3 The number of closed airways that reopen directly affects the crackle number, as each reopening event causes one or more crackles. 1, 3, 6 Crackle duration is related to airway size, with smaller airways thought to give rise to crackles of shorter duration. 1), which is determined as the time from the beginning of a crackle to the point where the crackle has completed 2 cycles 5 and quantity (such as the number of crackles per breathing cycle ). 3, 4 Crackles can be described in terms of duration (such as the crackle 2-cycle duration see Fig. The mechanism to generate crackles is believed to be associated with the sudden reopening of closed airways, which result from secretion obstruction, bronchoconstriction, chronic inflammation, and loss of airway cartilaginous support. Crackles have been reported to be the most frequent of adventious lung sounds that are indicative of pulmonary diseases. Recent technological advances mean that lung sounds and their characteristics can now be recorded and objectively quantified, providing useful information on lung health. Use of standard auscultation to listen to lung sounds is an accepted component of routine clinical assessment, but it is a subjective process.

Emphysema lung sounds