LUNG CLEARANCE INDEX: a new biomarker of ventilation inhomogeneity in pediatric respiratory diseases.

Conventional spirometry has long been considered the primary test of respiratory function deficit in children and adults. However, performing forced breathing manoeuvres is challenging in an uncooperative child. Furthermore, recent evidence suggests that conventional spirometry is not sensitive for the early detection of lung damage affecting the small airways or the evaluation of homogeneity of air ventilation. For these reasons, techniques such as gas dilutions and multiple-breath washout (MBW) have been implemented over the last few years because they allow for the early assessment of damage to small airways. These methods permit the identification of ventilatory inhomogeneity in the lungs by analyzing the clearance of an inert gas used as a tracer. The equipment consists of a mass spectrometer combined with a flow meter. For all tests, the lung clearance index (LCI) is the parameter that is most often used to evaluate ventilatory inhomogeneity. Because it is sufficient to breathe with a normal tidal volume during the examination, this examination is particularly suitable for studying respiratory function, even in uncooperative children. Considering the emerging role of the LCI in the evaluation of childhood respiratory diseases, the aims of my researches during the three years of PhD were: i) to evaluate this index in some pediatrics respiratory diseases including lung fibrosis in cancer survivors, cystic fibrosis, and finally in children healed from COVID-19; ii) to increase the scientific evidences on the role of LCI as a biomarker in pediatric respiratory diseases. In this sense, the work of these three years of doctorate has contributed to increase the scientific evidence on the MBW test in childhood respiratory diseases. Based on this, we can certainly affirm that LCI can be considered to all intents and purposes a biomarker of ventilatory inhomogeneity in children with bronchopulmonary disease.