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Rales, crackles or crepitations, are the clicking, rattling, or crackling noises heard on auscultation of the lungs with a stethoscope during inhalation. The sounds are caused by the "popping open" of small airways and alveoli collapsed by fluid, exudate, or lack of aeration during expiration.

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.

Crackles (or rales) are caused by explosive opening of small airways. Crackles are referred to as discontinuous 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 adult respiratory distress syndrome (ARDS).

• 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.

• Wheeze
• Rhonchi

• MedEd at Loyola medicine/pulmonar/images/earlyral.au Audio file of rales
• Pasterkamp H, Kraman SS, and Wodicka GR; "Respiratory sounds. Advances beyond the stethoscope"; Am J Respir Crit Care Med. 1997 Sep;156(3 Pt 1):974-87

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