What is the Breath Sound Score?
The breath sound score is a semi-quantitative clinical assessment tool that evaluates the intensity of breath sounds through chest auscultation at multiple sites, correlating with the severity of airflow obstruction, particularly in COPD patients. 1
Clinical Scoring Method
The breath sound intensity (BSI) score is obtained through systematic chest auscultation, typically at six standardized sites on the chest wall, where the clinician grades the intensity of breath sounds on a numerical scale. 1 This scoring approach was originally described by Pardee and colleagues and has been validated against objective lung function measurements. 1
Correlation with Lung Function
The BSI score demonstrates strong correlations with multiple indices of airflow obstruction:
- Forced expiratory volume to vital capacity ratio (FEV1/FVC): r = 0.860 1
- Maximal expiratory flow at 50% of vital capacity: r = 0.790 1
- Forced expiratory volume in one second (FEV1): r = 0.768 1
- Specific conductance: r = 0.759 1
The score correlates independently with both airflow obstruction and lung distension when analyzed through multiple correlation studies. 1
Clinical Utility and Limitations
When It Works Well
The breath sound score is useful for both detecting and quantifying the severity of airflow obstruction in patients with obstructive lung disease. 1 The European Respiratory Society notes that diminished breath sounds, when combined with hyperresonance, have a positive likelihood ratio >5.0 for COPD diagnosis. 2
Important Caveats
- Fails in restrictive disorders: The predictive power is significantly impaired in patients with coexisting restrictive lung disease. 1
- Misses mild obstruction: The score may fail to detect mild, pure airflow obstruction. 1
- Poor sensitivity overall: The European Respiratory Society explicitly warns that physical examination findings, including breath sounds, have poor sensitivity and variable reproducibility for detecting or excluding moderately severe COPD. 3
Paradoxical Findings in COPD
During resting tidal breathing, COPD patients may actually demonstrate increased breath sound intensity compared to healthy controls, particularly at higher frequency bands (>400 Hz), despite having diminished sounds during deep inspiration. 4 This counterintuitive finding occurs because the increased intensity during resting breathing reflects turbulent airflow, while the diminished sounds during deep breathing result from reduced airflow capacity. 4
Guideline Recommendations on Breath Sound Assessment
The European Respiratory Society and American Thoracic Society recommend against using breath sound assessment in isolation, emphasizing that it must be combined with spirometry, validated symptom questionnaires (CAT ≥10 or mMRC ≥2), and functional capacity testing rather than relying on physical examination alone. 2 The American Academy of Pediatrics similarly notes that breath sound quality (presence of wheezes, crackles, or other adventitious sounds) is just one component of comprehensive respiratory assessment. 2
Critical Warning from Guidelines
The European Respiratory Society explicitly cautions against relying on surrogate outcomes like theoretical breath sound scores unless they strongly correlate with patient-centered outcomes such as dyspnea, quality of life, exacerbation frequency, and mortality. 2 Physical signs, including breath sounds, are poor guides to the degree of airflow limitation and their absence does not exclude COPD. 3