Peak oxygen uptake and mortality in children with cystic fibrosis

Background: Single measurements of peak oxygen uptake (V̇O₂) have been shown to predict mortality in patients with cystic fibrosis (CF) although no longitudinal study of serial measurements has been reported in children. A study was undertaken to determine whether the initial, final, or the rate of fall of forced expiratory volume in 1 second (FEV₁) or peak V̇O₂ was a better predictor of mortality. Methods: Twenty eight children aged 8-17 years with CF performed annual pulmonary function and maximal exercise tests over a 5 year period to determine FEV₁ and peak V̇O₂, magnitude of their change over time, and survival over the subsequent 7-8 years. Analysis was done using Kaplan-Meier curves and Cox proportional hazard model. Results: Peak V̇O₂ fell during the observation period in 70% of the patients, with a mean annual decline of 2.1 ml/min/kg. Initial peak V̇O₂ was not predictive of mortality but rate of decline and final peak V̇O₂ of the series were significant predictors. Patients with peak V̇O₂ less than 32 ml/min/kg exhibited a dramatic increase in mortality, in contrast to those whose peak V̇O₂ exceeded 45 ml/min/kg, none of whom died. The first, last, and rate of decline in FEV₁ over time were all significant predictors of mortality. Conclusions: Higher peak V̇O₂ is a marker for longer survival in CF patients.