Airway resistance variability and response to bronchodilator in children with asthma

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

^* To whom correspondence should be addressed. E-mail: gmaksym{at}dal.ca.

	Abstract

Variability of airway function is a feature of asthma spanning timescales from months to seconds. Short-term variation in airway resistance (Rrs) 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 Rrs should decrease in response to bronchodilators, but this has not been investigated.

Using the forced oscillation technique, we measured Rrs and variation in Rrs from 4 to 34 Hz 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, we found that baseline Rrs at all frequencies and standard deviation of Rrs (SDRrs) below 14 Hz were elevated in asthma while neither FEV_1.0 nor FEF_25%-75% were different compared with controls. We found that SDRrs changed the most of any measure in asthma, and this was the only measure that changed significantly more in children with asthma following bronchodilator (p<0.005).

These 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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