Tidal changes in respiratory resistance are sensitive indicators of airway obstruction in children.

Rationale: Individual assessment of airway obstruction in preschool-age children requires sensitive and specific lung function methods with low demand of cooperation. Although the forced oscillation technique (FOT) is feasible in young children, conventional measurements of respiratory impedance (Zrs) have limited diagnostic power in individuals.

Objective: To find descriptors of within-breath Zrs that are sensitive indicators of airway obstruction during tidal breathing in children.