Methods
This transversal study was done in the pediatric lung function laboratory at Clínica Las Condes, Santiago, Chile between September, 2018 and March, 2020. We included the IOS and spirometry of 445 asthmatic children (between 3 and 17 years of age) for which their pediatricians requested a lung function test. We excluded children with other chronic pulmonary diseases, cardiopathies, and immunodeficiencies. For the lung function tests, the patients had to be free of respiratory tract infection during the previous 3 weeks and having experienced no short beta-2 agonist use in the previous 24 hrs. Written consent/assent was obtained from the parents/guardians and children who agreed to participate after receiving information about the study. The study was approved by the Ethics Committee of the institution.
We recorded the IOS and spirometry results, asthma severity (by GINA classification), and asthma controller therapy in a pre-codified database. The IOS and the spirometry were performed according to ATS/ERS guidelines13,14 using the Vyaire Vyntus model v-176430 (Mettawa, IL) with the Sentry Suit application. IOS was performed first, followed by spirometry, in order to avoid force maneuvers’ causing changes in the IOS. R5 (Kpa/Ls), Fres (1/s), X5 (Kpa/Ls), X5approx. (Kpa/Ls), AX (Kpa/Ls), and D5-20 (Kpa/Ls) basal values in the IOS and FEF25-75% (L/s) in the spirometry were recorded. In accordance with several studies,12,15-18 the following cutoffs for defining IOS abnormalities were used: R 5 ≥0.8, Fres ≥25 1/s, AX ≥2.5, and D5-20 ≥0.2 Kpa/Ls. These cutoffs were tested in a pilot study.
Also, the same day a skin prick test (SPTs) for twenty common inhalant and food allergens was performed on the forearms, as well as positive (histamine) and negative (solvent) controls. Atopy was defined as a positive reaction (wheal size diameter measuring 3 mm or more after subtraction of the control value) to one or more allergens.