Fine rales · crepitations (older terms)
In one sentenceBrief, high-pitched, explosive transient sounds, typically in mid-to-late inspiration. "Velcro" crackles.
Listen to the same sound in another patient. Breathing rate, chest wall, the pitch of the sound and the number of adventitious sounds vary within realistic limits.
What does it sound like?
They resemble hair rubbed between the fingers next to your ear, or Velcro being pulled apart. They recur at similar points in successive breaths.
Where is it heard?
Mostly at both bases, posteriorly.
What causes it?
Diseased small airways close during expiration. During inspiration, as the lung inflates, tension builds up and the airway suddenly opens. This sudden opening produces a sound wave that lasts milliseconds. In the stiff lung of fibrosis, opening happens only at the end of inspiration, when the inflating (transpulmonary) pressure is highest. The same airways open with each breath, so the crackles recur at similar points.
Quantitative criteria
- IDW (initial deflection width) ≈ 0.7 ms, 2CD (two-cycle duration) ≈ 5 ms (CORSA reference values).
- A single crackle lasts from a few ms to about 20 ms.
- In fibrotic ILD (52 patients, 702 recordings), inter-observer kappa for the presence of crackles was 0.57.
Clinical meaning
Fibrotic interstitial lung disease (including IPF), pulmonary congestion and other parenchymal processes. Persistent basal Velcro crackles are a reason for early investigation for ILD (HRCT), but they do not replace imaging. They change little with coughing. Soft basal crackles may be heard in people without clinical disease, especially after a period of shallow breathing.
Sounds it can be confused with
Coarse crackles are longer, lower-pitched, louder and earlier in inspiration. They may change with coughing.
A pleural rub is superficial, local and creaking. It recurs in both phases as a mirror image.
Ask the patient to take a few deep breaths and to cough. Basal crackles that disappear may be due to atelectasis. Those that persist are significant.
See the reference list for sources.