Which clinical finding is characteristic only of chronic bronchitis?

Chronic bronchitis is characterized by the inflammation of the bronchi, leading to persistent cough and mucus production. Cyanosis, which is a bluish discoloration of the skin or mucous membranes due to low oxygen saturation in the blood, is closely associated with chronic bronchitis. This occurs because the chronic inflammation and obstruction in the airways result in poor gas exchange and subsequently decreased oxygen levels.

While other findings like a dry cough, barrel chest, and wheezing can occur in various respiratory conditions, they are not exclusive to chronic bronchitis. For example, a dry cough might also occur in other conditions or respiratory infections, barrel chest is a feature often associated with emphysema, and wheezing can be seen in conditions such as asthma or bronchospasm.

In summary, cyanosis is unique to chronic bronchitis among the options listed, as it directly reflects the chronic low levels of oxygenation that can arise from the persistent airway obstruction and impaired gas exchange found in this condition.