Eligibility criteria include age 12-45 years, with current treatment of asthma with as-needed SABA only; and manifesting an acute response to SABA at screening of 40% or greater improvement in IOS low frequency reactance. After inclusion in the protocol, all subjects will receive active treatment, either with Advair or with Symbicort. Outcome measures will include large and small airway resistance and integrated low-frequency reactance calculated directly from IOS measures, and in addition, Large Airway Resistance, Small Airway Resistance and Small Airway Compliance derived from an electrical equivalent respiratory system model. Analysis of IOS data will be done post-testing by a respiratory physiologist, experienced with use of IOS and its analysis and interpretation, blinded to which treatment each individual received. Electrical-equivalent respiratory system model analyses will be done by a biomedical engineer, blinded to which treatment each individual received.
