What do different lung sounds indicate?

Understanding Different Lung Sounds and Their Clinical Significance

Lung sounds provide critical diagnostic information about respiratory conditions, and proper interpretation of these sounds can significantly impact patient morbidity and mortality by enabling early detection and appropriate treatment of respiratory diseases.

Normal Lung Sounds

• Vesicular (Alveolar) Sounds:

  • Heard primarily at lung bases
  • Soft, low-pitched sounds
  • Louder during inspiration than expiration (inspiration:expiration ratio of 3:1)
  • Represent normal air movement through smaller airways and alveoli 1

• Bronchial Sounds:

  • Heard over the sternum, apex, and interscapular areas
  • Higher pitched than vesicular sounds
  • Equal or louder during expiration
  • Represent air movement through larger airways 1

• Tracheal Sounds:

  • Heard over the trachea
  • Harsh, hollow quality
  • Represent turbulent airflow through the trachea 1

Abnormal (Adventitious) Lung Sounds

Continuous Sounds

• Wheezes:

  • High-pitched, musical sounds
  • Usually heard during expiration but can occur during inspiration
  • Mechanism: Flutter/flow limitation in airways causing airway wall oscillation
  • Clinical significance: Airway narrowing (asthma, COPD, bronchitis)
  • May not be as sensitive as changes in basic lung sounds for detecting acute airway narrowing 2

• Rhonchi:

  • Low-pitched, sonorous, snoring-like sounds
  • Usually heard during expiration
  • Mechanism: Secretions in larger airways or airway narrowing
  • Clinical significance: Chronic bronchitis, COPD, bronchiectasis 1
  • Often heard over the neck in cases of tracheal or major bronchial stenosis 1

Discontinuous Sounds

• Crackles (Rales):

  • Brief, non-musical, popping sounds
  • Can be fine (high-pitched, short duration) or coarse (lower-pitched, longer duration)
  • Fine crackles: Heard during late inspiration, not cleared by coughing
  • Coarse crackles: Heard during early inspiration, may clear with coughing
  • Mechanism: Sudden opening of previously closed small airways
  • Clinical significance: Pulmonary edema, pneumonia, pulmonary fibrosis, early COPD 3

• Pleural Friction Rub:

  • Creaking or grating sound
  • Heard during both inspiration and expiration
  • Mechanism: Inflamed pleural surfaces rubbing together
  • Clinical significance: Pleuritis, pleural inflammation 3

Advanced Diagnostic Applications

Lung Ultrasound

Lung ultrasound has emerged as a valuable diagnostic tool that can complement or even replace traditional auscultation in many settings:

• B-lines (Interstitial Syndrome):

  • Vertical hyperechoic artifacts arising from the pleural line
  • Clinical significance: Pulmonary edema, ARDS, pneumonia, pulmonary fibrosis
  • Number of B-lines correlates with severity of pulmonary congestion 3

• Lung Consolidation:

  • Subpleural echo-poor region with tissue-like echotexture
  • Clinical significance: Pneumonia, pulmonary embolism, atelectasis, lung contusion
  • Lung ultrasound can differentiate between these causes 3

• Pleural Effusion:

  • Anechoic space between parietal and visceral pleura
  • Internal echoes suggest exudate or hemorrhage
  • More accurate than supine radiography for detection 3

Pediatric Applications

• Respiratory Distress Syndrome (RDS):

  • Ultrasound signs: Pleural line abnormalities, absence of spared areas, bilateral confluent B-lines
  • As accurate as chest radiography for diagnosis 3, 4

• Transient Tachypnea of the Newborn (TTN):

  • Ultrasound signs: Bilateral confluent B-lines in dependent areas ("white lung") with normal appearance in superior fields
  • More specific findings than chest X-ray 3, 4

• Pneumonia in Children:

  • Lung ultrasound as accurate as chest radiography
  • Can detect pneumonia not visible on chest X-ray 4

Technological Advances in Lung Sound Analysis

• Computerized Analysis:

  • Cepstral-based features (particularly mel-frequency cepstral coefficients) outperform wavelet-based features for classifying normal, wheeze, and crackle sounds 5
  • Can distinguish between different respiratory conditions with high accuracy 6

• Noise Detection and Filtering:

  • Adaptive digital filters can reduce contaminating noises without sound-proof rooms 1
  • Algorithms can identify and filter different types of noise (vocalizations, chest movement, background voices) 7

Clinical Pearls and Pitfalls

• Forced Expiratory Wheeze (FEW):

  • May be an early sign of airway obstruction in asthma patients
  • Mechanism: Airway wall oscillation and vortex shedding in central airways 2

• Common Pitfalls:

  • Mistaking transmitted upper airway sounds for lung pathology
  • Failing to recognize that absence of wheezing doesn't rule out severe bronchospasm
  • Over-relying on lung sounds alone without clinical context
  • Not recognizing that the quality of lung sounds can be affected by body habitus, patient position, and breathing effort

• Best Practices:

  • Always compare symmetrical areas of both lungs
  • Listen through a complete respiratory cycle
  • Have patients take deep breaths through the mouth
  • Consider using lung ultrasound when available, especially in critical care settings 3

Conclusion

Proper interpretation of lung sounds remains a fundamental clinical skill that can guide diagnosis and management of respiratory conditions. The integration of traditional auscultation with newer technologies like lung ultrasound and computerized sound analysis offers improved diagnostic accuracy and monitoring capabilities for respiratory diseases, ultimately improving patient outcomes.