forced expiratory volume in one second

Last reviewed 07/2021

FEV1 is the volume of air expelled in the first second of maximal forced expiration from a position of full inspiration.

In normal subjects the fraction of the FVC which can be expelled in one second is:

  • >80 % predicted value


  • is reduced in obstructive respiratory disease e.g. asthma, mild to moderate chronic obstructive pulmonary disease (COPD)
  • is reduced in restrictive respiratory disease e.g. pulmonary fibrosis
  • correlates with maximal exercise capacity


  1. The Practitioner 2005; 249:180-188.