RI is a frequent phenomenon exist in moderate to severe persistent asthma children with a history of prematurity or low birth weight, and it is an indicator of alterations in lung function, especially in the parameters that evaluate the function of the peripheral airway. In asthmatics with RI by IOS, it was possible to identify a subgroup with greater peripheral airway obstruction and less bronchodilator response than the group in which the RI disappeared after the bronchodilator test. More studies should be done to confirm these findings.