Respiratory sounds
Other names	Breath sounds, lung sounds
Specialty	Respirology

Respiratory sounds, also known as lung sounds or breath sounds, refer to 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 adventitious or "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]

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.	Wheezing The sound of wheezing as heard with a stethoscope. Problems playing this file? See media help.
Stridor	continuous	high	inspiratory, expiratory, or both[6]	whistling/sibilant	epiglottitis, foreign body, laryngeal edema, croup	Stridor Inspiratory and expiratory stridor in a 13-month child with croup. Problems playing this file? See media help.
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	Crackles Crackles heard in the lungs of a person with pneumonia using a stethoscope. Problems playing this file? See media help.
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]

Continued

• Rales: Small clicking, bubbling, or rattling sounds in the lungs. They are heard when a person inhales. They are believed to occur when air opens alveoli. Rales can also be described as moist, dry, fine, and coarse.^[9]
• 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".^[8]
• 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.^[10]
• 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.^[11]

Other tests of auscultation

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/).

History

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:

Continuous

Wheezes (>400 Hz)

Rhonchi (<200 Hz)

Discontinuous

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.