Effect of DNase on exercise capacity in cystic fibrosis

DNase can reduce viscosity and facilitate expectoration of airway secretions in cystic fibrosis (CF) lung disease. We evaluated its effect on exercise performance in relation to resting pulmonary function. Fifteen sputum-producing CF patients (aged 9-28 years; FEV1 22-83% predicted) performed spirometry, body plethysmography, nitrogen washout, and incremental cardiopulmonary exercise testing before and after 8 weeks of first-time treatment with daily inhaled rhDNase. Most subjects reported increased amounts and fluidity of sputum. The effect on objective parameters was heterogeneous, without statistical significance. Groupwise, FEV1 increased by 6% without correlation to baseline values; individual patients gained up to 40%. Indices of hyperinflation and air trapping were slightly raised. Maximal workload and oxygen uptake (V'O2) increased by up to 20% in a number of patients. The treatment effect on V'O2 was neither related to baseline levels of pulmonary function and exercise capacity nor to the change in FEV1. Ventilatory equivalents for oxygen and carbon dioxide during exercise were slightly but insignificantly lower after DNase treatment; minimal O2 saturation was unaffected. We conclude that improvement of exercise performance with DNase is restricted to a subgroup of CF patients and may not be predicted or identified by spirometry and subject report alone.