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Expiratory wheezing

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wheezing airway obstruction pathophysiology

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Expiratory Wheezing

Pathophysiology

Wheezing is a high-pitched, musical respiratory sound produced by turbulent airflow through narrowed airways. Expiratory wheezing specifically occurs because airways naturally narrow during expiration (reduced elastic recoil + positive pleural pressure compresses airways), making obstruction more audible — or exclusively audible — during this phase.
Two key patterns (Harrison's, p. 7848):
  • Polyphonic wheezing — multiple pitches simultaneously, from diffuse small airway narrowing (classic in asthma, COPD)
  • Monophonic wheezing — single pitch, from a fixed obstruction of one airway (e.g., endobronchial tumor, foreign body)
RSV-induced airway remodeling and recurrent wheezing pathophysiology
Mechanism of post-viral airway remodeling leading to chronic expiratory wheezing (RSV model): Th2 upregulation, smooth muscle spasm, mucus plugging, and airway narrowing.

Etiology

CategoryConditions
Obstructive lung diseaseAsthma, COPD, bronchiectasis
CardiacCongestive heart failure ("cardiac asthma" — peribronchial edema)
InfectiousBronchiolitis (RSV, esp. in infants), acute bronchitis, pneumonia
Structural/mechanicalEndobronchial tumor, foreign body aspiration, tracheobronchomalacia
Allergic/immunologicAnaphylaxis, hypersensitivity pneumonitis, ABPA
OtherVocal cord dysfunction (mimicker), GERD-induced bronchospasm, medications (beta-blockers, NSAIDs in aspirin-exacerbated respiratory disease)
Key teaching point (Harrison's, p. 7848): "Clinicians must take care not to attribute all wheezing to asthma."

Clinical Features

  • Expiratory-only wheezing suggests mild-to-moderate obstruction; airflow is adequate to generate sound
  • Biphasic (inspiratory + expiratory) suggests severe obstruction or upper airway involvement
  • Silent chest in an asthmatic = critical obstruction — too little airflow to generate wheeze (ominous sign)
  • Associated symptoms guide etiology:
    • Episodic + atopy history → asthma
    • Chronic productive cough + smoking → COPD
    • Orthopnea + peripheral edema → CHF
    • Fever + URI prodrome in infant → bronchiolitis
    • Acute onset after meal/play in child → foreign body

Diagnosis

History

  • Onset (acute vs. chronic), triggers (allergens, exercise, cold air, NSAIDs), smoking, occupational exposures, atopy, cardiac history

Physical Exam

  • Confirm wheeze is truly expiratory (auscultate full respiratory cycle)
  • Accessory muscle use, prolonged expiratory phase, hyperinflation

Investigations

TestIndication
Spirometry (pre/post-bronchodilator)Confirm obstructive pattern; reversibility suggests asthma
Peak expiratory flow (PEF)Bedside severity assessment, monitoring
Chest X-rayHyperinflation (asthma/COPD), pulmonary edema (CHF), foreign body
CT chest (HRCT)Bronchiectasis, air trapping, endobronchial lesion
BronchoscopySuspected foreign body, tumor, structural lesion
Allergy testing / IgEAtopic workup
BNP/NT-proBNP + echoCHF differentiation
Methacholine challengeAirway hyperresponsiveness when spirometry normal

Management

Management is directed at the underlying cause:

Asthma

  • Acute: SABA (albuterol) via inhaler/nebulizer, systemic corticosteroids, ipratropium, Mg²⁺ sulfate (IV) in severe cases
  • Chronic: Stepwise GINA approach — low-dose ICS → ICS/LABA → add-ons (LAMA, biologic for eosinophilic/type 2)

COPD

  • Acute exacerbation: SABA ± SAMA, systemic steroids, antibiotics (if purulent/infective trigger), O₂ titrated to SpO₂ 88–92%
  • Chronic: LAMA ± LABA, ICS in frequent exacerbators, pulmonary rehab

Cardiac Asthma (CHF)

  • IV diuretics (furosemide), nitrates, treat underlying heart failure — bronchodilators have limited role

Bronchiolitis (infants)

  • Supportive: hydration, nasal suctioning, O₂ if needed; bronchodilators generally not recommended per AAP guidelines

Foreign Body

  • Urgent bronchoscopic removal

Anaphylaxis

  • IM epinephrine (0.3–0.5 mg, 1:1000), supine, airway support, IV antihistamines/steroids

Red Flags Requiring Urgent Action

  • Silent chest (absent wheeze with respiratory distress)
  • SpO₂ < 92% despite supplemental O₂
  • Inability to speak in full sentences
  • Cyanosis, altered mentation, paradoxical breathing
  • New-onset wheeze in elderly (consider CHF, malignancy)
  • Unilateral wheeze (foreign body or tumor until proven otherwise)
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