What clinical feature is most characteristic of bronchiolitis?

The most characteristic clinical feature of bronchiolitis is the presence of crackles or coarse breath sounds. Bronchiolitis, typically caused by viral infections such as respiratory syncytial virus (RSV), primarily affects infants and young children and is marked by inflammation and obstruction of the small airways (bronchioles).

As the disease progresses, mucus accumulation, airway edema, and bronchospasm can lead to these distinctive breath sounds. Crackles are heard as air moves through the narrowed and sometimes secretions-filled airways, which is a key sign of this condition.

While other features like cyanosis, wheezing, and excessive sweating may accompany bronchiolitis, they are not as definitive for the diagnosis. Cyanosis indicates oxygen deprivation and can occur in various respiratory conditions. Wheezing might be present but is often noted in broader contexts of airway obstruction and does not exclusively characterize bronchiolitis. Excessive sweating is not a typical feature of bronchiolitis.

Thus, crackles or coarse breath sounds fundamentally indicate the pathophysiological changes occurring in bronchiolitis, making it the most characteristic clinical feature.