The Alfred Step Test Exercise Protocol (A-STEP), for Adults With Cystic Fibrosis.

Overview

Exercise testing has become clinically important in the management and ongoing evaluation of patients with Cystic Fibrosis (CF) with higher rates of exercise tolerance and participation previously linked to lower mortality risk (1). Lower exercise capacity generally correlates with more severe lung disease (2,3) and landmark studies suggest that low exercise capacity as measured by peak oxygen capacity (VO2peak) and rate of decline in lung function (FEV1) are strong predictors of mortality (1,4). However not all studies have found pulmonary function tests (PFTs) to be reliable predictors of maximal exercise capacity (5), especially in relatively well preserved lung function (6,7). The wide distribution in physical capacity between fit individuals and end stage disease adds to complexity of assessment. Independent factors of age, genetics, habitual exercise, nutritional status and musculoskeletal conditions are all known to influence physical capacity in patients with CF (8,9). Maximal exercise testing places additional stress on cardiovascular, respiratory and peripheral systems providing more information around multiple influences on disease progression including degree of limitation in these major systems (10,11) and is useful for assessment of exercise desaturation, more common (but not always present) in advanced lung disease (5,12). With prediction of exercise performance and functional capacity from PFTs unreliable and the understanding that health status correlates better with exercise tolerance there has been an increase in maximal exercise testing for patient management (13). Many international centers now regard exercise testing as highly important with many assessing maximal exercise capacity annually to monitor disease progression, identify physical status and drive changes in medical, physiotherapy or nutritional management (14,15). The main vision is to develop a standardized incremental step test protocol suitable for adults with Cystic Fibrosis (CF), all ages, levels of fitness and disease state that is in line with current exercise testing recommendations (15). To develop a more useful field test to assess exercise tolerance and a more "user friendly" test than the currently available laboratory exercise test to allow for early detection of decline in physical function in the day-to-day clinical setting. To date no studies have been published in adults with CF where an incremental exercise step test has been investigated to assess exercise tolerance or determine maximum oxygen uptake (VO2max).

Many international centers now regard exercise testing as highly important with many measuring maximal exercise capacity annually to monitor disease progression, identify physical status and to drive changes in medical, physiotherapy or nutritional management (14,15). Cardiopulmonary Exercise Testing (CPET): The current best practice for assessing VO2max in adults with CF is a CPET using the Godfrey Protocol, a progressive and incremental maximal test performed on a cycle ergometer (13,14,15). Exercise testing should aim to achieve a maximal response within a time frame of 8-12 min and incremental protocols with stage duration of 1 minute are considered more efficient in eliciting the desired response within this time frame (14). During CPET, VO2max is determined while breath-by-breath gas analysis allows for a comprehensive assessment of exercise ventilation and circulation. This information can identify reasons for low exercise capacity and whether exercise limitation is due to deconditioning, or primarily within the respiratory, cardiovascular or peripheral systems. CPET is performed using a specialist ergometer, and requires specialist clinical expertise, monitoring and reporting equipment for interpretation of the test. The cost, space and expertise to carry out CPET in CF units around the world may limit its use for the regular assessment of exercise capacity in adults with CF (16). Field Tests: Field tests generally cannot determine absolute maximal exercise capacity, but do provide valuable information about the patient's functional abilities and limitations and compared to laboratory tests are inexpensive and easy to administer. Field tests that use a single step for assessment of exercise tolerance in patients with chronic lung disease include: 3-Minute Step Test (3MST): The 3MST is a feasible and acceptable measure of sub-maximal exercise performance in children and adults and a useful tool in the assessment of oxygen desaturation (17,18). The test is short in duration, simple to carry out, and has low cost and minimal space and equipment requirements however the sub-maximal nature and ceiling effect of the 3MST limits its usefulness clinically across the age spectrum (18,19). The Chester Step Test (CST): The CST is a 10-minute sub-maximal standardized multistage test and like the 3MST has minimal space and equipment requirements. The CST was originally designed for workplace screening and is now widely used for exercise prescription in the UK cardiac population (20). In healthy individuals one study reported a ceiling effect and a positive relationship between predicted VO2max using the CST and measured VO2max (21) however a subsequent study questioned this prediction validity (22). The CST has been found to be highly reproducible in patients with chronic obstructive lung disease (COPD) and reliable in patients with Bronchiectasis, but too challenging for both groups (23,24). The Modified Incremental Step Test (MIST): The MIST was designed to be more suitable for COPD patients and modeled from the CST(25). A reduction in work rate was not found to result in a difference in cardiopulmonary stress and exertion effort at peak exercise but did result in a higher exercise tolerance in patients with COPD. The MIST is reliable and better tolerated than the CST in patients with Bronchiectasis (23,24). The CST and CF: One study (published in abstract form) has shown the CST to be a useful field test when compared to the 3MST and 6MWT for those with mild to moderate CF. The authors commented this was likely due to the progressive nature being more representative of adult physical activity (26). The main vision is to develop a standardized incremental step test protocol suitable for adults with Cystic Fibrosis (CF), all ages, levels of fitness and disease state that is in line with current exercise testing recommendations (15). The test should be a more useful than the already available field tests and more "user friendly" test than the currently available laboratory exercise test to assess exercise tolerance and allow for early detection of decline in physical function in the day-to-day clinical setting. To date no studies have been published in adults with CF where an incremental exercise step test has been investigated to assess exercise tolerance or determine VO2max. 1. To design a standardized externally paced incremental step test that is portable, easy to administer, simple to perform, time, cost and space efficient (A-STEP). Study A: 2. To assess feasibility and reliability of the A-STEP to objectively assess exercise tolerance. 3. To determine if the A-STEP is a more useful tool than the 3-Minute Step Test. Study B: 4. To develop an alternative tool to determine maximum oxygen uptake (VO2max) to the "gold standard" CPET that is feasible across the whole spectrum of lung disease. 5. To determine if the A-STEPmax is a valid tool when compared to the VO2max achieved from a CPET performed on a cycle ergometer using the Godfrey Protocol. The principle investigator hypothesizes that the A-STEP will be a feasible tool to assess exercise capacity; and the A-STEP max will be a valid tool for the assessment of VO2max across the age range and disease spectrum in adults with CF.