Abstract
BackgroundSkeletal muscle function dysfunction has been reported in patients with cystic fibrosis (CF). Studies so far showed inconclusive data whether reduced exercise capacity is related to intrinsic muscle dysfunction in CF.MethodsTwenty patients with CF and 23 age-matched controls completed an incremental cardiopulmonary cycling test. Further, a Wingate anaerobic test to assess muscle power was performed. In addition, all participants completed an incremental knee-extension test with 31P magnetic resonance spectroscopy to assess muscle metabolism (inorganic phosphate (Pi) and phosphocreatinine (PCr) as well as intracellular pH). In the MRI, muscle cross-sectional area of the M. quadriceps (qCSA) was also measured. A subgroup of 15 participants (5 CF, 10 control) additionally completed a continuous high-intensity, high-frequency knee-extension exercise task during 31P magnetic resonance spectroscopy to assess muscle metabolism.ResultsPatients with CF showed a reduced exercise capacity in the incremental cardiopulmonary cycling test (VO2peak: CF 77.8 ± 16.2%predicted (36.5 ± 7.4 ml/qCSA/min), control 100.6 ± 18.8%predicted (49.1 ± 11.4 ml/qCSA/min); p < 0.001), and deficits in anaerobic capacity reflected by the Wingate test (peak power: CF 537 ± 180 W, control 727 ± 186 W; mean power: CF 378 ± 127 W, control 486 ± 126 W; power drop CF 12 ± 5 W, control 8 ± 4 W. all: p < 0.001). In the knee-extension task, patients with CF achieved a significantly lower workload (p < 0.05). However, in a linear model analysing maximal work load of the incremental knee-extension task and results of the Wingate test, respectively, only muscle size and height, but not disease status (CF or not) contributed to explaining variance. In line with this finding, no differences were found in muscle metabolism reflected by intracellular pH and the ratio of Pi/PCr at submaximal stages and peak exercise measured through MRI spectroscopy.ConclusionsThe lower absolute muscle power in patients with CF compared to controls is exclusively explained by the reduced muscle size in this study. No evidence was found for an intrinsic skeletal muscle dysfunction due to primary alterations of muscle metabolism.
Highlights
Skeletal muscle function dysfunction has been reported in patients with cystic fibrosis (CF)
Lung function was worse in patients with CF reflected by a lower Forced expiratory volume in 1 s (FEV1) (%predicted), a lower Forced vital capacity (FVC) (%predicted) and a higher residual volume/total lung capacity ratio (RV/TLC% predicted), diffusion capacity was comparable between the groups (Table 1)
Duration of the high-intensity exercise task showed no significant differences between controls and patients with CF (Table 4)
Summary
Skeletal muscle function dysfunction has been reported in patients with cystic fibrosis (CF). Several studies reported reduced muscle function in patients with CF compared to healthy controls leading to constraints in aerobic and anaerobic capacities [5, 6]. Studies have proven that improving lung function by bronchodilators does not increase peak aerobic capacity [11]; at the same time, patients with CF are able to fatigue peripheral muscles despite ventilatory limitations [12]. Both aspects highlight the importance of peripheral muscle function for exercise capacity
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