Adventitious Respiratory Sounds

Definition

• Adventitious sounds are abnormal, superimposed respiratory sounds heard on chest auscultation, which serve as critical clinical pointers to the anatomical level and etiology of respiratory pathology.

1. Stridor

• Definition & Pathophysiology: Stridor is a harsh, vibratory, and typically high-pitched sound produced by turbulent airflow through a partially obstructed respiratory passage.
• Anatomical Level: It originates from the upper respiratory tract, localizing the obstruction to the anatomical structures above the thoracic inlet, including the pharynx, larynx, and extra-thoracic trachea.
• Clinical Variants:
  • Inspiratory Stridor: A high-pitched sound produced when the child inspires through a spasmodically closed or obstructed glottis.
  • Expiratory Stridor: A singing or harsh sound resulting from tracheobronchial obstruction or semi-approximated vocal cords offering resistance to exhalation.
  • Biphasic Stridor: A harsh vibratory sound heard during both phases of respiration, caused by a fixed obstruction where there is minimal or no change in the airway diameter during the respiratory cycle.
• Clinical Conditions:
  • Infectious causes include croup (most common), diphtheria, bacterial tracheitis, retropharyngeal abscess, and acute epiglottitis.
  • Non-infectious causes include upper airway foreign body aspiration, angioneurotic edema (anaphylaxis), laryngomalacia, and airway burns.

2. Wheeze

• Definition & Pathophysiology: Wheeze is a high-pitched whistling sound predominantly heard during expiration. It is generated by vibrations during the passage of air through a narrowed or constricted airway lumen. In such scenarios, expiration becomes an active, energy-consuming process rather than a passive one, often accompanied by a prolonged expiratory phase.
• Anatomical Level: It denotes a lower airway obstruction, localizing the pathology to the intra-thoracic trachea, bronchi, and bronchioles.
• Clinical Conditions:
  • Infectious causes include acute viral bronchiolitis (e.g., Respiratory Syncytial Virus) and bronchopneumonia.
  • Inflammatory or reactive conditions include acute bronchial asthma and anaphylaxis.
  • Structural or mechanical obstructions include tracheobronchial foreign body aspiration, airway hemangiomas, vascular rings/slings, and extrinsic compression by mediastinal lymph nodes or tumors.
  • Cardiovascular conditions such as congestive cardiac failure (CCF) or myocarditis can also produce a "cardiac wheeze".
• Clinical Caveat: In severe lower airway obstruction (e.g., severe asthma), wheezing may disappear, resulting in a "silent chest"; this is an ominous sign indicating severely inadequate air exchange and imminent respiratory arrest.

3. Crepitations (Crackles)

• Definition & Pathophysiology: Crepitations are discontinuous, clicking, or rattling sounds primarily heard during the inspiratory phase. They result from the sudden opening of collapsed small airways and alveoli, or from air bubbling through fluid, exudates, or transudates in the alveolar spaces.
• Anatomical Level: The presence of crepitations localizes the primary pathology to the lung parenchyma, specifically the alveoli and interstitial spaces.
• Clinical Conditions:
  • Infectious etiologies include viral or bacterial community-acquired pneumonia.
  • Non-infectious etiologies include acute respiratory distress syndrome (ARDS), and cardiogenic or non-cardiogenic pulmonary edema (such as that seen in severe malaria, systemic inflammation, or congestive heart failure).

4. Grunting

• Definition & Pathophysiology: Grunting is a short, explosive, low-pitched sound heard during expiration. It is a compensatory physiological response where the patient exhales against a partially closed glottis. This maneuver generates intrinsic positive end-expiratory pressure (auto-PEEP), which stints the airways, prevents alveolar collapse, and helps maintain functional residual capacity.
• Anatomical Level: Although the sound itself is mechanically generated at the level of the upper airway (glottis), it is a classic clinical marker localizing the primary pathology to the lung parenchyma.
• Clinical Conditions:
  • It is most frequently observed in neonates, infants, and toddlers suffering from severe parenchymal lung diseases, primarily severe bacterial or viral pneumonia.
  • It is also a hallmark of severe hypoxemic states with poor lung compliance, such as ARDS or severe acute pulmonary edema.

Clinical Correlation of Adventitious Sounds