The effect of aging and severity of sleep apnea on heart rate variability indices in obstructive sleep apnea syndrome

Investigating the influence of an adjustable zoned air mattress on sleep: a multinight polysomnography study

Introduction

A comfortable mattress should improve sleep quality. In this study, we sought to investigate the specific sleep parameters that could be affected by a mattress and explore any potential differences between the effects felt by each sex.

Methods

A total of 20 healthy young adults (10 females and 20 males; 22.10 ± 1.25 years) participated in the experiments. A smart adjustable zoned air mattress was designed to maintain comfortable support, and an ordinary mattress was used for comparison. The participants individually spent four nights on these two mattresses in four orders for polysomnography (PSG) scoring. Sleep architecture, electroencephalogram (EEG) spectrum, and heart rate variability (HRV), which reflect the central and autonomic nervous activities, were used to compare the difference between the two mattresses.

Results

An individual difference exited in sleep performance. The modes of influence of the mattresses were different between the sexes. The adjustable air mattress and the increase in experimental nights improved female participants' sleep efficiency, while male participants exhibited a smaller response to different mattresses. With an increasing number of experiment nights, both sexes showed increased REM and decreased N2 proportions; the N3 sleep proportion decreased in the male participants, and the heart rate decreased in both sexes. The performance of the EEG spectrum supports the above results. In addition, the adjustable air mattress weakened automatic nerve activity during N3 sleep in most participants. The female participants appeared to be more sensitive to mattresses. Experiment night was associated with psychological factors. There were differences in the results for this influence between the sexes.

Conclusion

This study may shed some light on the differences between the ideal sleep environment of each sex.

Information-Based Similarity of Ordinal Pattern Sequences as a Novel Descriptor in Obstructive Sleep Apnea Screening Based on Wearable Photoplethysmography Bracelets

Obstructive sleep apnea (OSA) is a common respiratory disorder associated with autonomic nervous system (ANS) dysfunction, resulting in abnormal heart rate variability (HRV). Capable of acquiring heart rate (HR) information with more convenience, wearable photoplethysmography (PPG) bracelets are proven to be a potential surrogate for electrocardiogram (ECG)-based devices. Meanwhile, bracelet-type PPG has been heavily marketed and widely accepted. This study aims to investigate the algorithm that can identify OSA with wearable devices. The information-based similarity of ordinal pattern sequences (OP_IBS), which is a modified version of the information-based similarity (IBS), has been proposed as a novel index to detect OSA based on wearable PPG signals. A total of 92 PPG recordings (29 normal subjects, 39 mild-moderate OSA subjects and 24 severe OSA subjects) were included in this study. OP_IBS along with classical indices were calculated. For severe OSA detection, the accuracy of OP_IBS was 85.9%, much higher than that of the low-frequency power to high-frequency power ratio (70.7%). The combination of OP_IBS, IBS, CV and LF/HF can achieve 91.3% accuracy, 91.0% sensitivity and 91.5% specificity. The performance of OP_IBS is significantly improved compared with our previous study based on the same database with the IBS method. In the Physionet database, OP_IBS also performed exceptionally well with an accuracy of 91.7%. This research shows that the OP_IBS method can access the HR dynamics of OSA subjects and help diagnose OSA in clinical environments.

Association between autonomic function and obstructive sleep apnea: A systematic review

Obstructive sleep apnea (OSA) is an independent risk factor for hypertension and cardiovascular disease. Effects of OSA on the autonomic nervous system may mediate this association. We performed a systematic literature review to determine the profile of autonomic function associated with OSA. Three electronic databases were searched for studies of OSA patients aged ≥18 years in which autonomic function was assessed. Studies comparing patients with and without OSA, or examining the association of OSA severity with changes in autonomic function were included. Seventy-one studies met the inclusion criteria and autonomic function has been assessed using a range of techniques. The profile of autonomic function found in OSA include increased sympathetic activity, reduced parasympathetic activity and less consistently found low heart rate variability. Altered autonomic function in OSA may explain the pathophysiology of increased cardiovascular risk. Evidence from intervention studies is required to determine if treatment improves autonomic function associated with OSA.

Short-Term HRV Analysis Using Nonparametric Sample Entropy for Obstructive Sleep Apnea

Obstructive sleep apnea (OSA) is associated with reduced heart rate variability (HRV) and autonomic nervous system dysfunction. Sample entropy (SampEn) is commonly used for regularity analysis. However, it has limitations in processing short-term segments of HRV signals due to the extreme dependence of its functional parameters. We used the nonparametric sample entropy (NPSampEn) as a novel index for short-term HRV analysis in the case of OSA. The manuscript included 60 6-h electrocardiogram recordings (20 healthy, 14 mild-moderate OSA, and 26 severe OSA) from the PhysioNet database. The NPSampEn value was compared with the SampEn value and frequency domain indices. The empirical results showed that NPSampEn could better differentiate the three groups (p < 0.01) than the ratio of low frequency power to high frequency power (LF/HF) and SampEn. Moreover, NPSampEn (83.3%) approached a higher OSA screening accuracy than the LF/HF (73.3%) and SampEn (68.3%). Compared with SampEn (|r| = 0.602, p < 0.05), NPSampEn (|r| = 0.756, p < 0.05) had a significantly stronger association with the apnea-hypopnea index (AHI). Hence, NPSampEn can fully overcome the influence of individual differences that are prevalent in biomedical signal processing, and might be useful in processing short-term segments of HRV signal.

Application of the Variance Delay Fuzzy Approximate Entropy for Autonomic Nervous System Fluctuation Analysis in Obstructive Sleep Apnea Patients

Obstructive sleep apnea (OSA) is a fatal respiratory disease occurring in sleep. OSA can induce declined heart rate variability (HRV) and was reported to have autonomic nerve system (ANS) dysfunction. Variance delay fuzzy approximate entropy (VD_fApEn) was proposed as a nonlinear index to study the fluctuation change of ANS in OSA patients. Sixty electrocardiogram (ECG) recordings of the PhysioNet database (20 normal, 14 mild-moderate OSA, and 26 severe OSA) were intercepted for 6 h and divided into 5-min segments. HRV analysis were adopted in traditional frequency domain, and nonlinear HRV indices were also calculated. Among these indices, VD_fApEn could significantly differentiate among the three groups (p < 0.05) compared with the ratio of low frequency power and high frequency power (LF/HF ratio) and fuzzy approximate entropy (fApEn). Moreover, the VD_fApEn (90%) reached a higher OSA screening accuracy compared with LF/HF ratio (80%) and fApEn (78.3%). Therefore, VD_fApEn provides a potential clinical method for ANS fluctuation analysis in OSA patients and OSA severity analysis.

Effect of an Innovative Mattress and Cryotherapy on Sleep after an Elite Rugby Match

INTRODUCTION

This study aimed to explore the relationship between elite rugby union match and postmatch sleep architecture and to investigate the effects of a high-heat capacity mattress (MAT) and a whole-body cryotherapy (WBC) session on postmatch sleep architecture.

METHODS

Nineteen elite male U23 rugby union players performed in three official matches, followed by three experimental conditions, in a randomized order: MAT, WBC, and no intervention (CONT). Match load was evaluated using GPS trackers and video analyses. Sleep architecture was assessed by polysomnography (PSG). Core body temperature (CBT) and mattress surface temperature were monitored during sleep. Linear mixed-effects models were conducted to assess the effects of each experimental condition on sleep, with match load variables as covariates.

RESULTS

A lower wake after sleep onset (β = -10.5 min, P < 0.01) and higher rapid eye movement sleep proportion (β = +2.8%, P < 0.05) were reported for MAT compared with CONT. Moreover, lower mean CBT (β = -0.135°C, P < 0.001) and mean mattress surface temperature (β = -2.736°C, P < 0.001) during sleep were observed for MAT compared CONT. WBC did not affect nocturnal CBT nor interfere with sleep architecture. For every 100-m increase in high-speed running distance, a higher slow wave sleep (β = +1.1%, P = 0.05) and lower light sleep proportion (β = -1.2%, P < 0.05) proportion were observed. Conversely, for every 10 supplementary collisions, lower slow wave sleep (β = -1.9, P = 0.09) and higher light sleep (β = +2.9%, P < 0.001) proportion were observed.

CONCLUSION

MAT use had a positive effect on sleep architecture after an elite rugby union match, potentially through a more efficient nocturnal heat transfer.

Changes in heart rate variability (HRV) in patients with severe and moderate obstructive sleep apnea before and after acute CPAP therapy during nocturnal polysomnography

INTRODUCTION

Obstructive sleep apnea is an important risk factor for cardiovascular disease. Noninvasive positive pressure ventilation is the standard treatment of this disease, and it can reduce mortality in patients. Dysfunction of the autonomic system is one of the reasons for an increased risk of cardiovascular disease in these patients. The purpose of the present study was to investigate the effect of positive airway pressure (PAP) therapy on heart rate variability (HRV) indices.

METHODS

The study population was comprised of 55 patients, who underwent nocturnal polysomnography for the diagnosis of obstructive sleep apnea and PAP titration on the same night. The levels of continuous positive airway pressure (CPAP) and bilevel positive airway pressure were adjusted to relieve obstructive sleep apnea, hypopnea, and desaturation. The patients' heart changes and cardiac characteristics were recorded before and after the start of routine CPAP therapy. Finally, the cases' sleep and polysomnography tests were analyzed and interpreted in collaboration with a sleep specialist and their cardiac changes with the aid of a cardiologist before and after treatment with CPAP.

RESULTS

The participants were 55 patients at a mean age of 57.04±12.9 years. There were 34 (61.8%) male and 21 (38.2%) female cases. PAP therapy on the same night resulted in a decreased standard deviation of the N-N interval index (p=0.036) and a low-frequency index (p=0.021), as well as increased high-frequency index (p<0.001) and low frequency / high frequency ratios (p=0.008).

CONCLUSION

Our findings indicate a relative improvement in the activity of the autonomic system in patients with obstructive sleep apnea after 1 night of PAP therapy. Overwhelming evidence suggests that improvement in the sympathetic balance can reduce the risk of cardiovascular disease in patients.

Cardiac autonomic activity during sleep in high-altitude resident children compared with lowland residents

Study Objectives

We aimed to characterize heart-rate variability (HRV) during sleep in Andean children native to high altitude (HA) compared with age, gender, and genetic ancestry-similar low-altitude (LA) children. We hypothesized that the hypoxic burden of sleep at HA could induce variation in HRV. As children have otherwise healthy cardiovascular systems, such alterations could provide early markers of later cardiovascular disease.

Methods

Twenty-six LA (14F) and 18 HA (8F) children underwent a single night of attended polysomnography. Sleep parameters and HRV indices were measured. Linear mixed models were used to assess HRV differences across sleep stage and altitude group.

Results

All children showed marked fluctuations in HRV parameters across sleep stages, with higher vagal activity during nonrapid eye movement sleep and greater variability of the heart rate during rapid eye movement (REM). Moreover, HA children showed higher very low-frequency HRV in REM sleep and, after adjusting for heart rate, higher low-to-high frequency ratio in REM sleep compared with children living at lower altitude.

Conclusions

We confirmed previous findings of a stage-dependent modulation of HRV in Andean children living at both HA and LA. Moreover, we showed subtle alteration of HRV in sleep in HA children, with intriguing differences in the very low-frequency domain during REM sleep. Whether these differences are the results of an adaptation to high-altitude living, or an indirect effect of differences in oxyhemoglobin saturation remains unclear, and further research is required to address these questions.

Association between snoring and heart rate variability in adolescents: effects of gender and insufficient sleep

PURPOSE

We explored the association between subjective snoring frequency and heart rate variability (HRV) in a healthy adolescent population.

METHODS

A total of 102 healthy adolescents were recruited from high schools in South Korea, and reported their sleep habits and snoring frequency. HRV was assessed to indirectly measure autonomic function. We assessed correlations between snoring frequency and HRV indices. We also investigated the effects of sex and behaviorally induced insufficient sleep syndrome (BISS) on the associations between HRV parameters and snoring frequency.

RESULTS

Overall, significant correlations were apparent between snoring frequency and HRV indices including the standard deviation of the normal-to-normal intervals (SDNN) and the low-frequency/high-frequency (LF/HF) ratio. Associations were more evident in males and those with BISS compared to females and those without BISS.

CONCLUSIONS

Our findings suggest that snoring changes autonomic nervous system (ANS) activity in adolescents; the changes are more dramatic in males and those with insufficient sleep.

Nocturnal heart rate variation in diabetic and non-diabetic patients with sleep apnea syndrome

OBJECTIVES

Heart rate variability (HRV) analysis is used for the evaluation of autonomic function in the cardiovascular system. Decreased HRV is associated with disorders affecting the autonomous system such as diabetes mellitus (DM) and obstructive sleep apnea (OSA). Previous studies have shown an association between OSA and DM. However, the interrelationships of HRV with OSA and DM are not well known. The aim of this study was to assess nocturnal HRV in patients who suffered from OSA with and without DM.

METHODS

Sixty patients with OSA (27 with DM and 33 non-DM) underwent polysomnography for eight hours starting at midnight. From electrocardiogram (ECG) recordings taken as a part of polysomnography, time-domain and frequency-domain HRV parameters were evaluated to compare patients with regard to nocturnal HRV components such as low frequency (LF) and high frequency (HF), apnea-hypopnea index (AHI) and sleep parameters.

RESULTS

In the non-DM group, a direct relationship was observed between AHI and HRV rather than very low frequency (VLF) and LF/HF variables. This relationship was just significant between AHI and standard deviation of five-min average of normal R-R intervals and adjacent R-R intervals differing by 0.50 ms over 24 h (p < 0.05). In the DM group, the correlation between AHI and HRV parameters except HF and waking frequency was direct and non-significant. Intergroup comparison showed a significant difference between groups regarding AHI and HRV-index, LF and VLF (p < 0.05).

CONCLUSIONS

DM can affect HRV; however, this is not the case in OSA patients. This means that in the presence of OSA, the DM effect on HRV disappears.

Cardiac autonomic control in the obstructive sleep apnea

INTRODUCTION

The sympathetic activation is considered to be the main mechanism involved in the development of cardiovascular diseases in obstructive sleep apnea (OSA). The heart rate variability (HRV) analysis represents a non-invasive tool allowing the study of the autonomic nervous system. The impairment of HRV parameters in OSA has been documented. However, only a few studies tackled the dynamics of the autonomic nervous system during sleep in patients having OSA.

AIMS

To analyze the HRV over sleep stages and across sleep periods in order to clarify the impact of OSA on cardiac autonomic modulation. The second objective is to examine the nocturnal HRV of OSA patients to find out which HRV parameter is the best to reflect the symptoms severity.

METHODS

The study was retrospective. We have included 30 patients undergoing overnight polysomnography. Subjects were categorized into two groups according to apnea-hypopnea index (AHI): mild-to-moderate OSAS group (AHI: 5-30) and severe OSAS group (AHI>30). The HRV measures for participants with low apnea-hypopnea indices were compared to those of patients with high rates of apnea-hypopnea across the sleep period and sleep stages.

RESULTS

HRV measures during sleep stages for the group with low rates of apnea-hypopnea have indicated a parasympathetic activation during non-rapid eye movement (NREM) sleep. However, no significant difference has been observed in the high AHI group except for the mean of RR intervals (mean RR). The parasympathetic activity tended to increase across the night but without a statistical difference. After control of age and body mass index, the most significant correlation found was for the mean RR (p=0.0001, r=-0.248).

CONCLUSION

OSA affects sympathovagal modulation during sleep, and this impact has been correlated to the severity of the disease. The mean RR seemed to be a better index allowing the sympathovagal balance appreciation during the night in OSA.

Analysis of autonomic modulation after an acute session of resistance exercise at different intensities in chronic obstructive pulmonary disease patients

Purpose

Physical exercises are employed as part of the treatment of patients with chronic obstructive pulmonary disease (COPD); however information regarding cardiac autonomic modulation after an acute session of resistance exercise (RE) is unknown. The aim of this study was to evaluate the cardiac autonomic modulation, via heart rate variability after an acute session of RE applied at different intensities in COPD patients.

Patients and methods

Twelve COPD patients underwent an acute session of RE with an intensity of 60% and another of 90% of the one repetition maximum test. For analysis of autonomic modulation, heart rate was recorded beat-by-beat for 20 minutes at rest and after the training session. Heart rate variability indexes were obtained in the time and frequency domains for the assessment of autonomic modulation.

Results

Regardless of exercise intensity, RE acute sessions influenced the autonomic modulation when the recovery period was compared with the baseline. An increase in standard deviation of normal to normal RR intervals was observed throughout recovery time after the RE, as compared to baseline in both protocols: 60% and 90% of the one repetition maximum test. The spectral component of low frequency index (ms) was higher throughout recovery when compared to baseline in both protocols. The same was also observed in the spectral component of high frequency index (ms) for the protocols of 60% and 90%.

Conclusion

RE sessions impact on the autonomic modulation of COPD patients by promoting differences in the recovery period compared to baseline, regardless of the intensity of the exercise performed.

Effects of aging on genioglossus motor units in humans

The genioglossus is a major upper airway dilator muscle thought to be important in obstructive sleep apnea pathogenesis. Aging is a risk factor for obstructive sleep apnea although the mechanisms are unclear and the effects of aging on motor unit remodeled in the genioglossus remains unknown. To assess possible changes associated with aging we compared quantitative parameters related to motor unit potential morphology derived from EMG signals in a sample of older (n = 11; >55 years) versus younger (n = 29; <55 years) adults. All data were recorded during quiet breathing with the subjects awake. Diagnostic sleep studies (Apnea Hypopnea Index) confirmed the presence or absence of obstructive sleep apnea. Genioglossus EMG signals were analyzed offline by automated software (DQEMG), which estimated a MUP template from each extracted motor unit potential train (MUPT) for both the selective concentric needle and concentric needle macro (CNMACRO) recorded EMG signals. 2074 MUPTs from 40 subjects (mean±95% CI; older AHI 19.6±9.9 events/hr versus younger AHI 30.1±6.1 events/hr) were extracted. MUPs detected in older adults were 32% longer in duration (14.7±0.5 ms versus 11.1±0.2 ms; P  =  0.05), with similar amplitudes (395.2±25.1 µV versus 394.6±13.7 µV). Amplitudes of CNMACRO MUPs detected in older adults were larger by 22% (62.7±6.5 µV versus 51.3±3.0 µV; P<0.05), with areas 24% larger (160.6±18.6 µV.ms versus 130.0±7.4 µV.ms; P<0.05) than those detected in younger adults. These results confirm that remodeled motor units are present in the genioglossus muscle of individuals above 55 years, which may have implications for OSA pathogenesis and aging related upper airway collapsibility.

Heart rate variability is augmented in patients with positional obstructive sleep apnea, but only supine LF/HF index correlates with its severity

PURPOSE

Data on cardiac autonomic functioning, as expressed by heart rate variability (HRV), in patients with positional obstructive sleep apnea (p-OSA) disorder are lacking. The purpose of the study was to compare HRV indices between sleep segments derived from supine body position and another body position with and without apneic events, respectively. Our intention was to find some correlation between HRV indices and the pathophysiological characteristics of the corresponding temporal period.

METHODS

Nocturnal polysomnograms derived from twenty-seven patients (22 men) with documented positional apnea were retrospectively reviewed. Patients never treated for OSA and free from diseases/drugs altering HRV were examined. Data from total sleep studies were collected. Two N2 sleep segments, from supine body position with sleep-disordered breathing (SDB) and another body position without SDB were analyzed. Apneic events (namely, apneas, hypopneas, and respiratory effort-related arousals (RERAs)), arousals, number of desaturations, minimum pulse oximetry (SaO2min), time domain variables (average RR, SDNN, SDSD, RMSSD, pNN50, and HRV triangular index) and frequency domain variables (VLF, LF, HF, TP, LF/HF) were recorded for both temporal periods.

RESULTS

With the exception of average RR and HF, all other variables were significantly higher in segments with SDB. Only LF/HF_supine ratio was positively correlated with the apneic_supine_index (t = 3.13, p < 0.01) and negatively correlated with SaO2min (t = -2.9, p < 0.01) and the desaturation_supine_index (t = -2.5, p = 0.02). Arousals were negatively correlated with SaO2min (t = -2.8, p < 0.01).

CONCLUSIONS

SDB augments autonomic tone in patients with p-OSA, but only LF/HF correlates with its severity and might be used as a screening tool in the future. On the contrary, parasympathetic tone, as reflected by HF, remains constant in both periods.

Heart rate variability--current diagnosis of the cardiac autonomic neuropathy. A review

BACKROUND

The autonomic nervous system is one of the major homeostatic regulatory systems of the body. Detection of cardiac autonomic neuropathy (CAN), reflected by reduced heart rate variability (HRV), is an independent adverse prognostic factor: sympathovagal balance failure with a sympathetic dominance is the main trigger for lethal arrhythmias and sudden death.

METHODS AND RESULTS

PubMed database based on original articles from 1983 to 2013 and the author´s clinical experience. This review covers the current status of the methodology and the clinical uses of HRV, especially in the field of internal medicine.

CONCLUSION

Heart rate variability is making a valuable contribution to the diagnosis of cardiovascular autonomic dysfunction and CAN. It can be assessed from short-term and long-term ECG recordings. It is one of the few methods that allow outpatient CAN diagnosis, monitoring the progress, therapeutic effect and evaluation of patient prognosis. It is used as an independent prognostic factor in combination with other recognized risk factors in risk stratifying after myocardial infarction. It is a unique method of CAN diagnosis particularly in diabetology. Its diagnostic and prognostic potential in other medical fields is being intensively explored.

Heart rate variability and cardiorespiratory coupling in obstructive sleep apnea: elderly compared with young

INTRODUCTION

Aging is known to be a major contributing factor to the increased risk of obstructive sleep apnea (OSA). With aging, breathing undergoes significant changes during sleep, increasing the prevalence of apnea events, which affects heart rate variability (HRV) and cardiorespiratory coupling (CRC).

OBJECTIVES

To compare HRV and CRC during wakefulness and sleep between young and elderly patients with and without OSA; and to determine whether the presence of OSA in young and elderly patients has a different impact on HRV and CRC during sleep.

METHODS

One hundred subjects, 50 young (mean age, 27 ± 9; 20 normal and 30 OSA) and 50 elderly (mean age, 65 ± 7; 20 normal and 30 OSA), underwent polysomnography. Spectral, cross-spectrum, and HRV parameters were analyzed during wakefulness and sleep.

RESULTS

The spectral analysis indicated that age affected HRV, with higher values of low frequency (P < 0.05) in elderly subjects during wakefulness and an interaction between the presence of OSA and age. OSA influenced HRV during sleep with lower LF/HF ratios during stage 2 (S2) and rapid eye movement (REM) sleep (P <0.05), with an interaction between the presence of OSA and age in REM sleep. Elderly patients had significantly lower percent tachogram power coherent with respiration (%TPCR) during wakefulness (P < 0.05), and OSA led to lower %TPCR during S2.

CONCLUSIONS

Age and OSA have an unfavorable impact on HRV, with reduced autonomic modulation during wakefulness, S2, and REM sleep. Age affects CRC during wakefulness and the presence of OSA affects CRC during sleep.

Nocturnal parasympathetic modulation of heart rate in obesity-hypoventilation patients

Heart rate variation (HRV) reflects the activity of the autonomic nervous system. The aim of the study was to analyze HRV in obstructive sleep apnea (OSA) and obesity hypoventilation (OH) patients to answer the question of whether chronic alveolar hypoventilation influences autonomic heart rate regulation. In 41 patients, diagnosed with either 'pure' OSA (n=23, apnea/hypopnea index--AHI: 43.8±18.0 PaCO2≤45 mmHg) or OH syndrome (n=18, AHI 58.7±38.0 PaCO2>46 mmHg), the HRV was analyzed, based on an 8 h ECG recording during sleep. In the OH patients, compared with the OSA patients, there was a globally decreased HRV, with a corresponding decrease in high frequency power in the spectral analysis of HRV and increased low frequency/high frequency ratio (p<0.05), indicating a reduced parasympathetic and increased sympathetic heart rate modulation. We conclude that hypoxemia and hypercapnia of the sleep disordered breathing have an impact on the autonomic heart rate regulation. HRV indices have a potential to become prognostic factors for the development of cardiovascular complications in patients with sleep disordered breathing.

Gender-specific impacts of apnea, age, and BMI on parasympathetic nerve dysfunction during sleep in patients with obstructive sleep apnea

BACKGROUND

The gender-specific influences of various confounding factors, including apnea, age, BMI, and cigarette consumption, on the function of the parasympathetic nerve system (PNS) during sleep in OSA patients has never been investigated.

METHODS

One hundred ninety-seven males and 63 females with OSA were subjected to full PSG examinations including assessment of R-R intervals (RRIs) during an overnight ECG. The PNS-derived modulatory effect on the RRIs and the variability of this effect were quantified during REM and NREM using instantaneous time-frequency analysis with complex demodulation. The spectral domain with the maximum instantaneous amplitude in the high-frequency band between 0.15 and 0.4 Hz was defined as the main HF peak and used as a surrogate marker of PNS discharge. Based on density-spectrum-array maps of the main HF peaks (HF-DSA map), shifts in the central frequency of the main HF peak over time were continuously observed. When the main HF peaks on the HF-DSA maps maintained the same central frequency for more than 20 sec or 5 min, the PNS functions were considered to be "stable" or "very stable", respectively.

RESULTS

Apneas enhanced PNS-derived cardiac-modulation during REM in males, but more importantly, they made PNS-function unstable during both REM and NREM in males and during NREM in females. Aging blunted the PNS-derived cardiac-modulation during both REM and NREM regardless of gender, but aging had no impact on the stability of PNS-function. BMI blunted PNS-eliciting cardiac-modulation during REM in males and during NREM in both males and females. BMI made the PNS unstable during REM in females. Neither height nor cigarette consumption influenced any PNS-related parameter.

CONCLUSIONS

The PNS-derived cardiac-modulation was generally inhibited by aging and obesity, in which the effect of obesity was gender-specific. The PNS instability at nighttime was mainly induced by apneas but by obesity particularly during REM in females.