Which is the feature common to obstructive diseases?

• A. Increased resistance to airflow
• B. Increased total lung capacity
• C. Increased residual volume
• D. All of the above

Answer: (D)

Obstructive diseases are defined by increased resistance to airflow, particularly during expiration, due to narrowed or obstructed airways. This higher resistance slows exhalation, promoting air trapping so more air remains in the lungs after a breath, which raises residual volume. The trapped air also causes the lungs to become hyperinflated, increasing the total lung capacity, especially in conditions like emphysema where elastic recoil is lost and overdistension occurs. Because these changes commonly occur together in obstructive disease, all of the above features are observed.