Respiratory sounds

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

Respiratory sounds
Other namesBreath sounds, lung sounds
1) area for normal tracheal sound, 2) area for ascultation of upper lung fields, 3) area for normal bronchial sound. Blue marks ascultation area and red line marks heart.

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, medium or high) and intensity (soft, medium, loud or very loud) of the sounds heard.

Abnormal breath sounds

Common types of abnormal breath sounds include the following:[3]

Name Continuous/discontinuous Frequency/Pitch Inspiratory/expiratory Quality Associated conditions Example
Wheeze or rhonchi continuous high (wheeze) or lower (rhonchi) expiratory or inspiratory whistling/sibilant, musical Caused by narrowing of airways, such as in asthma, chronic obstructive pulmonary disease, foreign body.
Stridor continuous high either, mostly inspiratory whistling/sibilant, musical epiglottitis, foreign body, laryngeal oedema, 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 (aka crepitations or rales) discontinuous high (fine) or low (coarse), nonmusical inspiratory cracking/clicking/rattling pneumonia, pulmonary edema, tuberculosis, bronchitis
Pleural friction rub discontinuous low inspiratory and expiratory nonmusical, 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


  • Rales: Small clicking, bubbling, or rattling sounds in the lungs. They are heard when a person breathes in (inhales). They are believed to occur when air opens closed air spaces. Rales can be further described as moist, dry, fine, and coarse. This term is no longer much in use.
  • Rhonchi are coarse rattling respiratory sounds, usually caused by secretions in bronchial airways. The sounds resemble snoring. "Rhonchi" is the plural form of the singular word "rhonchus". Since the mid-1990s, it has no longer been considered appropriate terminology in auscultation of the thorax, as much confusion has been reported in the published literature which confuses this with crepitations and wheezes, so the exact nature of this term is unclear.
  • Stridor: Wheeze-like sound heard when a person breathes. Usually it is due to a blockage of airflow in the windpipe (trachea) or in the back of the throat.
  • Wheezing: High-pitched sounds produced by narrowed airways. They are most often heard when a person breathes out (exhales). Wheezing and other abnormal sounds can sometimes be heard without a stethoscope.[4]

Other tests of auscultation

Pectoriloquy, egophony and bronchophony are tests of auscultation. For example, in whispered pectoriloquy the person being examined whispers - typically 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 (//).


In 1957, Robertson and Coope proposed the two main categories of adventitious (added) lung sounds. Those categories were "Continuous" and "Interrupted" (or non-continuous).[5] In 1976, the International Lung Sound Association simplified the sub-categories as follows:

Wheezes (>400 Hz)
Rhonchi (<200 Hz)
Fine crackles
Coarse crackles[6][7]

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.


  1. Respiratory+sounds at the US National Library of Medicine Medical Subject Headings (MeSH)
  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. Bohadana, Abraham (February 20, 2014). "Fundamentals of Lung Auscultation". New England Journal of Medicine. 370 (8): 744–751. doi:10.1056/NEJMra1302901. PMID 24552321.
  4. "Breath sounds: Medline Plus". NIH. Retrieved 5 May 2015.
  5. Robertson, A (1957). "Rales, rhonchi, and Laennec". Lancet. 2 (6992): 417–23. doi:10.1016/S0140-6736(57)92359-0. PMID 13464086.
  6. American Thoracic Society Ad Hoc Committee on Pulmonary Nomenclature (1977). "Updated nomenclature for membership reaction". ATS News (3): 5–6.
  7. Loudon, R; Murphy, R (1984). "Lung Sounds". Am Rev Respir Dis.

Mansy, H.A., Royston, T.J., Balk, R.A. et al. Med. Biol. Eng. Comput. (2002) 40: 526.

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