Reliability and Minimal Detectable Change for Respiratory Muscle Strength Measures in Individuals With Multiple Sclerosis

Abstract

Background and Purpose: The test-retest reliability and minimal detectable changes (MDCs) for respiratory muscle strength measures have not been determined in individuals with multiple sclerosis (MS). This study determined the test-retest reliability and MDCs for specific respiratory muscle strength measures, as well as their associations with health-related quality of life (HRQoL), disability, dyspnea, and physical activity level measures in this population. In addition, the study examined differences in respiratory muscle strength between different degrees of disability.

Methods: Sixty-one individuals with MS attended 2 appointments separated by 7 to 10 days. Respiratory muscle strength was evaluated by maximal inspiratory and expiratory pressures (MIP/MEP), HRQoL by EuroQol-5D-5L (index and visual analog scale [EQ-VAS]), disability by the Expanded Disability Status Scale, dyspnea by the Medical Research Council scale, and physical activity levels by the International Physical Activity Questionnaire.

Results: Respiratory muscle strength measures had excellent test-retest reliability (ICC ≥ 0.92). The MDC for MIP is 15.42 cmH 2 O and for MEP is 17.84 cmH 2 O. Participants with higher respiratory muscle strength (MIP/MEP cmH 2 O and percentage of predicted values) had higher HRQoL ( r = 0.54-0.62, P < 0.01, EQ-5D-5L index; r = 0.30-0.42, P < 0.05, EQ-VAS); those with higher expiratory muscle strength (cmH 2 O and percentage of predicted values) had lower levels of disability ( r ≤ -0.66) and dyspnea ( r ≤ -0.61). There were differences in respiratory muscle strength between different degrees of disability ( P < 0.01; d ≥ 0.73).

Discussion and conclusion: Respiratory muscle strength measures provide excellent test-retest reliability in individuals with MS. MDCs can be interpreted and applied in the clinical setting. Low respiratory muscle strength can contribute to a poor HRQoL; specifically, expiratory muscle strength appears to have the strongest influence on disability status and dyspnea.