Prediction of peak oxygen uptake using the modified shuttle test in children and adolescents with cystic fibrosis.

BACKGROUND: Several tests may be used to assess exercise intolerance in cystic fibrosis (CF), including the gold standard cardiopulmonary exercise test (CPET) and the Modified Shuttle Test (MST).

OBJECTIVE: To evaluate the use of the MST as a predictor of peak oxygen uptake (VO2 peak) and to compare VO2 peak and maximal heart rate (HRmax) obtained in both tests.

METHODS: Cross-sectional study including individuals with CF aged between 6 and 20 years old. Participants who were unable to perform the tests and/or presented signs of pulmonary exacerbation were excluded. Demographic, anthropometric, clinical and spirometric values ​​were collected. CPET and the MST were performed in two consecutive outpatient visits. HRmax, peripheral oxygen saturation, dyspnea, and VO2 peak measured and estimated were compared.

RESULTS: Twenty-four patients, mean age 15.7 ± 4.2 years and FEV1 (% predicted) 76.4 ± 23.8, were included. Mean values ​​of HRmax (bpm) and HRmax in percent of predicted (HRmax%) were lower (P = 0.01) in the MST (171.6 ± 14.5 and 87.1 ± 7.5) compared to CPET (180.9 ± 10.0 and 91.9 ± 5.4). However, there was no significant differences between tests in the variation (delta) for HRmax and HRmax% (P = 0.17). A strong correlation (r = 0.79; P < 0.0001) was found between distance achieved (MST) and VO2 peak (CPET). The regression model to estimate VO2 peak resulted in the following equation: VO2 (mL · kg-1  · min-1 ) = 20.301 + 0.019 × MST distance (meters). There was no difference (P = 0.50) between VO2 peak measured (CPET) and estimated by the equation.

CONCLUSION: The MST may be an alternative method to evaluate exercise capacity and to predict VO2 peak in children and adolescents with CF.