ALPHA
FEV1 - volume of air forcefully expired in 1 second - calibre of vessels
FVC - volume of air to completely expel lung - total lung capacity
FEV1:FVC < 0.7 ⇒ obstructive condition something obstructs the vessels to make them smaller but volume hasn't changed proportionally. So FEV1 is lower than FVC. Eg COPD, asthma, bronchiectasis
FEV1:FVC > 0.7 ⇒ restrictive condition something is preventing the lungs from expanding to their full capacity - restricting them. Therefore the FVC decreases more than the FEV1. Eg pulmonary fibrosis, interstitial lung diseases