Assessment of bronchodilator responsiveness in preschool children using forced oscillations

Cindy Thamrin ¹, Catherine L Gangell ², Kanokporn Udomittipong ¹, Merci MH Kusel ¹, Hilary Patterson ¹, Takayoshi Fukushima ¹, Andre Schultz ¹, Graham L Hall ³, Stephen M Stick ³ and Peter D Sly ^4*

¹ Telethon Institute for Child Health Research, Centre for Child Health Research, UWA, Australia
² School of Paediatrics and Child Health, University of Western Australia, Australia
³ Princess Margaret Hospital and School of Paediatrics & Child Health, University of Western Australia, Australia
⁴ Telethon Institute for Child Health, Centre for Child Health Research, UWA, Australia

^* To whom correspondence should be addressed. E-mail: peters{at}ichr.uwa.edu.au.

Accepted 6 March 2007

Abstract

Background: The forced oscillation technique (FOT) requires minimal patient cooperation and is feasible in preschool children. Few data exist on respiratory function changes measured using FOT following inhaled bronchodilators (BD) in healthy young children, limiting clinical applications of BD testing in this age group. We aimed to determine the most appropriate method of quantifying BD responses using FOT in healthy young children, and those with common respiratory conditions, including cystic fibrosis (CF), neonatal chronic lung disease (nCLD), and those with a diagnosis of asthma and/or current wheeze.

Methods: A pseudorandom FOT signal (4 - 48 Hz) was used to examine respiratory resistance (Rrs) and reactance (Xrs) at 6, 8 and 10 Hz. Three to 5 acceptable measurements were made before and 15 minutes following the administration of salbutamol. Post-BD response was expressed both in absolute and relative (percentage of baseline) terms.

Results: Significant BD responses (BDR) were seen in all groups (Wilcoxon signed ranks test, p < 0.05). Absolute changes in BDR were related to baseline lung function within each group (linear regression, p < 0.001). Relative changes in BDR were less dependent on baseline and independent of height in healthy children.Those with nCLD showed a strong baseline dependence in their responses. The BDR in children with CF, asthma and wheeze (based on both group mean data and number of responders) were not greater than healthy children.

Conclusions: BD response assessed by the FOT in preschool children should be expressed as a relative change to account for the effect of baseline lung function. The limits for a positive BD response of -40% and 65% for Rrs and Xrs, respectively, are recommended.

Keywords: inhaled bronchodilators, paediatrics, respiratory system

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