Coronary collateral circulation in sleep apnea: a cardioprotective mechanism?

Does obstructive sleep apnea increase the risk of cancer and cancer mortality in combined community-based cohorts?

Obstructive sleep apnea (OSA) has been linked to cancer in several clinical and community-based cohorts. The effect in community-based studies free of clinical referral bias needs to be replicated. In this observational prospective cohort study, we pooled data from three community-based prospective cohorts (Uppsala Sleep and Health in Men cohort [UMEN]; Sleep and health in women [SHE]; Men Androgen Inflammation Lifestyle Environment and Stress Cohort [MAILES]; nTotal = 1467). All cohorts had objective data on obstructive sleep apnea and registry linkage data on cancer and cancer mortality. Analyses for different obstructive sleep apnea measures (apnea-hypopnea index [AHI], oxygen desaturation index [ODI], and minimal saturation) as risk factors for cancer incidence (all cancers) were performed using Cox proportional hazards models (follow-up 5-16 years). We did not find an overall increased risk of cancer after adjustment for age, sex, and BMI (HRAHI [95% CI] = 1.00 [0.98; 1.01] and HRODI [95% CI] = 0.99 [0.97; 1.01]). Stratifying by daytime sleepiness did not influence the association. Cancer mortality was not significantly associated with obstructive sleep apnea. Taken together, we did not observe an overall increased risk of cancer or cancer mortality in relation to obstructive sleep apnea, however, our confidence limits remain wide for important diagnostic categories of sleep apnea severity. The relationship between obstructive sleep apnea and cancer needs further investigation in a comprehensive multi-cohort approach with greater statistical precision. For future studies we may need to find and then combine every community-based cohort study that can provide a definitive answer to the question on the risk of cancer from obstructive sleep apnea in the general population.

My voyage in the enchanted world of sleep

In this paper, I describe my 45-year career in sleep research. I started my undergraduate studies at Tel Aviv University, where I was first introduced to the enchanted world of sleep, continued to my graduate studies with Wilse B. Webb at the University of Florida, and then to post-doctoral training with Dan Kripke at the University of California at San Diego. Then, I describe the evolution of my academic career at the Technion-Israel Institute of Technology, where I started in 1975 as an Assistant Professor and retired in 2019 as the President of the Institute. I describe the areas of research that I pursued and how the research developed, emphasizing unexpected results that guided me and my lab team in new directions. This includes my early studies on ultradian rhythms, inspired by Nathaniel Kleitman's Basic Rest Activity Cyle hypothesis, utilizing the ultrashort sleep-wake paradigm to chart the 24-hour sleep propensity function, and how these studies led us to explore the role of melatonin in sleep regulation. I also explain why we directed our attention to sleep apnea, and how clinical observations led to the provocative hypothesis that sleep apnea-typically seen as a disorder-may also play a protective role. Under the leadership of my research partner and wife, Lena, we confirmed this hypothesis. Also in this article, I describe my enthusiasm for the history of our field and, as derived from my experience as a Dean of Medicine and President of a university, I share my philosophy about the role of members of academia in society. I emphasize that none of my achievements could have been accomplished without the hard work and motivation of my students and research partners, who shared my enthusiasm and passion for the enchanted world of sleep. This paper is part of the Living Legends in Sleep Research series, which is sponsored by Idorsia Pharmaceuticals and Jazz Pharmaceuticals.

Markers of Carotid Plaque Destabilization in Patients With Sleep-Disordered Breathing

Sleep-disordered breathing (SDB) is a nightly respiratory condition characterized by intermittent hypoxia, leading to oxidative stress, inflammation, and atherosclerosis. However, most cellular markers of human carotid plaques in SDB have not yet been assessed. We aimed at characterizing the cellular, inflammatory, and nitro-oxidative stress markers in carotid plaques obtained from 25 patients undergoing endarterectomy and screened for SDB. Sleep studies were performed during their preoperative hospitalization night using the Watch-PAT 100 device. Oxygen desaturation index (ODI) was used for dividing patients into two groups. Fourteen patients with ODI >5 were designated as SDB and 11 patients with ODI ≤ 5 as non-SDB. Demographics, comorbidities, cardiovascular risk factors, and medications were recorded. Cellular markers in plaques were analyzed by immunofluorescence using confocal microscopy. The expression of neutrophils was identified by CD66b+ and neutrophil elastase, macrophage-foam cells were identified by CD163+, and scavenger receptors by CD68+ and CD36+ expression. Additional markers included 3-nitrotyrosine, endothelial CD31, and smooth muscle cell-actin (SMC-actin). Plaques' lipids were determined by immunohistochemistry with Oil Red O staining. Notably, significantly higher values were found for SDB as compared to patients with non-SDB for 3-nitrotyrosine (p <0.004) and intracellular lipids' content (p <0.02), whereas SMC-actin was lower (p <0.006). There were no significant differences between patients with carotid-associated symptoms (symptomatic) and patients without carotid-associated symptoms (asymptomatic). However, a sub-group of symptomatic patients with co-existent SDB expressed the highest 3-nitrotyrosin, and intracellular lipids levels, and the lowest SMC-actin levels, whereas non-SDB/asymptomatic patients expressed the lowest 3-nitrotyrosin and lipids levels and the highest SMS-actin levels among all patients. Accordingly, ODI was lowest in non-SDB/asymptomatic patients and highest in SDB/symptomatic. In conclusion, plaques of patients with SDB were characterized by markedly increased levels of 3-nitrotyrosine and intracellular lipids content. Conversely, SMC-actin levels were significantly lower. These three markers, such as increased 3-nitrotyrosine and intracellular lipids and decreased SMC-actin are associated with plaque vulnerability and instability. These findings are in line with earlier reports demonstrating increased intima-media thickness in large cohorts of sleep apnea and patients with SDB, and thus, may indicate a higher susceptibility to plaque vulnerability and rapture in patients with SDB.

Association Between Obstructive Sleep Apnea and Reduced Mortality in Critically Ill Patients: A Propensity Score-Based Analysis

Background

The impact of obstructive sleep apnea (OSA) on the prognosis of intensive care unit (ICU) patients remains controversial. Thus, this study aimed to determine the association between OSA status and outcomes in ICU patients.

Methods

We conducted a retrospective cohort study composed of 38,177 critically ill patients from the Medical Information Mart for Intensive Care III (MIMIC-III) database. Propensity score matching was used to evaluate the association between OSA and mortality in ICU adults.

Results

A total of 38,177 critically ill patients were included in this study. Among them, 1428 (3.71%) patients had OSA. Before matching, patients with OSA had a significantly lower 28-day mortality (relative risk (RR), 0.47; 95% confidence interval (CI), 0.38–0.58), 90-day mortality (RR, 0.50; 95% CI, 0.43–0.60), ICU mortality (RR, 0.41; 95% CI, 0.31–0.54), and in-hospital mortality (RR, 0.46; 95% CI, 0.36–0.57). After adjusting with propensity-score matching, the findings of reduced risk of mortality remained unchanged. The RR of 28-day mortality, 90-day mortality, ICU mortality, in-hospital mortality was 0.57 (95% CI, 0.34–0.57), 0.53 (95% CI, 0.40–0.70), 0.54 (95% CI, 0.37–0.79), and 0.55 (95% CI, 0.39–0.77), respectively.

Conclusion

This study indicated that ICU patients with OSA had a significantly lower risk of mortality compared with those without OSA.

Long-term Effect of CPAP Treatment on Cardiovascular Events in Patients With Resistant Hypertension and Sleep Apnea. Data From the HIPARCO-2 Study

BACKGROUND

There is some controversy about the effect of continuous positive airway pressure (CPAP) on the incidence of cardiovascular events (CVE). However, the incidence of CVE among patients with both obstructive sleep apnea (OSA) ans resistant hypertension (HR) has not been evaluated. Our objective was to analyze the long-term effect of CPAP treatment in patients with RH and OSA on the incidence of CVE.

METHODS

Multi-center, observational and prospective study of patients with moderate-severe OSA and RH. All the patients were followed up every 3-6 months and the CVE incidence was measured. Patients adherent to CPAP (at least 4h/day) were compared with those with not adherent or those who had not been prescribed CPAP.

RESULTS

Valid data were obtained from 163 patients with 64 CVE incidents. Treatment with CPAP was offered to 82%. After 58 months of follow-up, 58.3% of patients were adherent to CPAP. Patients not adherent to CPAP presented a non-significant increase in the total CVE incidence (HR:1.6; 95%CI: 0.96-2.7; p=0.07). A sensitivity analysis showed that patients not adherent to CPAP had a significant increase in the incidence of cerebrovascular events (HR: 3.1; CI95%: 1.07-15.1; p=0.041) and hypertensive crises (HR: 5.1; CI95%: 2.2-11.6; p=0.006), but the trend went in the opposite direction with respect to coronary events (HR: 0.22; CI95%: 0.05-1.02; p=0.053).

CONCLUSIONS

In patients with RH and moderate-severe OSA, an uneffective treatment with CPAP showed a trend toward an increase in the incidence of CVE (particularly neurovascular events and hypertensive crises) without any changes with respect to coronary events.

Intermittent Hypoxia Induced Formation of "Endothelial Cell-Colony Forming Units (EC-CFUs)" Is Affected by ROS and Oxidative Stress

Intermittent hypoxia (IH)—the hallmark of obstructive sleep apnea (OSA)—increases leukocyte activation, production of NADPH-oxidase dependent reactive oxygen species (ROS) and oxidative stress, affecting endothelial function. However, IH and oxidative stress can also stimulate adaptive-protective mechanisms by inducing the development of Endothelial Cell-Colony Forming Units (EC-CFUs), which are considered as a good surrogate marker for endothelial progenitor cells (EPCs), and likely reflect a reparatory response to vascular damage or tissue ischemia by leukocytes. Blood samples were obtained from 15 healthy consenting volunteers to evaluate the effects of IH and sustained hypoxia (SH) in vitro on EC-CFUs development and functions. The variables measured included: their numbers, the area, the proliferative capacity and ROS production. Additionally, NADPH-oxidase, VEGF and nuclear factor-erythroid 2 related factor 2 (Nrf2) expression, as well as their paracrine effects on endothelial tube formation were determined. The involvement of ROS was probed using the anti-oxidant N-acetylcysteine (NAC) and NADPH-oxidase inhibitors apocynin and diphenyl-iodide. Compared to normoxia, IH-dependent increases in EC-CFUs numbers were observed, showing an individual donor-dependent trait. Also, the expression of VEGF and gp91phox, a subunit of NADPH-oxidase, were significantly increased. ROS production and oxidative stress markers were also significantly increased, but Nrf2 expression and colony size were unaffected by IH. Additionally, conditioned media harvested from IH- and SH-treated mature EC-CFUs, significantly increased endothelial tube formation. These effects were markedly attenuated or diminished by the ROS and NADPH-oxidase inhibitors employed. In conclusion, we show here for the first time that IH-associated oxidative stress promotes EC-CFUs' vascular and paracrine capacities through ROS. However, the large inter-individual variability expressed in EC-CFUs numbers and functions to a given IH stimulus, may represent an individual trait with a potential clinical significance.

Estrogen/ERR-α signaling axis is associated with fiber-type conversion of upper airway muscles in patients with obstructive sleep apnea hypopnea syndrome

Estrogen is related with the low morbidity associated with obstructive sleep apnea hypopnea syndrome (OSAS) in women, but the underlying mechanisms remain largely unknown. In this study, we examined the relationship between OSAS and estrogen related receptor-α (ERR-α). We found that the expression levels of ERR-α and Myh7 were both downregulated in palatopharyngeal tissues from OSAS patients. In addition, we report that ERR-α is dynamically expressed during differentiation of C2C12 myoblasts. Knockdown of ERR-α via instant siRNA resulted in reduced expression of Myh7, but not Myh4. Furthermore, differentiation of C2C12 cells under 3% chronic intermittent hypoxia, a model resembling human OSAS, was impaired and accompanied by a obvious reduction in Myh7 expression levels. Moreover, activation of ERR-α with 17β-estradiol (E2) increased the expression of Myh7, whereas pretreatment with the ERR-α antagonist XCT790 reversed the E2-induced slow fiber-type switch. A rat ovariectomy model also demonstrated the switch to fast fiber type. Collectively, our findings suggest that ERR-α is involved in estrogen-mediated OSAS by regulating Myhc-slow expression. The present study illustrates an important role of the estrogen/ERR-α axis in the pathogenesis of OSAS, and may represent an attractive therapeutic target, especially in postmenopausal women.

Impact of Obstructive Sleep Apnea Syndrome on Endothelial Function, Arterial Stiffening, and Serum Inflammatory Markers: An Updated Meta-analysis and Metaregression of 18 Studies

BACKGROUND

Obstructive sleep apnea syndrome (OSAS) has been indicated to contribute to the development of cardiovascular disease; however, the underlying mechanism remains unclear. This study aimed to test the hypothesis that OSAS may be associated with cardiovascular disease by elevating serum levels of inflammatory markers and causing arterial stiffening and endothelial dysfunction.

METHODS AND RESULTS

Related scientific reports published from January 1, 2006, to June 30, 2015, were searched in the following electronic literature databases: PubMed, Excerpta Medica Database, ISI Web of Science, Directory of Open Access Journals, and the Cochrane Library. The association of OSAS with serum levels of inflammatory markers, endothelial dysfunction, and arterial stiffening were investigated. Overall, 18 eligible articles containing 736 patients with OSAS and 424 healthy persons were included in this meta-analysis. Flow-mediated dilation in patients with moderate-severe OSAS was significantly lower than that in controls (standardized mean difference -1.02, 95% CI -1.31 to -0.73, P<0.0001). Carotid-femoral pulse wave velocity (standardized mean difference 0.45, 95% CI 0.21-0.69, P<0.0001), augmentation index (standardized mean difference 0.57, 95% CI 0.25-0.90, P<0.0001), and serum levels of high-sensitivity C-reactive protein and C-reactive protein (standardized mean difference 0.58, 95% CI 0.42-0.73, P<0.0001) were significantly higher in patients with OSAS than in controls.

CONCLUSION

OSAS, particularly moderate-severe OSAS, appeared to reduce endothelial function, increase arterial stiffness, and cause chronic inflammation, leading to the development of cardiovascular disease.

Obstructive sleep apnoea syndrome

Obstructive sleep apnoea syndrome (OSAS) is a common clinical condition in which the throat narrows or collapses repeatedly during sleep, causing obstructive sleep apnoea events. The syndrome is particularly prevalent in middle-aged and older adults. The mechanism by which the upper airway collapses is not fully understood but is multifactorial and includes obesity, craniofacial changes, alteration in upper airway muscle function, pharyngeal neuropathy and fluid shift towards the neck. The direct consequences of the collapse are intermittent hypoxia and hypercapnia, recurrent arousals and increase in respiratory efforts, leading to secondary sympathetic activation, oxidative stress and systemic inflammation. Excessive daytime sleepiness is a burden for the majority of patients. OSAS is also associated with cardiovascular co-morbidities, including hypertension, arrhythmias, stroke, coronary heart disease, atherosclerosis and overall increased cardiovascular mortality, as well as metabolic dysfunction. Whether treating sleep apnoea can fully reverse its chronic consequences remains to be established in adequately designed studies. Continuous positive airway pressure (CPAP) is the primary treatment modality in patients with severe OSAS, whereas oral appliances are also widely used in mild to moderate forms. Finally, combining different treatment modalities such as CPAP and weight control is beneficial, but need to be evaluated in randomized controlled trials. For an illustrated summary of this Primer, visit: http://go.nature.com/Lwc6te.

Obstructive sleep apnea and acute respiratory failure: An analysis of mortality risk in patients with pneumonia requiring invasive mechanical ventilation

PURPOSE

Although obstructive sleep apnea (OSA) is common and pneumonia is a frequent cause of acute respiratory failure requiring admission to the intensive care unit, little is known about the effect of OSA on this patient population. This study examined outcomes associated with OSA in patients with pneumonia requiring invasive mechanical ventilation.

MATERIALS AND METHODS

The Nationwide Inpatient Sample was investigated for discharges with a primary diagnosis of pneumonia requiring invasive mechanical ventilation between 2009 and 2011. Persons aged 18 to 75 years with OSA were compared with patients without OSA. Outcomes included in-hospital mortality and nonroutine discharges.

RESULTS

Among 74032 hospitalizations, 13.8% (10227) were obese, and 10.3% (7610) had OSA. Obstructive sleep apnea patients had decreased in-hospital mortality (17.0% vs 25.8%; P < .01) and nonroutine discharge (74.4% vs 79.4%; P < .01) when compared with non-OSA patients. In adjusted logistic models, OSA was associated with a 27% decreased risk of in-hospital mortality (odds ratio, 0.73; 95% confidence interval, 0.68-0.79; P < .01) and a 21% decreased risk of nonroutine discharge (odds ratio, 0.79; 95% confidence interval, 0.74-0.84; P < .01).

CONCLUSIONS

In mechanically ventilated patients with pneumonia, OSA was associated decreased in-hospital mortality and nonroutine discharge. It is possible that differences in treatment pattern may partially explain improved survival.

Sleep-disordered breathing and postoperative outcomes after bariatric surgery: analysis of the nationwide inpatient sample

BACKGROUND

Sleep-disordered breathing (SDB), also known as obstructive sleep apnea (OSA), has been increasingly recognized as a possible risk factor for adverse perioperative outcomes in non-bariatric surgeries. However, the impact of SDB on postoperative outcomes in patients undergoing bariatric surgery remains less clearly defined. We hypothesized that SDB would be independently associated with worse postoperative outcomes.

METHODS

Data were obtained from the Nationwide Inpatient Sample database and included a total of 91,028 adult patients undergoing bariatric surgeries from 2004 to 2008. The primary outcomes were in-hospital death, total charges, and length of stay. There were two secondary outcomes of interest: respiratory and cardiac complications. Regression models were fitted to assess the independent association between SDB and the outcomes of interest.

RESULTS

SDB was independently associated with decreased mortality (OR = 0.34, 95% CI = 0.23-0.50, p < 0.001), total charges (-$869, p < 0.001), and length of stay (-0.25 days, p < 0.001). SDB was independently associated with significantly increased odds ratio of emergent endotracheal intubation (OR = 4.35, 95% CI = 3.97-4.77, p < 0.001), noninvasive ventilation (OR = 14.12, 95% CI = 12.09-16.51, p < 0.001), and atrial fibrillation (OR = 1.25, 95% CI = 1.11-1.41, p < 0.001). Emergent intubation occurred significantly earlier in the postoperative course in patients with SDB. Although non-SDB patients had an overall lower risk of emergent intubation compared to SDB patients, their outcomes were significantly worse when they did get emergently intubated.

CONCLUSIONS

In this large nationally representative sample, despite the increased association of SDB/OSA with postoperative cardiopulmonary complications, the diagnosis of SDB/OSA was negatively, rather than positively, associated with in-hospital mortality and resource use.

Impact of sleep-disordered breathing treatment on upper airway anatomy and physiology

Sleep-disordered breathing (SDB) is a major public health problem. Various anatomic, pathophysiologic, and environmental changes contribute to SDB. The successful treatment of SDB reverses many of these abnormal processes. The present article discusses the current clinical evidence that supports the reversibility and its potential application in the management of SDB. Continuous positive airway pressure reduces angiogenesis and inflammatory edema, increases pharyngeal size, and improves surrogate markers of vascular inflammation and tongue muscle fiber types. Mandibular advancement devices lead to favorable maxillary and mandibular changes, increase pharyngeal area, and improve hypertension. Uvulopalatopharyngoplasty increases posterior airway space and pharyngeal volume, reduces nasal and oral resistance, and lowers response to high CO2. Weight loss reduces nasopharyngeal collapsibility, critical closing pressure of the airway, apnea-hypopnea index, and improves oxygen saturations. Potential clinical benefits of these changes in the management of SDB and patient compliance with treatment are discussed.

Clinical implications of sleep disordered breathing in acute myocardial infarction

Background

Sleep disordered breathing (SDB), characterized by nightly intermittent hypoxia, is associated with multiple pathophysiologic alterations that may adversely affect patients with acute myocardial infarction (AMI). This prospective study investigated whether the metabolic perturbations associated with SDB are present when these patients develop AMI and if they affect clinical outcomes.

Methods

We prospectively enrolled 180 AMI patients. SDB was defined as oxygen desaturation index (ODI) >5 events/hour based on a Watch Pat-100 sleep study. Blood samples were obtained for high-sensitivity C-reactive protein (hs-CRP) and markers of oxidative stress (lipid peroxides [PD] and serum paraoxonase-1 [PON-1] (arylesterase activity). Echocardiography was performed to evaluate cardiac dimensions and pulmonary artery systolic pressure.

Results

SDB was present in 116 (64%) patients. Hs-CRP levels, PD and PON-1 were similar in patients with and without SDB. Echocardiography revealed higher left atrial dimension (4.1±0.5 vs 3.8±0.5 cm; P = 0.003) and a significant positive correlation between ODI and pulmonary artery systolic pressure (r = 0.41, P<0.0001). After a median follow up of 68 months, no significant differences were observed between the study groups with regard to clinical outcomes, including death, heart failure, myocardial infarction and unstable angina.

Conclusion

There is a high prevalence of previously undiagnosed SDB among patients with AMI. SDB in the setting of AMI is associated with higher pulmonary artery systolic pressure. SDB was not associated with adverse clinical outcomes.

Sleep-disordered breathing and postoperative outcomes after elective surgery: analysis of the nationwide inpatient sample

BACKGROUND

Systematic screening and treatment of sleep-disordered breathing (SDB) or obstructive sleep apnea (OSA) in presurgical patients would impose a significant cost burden; therefore, it is important to understand whether SDB is associated with worse postoperative outcomes. We sought to determine the impact of SDB on postoperative outcomes in patients undergoing four specific categories of elective surgery (orthopedic, prostate, abdominal, and cardiovascular). The primary outcomes were in-hospital death, total charges, and length of stay (LOS). Two secondary outcomes of interest were respiratory and cardiac complications.

METHODS

Data were obtained from the Nationwide Inpatient Sample database. Regression models were fitted to assess the independent association between SDB and the outcomes of interest.

RESULTS

The cohort included 1,058,710 hospitalized adult patients undergoing elective surgeries between 2004 and 2008. SDB was independently associated with decreased mortality in the orthopedic (OR, 0.65; 95% CI, 0.45-0.95; P = .03), abdominal (OR, 0.38; 95% CI, 0.22-0.65; P = .001), and cardiovascular surgery groups (OR, 0.54; 95% CI, 0.40-0.73; P &lt; .001) but had no impact on mortality in the prostate surgery group. SDB was independently associated with a small, but statistically significant increase in estimated mean LOS by 0.14 days (P &lt; .001) and estimated mean total charges by $860 (P &lt; .001) in the orthopedic surgery group but was not associated with increased LOS or total charges in the prostate surgery group. In the abdominal and cardiovascular surgery groups, SDB was associated with a significant decrease in adjusted mean LOS of 1.1 days and 0.35 days, respectively (P &lt; .001 for both groups), and adjusted mean total charges of $3,814 and $4,592, respectively (P &lt; .001 for both groups). SDB was independently associated with a significantly increased OR for emergent intubation and mechanical ventilation, noninvasive ventilation, and atrial fibrillation in all four surgical categories. Emergent intubation occurred significantly earlier in the postoperative course in patients with SDB. In the subgroup of patients requiring emergent intubation, LOS, total charges, pneumonias, and in-hospital death were significantly higher in those without SDB.

CONCLUSIONS

In this large national study, despite the increased independent association of SDB with postoperative cardiopulmonary complications, the diagnosis of SDB was not independently associated with an increased rate of in-hospital death. SDB had a mixed impact on LOS and total charges by surgical category.

Obstructive sleep apnea: no independent association to troponins

BACKGROUND

Cardiac troponins (cTn) are to date the most sensitive and specific biochemical markers of myocardial injury. Abnormal breathing patterns in patients with obstructive sleep apnea (OSA) may cause myocardial cell stress detectable by novel cTn assays. The objectives of this study were to investigate whether a new single-molecule cTnI (S-cTnI) assay and a commercially available high-sensitivity cTnT (hs-cTnT) assay would detect myocyte injury in individuals evaluated for possible OSA, and to explore their relation to variables of disordered breathing during sleep.

METHODS

Consecutive individuals referred to Lovisenberg Diakonale Hospital's sleep laboratory between 1 October 2009 and 1 March 2010 were included. We measured cTn in specimens collected the morning after sleep and studied these in relation to variables recorded during polygraphy or polysomnography.

RESULTS

All 222 (100 %) individuals had measurable cTn levels using either assay. Stratified into categories according to the apnea-hypopnea index (AHI), patients with OSA (AHI ≥5) had a different distribution of S-cTnI (P = 0.036) and hs-cTnT (P = 0.002) compared to those without (AHI <5). The median (quartiles 1-3) were 3.0 (1.9-6.0) versus 2.3 (1.6-3.8) ng/l for S-cTnI, and 7.0 (5.5-8.7) versus 6.2 (4.9-7.2) ng/l for hs-cTnT. However, in multiple median regression analyses adjusted for conventional predictors, neither S-cTnI (P = 0.57) nor hs-cTnT (P = 0.80) were significantly associated with AHI.

CONCLUSIONS

This study reveals no association independent of conventional predictors between OSA and myocardial cell injury measured by S-cTnI and hs-cTnT assays. Our findings support a search for novel biomarkers for prognostication of OSA.

Untreated obstructive sleep apnea and the risk for serious long-term adverse outcomes: a systematic review

BACKGROUND

Reports on the association between obstructive sleep apnea (OSA) and risk of death, cardiovascular (CV) events, diabetes and depression have been inconsistent.

METHODS

We conducted a systematic review of the prognostic value of clinical and polysomnographic (PSG) characteristics of OSA for adverse long-term outcomes of untreated OSA in adult patients. A comprehensive search strategy for prognosis studies, OSA, CV events, mortality, depression and diabetes was developed in collaboration with a medical information specialist. All English language studies, from Jan 1999 to Dec 2011, with longitudinal design in adults with OSA diagnosed by PSG recording, found through Medline, Embase and bibliographies of identified articles, were considered eligible. Quality was assessed using published guidelines.

RESULTS

Among 26 articles, ten evaluated the association of OSA with mortality, 9 with a composite CV outcome, 4 with stroke, 2 with diabetes and 1 with depression. Significant relationships between the apnea-hypopnea index (AHI) and outcomes of interest were reported in 18 studies: seven for all-cause mortality, six for composite CV events, three for stroke, one for diabetes and one for depression. The effect of AHI was attenuated by female gender, older age, absence of daytime sleepiness and higher body mass index. Due to clinical heterogeneity between studies, meta-analyses were not performed.

CONCLUSION

Evidence exists in men for a relationship between OSA and all-cause mortality and a composite CV outcome. Associations between OSA and other outcomes remain uncertain. Among OSA-specific markers, only AHI was a consistent predictor. Other consistent predictors were traditional CV risk factors. Research is required to identify effect modifiers and the predictive ability of various AHI threshold values and hypopnea definitions. An enhanced set of OSA-specific predictors will allow better risk stratification to guide OSA treatment.

Endothelial progenitor cells in cardiovascular disease and hypoxia--potential implications to obstructive sleep apnea

In recent years, endothelial progenitor cells (EPCs) have gained a central role in vascular regeneration and endothelial repair capacity through angiogenesis and restoring endothelial function of injured blood vessels. These bone-marrow-derived cells are capable of promoting neovascularization, improving blood perfusion, and facilitating the recovery of ischemic tissues through differentiation into functional endothelial cells and secretion of angiogenic mediators. Obstructive sleep apnea (OSA) syndrome is characterized by recurrent episodes of intermittent hypoxia (IH), which can lead to endothelial dysfunction, atherosclerosis, as well as cardiovascular morbidity and mortality. However, IH also may contribute to cardioprotection and the development of collateral vessels by mobilizing progenitor cells to the circulation and damaged myocardium. Accumulating evidence in recent years suggests that EPCs are decreased in patients with endothelial dysfunction and underlie an increased risk for cardiovascular morbidity in OSA. The current review highlights the potential role of EPCs in the pathogenesis of vascular diseases that is pertinent to OSA.