The sleep apnoea/hypopnoea syndrome depresses waking vagal tone independent of sympathetic activation

Potential Therapeutic Targets in Obesity, Sleep Apnea, Diabetes, and Fatty Liver Disease

Obesity and metabolic syndrome affect the majority of the US population. Patients with obesity are at increased risk of developing type 2 diabetes (T2DM), obstructive sleep apnea (OSA), and metabolic dysfunction-associated steatotic liver disease (MASLD), each of which carry the risk of further complications if left untreated and lead to adverse outcomes. The rising prevalence of obesity and its comorbidities has led to increased mortality, decreased quality of life, and rising healthcare expenditures. This phenomenon has resulted in the intensive investigation of exciting therapies for obesity over the past decade, including more treatments that are still in the pipeline. In our present report, we aim to solidify the relationships among obesity, T2DM, OSA, and MASLD through a comprehensive review of current research. We also provide an overview of the surgical and pharmacologic treatment classes that target these relationships, namely bariatric surgery, the glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), and glucagon receptor agonists.

Pulse Wave Amplitude Drops Index: A Biomarker of Cardiovascular Risk in Obstructive Sleep Apnea

Rationale: It is currently unclear which patients with obstructive sleep apnea (OSA) are at increased cardiovascular risk. Objective: To investigate the value of pulse wave amplitude drops (PWADs), reflecting sympathetic activations and vasoreactivity, as a biomarker of cardiovascular risk in OSA. Methods: PWADs were derived from pulse oximetry-based photoplethysmography signals in three prospective cohorts: HypnoLaus (N = 1,941), the Pays-de-la-Loire Sleep Cohort (PLSC; N = 6,367), and "Impact of Sleep Apnea syndrome in the evolution of Acute Coronary syndrome. Effect of intervention with CPAP" (ISAACC) (N = 692). The PWAD index was the number of PWADs (>30%) per hour during sleep. All participants were divided into subgroups according to the presence or absence of OSA (defined as ⩾15 or more events per hour or <15/h, respectively, on the apnea-hypopnea index) and the median PWAD index. Primary outcome was the incidence of composite cardiovascular events. Measurements and Main Results: Using Cox models adjusted for cardiovascular risk factors (hazard ratio; HR [95% confidence interval]), patients with a low PWAD index and OSA had a higher incidence of cardiovascular events compared with the high-PWAD and OSA group and those without OSA in the HypnoLaus cohort (HR, 2.16 [1.07-4.34], P = 0.031; and 2.35 [1.12-4.93], P = 0.024) and in the PLSC (1.36 [1.13-1.63], P = 0.001; and 1.44 [1.06-1.94], P = 0.019), respectively. In the ISAACC cohort, the low-PWAD and OSA untreated group had a higher cardiovascular event recurrence rate than that of the no-OSA group (2.03 [1.08-3.81], P = 0.028). In the PLSC and HypnoLaus cohorts, every increase of 10 events per hour in the continuous PWAD index was negatively associated with incident cardiovascular events exclusively in patients with OSA (HR, 0.85 [0.73-0.99], P = 0.031; and HR, 0.91 [0.86-0.96], P < 0.001, respectively). This association was not significant in the no-OSA group and the ISAACC cohort. Conclusions: In patients with OSA, a low PWAD index reflecting poor autonomic and vascular reactivity was independently associated with a higher cardiovascular risk.

The effect of transcutaneous electrical stimulation of the submental area on the cardiorespiratory response in normal and awake subjects

Background: Electrical stimulation has recently been introduced to treat patients with Obstructive sleep apnoea There are, however, few data on the effects of transcutaneous submental electrical stimulation (TES) on the cardiovascular system. We studied the effect of TES on cardiorespiratory variables in healthy volunteers during head-down-tilt (HDT) induced baroreceptor loading.

Method: Cardiorespiratory parameters (blood pressure, heart rate, respiratory rate, tidal volume, airflow/minute ventilation, oxygen saturation, and end-tidal CO2/O2 concentration) were recorded seated, supine, and during head-down-tilt (50) under normoxic, hypercapnic (FiCO2 5%) and poikilocapnic hypoxic (FiO2 12%) conditions. Blood pressure (BP) was measured non-invasively and continuously (Finapres). Gas conditions were applied in random order. All participants were studied twice on different days, once without and once with TES.

Results: We studied 13 healthy subjects (age 29 (12) years, six female, body mass index (BMI) 23.23 (1.6) kg·m−2). A three-way ANOVA indicated that BP decreased significantly with TES (systolic: p = 4.93E-06, diastolic: p = 3.48E-09, mean: p = 3.88E-08). Change in gas condition (systolic: p = 0.0402, diastolic: p = 0.0033, mean: p = 0.0034) and different postures (systolic: 8.49E-08, diastolic: p = 6.91E-04, mean: p = 5.47E-05) similarly impacted on BP control. When tested for interaction, there were no significant associations between the three different factors electrical stimulation, gas condition, or posture, except for an effect on minute ventilation (gas condition/posture p = 0.0369).

Conclusion: Transcutaneous electrical stimulation has a substantial impact on the blood pressure. Similarly, postural changes and variations in inspired gas impact on blood pressure control. Finally, there was an interaction between posture and inspired gases that affects minute ventilation. These observations have implications on our understanding of integrated cardiorespiratory control, and may prove beneficial for patients with SDB who are assessed for treatment with electrical stimulation.

Heart rate variability changes in patients with obstructive sleep apnea: A systematic review and meta-analysis

Obstructive sleep apnea is a common sleep breathing disorder related to autonomic nervous function disturbances. Heart rate variability is an important non-invasive indicator of autonomic nervous system function. The PubMed, Embase, Medline and Web of Science databases were systematically searched for English literature comparing patients with obstructive sleep apnea with controls up to May 2021. Heart rate variability outcomes, including integrated indices (parasympathetic function and total variability), time domain indices (the standard deviation of NN intervals and the root mean square of the successive differences between normal heartbeats) and frequency domain indices (high-frequency, low-frequency, very-low-frequency and the ratio of low-frequency to high-frequency) were derived from the studies. Twenty-two studies that included 2565 patients with obstructive sleep apnea and 1089 healthy controls were included. Compared with controls, patients with obstructive sleep apnea exhibited significantly reduced parasympathetic function. For the obstructive sleep apnea severity subgroup meta-analysis, patients with severe obstructive sleep apnea had significantly lower parasympathetic function, high-frequency, root mean square of the successive differences between normal heartbeats and standard deviation of NN intervals, and higher low-frequency and ratios of low-frequency to high-frequency. However, only the ratio of low-frequency to high-frequency was significantly higher in patients with moderate obstructive sleep apnea than in controls. Finally, for the collection time analysis, patients with obstructive sleep apnea had significantly higher low-frequency and ratio of low-frequency to high-frequency at night, significantly lower parasympathetic function, high-frequency, root mean square of the successive differences between normal heartbeats and standard deviation of NN intervals, and a higher ratio of low-frequency to high-frequency during the day than controls. Autonomic function impairment was more serious in patients with severe obstructive sleep apnea. During sleep, low-frequency can well reflect the impairment of autonomic function in obstructive sleep apnea, and the ratio of low-frequency to high-frequency may play an important role in obstructive sleep apnea diagnosis.

Thalamic altered spontaneous activity and connectivity in obstructive sleep apnea syndrome

BACKGROUND AND PURPOSE

Obstructive sleep apnea (OSA) syndrome is a sleep disorder characterized by excessive snoring, repetitive apneas, and nocturnal arousals, that leads to fragmented sleep and intermittent nocturnal hypoxemia. Morphometric and functional brain alterations in cortical and subcortical structures have been documented in these patients via magnetic resonance imaging (MRI), even if correlational data between the alterations in the brain and cognitive and clinical indexes are still not reported.

METHODS

We examined the impact of OSA on brain spontaneous activity by measuring the fractional amplitude of low-frequency fluctuations (fALFF) in resting-state functional MRI data of 20 drug-naïve patients with OSA syndrome and 20 healthy controls matched for age, gender, and body mass index.

RESULTS

Patients showed a pattern of significantly abnormal subcortical functional activity as compared to controls, with increased activity selectively involving the thalami, specifically their intrinsic nuclei connected to somatosensory and motor-premotor cortical regions. Using these nuclei as seed regions, the subsequent functional connectivity analysis highlighted an increase in patients' thalamocortical connectivity at rest. Additionally, the correlation between fALFF and polysomnographic data revealed a possible link between OSA severity and fALFF of regions belonging to the central autonomic network.

CONCLUSIONS

Our results suggest a hyperactivation in thalamic diurnal activity in patients with OSA syndrome, which we interpret as a possible consequence of increased thalamocortical circuitry activation during nighttime due to repeated arousals.

Alcohol Abuse and Insomnia Disorder: Focus on a Group of Night and Day Workers

The sleep-wake cycle plays a fundamental role in maintaining the physiological balance of our body. Its alteration favours the genesis of several organic alterations and diseases including sleep disorders and the consumption of several substances of abuse. It has been reported that the work activity, especially that carried out during the night, is able to influence the sleep-wake cycle, promoting the development of insomnia, which, in turn, would subject the worker to a stressful condition such as to encourage adverse behaviour such as the use/abuse of psychotropic substances. Based on the above premises, the aim of our research was to evaluate, in night workers: (i) the pattern of consumption of alcoholic beverages; (ii) the presence of insomnia; and (iii) the possible correlation between alcohol consumption and insomnia disorder. We used the AUDIT-C test (the abbreviated version of the Alcohol Use Disorders Identification Test) and the Insomnia Severity Index to assess alcohol consumption and insomnia disorder, respectively. All questionnaires were completed by workers of both sexes belonging to different types of work activities, exclusively day or night. The results of our research show a higher propensity of night workers to consume alcoholic beverages than those who work during daytime hours, often in binge-drinking mode. In addition, an increase in the amount of alcohol consumed was found to be related to insomnia disorder, especially in night workers. This study provides further awareness of the importance of the negative impact of alcohol consumption on sleep quality in night workers.

The Different Facets of Heart Rate Variability in Obstructive Sleep Apnea

Obstructive sleep apnea (OSA), a heterogeneous and multifactorial sleep related breathing disorder with high prevalence, is a recognized risk factor for cardiovascular morbidity and mortality. Autonomic dysfunction leads to adverse cardiovascular outcomes in diverse pathways. Heart rate is a complex physiological process involving neurovisceral networks and relative regulatory mechanisms such as thermoregulation, renin-angiotensin-aldosterone mechanisms, and metabolic mechanisms. Heart rate variability (HRV) is considered as a reliable and non-invasive measure of autonomic modulation response and adaptation to endogenous and exogenous stimuli. HRV measures may add a new dimension to help understand the interplay between cardiac and nervous system involvement in OSA. The aim of this review is to introduce the various applications of HRV in different aspects of OSA to examine the impaired neuro-cardiac modulation. More specifically, the topics covered include: HRV time windows, sleep staging, arousal, sleepiness, hypoxia, mental illness, and mortality and morbidity. All of these aspects show pathways in the clinical implementation of HRV to screen, diagnose, classify, and predict patients as a reasonable and more convenient alternative to current measures.

Heart rate variability during wakefulness as a marker of obstructive sleep apnea severity

STUDY OBJECTIVES

Patients with obstructive sleep apnea (OSA) exhibit heterogeneous heart rate variability (HRV) during wakefulness and sleep. We investigated the influence of OSA severity on HRV parameters during wakefulness in a large international clinical sample.

METHODS

1247 subjects (426 without OSA and 821 patients with OSA) were enrolled from the Sleep Apnea Global Interdisciplinary Consortium. HRV parameters were calculated during a 5-minute wakefulness period with spontaneous breathing prior to the sleep study, using time-domain, frequency-domain and nonlinear methods. Differences in HRV were evaluated among groups using analysis of covariance, controlling for relevant covariates.

RESULTS

Patients with OSA showed significantly lower time-domain variations and less complexity of heartbeats compared to individuals without OSA. Those with severe OSA had remarkably reduced HRV compared to all other groups. Compared to non-OSA patients, those with severe OSA had lower HRV based on SDNN (adjusted mean: 37.4 vs. 46.2 ms; p < 0.0001), RMSSD (21.5 vs. 27.9 ms; p < 0.0001), ShanEn (1.83 vs. 2.01; p < 0.0001), and Forbword (36.7 vs. 33.0; p = 0.0001). While no differences were found in frequency-domain measures overall, among obese patients there was a shift to sympathetic dominance in severe OSA, with a higher LF/HF ratio compared to obese non-OSA patients (4.2 vs. 2.7; p = 0.009).

CONCLUSIONS

Time-domain and nonlinear HRV measures during wakefulness are associated with OSA severity, with severe patients having remarkably reduced and less complex HRV. Frequency-domain measures show a shift to sympathetic dominance only in obese OSA patients. Thus, HRV during wakefulness could provide additional information about cardiovascular physiology in OSA patients.

CLINICAL TRIAL INFORMATION

A Prospective Observational Cohort to Study the Genetics of Obstructive Sleep Apnea and Associated Co-Morbidities (German Clinical Trials Register - DKRS, DRKS00003966) https://www.drks.de/drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00003966.

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.

Obstructive sleep apnea is associated with increased QT corrected interval dispersion: the effects of continuous positive airway pressure

Introduction

Severe obstructive sleep apnea is associated with increased QT corrected interval dispersion and continuous positive airway pressure is thought to improve this arrhythmogenic marker.

Objective

The aim of the study was to determine the decrease of ratio of cardiovascular risk in patients with obstructive sleep apnea.

Methods

The study included 65 patients with severe obstructive sleep apnea who had an apnea-hypopnea index score of >30. Each patient underwent 12-channel electrocardiogram monitoring and polysomnography. Patients with an apnea-hypopnea index score of <5 were used as the control group. The control group also underwent electrocardiogram monitoring and polysomnography testing. The QT corrected interval dispersion levels of both groups were calculated. Three months after continuous positive airway pressure treatment, electrocardiogram recordings were obtained from the 65 patients with severe obstructive sleep apnea again, and their QT corrected interval dispersion values were calculated.

Results

There were 44 male and 21 female patients with severe obstructive sleep apnea syndrome. The age, gender, body mass index, initial saturation, minimum saturation, average saturation, and desaturation index were determined in both groups. The QT corrected intervals of the obstructive sleep apnea patients (62.48 ± 16.29 ms) were significantly higher (p = 0.001) than those of the control group (29.72 ± 6.30 ms). There were statistically significant differences between the QT corrected values before and after the continuous positive airway pressure treatment, with pretreatment QT corrected intervals of 62.48 ± 16.29 ms and 3-month post-treatment values of 41.42 ± 16.96 ms (p = 0.001). There was a positive and significant correlation between QT corrected interval dispersion periods and the apnea-hypopnea index and hypopnea index in obstructive sleep apnea patients (p = 0.001; r = 0.71; p = 0.001; r = 0.679, respectively).

Conclusion

Continuous positive airway pressure treatment reduced the QT corrected interval dispersion in patients with severe obstructive sleep apnea. In addition, shortening the QT corrected interval dispersion periods in patients with severe obstructive sleep apnea may reduce their risk of arrhythmias and cardiovascular disease.

Heart Rate Variability Responses of Individuals With and Without Saline-Induced Obstructive Sleep Apnea

STUDY OBJECTIVES

Postoperative development of obstructive sleep apnea (OSA) has been attributed to the fluid overloaded state of patients during the postoperative period. In this context, alterations in cardiac autonomic regulation caused by OSA may explain the increased postoperative risk for adverse cardiovascular events. This study tests the hypothesis that individuals with fluid overload-induced OSA will experience autonomic dysregulation, compared to those without fluid overload-induced OSA.

METHODS

Twenty-one normotensive, nonobese (mean body mass index 24.5 kg/m²) males (mean age 37 years) underwent a sleep study. Participants were randomly assigned to infusion with saline during sleep either at the minimum rate (control) or as a bolus of 22 mL/kg body weight (intervention). Participants were blinded to the intervention and crossed over to the other study arm after 1 week. Measures of heart rate variability were calculated from electrocardiography recordings presaline and postsaline infusion in the intervention arm. Heart rate variability measures computed were: standard deviation of the RR interval; root mean square of successive differences; low-frequency, high-frequency, and total power; and the ratio of low-frequency to high-frequency power.

RESULTS

Although presaline infusion values were similar, postsaline infusion values of the standard deviation of the RR interval and high-frequency power were lower in the group whose apnea-hypopnea index increased in response to saline infusion, compared to the group whose apnea-hypopnea index did not increase in response to saline infusion (P < .05 for both).

CONCLUSIONS

Fluid overload-induced OSA is accompanied by a reduction in heart rate variability, consistent with vagal withdrawal. Future work should explore autonomic dysregulation in the postoperative period and its association with adverse events.

Apnea-hypopnea index prediction through an assessment of autonomic influence on heart rate in wakefulness

With the high prevalence of obstructive sleep apnea, the issue of developing a practical tool for obstructive sleep apnea screening has been raised. Conventional obstructive sleep apnea screening tools are limited in their ability to help clinicians make rational decisions due to their inability to predict the apnea-hypopnea index. Our study aimed to develop a new prediction model that can provide a reliable apnea-hypopnea index value during wakefulness. We hypothesized that patients with more severe obstructive sleep apnea would exhibit more attenuated waking vagal tone, which may result in lower effectiveness in decreasing heart rate as a response to deep inspiration breath-holding. Prior to conducting nocturnal in-laboratory polysomnography, 30 non-obstructive sleep apnea (apnea-hypopnea index<5events/h) subjects and 246 patients with obstructive sleep apnea participated in a 75-second experiment that consisted of a 60-second baseline measurement and consecutive 15-second deep inspiration breath-hold sessions. Two apnea-hypopnea index predictors were devised by considering the vagal activities reflected in the electrocardiographic recordings acquired during the experiment. Using the predictors obtained from 184 individuals, regression analyses and k-fold cross-validation tests were performed to develop an apnea-hypopnea index prediction model. For the remaining 92 individuals, the developed model provided an absolute error (mean±SD) of 3.53±2.67events/h and a Pearson's correlation coefficient of 0.99 (P<0.01) between the apnea-hypopnea index predictive values and the reference values reported by polysomnography. Our study is the first to achieve reliable and time-efficient prediction of the apnea-hypopnea index during wakefulness.

Sleep disordered breathing in pregnancy: Food for thought

The last few years have witnessed a number of publications linking sleep disordered breathing to adverse pregnancy and neonatal outcomes in various populations. Associations with preeclampsia, gestational diabetes and growth restriction have been consistent across many studies. Though the manuscripts reviewed here consist mostly of preliminary data and need further confirmation, the studies have highlighted new directions in the assessment of the impact of sleep disordered breathing and pregnancy, and paved the way for new fields of research in this area.

Utility of overnight pulse oximeter as a screening tool for sleep apnea to assess the 8-year risk of cardiovascular disease: Data from a large-scale bus driver cohort study

BACKGROUND

Professional drivers' work under conditions predisposes them for development of sleep-disordered breathing (SDB) and cardiovascular disease (CVD). However, the effect of SDB on CVD risk among professional drivers has never been investigated. A cohort study was used to evaluate the effectiveness of overnight pulse oximeter as a sleep apnea screening tool to assess the 8-year risk of CVD events.

METHODS

The Taiwan Bus Driver Cohort Study (TBDCS) recruited 1014 professional drivers in Taiwan since 2005. The subjects completed questionnaire interview and overnight pulse oximeter survey. This cohort was linked to the National Health Insurance Research Dataset (NHIRD). Researchers found 192 CVD cases from 2005 to 2012. Cox proportional hazards model was performed to estimate the hazard ratio for CVD. The statistical analysis was performed using SAS software in 2015.

RESULTS

ODI4 and ODI3 levels increased the 8-year CVD risk, even adjusting for CVD risk factors (HR: 1.36, 95% CI: 1.05 to 1.78; p=0.022, and HR: 1.40, 95% CI: 1.03 to 1.90; p=0.033). ODI4 and ODI3 thresholds of 6.5 and 10events/h revealed differences of CVD risks (HR: 1.72, 95% CI: 1.00 to 2.95; p=0.048, and HR: 1.76, 95% CI: 1.03 to 3.03; p=0.041). Moreover, the ODI levels had an increased risk for hypertensive disease (not including essential hypertension).

CONCLUSIONS

This study concludes that ODI for a sign of SDB is an independent predictor of elevated risk of CVD. Further research should be conducted regarding measures to prevent against SDB in order to reduce CVD risk in professional drivers.

Heart rate variability during daytime naps in healthy adults: Autonomic profile and short-term reliability

In healthy individuals, a reduction in cardiovascular output and a shift to parasympathetic/vagal dominant activity is observed across nocturnal sleep. This cardiac autonomic profile, often measured by heart rate variability (HRV), has been associated with significant benefits for the cardiovascular system. However, little is known about the autonomic profile during daytime sleep. Here, we investigated the autonomic profile and short-term reliability of HRV during daytime naps in 66 healthy young adults. Participants took an 80-120 min polysomnographically recorded nap at 1:30 pm. Beat-by-beat RR interval values (RR), high (HF) and low frequency (LF) power, total power (TP), HF normalized units (HF(nu)), and the LF/HF ratio were obtained for 5 min during presleep wakefulness and during nap sleep stages (N2, N3, REM). A subsample of 37 participants took two additional naps with 2 weeks between recordings. We observed lengthening of the RR, higher HF and HF(nu), and lower LF/HF during NREM, compared with REM and wake, and a marked reduction of LF and TP during N3. Intraclass correlation coefficients highlighted a short-term stability of RR and HF ranging across sleep stages between 0.52-0.76 and 0.52-0.80, respectively. Our results suggest that daytime napping in healthy young adults is associated with dynamic changes in the autonomic profile, similar to those seen during nocturnal sleep. Moreover, a reliable intraindividual measure of autonomic cardiac activity can be obtained by just a single daytime nap depending on specific parameters and recording purposes. Nap methodology may be a new and promising tool to explore sleep-dependent, autonomic fluctuations in healthy and at-risk populations.

Time-varying correlations between delta EEG power and heart rate variability in midlife women: the SWAN Sleep Study

No studies have evaluated the dynamic, time-varying relationship between delta electroencephalographic (EEG) sleep and high frequency heart rate variability (HF-HRV) in women. Delta EEG and HF-HRV were measured during sleep in 197 midlife women (M(age)  = 52.1, SD = 2.2). Delta EEG-HF-HRV correlations in nonrapid eye movement (NREM) sleep were modeled as whole-night averages and as continuous functions of time. The whole-night delta EEG-HF-HRV correlation was positive. The strongest correlations were observed during the first NREM sleep period preceding and following peak delta power. Time-varying correlations between delta EEG-HF-HRV were stronger in participants with sleep-disordered breathing and self-reported insomnia compared to healthy controls. The dynamic interplay between sleep and autonomic activity can be modeled across the night to examine within- and between-participant differences including individuals with and without sleep disorders.

Nocturnal snoring decreases daytime baroreceptor sensitivity

BACKGROUND

In patients with obstructive sleep apnea heart rate variability and baroreceptor sensitivity during night and daytime are impaired. Snoring without obstructive sleep apnea may already influence heart rate variability and baroreceptor sensitivity during daytime.

METHODS

Cardiovascular daytime testing was performed in 11 snorers and age, BMI, and gender matched controls. Sleep apnea and snoring were quantified by sleep recordings. Paced breathing was performed during daytime with ECG, non-invasive blood pressure, and respiration recorded. Heart rate variability and blood pressure variability were analyzed in the time and frequency domain. Baroreceptor sensitivity (alpha gain) was calculated.

RESULTS

In snorers a significant increase in high frequency systolic blood pressure variability (SBPV-HF) compared to control group (0.37 mm Hg(2) vs. 0.11 mm Hg(2) for 12 breaths and 0.35 mm Hg(2) vs. 0.10 mm Hg(2) for 15 breaths) was demonstrated. Furthermore a lower baroreceptor sensitivity was found in snorers compared to controls (9.2 ms/mm Hg vs. 16.2 ms/mm Hg for 12 breaths and 8.5 ms/mm Hg vs. 17.4 ms/mm Hg for 15 breaths per minute) using the paced breathing protocol. Mean heart rate was elevated in snorers as well.

CONCLUSIONS

Snorers may have a reduced parasympathetic tone during daytime rather than an increased sympathetic tone.

A pilot study investigating the effects of continuous positive airway pressure treatment and weight-loss surgery on autonomic activity in obese obstructive sleep apnea patients

BACKGROUND

We have previously demonstrated that severity of obstructive sleep apnea (OSA) as measured by the apnea-hypopnea index (AHI) is a significant independent predictor of readily-computed time-domain metrics of short-term heart rate variability (HRV).

METHODS

We aimed to assess time-domain HRV measured over 5-min while awake in a trial of obese subjects undergoing one of two OSA therapies: weight-loss surgery (n=12, 2 males, median and interquartile range (IQR) for BMI 43.7 [42.0, 51.4] kg/m2, and AHI 18.1 [16.3, 67.5] events/h) or continuous positive airway pressure (CPAP) (n=15, 11 males, median BMI 33.8 [31.3, 37.9] kg/m2, and AHI 36.5 [24.7, 77.3] events/h). Polysomnography was followed by electrocardiography during wakefulness; measurements were repeated at 6 and 12-18 months post-intervention.

RESULTS

Despite similar measurements at baseline, subjects who underwent surgery exhibited greater improvement in short-term HRV than those who underwent CPAP (p=0.04).

CONCLUSIONS

Our data suggest a possible divergence in autonomic function between the effects of weight loss resulting from bariatric surgery, and the amelioration of obstructive respiratory events resulting from CPAP treatment. Randomized studies are necessary before clinical recommendations can be made.

Estimation of parasympathetic nerve function during sleep in patients with obstructive sleep apnea by instantaneous time-frequency analysis

BACKGROUND AND OBJECTIVES

The pathophysiologic aspects of parasympathetic nerve (PN) function during sleep in patients with obstructive sleep apnea (OSA) studied by classical power spectrum analysis on heart rate variability (HRV) are highly controversial. The controversy is attributed to methodologic concerns, such as poor time resolution involved in power spectrum analysis. We aimed to establish the appropriate method for the investigation of PN function in OSA patients with apneas and hypopneas using instantaneous time-frequency analysis with complex demodulation (CD) and sufficient time resolution.

METHODS

A total of 30 patients with PSG-confirmed mild to severe OSA were recruited for the analysis of frequency spectra contained in R-R intervals (RRI) of overnight electrocardiograph (ECG) tracings. High-frequency (HF) domains ranging between 0.15 and 0.40 Hz were selected for analysis. Among these domains, the HF domain with the maximum instantaneous amplitude was defined as the main HF peak and was used as the surrogate marker of PN discharge. Based on density spectrum array (DSA) map for main HF peak constructed with a time scale of 1s and a frequency resolution of 0.002 Hz (HF-DSA map), the shift in central frequency (CF) of main HF peak over time was continuously monitored. When the main HF peak with the same CF lasted for more than 20 s or 5 min on HF-DSA map, the PN function was considered to be stable or very stable. The measurements were then repeated after continuous positive airway pressure (CPAP) treatment.

RESULTS

The extent of PN-evoked modulation of RRI was enhanced in nonrapid eye movement (NREM) sleep, though the stability was reduced in both NREM and rapid eye movement (REM) sleep. These peculiar behaviors of PN function were reversed by CPAP treatment.

CONCLUSION

We found that instantaneous time-frequency analysis allowed estimation of transitional changes in PN function during sleep in OSA patients.

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.

Nocturnal autonomic function in preschool children with sleep-disordered breathing

BACKGROUND

Obstructive sleep apnea (OSA) is associated with autonomic dysfunction in adults and school-aged children; however, this association has not been investigated in preschool children. We aimed to analyze heart rate variability (HRV) and catecholamine levels in preschool children with OSA.

METHODS

One hundred and forty-two snoring children aged 3-5years and 38 nonsnoring control group children underwent overnight polysomnography (PSG). Nocturnal urinary catecholamines were measured in 120 children. Children were grouped according to their obstructive apnea-hypopnea index (OAHI) (control [no snoring], OAHI⩽1event/h; primary snoring, OAHI⩽1event/h; mild OSA OAHI>1⩽5events/h; moderate to severe [MS] OSA, OAHI>5events/h). The HRV parameters for each child were averaged during rapid eye movement (REM) and non-REM (NREM) sleep.

RESULTS

During stable sleep, low-frequency (LF) HRV was similar between groups. High-frequency (HF) HRV was higher in the MS OSA group compared with the control group during all sleep stages (NREM sleep stages 1 and 2 [NREM1/2], 4234±523ms(2) vs 2604±457ms(2); NREM sleep stages 3 and 4 [NREM3/4], 4152±741ms(2) vs 3035±647ms(2); REM, 1836±255ms(2) vs 1456±292ms(2); P<.01 for all). The LF/HF ratio was lower in the MS OSA group compared with the control group (NREM1/2, 0.4±0.06 vs 0.7±0.05; NREM3/4, 0.3±0.06 vs 0.4±0.05; REM, 0.8±0.1 vs 1.3±0.1; P<.01 for all). Catecholamine levels were not different between groups.

CONCLUSIONS

In preschool children, OSA is associated with altered HRV, largely due to the HF fluctuations in heart rate (HR) which occur during respiratory events and are still evident during stable sleep. The preschool age may represent a window of opportunity for treatment of OSA before the onset of the severe autonomic dysfunction associated with OSA in adults and older children.

Autonomic markers of impaired glucose metabolism: effects of sleep-disordered breathing

BACKGROUND

The association between diabetes and abnormalities in autonomic function is well-known, but it is not clear if this association can be extended to subjects with prediabetic impaired glucose metabolism (IGM). Sleep-disordered breathing (SDB), which commonly occurs in this population, is often overlooked. We sought to determine how autonomic function, monitored in an overnight sleep study setting, may be impaired in subjects with IGM and/or SDB.

METHODS

Polysomnograms (PSGs) selected from the Cleveland Family Study database were categorized into four groups: normal, SDB (respiratory disturbance index > 5/h), IGM, and both SDB and IGM. Impaired glucose metabolism was defined as an oral glucose tolerance test (OGTT) level > 140 mg/dl. Time-domain and frequency-domain indices of heart rate variability were used to quantify autonomic impairment. Baroreflex sensitivity determined using pulse transit time (BRS(PTT)), an indirect measure of baroreflex sensitivity based on spontaneous pulse transit time fluctuations, was used as a surrogate measure of baroreflex sensitivity.

RESULTS

Based on 31 PSGs from subjects (16 males, 15 females) ages 20.8-61.2 years, both SDNN and BRS(PTT) were found to be 20-25% lower in SDB and ~40% lower in IGM and SDB + IGM as compared to subjects without either condition. In analyses of continuous measures, mean standard deviation of 5 min R-R intervals (SDNN) and BRS(PTT) were found to be negatively correlated with OGTT following adjustment for age and body mass index. Oral glucose tolerance test and age were the two most significant factors for predicting SDNN and BRS(PTT).

CONCLUSIONS

Our analyses suggest that cardiac autonomic control is impaired in IGM, regardless of whether SDB is present. The abnormal autonomic function involves degradation of baroreflex regulation.

Preschoolers' daytime respiratory sinus arrhythmia and nighttime sleep

We examined the association between preschoolers' (N=29; 20 boys; M age = 3.99 years, SD=.69) daytime parasympathetic nervous system (PNS) activity indexed by respiratory sinus arrhythmia (RSA) and their nighttime sleep. Children's baseline RSA was assessed in the laboratory. Sleep was monitored for seven consecutive nights at the child's home via actigraphy and the following sleep parameters were derived: sleep minutes, sleep activity index and sleep efficiency. Regression analyses showed that after controlling for potential confounds, higher RSA was a predictor of lower sleep activity and higher sleep efficiency. Results highlight the importance of physiological regulation for the sleep of healthy preschool children.

Heart rate recovery: a practical clinical indicator of abnormal cardiac autonomic function

The autonomic nervous system (ANS) and cardiovascular function are intricately and closely related. One of the most frequently used diagnostic and prognostic tools for evaluating cardiovascular function is the exercise stress test. Exercise is associated with increased sympathetic and decreased parasympathetic activity and the period of recovery after maximum exercise is characterized by a combination of sympathetic withdrawal and parasympathetic reactivation, which are the two main arms of the ANS. Heart rate recovery after graded exercise is one of the commonly used techniques that reflects autonomic activity and predicts cardiovascular events and mortality, not only in cardiovascular system disorders, but also in various systemic disorders. In this article, the definition, applications and protocols of heart rate recovery and its value in various diseases, in addition to exercise physiology, the ANS and their relationship, will be discussed.

Heart rate variability, sleep and sleep disorders

Heart rate (HR) is modulated by the combined effects of the sympathetic and parasympathetic nervous systems. Therefore, measurement of changes in HR over time (heart rate variability or HRV) provides information about autonomic functioning. HRV has been used to identify high risk people, understand the autonomic components of different disorders and to evaluate the effect of different interventions, etc. Since the signal required to measure HRV is already being collected on the electrocardiogram (ECG) channel of the polysomnogram (PSG), collecting data for research on HRV and sleep is straightforward, but applications have been limited. As reviewed here, HRV has been applied to understand autonomic changes during different sleep stages. It has also been applied to understand the effect of sleep-disordered breathing, periodic limb movements and insomnia both during sleep and during the daytime. HRV has been successfully used to screen people for possible referral to a Sleep Lab. It has also been used to monitor the effects of continuous positive airway pressure (CPAP). A novel HRV measure, cardiopulmonary coupling (CPC) has been proposed for sleep quality. Evidence also suggests that HRV collected during a PSG can be used in risk stratification models, at least for older adults. Caveats for accurate interpretation of HRV are also presented.

The price of obstructive sleep apnea-hypopnea: hypertension and other ill effects

This review addresses the cardiovascular, cerebrovascular, and metabolic consequences that accompany obstructive sleep apnea-hypopnea (OSAH) in conjunction with the mechanistic pathways implicated in mediating these effects. Particular emphasis is placed on the association with hypertension (HTN). Varying levels of evidence support a role of OSAH in perpetuating sustained HTN, nocturnal HTN, and difficult to control HTN as well as in contributing to the occurrences of nondipping of blood pressure (BP) and increased BP variability. In this context, the emergence of matched designs, adjusted analyses, meta-analyses as well as longitudinal and interventional studies strengthens causal inferences drawn from older observational studies, which suffered from such limitations as confounding.

Saliva production and surface tension: influences on patency of the passive upper airway

Pharyngeal patency is influenced by the surface tension (gamma) of the upper airway lining liquid (UAL), of which saliva is a major component. We investigated the influences of saliva production on gamma of the UAL, and upper airway re-opening and closing pressures. In 10 supine, male, anaesthetized, tracheostomised, mechanically ventilated New Zealand White rabbits, we measured re-opening and closing of the passive isolated upper airway at baseline and following graded (cumulative) doses of methacholine or atropine. Upper airway liquid volume index (UALVI) was assessed using a standardized suction procedure (secretion weight obtained per second) expressed as the natural logarithm (LnUALVI). The gamma of UAL samples were measured using the 'pull-off' force technique. Across all animals, baseline values were: LnUALVI -6.2 (-8.6 to -5.4) median (interquartile range), gamma of UAL 58.9 (56.6-59.9) mN m(-1), re-opening 8.6 (6.9-11.1) cmH(2)O, and closing pressures 3.2 (1.8-5.7) cmH(2)O. LnUALVI increased by approximately 0.17 per microg kg(-1) methacholine and decreased by approximately 0.14 per 100 microg kg(-1) atropine (both P < 0.03, linear mixed effects modelling). Surface tension was unchanged by methacholine but increased by approximately 0.6 mN m(-1) per 100 microg kg(-1) atropine (P < 0.004). When data were analysed across all animals, both re-opening and closing pressures increased as surface tension increased (by approximately 0.4 cmH(2)O mN(-1) and by approximately 0.7 cmH(2)O mN(-1), respectively; both P < 0.05). We conclude that saliva production influences upper airway mechanical properties partly via alterations in gamma of UAL. We speculate that in obstructive sleep apnoea, altered autonomic activity may reduce saliva production and increase surface tension of the upper airway lining liquid, thus increasing the likelihood of upper airway obstruction.

Obesity and obstructive sleep apnea-hypopnea syndrome

Obstructive sleep apnea-hypopnea syndrome involves recurring episodes of total obstruction (apnea) or partial obstruction (hypopnea) of airways during sleep. Obstructive sleep apnea-hypopnea syndrome affects mainly obese individuals and it is defined by an apnea-hypopnea index of five or more episodes per hour associated with daytime somnolence. In addition to anatomical factors and neuromuscular and genetic factors, sleep disorders are also involved in the pathogenesis of sleep apnea. Obesity affects upper airway anatomy because of fat deposition and metabolic activity of adipose tissue. Obstructive sleep apnea-hypopnea syndrome and metabolic syndrome have several characteristics such as visceral obesity, hypertension and insulin resistance. Inflammatory cytokines might be related to the pathogenesis of sleep apnea and metabolic syndrome. Sleep apnea treatment includes obesity treatment, use of equipment such as continuous positive airway pressure, drug therapy and surgical procedures in selected patients. Currently, there is no specific drug therapy available with proven efficacy for the treatment of obstructive sleep apnea-hypopnea syndrome. Body-weight reduction results in improvement of sleep apnea, and obesity treatment must be emphasized, including lifestyle changes, anti-obesity drugs and bariatric surgery.

[The physiopathology of dialysis-associated hypertension]

Hypertension in subjects on long term dialysis is frequent. Its origins are found in extracellular volume overload, which is complicated by increased peripheral arterial resistance. The latter is affected by many systems, including that of renin-angiotensin, endothelin, nitric oxide, the sympathetic nervous system, and others. The interaction between these factors may explain why the control of hypertension in dialysis patients requires ongoing attention to the many aspects of good dialysis.

Association between heart rate recovery and severity of obstructive sleep apnea syndrome

BACKGROUND

Obstructive sleep apnea syndrome (OSAS) is associated with autonomic dysfunction and metabolic abnormalities including obesity, dyslipidemia, and insulin resistance. Heart rate recovery at 1min after exercise termination (HRR-1) is a marker of vagal tone. We hypothesized that patients with more severe OSAS would have a lower HRR-1, either due to the co-existing metabolic abnormalities or OSAS.

METHODS

Sixty-three patients with untreated OSAS (49.2+/-9.8years) without glucose- or lipid-lowering or negatively chronotropic drugs underwent cardiopulmonary exercise testing including HRR-1 measurement and assessment of several metabolic parameters. Patients with severe OSAS (apnea-hypopnea index [AHI]>30h(-1); n=32) were compared to patients with mild to moderate OSAS (AHI 5-30h(-1); n=31).

RESULTS

Patients with severe OSAS were more likely to be male (25 vs. 3%; p=0.01) and to have hypertension (72 vs. 39%; p=0.01); they also had higher fasting glucose (5.4+/-0.5 vs. 5.1+/-0.4mmol/l; p=0.016) and C-peptide [905 (651-1353) vs. 749 (597-919)pmol/l; p=0.028] levels compared to patients with mild to moderate OSAS. The groups did not differ with respect to peak heart rate (p=0.2) or peak oxygen consumption (p=0.9), but HRR-1 was significantly lower in patients with severe OSAS compared to patients with mild and moderate OSAS [20 (15-25) vs. 24 (18-34)bpm; p=0.022]. Higher AHI (p=0.01) and lower peak heart rate (p=0.02), but not body mass index or insulin resistance, were independently associated with lower HRR-1.

CONCLUSIONS

The severity of OSAS expressed as higher AHI is independently associated with lower HRR-1, a measure of autonomic dysfunction.

Autonomic dysfunction in obstructive sleep apnea is associated with impaired glucose regulation

INTRODUCTION

Autonomic dysfunction has been theorized to be responsible for the increased risk of cardiovascular disease in obstructive sleep apnea (OSA). Previous studies did not control for the presence of impaired glucose regulation (IGR, comprising impaired fasting glucose (IFG), impaired glucose tolerance (IGT), and diabetes) which is also associated with abnormalities in autonomic function.

METHODS

Thirty-two patients were recruited for the study. Patients underwent autonomic testing consisting of heart rate response to deep breathing, valsalva maneuver, tilt-up, and quantitative sudomotor axon reflex testing. Polysomnography (PSG) and a 2-h oral glucose tolerance test were performed. Results were analyzed with logistic regression, with age, race, body mass index (BMI), and gender as covariates.

RESULTS

Nineteen of 24 patients with OSA had abnormal glucose (79%, p=0.04) compared to two of nine patients without OSA. The correlation between IGR, OSA and total autonomic dysfunction was similar (p=.10 for IGR, p=0.06 for OSA). However, cardiac autonomic function was more strongly associated with IGR than OSA (p=.10 vs. 0.50). Age was a significant confounder, as glucose correlated with adrenergic autonomic dysfunction significantly when age was removed from the model (p=0.006).

CONCLUSIONS

The presence of IGR may be a confounding factor in studies of autonomic function in OSA. Larger studies are needed to delineate whether OSA is directly associated with autonomic dysfunction or whether the previously described association between dysautonomia and OSA may have been due to glucose dysregulation.

Postnatal intermittent hypoxia alters baroreflex function in adult rats

Chronic perinatal intermittent hypoxia (IH) could have long-term cardiovascular effects by altering baroreflex function. To examine this hypothesis, we exposed rats (n = 6/group) for postnatal days 1-30 or prenatal embryonic days 5-21 to IH (8% ambient O2 for 90 s after 90 s of 21% of O2, 12 h/day) or to normoxia (control). Baroreflex sensitivity (BRS) and cardiac chronotropic responses were examined in anesthetized animals 3.5-5 mo later by infusing phenylephrine or sodium nitroprusside (6-12 microg/min iv, 1-2 min) during normoxia and after 18 min of acute IH (IHA). In controls after IHA, baroreflex gain was 42% (P < 0.05) less than during normoxia. BRS in the postnatal IH group during normoxia was approximately 50% less than in control rats and similar to controls after IHA. The heart rate response to phenylephrine in the IH group was also less than in controls (P < 0.05) and was not changed by IHA. BRS and heart rate responses in the prenatal IH group were similar to the normoxic control group. Vagal efferent projections to atrial ganglia neurons in rats after postnatal IH (n = 4) were examined by injecting tracer into the left nucleus ambiguous. After 35 days of postnatal IH, basket ending density was reduced by 17% (P < 0.001) and vagal axon varicose contacts by 56% (P < 0.001) compared with controls. We conclude that reduction of vagal efferent projections in cardiac ganglia could be a cause of long-term modifications in baroreflex function.

Continuous Positive Airway Pressure Treatment Improves the QT Rate Dependence Adaptation of Obstructive Sleep Apnea Patients

BACKGROUND

QT rate dependence is one of the major properties of ventricular repolarization, with its circadian and autonomic modulations. The alteration of cardiac autonomic tone occurring in obstructive sleep apnea syndrome (OSAS) patients could explain the altered rate-dependent adaptation of the myocardial repolarization. Thus, we postulated that dynamic alterations in QT interval adaptation could be ameliorated in OSAS patients under continuous positive airway pressure (CPAP) treatment. To assess ventricular repolarization features in patients with OSAS, we compared QT parameters and their dynamicities along RR intervals from 24-hour ECG.

METHODS

The study groups consisted of 38 consecutive OSAS patients and 38 healthy age-matched subjects. The syndrome was confirmed for OSAS patients according to standard polysomnographic criteria (apnea plus hypopnea index: 56.9 +/- 28.4/h). A second polysomnography synchronized with 24-hour ECG Holter and realized under efficient CPAP therapy confirmed the control of sleep-related breathing disorder.

RESULTS

QT length related to heart rate was found significantly altered in patients with OSAS compared with controls (QTend/RR slope: -0.126 +/- 0.031 vs -0.173 +/- 0.038; P < 0.01). This flattened relationship was significantly improved with the treatment of the OSAS (-0.151 +/- 0.051; P < 0.01 vs pretreatment status). There was no significant impact of CPAP therapy on ventricular ectopic activity as well as on static repolarization parameters (QT, RT, QTc, RTc) measured separately over daytime and nighttime.

CONCLUSIONS

The prognostic implications of such findings and the protective role of CPAP treatment to prevent sudden cardiac death in OSAS need to be evaluated.

Cerebral Structural Changes in Severe Obstructive Sleep Apnea

Obstructive sleep apnea is associated with abnormalities in neuropsychologic function, and defects in respiratory control may contribute to pathogenesis. Abnormalities may be reflected in structural brain changes. Twenty-seven male untreated patients with severe sleep apnea without comorbidities, and 24 age-matched control subjects, had T1-weighted brain imaging in a high-resolution magnetic resonance scanner. Twenty-three patients with sleep apnea had repeat imaging after 6 months of continuous positive airways pressure treatment. No areas of gray matter volume change were found in patients using an optimized voxel-based morphometry technique, at p < 0.05 adjusted for multiple comparisons (despite the method being sensitive to changes in gray matter fraction of 0.17 or less in all voxels). Furthermore, no differences were seen in bilateral hippocampal, temporal lobe, or whole brain volumes, assessed by manual tracing of anatomical borders. No longitudinal changes were seen in gray matter density or regional volumes after treatment, but whole brain volume decreased slightly. We have found no gray matter volume deficits nor focal structural changes in severe obstructive sleep apnea. Whole brain volume decreases without focal changes after 6 months of continuous positive airways pressure treatment.

Tongue mechanical characteristics and genioglossus muscle EMG in obstructive sleep apnoea patients

The increased genioglossus muscle (GGm) activity seen in obstructive sleep apnoea syndrome (OSAS) may lead to increased fatigability or longer recovery time of the tongue. Maximal force, endurance, and recovery times of the tongue, electromyogram (EMG) absolute value, and EMG spectral analysis of the GGm obtained during submaximal contractions were compared in eight individuals without chronic snoring and eight OSAS patients. Endurance time values were not significantly different between the two groups (P = 0.40). Time to recovery of initial maximal force was significantly greater in the OSAS group (P = 0.01). Final EMG median frequency was significantly higher (P = 0.01) and the final low-frequency EMG component smaller in the OSAS patients (P = 0.02). Patients did not have changes in endurance time or fatigability but had longer recovery times and changes in spectral analysis variations. This functional investigation may be helpful in determining the presence of OSAS and the potential contribution of the tongue to pharyngeal obstruction.

Alteration of QT rate dependence reflects cardiac autonomic imbalance in patients with obstructive sleep apnea syndrome

QT rate dependence is one of the major properties of ventricular repolarization with its circadian and autonomic modulations. The authors postulated that dynamic alterations in QT interval adaptation could help characterize patients with cardiac autonomic alterations, like those with obstructive sleep apnea syndrome (OSAS). To assess ventricular repolarization features in patients with OSAS, QT parameters and their dynamicity along RR intervals were compared from 24-hour ECG data of patients with and without this syndrome, assessing cardiac autonomic nervous system equilibrium by means of time-domain and frequency-domain analyses of heart rate variability (HRV). The study group consisted of 74 consecutive patients referred to the Sleep Laboratory for clinically suspected OSAS. The syndrome was confirmed in 30 (40.5%) patients according to standard polysomnographic criteria. QT length related to heart rate (HR) was found significantly shorter for HR < 70 beats/min in patients with OSAS(-1.32 +/- 0.35)compared with patients without OSAS(-1.99 +/- 0.40; P < 0.01). This flattened relationship was correlated with the severity of the sleep related disorder. Using multiple linear regression analysis, the apnea/hypopnea index and nocturnal normalized high frequencies (HFnu) were the most significant predictors of the QT/RR slope(R = 0.61; P < 0.0001). OSAS is significantly associated with a flattened relationship between QT duration and RR interval at low HRs. The alteration of cardiac parasympathetic tone occurring in severe OSAS patients may explain this altered rate dependent adaptation of myocardial repolarization.

Obstructive sleep apnoea

Obstructive sleep apnoea is a disease of increasing importance because of its neurocognitive and cardiovascular sequelae. Abnormalities in the anatomy of the pharynx, the physiology of the upper airway muscle dilator, and the stability of ventilatory control are important causes of repetitive pharyngeal collapse during sleep. Obstructive sleep apnoea can be diagnosed on the basis of characteristic history (snoring, daytime sleepiness) and physical examination (increased neck circumference), but overnight polysomnography is needed to confirm presence of the disorder. Repetitive pharyngeal collapse causes recurrent arousals from sleep, leading to sleepiness and increased risk of motor vehicle and occupational accidents. The surges in hypoxaemia, hypercapnia, and catecholamine associated with this disorder have now been implicated in development of hypertension, but the association between obstructive sleep apnoea and myocardial infarction, stroke, and congestive heart failure is not proven. Continuous positive airway pressure, the treatment of choice for obstructive sleep apnoea, reduces sleepiness and improves hypertension.