Relationship between FEV 1 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 $\dot VO_2$ ) within a given patient with cystic fibrosis. We hypothesized that there would be a concomitant decline in peak $\dot VO_2$ with FEV 1 over time. Twenty‐eight children aged 8–17 years with cystic fibrosis performed annual ergometer tests over a 5‐year period to determine peak $\dot VO_2$ and within‐patient predictors of change in peak $\dot VO_2$ . 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 $\dot VO_2$ 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 $\dot VO_2$ 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 $\dot VO_2$ (37.9 vs. 45.1 ml · min −1  · kg −1 ). In patients with FEV 1 <80% predicted, declining FEV 1 was highly correlated with falling peak $\dot VO_2$ , whereas it remained stable over 4–5 years in patients whose FEV 1 was >80% predicted and remained in that range. We conclude that peak $\dot VO_2$ remains stable or rises slightly over time in younger patients, while it shows a downward trend in older children with CF, particularly once FEV 1 falls below 80% predicted. Peak $\dot VO_2$ is correlated with FEV 1 during childhood in patients with cystic fibrosis, and both FEV 1 and age influence peak $\dot VO_2$ . Pediatr Pulmonol. © 2005 Wiley‐Liss, Inc.