Cut-off values for positive bronchodilator response in healthy Thai preschool children using forced oscillation technique.

BACKGROUND: Forced oscillation technique (FOT) requires minimal patient cooperation and is particularly useful in young children. Bronchodilator test is a valuable tool for wheezy and asthmatic patients. The cut-off value for bronchodilator response by FOT in healthy Thai children has not been reported.

OBJECTIVE: To determine the cut-off values for positive bronchodilator response in healthy Thai preschool children using pseudorandom FOT.

METHODS: FOT was used to measure respiratory function at baseline and after 400 mcg MDI salbutamol in healthy Thai children aged 3-6 years. Respiratory resistance (Rrs) and reactance (Xrs) at 6, 8, and 10 Hz were collected. Pre- and post-bronchodilator tests were compared using paired t-test. Absolute and percent changes after bronchodilator were calculated and their cut-off values were defined as mean ± 1.96 SD. Correlation between each of those and baseline data was analyzed using Pearson's correlation coefficient.

RESULTS: Of the 150 enrolled children, FOT measurement at baseline and after bronchodilator was successfully completed in 111 children (51 boys). The mean ± standard deviation age, height, and arm span was 5.2 ± 1.1 years, 109.3 ± 8.7 cm, and 107.2 ± 9.1 cm, respectively. No correlation was observed between any absolute or percent changes in bronchodilator response and gender, age, height, or arm span. The cut-off values established for bronchodilator response by percent change were, as follows: Rrs6: -23%, Rrs8: -20%, Rrs10: -20%, Xrs6: 36%, Xrs8: 60%, and Xrs10: 43%.

CONCLUSIONS: The cut-off values identified in this study will be useful for evaluating bronchodilator response by FOT in wheezy and asthmatic young children.