Measures of respiratory function correlate with fatigue in ambulatory persons with multiple sclerosis

Purpose: This article examines the association between measures of respiratory muscle function and fatigue in individuals with mild-to-moderate disability multiple sclerosis (MS). Methods: This was a cross-sectional study of 37 ambulatory volunteers with MS (28 F/9 M, 52.7 ± 10.2 years, Expanded Disability Status Scale [EDSS] = 3.5 ± 1.9). No patients withdrew from the study. Primary outcome variables included measures of respiratory function: maximal inspiratory (MIP) and expiratory pressures (MEP), forced vital capacity (FVC), forced expiratory volume in 1 s (FEV₁), maximal voluntary ventilation (MVV₁₂); and a self-reported measure of fatigue: the Modified Fatigue Impact Scale (MFIS). Secondary measures included 6-min walking test (6MWT), a timed stair climb, the Short Form (SF)-36, the Epworth Sleepiness Scale and the Physical Activity and Disability Scale (PADS). Results: Significant correlations were shown between expiratory muscle strength (MEP) and the MFIS total (p < 0.03, r = -0.362) and between MEP and physical fatigue scores (p < 0.03, r = -0.360), as well as between MVV₁₂ percent predicted (respiratory muscle endurance) and both the 6MWT (p = 0.045, r = 0.346) and the Epworth Sleepiness Scale (p = 0.006, r = 0.447). Conclusions: Respiratory muscle performance is correlated with perceived fatigue (MFIS), whereas respiratory endurance correlated to reductions in physical function and sleep quality among individuals with mild-to-moderate severity MS. ▸ Implications for Rehabilitation • Multiple sclerosis (MS) results in peripheral and respiratory muscle weakness and affected individuals report fatigue as one of their most disabling symptoms. • Expiratory muscle strength was correlated with self-reported physical fatigue, while respiratory muscle endurance was correlated with functional performance and sleepiness. • Respiratory muscle strength was not correlated with lung spirometry testing. • These findings highlight the importance of considering the effects of respiratory muscle weakness when evaluating causes of fatigue among individuals with mild-to-moderate MS.