Does the FEF25-75 or the FEF75 have any value in assessing lung disease in children with cystic fibrosis or asthma?

While the FEV1 had been recognized as an excellent indicator of disability, it is not very sensitive to early and mild disease. In cystic fibrosis (CF) small airway disease is believed to be one of the early hallmarks and indices such as the FEF25-75 and FEF75 have been proposed as sensitive markers of early disease. The site of early disease in asthma is not as well worked out. Recently a study of more than 20,000 spirometries found that neither of these indices added anything to the FEV1 /FVC but that study was not disease specific and contained both adults and children and the adults were the most numerous. To see if this would be true in children, 1,175 spirograms from children 6 to 18 years of age with CF or asthma whose FEV1 and FVC were above the lower limit of normal were taken from sequential studies. The data expressed in z scores was plotted with either the FEF25-75 or FEF75 plotted against FEV1 /FVC. In both diseases, but particularly in asthma, the FEV1 /FVC was more likely to be abnormal than either of the other two indices for suggesting that for children, early, or mild disease will be more apparent using the FEV1 /FVC than any other index.