Breath Sounds

Origination of Breath Sounds

  • Breath sounds originate in the large airways where air velocity and turbulence induce vibrations in the airway walls. 

  • Normal breath sound production is directly related to air flow velocity and airway lumen architecture. 

  • Air flow velocity is primarily determined by pulmonary ventilation  and TOTAL cross sectional airway area

  • terminal bronchioles (airways with a diameter <2 mm) and alveoli does not  contribute to breath sounds as the air velocity at this level is too slow to produce significant turbulence and sound waves. 

  • However, terminal airway and alveolar disease does modify the breath sounds heard at the surface by either increasing or decreasing the sound transmission through the diseased tissue.

  • Thus, the sounds that are heard at the periphery of the lung are produced in more central (hilar) regions and are altered in intensity and tonal quality as they pass through pulmonary tissue to the periphery.


Normal Breath Sounds

A. Vesicular Sounds

  • They are heard over the periphery of the lung field.
  • consist of a quiet, wispy inspiratory phase followed by a short, almost silent expiratory phase (because of decreasing airflow) 
  • As stated earlier, these sounds are NOT produced by air moving through the terminal bronchioles and alveoli but caused by turbulent flow in large airways. 
  • intensity may be associated with pulmonary consolidation.
  • breath sounds are loudest at the apex in early inspiration and at the bases in mid-inspiration.
  • Causes of diminished vesicular breathing( Reduced conduction,Reduced air flow )

  • Obesity/thick chest wall
  • Pleural effusion or thickening
  • Pneumothorax

  • Generalized, e.g. COPD
  • Localized, e.g. collapsed lung due to occluding lung cancer

B. Bronchial Sounds

  • They are normally heard over the trachea and larynx.
  • consist of a full inspiratory and expiratory phase
  • there is an audible gap between the inspiratory and expiratory phase sounds 
  • the inspiratory phase usually being louder. 
  • The sounds of bronchial breathing are generated by turbulent air flow in large airways
  • similar sounds can be heard in healthy patients by listening over the trachea.
  • not normally heard over the thorax in resting animals( can be heard after exercise)
  • Causes of bronchial breath sounds ( situation where sound conducted more effectively to the chest wall )

  • Lung consolidation (pneumonia)

  • Localized pulmonary fibrosis
  • At the top of a pleural effusion
  • Collapsed lung (where the underlying major bronchus is patent)

C. Bronchovesicular Sounds

  • They are normally heard over the hilar region
  • Bronchovesicular breath sounds consist of a full inspiratory phase with a shortened and softer expiratory phase. 
  •    Increased intensity of bronchovesicular sounds is most often  associated with increased ventilation or pulmonary consolidation.

Abnormal Breath Sounds (Added sounds)

A. Crackles

  • Crackles are discontinuous, explosive, "popping" sounds that originate within the airways. 
  • They are heard when an obstructed airway suddenly opens and the pressures on either side of the obstruction suddenly equilibrates resulting in transient, distinct vibrations in the airway wall. 
  • The dynamic airway obstruction can be caused by either accumulation of secretions within the airway lumen or by airway collapse caused by pressure from inflammation or edema in surrounding pulmonary tissue. 
  • Crackles can be heard during inspiration when intrathoracic negative pressure results in opening of the airways or on expiration when thoracic positive pressure forces collapsed or blocked airways open. 
  • Crackles may also be heard when air bubbles through secretions in major bronchi, dilated bronchi as in bronchiectasis or in pulmonary cavities
  • Crackles are heard more commonly during inspiration than expiration.

Phase of inspiration

  • Early : Small airways disease as in bronchiolitis
  • Middle : Pulmonary oedema
  • Late: Pulmonary fibrosis (fine-rubbing hair between the fingers),Pulmonary oedema (medium),Bronchial secretions in COPD, pneumonia, etc. (coarse) lung abscess, tubercular lung cavities (coarse)
  • Biphasic: Bronchiectasis (coarse)-throughout inspiration and expiration

B. Wheezes
  • Wheezes are continuous musical tones that are most commonly heard at end inspiration or early expiration. 
  • They result as a collapsed airway lumen gradually opens during inspiration or gradually closes during expiration. 
  • As the airway lumen becomes smaller, the air flow velocity increases resulting in harmonic vibration of the airway wall
  • Wheezes can be classified as either high pitched (disease of the small airways ) or low pitched (disease of larger airways) wheezes. 
  • Wheeze tends to be louder on expiration because airways normally dilate during inspiration and narrow on expiration.
  • Wheezes are significant as they imply decreased airway lumen diameter either due to thickening of reactive airway walls or collapse of airways due to pressure from surrounding pulmonary disease.
  • Wheeze is characteristic of asthma and COPD.
  • A fixed bronchial obstruction, most commonly due to lung cancer, may cause localized wheeze with a single musical note that does not clear on coughing.
  • It is very important to distinguish wheeze from inspiratory stridor.

C. Stridor

  • Stridor are intense continuous monophonic wheezes heard loudest over extrathoracic airways. 
  • Stridor is significant and indicates upper airway obstruction.
  • They tend to be accentuated during inspiration when extrathoracic airways collapse due to lower internal lumen (-) pressure. 
  • They can often be heard without the aid of a stethoscope. 
  • Careful auscultation with a stethoscope can usually identify an area of maximum intensity that is associated with the airway obstruction. 
  • This is typically either at the larynx or at the thoracic inlet. 
  • These extrathoracic sounds are often referred down the airways and can often be heard over the thorax and are often mistaken as pulmonary wheezes. 

D. Pleural friction rub
  • A pleural rub is produced when inflamed parietal and visceral pleura move over one another.
  • It is best heard with the diaphragm of the stethoscope.
  • It may be heard only on deep breathing at the end of inspiration and beginning of expiration.
  • A pleural rub is usually associated with pleuritic pain and may be heard over areas of inflamed pleura in pulmonary thromboembolism, pneumonia and pulmonary vasculitis.
  • If the pleura adjacent to the pericardium is involved a pleuropericardial rub may also be heard.
  • Pleural friction rubs disappear if an effusion separates the pleural surfaces. 


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