<prompt> Asthma - spirometry features areFEV upward ArrowFEV 1 FEV ratio downward arrowPEF upward ArrowRV downward arrow  <response>: In asthma,FEV will be decreased with decreased FEV1FVC ratio.RV will be increased due to exaggerated airway closure at low lung volumes,and this elevation of RV reduces FVC.Peak flow meter shows reduced PEF.A diurnal variation in PEF of more than 20 is considered diagnostic of asthma. Reference:Harrisons medicine-18th edition,page no:2094;Davidsons medicine-22nd edition,page no:668. 