Validity and Reliability Concerns Associated with Cardiopulmonary Exercise Testing Young People with Cystic Fibrosis

teau in oxygen uptake (V̇O 2 ) upon exhaustion, at least one of the following should be used to confirm a maximal effort: the patient achieves a predicted V̇O 2 peak or peak power output (W peak ), the patient reaches maximal heart rate (HR max ), peak ventilation approaches maximal voluntary ventilation, respiratory exchange ratio (RER) is >1.03, exertion is 9–10 on the 0–10 scale or ≥ 17 on a 7–20 scale. However, our research group recently demonstrated that the use of secondary criteria to confirm a maximal effort (e.g. RER >1.00 or 1.10, HR of 180 beats · min –1 or 95% age-predicted HR max ), in line with those recommended by Hebestreit et al. [1] , are invalid and can drastically underreport V̇O 2 max in some young people with CF [4] , a finding consistent with healthy children and adolescents [5] . Accepting submaximal or rejecting ‘true’ maximal values can distort the clinical application and interpretation of CPET, which is important given that V̇O 2 max is an indicator of prognosis [6, 7] , quality of life [8] and risk of hospitalisation for exacerbations [9] in people with CF. Given the limited use of secondary verification criteria to verify a maximal CPET effort in young people with CF, we have developed an alternative protocol to do so. A procedure termed the ‘supramaximal verification phase’ (S max ), in which an exhaustive ramp incremental test preceding an exhaustive individualised constant work rate test at an intensity above W peak can confirm whether a ‘true’ measure of V̇O 2 max has been obtained, which is fundamental to the utility of this outcome parameter in CF. Significantly, this finding is in line with data in healthy adults [10–18] , children [5] and other paediatric clinical groups [19] . Although the authors present information regarding ‘was the test maximal?’, they failed to reference this published evidence and presented inaccurate verification criteria as ‘best’ CPET practice for young people with CF, which we feel should be approached with caution. This statement also provides a summary of the reliability of exercise tests for young people with CF; however, again published evidence has been ignored. We recently reported both the shortand medium-term reproducibility of a valid CPET protocol for young people with CF [4] , which was shown to reduce the error of measurement when compared with an isolated incremental CPET to derived V̇O 2 peak [20] . To the best of our knowledge, we are not aware of any reproducibility or validity data for V̇O 2 max in young people with CF derived using the Godfrey protocol. Whilst the focus of this letter addresses validity and reproducibility issues with the Godfrey protocol, other important issues to consider are: ‘step’ increases in work rate derived exclusively from stature can result in insufficient test durations of ≤ 4 min [21] . This procedure limits our ability to characterise the progressive increase in V̇O 2 during exercise and determine submaximal measures of aerobic fitness (e.g. the gas exchange threshold or V̇O 2 mean response time), which, as highlighted in this consensus statement, may provide better predictors of mortality in adolescents with CF [22] . In accordance with others [23] , we recommend a ramp incremental exercise test, which aims to reach volitional exhaustion in 8–12 min [24] , followed by S max verification of maximal CPET paThe recent statement by Hebestreit and colleagues [1] on behalf of the European Cystic Fibrosis Society (ECFS) Exercise Working Group and endorsed by the European Respiratory Society should be commended for their efforts to establish consensus regarding exercise testing for young people with cystic fibrosis (CF). Exercise testing is a valuable investigative tool for the clinical management and scientific investigation of children and adolescents with CF and this document provides an international standpoint regarding the importance of cardiopulmonary exercise testing (CPET) within the management of this patient group. However, it is our view that the authors have missed an opportunity to provide a contemporary and comprehensive overview of the CPET ‘toolkit’ currently available. The authors state that this document will ‘describe the current best practice recommendations for conducting exercise tests in patients with CF’ and ‘summarises the information available on specific test protocols and outcome parameters’ (page 2). The authors recommend the Godfrey protocol [2] when using the cycle ergometer, with measures of arterial oxygen saturation and, when possible, pulmonary gas exchange and ventilation. Whilst this does represent progress from the routinely used shuttle and step tests, the authors failed to acknowledge several limitations inherent to the Godfrey protocol and the recommended use of criteria to verify a maximal test. This is surprising, given that the ECFS Clinical Trials Network Standardisation Committee recently called for research assessing the validity, reproducibility and feasibility of outcome measures utilised in the assessment of patients with CF and the most appropriate exercise test for paediatric patients [3] . The authors rightfully acknowledge that an issue with shuttle and step tests is that it can be difficult to determine whether a maximal effort was made. However, they then state that ‘the Godfrey protocol provides valid information for all CF relevant indications for an exercise test’. The authors recommend that since not all individuals display the tradition verification criterion of a plaPublished online: June 30, 2016