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Sleep Apnea Learning Zone

Obstructive & Positional Obstructive Sleep Apnea

Read time: 40 mins
Last updated:12th Mar 2020

Obstructive sleep apnea (OSA)

Obstructive sleep apnea (OSA) is the most common sleep-related breathing disorder. OSA is characterised by recurrent obstruction of the pharyngeal airway during sleep, resulting in reduced (hypopnea) or complete cessation (apnea) of airflow despite ongoing breathing efforts. These disruptions to breathing lead to intermittent oxygen desaturation, sleep disturbance, and sympathetic activation (Strollo et al., 1996). Consequences of OSA include excessive daytime sleepiness, fatigue, reduced quality of life, increased risk of traffic and occupational accidents and increased risk of developing cardiovascular disease. When patients experience most of their apneic events in the supine sleep position, the term of positional obstructive sleep apnea (POSA) is used.

Visit different sections within the Obstructive Sleep Apnea Learning Zone to find out more about the epidemiology, pathophysiology, symptoms and diagnosis and current treatment options.


Obstructive sleep apnea epidemiology

Before we discuss the epidemiology, let us consider what obstructive sleep apnea (OSA) actually looks like.

Figure 1 shows evidence of snoring on the flow tracing preceding the apneic event during which oxygen saturation progressively falls.


In this example, despite a lowered arousal threshold and progressive increases in EMGgg activity throughout the obstructive event, airflow was not able to be restored without an arousal (awakening) (Eckert & Malhotra, 2008). Learn more about the events that lead to OSA in the pathophysiology section.


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Obstructive sleep apnea pathophysiology

An obstructive sleep apnea (OSA) episode occurs when the soft tissues of the upper airway and tongue relax during sleep and block the flow of air into the lungs. These disruptions to breathing lead to intermittent blood gas disturbances (hypercapnia and hypoxemia) and are associated with increasing respiratory efforts and a brief awakening from sleep (arousal).

Finally, pharyngeal activity is restored, the airway opens and hyperventilation occur in an attempt to recover oxygen and carbon dioxide levels and the patient fall back to sleep (figure 4). This does not happen during wakefulness as there is a protective mechanism which maintain the airway patency (Jyothi et al., 2019).



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Positional sleep apnea pathophysiology

POSA is associated with increased waist-to-hip ratio in men (Heinzer et al., 2018). This suggests that abdominal obesity in men may induce POSA by pulling up the diaphragm in the supine position, which in turn decreases the tension exerted on the pharyngeal walls through the mediastinum, favouring pharyngeal collapse (Heinzer et al., 2018).

In addition, lung volume also plays a role in POSA as a higher positive airway pressure is required to keep the airway open when lung volume is reduced (Heinzer et al., 2005).

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Obstructive sleep apnea symptoms and diagnosis

Obstructive sleep apnea symptoms


Sleep apnea is insidious, and patients are often unaware of their associated symptoms. As a result, it often goes undiagnosed or is first noticed by others due to habitual loud snoring combined with daytime sleepiness.


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Current obstructive sleep apnea treatment options

Treatment is recommended for all patients with an AHI or respiratory-event index of ≥15 events per hour or 5–14 events per hour with symptoms of sleepiness, impaired cognition, mood disturbance or insomnia or with pre-existing conditions such as hypertension, ischaemic heart disease or a history of stroke (Veasey & Rosen, 2019).


Studies have shown evidence for body weight as an important factor in determining the evolution of sleep apnea. In the Sleep Heart Health Study, compared with a stable weight over treatment follow-up, men with a weight gain more than 10 kg had a 5.2-fold increase in AHI. For a comparable gain in weight, women had a 2.5-fold risk of AHI increase (Punjabi et al., 2008). Although weight loss is recommended (ELF, 2019) and known to decrease severity of OSA, it is commonly difficult to achieve and sustain.


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Developed by EPG Health for Medthority in collaboration with Philips, with content provided by Philips.