AGE-RELATED-CHANGES IN BRONCHIAL HYPERREACTIVITY DURING THE ADOLESCENT PERIOD

To evaluate the influence of branchial hyperreactivity on the improvem ent of asthma seen during adolescence, age-related changes of bronchia l reactivity to methacholine (BRm) in adolescence were evaluated in tw o studies. Study 1 included 261 asthmatic children and 89 controls, ag ed 6-26 years, and in Study 2, yearly BRm variations from age 11 to 16 years of 23 asthmatic children of study 1 were studied. Methacholine inhalation challenge was performed by using an oscillation method; tha t is, respiratory resistance (Rrs) was directly measured by an oscilla tion technique, and subsequent doses were then doubled, until a twofol d increase in Rrs from the baseline was reached. The cumulative dose o f methacholine at the inflection point of the Rrs was considered to re present the BRm. From ages 6 to 9, D-min in the asthmatic children wer e low (from 2.07 units to 1.38 units), but after age 12, the value gra dually increased, and finally became sustained after age 16 (from 2.27 units to 4.80 units). These same age-related changes were seen:in the age-matched controls. From ages 6 to 11, D-min in the control childre n were also low (from 8.07 units to 12.9 units), but after age 12, D-m in gradually increased, and finally became sustained after age 16 (fro m 18.5 units to 43.2 units). However, for each year, the D-min of the asthmatic children were significantly lower than those of the controls . Further, the mean of yearly D-min variation from age 13 was less tha n that of younger subjects (from 0.65 unit/year to 0.92 unit/year, fro m 1.16 units/year younger subjects (from 0.65 unit/year to 0.92 unit/y ear, from 1.16 units/year to 4.16 units/year, respectively). We, there fore, concluded that the natural age-related BRm changes and the incre ased stability of yearly BRm variation that occur in adolescence may p lay a role in the improvement of childhood asthma seen during this per iod.