14. Changes in forced expiratory volume (FEV)
Expiratory volume is a spirometry measure useful to evaluate the severity of COPD. There are four stages of the disease. Patients are assigned to stage 1 or mild COPD when the FEV is 80% or more. Stage 2 or moderate COPD features FEV of 50 to 79%. Severe COPD has an FEV of 30 to 49%. And very severe COPD features an FEV lower than 30%.