Age-related changes in bronchial hyperreactivity during the adolescent period

To evaluate the influence of bronchial hyperreactivity on the improvement of asthma seen during adolescence, age-related changes of bronchial reactivity to methacholine (BRm) in adolescence were evaluated in two studies. Study 1 included 261 asthmatic children and 89 controls, aged 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; that is, respiratory resistance (Rrs) was directly measured by an oscillation technique, and subsequent doses were then doubled, until a twofold increase in Rrs from the baseline was reached. The cumulative dose of methacholine at the inflection point of the Rrs was considered to represent the BRm. From ages 6 to 9, Dmin in the asthmatic children were low (from 2.07 units to 1.38 units), but after age 12, the value gradually 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, Dmin in the control children were also low (from 8.07 units to 12.9 units), but after age 12, Dmin gradually increased, and finally became sustained after age 16 (from 18.5 units to 43.2 units). However, for each year, the Dmin of the asthmatic children were significantly lower than those of the controls. Further, the mean of yearly Dmin variation from age 13 was less than that of younger subjects (from 0.65 unit/year to 0.92 unit/year, from 1.16 units/year younger subjects (from 0.65 unit/year to 0.92 unit/year, from 1.16 units/year to 4.16 units/year, respectively). We, therefore, concluded that the natural age-related BRm changes and the increased stability of yearly BRm variation that occur in adolescence may play a role in the improvement of childhood asthma seen during this period.