FEV1 volume divided by FVC expressed as percent.

I am going to create some confusion. There are two ways of judging the normal range.

• Observed percent less than 75% is indicative of obstruction.

• The children and old people were not included in the original normal data to develop the nomogram. Military recruits were the "normal" subjects. As you get older the elastic recoil decreases and a value less than 75% is normally seen. Hence percent predicted is used as an alternate method. In general we don't like to use percent of percent. Anyway if you are going to use % pred, the normal range is compact between 90-100.