Cross-sectional data do not truly convey the manner in which declining lung function affects peak oxygen uptake (peak VO2) within a given patient with cystic fibrosis. We hypothesized that there would be a concomitant decline in peak VO2 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 VO2 and within-patient predictors of change in peak VO2. Analysis was done using a mixed-effects model. During the study period, the annual decline in FEV1 averaged 2.7% of the predicted value per year. Peak VO2 fell during the observation period in 70% of patients, with an average annualized decline of 1.9 ml x min(-1) x kg(-1). This rate of decline was greater in older children in contrast to younger children, some of whom had an improvement in peak VO2 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 VO2 (37.9 vs. 45.1 ml x min(-1) x kg(-1)). In patients with FEV1 <80% predicted, declining FEV1 was highly correlated with falling peak VO2, whereas it remained stable over 4-5 years in patients whose FEV1 was >80% predicted and remained in that range. We conclude that peak VO2 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 VO2 is correlated with FEV1 during childhood in patients with cystic fibrosis, and both FEV1 and age influence peak VO2.
2005 Wiley-Liss, Inc.