Crackles and wheezes.

Abstract This is an essay on the genesis of adventitious lung sounds, based on clinical and experimental observations. Crackling is usually due to the explosive opening of airways in territories of the lung deflated to residual volume. Wheezing is generated by air passing at high velocity through an airway narrowed to the point of closure. The pitch of the wheeze is largely determined by the linear velocity of this jet of air and is independent of the calibre and length of the airway. The clinical interpretation of adventitious sounds is discussed in the light of these observations.