Unifying Concepts

Clinical Characteristics and Correlations of Respiratory Sounds

The clinical characteristics of normal and adventitious sounds are summarized.

Clinical Characteristics and Correlations of Respiratory Sounds

Respiratory Sound Clinical Characteristics Clinical Correlation
Normal tracheal sound Hollow and nonmusical, clearly heard in both phases of respiratory cycle Transports intrapulmonary sounds, indicating upper-airway patency; can be disturbed (e.g., become more noisy or even musical) if upper-airway patency is altered; used to monitor sleep apnea; serves as a good model of bronchial breathing
Normal lung sound Soft, nonmusical, heard only on inspiration and on early expiration Is diminished by factors affecting sound generation (e.g., hypoventilation, airway narrowing) or sound transmission (e.g., lung destruction, pleural effusion, pneumothorax); assessed as an aggregate score with normal breath sound; rules out clinically significant airway obstruction*
Bronchial breathing Soft, nonmusical, heard on both phases of respiratory cycle (mimics tracheal sound) Indicates patent airway surrounded by consolidated lung tissue (e.g., pneumonia) or fibrosis
Stridor Musical, high-pitched, may be heard over the upper airways or at a distance without a stethoscope Indicates upper-airway obstruction; associated with extrathoracic lesions (e.g., laryngomalacia, vocal-cord lesion, lesion after extubation) when heard on inspiration; associated with intrathoracic lesions (e.g., tracheomalacia, bronchomalacia, extrinsic compression) when heard on expiration; associated with fixed lesions (e.g., croup, paralysis of both vocal cords, laryngeal mass or web) when biphasic
Wheeze Musical, high-pitched; heard on inspiration, expiration, or both Suggests airway narrowing or blockage when localized (e.g., foreign body, tumor); associated with generalized airway narrowing and airflow limitation when widespread (e.g., in asthma, chronic obstructive lung disease); degree of airflow limitation proportional to number of airways generating wheezes; may be absent if airflow is too low (e.g., in severe asthma, destructive emphysema)
Rhonchus Musical, low-pitched, similar to snoring; lower in pitch than wheeze; may be heard on inspiration, expiration, or both Associated with rupture of fluid films and abnormal airway collapsibility; often clears with coughing, suggesting a role for secretions in larger airways; is nonspecific; is common with airway narrowing caused by mucosal thickening or edema or by bronchospasm (e.g., bronchitis and chronic obstructive pulmonary disease)
Fine crackle Nonmusical, short, explosive; heard on mid-to-late inspiration and occasionally on expiration; unaffected by cough, gravity-dependent, not transmitted to mouth Unrelated to secretions; associated with various diseases (e.g., interstitial lung fibrosis, congestive heart failure, pneumonia); can be earliest sign of disease (e.g., idiopathic pulmonary fibrosis, asbestosis); may be present before detection of changes on radiology
Coarse crackle Nonmusical, short, explosive sounds; heard on early inspiration and throughout expiration; affected by cough; transmitted to mouth Indicates intermittent airway opening, may be related to secretions (e.g., in chronic bronchitis)
Pleural friction rub Nonmusical, explosive, usually biphasic sounds; typically heard over basal regions Associated with pleural inflammation or pleural tumors
Squawk Mixed sound with short musical component (short wheeze) accompanied or preceded by crackles Associated with conditions affecting distal airways; may suggest hypersensitivity pneumonia or other types of interstitial lung disease in patients who are not acutely ill; may indicate pneumonia in patients who are acutely ill




  1. Bohadana A, Izbicki G, Kraman SS. Fundamentals of lung auscultation. N Engl J Med. 2014 Feb 20;370(8):744-51. [Medline]
  2. Pasterkamp H, Kraman SS, Wodicka GR. Respiratory sounds. Advances beyond the stethoscope. Am J Respir Crit Care Med. 1997 Sep;156(3 Pt 1):974-87.[Medline]


Created May 05, 2014.

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