Issue 9, 2009
HOT TOPICS IN RESPIRATORY MEDICINE
Sleep apnea: a new epidemic
Most physicians are aware that obstructive sleep apnea syndrome (OSAS) is associated with increased mortality rates, especially among younger adults. This issue of Hot Topics in Respiratory Medicine examines the burden of this condition, focusing on: 1) the latest epidemiological findings; 2) key points for understanding the pathophysiological mechanisms, cardiovascular disease associations, and outcomes; and 3) current treatment options. In the first chapter, Professor Carlos Zamarrón of Santiago de Compostela University, Spain, reviews the wide spectrum of clinical studies performed to date, from the earliest epidemiological investigations to recent large cohort studies, and their contribution to the understanding of the natural history and adverse health consequences of OSAS. Dr. Hisham Elsaid and Professor Frances Chung of the University of Toronto, Canada, who are strongly concerned about the high prevalence of undiagnosed OSAS in the general population, provide a comprehensive review of etiologic and predisposing factors. They then discuss screening tools for OSAS, mainly the most relevant questionnaires validated to date, and the need for their use in the preoperative setting. Concerning the connection of OSAS to cardiovascular disease, Dr. Kannan Ramar and Dr. Sean M. Caples of the Pulmonary and Critical Care Division at Mayo Clinic, Rochester, USA, detail how these repetitive and persistent apnea events are associated with oxyhemoglobin desaturation followed by central nervous system arousal. This complicated pathophysiologic mechanism, scrupulously described by the authors, is responsible for systemic hypertension, heart failure, stroke and cardiac arrhythmias. In this context, the authors highlight the potential implications for therapy. Interestingly, this topic is approached in the last chapter of the volume. The Spanish professors Dr. Josep M. Monserrat (Hospital Clínic, Barcelona) and Dr. Francisco Capote (Hospital Virgen del Rocío, Sevilla) focus on treatment of OSAS, and discuss the most notable recently published data, from conservative treatment to positive airway pressure, concluding with novel advances in surgical and medical choices.
Table of contents
Why an issue on sleep apnea? A simple answer is that sleep apnea is now known to be associated with increased mortality rates, especially in younger patients. As physicians, we need to be aware of the condition, be able to identify individuals at risk, be able to perform reliable diagnosis with methods that are within reach in terms of both practicality and cost, and be able to give all patients a chance of treatment, especially those of low socioeconomic status. However, the role of obstructive sleep apnea (OSA) in determining comorbidities or excess deaths has been disputed in the past . Many recent studies, performed on clinical and general population samples, have demonstrated an excess of deaths in patients with moderate to severe sleep apnea, especially in the younger cohorts (usually <60 years old) [2-4].
The term "new epidemic" is appropriate because recent epidemiological studies demonstrated that about one quarter of the general population older than 30 years suffers from sleep-disordered breathing (SDB), and that in 2% of females and 4% of males the presence of SDB and clinical symptoms has been found. Of course, this new epidemic could be attributed to the "obesity pandemic", as excess weight is the strongest contributing factor for the development of sleep apnea. However, it was recently demonstrated that only 40-50% of sleep apnea incidence could be attributed to excess weight.
Sleep apnea has many pathological consequences, including cardiovascular disease, sleep fragmentation, reduction in quality of life, daytime sleepiness, increased risk for motor vehicle accidents, and, finally, chronic respiratory failure with cor pulmonale, especially in patients with other respiratory comorbidities.
The diagnosis of OSA requires a clinical assessment and an overnight sleep study. Full-standard laboratory polysomnography has long been considered the only tool to diagnose sleep apnea, but it is expensive, requiring highly trained personnel and sophisticated equipment, too. Therefore, sleep laboratories have long waiting lists for in-lab polysomongraphy, resulting in delays to diagnosis and treatment. Fortunately, different diagnostic tools are now available for patients with a high probability of OSA, based on clinical assessment associated with the use of portable monitors such as portable polysomnography, cardiorespiratory monitoring or devices for photoplethysmographic or pulse-transit-time recording .
Continuous positive airway pressure (CPAP)-treated patients compliant with treatment had mortality rates similar to those recorded in the general population, and the major determinant of long-term outcome was compliance with CPAP treatment rather than severity of OSA at diagnosis . These data stress that great effort should be expended to achieve early diagnosis of this condition, thus affording effective treatment.
However, the new protocol proposed for the identification of respiratory events during sleep may result in a lower sensitivity. The new definition of hypopnea—any discernible reduction of airflow associated with a desaturation of >4% —and the use of portable monitors result in an underestimation of the number of identified respiratory events. As a result of this bias, the apnea-hypopnea index is also underestimated in patients with relevant symptoms, leading to delays in starting adequate therapy [8,9].
In conclusion, this new issue summarizes the latest findings on the epidemiology of OSA as well as developments in screening tools and therapeutic strategies that may help clinicians in their diagnosis and treatment of this important sleep disorder.
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2. Marin JN, Carrizo SJ, Vicente E, Agust AGN. Long-term cardiovascular outcomes in men with obstructive sleep apnoea-hypopnoea with or without treatment with continuous positive airway pressure: an observational study. Lancet 2005;365:1046–1053.
3. Marshall NS, Wong KKH, Liu PY, Cullen SRJ, Knuiman MW, Grunstein RR. Sleep apnea as an independent risk factor for all-cause mortality: The Busselton Health Study. Sleep 2008;31:1079-1085.
4. Young T, Finn L, Peppard P, et al. Sleep-disordered-breathing and mortality: Eighteen-year follow-up of the Wisconsin Sleep Cohort. Sleep 2008;31:1071-1078.
5. Collop NA, Anderson WM, Boehlecke B, et al. Clinical guidelines for the use of unattended portable monitors in the diagnosis of obstructive sleep apnea in adult patients. J Clin Sleep Med 2007;3:737-747.
6. Campos-Rodriguez F, Pena-Grinan N, Reyes-Nunez N, et al. Mortality in obstructive sleep apnea-hypopnea patients treated with positive airway pressure. Chest 2005;128:624–633.
7. Iber C, Ancoli-Israel S, Chesson AL, Quan SF. The AASM manual for the scoring of sleep and associated events: rules, terminology, and technical specifications, 1st ed. American Academy of Sleep Medicine. Westchester, IL, 2007.
8. Ruehland WR, Rochford PD, O’Donoghue FJ, Pierce RJ, Singh P, Thomton AT. The new AASM criteria for scoring hypopneas: impact on the apnea hypopnea index. Sleep 2009;32:150-157.
9. Masa JF, Corral J, Teran J, et al. Apneic and obstructive non-apneic sleep respiratory events (ONEs). Eur Respir J 2009 Feb 12. [Epub ahead of print]
Prevalence of sleep apnea in adults
Screening adults for obstructive sleep apnea
Frances Chung, Hisham Elsaid
Sleep-disordered breathing and cardiovascular disease
Sean M. Caples, Kannan Ramar
Advances in the treatment of sleep apnea
Francisco Capote, Josep M. Montserrat
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Marc Miravitlles - MD
Over the last 15 years there has been a decrease in mortality due to preventable diseases, with the exception of chronic obstructive pulmonary disease (COPD), which is an example that highlights the r...