Exercise Ventilatory Limitation in Cystic Fibrosis Patients with Normal Breathing Reserve

Aim: Exercise ventilatory limitation (EVL) is conventionally defined by a reduced breathing reserve (BR). We hypothesized that EVL may be present despite a normal BR in cystic fibrosis (CF).

Methods: Fifteen adults (f=8, age 34y, 18-43y) CF patients with a wide range of pulmonary obstruction performed a symptom-limited exercise test on a cycle ergometer. We measured exercise inspiratory capacity (IC) and analyzed exercise flow-volume loops.

Results: BR was reduced in the six patients with FEV₁ 50%pred. The remaining nine patients had mild to moderate obstructive defects on spirometry (median FEV₁ 61% predicted, range 50-86%), and a normal BR (21 L/min, 12-44 L/min). In spite of a normal BR, the patients had clear evidence of a ventilatory limitation during exercise. In this subgroup, dynamic hyperinflation was seen (IC decreased during exercise by 250 ml (100-860 ml); and an expiratory flow limitation was present over 78% (41-90%) of expiratory volume.

Conclusions: EVL was present in all CF patients studied. In six of 14 with FEV150%pred., BR was reduced.