Where does the obstruction occur in obstructive sleep apnea (OSA)?

Anatomical Location of Obstruction in Obstructive Sleep Apnea

In obstructive sleep apnea (OSA), the primary site of airway closure is most frequently located in the velopharynx (nasopharynx), but obstruction can also occur in the oropharynx and/or hypopharynx, often involving multiple sites simultaneously. 1

Primary Sites of Obstruction

The pharyngeal airway is the main location where obstruction occurs in OSA, with specific sites including:

1. Velopharynx (Nasopharynx):

   • Primary site of closure in approximately 80% of OSA patients 1, 2
   • Located behind the soft palate

2. Oropharynx:

   • Common secondary site of obstruction
   • Located behind the oral cavity

3. Hypopharynx:

   • Located at the base of the tongue
   • Often involved as a secondary site of obstruction

Patterns of Obstruction

Research shows that multiple sites of obstruction are common in OSA patients (82%), with four main patterns identified 2:

• Primary narrowing only at the nasopharynx (18%)
• Primary narrowing at the nasopharynx plus other sites of secondary narrowing (40%)
• Primary narrowing at the nasopharynx plus other sites of primary narrowing (22%)
• Other patterns (20%)

Mechanism of Obstruction

The collapse of the pharyngeal airway during sleep occurs due to:

• Loss of upper airway muscle activity during sleep 1
• Positive closing pressure in the pharynx (unlike the normal subatmospheric pressure) 1
• Transmission of subatmospheric intrathoracic pressure into the pharyngeal airway 1

Contributing Factors

Several factors contribute to upper airway obstruction in OSA:

• Obesity
• Craniofacial abnormalities
• Altered upper airway muscle function
• Pharyngeal neuropathy
• Fluid shift toward the neck 3

Clinical Implications

Understanding the site of airway closure is clinically important because:

1. It determines the outcome of surgical interventions such as uvulopalatopharyngoplasty 1
2. It guides the selection of appropriate treatment modalities
3. It explains why nasal obstruction can worsen OSA (patients with nasal obstruction tend to breathe through the mouth, promoting more negative intraluminal pressure in the pharynx) 1

Diagnostic Approaches

The site of pharyngeal airway closure during sleep can be determined by:

• Placement of catheters with pressure transducers at different levels in the pharyngeal airway 1
• Imaging the upper airway with fiberoptic scope during sleep 1
• Fast acquisition MRI or computed tomography scans 1

Understanding the anatomical location of obstruction in OSA is crucial for effective treatment planning, particularly when considering surgical interventions or determining the most appropriate positive airway pressure therapy approach.