Volumetric capnography as a tool to detect early peripheric lung obstruction in cystic fibrosis patients.

Objective: To compare spirometry and volumetric capnography (VCap) to determine if the capnographic values add more information about early lung disease in cystic fibrosis (CF) patients.

Methods: This was a cross-sectional study involving CF patients: Group I (42 patients, 6-12 years of age); and Group II (22 patients, 13-20 years of age). The corresponding control groups were comprised of 30 and 50 healthy subjects, respectively. Forced vital capacity (FVC), forced expiratory volume in one second (FEV(1)), and the FEV(1)/FVC ratio was determined by spirometry. Using VCap, we measured peripheral oxygen saturation (SpO(2)), respiratory rate (RR), inspiratory time (IT), expiratory time (ET), and the phase III slope normalized by expiratory volume (phase III slope/Ve).

Results: In comparison with control groups, all CF patients presented higher phase III slope/Ve values (p < 0.001) independent of the pulmonary disease stage. The phase III slope/Ve was significantly higher in the 24 patients who presented normal spirometry results (p = 0.018). The Group II patients showed lower FVC, FEV(1), FEV(1)/FVC (p < 0.05), and also lower SpO(2) values (p < 0.001) when compared with Group I patients. In comparison with Control Group II, the Group II patients presented higher RR (p < 0.001), and lower IT and ET values (p < 0.001).

Conclusions: Compared to the controls, all studied CF patients showed an increase in phase III slope/Ve values. VCap identified the heterogeneity of the ventilation distribution in the peripheral airways of CF patients who presented normal spirometry.