Stridor

Description

• High-pitched audible wheezing and vibratory harsh sounds mainly on inspiration
• Impedance of air movement through the upper airway
• It implies a laryngotracheal airway obstruction
• Inspiratory stridor:
  • Occurs due to extrathoracic airway obstruction (above the thoracic inlet)
  • During inspiration, the pressure inside the airway falls below atmospheric pressure, leading to airway collapse
  • The Bernoulli effect contributes to further narrowing and turbulent airflow
  • High pitched, loudest over the neck, worsens with crying, improves with neck extension, suggests supraglottic or glottic obstruction
• Expiratory stridor:
  • Occurs due to intrathoracic airway obstruction (below the thoracic inlet, typically in the trachea or bronchi)
  • During expiration, intrathoracic pressure rises, causing dynamic airway collapse if the structural integrity is weak
  • Low pitched, best heard over the chest, worsens with forced expiration, improves prone, suggests intrathoracic airway collapse
• Biphasic stridor:
  • Indicates a fixed, central airway obstruction, usually involving the subglottic area or upper trachea
  • Both inspiratory and expiratory airflow is disrupted due to a rigid narrowing of the airway lumen
  • Low pitched, best heard over the chest, worsens with forced expiration, improves prone, suggests intrathoracic airway collapse
• Stridor is significantly more common in pediatric populations
• Viral croup causes 90% of all cases of stridor in children:
  • Strong seasonal pattern, peaking in late fall and early winter

Etiology