Effect of respiratory rate on airway deadspace ventilation during exercise in cystic fibrosis

Gas exchange during exercise in patients with cystic fibrosis (CF) is characterised by an elevated physiological deadspace to tidal volume ratio. While this has been attributed to alveolar ventilation–perfusion mismatch, there are other potential causes of the high proportion of wasted ventilation, including factors relating to the volume and the ventilation of the airway deadspace. CF ( n=6, F=1, FEV 1 26–63% pred) and control ( n=6, F=2) subjects completed steady-state exercise on a cycle ergometer. Gas exchange was measured breath-by-breath and the volume of the airway deadspace ( V D aw ) determined using the equal areas method. Exercise data were interpolated to a CO 2 output of 0.7 l/min. V D aw was similar in the two groups both at rest and during exercise. However, the airway deadspace ventilation ( V ̇ D aw ) (median (inter-quartile range)), patients, 6.8 (5.1–7.1) l/min; controls, 4.9 (3.5–5.6) l/min, P