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Miguel Ángel Díaz Palacios,1 David Hervás Marín,2 Ana Giner Valero,1 Noelia Colomer Hernández,1 Carla Torán Barona,1 Dolores Hernández Fernández de Rojas11Department of Allergy, Hospital Universitari La Fe, Valencia, Spain; 2Department of Biostatistics, Instituto de Investigación Sanitaria La Fe, Valencia, SpainPurpose: Impulse oscillometry (IOS) has been proposed as an alternative test to evaluate the obstruction of small airways and to detect changes in airways earlier than spirometry. In this study, we sought to determine the utility and association of IOS parameters with spirometry and asthma control in an adult population.Patients and methods: Adults 14–82 years of age with asthma were classified into uncontrolled asthma (n=48), partially controlled asthma (n=45), and controlled asthma (n=49) groups, and characterized with fractional exhaled nitric oxide (FENO), IOS, and spirometry in a transversal analysis planned as a one-visit study. The basic parameters evaluated in IOS are resistance at 5 Hz (R5), an index affected by the large and small airway; resistance at 20 Hz (R20), an index of the resistance of large airways; difference between R5 and R20 (R5–R20), indicative of the function of the small peripheral airways; reactance at 5 Hz (X5), indicative of the capacitive reactance in the small peripheral airways; resonance frequency (Fres), the intermediate frequency at which the reactance is null, and reactance area (XA), which represents the total reactance (area under the curve) at all frequencies between 5 Hz to Fres.Results: There were statistical differences between groups in standard spirometry and IOS parameters reflecting small peripheral airways (R5, R10, R5–R20, Fres, XA and X5) (P