Obstructive Sleep Apnea

Obstructive Sleep Apnea

Nirav P Patel, Richard J Schwab
US Respiratory Disease 2007
Published: October 2008
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Obstructive sleep apnea (OSA) is a highly prevalent disease that represents the most frequent form of sleep-disordered breathing (SDB) encountered, and is associated with serious medical, public health, and economic consequences. The first definitive description of OSA was in 1966 by Gastuaut,1 although descriptions of SDB date back to the 19th century.2

OSA is characterized by repetitive episodes of partial or complete obstruction of the upper airway during sleep, disrupting airflow into the respiratory tract in spite of continued thoracic efforts to breath. The disorder is categorized in two ways:

• hypopnea—manifests as transient decrements causing a reduction in airflow by 25–50%, and is associated with a decrease in oxygen saturation by 3–4% and/or an arousal or fragmentation of sleep; or
• apnea: a cessation of airflow for at least 10 seconds.

Occlusion of the airway institutes several immediate physiological abnormalities: large swings in intra-thoracic pressures associated with continued thoracic effort during airway obstruction compromise left ventricular filling; intermittent hypoxia results in elevations in levels of reactive oxygen species, oxidative stress, and an inflammatory state; and stimulation of the sympathetic nervous system in response to apnea, hypoxia, and arousal results in increased systemic blood pressure and heart rate.2

Definitions
The criteria most commonly employed to assess the frequency of obstructive events is the apnea–hypopnea index (AHI), which is the number of apneas and hypopneas per hour of sleep that can be noted during a sleep study. An AHI >5 suggests the presence of OSA. In the presence of concomitant symptoms such as excessive daytime somnolence, unrefreshing sleep, snoring, or nocturnal choking, the diagnosis of OSA is established. Detailed diagnostic criteria have been published by the American Academy of Sleep Medicine (AASM).3

Epidemiology
There is considerable variation in the population estimates of OSA due to population heterogeneity, differences in methodology in measuring sleep, and variation in thresholds that differentiate abnormal from normal subjects. Estimates of the prevalence of OSA (defined as AHI >5 events/hour) using laboratory polysomnography range between 9 and 28%.4–7 The prevalence of OSA with daytime symptoms is in the region of 5%.4 Several risk factors for OSA have been reported, of which obesity is the most convincing (see Table 1).

Table 1: Risk Factors for Obstructive Sleep Apnea
Risk Factors in Obstructive Sleep Apnea
OSA = obstructive sleep apnea.


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