Use of Capnography for the Follow-up of Cystic Fibrosis Children (MUCOCAP)

Cystic fibrosis (CF) is the most common inherited genetic disorder in Caucasian children. It affects several organs, the most important being the involvement of the respiratory system. The respiratory condition influences the prognosis and the course of the disease, the respiratory complications being the main cause of mortality and morbidity. The respiratory assessment is based on spirometry, but the maximal expiratory volume in the first second (FEV1) does not reflect the initial peripheral impairment of airways and can remain within normal limits for a long time. Another pulmonary function test (PFT) validated for the follow-up of CF children is the measurement of "gas trapping", very frequent in these children, reflecting the ventilation inhomogeneity and incipient airways impairment. "Gas trapping" can be obtained by the measurement of lung volume (functional residual capacity, FRC) by plethysmography and helium dilution technique, but these tests are very inconvenient for children due to their long length (~ 30 minutes). This complete PFT is routinely performed every year. It also includes a measurement of Lung Clearance Index (LCI) which reflects the presence of ventilation inhomogeneity. Capnography is a non-invasive PFT technique that does not require subject's active cooperation, is of short duration and could replace the traditional PFT techniques for the follow-up of CF children. Capnographic indices also reflect the presence of ventilation inhomogeneity. The capnograph is integrated into the device that measures the LCI and data can be retrieved and analyzed following the LCI measurement.

In this study, 2 groups of children will be identified by the gold-standard: 1 / children with "gas trapping" (defined by the ratio between the difference in the plethysmographic FRC (FRCpleth) and FRC obtained by the helium dilution technique (FRCHe) divided by FRCpleth of >10%) and 2 / children without "gas trapping" (defined by (FRCpleth-FRCHe) / FRCpleth of ≤ <10%). Capnography data (included in LCI measurement) will be collected in these children and capnographic indices will be compared between these two groups.

The study hypothesis is that capnographic indices change in the presence or absence of "gas trapping" in CF children.

The importance of capnography is that is a test less inconvenient for follow-up and better accepted by children because of its short length, easy-to-use tool for monitoring disease progression and monitoring the effectiveness of treatments.

The main objective is to show that the capnographic index of efficacy (EFFi), in CF children is significantly different between subjects "with gas trapping" (defined by the gold standard ((FRCpleth - FRCHe) / FRCpleth) > 10%) and subjects "without gas trapping" (defined by the gold standard ((FRCpleth-FRCHe) / FRCpleth) ≤10%).

The secondary objectives are:

• to compare the other capnographic indices between CF children "with gas trapping" and CF children "without gas trapping": the slope of the ascending phase, α; the slope of the alveolar plateau, β; the angle Q between α and β; the positive peak of the first-order derivative, F'CO2, which reflects the ascending phase; the first negative peak of the 2nd order derivative, F"CO2, which reflects the curvature between the ascending phase and the alveolar plateau.
• to compare the results of the capnographic indices with the results of the FEV1 in identifying the presence / absence of "gas trapping";
• to compare the results of the capnographic indices with the results of the LCI in identifying the presence / absence of "gas trapping",