What are the different types of lung sounds?

Types of Lung Sounds

The main types of lung sounds include normal breath sounds (vesicular, bronchial, and tracheal) and abnormal or adventitious sounds (crackles, wheezes, rhonchi, and pleural rubs), which provide critical diagnostic information about respiratory conditions and can significantly impact morbidity and mortality when properly identified.

Normal Breath Sounds

Normal lung sounds are produced by turbulence in the airways during respiration and can be classified into three main types:

1. Vesicular (Alveolar) Sounds

   • Heard primarily at the lung bases
   • Soft, low-pitched, gentle sounds
   • Definitely louder during inspiration than expiration
   • Inspiration:expiration ratio approximately 3:1
   • Represent normal air movement in the peripheral lung fields

2. Bronchial Sounds

   • Heard over the sternum, interscapular area, and apex of lungs
   • Louder and higher-pitched than vesicular sounds
   • Equal or louder during expiration compared to inspiration
   • Inspiration:expiration ratio approximately 1:1 or 1:2
   • Normal when heard over the large airways but abnormal when heard over peripheral lung fields

3. Tracheal Sounds

   • Heard over the trachea (neck)
   • Loud, harsh, hollow sounds
   • Similar intensity during both inspiration and expiration
   • Contain the highest frequency components of all breath sounds

Abnormal (Adventitious) Lung Sounds

Abnormal lung sounds are classified into two main categories:

1. Continuous Adventitious Sounds

• Wheezes

  • High-pitched continuous sounds with dominant frequency ≥400 Hz 1
  • Musical, whistling quality
  • Usually heard during expiration but can occur in both phases
  • Associated with airway narrowing (asthma, COPD, bronchitis)
  • Produced by fluttering of airway walls when critical airflow velocity is reached
  • Duration of wheezing correlates with degree of bronchial obstruction

• Rhonchi

  • Low-pitched continuous sounds with dominant frequency ≤200 Hz 1
  • Sonorous, snoring-like quality
  • Often clear with coughing (unlike wheezes)
  • Associated with secretions in larger airways or airway thickening
  • Important clinical sign when heard over the neck, indicating potential major airway obstruction 2

2. Discontinuous Adventitious Sounds

• Crackles (Rales)

  • Brief, non-musical, explosive sounds
  • Caused by abrupt opening of previously collapsed alveoli and adjacent airways 3
  • Can be further classified as:
    • Fine crackles: high-pitched, short duration, heard during late inspiration
    • Coarse crackles: lower-pitched, longer duration, heard during early inspiration
  • The presence of crackles increases the likelihood of radiographic pneumonia 3

• Pleural Rub

  • Creaking or grating sound
  • Heard during both inspiration and expiration
  • Caused by inflamed pleural surfaces rubbing against each other
  • Not cleared by coughing

Clinical Significance

The proper identification of lung sounds has important diagnostic implications:

1. Diagnostic Value:

   • Physicians can discriminate wet from dry cough sounds, though they are less able to differentiate between specific causes like fibrosis, asthma, COPD, or bronchiectasis 3
   • Digital analysis of sound properties can help differentiate between wet and dry cough and potentially identify specific conditions like asthma, COPD, pertussis, and pneumonia 3

2. Disease Assessment:

   • In heart failure, fine rales may be heard over lung fields, indicating pulmonary congestion 3
   • In COPD, diminished breath sounds and hyperresonance have a positive likelihood ratio >5.0, making this combination a moderately strong predictor of COPD 3

3. Limitations:

   • Lung auscultation requires specialized training to differentiate sounds
   • Interpretation can be variable between examiners
   • Requires a quiet examination area, which may be difficult in some settings 3
   • WHO guidelines for frontline healthcare providers in resource-limited settings do not include lung auscultation in diagnostic criteria for child pneumonia due to these challenges 3

Emerging Technologies

Recent advances in technology are improving lung sound analysis:

• Digital stethoscopes and automated lung sound analysis may overcome educational and interpretation limitations 3
• Adaptive digital filters can reduce contaminating noises without sound-proof rooms 2
• Quantified lung sounds are being correlated with clinical, physiologic, and radiologic information 4

Lung sound analysis offers many advantages as it is safe, non-invasive, low-cost, and repeatable, making it a promising method to supplement other pulmonary function studies 2.