Wheezing

Definition and Etiology

Definition

• High-pitched, shrill, or coarse sounds that are usually continuous 
• Can occur in either the expiratory (more commonly) or inspiratory phase
• Generally louder than normal breath sounds, but mild forms may require a stethoscope to be detected

Etiology

• In adults, asthma and chronic obstructive pulmonary disease (COPD) are the most common causes of wheezing.
  • Wheezing is asthma is associated with an exacerbation, or “asthma attack.”
  • Wheezing in COPD is associated with worse symptoms, more exacerbations, and worse lung function. 
• In children, asthma, allergies, and respiratory tract infections are the most common causes. 
• Other causes include anything that narrows the airways.
  • Airway obstruction, most commonly by:
    • Bronchospasm or bronchiectasis
    • Mucus (e.g., in cystic fibrosis)
    • Foreign body
    • Vocal cord dysfunction
  • External compression by a tumor
  • Peribronchial edema in congestive heart failure
  • Inflammation due to anaphylaxis or toxic inhalation

Pathophysiology

• Caused by a narrowing of the airways resulting in the oscillation of opposing airway walls
• Wheezing is an example of Bernoulli’s principle: 
  • When airflow is forced through a narrowed tube, its velocity increases and the pressure decreases.
  • The airway just distal to the narrowing collapses and vibrates, generating a high-pitched sound.
• Depending on where the narrowing occurs within the respiratory tract, the qualities of the sound will vary.

Upper versus lower airways:

• Polyphonic wheezing: 
  • Narrowing or obstruction of the small lower airways and at multiple sites
  • Described as musical, continuous, and variable if auscultated at different regions 
  • Examples: asthma, COPD, liquid aspiration, unilateral emphysema
• Monophonic wheezing: 
  • Narrowing or obstruction of the large airways, usually in one location
  • Described as loud, low, and fixed throughout the thoracic cavity
  • Examples: foreign body aspiration, accumulation of blood or secretions, external compression or by tumor or lymph nodes

Unilateral versus bilateral wheezing:

• Bilateral/symmetric wheezing is caused by: 
  • Asthma
  • COPD
• Unilateral wheezing is caused by:
  • Foreign body aspiration
  • Intrinsic or extrinsic bronchial compression
    • Tumor
    • Bronchial stenosis
    • Unilateral bronchomalacia
    • Lymphadenopathy
    • Abnormal vasculature
    • Kyphoscoliosis

Diagnosis

The medical history and physical exam findings (both pulmonary and extrapulmonary) will suggest the most likely cause. Further laboratory studies and imaging are usually not needed if typical features of the underlying condition are present.

Laboratory studies

• Pulse oximetry to evaluate oxygenation
• Pulmonary function testing:
  • With testing performed pre- and post-bronchodilator (to distinguish between asthma and COPD)
  • Evaluation of the flow-volume loop:
    • If the bottom of the loop (inspiratory phase) is flat, it suggests an upper airway (extrathoracic) obstruction. 
    • If the top of the loop (expiratory phase) is flat, it suggests a lower airway (intrathoracic) obstruction. 

Imaging

• Chest or neck X-ray will confirm airway obstruction.
• Nasopharyngo-, laryngo-, or bronchoscopy to directly visualize the airways and obstruction, and extract in the case of a foreign body aspiration

Management

Symptomatic relief can be achieved with supplemental oxygen, but it is important to identify and correct the underlying condition for long-term treatment.

• Asthma
  • Inhaled bronchodilators, corticosteroids, other 
  • 5-step treatment strategy from the Global Initiative for Asthma (GINA)
  • Asthma medication
• COPD exacerbations 
  • Bronchodilator therapy and a course of oral glucocorticoids
  • Possible oral antibiotics (antivirals if there is evidence of influenza)
  • Supplemental oxygen if hypoxic, and pulmonary rehabilitation program
• Pneumonia/infectious causes: requires the appropriate antibiotic for the causative pathogen
• Foreign body aspiration: requires location and extraction of the foreign body
• Heart failure 
  • Treatment depends on the type of heart failure and severity.
  • Follow published guidelines for treatment.
  • Heart failure and angina medication

Differential Diagnosis

The following abnormal breath sounds should be distinguished from wheezing:

• Stridor: an abnormal, high-pitched sound produced by turbulent airflow through a partially obstructed airway anywhere from the supraglottis to the trachea. There are 3 types of stridor: inspiratory (most common, due to laryngeal obstruction), expiratory (due to tracheobronchial obstruction), and biphasic (due to subglottic or glottic obstruction). Stridor can be acute, subacute, or chronic:
  • Acute and subacute causes: laryngotracheitis, foreign body aspiration, epiglottitis, anaphylaxis, retropharyngeal or peritonsillar abscess 
  • Chronic causes: laryngomalacia, tracheomalacia, vocal cord dysfunction, papillomatosis (warts), tumors
• Stertor and snoring: a narrowing of the airway in the nasal, nasopharyngeal, or oropharyngeal areas that produces a low-pitched sound often referred to as snoring during sleep and stertor if the patient is awake. Stertor and snoring are caused by hypertrophy of tonsillar tissue, micrognathia, or macroglossia.