What is a significant feature of chronic obstructive pulmonary disease (COPD)?

Chronic obstructive pulmonary disease (COPD) is characterized primarily by chronic airflow limitation that is not fully reversible. A significant feature of COPD is increased breathlessness, particularly during physical activity, and difficulty in expelling mucus due to obstructive airways. This symptom arises from inflammation and damage to the airways, which leads to narrowing and increased resistance to airflow.

Patients often experience chronic bronchitis, one of the two main components of COPD, which involves persistent cough and sputum production. However, the focus on breathlessness and mucus retention underscores the obstructive nature of the disease. The difficulty in clearing mucus can lead to further respiratory complications and exacerbate underlying conditions, making this feature critical for understanding COPD's impact on an individual's respiratory function.

In contrast to the other choices, the features associated with them either do not align with typical COPD symptoms or may represent other pulmonary conditions. For example, periodic coughing without phlegm can be seen in other respiratory diseases or conditions that do not involve obstruction; sudden chest pain when breathing might suggest pleurisy or pulmonary embolism, and stridor during rest indicates upper airway obstruction rather than the lower airway issues characteristic of COPD. Thus, the correct identification of increased breathlessness and difficulty expelling mucus