ABSTRACT
D isco n tin u o u s S o u n d s Crackles are discrete vibrations that result from the sudden release of energy stored in elastic recoil or surface tension forces within the lung. Forgacs postulated that the sudden opening of collapsed airways is the likely cause of crackles in such conditions as atelectasis or pulmonary fibrosis. It is probably the mechanism for some of the crackles of congestive heart failure (CHF) as well. Dependent portions of the lung tend to collapse because the lung sits on its own weight. According to this theory, crackles occur as closed airways reopen. Some credence for this belief is provided by the observation that when placed in either lateral decubitus position, a patient with CHF will tend to have more crackles on the dependent side. Another mechanism for the production of crackles is related to fluid or secretions in the lung. The coarse, discontinuous sounds occurring in pulmonary edema or other conditions in which fluid is found in the airways are probably caused by rupture of bubbles or disruption of fluid films. Such crackles often occur during both inspiration and expiration. Figure 4 diagrams the mechanisms believed to be responsible for crackles.
