Crackles Expiratory crackles 2018-07-15T21:50:28Z Crackles that occur during expiration. Crackles are predominantly inspiratory in nature, but can also occur during expiration. It has been described in COPD, bronchiectasis, and IPF. One theory of the pathogenesis of expritory crackles states that some airways collapse during early expiration and air trapping develops. As expiration progresses, the pressure in the trapped region gradually increase, leading to a widened pressure difference across the airways. Once this pressure difference reaches the critical opening pressure, the airway pops open during expiration, producing crackles.