Sleep Apnea

Introduction

Sleep disordered breathing is an important public health problem. Without adequate high quality sleep people cannot function effectively at home, at work or in the community.

Sleep apnea is the most common of the syndromes described as sleep disordered breathing. It is characterized by episodes of pauses in breathing lasting from 10 to 30 seconds during sleep which sometimes recur hundreds of times a night. With each episode, the brain briefly rouses the sleeper to resume breathing, resulting in a fragmented, poor quality sleep.

The most common form of sleep disordered breathing is obstructive sleep apnea. In this form, episodes occur due to a collapse of soft tissue in the back of the throat which closes off the airway. The blockage can be the result of relaxed throat muscles, a narrow airway, a large tongue or extra fatty tissue in the throat.

Central sleep apnea is a rarer type of sleep apnea. In central sleep apnea the part of the brain that regulates breathing doesn't work properly.

Sleep hypoventilation syndrome is another rare type of sleep disordered breathing that occurs when not enough oxygen is absorbed during sleep.

Risk factors

Obstructive sleep apnea occurs when the loss of upper airway muscle tone during sleep is combined with upper airway narrowing.1 Upper airway size is determined by a variety of factors.

• Obesity is a major risk factor for obstructive sleep apnea. Upper body obesity results in fat deposition both around the airway and in the related soft tissues.
• Hormonal factors influence upper body obesity; this is probably why obstructive sleep apnea is less common in pre-menopausal women than in men or postmenopausal women.
• Increasing age is associated with narrower and possibly more collapsible upper airways.
• Individual variations in jaw, tongue and soft palate size and position contribute to upper airway size. These individual variations are in part genetically determined.2
  Obstructive sleep apnea is also more common in patients who smoke.

Obstructive sleep apnea in children is usually associated with enlarged adenoids or tonsils. It has been suggested that enlarged adenoids or tonsils during childhood may cause abnormal craniofacial development and a narrower adult upper airway.

Central sleep apnea occurs in patients with brain stem abnormalities caused by infection, inflammation or tumour. In other circumstances, it is present at high altitude or secondary to drug or substance abuse. Central sleep apnea is also caused by prolonged circulation time present in patients with cardiac disease and/or abnormal respiratory control secondary to cerebrovascular disease.

Sleep hypoventilation syndrome usually occurs in association with restrictive lung disease in morbidly obese individuals, or with respiratory muscle weakness, or obstructive lung disease such as COPD.

Prevalence

There is a lack of information on the Canadian prevalence of sleep disordered breathing. The Wisconsin Sleep Cohort Study is a landmark population-based prospective study in which polysomnography (an assessment of the quality of sleep and air flow to the nose and mouth during sleep) was performed on a random sample of middle-aged state employees.3 Moderate to severe obstructive sleep apnea was present in 4% of men and 2% of women. Population studies suggest that sleep disordered breathing is at least as prevalent in Canada as in other industrialized nations.4

Central sleep apnea and sleep hypoventilation syndrome are relatively uncommon, but a form of central sleep apnea is quite common in patients with cardiac or neurological disease. One study suggests that 45% of patients with congestive heart failure have sleep disordered breathing.5

The prevalence of sleep disordered breathing in children is not well established. In an Italian study, 1.8% of 1,207 children between the ages of 3 years and 11 years had obstructive sleep apnea.6 The prevalence of sleep disordered breathing in adolescents appears similar to that in younger children.

Health Outcomes

Sleep disordered breathing impairs cognitive function and reduces quality of life. Sleepiness, the hallmark symptom of obstructive sleep apnea, increases the rate of motor vehicle crashes and work-related accidents. Men and women with moderate or severe obstructive sleep apnea are seven times more likely than individuals without obstructive sleep apnea to have multiple motor vehicle crashes in a 5-year period.7 These crash rates return to normal with effective treatment.8

Clinical trial data now show that obstructive sleep apnea is associated with systemic hypertension and that blood pressure falls when severe obstructive sleep apnea is treated with continuous positive airways pressure (CPAP) therapy.9 CPAP works by gently blowing pressurized room air through the airway at a pressure high enough to keep the throat open. Obstructive sleep apnea has also been shown to be an independent risk factor for the development of coronary artery disease.10 Patients with severe obstructive sleep apnea are twice to four times more likely to develop complex arrhythmias, abnormal heart rhythms, than patients without obstructive sleep apnea.11 Cardiac dysfunction can cause sleep disordered breathing, and obstructive sleep apnea can contribute to systolic and diastolic dysfunction. In direct contrast to the general population, patients with obstructive sleep apnea have an increase in death from cardiac causes when asleep.12 A long-term observational study has demonstrated an increased risk of both fatal and non-fatal cardiovascular events in untreated men with severe obstructive sleep apnea.13 Sleep disordered breathing is very common in patients with cerebrovascular disease and is associated with a poorer prognosis. More recent longitudinal data on mortality from stroke found an increasing risk of events with obstructive sleep apnea severity.14 The causative relationship between obstructive sleep apnea and cerebrovascular disease remains circumstantial because of multiple confounding factors.

Economic Impact

Patients with sleep disordered breathing have elevated health care expenditures for many years prior to diagnosis. Patients with sleep disordered breathing use health care services at approximately twice the rate of control subjects prior to diagnosis, and for up to 10 years prior to the diagnosis of sleep disordered breathing15, 16 Sleep hypoventilation syndrome is the sleep disordered breathing syndrome associated with the highest health care expenditures because it often requires hospitalization.17 Direct health care costs of sleep disordered breathing are easier to estimate than indirect costs, which might include effects on the patient’s family, decreased work productivity and work-related and transportation-related accidents.18 The costs for car and other transportation accidents may be substantial. There have been documented railway accidents and fatalities involving Canadian trains operated by personnel with untreated or under-treated sleep disordered breathing.19 The Canadian railway industry now has rigorous guidelines about employees who have been diagnosed with or impaired by sleep disordered breathing.20

CPAP treatment decreases health care expenditures during the first two years after diagnosis of obstructive sleep apnea.21 The cost-effectiveness of medical treatment is usually assessed by the incremental cost-effectiveness ratio, which is the ratio of the incremental costs associated with treatment divided by the incremental quality-adjusted life years (QALY). In a conservative analysis, which included the economic benefits of a reduction in motor vehicle crashes but did not include any potential cardiovascular benefits, CPAP treatment had an incremental cost-effectiveness ratio of $2,618 per QALY over no treatment.22 A ratio of less than $10,000/QALY is generally considered extremely cost-effective.

Diagnosis and Treatment

The Canadian Thoracic Society has recently developed national guidelines for the diagnosis and treatment of sleep disordered breathing.23 As with any medical condition, the diagnosis of sleep disordered breathing starts with history and physical examination. Symptoms of sleep disordered breathing include choking, gasping or snoring during sleep, recurrent awakenings during sleep, unrefreshing sleep, daytime fatigue and impaired concentration. The presence of two or more of these symptoms and the results of polysomnography are used to diagnose the condition. Sleep monitoring results determine the type and severity of the condition.

Conventional CPAP at a fixed pressure is the primary treatment for patients with obstructive sleep apnea. Oral appliances, sometimes called dental appliances, may be an appropriate therapeutic choice for patients with mild-moderate obstructive sleep apnea with minimal daytime symptoms. These devices are intended to treat apnea by keeping the airway open in one of three ways: by pushing the lower jaw forward, by preventing the tongue from falling back over the airway, or by combining both mechanisms. Corrective surgery may be considered for the upper airway in selected patients with obstructive sleep apnea in whom CPAP or oral appliance treatment have been unsuccessful. The intention of surgery is to open the airway sufficiently to eliminate or to reduce obstructions. In order to do this, surgical therapy in adults often must reconstruct the soft tissues (such as the uvula and the palate) or the bony tissues (the jaw) of the throat.

Discussion and Implications

Sleep disordered breathing is common and is associated with reduced quality of life, decreased cardiovascular health and increased health care utilization, transportation accidents and mortality. Though several well-tolerated and effective treatments have been shown to improve quality of life and cardiovascular health and reduce health care utilization and motor vehicle crashes, the majority of Canadians with sleep disordered breathing remain undiagnosed and untreated. Since obesity is a major risk factor for sleep apnea, efforts to promote healthy weights will have the greatest impact on the prevention of this disease.

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8 George CF. Reduction in motor vehicle collisions following treatment of sleep apnoea with nasal CPAP. Thorax 2001;56(7):508-12.

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11 Mehra R, Benjamin EJ, Shahar E, Gottlieb D J, Nawabit R, Kirchner HL, Sahadevan J, Redline S. Association of nocturnal arrhythmias with sleep-disordered breathing: The Sleep Heart Health Study. Am J Respir Crit Care Med 2006 173:910-916.

12 Gami AS, Howard DE, Olson EJ, Somers VK. Day-night pattern of sudden death in obstructive sleep apnea. N Engl J Med 2005;352(12):1206-14.

13 Marin JM, Carrizo SJ, Vicente E, Agusti AG. Long-term cardiovascular outcomes in mean with obstructive sleep apnoea-hypopnea with or without treatment with continuous positive airway pressure: an observational study. Lancet 2005;365:1046-53.

14 Yaggi HK, Concato J, Kernan WN, Lichtman JH, Brass LM, Mohsenin V. Obstructive sleep apnea as a risk factor for stroke and death. N Engl J Med 2005;353:2034-41.

15 Smith R, Ronald J, Delaive K, Walld R, Manfreda J, Kryger MH. What are obstructive sleep apnea patients being treated for prior to this diagnosis? Chest. 2002;121(1):164-72.

16 Shepertycky MR, Banno K, Kryger, MH. Differences between men and women in the clinical presentation of patients diagnosed with obstructive sleep apnea syndrome. Sleep 2005;28:309-14.

17 Berg G, Delaive K, Manfreda J, Walld R, Kryger MH. The use of health-care resources in obesity-hypoventilation syndrome. Chest. 2001;120(2):377-383.

18 Wittmann V, Rodenstein DO. Health care costs and the sleep apnea syndrome. Sleep Med Rev 2004;8(4):269-79.

19 National Transportation Safety Board. Railroad accident report: Collision of two Canadian National/Illinois Central railway trains near Clarkston, Michigan, November 15, 2001. RAR-02/04. Washington, 2002. Available at: http://www.ntsb.gov/Publictn/2002/RAR0204.pdf

20 Railway Association of Canada. Canadian railway medical rules handbook (for positions critical to safe railway operations. Ottawa: the Association, 2001. Available at: http://www.railcan.ca/documents/circulars/
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22 Ayas NT, FitzGerald JM, Fleetham JA, White DP, Schulzer M, Ryan CF, Ghaeli R, Mercer GW, Cooper P, Marra CA. A cost-effectiveness analysis of continuous positive airway pressure (CPAP) therapy versus no CPAP therapy for obstructive sleep apnea hypopnea. Arch Intern Med 2006;166: 977-984.

23 Fleetham J, Ayas N, Bradley D, Ferguson K, Fitzpatrick M, George C, Hanley P, Hill F, Kimoff J, Kryger M, Morrison D, Series F, Tsai W. Canadian Thoracic Society Guidelines: Diagnosis and treatment of sleep disordered breathing in adults. Can Respir J 2006;13(7):387-392.