values vary in the population and are influenced by age, sex, wt.,
ht. and race. Normal values will depend upon predicted reference
equations. General guidelines: Obstruction:
FEV1/FVC >= 70% = N; 60-69% = Mild; 40-59% = Mod.; 30-39% = Severe;
<30% = Very severe. Restriction:
VC >= 80% = N; 60-79% = Mild; 50-59% = Mod.; 35- 49% = Severe;
<35% = Very severe. Use TLC instead of VC if obstruction is present.