Cardiorespiratory Responses to Repeated 2‐min Constant Work Rate Exercise in Children with Cystic Fibrosis

In patients with cystic fibrosis (CF), physical fitness is associated with enhanced longevity and improved quality of life even though cardiorespiratory responses to exercise are abnormal. Studies in CF children typically utilize prolonged or maximal exercise, protocols that do not mimic real life patterns of physical activity. We hypothesized that abnormal responses to brief exercise would occur in CF and that the abnormalities would worsen with repeated bouts. 12 CF (mild‐moderate) and 39 control participants (range 9 to 15 y.o.) performed a series of 2‐min constant work rate cycle ergometry (with 1‐min rest intervals) at a work rate equivalent to about 70% peak. Gas exchange was measured breath‐by‐breath. We applied linear mixed models with quadratic form of Bout (1 to 9) and Time (1 to 2 minutes) for statistical analysis. Significant differences were found in a number of key parameters. For example, V E (Figure‐‐group mean data) in both groups progressively increased. In CF, V E was consistently higher and recovery from each bout was prolonged. Abnormal responses were also observed for VO 2 and HR. While control subjects easily completed 10 bouts, most CF subjects stopped exercise after 9. In conclusion, brief repeated bouts of exercise lead to progressive change in the kinetics of key cardiorespiratory responses in both healthy children and those with CF. In CF responses are abnormal and worsen. Ventilatory responses to exercise change dynamically and quickly in children. Prolonged recovery even after brief exercise bouts in CF children may contribute to exercise intolerance.