crackles

Crackles are brief, discontinuous, popping or crinkling sounds heard through the stethoscope, classically compared to the sound of pulling apart Velcro or crinkling cellophane near your ear. They are made when small air spaces that had been collapsed or filled with fluid suddenly snap open as air rushes in.

Unlike the continuous tones of wheezes and rhonchi, crackles are a series of tiny separate clicks. Their timing and quality carry information. Fine, late-inspiratory crackles at the lung bases are typical of pulmonary fibrosis or early fluid; coarser, earlier crackles that may change with coughing suggest secretions or larger-airway disease; crackles that clear when the patient takes a few deep breaths often come from areas that were simply under-aerated.

Crackles appear in many conditions: pneumonia, pulmonary edema from heart failure, interstitial lung disease and bronchiectasis among them. They are sensitive but not specific, so their location, fineness and timing — together with the rest of the examination and imaging — point toward the cause rather than naming it outright.