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

Abstract

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 (VO 2 peak) and to compare VO 2 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 VO 2 peak measured and estimated were compared.Results: Twenty-four patients, mean age 15.7 ± 4.2 years and FEV 1 (% 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 VO 2 peak (CPET). The regression model to estimate VO 2 peak resulted in the following equation: VO 2 (mL · kg −1 · min −1 ) = 20.301 + 0.019 × MST distance (meters). There was no difference (P = 0.50) between VO 2 peak measured (CPET) and estimated by the equation. Conclusion:The MST may be an alternative method to evaluate exercise capacity and to predict VO 2 peak in children and adolescents with CF.

Reply

“…Selvadurai et al evaluated children and concluded that “When formal exercise testing with a treadmill or cycle ergometer cannot be performed, shuttle tests provide a reproducible and valid alternative,” suggesting the following equation: VO 2 = (0.0289 × distance) + 17.46. Our study extends current literature by demonstrating the relationship between VO 2 peak and the MST performance using the 10‐meter and 15‐level test for children and adolescents with CF.…”

“…(3) External validation should be conducted in future studies, as it requires a different sample. (4) We agree that the sample size of our study may be considered as a limitation, although a sample size estimation was performed and both the standard error of the estimate (3.67) and the coefficient of determination (0.628) are acceptable …”

“…Apart from that, it is worth noting the following recommendation from the Statement on Exercise Testing in Cystic Fibrosis: “Not all individuals tested will show a leveling‐off of VO 2 during the test. Therefore, it has been suggested to assume a maximal effort if at least one of the following criteria is met during an exercise test: (a) The patient achieves predicted VO 2 peak and/or predicted maximal work rate; (b) The patient reaches a maximal HR at or above predicted peak HR; (c) Peak ventilation approaches or exceeds (estimated) MVV; (d) Maximal respiratory exchange ratio during exercise exceeds 1.03 (cycle ergometry) or 1.0 (treadmill) in children and adolescents; (e) rating of 9‐10 on a 0‐10 Borg scale for perceived exertion or ≥17 on a 6‐20 scale.” When the VO 2 peak measured in the sample of our study was normalized for healthy peers, only three patients were below normal values. We believe that, in addition to the three other criteria described and achieved by patients, indicate that maximum effort was attained.…”

“…Second, as for the error of the estimate, a misinterpretation of results led to an inaccurate conclusion. The model described in our study presents a standard error of the estimate of 3.67 mL·kg −1 ·min −1 for the VO 2 . The variation described as 7.8 mL·kg −1 ·min −1 represents the maximum difference found in the agreement analysis, which occurred in a few patients, as shown in Figure 2.…”

“…We appreciate the comments by Williams et al to our recent publication in Pediatric Pulmonology . Although some interesting methodological issues were raised, results and related literature seem to have been partially misinterpreted.…”