Assessment of neuromuscular damage in COVID-19 post-intensive care syndrome patients

Purpose: Following hospitalization, Covid-19 post-intensive care syndrome (PICS) patients acquired prolonged physical, mental and cognitive impairments due to the symptoms of the disease, prolonged immobility and neuromuscular complications. The study aims at evaluating the correlation between functional variables i.e. the maximal voluntary contraction (MVC), and electrophysiological variables i.e. the compound muscles action potential (CMAP) and the motor unit number index (MUNIX), to determine a strategy for assessing neuromuscular damage and fatigue in COVID-19 PICS patients both during and post-intensive care unit (ICU) hospitalization. Methods: Fifty-one critically ill patients (37 males, 14 females) were recruited from the ICU of Spedali Civili Hospital in Brescia and underwent a follow-up assessment at 3-, 6- and 12-months following ICU discharge. The protocol consisted of a stimulation and a voluntary protocol. During the stimulation protocol, the CMAP was estimated by stimulating the common peroneal nerve (CPN). During the voluntary protocol, patients performed submaximal isometric foot dorsiflexions at 30, 50, and 70% MVC. The MUNIX was calculated using the CMAP and the surface electromyographic interference patterns (SIP) recorded during the isometric contractions. The CMAP and the SIP were derived from the HD-sEMG signals recorded from the TA with a 64-channel matrix placed over the belly of the tibialis anterior. Results: The mean variations in MVC between 3- and 6-months follow-up (10.75%) and between 6- and 12-months (16%) following COVID-19 ICU discharge were paralleled by changes in CMAP for the same period (? 10.85% at 6 compared to 3 months, and ? 1.09% at 12 compared to 6 months). The linear regression analysis showed a moderate correlation between MVC and CMAP (R2= 0.20; p\0.001) and between MVC and MUNIX (R2= 0.18; p\0.001). Conclusions: The MVC was significantly correlated with CMAP and MUNIX estimations. The correlation between functional and electrophysiological variables allows to longitudinal assess the neuromuscular damage in COVID-19 PICS individuals and opens the possibility for an early clinical evaluation of non- collaborating patients admitted to the ICU and their subsequent follow-up.