Cardiopulmonary Exercise Testing Provides Additional Prognostic Information in Cystic Fibrosis

Rationale: The prognostic value of cardiopulmonary exercise testing (CPET) for survival in cystic fibrosis (CF) in the context of current clinical management, when controlling for other known prognostic factors, is unclear. Objectives: To determine the prognostic value of CPET-derived measures beyond peak oxygen uptake ((V) over dot(O2)peak) following rigorous adjustment for other predictors. Methods: Data from 10 CF centers in Australia, Europe, and North America were collected retrospectively. A total of 510 patients completed a cycle CPET between January 2000 and December 2007, of which 433 fulfilled the criteria for a maximal effort. Time to death/lung transplantation was analyzed using Cox proportional hazards regression. In addition, phenotyping using hierarchical Ward clustering was performed to characterize high-risk subgroups. Measurements and Main Results: Cox regression showed, even after adjustment for sex, FEV1% predicted, body mass index (z-score), age at CPET, Pseudomonas aeruginosa status, and CF-related diabetes as covariates in the model, that (V) over dot(O2)peak in % predicted (hazard ratio [HR], 0.964; 95% confidence interval [CI], 0.944-0.986), peak work rate (% predicted; HR, 0.969; 95% CI, 0.951-0.988), ventilatory equivalent for oxygen (HR, 1.085; 95% CI, 1.041-1.132), and carbon dioxide (HR, 1.060; 95% CI, 1.007-1.115) (all P, 0.05) were significant predictors of death or lung transplantation at 10-year follow-up. Phenotyping revealed that CPET-derived measures were important for clustering. We identified a high-risk cluster characterized by poor lung function, nutritional status, and exercise capacity. Conclusions: CPET provides additional prognostic information to established predictors of death/lung transplantation in CF. High-risk patients may especially benefit from regular monitoring of exercise capacity and exercise counseling.