 In preschool aged children, the most suitable techniques to assess airway obstruction is debit interruption technic Rint and plethysmographic measure of specific airway resistance sRaw. Even if Rint is easily and routinely performed, it also includes a component of lung tissue and chest wall resistance as well as respiratory tissue viscoelasticity. sRaw seems to be better for discriminating airway obstruction. These two techniques will be compared in terms of concordance in the diagnosis of pulmonary obstruction and bronchodilator response. 