Is it possible for a Subject to have vital capacity single stage within normal range but value FEV1 below range?

Yes, it is possible for a subject to have vital capacity single stage within normal range but value FEV1 below range. This can occur in restrictive lung diseases, where the lungs are unable to expand fully, resulting in a reduced FEV1, but the subject may still have a normal vital capacity. Vital capacity measures the total amount of air a person can exhale after taking the deepest breath possible, while FEV1 measures the amount of air that can be forcefully exhaled in the first second of exhalation. In certain restrictive lung diseases, the inability to fully expand the lungs can affect the ability to exhale forcibly, which leads to a decreased FEV1, while the vital capacity may remain within the normal range.