Crackles are discontinuous, brief sounds heard more commonly on inspiration. Synonyms: crepitations; rales.
They can be classified as
- fine (high pitched, very brief) or
- coarse (low pitched, brief).
Crackles can be produced by two common mechanisms.
- When previously closed small airways suddenly open. To see how this can happen, gently close your wet lips and open them suddenly. You will hear a 'plop'. When this happens in the terminal bronchioles, fine crackels are produced.
- Another explanation is that air bubbles through secretions as in pulmonary edema and resolving pneumonia.
Listen to the audio of crackles:
Causes of crackles:
- pulmonary edema
- chronic bronchitis
- interstitial lung disease
Wheezes are continuous, high pitched, musical sounds heard usually on expiration. They are produced when air flows through airways narrowed by secretions, foreign bodies, or obstructive lesions. The proportion of the respiratory cycle occupied by the wheeze roughly corresponds to the degree of airway obstruction. Wheezes resemble the sound of a violin playing.
There are two types of wheezes:
- monophonic (suggesting obstruction of one airway, often a malignant tumour compressing on a bronchiole) or
- polyphonic (suggesting generalized obstruction of airways, as in asthma).
Listen to the audio of wheezes:
- chronic bronchitis
- acute bronchitis
- sometimes in pulmonary edema
The presence of expiratory wheezing signifies that the patient's peak expiratory flow rate is less than 50% of normal, and due to a dynamic bronchoconstriction as in bronchial asthma.
Wheezing heard during inspiration most often signifies a more static bronchoconstriction usually caused by tumors, foreign bodies or fibrosis. This is especially true if they are monophonic wheezes. These generally are sinister in their implication. They are usually heard when a single or a very limited number of bronchioles is/are compressed, commonly seen in bronchogenic carcinoma.
The location on the chest where the wheezes are heard also hints at the cause. If wheezes are heard in all areas, they are most likely due to generalized bronchoconstriction as in asthma, when it will also be polyphonic.
The term 'rhonchi' is also used sometimes as a synonym for wheezes. But they also have a different description (see below).
Rhonchi are low pitched, continous sounds that are similar to wheezes. They usually imply obstruction of a slightly larger airway by secretions.
They are often also described as the "coarse rattling sound somewhat like snoring, usually caused by secretion in bronchial airways".
Rhonchi is the plural form of the singular word 'rhonchus'. However, this term is also used as a synonym for wheezes (see above).
Squawks are short inspiratory wheezes. They are almost always associated with crackles.
- hypersensitivity pneumonitis
- interstitial fibrosis
Listen to the audio of squawks:
This is an obsolete term, used as a synonym for crackles, especially coarse crackles. It is pronounced as 'raahls'.
Stridor is an inspiratory noisy sound heard loudest over the trachea during inspiration.
Stridor is indicative of an obstructed trachea or larynx and is therefore a medical emergency that demands immediate attention.
Pleural rubs are creaking sounds produced when the pleural surfaces are inflammed or roughened and rub against each other. It is produced due to friction between the two pleural surfaces.
They may be discontinuous or continuous sounds. They can usually be localized to a particular place on the chest wall and are heard during both the inspiratory and expiratory phases.
- sometimes in pleural effusion, above the level of fluid
The mp3 audio clips used in this article can be downloaded from our downloads section. Please remember that these are for teaching-learning purposes only.