Physiological & pathological breath sounds

Assessment of Breath Sounds

If possible, auscultation of the chest should be done with the patient in the seated position. The diaphragm of the stethoscope should be used. The examiner should warm the stethoscope between his or her palms before placing it on the patient’s chest. The stethoscope should be placed against the patient’s bare skin; the examiner should not try to listen through the patient’s clothes.

The examination should include listening to the anterior chest, the midaxillary region, and the posterior chest. The posterior chest should be examined from the apex to the base of the chest. The breath sounds should be assessed during both quiet and deep breathing. A full breath should be auscultated in each location. The examiner should listen for the pitch, intensity, duration, and distribution of breath sounds, as well as note any abnormal or adventitious sounds.[2, 3]

Types of Breath Sounds

Breath sounds can be divided into 2 categories: normal and abnormal (adventitious).


Normal breath sounds

Normal breath sounds can be further divided into 2 subcategories: vesicular and tracheal. Vesicular breath sounds are the sounds heard during auscultation of the chest of a healthy person (listen to the audio recording below). The inspiratory component predominates and is generated by turbulent airflow within the lobar and segmental bronchi, whereas the expiratory component is due to flow within the larger airways.

Tracheal sounds are the sounds heard over the sternum. They are louder and higher pitched than vesicular sounds are. With tracheal sounds, the expiratory phase is as long as or longer than the inspiratory phase.

Abnormal (adventitious) breath sounds


A wheeze is defined as a continuous musical sound lasting longer than 250 ms (listen to the audio recording below). It is thought to be due to oscillation of opposing airway walls that are narrowed almost to the point of contact. A wheeze may be either expiratory or inspiratory and may contain either a single note or multiple notes. Wheezing is common, estimated to occur in 25% of the population at some point. It is frequently more audible at the trachea than in the chest.[5]

Clinically, wheezing indicates airflow obstruction, though its absence does not exclude obstruction. Such obstruction may occur at any point along the airway. Conditions associated with wheezing include infection (croup, whooping cough, bronchiolitis), laryngeal or tracheal tumors, tracheal stenosis, tracheomalacia, foreign body aspiration, other causes of large airway compression or stenosis, vocal cord dysfunction, asthma, chronic obstructive pulmonary disease (COPD), cystic fibrosis, bronchiectasis, hypersensitivity pneumonitis, and pulmonary edema.

A wheeze may be detected during forced expiration in normal subjects. Although wheezing is associated with airflow obstruction, the degree of obstruction cannot be reliably predicted by the presence or absence of wheezing. Generally, a polyphonic wheeze (ie, a wheeze with multiple notes) is characteristic of large airway obstruction, whereas a monophonic wheeze is more typical of small airway obstruction.[4, 5]


Crackles are defined as a short, explosive, nonmusical sound (listen to the audio recording below). The can be divided into 2 types: fine and coarse. Compared with coarse crackles, fine crackles have a higher frequency and a shorter duration. Fine crackles are caused by the sudden opening of a closed airway; coarse crackles are thought to be related to secretions.

Crackles may occur on either inspiration or expiration but are more common during inspiration. Inspiratory crackles may be classified as early inspiratory, midinspiratory, or late inspiratory. Crackles are more frequently heard in the basilar regions of the lungs because the distribution of airway closure is gravity dependent.

Crackles may be heard in cardiac disease, fibrotic lung disease, obstructive lung disease, and pulmonary infections. They may also be heard in healthy older individuals.[4, 6]

General characteristics of these crackles have been described for many different disorders (although there may be variations among individual patients). In idiopathic pulmonary fibrosis, crackles have been described as fine, short in duration, higher pitched, and occurring in late inspiration. A basilar predominance exists in early disease.

Asbestosis is associated with fine crackles. The presence of crackles has been shown to be associated with honeycombing on imaging and with the duration of dust exposure. In bronchiectasis, crackles have been described as high frequency and coarse. They occur in early inspiration or midinspiration and are thought to be secondary to bronchial wall collapse during expiration and sudden opening in inspiration.

In COPD, crackles are most commonly due to airway secretions and typically disappear after coughing; they may also be due to the opening and closing of narrowed bronchi with weakened airway walls. Crackles in COPD are characterized as coarse, early, and low pitched and tend to be infrequent.

The crackles associated with pulmonary edema are attributed to the opening of airways narrowed by peribronchial edema. They are described as coarse, late occurring, and high pitched. They may be inspiratory or expiratory.

In pneumonia, 2 types of crackles have been described. Early pneumonia is associated with coarse, midinspiratory crackles. Crackles during the recovery phase are described as shorter and occurring at the end of expiration.


Rhonchi are defined as low-pitched, continuous sounds that have a tonal, sonorous quality. They are caused by the rupture of fluid films and airway wall vibrations and are associated with disorders that cause increased airway secretion or reduced clearance of secretions. Rhonchi tend to clear with coughing


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