The iStep Study: Development and Validation of an Incremental Exercise Step Test for Children With Cystic Fibrosis

The progression of lung disease in cystic fibrosis (CF) results inevitably in a reduction in exercise capacity. The assessment of fitness and exercise capacity in CF is an important measure of the impact of the disease process, particularly if it is repeated over time. With recent advances in clinical management, CF lung disease in children can be relatively mild and exercise tolerance good. The currently available field tests e.g. 3 minute step test, are often completed too easily. These tests provide limited information relating to maximal exercise performance. By contrast, the maximal CardioPulmonary Exercise Test (CPET), a progressive, incremental, gold standard exercise test with breath by breath analysis of expired gas, has proved to be a valuable means of assessing exercise response in patients with CF. Its only limitation is the requirement for specialist laboratory facilities, equipment and staff.

A new field test for evaluating exercise capacity in children is needed. This should be portable, easy to administer and simple to perform by young children, while providing a higher intensity of exercise which correlates with day to day activity patterns of children, and clinically relevant information in the short term and longitudinally. This test needs to be a good surrogate measure of exercise capacity when formal CPET is unable to be undertaken. By providing accurate and useful information the results can be used to prescribe and train individuals with CF safely and effectively and can also be used in the short and long term for guidance of the medical management of these complex patients.

The aim of this study is to develop and validate the use of a new incremental step test to assess exercise tolerance/capacity in children with CF, compare this with the gold standard CPET and to provide normative healthy control comparison data The main objectives of the study are

1. To develop an incremental step test to assess exercise tolerance / capacity in children with CF. 2. To compare the incremental step test with the gold standard CPET 3. To assess the level of exercise response produced by the incremental step test 4. To assess the correlation between independent variables of lung function measurements, age, weight and height with VO2peak and other exercise test outcomes 5. To assess the repeatability and evaluate the normal variability of the new incremental step test 6. To provide healthy control normative data for comparison