Symptoms, lactate and exercise limitation at peak cycle ergometry in adults with cystic fibrosis

The purpose of this study was to investigate symptoms, lactate accumulation and limiting factors at peak exercise in cystic fibrosis (CF) patients. In total, 104 CF adults attending an adult CF centre and 27 controls performed progressive cycle ergometry to a symptom-limited maximum. Measurements taken at peak exercise included: heart rate, ventilation, oxygen uptake, carbon dioxide output, oxygen saturation and blood lactate. Symptom scores of perceived breathlessness and muscle effort were recorded using Borg scales. The CF subjects had a lower mean body mass index, forced expiratory volume in one second (FEV(1)) and peak oxygen uptake than controls. Peak lactate concentrations were very similar to controls (mean+/-sd 6.8+/-2.0 mmol x L(-1) versus 7.4+/-1.0 mmol x L(-1)). Symptom scores were no different to controls for either breathlessness (4.5+/-2.0 versus 4.3+/-1.0) or perceived muscle effort (6.1+/-2.0 versus 6.5+/-1.0), with higher scores for muscle effort than breathlessness in both groups. In addition, peak ventilation was lower than the predicted maximum, and high peak heart rates were recorded supporting nonpulmonary factors as important in limiting peak exercise. Peak oxygen uptake was correlated with FEV(1). Comparison of CF subjects with mild or moderate pulmonary disease and controls revealed similar exercise responses. In contrast, those CF patients with severe lung disease (FEV(1) <40% predicted) had significantly higher breathlessness, lower muscle effort scores, lower peak lactate, lower peak heart rate and a mean ventilation exceeding predicted, thus confirming that ventilation was the major factor limiting exercise. In conclusion, cystic fibrosis subjects have a reduced peak exercise capacity, but their exercise response is similar to controls in generating high blood-lactate concentrations and symptoms of muscle effort in excess of dyspnoea. Nonpulmonary factors influence peak performance more in those without severe disease.