What causes crackles (rales) in the lungs?

Crackles, also known as rales, are abnormal lung sounds that occur when air moves through fluid-filled spaces within the lungs. This phenomenon is most commonly associated with conditions that lead to pulmonary edema, pneumonia, or other scenarios where fluid accumulates in the alveoli or bronchioles. When the air passes through these fluid areas, it creates a characteristic crackling sound, which can be heard during auscultation.

This sound is indicative of pathological processes affecting lung function, which may require medical intervention. In contrast, other options refer to different respiratory conditions or situations that do not lead to the distinctive crackling sound associated with fluid in the airways. Thus, the connection between crackles and the movement of air through liquid is fundamental in understanding their clinical significance in respiratory assessment.