The value of extra-diaphragmatic inspiratory muscle surface electromyography during postural control tasks in patients with chronic obstructive pulmonary disease

Abstract

Concurrent dysfunctions in postural control and diaphragm are observed in patients with chronic obstructive pulmonary disease (COPD). Measuring diaphragm activation traditionally involves transesophageal diaphragm electromyography (EMG(di)), which is costly and relatively invasive. Extra-diaphragmatic inspiratory muscle surface electromyography may serve as a useful physiological marker for EMG(di). This study compared EMG(di) amplitude with surface EMG amplitude of other inspiratory muscles, including sternocleidomastoid (sEMG(scm)), scalene (sEMG(scal)), and parasternal intercostal muscles (sEMG(ic)) during postural control tasks in nine patients with COPD (5 males; age: 65 +/- 6 years; forced expiratory volume in the first second: 60 +/- 27 % predicted). Simultaneous recordings of EMG(di), sEMG(scm), sEMG(scal), and sEMG(ic) amplitudes were obtained during six postural control tasks involving upright standing with ballistic arm movements under different conditions of support surface (stable/foam), arm movement frequency (single/repetitive), and breathing modes (normal/breath-hold at end-expiration). EMG amplitudes were normalized to each muscle's maximum voluntary contraction. A linear mixed model with Bonferroni-Holm post-hoc tests and Bland-Altman analyses were performed. There was a significant EMG-by-task interaction (p = 0.0223). The amplitude of EMG(di) was significantly lower than sEMG(ic) across all tasks (p < 0.0001 to 0.0007), while no significant differences were observed between EMG(di) and sEMG(scm) or EMG(di) and sEMG(scal) after Bonferroni-Holm correction (p = 0.019-0.858). Bland-Altman analyses indicated reasonable agreement between EMG(di) and both sEMG(scm) and sEMG(scal) (mean biases: 1.8 % and -3.7 %), while sEMG(ic) had a significantly higher overall bias of -20.7 %. These findings suggest that both sEMG(scal) and sEMG(scm) can serve as useful physiological markers for EMG(di) in postural control assessments in patients with COPD.