Higher Respiratory Disturbance Index Research Articles

Undiagnosed obstructive sleep apnea syndrome as a treatable cause of new-onset sleepiness in some post-COVID patients.

Infection with COVID-19 can lead to persistent sequelae, such as fatigue, daytime sleepiness or disturbed sleep, that can remain for more than 12 weeks and that are summarized as post-COVID syndrome. The causes remain unclear. The present study investigated the presence of sleep disorders in patients with post-COVID syndrome using polysomnography. Thirty-four patients with post-COVID syndrome and new-onset fatigue and sleepiness after a SARS-CoV2 infection underwent polysomnography in accordance with American Association of Sleep Medicine (AASM) standards as part of their clinical workup. Analysis was performed visually based on AASM criteria (scoring manual version 2.6, 2020). Polysomnography revealed a sleep efficiency of <80% in 50% of patients and a mean respiratory disturbance index (RDI) of 9.9 ± 15.4/h. Excluding central apneas, 12 patients (35%) had an RDI of ≥5/h, pointing to obstructive sleep apnea syndrome (OSAS; AASM 2014). Patients with a high RDI were significantly older (p = 0.01) and showed a trend towards a higher body mass index (p = 0.08) than patients with a normal RDI but had no other risk factors for OSAS. Six patients agreed to long-term treatment of their OSAS and all reported discontinuation of daytime symptoms. Post-COVID symptoms such as daytime sleepiness, fatigue and memory and concentration problems may in part be a result of reduced sleep efficiency and sleep apnea in a relevant percentage of patients. This possibly treatable cause of the symptoms should be kept in mind in patients presenting with post-COVID syndrome.

0558 Sleep Bruxism and Sleep Breathing Disorder

Abstract Introduction Sleep bruxism (SB) is reported by 8-9% of the adult population and is mainly associated with rhythmic masticatory muscle activity (RMMA) characterized by repetitive jaw muscle contractions (3 bursts or more at a frequency of 1 Hz). The purpose of this study was to evaluate the relationship between the nature of sleep bruxism and the sleep breathing disoredr. Methods We prospectively studied 32 patients who were referred to the clinical sleep apnea laboratory for study. They underwent standard nocturnal polysomnographic examination; in addition, masticatory activity was measured with a masseter electromyogram. Patients slept in the supine and lateral decubitus positions. Results Nocturnal clenching was higher in patients with higher respiratory disturbance index. 28 among 32 patients were included in the criteria of obstructive sleep apnea; average respiratory disturbance index (RDI) was 12.7 280 clenches demonstrated in all patients. Conclusion We conclude that there is an association between sleep related breathing disorder and bruxisms that sleep position affects the incidence of both sleep disordered breathing and bruxisms, and that analysis of apneas and hypopneas and clenching events in both supine and lateral decubitus sleeping positions may be helpful. Support (if any)

Respiratory disturbance index as a predictor of atrial fibrillation

Abstract Background Obstructive sleep apnea (OSA) is a risk factor for development of atrial fibrillation (AF). Recent pacemakers have specific algorithms for detecting of OSA based on impedance measurement. Purpose The aim was to determine the burden of AF in patients with high respiratory disturbance index (RDI). It was also intended to determine if the onset of continuous positive airway pressure (CPAP) reduced the AF burden. Methods Retrospective observational study carried out through the analysis of the patient records. It included patients with pacemakers evaluated in an outpatient clinic during the first 8 months of 2018. All had the RDI algorithm. AF burden was assessed according to automatic mode switch (AMS) duration. The percentage of nights with an RDI&amp;gt;20/h was analysed to assess the risk of OSA. Results 108 patients were included (mean age=70.3±9.0 years; 56.5% men). The most prevalent indication for cardiac pacing was atrioventricular node dysfunction (59.3%). The average percentage of nights with an RDI&amp;gt;20/h was 44.2%. The average follow-up (FU) period was 4.1 years. Of all cardiovascular risk factors, diabetes mellitus was the only one associated with a higher incidence of AF at FU (p=0.044). Considering just the patients with an RDI &amp;gt;20/h in more than 20% of nights (RDI20%), male gender was associated with higher rate of major adverse cardiovascular events [(acute myocardial infarction, stroke, acute heart failure and death) (p=0.019)]. Considering patients with AF prior to pacemaker implantation (n=34), 76% of patients had an RDI &amp;gt;20/h in more than 20% of nights (mean of 58.1%). 23 of these patients had long standing persistent AF at the end of FU (vs 17 at the beginnig of FU). Considering patients who developed AF after pacemaker implantation (n=24), 58% of patients had an RDI&amp;gt;20/h in more than 20% of nights (mean of 45.3%). Most patients had paroxismal AF (83%). Patients with prior paroxysmal AF or those who developed AF during FU (n=37) had a higher burden of AF at the end of FU when they had RDI &amp;gt;20/h in more than 50% of nights (mean burden of 24.66% vs 14.69%, p=0.005). There was no statistically significant correlation between the percentage of nights with RDI &amp;gt;20/h and the Apnea Hypopnea Index (AHI) value. Patients who underwent polysomnography (n=30) had a mean AHI of 16/h (which corresponds to moderately severe OSA). 63% of patients who were referred from the pacemaker consultation to pneumology and performed polysomnography started CPAP. CPAP use was not associated with a statistically significant reduction in any endpoints or AF burden. Conclusion A high RDI was associated with onset of de novo AF and higher AF burden in patients with paroxysmal AF. Thus, there is a rationale for early diagnosis and treatment of OSAS to prevent and reduce AF progression. In this study, CPAP was not shown to significantly reduce this endpoint, probably due to reduced polysomnography and CPAP treatment. Funding Acknowledgement Type of funding sources: None.

Sleep apnea in postmenopausal women is associated with joint pain severity and fatigability: a cross-sectional study.

This study aimed to investigate the relationships between sleep apnea parameters and various symptoms in postmenopausal women who had treatment-resistant sleep disorders. The respiratory disturbance index (RDI), the number of times apnea-hypopnea occurred in an hour, and transcutaneous oxygen saturation (SpO2) were monitored during one night of sleep using a portable monitoring device in 51 postmenopausal women who did not have an improved subjective sleep quality with the use of hypnotics. Physical and psychological health statuses and subjective sleep disturbance were evaluated using validated questionnaires, including the Epworth Sleepiness Scale, the Cornell Medical Index, and the Questionnaire for Assessment of Climacteric Syndrome in Japanese Women. The associations between RDI, nadir SpO2 and various symptoms, as well as cardiovascular parameters, such as blood pressure, serum lipid profile, and glucose tolerance, were analyzed separately. Among the 51 study participants, seven (13.7%) were diagnosed with obstructive sleep apnea. After adjustment for age, body mass index, and the background factors related to RDI and nadir SpO2, the association remained significant between a higher RDI and joint pain (Questionnaire for Assessment of Climacteric Syndrome in Japanese Women) (standardized partial regression coefficient [β] = 0.423, P = 0.016), and between lower nadir SpO2 and fatigability (Cornell Medical Index) (β = -0.472, P = 0.007). Detailed examination of sleep-disordered breathing is warranted in women with severe joint pain and fatigability.

The variability and burden of severe sleep apnea and the relationship with atrial fibrillation occurrence: analysis of pacemaker-detected sleep apnea

Study objectivesThis was a pilot study to evaluate the long-term variability and burden of respiratory disturbance index (RDI) detected by pacemaker and to investigate the relationship between RDI and atrial fibrillation (AF) event in patients with pacemakers.MethodsThis was a prospective study enrolling patients implanted with a pacemaker that could calculate the night-to-night RDI. The mean follow-up was 348 ± 34 days. The RDI variability was defined as the standard deviation of RDI (RDI-SD). RDI burden was referred to as the percentage of nights with RDI ≥ 26. The patient with RDI ≥ 26 in more than 75% nights was considered to have a high sleep apnea (SA) burden. An AF event was defined as a daily AF duration > 6 h.ResultsAmong 30 patients, the mean RDI of the whole follow-up period was 24.5 ± 8.6. Nine (30%) patients were diagnosed with high SA burden. Patients with high SA burden had a higher BMI (26.7 ± 4.8 vs 23.2 ± 3.9, p = 0.036), a higher prevalence of hypertension (86% vs 39%, p = 0.031), and a larger left ventricular diastolic diameter (49.2 mm vs 46.7 mm, p = 0.036). The RDI-SD in patients with a higher burden was significantly greater than that in the patients with less burden (10.7 ± 4.9 vs 5.7 ± 1.4, p = 0.036). Linear regression showed that participants with a higher RDI tended to have a higher SD (R = 0.661; p < 0.001). The mean RDI (OR = 1.118, 95%CI 1.008–1.244, p = 0.044) was associated with AF occurrence.ConclusionUsing a metric such as burden of severe SA may be more appropriate to demonstrate a patient’s true disease burden.

Compared to Individuals with Mild to Moderate Obstructive Sleep Apnea (OSA), Individuals with Severe OSA Had Higher BMI and Respiratory-Disturbance Scores.

Objective: Individuals with obstructive sleep apnea (OSA) are at increased risk to suffer from further somatic and sleep-related complaints. To assess OSA, demographic, anthropometric, and subjective/objective sleep parameters are taken into consideration, but often separately. Here, we entered demographic, anthropometric, subjective, and objective sleep- and breathing-related dimensions in one model. Methods: We reviewed the demographic, anthropometric, subjective and objective sleep- and breathing-related data, and polysomnographic records of 251 individuals with diagnosed OSA. OSA was considered as a continuous and as categorical variable (mild, moderate, and severe OSA). A series of correlational computations, X2-tests, F-tests, and a multiple regression model were performed to investigate which demographic, anthropometric, and subjective and objective sleep dimensions were associated with and predicted dimensions of OSA. Results: Higher apnea/hypopnea index (AHI) scores were associated with higher BMI, higher daytime sleepiness, a higher respiratory disturbance index, and higher snoring. Compared to individuals with mild to moderate OSA, individuals with severe OSA had a higher BMI, a higher respiratory disturbance index (RDI) and a higher snoring index, while subjective sleep quality and daytime sleepiness did not differ. Results from the multiple regression analysis showed that an objectively shorter sleep duration, more N2 sleep, and a higher RDI predicted AHI scores. Conclusion: The pattern of results suggests that blending demographic, anthropometric, and subjective/objective sleep- and breathing-related data enabled more effective discrimination of individuals at higher risk for OSA. The results are of practical and clinical importance: demographic, anthropometric, and breathing-related issues derived from self-rating scales provide a quick and reliable identification of individuals at risk of OSA; objective assessments provide further certainty and reliability.

Effects of Sleep-Related Disorders on the Prognosis of Amyotrophic Lateral Sclerosis

Background/Objective: In this study, we demonstrated the effects of obstructive sleep apnea syndrome (OSAS) on the prognosis of amyotrophic lateral sclerosis (ALS). However, the effects of sleep-related disorders other than breathing problems are still waiting to be delineated. Methods: In this longitudinal retrospective and prospective study, we investigated 73 patients with ALS compared to 20 healthy subjects, to determine sleep-related disorders and their impact on disease prognosis. Results: In patients with ALS, the mean respiratory disturbance index (RDI) was 28.0/h, which was significantly higher than that in the controls (p < 0.001). OSAS was present in 67% of the patients, sleep-related hypoxemia was observed in 13.7% of the patients, and 5.4% had central sleep apnea syndrome. In patients with bulbar-onset disease, higher RDI was almost significantly associated with lower survival (p = 0.056). The mean index of periodic leg movements in sleep was significantly higher in patients with ALS (34.0 ± 19.9/h) than that in the controls (12.5 ± 15.5/h; p < 0.001). Periodic leg movements disorder (PLMD) was diagnosed in 23 patients with ALS (31.5%); fragmentary myoclonus was present in 13.7% of patients, and REM-sleep behavior disorder was diagnosed in 4 patients (5.4%). The presence of PLMD in addition to OSAS was significantly associated with worse prognosis and poorer survival (p = 0.040). Conclusions: These findings emphasize that sleep-related disorders other than OSAS deserve attention in ALS. ALS is a catastrophic and frustrating disease for both patients and physicians; thus, the diagnosis and treatment of comorbid sleep disorders could improve the survival of patients with ALS.

Increased respiratory disturbance index measured using an advanced device algorithm is associated with heart failure development.

Previous studies suggested that sleep-disordered breathing was associated with cardiovascular diseases such as heart failure (HF). Recently, algorithms of cardiac implantable electronic devices (CIEDs) have been developed to detect advanced sleep apnea (SA); the Apnea Scan (AP Scan) being an example. The purpose of this study was to investigate the association between respiratory disturbance index (RDI) measured using the AP Scan algorithm and HF development. We retrospectively studied consecutive patients with CIEDs equipped with the AP Scan algorithm which were implanted between December 1, 2011 and March 31, 2019. These patients were divided into 2 groups according to the trends of RDI: patients with a continually high RDI > 30 (severe SA group) and those without a continually high RDI (non-severe SA group). There were 16 and 46 patients in the severe and non-severe SA groups, respectively. Increased left ventricular end-diastolic and end-systolic dimensions were observed in the severe SA group. Regarding cardiovascular events, HF was observed in 8 patients (50.0%) in the severe SA group and 1 patient (2.2%) in the non-severe SA group; thus, there was a significantly higher proportion of patients with HF in the severe SA group. In conclusion, continually high RDI was associated with HF development in patients with CIEDs equipped with the AP Scan algorithm. Therefore, an elevated RDI may be a risk factor for the development of HF in patients with CIEDs.

Relationship between sleep-disordered breathing and central systolic blood pressure in a community-based population: the Toon Health Study.

Sleep-disordered breathing (SDB) is linked with brachial blood pressure. Although central systolic blood pressure (cSBP) is a better predictor of cardiovascular diseases than is brachial blood pressure, the association between SDB and cSBP is not fully understood. This cross-sectional study included 1484 participants without cardiovascular diseases who were enrolled in the Toon Health Study between 2009 and 2012. The respiratory disturbance index (RDI) was estimated with a one-night sleep test using an airflow monitor. Participants were grouped into three categories according to RDI level: mild (<10 events/h), moderate (10 to <20 events/h), and severe (≥20 events/h). The cSBP was measured using a noninvasive automated tonometer. Multivariable-adjusted cSBP means for the mild, moderate, and severe RDI categories were, respectively, 116.0, 118.0, and 120.7 mm Hg (p for trend = 0.02) for men and 111.8, 113.7, and 111.7 mm Hg (p for trend = 0.59) for women. The association for men was no longer significant after adjusting for BMI. When stratified by BMI (<22 or ≥22 kg/m2), the RDI was associated with cSBP among men with BMI ≥ 22 kg/m2, and this association was of borderline significance. Augmentation index, pulse pressure amplification, and brachial blood pressure were not significantly associated with the RDI. Higher RDI values were associated with increased multivariable-adjusted cSBP means among men. This association was more evident among those with BMI ≥ 22 kg/m2. In conclusion, we found that the RDI was associated with cSBP among men, and this association was independent of confounding variables among individuals above the ideal weight.

Sleep disorders in spinocerebellar ataxia type 10.

As sleep disturbances have been reported in spinocerebellar ataxias (SCAs), including types SCA1, SCA2, SCA3, SCA6 and SCA13, identification and management of these disturbances can help minimise their impact on SCA patients' overall body functions and quality of life. To our knowledge, there are no studies that investigate sleep disturbances in SCA10. Therefore, the aim of this study was to assess sleep disturbances in patients with SCA10. Twenty-three SCA10 patients and 23 healthy controls were recruited. Patients were evaluated in terms of their demographic and clinical data, including disease severity (Scale for the Assessment and Rating of Ataxia, SARA) and excessive daytime sleepiness (Epworth Sleepiness Scale, ESS), and underwent polysomnography. SCA10 patients had longer rapid eye movement (REM) sleep (p=.04) and more REM arousals than controls (p<.0001). There was a correlation of REM sleep onset with the age of onset of symptoms (r=.459), and with disease duration (r=-.4305). There also was correlation between the respiratory disturbance index (RDI) and SARA (r=-.4013), and a strong indirect correlation between arousal index and age at onset of symptoms (r=-.5756). In conclusion, SCA10 patients had sleep abnormalities that included more REM arousals and higher RDI than controls. Our SCA10 patients had sleep disorders related to shorter disease duration and lower severity of ataxia, in a pattern similar to that of other neurodegenerative diseases.

Wakefulness evaluation during sleep for healthy subjects and OSA patients using a patch-type device

ObjectivesObstructive sleep apnea (OSA) is a major sleep disorder that causes insufficient sleep, which is linked with daytime fatigue and accidents. Long-term sleep monitoring can provide meaningful information for patients with OSA to prevent and manage their symptoms. Even though various methods have been proposed to objectively measure sleep in ambulatory environments, less reliable information was provided in comparison with standard polysomnography (PSG). Therefore, this paper proposes an algorithm for distinguishing wakefulness from sleep using a patch-type device, which is applicable for both healthy individuals and patients with OSA. MethodsElectrocardiogram (ECG) and 3-axis accelerometer signals were gathered from the single device. Wakefulness was determined with six parallel methods based on information about movement and autonomic nervous activity. The performance evaluation was conducted with five-fold cross validation using the data from 15 subjects with a low respiratory disturbance index (RDI) and 10 subjects with high RDI. In addition, wakefulness information, including total sleep time (TST), sleep efficiency (SE), sleep onset latency (SOL), and wake after sleep onset (WASO), were extracted from the proposed algorithm and compared with those from PSG. ResultsAccording to epoch-by-epoch (30 s) analysis, the performance results of detecting wakefulness were an average Cohen's kappa of 0.60, accuracy of 91.24%, sensitivity of 64.12%, and specificity of 95.73%. Moreover, significant correlations were observed in TST, SE, SOL, and WASO between the proposed algorithm and PSG (p < 0.001). ConclusionsWakefulness-related information was successfully provided using data from the patch-type device. In addition, the performance results of the proposed algorithm for wakefulness detection were competitive with those from previous studies. Therefore, the proposed system could be an appropriate solution for long-term objective sleep monitoring in both healthy individuals and patients with OSA.

Maxillomandibular Advancement for Treatment of Obstructive Sleep Apnea

Maxillomandibular advancement (MMA) is an invasive yet effective surgical option for obstructive sleep apnea (OSA) that achieves enlargement of the upper airway by physically expanding the facial skeletal framework. To identify criteria associated with surgical outcomes of MMA using aggregated individual patient data from multiple studies. The Cochrane Library, Scopus, Web of Science, and MEDLINE from June 1, 2014, to March 16, 2015, using the Medical Subject Heading keywords maxillomandibular advancement, orthognathic surgery, maxillary osteotomy, mandibular advancement, sleep apnea, surgical, surgery, sleep apnea syndrome, and obstructive sleep apnea. Inclusion criteria consisted of studies in all languages of (1) adult patients who underwent MMA as treatment for OSA; (2) report of preoperative and postoperative quantitative outcomes for the apnea-hypopnea index (AHI) and/or respiratory disturbance index (RDI); and (3) report of individual patient data. Studies of patients who underwent adjunctive procedures at the time of MMA (including tonsillectomy, uvulopalatopharyngoplasty, and partial glossectomy) were excluded. Three coauthors systematically reviewed the articles and updated the review through March 16, 2015. The PRISMA statement was followed. Data were pooled using a random-effects model and analyzed from July 1, 2014, to September 23, 2015. The primary outcomes were changes in the AHI and RDI after MMA for each patient. Secondary outcomes included surgical success, defined as the percentage of patients with more than 50% reduction of the AHI to fewer than 20 events/h, and OSA cure, defined as a post-MMA AHI of fewer than 5 events/h. Forty-five studies with individual data from 518 unique patients/interventions were included. Among patients for whom data were available, 197 of 268 (73.5%) had undergone prior surgery for OSA. Mean (SD) postoperative changes in the AHI and RDI after MMA were -47.8 (25.0) and -44.4 (33.0), respectively; mean (SE) reductions of AHI and RDI outcomes were 80.1% (1.8%) and 64.6% (4.0%), respectively; and 512 of 518 patients (98.8%) showed improvement. Significant improvements were also seen in the mean (SD) postoperative oxygen saturation nadir (70.1% [15.6%] to 87.0% [5.2%]; P < .001) and Epworth Sleepiness Scale score (13.5 [5.2] to 3.2 [3.2]; P < .001). Rates of surgical success and cure were 389 (85.5%) and 175 (38.5%), respectively, among 455 patients with AHI data and 44 (64.7%) and 13 (19.1%), respectively, among 68 patients with RDI data. Preoperative AHI of fewer than 60 events/h was the factor most strongly associated with the highest incidence of surgical cure. Nevertheless, patients with a preoperative AHI of more than 60 events/h experienced large and substantial net improvements despite modest surgical cure rates. Maxillomandibular advancement is an effective treatment for OSA. Most patients with high residual AHI and RDI after other unsuccessful surgical procedures for OSA are likely to benefit from MMA.

A Novel Approach to Prediction of Mild Obstructive Sleep Disordered Breathing in a Population-Based Sample: The Sleep Heart Health Study

This manuscript considers a data-mining approach for the prediction of mild obstructive sleep disordered breathing, defined as an elevated respiratory disturbance index (RDI), in 5,530 participants in a community-based study, the Sleep Heart Health Study. The prediction algorithm was built using modern ensemble learning algorithms, boosting in specific, which allowed for assessing potential high-dimensional interactions between predictor variables or classifiers. To evaluate the performance of the algorithm, the data were split into training and validation sets for varying thresholds for predicting the probability of a high RDI (≥7 events per hour in the given results). Based on a moderate classification threshold from the boosting algorithm, the estimated post-test odds of a high RDI were 2.20 times higher than the pre-test odds given a positive test, while the corresponding post-test odds were decreased by 52% given a negative test (sensitivity and specificity of 0.66 and 0.70, respectively). In rank order, the following variables had the largest impact on prediction performance: neck circumference, body mass index, age, snoring frequency, waist circumference, and snoring loudness.

Predictors for Treating Obstructive Sleep Apnea With an Open Nasal Cannula System (Transnasal Insufflation)

Obstructive sleep apnea (OSA) is a disorder that is associated with increased morbidity and mortality. Although continuous positive airway pressure effectively treats OSA, compliance is variable because of the encumbrance of wearing a sealed nasal mask throughout sleep. In a small group of patients, it was recently shown that an open nasal cannula (transnasal insufflation [TNI]) can treat OSA. The aim of this larger study was to find predictors for treatment responses with TNI. Standard sleep studies with and without TNI were performed in 56 patients with a wide spectrum of disease severity. A therapeutic response was defined as a reduction of the respiratory disturbance index (RDI) below 10 events/h associated with a 50% reduction of the event rate from baseline and was used to identify subgroups of patients particularly responsive or resistant to TNI treatment. For the entire group (N = 56), TNI decreased the RDI from 22.6 +/- 15.6 to 17.2 +/- 13.2 events/h (P < .01). A therapeutic reduction in the RDI was observed in 27% of patients. Treatment responses were similar in patients with a low and a high RDI, but were greater in patients who predominantly had obstructive hypopneas or respiratory effort-related arousals and in patients who predominantly had rapid eye movement (REM) events. The presence of a high percentage of obstructive and central apneas appears to preclude efficacious treatment responses. TNI can be used to treat a subgroup of patients across a spectrum from mild-to-severe sleep apnea, particularly if their sleep-disordered breathing events predominantly consist of obstructive hypopneas or REM-related events but not obstructive and central apneas.

Relation betweenobstructive sleep apnea and bradyarrhythmia

：Objective To analyze therelations between obstructive sleep apnea and bradyarrhythmia.Methods From 1999 to2005,203 patients who came from Bering Tongren Hospital and Fuwai Hospital were found tohave sleep apnea in an ambulatory study. A Hoher electrecardiogram was recorded for 24hours within 2 weeks after patients were diagnosed as obstructive sleep apnem ResultsNocturnal episodes of bradyarrhythmia were identified in 12(5.9%)of 203 patients.Body massindex and respiratory disturbance index in patients with bradyarrhythmia(n=12)were higherthan those in patientswithour bradyarrhymia(n=191)(34±5 735.24±6 and 63±15 vs.25±5,respectively,bothP<0.01).There was a significant difference in end-apneic oxygen saturation inapnea/hypopnea episodes with and without bradyarrhythmia(63%±15% vs.75%±11%,P<0.05).Alinear relation between end-apneic oxygen saturation and number of sinus arrests and heartblocks was not found.Conclusions Patients with apnea-associated bradyarrhythmia havehigher body mflgB index and higher respiratory disturbance index than patients withoutbradyarrhythmi&Bradyarrhythmia occurres independently from decrease in oxygensaturation.

Overlap syndrome: an indication for sleep studies?

The coexistence of obstructive sleep apnea (OSA) and chronic obstructive pulmonary diseases (COPD) is known as overlap syndrome (OS); it occurs in 10-20% of patients with OSA. Patients with OS have a higher risk of pulmonary hypertension and worse nocturnal hypoxemia than those with either disease alone. Differences may be seen according to severity of COPD, anthropometric measures, and polysomnography (PSG) features of patients. Recent studies have suggested that long-term use of continuous positive airway pressure for OSA is associated with worsening of coexistent COPD. This stresses the importance of identifying this subgroup of patients in order to provide adequate therapy. This study aims to describe the presence of OS among subjects at our institution and study its association to daytime hypercapnia, nocturnal hypoxemia, and severity of OSA and of COPD. We reviewed the records of patients who underwent PSG and pulmonary function test (PFT) at our center since 2002. Data gathered from PSG and PFTs included respiratory disturbance index (RDI), apnea index, lowest nocturnal desaturation, forced expiratory volume in 1 s (FEV1), FEV1/forced vital capacity ratio, arterial blood gasses, and anthropometric measures. Five hundred forty-seven records were reviewed, but only 73 met all inclusion criteria for analysis. Thirty-six patients had COPD, 52 had OSA, and 29 had OS. The mean predicted FEV1 percent of all subjects was 80%, and the mean diurnal partial pressure of carbon dioxide (pCO(2)) was 39 mmHg. There were no significant differences in average pCO(2) or RDI between subjects with OSA and OS. In all subjects, hypercapnia significantly correlated with worse RDI (p = 0.01) and with worse nocturnal desaturation (p = 0.01). During rapid eye movement (REM) sleep, those with FEV1 less than 80% predicted had higher RDI than those with higher FEV1 (p = 0.010). In these preliminary results, the prevalence of OS in our population is similar to that previously reported. Daytime hypercapnia correlated with the more severe sleep-disordered breathing (SDB) and worse nocturnal hypoxemia in all subjects. Severity of obstructive ventilatory impairment is associated with worse SDB during REM sleep. Randomized trials to determine if PSGs are indicated in all patients with severe COPD should be considered. This is an ongoing study.

An overview of observational sleep research with application to sleep stage transitioning

Sleep is an essential component of human existence, consuming roughly one third of our lives. Fatigue, jet-lag, poor sleep and vivid dreams are frequent points of our morning discussions. We look and feel terrible after getting too little sleep; hence a twenty billion dollar industry of beds, pillows, pills and other tools has cropped up to help us sleep better. Correspondingly, there are plenty of products designed to keep us awake. Despite the importance of sleep in our lives, and the lives of so many other species, a definitive answer on the specific neuro-biological or physiologic purpose of sleep eludes researchers. However, substantial advancements in the field are uncovering the crucial role that sleep plays in our health, behavior and well being. For example, studies of sleep duration have found associations with a variety of important health outcomes. Short sleep duration correlates with impaired cognitive function, hypertension, glucose intolerance, altered immune function, obesity and even mortality. This point is driven home by the fact that sleep deprivation is a well recognized form of torture. Consider the following quote from former Israeli Prime Minister Menachem Begin, who suffered forced sleep deprivation as a KGB prisoner: In the head of the interrogated prisoner, a haze begins to form. His spirit is wearied to death, his legs are unsteady, and he has one sole desire: to sleep, to sleep just a little, not to get up, to lie, to rest, to forget... Anyone who has experienced this desire knows that not even hunger and thirst are comparable with it. Quantity of sleep is only one measurable facet of sleep that is associated with health. Table 1 gives a few of the more common measurements of sleep and sleep disturbance. The next section describes sleep measurement in greater detail. Table 1 Measurements of sleep taken during an overnight sleep study and routine clinical evaluation of sleep. A common sleep disorder that is of particular public health interest is sleep apnea. This is a chronic condition characterized by collapses of the upper airway during sleep. Complete collapses lead to so-called “apneas”, whereas partial collapses to so-called “hypopneas”. Over the last decade, research has shown that these events can lead to several physiologic consequences, including changes in metabolism, glucose tolerance and cardiac function. The respiratory disturbance index (RDI), sometimes also called the apnea/hypopnea index (AHI), is the principal measure of severity of sleep apnea. This rate index is the count of the number of apneas and hypopneas divided by the total time slept in hours. A severely affected patient may have an RDI of thirty events per hour or higher! Hence such a patient is, on average, having a disruption in their sleep and breathing every two minutes. As one can imagine, such frequent disruptions in sleep and oxygen intake can have negative health consequences. Young, Peppard and Gottlieb review that a high RDI has been shown to be associated with hypertension, cardiovascular disease, cerebrovascular disease, excessive daytime sleepiness, decreased cognitive function, decreased health-related quality of life, increased motor vehicle crashes and occupational accidents, and mortality. In this article, we relate measures of sleep apnea with transitions that occur between “sleep states”. Sleep states are based on visual classification of brain electroencephalograms (EEGs) patterns (see below). Two major sleep states are rapid eye movement (REM) and non-REM. Sleep states can be seen as a categorical response time series. Crude summaries of these states, such as the percentage time spent in each one, are often used as predictors of health. Instead, we investigate the role that sleep apnea has on the rate of transitioning between the states. We emphasize that the rate of transitioning contains more important additional information than the crude percentage of time spent in each state. Notably, we use matching to account for other variables that might be related to both disease status and sleep behavior and hence compare a severely diseased group with a matched non-diseased group. In the next section we give a brief overview of sleep measurement. Following that, we discuss an analysis of sleep transition rates comparing those with moderate to severe sleep apnea to those without. We end the article with a discussion.

How much sleep apnea is too much? Authors' response

Our study [1] had two main purposes: first, to examine the occurrence of sleep-disordered breathing (SDB) in patients with chronic fatigue syndrome (CFS), and then to exclude patients with this confound in order to evaluate the structure of sleep in a group of patients with pure CFS to look for relations with the symptoms of fatigue and sleepiness. In order to do this, we had to define an upper limit for the occurrence of respiratory events that might explain the daytime symptoms. Martinez and Cassol are correct that the currently accepted cutpoint for abnormality proposed by the American Academy of Sleep Medicine (AASM) and Centers for Medicare & Medicaid Services (CMS) in the US is an apnea-hypopnea index (AHI) ≥ 5 per hour but less than 15 per hour – but only if symptoms such as EDS are present. However, the AHI is an insensitive measure of the severity of mild respiratory events (such as respiratory event-related arousals (RERAs)) as it requires either a 3 or 4% desaturation for the definition of hypopnea and this is frequently not present in respiratory events that cause arousal and may contribute to sleep disruption (RERA). For this reason, our cutpoint for SDB is based on a respiratory disturbance index (RDI) of 18 events per hour and not the AHI. The RDI includes RERAs along with the AHI, although we used a slightly different definition of hypopneas beginning with any event showing flow limitation rather than the current amplitude based entry criterion. The rationale for this is from an earlier paper by our group [2] that shows that the sensitivity and specificity for explaining EDS in a group composed of symptomatic but mild SDB and non-complaining controls were greater using the RDI criterion than the AHI criterion. Since that paper, it has become customary to use a cut-off of 15 events per hour for RDI in many applications. It is important to note that for RDI, using 5 events per hour will include essentially 80% of the normal population. Furthermore, as pointed out in our current paper [1], although we chose 18 events per hour as a cut-off to exclude three subjects (one with CFS and two normal subjects) when defining the final group for our sleep analysis who might have SDB, in fact the highest RDIs we saw in the non-SDB group were 10.4, 10.8, 10.1, and 9.5 events per hour; we feel these numbers are within a range seen in many normal subjects without EDS [2]. Thus, our cut-off of 18 is not effectively different from the more recently accepted number of 15 events per hour. And after excluding those subjects with high RDI values, there was no significant difference in the AHI of patients with only CFS, those with CFS and fibromyalgia and healthy controls (1.7 ± 1.6, 2.8 ± 2.6, and 2.2 ± 1.7, respectively). In fact, the above logic is not fundamentally different from the choice made by Martinez and Cassol in their own work [3-6], where they define SDB as present in fibromyalgia when the AHI <5 and when more than 10 RERAs per hour occurred (5 + 10 events = 15 per hour, similar to our cut-off of 18 per hour).

Apnoeic–hypopnoeic episodes during obstructive sleep apnoea are associated with histological nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) and obstructive sleep apnoea are associated with metabolic syndrome and atherosclerotic heart disease. This study evaluates the potential association between the NAFLD subtypes and a number of polysomnographical (PSG) parameters. This study included patients undergoing bariatric surgery with extensive clinical and histological data for whom complete PSG data before surgery were also available. Excess alcohol intake and other causes of liver disease were excluded. Apnoea, hypopnoea and apnoea-hypopnoea index (AHI) were calculated as described previously. In this study, a total of 101 patients [77 nonalcoholic steatohepatitis (NASH) and 22 non-NASH controls] with PSG data were included (age 42.9 +/- 11.4 years, body mass index 51.6 +/- 9.5 kg/m(2), fasting serum glucose 117.4 +/- 53.4 mg/dl, fasting serum triglycerides 171.3 +/- 82.9 mg/dl, 58% hypertension and 33% diabetes mellitus). Subjects with histological NASH had significantly lower lowest desaturation (77 vs. 85%, P=0.006), lower mean nocturnal oxygen saturation (91 vs. 93%, P=0.05), higher AHI (35 vs. 22, P=0.03), higher respiratory disturbance index (46 vs. 21, P=0.02) and higher alanine aminotransferase/aspartate aminotransferase ratio (1.4 vs. 1.3, P=0.05) compared with non-NASH controls. In multivariate analysis, the lowest desaturation (P=0.04) was independently associated with histological NASH. Lowest desaturation and mean nocturnal oxygen saturation were significantly lower in subjects with fibrosis (76 vs. 85%, P=0.004 and 90.4 vs. 93.0%, P=0.02). Our results suggest that the frequent nocturnal hypoxic episodes in NAFLD patients may be a risk factor for developing NASH. Additional studies are needed to study the effect of optimizing sleep apnoea management on the outcomes of patients with NAFLD.

Renal function and sleep-disordered breathing in older men

Sleep-disordered breathing (SDB) is common in severe chronic kidney disease (CKD) and may contribute to morbidity and mortality in this population. However, the association between mild to moderate CKD and likelihood of SDB is uncertain. We studied 2696 men >or=65 years (mean 73.0 +/- 5.5) enrolled in the Outcomes of Sleep Disorders in Older Men (MrOS Sleep) study who had serum creatinine (SCr) measured 3.4 years prior to overnight polysomnography (PSG). CKD was expressed as quartiles of estimated glomerular filtration rate (eGFR) using the four-variable Modification of Diet in Renal Disease (MDRD) formula. SDB was assessed using the respiratory disturbance index (RDI) with >or=4% oxygen desaturation. Mean SCr was 0.99 +/- 0.20 mg/dl; 14.8% had eGFR <60 ml/min/1.73 m(2). Median RDI was 7.4 events/hour (inter-quartile range 2.6-15.8). Lower eGFR was not associated with higher mean RDI in the unadjusted model (P for trend = 0.180). There was evidence of an interaction between eGFR and age for the prediction of RDI; an association between lower eGFR and higher RDI was evident only among men <or=72 (median) years. Among this age group, however, the association was not statistically significant after further adjustment for body mass index (BMI) (P for trend = 0.278). In this cohort of older community-dwelling men, reduced renal function was not associated with greater evidence of SDB, except among younger old men. However, this association was largely explained by higher BMI at lower eGFR. Further prospective study in younger populations is needed to clarify our findings.