Endurance exercise capacity in adults with cystic fibrosis

We have compared the maximal and endurance exercise capacities in 22 (15 male) adult cystic fibrosis (CF) patients with a resting oxygen saturation (SaO2) > or = 90%, with age and sex matched controls (CON). The maximum oxygen uptake (VO2max) and heart-rate were lower for the CF group whereas the maximum ventilation reached a higher percentage of predicted. Furthermore, for the CF group there was a relationship between the % predicted VO2max and measures of lung function, confirming a ventilatory limit to maximum exercise in patients with more severe disease and a near normal maximum exercise capacity in those with mild disease. Endurance capacity, defined as the duration of exercise at 80% of each individuals VO2max, was however similar for the two groups [CF: 22.21 (15.82) vs. CON: 24.94 (13.05) min]; despite the CF group exercising under less efficient ventilatory conditions. Endurance capacity was not related to the measurements of lung function. Of the seven CF patients desaturating at maximal exercise (SaO2 < 90%), five desaturated at a work load of 80% VO2max, whereas only one desaturated at 50% VO2max. This study confirms that with increasing severity of disease, maximal exercise capacity may be limited in adult CF patients, whereas endurance capacity (at the same relative work load) is unimpaired. Furthermore, CF patients who desaturate during a progressive maximal exercise test are likely to desaturate during constant work load exercise if the intensity is high but unlikely to do so if the intensity is low. The information from these exercise tests would be of value for prescribing individual training programmes and for evaluating the effects.