IOS measurements
IOS measurements were performed using a Vyntus® APS/IOS (Vyaire GmbH,
Höchberg, Germany), calibrated daily with a 3 L syringe as directed by
the manufacturer, and analysed using the SentrySuite® software package
(version 3.10). According to current international recommendations,
measurements were taken before spirometry to avoid the effect of forced
spirometry manoeuvres on bronchial tone [15]. IOS measurements were
performed in accordance with ERS guidelines [28]. Prior to testing,
each child was familiarized with the procedure. During the measurement,
the patient remained seated with the head in a neutral or slightly
extended position, breathing through a mouthpiece and wearing a nose
clip; moreover, the patient’s cheeks were firmly maintained by the hands
of the investigator or caregiver to minimize pressure losses. Only
triplicate artefact-free IOS measurements lasting ≥20 s with a coherence
value ≥ 0.8 in R5 and ≥ 0.9 in R20 and a coefficient of variation ≤ 15%
were selected.