Sleep Medicine

Editorial Board

2012-02-01

Daytime symptoms in restless legs syndrome – An underestimated problem?

Paul Christian Baier — 2012-02-01

Restless legs syndrome (RLS) is typically characterized by unpleasant sensations in the limbs, often the lower limbs, and associated with an urge to move them. Since the historic description by Ekbom in the 1940s it has been widely assumed that these paraesthesias are “...mostly felt during the night...” and “...are either entirely absent or are of a mild degree...” during the daytime . Ekbom’s observation was later confirmed by a few studies that systematically investigated RLS symptoms during the course of the day and found that the severity of subjective leg discomfort measured with (modified) suggested immobilization tests in untreated patients increases during the late evening and peaks in the middle of the night, with a minimum of symptoms in the morning . Although Ekbom already found that daytime symptoms occur, the obvious and frequent problem of patients’ difficulties falling and staying asleep identified Restless-Legs-Syndrome as a sleep disorder. This might explain why previous questionnaire surveys reported an impact on daytime functioning in around 50% of patients , but did not differentiate if this resulted from daytime symptoms or from impaired sleep. Furthermore, a previous epidemiological study reported that 10% of the patients had daytime symptoms, but defined daytime only as before 6p.m. .

Move over LOCF: Principled methods for handling missing data in sleep disorder trials

2012-02-01

Abstract: Missing data, e.g. patient attrition, are endemic in sleep disorder clinical trials. Common approaches for dealing with this situation include complete-case analysis (CCA) and last observation carried forward (LOCF). Although these methods are simple to implement, they are deeply flawed in that they may introduce bias and underestimate uncertainty, leading to erroneous conclusions. There are alternative principled approaches, however, that are available in statistical software namely mixed-effects models and multiple imputation. In this paper we introduce terminology used to describe different assumptions about missing data. We emphasize that understanding reasons for missingness is a critical step in the analysis process. We describe and implement both linear mixed-effects models and an inclusive multiple imputation strategy for handling missing data in a randomized trial examining sleep outcomes. These principled strategies are compared with “complete-case analysis” and LOCF. These analyses illustrate that methodologies for accommodating missing data can produce different results in both direction and strength of treatment effects. Our goal is for this paper to serve as a guide to sleep disorder clinical trial researchers on how to utilize principled methods for incomplete data in their trial analyses.

Efficacy and safety of doxepin 6mg in a four-week outpatient trial of elderly adults with chronic primary insomnia

2012-02-01

Abstract: Introduction: The efficacy and safety of doxepin (DXP), a histamine H1 receptor antagonist, was evaluated in elderly adults with sleep maintenance insomnia.Methods: This was a randomized, double-blind, placebo-controlled outpatient trial. Elderly adults meeting DSM-IV-TR criteria for primary insomnia were randomized to four weeks of nightly treatment with either DXP 6mg (N=130) or placebo (PBO; N=124). Efficacy was assessed using patient self-report instruments and clinician ratings. Patient-reported endpoints included subjective total sleep time (sTST), subjective wake after sleep onset (sWASO), latency to sleep onset (LSO), sleep quality, and a Patient Global Impression scale (PGI). The primary endpoint was sTST at week 1.Results: DXP 6mg produced significantly more sTST and less sWASO at week 1 (both p-values <0.0001) than PBO. These significant improvements versus placebo were maintained at weeks 2–4 (all p-values <0.05). There were no significant differences in LSO for DXP 6mg versus PBO. DXP 6mg significantly improved sleep quality (weeks 1, 3, and 4, p<0.05) and several outcome-related parameters, including several items on the PGI, the severity and improvement items of the Clinician Global Impression scale (CGI; weeks 1 and 2) and the Insomnia Severity Index (ISI; weeks 1–4), all versus PBO. There were no reports of anticholinergic effects (e.g., dry mouth) or memory impairment. The safety profile of DXP 6mg was comparable to that of PBO.Conclusions: In elderly adults with insomnia, DXP 6mg produced significant improvements in sleep maintenance, sleep duration, and sleep quality endpoints that were sustained throughout the trial. These data suggest that DXP 6mg is effective for treating sleep maintenance insomnia and is well-tolerated in elderly adults with chronic primary insomnia.

Sleep duration pattern and chronic diseases in Brazilian adults (ISACAMP, 2008/09)

2012-02-01

Abstract: Objective: The aim of the present study was to assess sleep patterns in the adult population of the city of Campinas (Brazil) according to socioeconomic/demographic variables, chronic diseases, and symptoms.Methods: A population-based cross-sectional study was conducted using data from the Campinas Health Survey (ISACAMP) carried out in 2008 and 2009. A total of 2637 individuals aged 18years or older (obtained from a probabilistic sample) were analyzed. Associations between sleep pattern and the independent variables were determined using the chi-square test. Multinomial logistic regression models were used to adjust for confounders.Results: The prevalence of six or fewer hours of sleep was greater among individuals aged 40years or older and among divorced or single individuals. The sleep pattern of nine or more hours was more prevalent among those with less than 40years of age, among those who were divorced, or single, among those with a lower level of schooling, those who did not work and housewives. Both short and long sleep patterns were more prevalent among individuals with heart disease, vascular problems, rheumatism/arthritis/arthrosis, osteoporosis, or emotional problems. The prevalence of the short sleep duration was greater among individuals with back problems and those with three or more health conditions. A strong association was found between sleep duration and sleep quality.Conclusions: Socio-demographic factors and health diseases were associated to sleep duration. This issue should be considered in health promotion strategies.

Sleep duration and hypercholesterolaemia: Results from the National Health Interview Survey 2008

Charumathi Sabanayagam, Anoop Shankar — 2012-02-01

Abstract: Background: Previous studies have shown an inconsistent association between sleep duration and hypercholesterolaemia. This study examined the association between sleep duration and hypercholesterolaemia in a nationally representative sample of US adults.Methods: A cross-sectional study of 16,652 participants in the 2008 National Health Interview Survey (aged ⩾18years, 52.5% women) was conducted. Sleep duration was categorized as ⩽5, 6, 7, 8, or ⩾9h. Hypercholesterolaemia (n=5578) was assessed by questionnaire.Results: A significant gender difference was found in the association between sleep duration and hypercholesterolaemia (P interaction=0.003). Among women, sleep duration ⩽5h was positively associated with hypercholesterolaemia after adjusting for potential confounders and mediators including physical activity, psychological distress, body mass index, diabetes mellitus, and hypertension. Compared with a sleep duration of 7h (referent), the multivariate odds ratio (OR) of hypercholesterolaemia was 1.27 (95% confidence interval [CI] 1.04–1.54) for sleep duration ⩽5h. In contrast, among men, sleep duration ⩾8h was inversely associated with hypercholesterolaemia. Compared with a sleep duration of 7h (referent), the multivariate OR of hypercholesterolaemia was 0.80 (95% CI 0.69–0.94) and 0.78 (95% CI 0.60–1.00) for sleep durations of 8 and ⩾9h, respectively. In subgroup analyses, the positive association between sleep duration ⩽5h and hypercholesterolaemia in women, and the inverse association between sleep duration ⩾8h and hypercholesterolaemia in men, were more pronounced among those aged <60years and race/ethnic groups other than non-Hispanic Whites.Conclusion: Sleep duration ⩽5h was positively associated with hypercholesterolaemia in women, whereas sleep duration ⩾8h was inversely associated with hypercholesterolaemia in men.

Breakthrough symptoms during the daytime in patients with restless legs syndrome (Willis-Ekbom disease)

2012-02-01

Abstract: Background: It is often assumed that most patients with restless legs syndrome (RLS) only experience symptoms at night. However, previous studies have estimated the prevalence of daytime symptoms to be 10–60%. This study sought to investigate the prevalence and pattern of daytime symptoms in patients with moderate-to-severe RLS.Methods: Observational, cross-sectional investigation. A self-administered questionnaire was sent out, on a random basis, to 310 patients with RLS by the Spanish RLS patient support group. Only individuals with a confirmed diagnosis of RLS were included in the final survey.Results: In total, 224 individuals were included in the survey (response rate 72%). Over 55% of patients reported daytime crises on most (>3) days of the week, and 41% suffered daytime symptoms on a daily basis. These breakthrough crises were characterized by unexpected and sudden symptoms and were frequently precipitated by a reduction in daytime activity. The mean severity of these crises on a visual analogue scale (range 0–10) was 6.8 (standard deviation 2.1), and they had a major impact on quality of life. The prevalence of breakthrough crises was related to duration of illness but not to duration of treatment.Conclusion: This study suggests that breakthrough crises are common in moderate-to-severe RLS and have a negative effect on quality of life. More studies are needed to investigate whether breakthrough crises reflect disease progression or, at least for those patients undergoing dopaminergic treatment, whether they represent an early indication of RLS augmentation.

Effects of nasal continuous positive airway pressure on panic disorder comorbid with obstructive sleep apnea syndrome

Yoshikazu Takaesu, Yuichi Inoue, Yoko Komada, Tatsuo Kagimura, Makio Iimori — 2012-02-01

Abstract: Backgrounds: Both obstructive sleep apnea syndrome (OSAS) and panic disorder (PD) are common disorders that often coexist. Continuous positive airway pressure (CPAP) has been established as the first-line treatment for OSAS. In this study, we examined the efficacy of CPAP on PD comorbid with OSAS by conducting a randomized crossover study using sham CPAP as control.Methods: PD patients (n=12) with an apnea hypopnea index (AHI) of 20/h or higher completed the study. At baseline, the subjects were asked to write their own records pertaining to the frequency of attacks and their score on the panic disorder severity scale (PDSS), and then they participated in the randomized crossover trial period, which measured optimal CPAP and sham CPAP set at 4cmH2O during nighttime sleep for each 4-week assignment.Results: The frequency of panic attacks, total PDSS score, and the frequency of alprazolam use for alleviating the attack symptoms were significantly decreased during the optimal CPAP period than during the baseline period and the sham CPAP period. Among the PDSS subitems, the frequency of attacks, panic distress, work impairment, and social impairment showed significant improvements during the optimal pressure period.Conclusion: Our results suggest that OSAS contributes to PD aggravation, and a combination of pharmaceutical treatment for PD and OSAS-specific treatments such as CPAP could be recommended for patients with PD comorbid with OSAS.

Effect of three weeks of continuous positive airway pressure treatment on mood in patients with obstructive sleep apnoea: A randomized placebo-controlled study

2012-02-01

Abstract: Background: Patients with obstructive sleep apnoea (OSA) commonly have mood symptoms such as depression and anxiety. However, the results of randomized controlled trials on the therapeutic effect of CPAP on mood symptoms have been inconsistent. The present study examined whether three weeks of CPAP treatment had specific therapeutic effects on mood symptoms in patients with OSA compared with placebo.Methods: A double-blind, parallel, randomized controlled trial using therapeutic and placebo CPAP was performed in 71 patients newly diagnosed with OSA (apnoea–hypopnoea index [AHI]⩾10). Mood was assessed by the Center for Epidemiologic Studies-Depression (CES-D) Scale, the Profile of Mood States (POMS), and the Brief Symptom Inventory (BSI) before and after three weeks of treatment. AHI was used to assess the severity of apnoea. The two groups were compared using a simple comparison of the changes within each arm and repeated measures analysis of variance.Results: Fifty-six subjects completed the study: 26 in the CPAP group and 30 in the placebo group. The two groups were well matched at baseline, with no significant differences in demographic, mood and apnoea variables. Both groups had severe apnoea, mild depression, and anxiety at baseline. After three weeks of treatment, AHI decreased significantly in the CPAP group. The mean change in AHI was −30.7 (standard deviation [SD] 23.1) in the CPAP group and −5.8 (SD 18.3) in the placebo group (difference between groups P<0.001). However, after three weeks of treatment, there were no significant time by treatment effects in relation to mood, as assessed by the CES-D, POMS Depression, POMS Tension, BSI Depression, or BSI Anxiety (all P>0.05).Conclusion: In conclusion, three weeks of CPAP treatment did not show a specific therapeutic effect on mood symptoms in patients with OSA.

Melatonin concentration as a marker of the circadian phase in patients with obstructive sleep apnoea

2012-02-01

Abstract: Objective: The effects of obstructive sleep apnoea (OSA) on the markers of glucose metabolism and other hormones are of interest, particularly since there is growing evidence that OSA may be a risk factor for disorders such as insulin resistance. However, interpreting these studies depends on the target hormone not having a diurnal rhythm and the circadian rhythm not being altered by the sleep fragmentation that occurs in OSA. Therefore, the aim of our study was to test the hypothesis that OSA displaces the circadian rhythm.Methods: We carried out a prospective, observational, controlled, parallel study in 22 OSA patients (mean [SD] age: 45.1 [8.8]years; apnoea/hypopnoea index (AHI): 37 [24] events/h) and 22 age matched healthy subjects (age: 47.9 [7.9]years; AHI: 3 [1] events/h). Saliva samples for the measurement of melatonin were collected from participants resting in dim light at 30min intervals between 19:30 and 22:30h. Dim light melatonin onset (DLMO), a marker of the circadian phase, was taken at the end of the 30min interval in which the greatest rise in melatonin occurred.Results: The group median (interquartile range) DLMO did not differ in OSA patients compared to healthy subjects (OSA patients: 90 [60–150]min; healthy subjects: 135 [90–150]min, p=0.19).Conclusion: The circadian phase is the same in OSA patients and healthy subjects using salivary melatonin concentration as a marker of the circadian phase.

Barriers to treatment of paediatric obstructive sleep apnoea: Development of the adherence barriers to continuous positive airway pressure (CPAP) questionnaire

Stacey L. Simon, Christina L. Duncan, David M. Janicke, Mary H. Wagner — 2012-02-01

Abstract: Background: Continuous positive airway pressure (CPAP) treatment is often prescribed for youth as a treatment for obstructive sleep apnoea (OSA). Efficacy research in youth is limited, though some evidence suggests that it may relieve symptoms of OSA and possibly prevent future physical, emotional, and behavioural complications. However, the device must be used consistently for benefits to be realised. Non-adherence to medical treatment is prevalent among youth with chronic illness, yet little is known regarding adherence to CPAP in paediatric OSA.Methods: Using a sample of 51 youth (age 8–17years) recruited from a paediatric sleep specialty clinic, the aims of the current study were to: (1) present descriptive data regarding CPAP adherence in youth with OSA, and (2) develop a psychometrically sound measure of barriers for adherence to CPAP use for youth with OSA.Results: Results indicated that adherence to CPAP is poor: youth in the current sample used their CPAP on average 3.35h per night. The adherence barriers measure demonstrated excellent psychometric properties.Conclusions: The adherence barriers to CPAP questionnaire has the potential to be a useful clinic-based tool for identifying patient-specific issues with CPAP adherence in youth with OSA.

REM and NREM sleep-state distribution of respiratory events in habitually snoring school-aged community children

Karen Spruyt, David Gozal — 2012-02-01

Abstract: Background: Studies ascribe different functions to rapid eye movement (REM) and non-rapid eye movement (NREM) sleep, such that their disruption could result in discrepant clinical outcomes. Although sleep architecture is globally preserved in children with obstructive sleep apnoea (OSA), it is considered to be an REM sleep REMS disorder. Furthermore, body position during sleep affects the occurrence of respiratory events, while the presence of obesity has been claimed to affect sleep-state distribution of respiratory disturbance.Methods: To explore the distribution of respiratory events during REMS and NREM sleep NREMS and its potential predictors, a cross-sectional analysis of 335 overnight sleep studies in snoring children from the community was conducted. The ratio of REMS to NREMS respiratory events was compared, and potential associations were assessed using general linear modelling (GLM).Results: Children were 7.3±1.2years old and had a body mass index (BMI) z-score of 1.0±1.3. The obstructive apnoea–hypopnea index (OAHI) was 1.7±3 and 45.8% of children had an apnoea–hypopnea index (AHI) >1h−1 total sleep time (TST). Obstructive respiratory events were 3.8times more likely in REMS (2.0h−1) than NREMS (0.5h−1), and the GLM revealed distinctive predictive associations for the apnoeic and hypopneic indices separately, and for body position, the latter indicating that the REMS/NREMS distribution of respiratory events depends on body position.Conclusion: Obstructive respiratory events are predominantly, albeit not exclusively, present in REMS in school-aged children. NREMS respiratory events are more likely in the presence of lower oxyhaemoglobin saturations during event, side body position and in African–American children. However, REMS dominance is not affected by either BMI z-score or obesity. Our findings suggest that incorporating comprehensive respiratory event profiles of children may enhance our understanding of the pathophysiology and adverse outcomes in the context of paediatric OSA.

Infant sleep and early parental sleep-related cognitions predict sleep in pre-school children

Liat Tikotzky, Lee Shaashua — 2012-02-01

Abstract: Objective: To investigate early predictors of sleep patterns in pre-school age children. Specifically, we were interested in exploring whether infant sleep patterns and parenting factors assessed at 12months would predict sleep in four year-old children.Methods: This was a follow-up study of a home-based longitudinal study, exploring the links between parental cognitions and children’s sleep. The present study included 71 families (boys 58%) and focused on data collected when children were 12months and four years old. Sleep at both time points was assessed for four weekdays by actigraphy and parental reports.Results: Statistically significant zero-order correlations were found between early sleep patterns, maternal cognitions, and soothing behaviors at 12months, and sleep patterns at four years. Multiple regression analysis revealed that 12months maternal cognitions reflecting difficulties with limiting parental nighttime involvement were a statistically significant predictor of fragmented child’s sleep and of parental bedtime involvement at four years. More objective infant night-wakings at 12months predicted lower sleep efficiency at four years.Conclusions: Both early sleep patterns and maternal sleep-related cognitions during infancy are significant predictors of sleep quality of pre-school children. These findings are clinically meaningful as they suggest that improving infant sleep and addressing early parental beliefs and perceptions regarding infant sleep may help in preventing sleep problems of pre-school children.

Prevalence and correlates of delayed sleep phase in high school students

2012-02-01

Abstract: Purpose: To investigate prevalence and correlates of delayed sleep phase, characterized by problems falling asleep in the evening and rising at adequate times in the morning, in a large sample of Norwegian high school students.Methods: A randomized sample of 1285 high school students (aged 16–19years) participated in an internet based study answering questions about sleep habits, height, weight, smoking, alcohol use, school grades, and anxiety and depression symptoms. Delayed sleep phase was operationalized as difficulties falling asleep before 2a.m. at least three nights per week together with much or very much difficulty waking up in the morning.Results: The results show a prevalence of delayed sleep phase of 8.4%. In all, 68% of these students (5.7% of the total sample) also reported problems advancing their sleep period as well as one daytime consequence (oversleeping at least two days a week or experiencing much/very much sleepiness at school). Delayed sleep phase was associated with lower average school grades, smoking, alcohol usage, and elevated anxiety and depression scores.Conclusions: Delayed sleep phase appears to be common amongst Norwegian adolescents and is associated with negative outcomes such as lower average school grades, smoking, alcohol usage, and elevated anxiety and depression scores.

Quality of life in patients with narcolepsy with cataplexy, narcolepsy without cataplexy, and idiopathic hypersomnia without long sleep time: Comparison between patients on psychostimulants, drug-naïve patients and the general Japanese population

2012-02-01

Abstract: Objective: To assess the quality of life of patients with narcolepsy with cataplexy (NA–CA), narcolepsy without cataplexy (NA w/o CA), and idiopathic hypersomnia without long sleep time (IHS w/o LST) who were taking psychostimulant medication, and to ascertain which factors (including psychosocial and environmental variables) influence quality of life in this population.Methods: In total, 185 patients who had received regular treatment were enrolled in the study (NA–CA, n=83; NA w/o CA, n=48; IHS w/o LST, n=54). Patients were asked to complete questionnaires including the Short Form-36 Health Survey (SF-36), the Epworth Sleepiness Scale (ESS), and items concerning psychosocial and environmental variables.Results: All three diagnostic groups had significantly lower scores for most SF-36 domains compared with the Japanese normative data, and the ESS score was significantly reduced with treatment. Multiple logistic regression analyses revealed that several SF-36 domains were associated with the ESS score; autonomy in controlling own job schedule, experience of divorce or break up with a partner due to symptoms, experience of being forced to relocate or being dismissed due to symptoms, and perception of support from others.Conclusions: The severity of subjective sleepiness and psychological and environmental variables influenced quality of life in patients with these hypersomnias of central origin.

The Spanish version of the Insomnia Severity Index: A confirmatory factor analysis

2012-02-01

Abstract: Objective: To examine the psychometric properties of the Spanish version of the Insomnia Severity Index (ISI) and to determine its factor structure with confirmatory factor analysis (CFA).Methods: Self-reported information was collected from a sample of 500 adults (mean age 39.13 [standard deviation 15.85]years) drawn from a population of medical students and their social networks. Together with the ISI, a measure of the subjective severity of insomnia, subjects completed the Pittsburg Sleep Quality Index, the Epworth Sleepiness Scale, and the Profile of Mood States to study concurrent validity of the ISI. CFA was used to test alternative models to ascertain the factorial structure of the ISI.Results: The Spanish version of the ISI showed adequate indices of internal consistency (Cronbach’s α=0.82). CFA showed that a three-factor structure provided a better fit to the data than one-factor and two-factor structures. The ISI was significantly correlated with poor sleep quality, fatigue, anxiety, and depression, and discriminated between good and poor sleepers.Conclusions: The ISI is a reliable and valid instrument to assess the subjective severity of insomnia in Spanish-speaking populations. Its three-factor structure (i.e., night-time sleep difficulties, sleep dissatisfaction and daytime impact of insomnia) makes it a psychometrically robust and clinically useful measure.

Young-onset REM sleep behavior disorder: Beyond the antidepressant effect

S.P. Lam, S.X. Li, Vincent Mok, Y.K. Wing — 2012-02-01

We read with interest the recent paper by Ju et al. on the comparison of early-onset REM sleep behavior disorder (RBD) (age <50) to late onset cases . Albeit limited by the retrospective design, the findings are consistent with the recent literature, including a lower male to female ratio, and less co-morbid neurodegenerative diseases in early onset group .

RBD and antidepressants

Yo-El Ju, Linda Larson-Prior, Stephen Duntley — 2012-02-01

We appreciate the letter from Dr. Lam and colleagues, particularly for alerting readers to their 2010 study , which regrettably was published after the submission of our publication, Changing demographics in REM sleep behavior disorder , and therefore could not be included in the discussion. Their prior findings of high rates of RBD symptoms among psychiatric patients taking serotonergic antidepressants concur with the findings in our case series and other reports , and we read with interest their follow-up study with polysomnographic confirmation, which is critical for distinguishing RBD from its multiple mimics. The intriguing finding that, despite a decrease in subjective dream enactment episodes with antidepressant change or discontinuation, there was persistent REM without atonia (RWA) noted objectively on polysomnogram , lends further credence to a contributory role of antidepressants in RBD and RWA in susceptible individuals. However, studies with polysomnograms before and after antidepressant initiation, demonstrating RBD occurring as a consequence of antidepressants, are still lacking. We certainly agree that further investigation is necessary in this area, particularly as antidepressant usage becomes increasingly widespread. Additionally, long-term follow-up studies are required to determine any relationship between antidepressant-related RBD and neurodegenerative disease.

Helicobacter pylori may play a role in both obstructive sleep apnea and metabolic syndrome

2012-02-01

To the Editor We read with interest the paper by Theorell-Haglöw et al. , which concluded that obstructive sleep apnea (OSA) is closely associated with metabolic syndrome and its components in a Swedish population.

What is cause and what is effect?

Jenny Theorell-Haglöw, Christian Berne, Christer Janson, Eva Lindberg — 2012-02-01

We would like to thank Prof. Kountouras and co-workers for their interest in our article . Kountouras et al. raise the question whether Helicobacter pylori infection (Hp-I) could be a potential confounder involved in obstructive sleep apnea (OSA) and gastroesophageal reflux disease (GERD) pathophysiology associated with metabolic syndrome. The concept is interesting as OSA, GERD and metabolic syndrome are all common disorders.

Desaturation during sleep in mild to moderate COPD: A marker of poor sleep quality alone?

Paulo T. Mueller — 2012-02-01

In their interesting and well conducted study on sleep profiles and symptoms of sleep disorders in COPD patients, Valipour et al. found new evidence that nocturnal desaturation is significantly linked to symptoms in independent scales of the questionnaire on sleep disorders in mild to moderate stages of COPD .

Hypoxemia and cardiovascular disease in COPD. Not related to sleep disordered breathing after all

Arschang Valipour, Otto Chris Burghuber — 2012-02-01

Dr. Mueller raised an important point with respect to the potential relationship between sleep disordered breathing and cardiovascular disease in patients with COPD. Referring to findings from their own work , the authors pointed out that nocturnal hypoxemia may be an important determinant of systemic inflammation and, thus, cardiovascular morbidity and mortality in COPD. We have similarly observed elevated circulating levels of interleukin-6 and plasma fibrinogen in patients with stable COPD compared with age-, gender, and body-mass-index matched controls . In fact, systemic inflammatory markers were amongst the most significant predictors of systemic vascular dysfunction and, thus, cardiovascular morbidity and mortality in patients with COPD . However, we did not detect an independent relationship between arterial oxygenation and systemic inflammation in these reports, though we did not assess nocturnal hypoxemia explicitly. Furthermore, we were not able to find a link between the use of long-term oxygen therapy and cardiovascular function in COPD (3), suggesting that chronic hypoxemia may have less direct cardiovascular consequences than systemic inflammation. Thus, we agree with Dr. Mueller that mild nocturnal desaturations may not be able to trigger molecular mechanisms to result in cardiovascular disease in this patient population. Whether other sleep related factors contribute to an increased cardiovascular risk in COPD, such as sleep fragmentation or short sleep duration, remains yet to be determined. The latter, however, would indicate that improving sleep quality in patients with COPD may reduce cardiovascular risk, an unproven hypothesis. The lack of an answer to these and many other questions should trigger future studies in this field and convince clinicians to pay more attention to the role of sleep in chronic respiratory disorders.

News and announcement

2012-02-01