Measurement of bronchial responsiveness in young children: Comparison of transcutaneous oxygen tension and functional residual capacity during induced bronchoconstriction and ‐dilatation

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Abstract
Demonstration of an increased bronchial responsiveness in preschool children may support the diagnosis of asthma. Most young children cannot perform routine lung function tests. Transcutaneous P(Ptc) measurement has been applied successfully in young children, and changes in Ptchave been shown to correlate well with changes in forced expiratory volume in 1 second (FEV1) during bronchoprovocation testing with methacholine. Ptcis, however, an indirect measure of the effect of inhaled spasmogens. As functional residual capacity (FRC) can also be measured by helium dilution spirometry in preschool children, we compared Ptcand FRC during methacholine inhalation challenges and after inhaled terbutaline, in order to determine whether FRC is useful as a more direct measure of induced bronchoconstriction and ‐dilatation than Ptc. We studied 41 allergic asthmatic children (mean age, 5.2 years) who underwent a methacholine bronchoprovocation test; 38 children received terbutaline 1 h after the final methacholine dose. The provocative concentration of methacholine that caused a 20% decrease of Ptcwas determined, and changes in FRC and Ptcafter each methacholine dose step were compared. Similarly, changes in Ptcand FRC before, and 15 and 30 min after, terbutaline were compared. All children had a drop in Ptcafter increasing doses of methacholine; a 20% change was reached in 38 patients. Mean FRC values increased significantly but variably with increasing doses of methacholine, and changes in Ptcand FRC did not correlate. After terbutaline, Ptcincreased slightly but significantly, and FRC again varied unpredictably. In a separate group of 11 children, the effect of terbutaline was assessed directly after the final methacholine dose, when significant bronchoconstriction was still present. In this group, FRC changes were not significant and were not related to the increase in Ptc. Our study suggests that FRC cannot be recommended to monitor the effects of inhaled bronchoconstrictors and bronchodilators in young children. Ptcmeasurement is one of the few convenient and safe methods to be used in children too young to perform conventional tests of lung function during bronchoprovocation testing.