Cystic fibrosis (CF) is the most common life-limiting, recessively inherited disease in the white population, associated with significantly high morbidity and mortality rates; CF pulmonary disease, assessed by pulmonary function tests, arterial blood gases and the Schwachman score, remains the most prevalent in terms of morbidity in the adult CF population.

The aim of the present study was to evaluate the relationship between resting respiratory variables and exercise capacity in adult patients with CF.

Study investigations undertaken in 18 CF patients and 11 healthy volunteers showed that among the resting lung function parameters, inspiratory capacity (IC) at rest was the only significant predictor of VO₂ peak (r=0.67, p<0.007) and VO₂/t-slope (r=0.86, p<0.0001). The percentage of predicted FEV₁ in adult CF patients was 77±33% pred. vs 104±16% pred. in healthy subjects (p<0.006); the corresponding percentage of IC at rest was 82±36% pred. in patients vs 116±20% pred. in healthy (p<0.003). CF patients presented with a significantly prolonged rapid breathing after exercise (32br per minute at recovery for CF vs 22 for healthy; p<0.001), as well as a shortened inspiratory time.

Adult patients with CF show a limited exercise capacity with lower peak oxygen consumption and prolonged oxygen kinetics. Interestingly, decreased IC qualified as the only significant predictor of exercise capacity in our study.