Respiratory factors do not limit maximal symptom-limited exercise in patients with mild cystic fibrosis lung disease

To evaluate whether respiratory factors limit exercise capacity in patients with mild cystic fibrosis (CF) lung disease (mean FEV1 = 76 ± 7.7% predicted) we stressed the respiratory system of seven patients using added dead space (VD). Primary outcomes were exercise duration (Exdur) and maximal oxygen uptake (V¨O2 max). Dyspnoea/leg-discomfort were assessed at end-exercise.Exdur was identical between control and VD studies (520 ± 152 versus 511 ± 166 s, p = NS) as was V¨O2 max (1.6 ± 0.5 versus 1.6 ± 0.6 L/min, p = NS). Significant resting, sub-maximal and maximal workload increases in minute ventilation (V¨E) were detected (70.8 ± 13.7 versus 79.5 ± 16.9 L/min, p < 0.05). Analysis of breathing pattern revealed increases inV¨E were attributable to increases in tidal volume (2.0 ± 0.5 versus 2.2 ± 0.6 L, p < 0.05) with no change in respiratory frequency. There was no difference in dyspnoea/leg discomfort between tests. The increase in V¨E in response to VD, with no change in Exdur/V¨O2 max suggests maximal symptom-limited exercise limitation is not primarily limited by respiratory factors in mild CF lung disease. Focused investigation and treatment of non-respiratory factors contributing to exercise limitation may improve exercise rehabilitation in this patient group.