Abstract
The muscle wasting and loss of specific force associated with Critical Illness Myopathy (CIM) is, at least in part, due to a preferential loss of the molecular motor protein myosin. This acquired myopathy is common in critically ill immobilized and mechanically ventilated intensive care patients (ICU). There is a growing understanding of the mechanisms underlying CIM, but the role of nutritional factors triggering this serious complication of modern intensive care remains unknown. This study aims at establishing the effect of nutritional status in the pathogenesis of CIM. An experimental ICU model was used where animals are mechanically ventilated, pharmacologically paralysed post-synaptically and extensively monitored for up to 14 days. Due to the complexity of the experimental model, the number of animals included is small. After exposure to this ICU condition, animals develop a phenotype similar to patients with CIM. The results from this study show that the preferential myosin loss, decline in specific force and muscle fiber atrophy did not differ between low vs. eucaloric animals. In both experimental groups, passive mechanical loading had a sparing effect of muscle weight independent on nutritional status. Thus, this study confirms the strong impact of the mechanical silencing associated with the ICU condition in triggering CIM, overriding any potential effects of caloric intake in triggering CIM. In addition, the positive effects of passive mechanical loading on muscle fiber size and force generating capacity was not affected by the nutritional status in this study. However, due to the small sample size these pilot results need to be validated in a larger cohort.
Highlights
The most frequent neuromuscular disorders underlying muscle weakness in intensive care unit (ICU) patients is critical illness myopathy (CIM)
The aim of this study is to investigate the effects of the nutritional status in the pathogenesis of CIM
The major findings from this study is that low vs. eucaloric parenteral nutrition had no significant effect on the size or force generating capacity in single muscle fibers and myosin:actin ratios were not affected in either the slow-twitch soleus or the fast-twitch extensor digitorum longus (EDL) muscles in animals exposed to a mimicked ICU setting over a period of 10–14 days
Summary
The most frequent neuromuscular disorders underlying muscle weakness in intensive care unit (ICU) patients is critical illness myopathy (CIM). The incomplete understanding of underlying mechanisms is, at least in part, related to insufficient diagnostic tools and the complex study of generalized muscle weakness in ICU patients, such as differences in underlying disease, age and gender. It has been impeded by a delay in the collection of muscle samples and preceded by several weeks after exposure to factors triggering a cascade of complex signaling pathways controlling protein synthesis and degradation
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