Computed cardiopulmonography and the idealised lung clearance index, iLCI 2.5 , in early stage cystic fibrosis.

This study explored the use of computed cardiopulmonography (CCP) to assess lung function in early stage cystic fibrosis (CF). CCP has two components. The first is a particularly accurate technique for measuring gas exchange. The second is a computational cardiopulmonary model where patient-specific parameters can be estimated from the measurements of gas exchange. Twenty-five participants (14 healthy controls, 11 early stage CF) were studied with CCP. They were also studied with a standard clinical protocol to measure the lung clearance index (LCI). Ventilation inhomogeneity, as quantified though CCP parameter σlnCL, was significantly greater (p<0.005) in CF than in controls, and anatomical deadspace relative to predicted functional residual capacity (DS/FRCpred) was significantly more variable (p<0.002). Participant-specific parameters were used with the CCP model to calculate idealised values for LCI (iLCI) where extrapulmonary influences on the LCI, such as breathing pattern, had all been standardised. Both LCI and iLCI distinguished clearly between CF and control participants. LCI values were mostly higher than iLCI values in a manner dependent on the participant's respiratory rate (r=0.46, p<0.05). The within-participant reproducibility for iLCI appeared better than for LCI, but this did not reach statistical significance (F-ratio=2.2, p=0.056). Both a sensitivity analysis on iLCI and a regression analysis on LCI revealed that these depended primarily on an interactive term between CCP parameters of the form σlnCL*(DS/FRC). In conclusion, the LCI (or iLCI) probably reflect an amalgam of different underlying lung changes in early-stage CF that would require a multi-parameter approach, such as potentially CCP, to resolve.