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Airway obstruction is a respiratory problem caused by increased resistance in the bronchioles (usually from a decreased radius of the bronchioles) that reduces the amount of air inhaled in each breath and the oxygen that reaches the pulmonary arteries. It is different from airway restriction (which prevents air from diffusing into the pulmonary arteries because of some kind of blockage in the lungs).

Obstruction can be measured using spirometry. A decreased FEV1/VC ratio (versus the normal of about 80%) is indicative of an airway obstruction, as the normal amount of air can no longer be exhaled in the first second of expiration. An airway restriction would not produce a reduced FEV1/VC ratio, would produce a reduced vital capacity. The ventilation is therefore affected leading to a ventilation perfusion mismatch and hypoxia.

Possible causes include:

  • Foreign bodies (e.g., aspirated peanut, aspirated wire)
  • Tumor formation (e.g., laryngeal papillomatosis, squamous cell carcinoma)
  • Infections (e.g., epiglottitis, retropharyngeal abscess, croup)
  • Airway edema (e.g., following instrumentation of the airway intubation, drug side effect, allergic reaction)
  • Laryngomalacia (the most common congenital cause of stridor)
  • Vascular rings compressing the trachea
  • Abnormalities of vocal cord function
  • Tracheomalacia or Tracheobronchomalacia (e.g., collapsed trachea)
  • Congenital anomalies of the airway are present in 87% of all cases of stridor in infants and children