Noninvasive Assessment of Neuromechanical and Neuroventilatory Coupling in COPD

This study explored the use of parasternal second intercostal space and lower intercostal space surface electromyogram (sEMG) and surface mechanomyogram (sMMG) recordings (sEMG
_para
and sMMG
_para
, and sEMG
_lic
and sMMG
_lic
, respectively) to assess neural respiratory drive (NRD), neuromechanical (NMC) and neuroventilatory (NVC) coupling, and mechanical efficiency (MEff) noninvasively in healthy subjects and chronic obstructive pulmonary disease (COPD) patients. sEMG
_para
, sMMG
_para
, sEMG
_lic
, sMMG
_lic
, mouth pressure (P
_mo
), and volume (V
_i
) were measured at rest, and during an inspiratory loading protocol, in 16 COPD patients (8 moderate and 8 severe) and 9 healthy subjects. Myographic signals were analyzed using fixed sample entropy and normalized to their largest values (fSEsEMG
_para%max
, fSEsMMG
_para%max
, fSEsEMG
_lic%max
, and fSEsMMG
_lic%max
). fSEsMMG
_para%max
, fSEsEMG
_para%max
, and fSEsEMG
_lic%max
were significantly higher in COPD than in healthy participants at rest. Parasternal intercostal muscle NMC was significantly higher in healthy than in COPD participants at rest, but not during threshold loading. P
_mo
-derived NMC and MEff ratios were lower in severe patients than in mild patients or healthy subjects during threshold loading, but differences were not consistently significant. During resting breathing and threshold loading, V
_i
-derived NVC and MEff ratios were significantly lower in severe patients than in mild patients or healthy subjects. sMMG is a potential noninvasive alternative to sEMG for assessing NRD in COPD. The ratios of P
_mo
and V
_i
to sMMG and sEMG measurements provide wholly noninvasive NMC, NVC, and MEff indices that are sensitive to impaired respiratory mechanics in COPD and are therefore of potential value to assess disease severity in clinical practice.