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

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).

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.

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.

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.

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