DIAGNOSTIC ROLE OF RESIDUAL VOLUME IN PEDIATRIC-PATIENTS WITH CHRONICSYMPTOMS OF THE LOWER AIRWAYS

In bronchial asthma, measurement of absolute lung volumes may reveal l ung 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 air ways (OSLA) were studied, and the plethysmographic results were compar ed with data obtained from 36 healthy volunteers aged 6-16 years. In t he first test session, repeatability of forced expiratory volume in on e second (FEV1), forced vital capacity (FVC), residual volume (RV), fu nctional residual capacity (FRC) and total lung capacity (TLC) were go od. Control subjects were also tested the next day, and intra-subject variability of repeat pulmonary function testing was in the normal ran ge. The FEV1/FVC ratio was significantly higher in control subjects th an 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 greate r than or equal to 5 % in FEV1 had a positive predictive value of 44% and a negative predictive value of 68% for the clinical diagnosis of b ronchial asthma; for a decrease of greater than or equal to 24% in RV, the figures were 86% and 71% respectively. The support of baseline ab solute lung volumes on clinical decisionmaking is not necessarily grea t. Bronchodilator response, particularly in RV, is more pertinent and may enhance the detection of reversible lung dysfunction.