Gas flow at 50% of forced expiration/Gas flow at 50% of forced inspiration^post bronchodilation:RelVRat:Pt:Respiratory system:Qn
gas flow at 50% of forced expiration/gas flow at 50% of forced inspiration^post bronchodilation:relvrat:pt:respiratory system:qn
FEF 50%/FIV 50% p BD
fef 50%/fiv 50% p bd