What do you think the vital capacity of Michael Jordan! When I was at Northwestern University as a fellow, Dr David Cugell (my mentor) was performing PFT in all of the then Chicago bulls. The values were unbelievable. On the same day there was a 70 year old veteran 4 feet 10 inches tall having PFT. What do you think his vital capacity was!. You got the picture.

Normal PFT values depend on many variables like height, weight, sex etc. A nomogram is developed using a large number of normal people and the value will be compared to that obtained from predicted based on his/her height weight etc. A normal range is 2 standard deviation from mean and it varies from test to test. In general it is 20%. Hence if you are looking at a first PFT you can consider a value as abnormal only if it is outside 2 standard deviation( 80-120%). Hence I always start by looking at percent predicted value to make a decision whether it is in normal range or not. Don't worry about the actual observed value (for now).