Definition and epidemiology
Sleep apnea refers to recurrent episodes of partial or complete cessation of airflow during sleep, lasting at least 10 seconds, resulting in fragmented sleep and intermittent hypoxemia. Two main types exist:
- Obstructive sleep apnea (OSA): upper airway collapses despite ongoing respiratory effort. This is by far the most common type.
- Central sleep apnea (CSA): brainstem fails to signal respiratory effort; airway stays open but breathing stops.
OSA affects an estimated 10-30% of adults depending on diagnostic criteria and population studied, with higher prevalence in men, older adults, and those with obesity. Many cases remain undiagnosed. CSA is far less common and usually occurs in the context of heart failure, opioid use, or high-altitude exposure.
- Diagnosis requires AHI ≥5/hr with symptoms or ≥15/hr regardless of symptoms on polysomnography
- Obesity and large neck circumference are the strongest risk factors for OSA
- CPAP is first-line therapy for moderate-severe OSA
- Obstructive events show continued respiratory effort against a closed airway; central events show no effort
- Cheyne-Stokes breathing pattern suggests central sleep apnea, classically with heart failure
- STOP-BANG and Epworth Sleepiness Scale are screening tools, not diagnostic
- Adaptive servo-ventilation is contraindicated in heart failure with reduced ejection fraction and CSA (increased mortality)
- Untreated OSA increases risk of hypertension, atrial fibrillation, stroke, and type 2 diabetes
Etiology and risk factors
Obstructive sleep apnea
- Obesity (strongest modifiable risk factor), particularly central/neck adiposity
- Male sex and postmenopausal status in women
- Craniofacial abnormalities: retrognathia, macroglossia, large tonsils/adenoids (common cause in children)
- Neck circumference greater than 40 cm (about 16 inches)
- Alcohol, sedative, or opioid use before sleep
- Smoking
- Family history
Central sleep apnea
- Heart failure with reduced ejection fraction (Cheyne-Stokes breathing pattern)
- Chronic opioid use
- High altitude
- Stroke or other central nervous system lesions affecting respiratory centers
Pathophysiology
In OSA, pharyngeal muscle tone decreases during sleep (especially REM sleep), and the airway narrows or collapses behind the soft palate or tongue base. Anatomic narrowing from obesity or craniofacial structure increases susceptibility. Airflow cessation causes progressive hypoxemia and hypercapnia, triggering an arousal that restores muscle tone and airway patency, often with a loud snort or gasp. This cycle repeats throughout the night, fragmenting sleep architecture and reducing slow-wave and REM sleep.
Repeated hypoxia and sympathetic surges contribute to systemic effects: increased sympathetic tone, oxidative stress, endothelial dysfunction, and insulin resistance, which drive the long-term cardiovascular and metabolic complications.
In CSA, the problem is a defective ventilatory drive rather than mechanical obstruction. In heart failure, prolonged circulation time and altered chemoreceptor sensitivity produce a cyclical hyperventilation-hypoventilation pattern (Cheyne-Stokes respiration).
Clinical features
- Loud, habitual snoring (often reported by bed partner)
- Witnessed apneic episodes or gasping/choking arousals
- Excessive daytime sleepiness, even after seemingly adequate sleep duration
- Morning headaches
- Nonrestorative sleep, fatigue, impaired concentration
- Nocturia
- Irritability, mood changes, decreased libido
- In children: hyperactivity, poor school performance, failure to thrive rather than classic daytime sleepiness
Examination may reveal obesity, large neck circumference, crowded oropharynx, retrognathia, or enlarged tonsils. Hypertension is common and sometimes resistant to standard therapy.
Diagnosis
Clinical suspicion is often raised using validated screening tools such as the STOP-BANG questionnaire (snoring, tiredness, observed apnea, blood pressure, BMI, age, neck circumference, gender) or the Epworth Sleepiness Scale for daytime sleepiness.
Definitive diagnosis requires sleep testing:
- Polysomnography (PSG): gold standard, performed in a sleep lab, measures airflow, respiratory effort, oxygen saturation, EEG, EMG, and ECG.
- Home sleep apnea testing: acceptable alternative for patients with high pretest probability and no significant comorbidities.
Diagnostic criteria
AHI (average number of apneas plus hypopneas per hour of sleep):
| AHI | Severity |
|---|---|
| 5-14 | Mild |
| 15-29 | Moderate |
| ≥30 | Severe |
Diagnosis is confirmed with AHI ≥5/hr plus symptoms (daytime sleepiness, snoring, witnessed apneas) or AHI ≥15/hr even without symptoms. PSG also distinguishes obstructive events (continued respiratory effort) from central events (absent effort).
Differential diagnosis
- Primary snoring: snoring without significant apneic events, hypoxemia, or daytime symptoms
- Insomnia: difficulty initiating or maintaining sleep rather than sleep fragmentation from apneas
- Narcolepsy: excessive daytime sleepiness with cataplexy, sleep paralysis, hypnagogic hallucinations; distinguished on multiple sleep latency testing
- Hypothyroidism: can cause fatigue and contribute to OSA risk; check TSH if suspected
- Depression: fatigue and poor concentration without the characteristic snoring/apnea pattern
- Restless legs syndrome/periodic limb movement disorder: sleep fragmentation from limb movements rather than respiratory events
- Obesity hypoventilation syndrome: chronic daytime hypercapnia and hypoxemia in obese patients, often coexists with OSA but is a distinct entity
Management
General measures
- Weight loss (even modest reduction improves AHI)
- Avoidance of alcohol, sedatives, and opioids before bedtime
- Positional therapy if apnea is worse in supine position
- Treatment of nasal congestion or allergies if contributing
First-line therapy
Continuous positive airway pressure (CPAP) is first-line for moderate to severe OSA and is the most effective treatment for reducing AHI, improving daytime sleepiness, and lowering blood pressure. Adherence is the main limitation.
Alternatives and adjuncts
- Oral appliances (mandibular advancement devices): option for mild-moderate OSA or for patients who cannot tolerate CPAP
- Bilevel positive airway pressure (BiPAP): used when higher pressures are needed or CPAP is poorly tolerated
- Surgery (uvulopalatopharyngoplasty, adenotonsillectomy in children, maxillomandibular advancement): reserved for anatomic abnormalities or CPAP failure
- Hypoglossal nerve stimulation: an option for select CPAP-intolerant patients with moderate-severe OSA
- Bariatric surgery may be considered in eligible obese patients
Central sleep apnea
Management targets the underlying cause: optimizing heart failure therapy, reducing opioid dose, or adaptive servo-ventilation (used cautiously, as it is contraindicated in patients with heart failure with reduced ejection fraction and CSA due to increased mortality shown in trials). US and European guidelines concur that adaptive servo-ventilation should be avoided in this specific population.
Complications and prognosis
Untreated OSA is associated with:
- Systemic and resistant hypertension
- Increased risk of atrial fibrillation and other arrhythmias
- Coronary artery disease and heart failure
- Pulmonary hypertension and cor pulmonale (severe, longstanding cases)
- Stroke
- Type 2 diabetes and metabolic syndrome
- Motor vehicle accidents due to daytime sleepiness
- Perioperative complications (difficult airway, increased sensitivity to sedatives/opioids)
With effective CPAP use and weight management, daytime symptoms, blood pressure, and cardiovascular risk improve substantially. Prognosis is generally good with adherence to therapy; untreated severe OSA carries meaningfully increased cardiovascular morbidity and mortality.
STOP-BANG for OSA risk screening: Snoring, Tiredness, Observed apnea, blood Pressure, BMI >35 kg/m2, Age >50, Neck circumference >40cm, Gender (male)
Practice questions
1. A 52-year-old man presents with his wife reporting loud snoring and episodes where he stops breathing for brief periods during sleep. He has a BMI of 34 kg/m2 and a neck circumference of 44 cm. He reports falling asleep during meetings. Polysomnography shows an apnea-hypopnea index of 22 events per hour with preserved respiratory effort during events. Which of the following is the most appropriate initial treatment?
2. A 68-year-old woman with a history of heart failure with reduced ejection fraction is found to have a cyclical pattern of waxing and waning tidal volumes alternating with brief apneic pauses on overnight monitoring, with absent respiratory effort during the pauses. Which of the following is true regarding her condition?
3. A 9-year-old boy is brought in due to snoring, mouth breathing, and poor attention at school. Examination reveals markedly enlarged tonsils. His parents deny excessive daytime sleepiness but note he is often irritable and hyperactive. Which of the following is the most likely diagnosis and best next step?
Frequently asked questions
What causes sleep apnea?
Obstructive sleep apnea is caused by repeated collapse of the upper airway during sleep, most often due to obesity, large tonsils, or craniofacial anatomy that narrows the airway. Central sleep apnea is caused by the brain failing to send proper signals to breathing muscles, commonly linked to heart failure, opioid use, or high altitude. Risk is increased by alcohol, sedatives, smoking, and male sex.
What are the first symptoms of sleep apnea?
The earliest and most common symptoms are loud habitual snoring, witnessed pauses in breathing or gasping during sleep, and excessive daytime sleepiness despite seemingly adequate sleep time. Morning headaches, fatigue, poor concentration, and nocturia are also frequent. A bed partner often notices the snoring and apneic episodes before the patient does.
How is sleep apnea diagnosed?
Sleep apnea is diagnosed with a sleep study, either in-lab polysomnography or a home sleep apnea test, which measures breathing pauses, oxygen levels, and sleep stages overnight. Diagnosis is confirmed when the apnea-hypopnea index is 5 or more events per hour with symptoms, or 15 or more per hour even without symptoms. Screening questionnaires like STOP-BANG help identify who should be tested.
Is sleep apnea curable?
Sleep apnea is usually a chronic condition managed rather than cured, though weight loss can significantly reduce or sometimes resolve mild cases. CPAP therapy effectively controls symptoms and reduces health risks but does not permanently fix the underlying airway anatomy, so most patients need ongoing treatment. Surgery or oral appliances can help select patients but are not guaranteed cures either.
Obstructive vs central sleep apnea — what is the difference?
Obstructive sleep apnea involves a physically blocked airway while the body still tries to breathe, so respiratory effort continues against the obstruction. Central sleep apnea involves the brain failing to trigger breathing at all, so there is no respiratory effort during the pause. OSA is far more common and tied to obesity and anatomy, while CSA is often linked to heart failure or opioid use.
Key drugs
Related conditions and differentials
Sources and further reading
StatPearls (NCBI Bookshelf)MedlinePlusWHO ICD-10: G47.3
Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.