From the Guidelines
Patients with interstitial pneumonia (PNA) on chest X-ray (CXR) typically present with fine crackles (also called rales) on lung auscultation, characterized as "velcro" crackles, which are usually bilateral, predominantly heard during inspiration, and most prominent at the lung bases 1. These crackles have a fine, high-pitched quality often described as similar to the sound of rubbing hair between your fingers near your ear or like Velcro being pulled apart. The key characteristics of these lung sounds include:
- Fine, high-pitched quality
- Bilateral distribution
- Predominantly heard during inspiration
- Most prominent at the lung bases
- Described as "velcro" crackles These sounds occur due to the sudden opening of small airways and alveoli that were previously closed or fluid-filled, which is characteristic of the inflammatory process and fluid accumulation in the interstitial spaces of the lungs. In some cases, patients may also have decreased breath sounds in affected areas due to reduced air movement. Unlike lobar pneumonia, which often produces bronchial breath sounds and egophony, interstitial pneumonia typically maintains vesicular breath sounds with superimposed crackles. The extent and intensity of these crackles generally correlate with disease severity, though auscultation findings should always be interpreted alongside clinical presentation and imaging results 1.
From the Research
Lung Sounds on Auscultation for Interstitial PNA
- The lung sound on auscultation for a patient with interstitial PNA on CXR is typically characterized by crackles 2, 3.
- Crackles are high-pitched sounds that are often heard during inspiration, and sometimes during expiration 2.
- In patients with interstitial pulmonary fibrosis, crackles tend to have a higher frequency and lower transmission coefficient compared to those with pneumonia or congestive heart failure 3.
- The crackle frequency in interstitial pulmonary fibrosis averaged 462 +/- 50 Hz, which is statistically different from that in pneumonia (302 +/- 47 Hz) and congestive heart failure (311 +/- 62 Hz) 3.
- The crackle transmission coefficient in interstitial pulmonary fibrosis averaged 14 +/- 4%, which is also statistically different from that in pneumonia (24 +/- 5%) and congestive heart failure (25 +/- 8%) 3.
Characteristics of Crackles
- Inspiratory crackles are almost twice as numerous as expiratory crackles and have predominately negative polarity 2.
- The mechanism of crackle generation is thought to be related to sudden airway closure events during expiration and sudden airway reopening during inspiration 2.
- The characteristics of crackles can vary depending on the underlying condition, and may be useful in differentiating between interstitial pulmonary fibrosis, pneumonia, and congestive heart failure 3.