, are the clicking, rattling, or crackling noises heard on auscultation of (listening to) the lung
with a stethoscope
. The sounds are caused by the "popping open" of small airways and alveoli
collapsed by fluid, exudate, or lack of aeration during expiration. The word "rales" derives from the French word râle
Rales can be heard in patients with pneumonia, atelectasis, pulmonary fibrosis, acute bronchitis, or bronchiectasis. Pulmonary edema secondary to left-sided congestive heart failure can also cause rales.
The sound of rales
Crackles (or rales) are caused by explosive opening of small airways. Cracklinuous sounds; they are intermittent
, nonmusical and brief. Crackles are much more common during the inspiratory than the expiratory phase of breathing, but they may be heard during the expiratory phase. Crackles are often associated with inflammation or infection of the small bronchi, bronchioles, and alveoli. Crackles that don't clear after a cough may indicate pulmonary edema or fluid in the alveoli due to heart failure or Acute respiratory distress syndrome
- Crackles are often described as fine, medium, and coarse. They can also be characterized as to their timing: fine crackles are usually late-inspiratory, whereas coarse crackles are early inspiratory.
- Fine crackles are soft, high-pitched, and very brief. This sound can be simulated by rolling a strand of hair between one's fingers near the ears, or by moistening one's thumb and index finger and separating them near the ears. Their presence usually indicates an interstitial process, such as pulmonary fibrosis or congestive heart failure.
- Coarse crackles are somewhat louder, lower in pitch, and last longer than fine crackles. They have been described as sounding like opening a Velcro fastener. Their presence usually indicates an airway disease, such as bronchiectasis.