Wheezing

Basics

Description

  • Wheezing is a high-pitched, musical respiratory sound caused by airflow turbulence through narrowed airways
  • Categories of wheezing:
    • Monophonic wheeze:
      • Single, uniform pitch; suggests localized airway obstruction
    • Polyphonic wheeze:
      • Multiple pitches; associated with widespread airway narrowing (eg, asthma, COPD)​
    • Expiratory wheeze:
      • More common; indicates lower airway obstruction
    • Inspiratory wheeze:
      • Suggests upper airway obstruction (eg, tracheal stenosis, vocal cord dysfunction)
    • Biphasic wheeze:
      • Occurs in both inspiration and expiration
      • Seen in fixed airway obstructions​
  • Due to airway narrowing between 2 and 5 mm:
    • Wheezing is very low pitched with airway diameters of 5 mm
    • Result of turbulent airflow
    • High-pitched sound with dominant frequency at 400 Hz
    • Resonant vibration of the bronchial walls when airflow velocity reaches critical values
  • Airway narrowing is caused by a combination of ≥1 of the following:
    • Smooth muscle constriction
    • Peribronchial interstitial edema
    • Inflammation (eg, tumor, vascular anomalies)
    • External compression (eg, tumor, vascular anomalies)
    • Obstruction:
      • Mucus plugging
      • Foreign body
      • Tumor
      • Airway collapse (tracheomalacia, neuromuscular disorders)
      • Blood clots or hemorrhage
      • Fibrosis/remodeling (eg, chronic asthma)
      • Thickened secretions (eg, dehydration)
      • Vocal cord dysfunction (eg, paradoxical motion)

Etiology

  • Pulmonary (small airway):
    • Asthma
    • Chronic obstructive pulmonary disease
    • Acute respiratory distress syndrome
    • Anaphylaxis
    • Aspiration pneumonia:
      • Wheezing occurs early in the disease due to intense bronchospasm following the event
    • Byssinosis:
      • Occupational lung disease of textile workers exposed to cotton dust
    • Drugs:
      • Angioedema or allergic reaction
      • ACE inhibitors
      • β-Blockers
      • Aspirin and NSAIDs
    • Forced exhalation in normal patients
    • Hyperventilation
    • Chronic cor pulmonale
    • Chemical pneumonitis
    • Carcinoid tumors
    • Paroxysmal nocturnal dyspnea
    • Pulmonary edema
    • Pulmonary embolism:
      • Rarely associated with wheezing
      • Focal
    • Pneumonia
    • Sleep apnea
  • Pulmonary (large airway):
    • Bronchitis:
      • Most common large airway etiology of wheezing
    • Vocal cord dysfunction (paralysis, paradoxical movement)
    • Foreign body
    • Epiglottitis:
      • Wheezing associated with stridor in 10% of cases
    • Diphtheria
    • Smoke inhalation
    • Tracheobronchial tumors

Pediatric Considerations

  • Viral bronchiolitis (RSV):
    • Seen in children <3 yr of age
  • Asthma
  • Viral infection:
    • Croup (stridor more common)
  • Epiglottitis (stridor more common)
  • Gastroesophageal reflux
  • Foreign-body aspiration
  • Congenital abnormalities:
    • Tracheomalacia
    • Tracheal stenosis
    • Vascular ring
  • Cystic fibrosis
  • Cardiac disease
  • Paradoxical vocal cord dysfunction:
    • Characterized by abnormal vocal cord adduction during inspiration

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