Types of breath sound
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Types of Breath Sounds
Breath sounds are classified into normal (physiologic) and adventitious (abnormal) sounds. The classification below follows standardized American Thoracic Society (ATS) nomenclature. - Murray & Nadel's Textbook of Respiratory Medicine, p. 398
I. Normal Breath Sounds
1. Normal Breath Sounds (formerly "Vesicular")
- Frequency: 200-600 Hz, decreasing power with increasing Hz
- Character: Soft, nonmusical, heard mainly on inspiration; expiratory phase is softer or even inaudible
- Where heard: Over most of the lung periphery
- Origin: Turbulent airflow within lobar and segmental bronchi (NOT air entering alveoli - that is a silent diffusion process)
- Expiratory sounds are softer because they originate in larger, more central airways where the large air volume of the lungs dampens them
Note: The old term "vesicular" is discouraged because it incorrectly implied the sounds came from air entering the alveolar vesicles.
2. Tracheal Breath Sounds
- Frequency: 75-1600 Hz; flat until a sharp decrease at ~900 Hz
- Character: Hollow, tubular, nonmusical; heard in both inspiration AND expiration equally
- Where heard: Just below the suprasternal notch / over the trachea
- Clinical value: Audible tracheal sounds confirm open central and upper airways
II. Adventitious (Abnormal) Breath Sounds
A. Bronchial Breath Sounds
- Character: Loud, medium-pitched, tubular; as loud or louder on expiration than on inspiration (equal I:E ratio)
- Same acoustic quality as tracheal sounds but heard in the lung periphery
- Clinical significance: Classic sign of lung consolidation (pneumonia, pulmonary edema, hemorrhage) - consolidated lung amplifies and transmits centrally generated sounds to the periphery. Also confirms the airway to that region is patent.
B. Diminished / Absent Breath Sounds
- Occur when a sound barrier interposes between central airways and the chest wall
- Causes: Pleural effusion, pneumothorax, peripheral bulla, obstructing mass, COPD (hyperinflation), obesity, thick chest wall
III. Adventitious Sounds - Two Main Categories
Adventitious sounds are divided into discontinuous (crackles) and continuous (wheezes, rhonchi, stridor).
Discontinuous Sounds
1. Fine Crackles (Fine Rales / Crepitations)
| Feature | Detail |
|---|---|
| Sound | Softer, shorter, higher-pitched pops |
| Timing | Mid-to-late inspiration |
| Mechanism | Explosive opening of small airways that had collapsed due to surface tension forces |
| Clinical | Atelectasis, pulmonary fibrosis (ILD), early pulmonary edema, CHF |
| Behavior | May disappear after several deep breaths or coughing (if small airways stay open) |
| Late inspiratory crackles | More typical of restrictive disease (fibrosis) - greater tension needed to pop open stiff airways |
2. Coarse Crackles (Coarse Rales)
| Feature | Detail |
|---|---|
| Sound | Louder, lower-pitched, longer explosive sounds |
| Timing | Early inspiration or expiration |
| Mechanism | Intermittent airway opening; rupture of fluid films; secretions in distal airways |
| Clinical | Bronchiectasis, secretions, resolving pneumonia |
| Behavior | May change with cough but rarely disappear entirely |
Continuous Sounds (duration > 250 msec)
3. Wheezes
| Feature | Detail |
|---|---|
| Frequency | High-pitched; dominant frequency ≥ 400 Hz |
| Character | Hissing, musical quality |
| Timing | Predominantly expiratory (but can be biphasic) |
| Mechanism | Fluttering of airway walls at or above critical flow velocity |
| Clinical | Airway narrowing - diffuse = asthma/COPD; focal = intraluminal lesion or extrinsic compression |
| Note | Pitch and intensity do NOT correlate with degree of obstruction; duration in the respiratory cycle does |
4. Rhonchi
| Feature | Detail |
|---|---|
| Frequency | Low-pitched; dominant frequency < 200 Hz (snoring quality) |
| Character | Continuous, gurgling/snoring sound |
| Mechanism | Rupture of fluid films + airway wall vibrations in large airways |
| Clinical | Secretions in large airways (bronchitis, post-aspiration) |
| Behavior | Clears with coughing or suctioning - distinguishes from wheeze |
5. Stridor
| Feature | Detail |
|---|---|
| Character | Continuous, high-pitched, mainly inspiratory sound |
| Where heard | Best heard over the neck |
| Mechanism | Extrathoracic variable or fixed upper airway obstruction |
| Clinical | Urgent! - anaphylaxis, epiglottitis, croup, foreign body, laryngeal edema |
IV. Extrapulmonary Sound
Pleural Friction Rub
- Character: Creaking or leather-rubbing sound, heard in both inspiration and expiration
- Mechanism: Inflamed pleural surfaces rubbing against each other
- Clinical: Pleuritis (pleurisy), pulmonary infarction, pleural mesothelioma
- Distinguishing feature: Does NOT change with coughing; disappears if effusion develops (separates the surfaces)
Quick Summary Table
| Sound | Type | Pitch | Phase | Key Condition |
|---|---|---|---|---|
| Normal breath sounds | Normal | Low | Inspiratory dominant | Normal lung |
| Tracheal sounds | Normal | High | Both phases | Normal trachea |
| Bronchial sounds (peripheral) | Abnormal | Medium-high | Equal I+E | Consolidation |
| Fine crackles | Adventitious - discontinuous | High | Late inspiration | Fibrosis, pulmonary edema |
| Coarse crackles | Adventitious - discontinuous | Low | Early inspiration/exp | Secretions, bronchiectasis |
| Wheeze | Adventitious - continuous | High (>400 Hz) | Expiratory | Asthma, COPD, airway narrowing |
| Rhonchi | Adventitious - continuous | Low (<200 Hz) | Both (clears with cough) | Large airway secretions |
| Stridor | Adventitious - continuous | High | Inspiratory (neck) | Upper airway obstruction |
| Pleural friction rub | Extrapulmonary | Variable | Both phases | Pleuritis |
Here is a stethoscope placement reference for auscultation:
Sources: Murray & Nadel's Textbook of Respiratory Medicine, pp. 398-399; Fishman's Pulmonary Diseases and Disorders; Textbook of Family Medicine, 9e
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