Effects of slow and regular breathing exercise on cardiopulmonary coupling and blood pressure

Investigation of the interaction between cardiovascular variables and respiration provides a quantitative and noninvasive approach to assess the autonomic control of cardiovascular function. The aim of this paper is to investigate the changes of cardiopulmonary coupling (CPC), blood pressure (BP) and pulse transit time (PTT) during a stepwise-paced breathing (SPB) procedure (spontaneous breathing followed by paced breathing at 14, 12.5, 11, 9.5, 8 and 7 breaths per minute, 3 min each) and gain insights into the characteristics of slow breathing exercises. RR interval, respiration, BP and PTT are collected during the SPB procedure (48 healthy subjects, 27 ± 6 years). CPC is assessed through investigating both the phase and amplitude dynamics between the respiration-induced components from RR interval and respiration by the approach of ensemble empirical mode decomposition. It was found that even though the phase synchronization and amplitude oscillation of CPC were both enhanced by the SPB procedure, phase coupling does not increase monotonically along with the amplitude oscillation during the whole procedure. Meanwhile, BP was reduced significantly by the SPB procedure (SBP: from 122.0 ± 13.4 to 114.2 ± 14.9 mmHg, p < 0.001, DBP: from 82.2 ± 8.6 to 77.0 ± 9.8 mmHg, p < 0.001, PTT: from 172.8 ± 20.1 to 176.8 ± 19.2 ms, p < 0.001). Our results demonstrate that the SPB procedure can reduce BP and lengthen PTT significantly. Compared with amplitude dynamics, phase dynamics is a different marker for CPC analysis in reflecting cardiorespiratory coherence during slow breathing exercise. Our study provides a methodology to practice slow breathing exercise, including the setting of target breathing rate, change of CPC and the importance of regular breathing. The applications and usability of the study results have also been discussed.     

Zazen and cardiac variability

OBJECTIVE: This study examined the effects of "tanden breathing" by Zen practitioners on cardiac variability. Tanden breathing involves slow breathing into the lower abdomen. METHODS: Eleven Zen practitioners, six Rinzai and five Soto, were each studied during 20 minutes of tanden breathing, preceded and followed by 5-minute periods of quiet sitting. During this time, we measured heart rate and respiration rate. RESULTS: For most subjects, respiration rates fell to within the frequency range of 0.05 to 0.15 Hz during tanden breathing. Heart rate variability significantly increased within this low-frequency range but decreased in the high-frequency range (0.14-0.4 Hz), reflecting a shift of respiratory sinus arrhythmia from high-frequency to slower waves. Rinzai practitioners breathed at a slower rate and showed a higher amplitude of low-frequency heart rate waves than observed among Soto Zen participants. One Rinzai master breathed approximately once per minute and showed an increase in very-low-frequency waves (<0.05 Hz). Total amplitude of heart rate oscillations (across frequency spectra) also increased. More experienced Zen practitioners had frequent heart rhythm irregularities during and after the nadir of heart rate oscillations (ie, during inhalation). CONCLUSIONS: These data are consistent with the theory that increased oscillation amplitude during slow breathing is caused by resonance between cardiac variability caused by respiration and that produced by physiological processes underlying slower rhythms. The rhythm irregularities during inhalation may be related to inhibition of vagal modulation during the cardioacceleratory phase. It is not known whether they reflect cardiopathology.     

Hyperoxia-induced alterations in cardiovascular function and autonomic control during return to normoxic breathing

Hyperoxia causes hemodynamic alterations. We hypothesized that cardiovascular and autonomic control changes last beyond the end of hyperoxic period into normoxia. Ten healthy volunteers were randomized to breathe either medical air or 100% oxygen for 45 min in a double-blind study design. Measurements were performed before (baseline) and during gas exposure, and then 10, 30, 60, and 90 min after gas exposure. Hemodynamic changes were studied by Doppler echocardiography. Changes in cardiac and vasomotor autonomic control were evaluated through changes in spectral power of heart rate variability and blood pressure variability. Cardiac baroreflex sensitivity was assessed by the sequence method. Hyperoxia significantly decreased heart rate and increased the high frequency power of heart rate variability, suggesting a chemoreflex increase in vagal activity since the slope of cardiac baroreflex was significantly decreased during hyperoxia. Hyperoxia increased significantly the systemic vascular resistances and decreased the low frequency power of blood pressure variability, suggesting that hyperoxic vasoconstriction was not supported by an increase in vascular sympathetic stimulation. These changes lasted for 10 min after hyperoxia (p < 0.05). After the end of hyperoxic exposure, the shift of the power spectral distribution of heart rate variability toward a pattern of increased cardiac sympathetic activity lasted for 30 min (p < 0.05), reflecting a resuming of baseline autonomic balance. Cardiac output and stroke volume were significantly decreased during hyperoxia and returned to baseline values (10 min) later than heart rate. In conclusion, hyperoxia effects continue during return to normoxic breathing, but cardiac and vascular parameters followed different time courses of recovery.     

Efficacy of paced breathing for insomnia: Enhances vagal activity and improves sleep quality

Fourteen self‐reported insomniacs (SRI) and 14 good sleepers (GS) had their cardiac neuronal activity assessed by heart rate variability (HRV) under controlled respiration at a slow frequency rate of 0.1 Hz, and a forced rate of 0.2 Hz during daytime rest. Nighttime sleep was measured by polysomnography. The SRI showed depressed high frequency power of HRV compared to the GS. An increased total power of HRV was observed among the SRI during slow, paced breathing compared with spontaneous breathing and 0.2 Hz. Sleep onset latency, number of awakenings, and awakening time during sleep were decreased and sleep efficiency was increased if SRI practiced slow, paced breathing exercises for 20 min before going to sleep. Our results indicate that there is autonomic dysfunction among insomniacs, especially in relation to vagal activity; however, this decreased vagal activity can be facilitated by practicing slow, paced breathing, thereby improving sleep quality.     

Influence of respiratory rate on the variability of blood volume pulse characteristics

Photoplethysmogram (PPG) measures have been proven useful for the quantification of sympathetic reactivity and continuous monitoring of vascular reactivity. This study was designed to delineate the influence of respiratory rate on the variability of various PPG characteristics in time and frequency domains. PPG, electrocardiogram (ECG) and respiration were simultaneously recorded for 2 min from eight healthy volunteers during paced respiration of 6, 12 and 18 cycles min^?1. The PPG characteristics such as peak-to-peak interval (PPI), systolic peak amplitude, slope, T_crest, T_decay and pulse transit time (PTT) were computed for every pulse. In time domain, the mean of amplitude, slope and T_crest were not significantly different amongst three different respiratory rates. However, the mean of T_decay, PPI and PTT were significantly increased (p < 0.05, p < 0.05 and p < 0.01, respectively) during respiration of 6 cycles min^?1 compared to 12 cycles min^?1. The maximal spectral powers of the variability of all PPG measures were centred on the respiratory frequency in frequency domain. In conclusion, the results that the amplitude and slope in time domain are not altered by the respiratory frequency suggest their application in faithful assessment of cardiovascular reactivity. As the variability of PPI, T_decay and PTT are altered by the slow respiration, the influence of respiration on these time derivatives should not be ignored during interpretation of vascular reactivity.     

Nonlinear Mechanisms Determining Expiratory Flow Limitation in Mechanical Ventilation: A Model-Based Interpretation

A nonlinear model of breathing mechanics, in which the tracheobronchial airways are considered in three serial segments, is presented to obtain insights into the mechanisms underlying expiratory flow limitation (EFL) in mechanically ventilated patients. Chronic obstructive pulmonary disease (COPD) and normal conditions were simulated and EFL was detected by application of negative expiratory pressure at the mouth or resistance reduction of the expiratory circuit. Simulation results confirm that both techniques reveal remarkable differences in the flow–volume curves between normal subjects and COPD patients, the former showing absence of EFL and the latter exhibiting EFL over most of the expiration. To interpret the role of different nonlinear mechanisms in producing EFL, different flow–volume curves obtained by changing model parameter values were analyzed. An increase in lower-airway resistance did not give rise to EFL, whereas a change in the pressure–volume characteristic of the intermediate-airway segment, towards increased resistance and easier collapse, significantly modified system behavior. In particular, EFL was observed when this intermediate-segment change was combined with an increase in lower-airway resistance. This evidence suggests that modifications, producing loss of radial traction and consequent narrowing of the airways in the peribronchial region, may play a leading role in EFL in COPD patients. © 2003 Biomedical Engineering Society. PAC2003: 8719Uv, 8710+e, 8719Xx     

Effects of a Saddle Shaped Annulus on Mitral Valve Function and Chordal Force Distribution: An <Emphasis Type="Italic">In Vitro</Emphasis> Study

Studies have concluded that the shape of the human mitral valve annulus is a three-dimensional saddle. The objective of this study was to investigate the effects of a saddle shaped annulus on chordal force distribution and mitral valve function. Eleven human mitral valves were studied in a physiological left heart simulator with a variable shaped annulus (flat versus saddle). Cardiac output and transmitral pressure were analyzed to determine mitral regurgitation volume. In six experiments, force transducers were placed on six chordae tendineae to measure chordal force distribution. Valves were tested in normal and pathophysiologic papillary muscle positions. When comparing the flat and saddle shaped configurations, there was no significant difference in mitral regurgitation volume 11.2% ± 24.7% (p=0.17). In the saddle shaped configuration, the tension on the anterior strut chord was reduced 18.5% #x00B1 16.1% (p < 0.02), the tension on the posterior intermediate chord increased 22.3% #x00B1 17.1% (p < 0.03), and the tension of the commissural chord increased 59.0% #x00B1 32.2% (p < 0.01). Annular shape also altered the tensions on the remaining chords. Annular shape alone does not significantly affect mitral regurgitation caused by papillary muscle displacement. A saddle shaped annulus redistributes the forces on the chords by altering coaptation geometry, leading to an optimally balanced anatomic/physiologic configuration. © 2003 Biomedical Engineering Society. PAC2003: 8719Hh, 8719Uv, 8719Rr     

Inclusion of a rest period in diaphragmatic breathing increases high frequency heart rate variability: Implications for behavioral therapy

Heart rate variability (HRV) is associated with positive physiological and psychological effects. HRV is affected by breathing parameters, yet debate remains regarding the best breathing interventions for strengthening HRV. The objective of the current study was to test whether the inclusion of a postexhalation rest period was effective at increasing HRV, while controlling for breathing rate. A within‐subject crossover design was used with 40 participants who were assigned randomly to a breathing pattern including a postexhalation rest period or a breathing pattern that omitted the postexhalation rest period. Participants completed training on each breathing pattern, practiced for 6 min, and sat quietly during a 5‐min washout period between practices. Participants were given instructions for diaphragmatic breathing at a pace of six breaths/minute with or without a postexhalation rest period. Recordings of heart rate, breathing rate, HF‐HRV, RMSSD, LF‐HRV, and SDNN were collected before and during each of the breathing trials. HRV indices were derived from Lead 1 ECG recordings. Pairwise contrasts showed that inclusion of a postexhalation rest period significantly decreased heart rate (p < .001) and increased HF‐HRV (p < .05). No differences were found for breathing rates (p > .05), RMSSD (p > .05), and SDNN (p > .05). Results indicated that omission of the postexhalation rest period resulted in higher LF‐HRV (p < .05). A postexhalation rest period improves HF‐HRV, commonly associated with self‐regulatory control, yet the importance of a postexhalation rest period requires further exploration.     

Influence of inspiratory threshold load on cardiovascular responses to controlled breathing at 0.1 Hz

Slow, deep breathing is being used as a self‐management intervention for various health conditions including pain and hypertension. Stimulation of the arterial baroreceptors and increased vagal modulation are among the proposed mechanisms for the therapeutic effects of slow, deep breathing. We investigated whether adding inspiratory threshold load can enhance the cardiovascular responses to controlled breathing at the frequency of 0.1 Hz, a common form of slow, deep breathing. Healthy volunteers (N = 29) performed controlled breathing at 0.1 Hz (6 breaths/minute) without load and with inspiratory threshold loads of 5 cmH₂O and 10 cmH₂O. Respiratory airflow, heart rate, and blood pressure were continuously recorded. The amplitude of the systolic blood pressure variation during respiratory cycles increased with increasing loads. Respiratory sinus arrhythmia was higher during controlled breathing at 0.1 Hz with the load of 10 cmH₂O compared to without load. Baroreflex sensitivity was not affected by loads. The effect of loads on respiratory sinus arrhythmia was mediated by increasing the amplitude of systolic blood pressure variation during respiratory cycles. These results suggest that applying small inspiratory threshold loads during controlled breathing at 0.1 Hz increases cardiac vagal modulation by this breathing exercise. This effect seems to be mediated by stronger stimulation of the arterial baroreceptors because of larger systolic blood pressure swings along the respiratory cycle. The potential benefit of long‐term practice of controlled breathing at 0.1 Hz with inspiratory threshold loads on baroreflex function and cardiac vagal control needs to be investigated, particularly in pain and hypertension patients.     

Vagal tone during quiet sleep in normal human term fetuses

The purpose of this paper was to calculate vagal tone (V) for 17 normal human fetuses in quiet sleep (QS) between 36 and 40 weeks gestation. The fetal cardiac electrical signal was captured transabdominally in 3-min blocks at a rate of 833 times per second and fetal R-waves were extracted using adaptive signal processing techniques. Fetal R-wave interbeat intervals were converted to equally spaced, time-based data, and the low-frequency component was removed using a 21-point third-order moving polynomial. The parameter V was calculated by taking the natural logarithm of the sum of the power densities between 0.3 Hz and 1.3 Hz. We found that fetal breathing was associated with an approximately 25% increase in V as compared to nonbreathing, 3.33 ± 0.48 versus 2.57 The Official Journal of the International Society for Developmental Psychobiology 0.47, p < 0.0001. Furthermore, there was a significant linear relationship between the mean single-fetus V during spontaneous respiration and the mean single-fetus V during normally occurring apneic periods, r = 0.772, p < 0.002. We conclude that respiratory activity is associated with a significant increase in vagal tone for normal human fetuses in QS.©1994 John Wiley & Sons, Inc.     

Effect of Specimen Size and Aspect Ratio on the Tensile Properties of Porcine Aortic Valve Tissues

The measurement of mechanical properties of biological tissues is subject to artifacts such as natural variability and inconsistency in specimen preparation. As a result, data cannot be easily compared across laboratories. To test the effects of variable specimen dimensions, we systematically modified the size and aspect ratio (AR) of porcine aortic valve tissues and measured their stiffness and extensibility. We found that: (i) as the AR of circumferential specimens increased from 1:1 to 5:1, their stiffness increased by 36% (p < 0.001) and their extensibility decreased by 21% (p < 0.001); (ii) as the AR of radial specimens increased from 0.8:1 to 4:1, their stiffness increased by 36% (p < 0.001) and their extensibility decreased by 34% (p < 0.001); (iii) as the size of circumferential specimens was reduced from 128 to 32 mm² at fixed AR (2:1), their stiffness decreased by 6% (p=0.05), and their extensibility increased by 17% (p < 0.001); and (iv) as the size of radial specimens was reduced from 72 to 32 mm² at fixed AR (2:1), their stiffness decreased by 7% (p=0.03) and their extensibility increased by 16% (p=0.005). Thus, as specimens of constant length became narrower, they became stiffer and less extensible, and as specimens of fixed aspect ratio became smaller, they became less stiff and more extensible. Statistical models of these trends were predictive and can thus be used to integrate materials test data across different laboratories. © 2003 Biomedical Engineering Society. PAC2003: 8719Rr, 8715La, 8710+e     

Effects of sensory stimulation on respiratory cardiac cycle variability in humans

The effects of the phase of respiration on the response of respiratory cardiac cycle variability to sensory stimulation were studied in five healthy young male subjects. Transcutaneous electrical stimulation of the ulnar nerve or hand-grip exercise was applied during inspiration or expiration. Although both electrical stimulation and hand-grip exercise depressed respiratory cardiac cycle variability, the nature of the depression differed according to where in the respiration cycle the stimuli were applied. The amplitude of respiratory cardiac cycle variation was significantly decreased when either stimulus was applied during expiration (P < 0.05), and was unchanged when applied during inspiration (P > 0.05). These findings would suggest that cardiac vagal efferent activity was effectively inhibited by sensory stimulation during expiration, but was not inhibited by such stimulation during inspiration. This mechanism may account, in part, for the known suppression of respiratory cardiac cycle variability during exercise. Present address: Department of Biomechanics and Physiology, Faculty of Liberal Arts, University of Yamaguchi, Yamaguchi City, 1677-1 Yoshida, Yamaguchi 753, Japan     

Effects of Periodic Body Acceleration on the <Emphasis Type="Italic">In Vivo</Emphasis> Vasoactive Response to N-<Emphasis Type="Italic">w</Emphasis>-nitro–L-arginine and the <Emphasis Type="Italic">In Vitro</Emphasis> Nitric Oxide Production

Periodic acceleration (pGz), a novel method of ventilatory support, is achieved using a platform that moves cyclically in the headward–footward direction. PGz has been shown to increase vascular shear stress and regional blood flows, as well as decrease pulmonary and systemic vascular resistances. PGz also increases nitric oxide (NO) production. This study was undertaken to determine the effects of pGz on the NO inhibiting effects of N-w-nitro–L-arginine (L-NAME) in vivo, and to determine if increased NO production due to pGz could be reproduced in vitro with isolated arteries. Pigs were assigned to conventional ventilation (CV), or pGz, with no additional breathing assistance. L-NAME was infused in cumulative doses of 1, 3, 10, 30, and 100 mg/kg. Cardiac output decreased in both groups by 50%. There was also a dose-dependent increase in blood pressure, pulmonary artery pressure, and vascular resistances. However, pGz attenuated the vascular response of L-NAME. Isolated porcine aortas exposed to nonpulsatile, pulsatile, and pulsatile flow plus pGz exhibited an increase in nitrites with the addition of pulsatile flow (300%, relative to steady flow), and a further increase with pGz (1000%, relative to steady flow). It has been determined that pGz, a novel method of increasing shear stress on the vascular endothelium, attenuates the vasoactive response to L-NAME. The in vitro experiments demonstrated that increases in NO production in vivo could be reproduced in vitro, which provides the opportunity to investigate the mechanisms of cardiovascular pGz effects. © 2003 Biomedical Engineering Society. PAC2003: 8719Uv, 8719Rr, 8780-y     

Characterization of Atrioventricular Nodal Response to Electrical Left Vagal Stimulation

The dynamic effect of left vagal stimulation on atrioventricular conduction was studied in six isofluorane-anesthetized dogs ranging in weight from 22 to 29 kg. The cervical vagus nerve trunks were left intact and no beta-adrenergic blockade was produced so that any influences of the sympathetic nervous system and autonomic reflex activity could be observed. Atrial pacing was used to control the heart rate while single, short trains of left vagal stimulation were delivered and timed to occur at different instants during the cardiac cycle. The magnitude of the A—V delay depended on the instant of delivery of the train of vagal stimuli during the cardiac cycle. Vagal effect curves were constructed and fit to a mathematical equation which describes the pharmacokinetic behavior of a bolus injection of a drug whose onset time is of the same order as its half-life. The three parameters of this equation have physiologic significance and are related to nerve propagation time and synaptic delay, acetylcholine concentration rise, and the acetylcholineesterase mechanism. The maximum A—V delay occurred when the short train of left vagal stimuli was applied 200–300 ms after the atrial pacing stimulus and the total effect was virtually over by 800–1000 ms. © 1999 Biomedical Engineering Society. PAC99: 8719Nn, 8754Dt, 8719Ff     

Nonlinear and Frequency-Dependent Mechanical Behavior of the Mouse Respiratory System

The assessment of the mechanical properties of the respiratory system is typically done by oscillating flow into the lungs via the trachea, measuring the resulting pressure generated at the trachea, and relating the two signals to each other in terms of some suitable mathematical model. If the perturbing flow signal is broadband and not too large in amplitude, linear behavior is usually assumed and the input impedance calculated. Alternatively, some researchers have used flow signals that are narrow band but large in amplitude, and invoked nonlinear lumped-parameter models to account for the relationship between flow and pressure. There has been little attempt, however, to deal with respiratory data that are both broadband and reflective of system nonlinearities. In the present study, we collected such data from mice. To interpret these data, we first developed a time-domain approximation to a widely used model of respiratory input impedance. We then extended this model to include nonlinear resistive and elastic terms. We found that the nonlinear elastic term fit the data better than the linear model or the nonlinear resistance model when amplitudes were large. This model may be useful for detecting overinflation of the lung during mechanical ventilation. © 2003 Biomedical Engineering Society. PAC2003: 8719Rr, 8719Uv     

Time domain, geometrical and frequency domain analysis of cardiac vagal outflow: effects of various respiratory patterns.

The purpose of this study was to compare the applicability of four different measures of heart rate variability (HRV) in the assessment of cardiac vagal outflow, with special reference to the effect of breathing pattern. The anticholinergic effects of an intravenous glycopyrrolate infusion (5 microg x kg(-1) x h(-1) for 2 h) during spontaneous and controlled (15 min(-1)) breathing rate were investigated in eight volunteers, and the effects of different fixed breathing rates (6-15-24 min(-1)) and hyperventilation in 12 subjects. Cardiac vagal activity was assessed by ECG recordings in which the following measures of HRV were computed: the high-frequency (HF) spectral component, the instantaneous RR interval (RRI) variability (SD1) analysed from the Poincaré plots, the percentage of differences between successive RRIs greater than 50 ms (pNN50), and the square root of the mean squared differences of successive RRIs (RMSSD). On average, glycopyrrolate reduced the HF spectral component by 99.8%, SD1 by 91.3%, pNN50 by 100% and RMSSD by 97.0%. The change of breathing pattern from controlled to spontaneous decreased significantly the HF component and pNN50, but did not affect SD1 or RMSSD. Rapid breathing rate (24 min(-1)) decreased the HF component, but had no effects on the other measures. A controlled breathing rate is needed for a reliable assessment of cardiac vagal outflow by the spectral analysis technique. The quantitative geometrical analysis of short-term RRI variability from the Poincaré plots and the time domain measure RMSSD were not significantly affected by changes in the breathing rate, suggesting that these indices are more suitable for the measurement of cardiac vagal outflow during the 'free-running' ambulatory conditions.     

Transient phase locking patterns among respiration,heart rate and blood pressure during cardiorespiratory synchronisation in humans

The interactions between respiration, heart rate and blood pressure variability (HRV, BPV), are considered to be of paramount importance for the study of the functional organisation of the autonomic nervous system (ANS). The aim of the reported study is to detect and classify the intermittent phase locking (PL) phenomena between respiration, HRV and BPV during cardiorespiratory synchronisation experiments, by using the following time-domain techniques: Poincaré maps, recurrence plots, time-space separation plots and frequency tracking locus. The experimental protocol consists of three stages, with normal subjects in paced breathing at 15, 12 and 8 breaths min⁻¹. Transient phenomena of coordination between respiration and the major rhythms of HRV and BPV (low and high frequency, LF and HF) have been detected and classified: no interaction between LF and HF rhythms at 15 breaths min⁻¹; short time intervals of stable 1∶2 frequency and phase synchronisation during the 12 breaths min⁻¹ stage; 1∶1 PL during the 8 breaths min⁻¹ stage. 1∶1 and 1∶2 PL phenomena occurred when the respiration frequency was quite close to the LF frequency or when it was about twice the LF frequency, respectively. The complex organisation of the ANS seems to provoke transient rather than permanent PL phenomena between the co-ordinating components of respiration and cardiovascular variability series.     

Cardio-respiratory coupling in untreated patients with major depression

BackgroundDepressive disorders are known to be associated with higher risks of cardiovascular diseases. Several studies have reported an imbalance within the autonomic nervous system (ANS) as one putative cause. Previous investigations showed decreased cardio-respiratory coupling in depressive patients that were treated with nortriptyline. We aimed to compare parameters of heart rate variability and cardio-respiratory coupling between unmedicated patients suffering from major depressive disorder (MDD) and healthy controls in order to further understand autonomic dysfunction in the disease.MethodsWe investigated eighteen unmedicated patients with major depressive disorder and eighteen matched healthy controls. Electrocardiogram and respiratory signals were obtained during a twenty minute resting period. Time- and frequency based parameters of HRV, respiratory sinus arrhythmia (RSA), approximate entropy of heart rate (ApEn_RR) and respiratory rate (ApEn_Resp) were calculated. Additionally, cross-ApEn between RR-intervals and respiration time series was determined, reflecting coupling of both signals.ResultsPatients showed an increased heart rate and LF/HF-ratio. Respiratory sinus arrhythmia (RSA) and ApEn_RR were reduced in patients in comparison to controls. Breathing rate, ApEn_Resp and cross-ApEn did not differ between the two groups.DiscussionIncreased heart rate, increased LF/HF-ratio, reduced RSA and reduced ApEn_RR indicate a decrease of cardiac vagal modulation in depressive patients. No difference of cardio-respiratory coupling was observed. Respiratory parameters and cross-ApEn did not differ between both groups, and thus we conclude that diminished vagal modulation is mainly limited to cardiac modulation.     

Changes in resting heart rate variability across the menstrual cycle

Heart rate variability (HRV) is a noninvasive indicator of autonomic control. This study examines HRV changes across a normal menstrual cycle and proposes a novel piecewise function controlling for the effects of breathing on HRV spectral parameters. A resting ECG was collected from 13 women at five points in their menstrual cycle. Both heart rate and breathing rate increased across the cycle (p < .01) while time‐domain variability decreased (p = .04). Use of the piecewise function for breathing rate in HRV spectral analysis was confirmed by a substantial increase in model goodness‐of‐fit. HRV spectral parameters, controlled for breathing with the piecewise function, confirm that the decrease in variability is likely due to a parasympathetic withdrawal, since high frequency HRV decreases (p = .02).     

Reduced heart rate variability predicts poor sleep quality in a case–control study of chronic fatigue syndrome

Parasympathetic function is important in the induction and maintenance of sleep. We examined whether nocturnal vagal modulation of heart rate is related to the poor sleep quality commonly reported in chronic fatigue syndrome (CFS). Heart rate (HR, as R–R intervals) was continuously monitored during sleep in 20 patients with CFS and 20 matched control subjects. Questionnaires assessed demographic information, symptoms, functional impairment, and subjective sleep quality. CFS was associated with more sleep problems in general and poorer subjective sleep quality on the study night (all p < 0.003), and reports of repeated awakening during the night were 7 times more likely compared to healthy subjects (p = 0.017). Time and frequency-domain parameters of HR variability during sleep were significantly lower in patients with CFS (all p < 0.006). Multiple regression analyses revealed that heart rate variability (HRV) parameters were the best predictors of subjective sleep measures. This study identified significant reductions in vagal modulation of heart rate during sleep in CFS. Low HRV strongly predicted sleep quality—suggesting a pervasive state of nocturnal sympathetic hypervigilance in CFS.