Six-minute walk test vs cardiopulmonary exercise test in the assessment of exercise tolerance in adults with cystic fibrosis

Background: Reduced exercise tolerance is a clear hallmark of cystic fibrosis (CF) and also an important prognostic factor. To date, it is not well established whether six-minute walk test (6MWT) and cardiopulmonary exercise test (CPET) provide similar sensitivity results in the assessment of exercise tolerance in adults with CF. Objective: The aim of the study was to compare 6MWT and CPET in the evaluation of exercise tolerance in CF adults with mild to moderate lung impairment. Methods: 30 stable CF adults (20 males, 10 females; age 32.9±8.8 years; FEV1 70.2±19.1% predicted, BMI 22.6±2.7 kg/m2) and 15 age-sex-BMI matched healthy controls (HC) were recruited. All participants underwent 6MWT and incremental CPET on cycle-ergometer: maximal distance at 6MWT (6MWD) and peak oxygen uptake (V'O2 peak) at CPET were measured, together with other physiologic variables. Lower limits of normal values (LLN) were calculated from the 5th percentile of HC results’ distributions. Results: 6MWD was similar between CF patients and HC (656.3±65.5 vs 719.6±100.9 m, p=ns). By contrast, V'O2 peak was significantly lower in CF patients, both as normalized for body weight (28.7±5.0 vs 38.1±4.2 ml/min/kg, p<0.0001) and as percentage of predicted value (76.3±13.4 vs 98.2±13.1%, p