Fine crackles sound like hook and loop fasteners (e.g. Velcro) when they are pulled apart. These sounds are brief, high-pitched sounds. They have also been compared to wood crackling in a fireplace. Crackles are also know as rales.
Fine crackles appear in both inspiration and expiration. Observation of the timing of fine crackles within the breath cycle has diagnostic value. For example, late inspiratory fine crackles may suggest pneumonia, atelectasis or congestive heart failure. Early inspiratory or expiratory crackles are sometimes observed in patients with chronic bronchitis.