Table 3

Results of linear mixed model analysis to identify factors associated with change in lung clearance index (LCI)

FactorCoefficientSE95% CIP value
Time (days)0.00020.0001−0.00002 to 0.00050.075
LCI at baseline0.7580.0850.591 to 0.925<0.001
Age0.0400.0170.007 to 0.0730.019
Gender−0.2760.240−0.746 to 0.1940.250
BMI (kg/m2)−0.0280.040−0.106 to 0.0510.486
Pseudomonas aeruginosa status−0.6680.337−1.328 to −0.0090.047
FEV1 z-score−0.3220.116−0.550 to −0.0950.006
Rate of all exacerbations/year−0.1190.130−0.374 to 0.1350.357
Number of courses of intravenous antibiotics/year0.7550.3380.092 to 1.4170.026
Pancreatic status−0.1580.292−0.731 to 0.4140.588
  • The coefficient for time reflects the rate of change (per day) of LCI taking into account the effect of the other variables in the model. The remaining covariates are fixed at baseline and not time-varying, so their model coefficients represent the change in the mean LCI associated with a unit increase in that term while everything else in the model is the same. For categorical covariates such as Pseudomonas status, we can interpret the coefficient as an adjusted mean difference between the dichotomous groups.

  • Pseudomonas aeruginosa status: chronically or intermittently infected with Pseudomonas aeruginosa versus previous or never infected.

  • Bold values indicate statistical significance.

  • BMI, body mass index; FEV1, forced expiratory volume in 1 second; LCI, lung clearance index.