The impairment of excitation-contraction coupling in icu-acquired weakness

Abstract

The aim of this study is to elucidate the impairment of excitation-contraction (E-C) coupling in ICU-acquired weakness (ICUAW) using a unique electrophysiologic method in patients received the intensive care in ICU. We examined 9 patients with ICUAW and 10 normal controls. We performed successive recordings of electrophysiological tests after ICU admission. First, CMAPs of abductor hallucis muscle (AH) and sural SNAPs were recorded using a conventional method. In addition, the tibial nerve was stimulated at the popliteal fossa using a supramaximal rectangular pulse to record CMAPs from soleus muscle (SOL). Simultaneously, movement-related potential (MRP) was recorded using an accelerometer (SV1101) taped at the base of hallux and calculated E-C coupling time (ECCT) based on the latency differences between soleus CMAP and MRP. MRPs as well as CMAP amplitudes of AH and SOL were significantly smaller in patients than in controls. Also, ECCTs and CMAP durations of AH were significantly longer in patients than in controls. Nine patients were subdivided into 6 patients with critical illness myopathy (CIM) and 3 patients with critical illness polyneuropathy (CIP) based on the sural SNAP abnormality. All CIM patients consistently showed significantly prolonged ECCTs, and 5 CIM patients showed significantly decreased MRPs. These abnormalities occurred within several days after ICU admission. The E-C coupling may be impaired in the very early stages of CIM. Noninvasive measurement of MRP and ECCT is easy to perform, and may be an useful indicator of muscle involvement in the early stages of ICUAW.