[The role of lung volume measurements by plethysmography in the follow-up of asthma in children].

In asthmatic children, control of the disease is perfect when no symptoms occur and lung function is normal. The aim of this study is to analyse the role of plethysmography in the follow-up of asthmatic children. We present the results of a retrospective study of lung function (plethysmography and forced expiratory flow) in about 100 asthmatic children aged five to 16years. FEV1/FVC less than 80% predicted was considered as pathological (airflow obstruction). The ratio RV/TLC was considered pathological if greater than 30% and RV was considered pathological if greater than 120% (lung hyperinflation). Bronchodilator reversibility was performed in all patients. All patients were studied in a stable condition. None had developed any asthmatic exacerbations during the past month. We found a significant correlation between the residual volume/total lung capacity (RV/TLC) ratio and, on one hand: FEV1 (p<0.0001, R=-0.374), and on the other hand FEV1/FVC (p=0.07, R=-0.182) or forced expiratory flow 25-75 (p=0.03, R=-0.216). When comparing children with (n=40) and without (n=60) lung hyperinflation, we noticed more diurnal symptoms (30/40 vs 10/60, p=0.05), lower weight (33.9kg vs 41.8kg, p<0.05) and lower body mass index (16.9kg/m(2) vs 18.4kg/m(2), p<0.01). Among the children with defined airway obstruction, 49% also had lung hyperinflation. Twenty-three children had normal forced expiratory ratios but an increase of the ratio RV/TLC or of RV. When compared with children without lung hyperinflation, the age at diagnosis was significantly lower (3.9+/-1.9years vs 6.2+/-3.1years, p<0.01) and weight slightly lower (31+/-10kg vs 40+/-11kg, p=0.04). In conclusion, the use of plethysmography and thus the evaluation of pulmonary hyperinflation contributed to a better appreciation of the asthmatic phenotype in children.