What are the different types of breath sounds and their characteristics?

Types of Breath Sounds

Breath sounds are classified into two major categories: normal (vesicular, bronchial, and bronchovesicular) and adventitious (abnormal) sounds, which include crackles, wheezes, rhonchi, and stridor. 1, 2, 3

Normal Breath Sounds

Vesicular Breath Sounds

• Soft, low-pitched sounds heard over most of the lung fields during normal breathing, with inspiration longer and louder than expiration. 4, 5
• Produced by turbulent airflow in the smaller airways and alveoli. 5
• Intensity typically ranges from 20-23 dB with median frequency of 367-391 Hz during inspiration. 6
• Absence or marked diminution suggests underlying pathology such as pneumonia, pleural effusion, or pneumothorax. 1, 7

Bronchial Breath Sounds

• Harsh, high-pitched sounds with a tubular quality, heard normally only over the trachea and main bronchi. 5, 8
• Expiration is louder and longer than inspiration, with a distinct pause between phases. 5
• When heard over peripheral lung fields, indicates consolidation (pneumonia) or dense fibrosis. 1, 7

Bronchovesicular Breath Sounds

• Intermediate sounds between vesicular and bronchial, heard normally over the first and second intercostal spaces anteriorly and between the scapulae posteriorly. 5
• Inspiration and expiration are approximately equal in duration and intensity. 5

Adventitious (Abnormal) Breath Sounds

Crackles (Rales)

• Discontinuous, explosive, popping sounds typically heard during inspiration, representing the sudden opening of collapsed alveoli and airways. 1, 2, 3
• Present in approximately 81% of pneumonia patients, making them the most diagnostically significant finding for pneumonia. 1
• Can be classified as fine (high-pitched, brief) or coarse (lower-pitched, longer duration). 3, 5
• Common in pneumonia, pulmonary edema, interstitial lung disease, and bronchiolitis. 1, 2, 6
• Detection varies significantly between spontaneous and standardized breathing (only 26% agreement), requiring careful examination technique. 6

Wheezes

• High-pitched, continuous whistling sounds with a dominant frequency of 400 Hz or more, typically heard during expiration. 2, 9
• Produced by airflow through narrowed airways causing flutter of airway walls at critical flow velocity. 9
• Characteristic of asthma and COPD, but presence alone does not significantly increase likelihood of pneumonia on chest radiograph. 1, 2
• Duration of wheeze relative to respiratory cycle (tw/ttot) correlates better with obstruction severity than intensity or pitch. 9
• Physical examination findings including wheezes are insufficient for diagnosis and must be confirmed with spirometry. 2

Rhonchi

• Low-pitched, continuous rumbling sounds with a dominant frequency of approximately 200 Hz or less, typically heard during forced expiration and often clearing with coughing. 2, 3, 9
• Indicate secretions in larger airways rather than small airway obstruction. 7
• Common in bronchitis, COPD, and pneumonia with significant secretions. 2, 7
• Like wheezes, treatment decisions should be based on spirometry results rather than presence of rhonchi alone. 2

Stridor

• High-pitched, harsh sound heard primarily during inspiration, indicating upper airway obstruction at the level of the larynx or trachea. 2
• Most common indication for flexible bronchoscopy in infants, with laryngomalacia being the most frequent congenital cause. 2
• Requires urgent evaluation as it may indicate life-threatening airway compromise. 2

Clinical Application and Diagnostic Pitfalls

Key Diagnostic Combinations

• The combination of crackles, diminished breath sounds, fever ≥38°C, tachypnea, and dyspnea strongly indicates pneumonia and warrants chest radiography. 1, 7
• Absence of runny nose combined with breathlessness, crackles, and diminished breath sounds significantly increases pneumonia likelihood with high negative predictive value (97%). 1
• Quiet breath sounds combined with prolonged expiratory duration has a positive likelihood ratio >5.0 for COPD when combined with hyperresonance. 2

Common Pitfalls to Avoid

• Wheezing, cough, prolonged expirations, or rhonchi alone do not significantly increase the likelihood of pneumonia. 1
• The degree of airway obstruction cannot be predicted from breath sounds alone; spirometry is required. 2
• Detection of adventitious sounds varies significantly between spontaneous and standardized breathing, with less than half of subjects identified by both methods. 6
• Individual patient perception of breathlessness varies considerably for the same degree of airflow limitation, particularly in geriatric populations. 2

When to Obtain Imaging

• Chest radiography should be performed when abnormal vital signs are combined with abnormal breath sounds in suspected pneumonia. 1, 7
• In patients with normal vital signs and normal lung examination, routine antibiotics are not recommended. 1
• Retrocardiac opacity with rhonchi and productive cough indicates bacterial pneumonia rather than heart failure, which would show bilateral interstitial patterns with Kerley B lines. 7