the normal distribution is found to be more appropriate than that of the chi-square distribution for statistical processing. Therefore, we expect that the proposed method can be used to evaluate parasympathetic nervous activity with high accuracy in everyday situations. © 2013 Wiley Periodicals, Inc. Electron Comm Jpn, 96(9): 23–32, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.11441