Check FEV1/FVC ratio
If FEV1/FVC is low, think obstructive pattern
If FEV1/FVC is normal or high, think restrictive pattern or normal
Check FVC
If FVC is low with low FEV1/FVC, obstruction with air trapping is likely
If FVC is low with normal or high FEV1/FVC, restriction is likely
Check TLC
Low TLC confirms restriction
Normal or high TLC argues against restriction
Check RV
High RV suggests air trapping
Check DLCO
Low DLCO suggests impaired gas transfer
Low DLCO with obstruction suggests emphysema or other parenchymal disease
Low DLCO with restriction suggests interstitial lung disease
Normal DLCO with restriction suggests extrapulmonary restriction
Compare pre-bronchodilator and post-bronchodilator values
Significant FEV1 or FVC improvement suggests reversible obstruction
Assess severity using percent predicted values
Review flow-volume loop shape
Scooped expiratory limb suggests obstruction
Small loop with preserved shape suggests restriction
Flattened inspiratory limb suggests variable extrathoracic obstruction
Flattened expiratory limb suggests variable intrathoracic obstruction
Flattened both limbs suggests fixed upper airway obstruction