In what situation can a higher residual volume be clinically significant?

A higher residual volume is clinically significant primarily in cases of obstructive lung disease. In these conditions, such as chronic obstructive pulmonary disease (COPD) or asthma, the airways become narrowed or obstructed, leading to difficulty in expelling air from the lungs. As a result, the air that remains in the lungs after exhalation — referred to as residual volume — becomes elevated.

This increase in residual volume reflects the trapping of air and indicates the impaired ability of the lungs to ventilate effectively, which can lead to a buildup of carbon dioxide and decreased oxygen exchange. Clinicians often monitor residual volume to assess the severity of obstructive lung diseases and guide treatment decisions.

In contrast, restrictive lung diseases typically lead to a decrease in total lung capacity and residual volume due to the stiffening of the lung tissue or the pleura, rather than an increase. Healthy individuals usually have normal values of residual volume, while an increase during normal expiration is not clinically significant, as residual volume is expected to remain in the lungs after exhalation. Therefore, recognizing elevated residual volume in the context of obstructive lung disease is vital for proper patient management.