Specific motor cortex hypoexcitability and hypoactivation in COPD patients with peripheral muscle weakness

Abstract

Background: Peripheral muscle weakness can be caused by both peripheral muscle and neural alterations. Although peripheral alterations cannot totally explain peripheral muscle weakness in COPD, the existence of an activation deficit remains controversial. The heterogeneity of muscle weakness (between 32 and 57% of COPD patients) is generally not controlled in studies and could explain this discrepancy. This study aimed to specifically compare voluntary and stimulated activation levels in COPD patients with and without muscle weakness. Methods: Twenty-two patients with quadriceps weakness (COPD MW), 18 patients with preserved quadriceps strength (COPD NoMW) and 20 controls were recruited. Voluntary activation was measured through peripheral nerve (VA peripheral) and transcranial magnetic (VA cortical) stimulation. Corticospinal and spinal excitability (MEP/Mmax and Hmax/Mmax) and corticospinal inhibition (silent period duration) were assessed during maximal voluntary quadriceps contractions. Results: COPD MW exhibited lower VA cortical and lower MEP/Mmax compared with COPD NoMW (p < 0.05). Hmax/Mmax was not significantly different between groups (p = 0.25). Silent period duration was longer in the two groups of COPD patients compared with controls (p < 0.01). Interestingly, there were no significant differences between all COPD patients taken together and controls regarding VA cortical and MEP/Mmax. Conclusions: COPD patients with muscle weakness have reduced voluntary activation without altered spinal excitability. Corticospinal inhibition is higher in COPD regardless of muscle weakness. Therefore, reduced cortical excitability and a voluntary activation deficit from the motor cortex are the most likely cortical mechanisms implicated in COPD muscle weakness. The mechanisms responsible for cortical impairment and possible therapeutic interventions need to be addressed.

Is bilateral corticospinal connectivity impaired in patients with chronic obstructive pulmonary disease?

“…First, the dominant leg was determined by inducing a slight forward imbalance and observing which leg stepped forward (Hoffman et al 1998;Hardy et al 2008;Okada et al 2015;Zalai et al 2015;Alexandre et al 2020). Then, the participants performed a standardized warm-up of low-intensity submaximal voluntary isometric contractions.…”

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