Exhibiting variable airway obstruction is a key factor in the diagnosis of asthma but too often it is undetected by spirometry.

Study hypothesis: The forced oscillation technique (FOT) will show airway obstruction in asthmatic children with normal spirometry pointing out its advantage in measuring AW obstruction in this population.

We will conduct a prospective observational study in 6-18 years old children with the diagnosis of asthma and a normal spirometry results.

Each subject will undergo evaluation including: asthma control questionnaire, spirometry, FOT and Fractional exhaled nitric oxide (FeNO) to assess the sensitivity of FOT in diagnosing airway obstruction in this circumstances.

Background: Asthma diagnosis and control are based on history of recurrent typical symptoms and variable airflow obstruction by by measuring maximal expiratory flows with spirometry. However, in many children with asthma spirometry can be normal. The forced oscillation technique (FOT) is a simple, noninvasive technique performed during tidal breathing that is relatively easy to apply.

The objective of this study is to assess the sensitivity of FOT in children with asthma and normal spirometry.

Study design: this will be a prospective observational study. Population: 6-18 years old children visiting the pediatric pulmonary clinic at the investigators institution with the diagnosis of asthma and normal spirometry results (FEV1 & FEV1/FVC >80% and FEF25-75>65%) either on treatment or before treatment.

Study protocol:

After obtaining written informed consent, participants will fill asthma control questionnaires. Family history and risk factors for asthma will be reviewed. Data on blood eosinophils and skin prick test for allergy will be collected from the medical files. Medication (controller and reliever) will be also documented.

FOT will be measured using the TremoFlo C-100 Airwave Oscillometry System (Thorasys , Montreal, Quebec, Canada). R5, R20, R5-20 (resistances at the reported frequency), X5 (reactance at 5hz), AX5 (reactance area at 5hz), Fres (resonance frequency) will be reported.

Fractional exhaled nitric oxide (FeNO) will be measured using the single breath exhalation technique.

Inclusion Criteria:

• Diagnosis of asthma
• Must be able to perform spirometry and FOT tests
• Normal spirometry results (FEV1 & FEV1/FVC >80% and FEF25-75>65%)

Exclusion Criteria:

• Chronic lung disease other than asthma
• Severe chronic medical condition such as heart failure, neuromuscular disease etc.

Children with the diagnosis of asthma and a normal spirometry results