Is static hyperinflation a limiting factor during exercise in adolescents with cystic fibrosis?

Increased work of breathing is considered to be a limiting factor in patients with cystic fibrosis (CF) performing aerobic exercise. We hypothesized that adolescents with CF and with static hyperinflation are more prone to a ventilatorily limited exercise capacity than non‐static hyperinflated adolescents with CF. Exercise data of 119 adolescents with CF [range 12–18 years], stratified for static hyperinflation, defined as ratio of residual volume to total lung capacity (RV/TLC) > 30%, were obtained during a progressive bicycle ergometer test with gas analysis and analyzed for ventilatory limitation. Static hyperinflation showed a significant, though weak association (Φ 0.38; P  < 0.001) with a ventilatorily limited exercise capacity (breathing reserve index at maximal effort >0.70; FEV 1  < 80% predicted and reduced exercise capacity, defined as VO 2peak  < 85% predicted). Analysis of association for increasing degrees of hyperinflation showed an increase to Φ 0.49 ( P  < 0.001) for RV/TLC > 50%. In adolescents with static hyperinflation, peak work rate (W peak ; 3.1 ± 0.7 W/kg (75.1 ± 17.3% of predicted), peak oxygen uptake (VO 2peak /kg (ml/min/kg); 39.2 ± 9.2 ml/min/kg (91.0 ± 20.3% of predicted), peak heart rate (HR peak ; 176 ± 19 beats/min) were significantly ( P  < 0.05) decreased when compared with non‐static hyperinflated adolescents (W peak 3.5 ± 0.5 W/kg (81.4 ± 10.0% of predicted)); VO 2peak /kg (ml/min/kg); 43.1 ± 7.5 ml/min/kg (98.0 ± 15.1% of predicted); and HR peak 185 ± 14 beats/min). Additionally, no difference was found in the degree of association of FEV 1 (%) and RV/TLC (%) with VO 2peak /kg pred and W peak /kg Pred , but we found the RV/TLC (%) to be a slightly stronger predictor of VO 2peak /kg pred and W peak /kg Pred than FEV 1 (%). These results indicate that the presence of static hyperinflation in adolescents with CF by itself does not strongly influence ventilatory constraints during exercise and that static hyperinflation is only a slightly stronger predictor of W peak /kg Pred and VO 2peak /kg Pred than airflow obstruction (FEV 1 (%)). Pediatr. Pulmonol. 2011; 46:119–124. © 2011 Wiley‐Liss, Inc.