Which of the following lung volumes would show to be increased if the patient was obstructed and air trapping?

Functional residual capacity (FRC) is the correct choice because it represents the volume of air remaining in the lungs after a normal expiration. In patients with obstructive lung disease, such as asthma or chronic obstructive pulmonary disease (COPD), airflow limitation leads to difficulty in fully exhaling air from the lungs. This results in a phenomenon known as air trapping, where air becomes retained in the lungs after expiration.

As a result, FRC is increased because the total amount of air left in the lungs reflects not only the residual volume (the air remaining after a forced expiration) but also the end-expiratory lung volume, which can be elevated due to air trapping. Thus, in conditions of obstruction, the functional residual capacity is typically higher than normal, demonstrating the impact of air trapping.

The other volumes, such as inspiratory capacity, tidal volume, and expiratory reserve volume, would not necessarily show an increase due to air trapping. Inspiratory capacity could potentially decrease due to the inability to take deep breaths, tidal volume may remain relatively unchanged during normal breathing patterns, and expiratory reserve volume would decrease as a result of the lungs already being over-inflated from the trapped air.