What sound is typically heard during expiration in patients with obstructive airway diseases?

Wheezes are typically heard during expiration in patients with obstructive airway diseases due to the narrowing of the airways. This narrowing can be a result of conditions such as asthma, chronic obstructive pulmonary disease (COPD), or bronchitis. As the air is forced out of the lungs during expiration, it encounters resistance in the narrowed airways, leading to a high-pitched whistling or musical sound known as a wheeze.

In obstructive airway diseases, this sound is more pronounced during expiration because it is when the airways are most constricted, making it difficult for air to flow smoothly out of the lungs. The presence of wheezes can indicate the severity of airway obstruction and help in assessing the responsiveness to bronchodilator therapy, which relaxes the airway muscles.

Other sounds such as stridor, which is typically associated with upper airway obstruction, would be heard during inhalation rather than expiration. Crackles, which indicate the presence of fluid in the airways or alveoli, are not characteristic of obstructive disease but rather seen in conditions such as pneumonia or heart failure. A friction rub is a sound produced by the movement of inflamed pleural surfaces and is not related to the obstructive airway pathology. Thus