"Small airways disease" in children: no test is best.

Tests claimed to detect small airway disease were evaluated in children. Fifty-two 
subjects who were normal, 30 with cystic fibrosis (CF), and 35 
with asthma were selected on the basis of normal spirometry, informed 
consent being obtained from them and their parents. Tests undertaken were 
measurement of maximum expiratory flow volume curves breathing air and a 
helium-oxygen mixture, single breath nitrogen washout curves, lung volumes, and, except 
in the normal subjects, measurement of arterial oxygen tension. Closing volumes 
were normal in most children with CF and asthma, whereas the 
slope of the alveolar plateau was abnormal in 83%. Maximum expiratory 
flow rate at 50% of total lung capacity was reduced in 
65% and maximum mid-expiratory flow rate in 57%; residual volume increased 
in 51%, and results of other tests were abnormal in less 
than 50% of the children. There was evidence suggesting that lung 
disease was more patchy in children with mild CF than in 
those with interval phase asthma. These tests do not detect specific 
pathological processes in small airways but reflect the consequences of small 
airway abnormalities, which may vary in the same disease as well 
as in different diseases. No one test alone appears most useful. 
Together they contribute to understanding the functional abnormalities present in each 
individual. 