During auscultation of a patient's chest, you hear coarse crackles throughout both inspiration and expiration. These sounds clear when the patient coughs. Which of the following is the most likely cause of these adventitious sounds?

a. Opening of closed smaller airways or al-veoli
b. Opening of collapsed large, proximal air-ways
c. Variable obstruction to flow in the upper airway
d. Movement of excessive secretions in the airways

ANS: D
Excessive mucus in the airways causes crackles that are usually coarse (low pitched) and heard during inspiration and expiration. These crackles often clear when the patient coughs or when the upper airway is suctioned.