Abnormalities of plethysmographic lung volumes in asthmatic children

While lung hyperinflation is frequent in asthma, measurement of lung volumes is not recommended in current guidelines. The aim of this descriptive functional study was to assess whether systematic measurement of volumes by plethysmography may detect isolated hyperinflation with normal expiratory flows.

One hundred sixty asthmatic children (mean age + or - SD: 10.8 + or - 2.7 years; 50 girls) receiving inhaled corticosteroid underwent lung function tests before and after bronchodilation (BD). To avoid the problem of dysanaptic lung growth on predicted values in childhood, airflow limitation and hyperinflation were defined by ratios (FEV(1,%pred)/FVC(%pred) for the former, RV/TLC for the latter) and values below and above the 5th or 95th percentiles of reference values, were chosen as cut-off values.

Different functional phenotypes were evidenced, mainly normal lung function (142/160 [89%] after BD), but also isolated airflow limitation (35/160 [22%] before and 7/160 [4%] after BD) and isolated hyperinflation (17/160 [11%] before and 11/160 [7%] after BD), while the combination of both impairments before BD (13/160 [8%]) was never observed after BD. There was no statistical relationship between airflow limitation and hyperinflation, either before or after BD. Indices of spirometry (FEV(1), FEF(50%)) were unable to predict isolated hyperinflation that corresponds to small airway obstructive syndrome.

Isolated hyperinflation is not infrequent in asthmatic children (7-11%) and small airway obstruction is not detected by forced expiratory flows.