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Respiratory sounds
Other namesBreath sounds, lung sounds

Respiratory sounds, also known as lung sounds or breath sounds, are the specific sounds generated by the movement of air through the respiratory system.[1] These may be easily audible or identified through auscultation of the respiratory system through the lung fields with a stethoscope as well as from the spectral characteristics of lung sounds.[2] These include normal breath sounds and added sounds such as crackles, wheezes, pleural friction rubs, stertor, and stridor.

Description and classification of the sounds usually involve auscultation of the inspiratory and expiratory phases of the breath cycle, noting both the pitch (typically described as low (≤200 Hz), medium or high (≥400 Hz)) and intensity (soft, medium, loud or very loud) of the sounds heard.[3]

Normal breath sounds

Normal breath sounds are classified as vesicular, bronchovesicular, bronchial or tracheal based on the anatomical location of auscultation.[4][3] Normal breath sounds can also be identified by patterns of sound duration and the quality of the sound as described in the table below:[4]

Name Location where heard normally Quality of sound Sound duration Example
tracheal over the trachea very loud expiratory sound duration is equivalent to inspiratory sound
bronchial over the manubrium loud, high pitched expiratory sound duration is longer than inspiratory sound
bronchovesicular anteriorly between the 1st and 2nd intercostal space;

posteriorly in-between the scapulae

intermediate expiratory sound duration is about equivalent to inspiratory sound
vesicular over most of both lungs soft, low pitched expiratory sound duration is shorter than inspiratory sound

Abnormal breath sounds

Common types of abnormal breath sounds include the following:[5]

Name Continuous/discontinuous Frequency/pitch Inspiratory/expiratory Quality Common Causes Example
Wheeze or rhonchi continuous high (wheeze) or lower (rhonchi) expiratory or inspiratory whistling/sibilant Caused by narrowing of airways, such as in asthma, chronic obstructive pulmonary disease, foreign body.
Stridor continuous high inspiratory, expiratory, or both[6] whistling/sibilant epiglottitis, foreign body, laryngeal edema, croup
Inspiratory gasp continuous high inspiratory whoop pertussis (whooping cough) see New England Journal of Medicine, Classic Whooping Cough sound file, Supplement to the N Engl J Med 2004; 350:2023-2026
Crackles (rales) continuous high (fine) or low (coarse) inspiratory cracking/clicking/rattling[7] pneumonia, pulmonary edema, tuberculosis, bronchitis, heart failure
Pleural friction rub discontinuous low inspiratory and expiratory many repeated rhythmic sounds inflammation of lung linings, lung tumors not available
Hamman's sign (or Mediastinal crunch) discontinuous neither (heartbeat) crunching, rasping pneumomediastinum, pneumopericardium not available
Grunting Continuous low expiratory snoring surfactant deficiency, pneumonia, cardiac abnormalities[8]


Other tests of auscultation

A clinician auscultating the posterior lung of a patient.

Pectoriloquy, egophony and bronchophony are tests of auscultation that utilize the phenomenon of vocal resonance.[3] Clinicians can utilize these tests during a physical exam to screen for pathological lung disease. For example, in whispered pectoriloquy, the person being examined whispers a two syllable number as the clinician listens over the lung fields. The whisper is not normally heard over the lungs, but if heard may be indicative of pulmonary consolidation in that area. This is because sound travels differently through denser (fluid or solid) media than the air that should normally be predominant in lung tissue. In egophony, the person being examined continually speaks the English long-sound "E" (/i/). The lungs are usually air filled, but if there is an abnormal solid component due to infection, fluid, or tumor, the higher frequencies of the "E" sound will be diminished. This changes the sound produced, from a long "E" sound to a long "A" sound (/eɪ/).


In 1957, Robertson and Coope proposed the two main categories of adventitious (added) lung sounds. Those categories were "Continuous" and "Interrupted" (or non-continuous).[12] In 1976, the International Lung Sound Association simplified the sub-categories as follows:

Wheezes (>400 Hz)
Rhonchi (<200 Hz)
Fine crackles
Coarse crackles[13][14]

Several sources will also refer to "medium" crackles, as a crackling sound that seems to fall between the coarse and fine crackles. Crackles are defined as discrete sounds that last less than 250 ms, while the continuous sounds (rhonchi and wheezes) last approximately 250 ms. Rhonchi are usually caused by a stricture or blockage in the upper airway. These are different from stridor.

See also


  1. ^ "Breath sounds: MedlinePlus Medical Encyclopedia". Retrieved 2021-11-11.
  2. ^ Sengupta, Nandini; Sahidullah, Md; Saha, Goutam (August 2016). "Lung sound classification using cepstral-based statistical features". Computers in Biology and Medicine. 75 (1): 118–129. doi:10.1016/j.compbiomed.2016.05.013. PMID 27286184.
  3. ^ a b c Zimmerman, Barret; Williams, Donna (2021), "Lung Sounds", StatPearls, Treasure Island (FL): StatPearls Publishing, PMID 30725938, retrieved 2021-11-11
  4. ^ a b Bickley, Lynn S (2013). Bates' Guide to Physical Examination and History-Taking. Wolters Kluwer Health/Lippincott Williams & Wilkins. pp. 311–312. ISBN 978-1609137625.
  5. ^ Bohadana, Abraham (February 20, 2014). "Fundamentals of Lung Auscultation". New England Journal of Medicine. 370 (8): 744–751. doi:10.1056/NEJMra1302901. PMID 24552321. S2CID 17871815.
  6. ^ Leung, Alexander K. C.; Cho, Helen (1999-11-15). "Diagnosis of Stridor in Children". American Family Physician. 60 (8): 2289–2296. ISSN 0002-838X. PMID 10593320.
  7. ^ "Breath sounds: MedlinePlus Medical Encyclopedia". Retrieved 2022-05-06.
  8. ^ a b McGann, Kathleen A.; Long, Sarah S. (2018-01-01), Long, Sarah S.; Prober, Charles G.; Fischer, Marc (eds.), "21 - Respiratory Tract Symptom Complexes", Principles and Practice of Pediatric Infectious Diseases (Fifth Edition), Elsevier, pp. 164–172.e2, ISBN 978-0-323-40181-4, retrieved 2022-05-06
  9. ^ "Breath sounds: MedlinePlus Medical Encyclopedia". Retrieved 2022-05-30.
  10. ^ "Stridor: MedlinePlus Medical Encyclopedia". Retrieved 2022-05-30.
  11. ^ "Breath sounds: Medline Plus". NIH. Retrieved 5 May 2015.
  12. ^ Robertson, A (1957). "Rales, rhonchi, and Laennec". Lancet. 2 (6992): 417–23. doi:10.1016/S0140-6736(57)92359-0. PMID 13464086.
  13. ^ American Thoracic Society Ad Hoc Committee on Pulmonary Nomenclature (1977). "Updated nomenclature for membership reaction". ATS News (3): 5–6.
  14. ^ Loudon, R; Murphy, R (1984). "Lung Sounds". Am Rev Respir Dis. 130 (4): 663–73. doi:10.1164/arrd.1984.130.4.663 (inactive 31 January 2024). PMID 6385790.((cite journal)): CS1 maint: DOI inactive as of January 2024 (link)

Mansy, H. A.; Royston, T. J.; Balk, R. A.; Sandler, R. H. (2002). "Pneumothorax detection using computerised analysis of breath sounds". Medical & Biological Engineering & Computing. 40 (5): 526–532. doi:10.1007/BF02345450. PMID 12452412. S2CID 7413897.