Background: Spirometry is widely used in the diagnosis and quantification of respiratory disorders such as asthma. A microspirometer is a portable and easily used apparatus that can substitute for a regular spirometer, although there is little evidence of its accuracy. Objective: To compare the microspirometer to a regular spirometer for use in asthmatic children and adolescents. Methods: The instruments used were a Micro Spirometer, manufactured by Micro Medical, and a conventional Cosmed Pony Graphic 3.5 spirometer, both with turbinometers (flow sensors). The study sample consisted of 62 children and adolescents, of both genders, clinically diagnosed with asthma and under treatment at a pulmonology clinic. Ages ranged from 5 and 16 years. All spirometric tests were carried out according to the guidelines established by the American Thoracic Society and by the Associacão Brasileira de Normas Técnicas (Brazilian Technical Standards Association). For each patient, microspirometry was performed first, followed by conventional spirometry. The parameters analyzed in both devices were forced vital capacity, forced expiratory volume in one second and peak expiratory flow. Data were analyzed using the Student's t-test and Pearson's correlation test. Results: Strong correlations were found between the two devices in the parameters analyzed: forced expiratory volume in one second: r = 0.97; forced vital capacity: r = 0.97; and peak expiratory flow: r = 0.91. Conclusion: These results demonstrate that the microspirometer is a useful diagnostic tool that can be used when a conventional spirometer is unavailable.

Keywords: Key words: Asthma. Spirometry. Micro spirometer. Puomonary ventilation.