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Airway resistance variability and response to bronchodilator in children with asthma

¹ School of Biomedical Engineering, ² Faculty of Medicine, and ³ Division of Respirology, Dept of Medicine, Dalhousie University, Halifax, NS, Canada, ⁴ Division of Allergy, Immunology and Pulmonology, Dept of Paediatrics and Adolescent Medicine, Mayo Clinic, Rochester, MN, USA.

CORRESPONDENCE: G. N. Maksym, School of Biomedical Engineering, Dalhousie University, 5981 University Ave, Room 5241, Halifax B3H 1W2, NS, Canada. Fax: 1 9024946621. E-mail: gmaksym{at}dal.ca

Keywords: Airway resistance, asthma severity, bronchodilator, children, forced oscillation technique, variation

Received: May 11, 2006
Accepted February 16, 2007

Variability of airway function is a feature of asthma, spanning timescales from months to seconds. Short-term variation in airway resistance (R_rs) is elevated in asthma and is thought to be due to increased variation in the contractile activation of airway smooth muscle. If true, then variation in R_rs should decrease in response to bronchodilators, but this has not been investigated.

Using the forced oscillation technique, R_rs and the variation in R_rs from 4–34 Hz were measured in 39 children with well-controlled mild-to-moderate asthma and 31 healthy controls (7–13 yrs) before and after an inhaled bronchodilator (200 µg salbutamol) or placebo.

In agreement with other findings, baseline R_rs at all frequencies and the SD of R_rs (R_rs SD) below 14 Hz were found to be elevated in asthma while neither forced expiratory volume in one second nor the mean forced expiratory flow between 25 and 75% of forced vital capacity were different compared with controls. The present authors found that R_rs SD changed the most of any measurement in asthma, and this was the only measurement that changed significantly more in children with asthma following bronchodilator administration.

The present results show that like airway narrowing, short-term airway variability of resistance may be a characteristic feature of asthma that may be useful for monitoring response to therapy.

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