THE EFFECT OF SIZE AND AGE OF SUBJECT ON AIRWAY RESPONSIVENESS IN CHILDREN

Methodologies used to assess airway responsiveness (AR) in children ad minister the same dosage schedule to all children despite the great ra nge in the size of subjects. The aim of this study was to examine the hypothesis that the level of AR is size dependent within same-age coho rts and between different ages. Among a birth cohort of 1,037 New Zeal and children participating in a longitudinal study, 818 had at least t wo measurements of airway responsiveness between ages 9 and 15 yr. Eac h child performed spirometry and a four-dose methacholine inhalation t est. A continuous slope index of methacholine responsiveness was compu ted. AR slope indexes were analyzed using longitudinal methods, which included an indicator variable for subjects who reported having any wh eeze. AR was lowest in both males and females in the upper quartile fo r height than those in the lower quartile, independently of age. AR te nded to be higher (responded to lower concentrations of methacholine) in boys than girls and to decline with age among wheezers. The greater level of responsiveness in smaller or younger children could be expla ined by these individuals having received a dose of methacholine that was relatively large for their size.