Forced Expiratory Volume (FEV1), and Forced Vital Capacity (FVC) ratio is significant when determining lung diseases. This ratio determines if the patient is experiencing an obstructive or restrictive lung disease. Also, it is a significant indicator for COPD diagnosis. When in a restrictive condition, the patient has difficulties inhaling. In obstructive conditions, patients’ ability to exhale is interrupted.
Diseases like COPD & asthma get into the category of obstructive lung diseases. In cases like this, the FEV1 value is lower because there is an obstruction of air that escapes the lungs. That's why the FEV1/FVC ratio is low. According to The National Institute for Clinical Excellence, if the FEV1 value is less than 80% predicted and FEV1/FVC ratio is less than 70%, that can lead to a COPD diagnosis. In cases where the FEV1 value is less than 50% predicted, the diagnosis can be severe COPD.
On the other hand, FEV1 and FVC values may be equally reduced in restrictive conditions, such as pulmonary fibrosis. So, the FEV1/FVC ratio should be normal or the decrease in FVC should be higher than the decrease in FEV1 and the FEV1/FVC ratio should increase.