Lung Sounds

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Introduction

Lung sounds can be classified into the following three categories:

1. Breath sounds
2. Voice sounds
3. Adventitious sounds

Breath sounds

Normal breath sounds (Vesicular sounds)
The intensity and quality of breath sounds depends on the site of Auscultation. Sounds produced in the large airways have some of their energy content attenuated and filtered during conduction through pulmonary tissue, so that only a narrow range of frequencies (<500 Hz) is heard over the chest wall in normal patients. Thus in health, over most of the chest, the breath sounds are low-pitched and have a relatively quiet expiratory phase.

Bronchial breathing
Breath sounds heard close to large air passages have a louder and longer expiratory phase and their energy components extend over a broad frequency range (<200 – 4000 Hz). In health, such sounds are heard only over the large air passages e.g. the trachea. In the presence of consolidation or cavitation there is less filtration and attenuation of the sounds produced in the large airways, so that the sounds heard over the chest wall are similar to those heard over large air passages such as the trachea. Amphoric and cavernous breathing are varieties of bronchial breathing, which are heard over cavities communicating with a bronchus (selective amplification of low frequency sounds).

Soft breath sounds
Fluid or air in the pleural space deflects sound waves away from the chest wall back into the lung and therefore breath sounds are reduced in intensity.

Voice sounds

Voice sounds produced in the larynx are also filtered and attenuated during their conduction through lung tissue, and because of this, speech is incomprehensible when we listen to it over the chest wall with a stethoscope. In the presence of consolidation or cavitation of the lung, less filtration and attenuation occurs and therefore voice sounds can be heard more clearly over the chest wall.

The term used to describe the voice sounds heard over consolidated lung is bronchophony (also called vocal resonance). It can be determined through the stethoscope when the patient says “99”, usually just audible but becoming louder when the lung is consolidated. Pectoriloquy is abnormal transmission of the patient’s voice sounds through the chest wall so that they can be clearly heard through the stethoscope. The term used to describe whispered speech heard over consolidated lung (as in pneumonia), is whispering pectoriloquy. Bronchophony and whispering pectriloquy have the same implications as bronchial breathing i.e. consolidation or cavitation of the lung with improved transmission of sound. Aegophony is a form of bronchophony in which the spoken syllables have a peculiar nasal or bleating quality, and these arise from the transmission of sound through compressed lung just above a pleural effusion.

Adventitious sounds

Crackles
These may be either coarse or fine. They are discontinuous, interrupted explosive sounds. Coarse crackles or crepitations are associated with bronchiectasis or resolving pneumonia, whereas fine crackles can be heard with either pulmonary oedema or interstitial fibrosis.

Wheezes
These may be high pitched or low pitched and are continuous sounds associated with airway narrowing due to a variety of causes, including bronchoconstriction and excessive secretions. Loud wheezes are heard with the naked ear, soft wheezes only with the stethoscope.

Mediastinal crunch
A hoarse crackling sound synchronous with systole, heard over the pericardium in the presence of mediastinal emphysema.

Pleural rub
A discontinuous grating sound or creak in phase with breathing that occurs in the presence of pleural inflammation. Friction rubs are heard better when the stethoscope is applied firmly to the chest wall. Pleural rubs must be distinguished from similar sounds produced by movement of the scapula, ribs and thoracic musculature under the stethoscope. The latter disappear on repositioning of the stethoscope, changing pressure of application to the chest wall or by repositioning of the patient.

Pleuro-pericardial rub
A sound with features of both pleural and pericardial rub.

Unclassified noises
These are adventitious sounds not easily characterised by the above term. These include rattles, squeaks, gurgling, etc.

Recent Related Research (from Pubmed)

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References

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