Wheezing

Basics

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)

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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