Lung volumes show significantly decreased functional residual capacity , but otherwise normal, what's this mean? doc says i have asthma but decreased frc online says restrictive disease im scared!

Decrease FRC: Frc is the volume of air present in the lungs at the end of passive expiration. Obesity and posture will decrease the frc. I am imaging you just got a complete pulmonary function test. In asthmatic patient, the FRC can be normal or high if associated with emphysema or more chronic obstructive conditions. Low FRC with normal pft is not diagnostic of restrictive lung disease. Trust your lung doctor.

Complicated question: It's hard to give a great answer without the entire results of your breathing test, but if only your FRC is reduced there may be nothing much at all wrong with you. One common cause of this is obesity which makes the lungs "squish up" and appear small on tests. If you're fairly skinny, however, it may be a little more complicated. Talk with your doc or ask about a lung specialist if worried.