Medicine – Obstructive Sleep Apnoea

Obstructive sleep apnoea (OSA) is a common sleep-related breathing disorder characterised by recurrent episodes of partial or complete upper-airway obstruction during sleep. These episodes cause intermittent hypoxaemia, sleep fragmentation, and repeated arousals, which can result in significant daytime symptoms and long-term cardiovascular and metabolic complications.

1. Epidemiology

OSA is particularly common in middle-aged men, although it can occur in both sexes and at any age. Older teaching often quoted a prevalence of approximately 1–2%, but modern studies suggest that OSA is substantially more common, particularly when milder disease is included.

Risk increases with age, obesity, male sex, and abnormalities that narrow the upper airway. In women, prevalence rises after menopause.

2. Apnoeic Episodes

An apnoea is a period of complete or near-complete cessation of airflow lasting at least 10 seconds. OSA severity is now assessed primarily using the apnoea–hypopnoea index (AHI), which measures the average number of apnoeas and hypopnoeas occurring per hour of sleep.

An AHI of 5–14 events/hour is mild, 15–29 is moderate, and ≥30 is severe OSA, when interpreted together with the clinical context. Therefore, the older definition of “10 or more apnoeas per hour” should not be used as the sole modern diagnostic criterion.

3. Relationship to Sleep Stage

Obstructive events may occur during any stage of sleep, but they can become particularly frequent or severe during rapid eye movement (REM) sleep.

During REM sleep, physiological reduction in skeletal muscle tone can further decrease the activity of muscles responsible for maintaining upper-airway patency.

4. Mechanism of Airway Obstruction

During sleep, the muscles supporting the upper airway relax. In susceptible individuals, this allows the airway to become narrowed or completely obstructed, commonly around the base of the tongue and soft palate/pharynx.

The patient continues making respiratory efforts against the obstructed airway. Falling oxygen levels and rising respiratory effort eventually trigger a brief arousal, restoring muscle tone and reopening the airway. This cycle may occur repeatedly throughout the night, causing severe sleep fragmentation.

5. Clinical Features

Heavy snoring is one of the most characteristic features of OSA. Sleep may be restless, and a partner may report episodes in which the patient stops breathing, followed by gasping, choking, or loud snoring when breathing resumes.

Repeated sleep disruption causes excessive daytime sleepiness, impaired concentration, reduced attention, irritability, and poor work performance. Severe daytime somnolence can increase the risk of road traffic and occupational accidents.

Morning headache may also occur. Other possible features include waking with a dry mouth, nocturia, reduced libido, and unrefreshing sleep despite apparently spending an adequate amount of time in bed.

6. Causes and Predisposing Factors

Obesity is the most important modifiable risk factor for OSA. Excess soft tissue around the neck and pharynx narrows the upper airway and makes it more susceptible to collapse during sleep.

Alcohol can worsen OSA because it reduces upper-airway muscle tone and may suppress normal arousal responses. Symptoms are therefore often more severe after drinking alcohol, particularly close to bedtime.

Acromegaly predisposes to OSA through enlargement of the tongue and other upper-airway soft tissues. Craniofacial and pharyngeal changes can further narrow the airway.

Hypothyroidism is another recognised association. Soft-tissue changes, weight gain, and reduced ventilatory function may contribute to upper-airway obstruction.

7. Diagnosis

The Epworth Sleepiness Scale can be used to assess the degree of daytime sleepiness, but it is a screening and symptom-assessment tool rather than a diagnostic test for OSA.

Overnight pulse oximetry may demonstrate repeated episodes of oxygen desaturation and can support further investigation. However, definitive assessment generally requires an overnight sleep study, using either home respiratory polygraphy or laboratory polysomnography depending on the clinical situation.

The sleep study allows calculation of the AHI and provides information about the frequency and severity of respiratory disturbances.

8. Treatment

Weight loss is particularly important in overweight or obese patients and can substantially reduce the severity of OSA. Patients should also reduce or avoid alcohol, particularly before bedtime, and address other contributing factors where possible.

Continuous positive airway pressure (CPAP) is a major treatment for clinically significant OSA. A mask delivers positive airway pressure during sleep, effectively acting as a pneumatic splint that prevents collapse of the upper airway.

Other selected patients may benefit from mandibular advancement devices, positional therapy, or upper-airway surgery, depending on the severity and anatomical cause of the obstruction.

Key Clinical Pattern

Think of obstructive sleep apnoea in a patient—particularly one with obesity—who has loud snoring, witnessed apnoeas or nocturnal choking, unrefreshing sleep, morning headaches, and excessive daytime sleepiness.

The underlying problem is recurrent upper-airway collapse during sleep. Diagnosis is established with appropriate sleep testing, while treatment commonly involves weight reduction and CPAP, together with management of contributing factors such as alcohol use and endocrine disorders.

1. Epidemiology OSA is particularly common in middle-aged men, although it can occur in both sexes and at any age. Older teaching often quoted a prevalence of approximately 1–2%, but modern studies suggest that OSA is substantially more common, particularly when milder disease is included. Risk increases with age, obesity, male sex, and abnormalities that narrow the upper airway. In women, prevalence rises after menopause. 

2. Apnoeic Episodes An apnoea is a period of complete or near-complete cessation of airflow lasting at least 10 seconds. OSA severity is now assessed primarily using the apnoea–hypopnoea index (AHI), which measures the average number of apnoeas and hypopnoeas occurring per hour of sleep. An AHI of 5–14 events/hour is mild, 15–29 is moderate, and ≥30 is severe OSA, when interpreted together with the clinical context. Therefore, the older definition of “10 or more apnoeas per hour” should not be used as the sole modern diagnostic criterion. 

3. Relationship to Sleep Stage Obstructive events may occur during any stage of sleep, but they can become particularly frequent or severe during rapid eye movement (REM) sleep. During REM sleep, physiological reduction in skeletal muscle tone can further decrease the activity of muscles responsible for maintaining upper-airway patency. 

4. Mechanism of Airway Obstruction During sleep, the muscles supporting the upper airway relax. In susceptible individuals, this allows the airway to become narrowed or completely obstructed, commonly around the base of the tongue and soft palate/pharynx. The patient continues making respiratory efforts against the obstructed airway. Falling oxygen levels and rising respiratory effort eventually trigger a brief arousal, restoring muscle tone and reopening the airway. This cycle may occur repeatedly throughout the night, causing severe sleep fragmentation. 

5. Clinical Features Heavy snoring is one of the most characteristic features of OSA. Sleep may be restless, and a partner may report episodes in which the patient stops breathing, followed by gasping, choking, or loud snoring when breathing resumes. Repeated sleep disruption causes excessive daytime sleepiness, impaired concentration, reduced attention, irritability, and poor work performance. Severe daytime somnolence can increase the risk of road traffic and occupational accidents. Morning headache may also occur. Other possible features include waking with a dry mouth, nocturia, reduced libido, and unrefreshing sleep despite apparently spending an adequate amount of time in bed. 

6. Causes and Predisposing Factors Obesity is the most important modifiable risk factor for OSA. Excess soft tissue around the neck and pharynx narrows the upper airway and makes it more susceptible to collapse during sleep. Alcohol can worsen OSA because it reduces upper-airway muscle tone and may suppress normal arousal responses. Symptoms are therefore often more severe after drinking alcohol, particularly close to bedtime. Acromegaly predisposes to OSA through enlargement of the tongue and other upper-airway soft tissues. Craniofacial and pharyngeal changes can further narrow the airway. Hypothyroidism is another recognised association. Soft-tissue changes, weight gain, and reduced ventilatory function may contribute to upper-airway obstruction. 

7. Diagnosis The Epworth Sleepiness Scale can be used to assess the degree of daytime sleepiness, but it is a screening and symptom-assessment tool rather than a diagnostic test for OSA. Overnight pulse oximetry may demonstrate repeated episodes of oxygen desaturation and can support further investigation. However, definitive assessment generally requires an overnight sleep study, using either home respiratory polygraphy or laboratory polysomnography depending on the clinical situation. The sleep study allows calculation of the AHI and provides information about the frequency and severity of respiratory disturbances. 

8. Treatment Weight loss is particularly important in overweight or obese patients and can substantially reduce the severity of OSA. Patients should also reduce or avoid alcohol, particularly before bedtime, and address other contributing factors where possible. Continuous positive airway pressure (CPAP) is a major treatment for clinically significant OSA. A mask delivers positive airway pressure during sleep, effectively acting as a pneumatic splint that prevents collapse of the upper airway. Other selected patients may benefit from mandibular advancement devices, positional therapy, or upper-airway surgery, depending on the severity and anatomical cause of the obstruction. 

Key Clinical Pattern Think of obstructive sleep apnoea in a patient—particularly one with obesity—who has loud snoring, witnessed apnoeas or nocturnal choking, unrefreshing sleep, morning headaches, and excessive daytime sleepiness. The underlying problem is recurrent upper-airway collapse during sleep. Diagnosis is established with appropriate sleep testing, while treatment commonly involves weight reduction and CPAP, together with management of contributing factors such as alcohol use and endocrine disorders.