Diagnostic role of residual volume in paediatric patients with chronic symptoms of the lower airways.

In bronchial asthma, measurement of absolute lung volumes may reveal lung dysfunction more readily than forced expiratory spirometry. Sixty-one children (aged 4-16 years) with mild to moderate bronchial asthma and 35 children (aged 7-16 years) with other symptoms of the lower airways (OSLA) were studied, and the plethysmographic results were compared with data obtained from 36 healthy volunteers aged 6-16 years. In the first test session, repeatability of forced expiratory volume in one second (FEV1), forced vital capacity (FVC), residual volume (RV), functional residual capacity (FRC) and total lung capacity (TLC) were good. Control subjects were also tested the next day, and intra-subject variability of repeat pulmonary function testing was in the normal range. The FEV1/FVC ratio was significantly higher in control subjects than in patients with asthma or OSLA, but only the decrease in RV after bronchodilator challenge separated patients with asthma from patients with OSLA. Changes in FEV1 and RV after bronchodilator challenge had a significant, although low, inverse correlation. An increase of > or = 5% in FEV1 had a positive predictive value of 44% and a negative predictive value of 68% for the clinical diagnosis of bronchial asthma; for a decrease of > or = 24% in RV, the figures were 86% and 71% respectively. The support of baseline absolute lung volumes on clinical decision-making is not necessarily great. Bronchodilator response, particularly in RV, is more pertinent and may enhance the detection of reversible lung dysfunction.