Obstructive sleep apnea

Definition

Obstructive sleep apnea consists of repeated episodes of partial or complete closure of the upper airway during sleep. They cause apneas or hypopneas, followed by arousals and hyperpnea. Typical complaints are daytime sleepiness, restless sleep, snoring, recurrent awakening and morning headache.

Occurrence & epidemiology

Obstructive sleep apnea is widespread; an estimated 1 billion people are affected worldwide, most of them undiagnosed. Symptomatic obstructive sleep apnea is present in 8–16 % of adults. Men are affected up to four times and people with obesity (BMI ≥ 30) seven times more often; however, a third of patients are neither overweight nor obese. Frequency rises with the spread of obesity.

Aetiopathogenesis

• Anatomical risk factors: a crowded oropharynx with a short or retruded mandible, prominent tongue base or large tonsils, round head shape and short neck, neck circumference above 43 cm in men or above 41 cm in women, thick lateral pharyngeal walls and parapharyngeal fat pads.
• Other risk factors: postmenopausal status, ageing, overweight and obesity, alcohol or sedatives.
• Contributing conditions: nocturnal gastresophageal reflux, acromegaly, hypothyroidism, previous stroke.
• Familial clustering: 25–40 % of adults have a positive family history (polygenic factors).

Pathophysiology: Sleep destabilizes upper airway patency, so that the nasopharynx and/or oropharynx repeatedly collapse partially or completely. Nocturnal redistribution of edema fluid to the neck when lying down can contribute. The apneas and hypopneas cause hypoxia and hypercapnia and fragment sleep through arousals from NREM and REM sleep. Respiratory efforts against the closed airway generate large intrathoracic pressure swings that impair cardiac output; endothelial and neurotransmitter dysfunction are added.

Clinical features

• Loud, disruptive snoring (in 85 % of patients; most snorers, however, do not have sleep apnea)
• Choking, gasping or snorting during sleep, restless and unrefreshing sleep, difficulty staying asleep; nocturnal symptoms are often first noticed by the bed partner
• Morning sore throat, dry mouth or headache
• Daytime sleepiness, fatigue and poor concentration; not all patients are sleepy
• Findings: signs of nasal obstruction, tonsillar hypertrophy and pharyngeal abnormalities, graded with the modified Mallampati score

Consequences and comorbidities: arterial hypertension (closely associated), heart failure, coronary heart disease, atrial fibrillation and other arrhythmias, stroke and an increased risk of accidents, e.g. in road traffic.

Further consequences

• Metabolic Consequences: Increased risk for insulin resistance and type 2 diabetes.
• Psychological Consequences: Depression, anxiety disorders.

Diagnosis

• History and questionnaires: information from bed partners is helpful. STOP-BANG, the Berlin Questionnaire and the Epworth Sleepiness Scale serve for risk assessment but have low specificity; STOP-BANG and the Berlin Questionnaire are more specific than the Epworth scale and have a good negative predictive value.
• Diagnostic criteria: daytime and/or night-time symptoms together with an apnoea-hypopnea index (AHI) of ≥ 5 per hour, or ≥ 15 per hour without symptoms. An AHI ≥ 15 corresponds to at least moderate sleep apnea.
• In-laboratory polysomnography: the gold standard; records sleep stages (EEG, electro-oculography, chin EMG), airflow at nose and mouth, respiratory effort via chest and abdominal sensors, oxygen saturation, ECG, leg movements, body position and video.
• Home sleep test (polygraphy): few channels (heart rate, pulse oximetry, respiratory effort, position, nasal airflow); may underestimate the breathing disorder, and a negative result with symptoms requires polysomnography.
• TSH: only if hypothyroidism is clinically suspected.

AHI and severity grades

The apnea-hypopnea index (AHI) is the number of apneas and hypopneas per hour of sleep. According to the scoring rules of the American Academy of Sleep Medicine, in adults:

• Apnea: drop in the airflow signal by ≥ 90 % for ≥ 10 seconds.
• Hypopnea: drop by ≥ 30 % for ≥ 10 seconds with an oxygen desaturation of ≥ 3 % or an arousal.
• Severity grades: mild AHI 5 to below 15, moderate 15–30, severe above 30 per hour.

Keep learning in the app

Further reading (open access)

1. MSD Manual Profi-Ausgabe: Obstruktive Schlafapnoe
2. AWMF-Leitlinienregister 063-001: Schlafbezogene Atmungsstörungen
3. StatPearls: Obstructive Sleep Apnea
4. Berry RB et al.: Rules for Scoring Respiratory Events in Sleep – Update of the 2007 AASM Manual (PMC3459210)
5. MSD Manual Professional Edition: Obstructive Sleep Apnea (OSA)

Cross-references