Flow-Volume Loop

• Variable Extrathoracic Upper Airway Obstruction: adversely affects predominantly inspiratory flow (as inspiratory negative intraluminal pressures exacerbate the inspiratory airway narrowing, while expiratory positive intraluminal pressures splints the obstruction open)
  • Example: vocal cord paralysis -> inspiratory stridor with no expiratory obstruction
• Variable Intrathoracic Upper Airway Obstruction: adversely affects predominantly expiratory flow (as inspiratory negative pressures decrease the inspiratory airway narrowing, while expiratory positive intrapleural pressures exacerbate the airway obstruction)
  • Example: tracheomalacia -> expiratory worsening of airway obstruction
• Fixed Upper Airway Obstruction: adversely affects both inspiratory and espiratory flows