Obstructive Sleep Apnea–Hypopnea Syndrome

General Principles


Obstructive sleep apnea (OSA) is a disorder in which patients experience apneas or hypopneas because of upper airway narrowing. When it is associated with excessive daytime somnolence, it is referred to as obstructive sleep apnea–hypopnea syndrome (OSAHS).1


  • Apneas represent complete cessation of airflow.
    • Obstructive events are associated with continued respiratory effort.
    • Central events are associated with no respiratory effort.
  • Hypopneas represent diminished airflow associated with at least a 3%–4% oxygen desaturation.
  • Respiratory effort–related arousals (RERAs) represent changes in airflow that lead to an arousal, but do not meet criteria for an apnea or hypopnea.
  • All respiratory events must last at least 10 seconds to be counted.
  • Apnea–hypopnea index (AHI) is the number of apneas and hypopneas per hour of sleep.
  • Respiratory disturbance index (RDI) is the number of apneas, hypopneas, and RERAs per hour of sleep.


  • The prevalence of OSAHS in the general population is estimated to be about 4%, with men being twice as likely as women to be affected.2
  • Obesity is a significant risk factor for OSA.2
  • Given the significant increase in the prevalence of obesity since the original epidemiological studies on OSA were performed, it is estimated that the current prevalence of moderate OSA as defined by an AHI > 15 is 13% in men and 6% in women.3


  • OSA: Narrowing of the upper airway because of excessive soft-tissue or structural abnormalities.
  • Central sleep apnea: Disturbance of central control of respiration during sleep.


OSA occurs because of narrowing of the upper airway, which results in diminished airflow or cessation of airflow leading to arousals that fragment sleep.

Risk Factors

Risk factors for OSA include obesity (body mass index [BMI] > 30 kg/m2), large neck circumference (>17 in for men and >16 in for women), increased soft tissue of the posterior oropharynx (enlarged tonsils, macroglossia, or elongated uvula), and abnormal jaw structure (micrognathia or retrognathia). Patients with comorbid conditions such as congestive heart failure, coronary artery disease, atrial fibrillation (AFib), difficult-to-control hypertension, and diabetes are also more likely to have OSA.4


  • Weight loss
  • Avoiding sedatives such as hypnotic medications or alcohol

Associated Conditions

  • Cardiovascular disease, including systemic hypertension, heart failure, arrhythmia, myocardial infarction, and stroke.5 OSA has been established as an independent risk factor for hypertension.6
  • Increased risk of death in moderate-to-severe OSA, mainly because of cardiovascular events.7,8
  • Increased prevalence of diabetes has been noted in patients with OSAHS, independent of the effect of obesity.9
  • There is approximately a 2.5-fold increased risk of motor vehicle accidents (MVA) in patients with OSA when compared with those without OSA. However, compliance with continuous positive airway pressure (CPAP) treatment can significantly reduce the risk of MVA in patients with OSA.10

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