Pulmonary function testing

	Obstructive lung disease	Restrictive lung disease
Spirometric findings
FEV1	↓ < 80% of the predicted value or the LLN	Normal or ↓
FEV1/FVC	↓ (because ↓ in FEV1 > ↓ in FVC)	Normal or ↑ (because ↓ in FEV1 is proportional to ↓ in FVC)
VC	↓ < 80% of the predicted value or the LLN	↓
Flow-volume loop	Air trapping: scalloping of the expiratory limb; seen in conditions such as emphysema and in patients who have undergone a pneumectomy	Narrow flow-volume loop
Plethysmograph findings
RV	↑ ≥ 120% of the predicted value or the ULN	Normal or ↓
FRC	↑	↓
TLC	Normal or ↑	↓
Airway resistance	↑	Normal
Lung compliance	Normal	Normal (extrinsic causes) or ↓ (intrinsic causes)
DLCO	Variable (e.g., ↓ in emphysema, ↑ or normal in bronchial asthma, normal in chronic bronchitis)	Variable (e.g., normal with extrinsic causes, ↓ with intrinsic causes)