Relationship between FEV₁ and peak oxygen uptake in children with cystic fibrosis

Cross-sectional data do not truly convey the manner in which declining lung function affects peak oxygen uptake (peak V̇O₂) within a given patient with cystic fibrosis. We hypothesized that there would be a concomitant decline in peak V̇O₂ with FEV₁ over time. Twenty-eight children aged 8-17 years with cystic fibrosis performed annual ergometer tests over a 5-year period to determine peak V̇O₂ and within-patient predictors of change in peak V̇O₂. Analysis was done using a mixed-effects model. During the study period, the annual decline in FEV ₁ averaged 2.7% of the predicted value per year. Peak V̇O ₂ fell during the observation period in 70% of patients, with an average annualized decline of 1.9 ml · min^-1 · kg ^-1. This rate of decline was greater in older children in contrast to younger children, some of whom had an improvement in peak V̇O₂ over the first few years, consistent with growth and maturation. There was no difference in this rate of decline between sexes, but girls started with a slightly lower peak V̇O₂ (37.9 vs. 45.1 ml · min ^-1 · kg^-1). In patients with FEV₁ <80% predicted, declining FEV₁ was highly correlated with falling peak V̇O₂, whereas it remained stable over 4-5 years in patients whose FEV₁ was >80% predicted and remained in that range. We conclude that peak V̇O₂ remains stable or rises slightly over time in younger patients, while it shows a downward trend in older children with CF, particularly once FEV₁ falls below 80% predicted. Peak V̇O₂ is correlated with FEV₁ during childhood in patients with cystic fibrosis, and both FEV₁ and age influence peak V̇O₂ Pediatr Pulmonol.