Abstract
ObjectiveThe 6-minute walk test is widely used to assess functional status in neurological disorders. However, the test is subject to great inter-test variability due to fluctuating motivation, fatigue and learning effects. We investigated whether inter-test variability of the 6MWT can be reduced by heart rate correction.MethodsSixteen patients with neuromuscular diseases, including Facioscapulohumeral muscular dystrophy, Limb-girdle muscular dystrophy, Charcot-Marie-Tooths, Dystrophia Myotonica and Congenital Myopathy and 12 healthy subjects were studied. Patients were excluded if they had cardiac arrhythmias, if they received drug treatment for hypertension or any other medical conditions that could interfere with the interpretation of the heart rate and walking capability. All completed three 6-minute walk tests on three different test-days. Heart rate was measured continuously.ResultsSuccessive standard 6-minute walk tests showed considerable learning effects between Tests 1 and 2 (4.9%; P = 0.026), and Tests 2 and 3 (4.5%; P = 0.020) in patients. The same was seen in controls between Tests 1 and 2 (8.1%; P = 0.039)). Heart rate correction abolished this learning effect.ConclusionA modified 6-minute walk test, by correcting walking distance with average heart rate during walking, decreases the variability among repeated 6-minute walk tests, and should be considered as an alternative outcome measure to the standard 6-minute walk test in future clinical follow-up and treatment trials.
Highlights
The 6-minute walk test (6MWT) is a submaximal exercise test, which despite pitfalls, is widely used to assess treatment efficacy or disease progression in neurological diseases, because walking capability is a central function of life and reflects an important functional capacity of daily living [1, 2]
We investigated whether inter-test variability of the 6MWT can be reduced by heart rate correction
We wanted to test if the learning effect after repeated 6MWTs is present in a broad group of patients with neuromuscular disorders (NMD), if their walking distance correlates with heart rate (HR), and if HR correction of the 6MWT can reduce inter-test variability
Summary
The 6-minute walk test (6MWT) is a submaximal exercise test, which despite pitfalls, is widely used to assess treatment efficacy or disease progression in neurological diseases, because walking capability is a central function of life and reflects an important functional capacity of daily living [1, 2]. The test is subject to a high inter-test variability, related to fluctuating motivation, fatigue, and learning effects [3,4,5,6,7,8]. Cardiac output (CO) is known to be linearly correlated to work load, irrespective of fatigue and motivation, and since heart rate (HR) is a function of CO (CO 5 stroke volume x HR) [9, 10], we hypothesized that a correction of the reliability and feasibility of the 6MWT, for adult patients, has only been validated in one other study of neuromuscular disorders (NMD) [2]. We wanted to test if the learning effect after repeated 6MWTs is present in a broad group of patients with NMD, if their walking distance correlates with HR, and if HR correction of the 6MWT can reduce inter-test variability
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