Abnormal Breath Sounds: Clinical Examples
Abnormal breath sounds are classified into two main categories: continuous sounds (wheezes and stridor) and discontinuous sounds (crackles), each with distinct acoustic characteristics and clinical significance. 1
Continuous Adventitious Sounds
Wheezing
- High-pitched, whistling sound heard primarily on expiration (though can occur on inspiration)
- Associated with lower airway obstruction
- Caused by turbulent airflow through narrowed airways 1
- Common in asthma, COPD, and bronchospasm
Stridor
- Loud, harsh inspiratory noise associated with upper airway obstruction 1, 2
- Heard over the neck and trachea
- Key differentiating feature: Occurs during inspiration and peaks during exercise in conditions like exercise-induced laryngeal dysfunction (EILD) 2
- In infants, stridor is most commonly caused by laryngomalacia 2
- Resolves within approximately 5 minutes after stopping exercise in EILD patients 2
Rhonchi
- Large continuous sounds heard with stenosis of trachea or major bronchus 3
- Easily audible over the neck
- Lower-pitched than wheezes
Discontinuous Adventitious Sounds
Crackles (Rales)
Fine Crackles:
- High-pitched, brief sounds
- Typically heard during inspiration
- In COVID-19 pneumonia, fine crackles detected ground-glass opacities with 84.6% sensitivity 4
Coarse Crackles:
- Lower-pitched, longer duration than fine crackles
- Associated with secretions in larger airways
- Detected consolidation with 88.9% sensitivity in COVID-19 patients 4
Velcro Crackles:
- Distinctive sound resembling the separation of Velcro strips
- More commonly identified at posterior chest in basal fields 4
- Associated with pulmonary fibrosis and interstitial lung disease 5
- In COVID-19 pneumonia, Velcro crackles identified ground-glass opacities with 41% sensitivity but 81.3% specificity 4
Distribution Patterns
Important clinical pearl: In pneumonia and COVID-19, abnormal breath sounds follow predictable patterns:
- Upper lung fields: Usually normal breath sounds
- Basal fields: Increased proportion of abnormal sounds 4
- Bilateral involvement: Common in viral pneumonias (96.4% in COVID-19) 4
Clinical Context for Pneumonia Diagnosis
When evaluating for pneumonia, the absence of normal findings is as important as presence of abnormal ones 6:
- Diminished breath sounds on auscultation suggest pneumonia
- Absence of runny nose combined with breathlessness and crackles increases likelihood of pneumonia 6
- Normal breath sounds with normal vital signs argue against pneumonia 6
Key Diagnostic Considerations
Timing matters for differential diagnosis:
- Wheezing that peaks 5-20 minutes after exercise suggests exercise-induced bronchoconstriction
- Stridor that peaks during exercise and resolves within 5 minutes suggests EILD 2
Common pitfall: The term "rhonchi" is frequently misused to describe both continuous and discontinuous sounds, leading to confusion 7. Use specific terms: wheezes for continuous sounds, crackles for discontinuous sounds.
Physical examination findings in advanced disease 8: