Computed cardiopulmonography and the idealized 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 (LCI2.5). Ventilation inhomogeneity, as quantified through CCP parameter rlnCL, was significantly greater (P < 0.005) in CF than in controls, and anatomical deadspace relative to predicted functional re-sidual capacity (DS/FRCpred) was significantly more variable (P < 0.002). Participant-specific parameters were used with the CCP model to calculate idealized values for LCI2.5 (iLCI(2.5)) where extrapulmonary influences on the LCI2.5, such as breathing pat-tern, had all been standardized. Both LCI2.5 and iLCI(2.5) distinguished clearly between CF and control participants. LCI2.5 values were mostly higher than iLCI(2.5) values in a manner dependent on the participant's respiratory rate (r = 0.46, P < 0.05). The within-participant reproducibility for iLCI(2.5) appeared better than for LCI2.5, but this did not reach statistical significance (F ratio = 2.2, P = 0.056). Both a sensitivity analysis on iLCI(2.5) and a regression analysis on LCI2.5 revealed that these depended primarily on an interactive term between CCP parameters of the form rlnCL*(DS/FRC). In conclusion, the LCI2.5 (or iLCI(2.5)) probably reflects an amalgam of different underlying lung changes in early-stage CF that would require a multiparameter approach, such as potentially CCP, to resolve.