Mechanisms underlying ICU muscle wasting and effects of passive mechanical loading

Intensive care unit-acquired weakness - preventive, and therapeutic aspects; future directions and special focus on lung transplantation

In this editorial, comments are made on an interesting article in the recent issue of the World Journal of Clinical Cases by Wang and Long. The authors describe the use of neural network model to identify risk factors for the development of intensive care unit (ICU)-acquired weakness. This condition has now become common with an increasing number of patients treated in ICUs and continues to be a source of morbidity and mortality. Despite identification of certain risk factors and corrective measures thereof, lacunae still exist in our understanding of this clinical entity. Numerous possible pathogenetic mechanisms at a molecular level have been described and these continue to be increasing. The amount of retrievable data for analysis from the ICU patients for study can be huge and enormous. Machine learning techniques to identify patterns in vast amounts of data are well known and may well provide pointers to bridge the knowledge gap in this condition. This editorial discusses the current knowledge of the condition including pathogenesis, diagnosis, risk factors, preventive measures, and therapy. Furthermore, it looks specifically at ICU acquired weakness in recipients of lung transplantation, because - unlike other solid organ transplants- muscular strength plays a vital role in the preservation and survival of the transplanted lung. Lungs differ from other solid organ transplants in that the proper function of the allograft is dependent on muscle function. Muscular weakness especially diaphragmatic weakness may lead to prolonged ventilation which has deleterious effects on the transplanted lung - ranging from ventilator associated pneumonia to bronchial anastomotic complications due to prolonged positive pressure on the anastomosis.

Revisiting the compound muscle action potential (CMAP)

The compound muscle action potential (CMAP) is among the first recorded waveforms in clinical neurography and one of the most common in clinical use. It is derived from the summated muscle fiber action potentials recorded from a surface electrode overlying the studied muscle following stimulation of the relevant motor nerve fibres innervating the muscle. Surface recorded motor unit potentials (SMUPs) are the fundamental units comprising the CMAP. Because it is considered a basic, if not banal signal, what it represents is often underappreciated. In this review we discuss current concepts in the anatomy and physiology of the CMAP. These have evolved with advances in instrumentation and digitization of signals, affecting its quantitation and measurement. It is important to understand the basic technical and biological factors influencing the CMAP. If these influences are not recognized, then a suboptimal recording may result. The object is to obtain a high quality CMAP recording that is reproducible, whether the study is done for clinical or research purposes. The initial sections cover the relevant CMAP anatomy and physiology, followed by how these principles are applied to CMAP changes in neuromuscular disorders. The concluding section is a brief overview of CMAP research where advances in recording systems and computer-based analysis programs have opened new research applications. One such example is motor unit number estimation (MUNE) that is now being used as a surrogate marker in monitoring chronic neurogenic processes such as motor neuron diseases.

Post-translational modifications of vertebrate striated muscle myosin heavy chains

Post-translational modifications (PTMs) play a crucial role in regulating the function of many sarcomeric proteins, including myosin. Myosins comprise a family of motor proteins that play fundamental roles in cell motility in general and muscle contraction in particular. A myosin molecule consists of two myosin heavy chains (MyHCs) and two pairs of myosin light chains (MLCs); two MLCs are associated with the neck region of each MyHC's N-terminal head domain, while the two MyHC C-terminal tails form a coiled-coil that polymerizes with other MyHCs to form the thick filament backbone. Myosin undergoes extensive PTMs, and dysregulation of these PTMs may lead to abnormal muscle function and contribute to the development of myopathies and cardiovascular disorders. Recent studies have uncovered the significance of PTMs in regulating MyHC function and showed how these PTMs may provide additional modulation of contractile processes. Here, we discuss MyHC PTMs that have been biochemically and/or functionally studied in mammals' and rodents' striated muscle. We have identified hotspots or specific regions in three isoforms of myosin (MYH2, MYH6, and MYH7) where the prevalence of PTMs is more frequent and could potentially play a significant role in fine-tuning the activity of these proteins.

Physical and Cognitive Impairment in Acute Respiratory Failure

Recent research has brought renewed attention to the multifaceted physical and cognitive dysfunction that accompanies acute respiratory failure (ARF). This state-of-the-art review provides an overview of the evidence landscape encompassing ARF-associated neuromuscular and neurocognitive impairments. Risk factors, mechanisms, assessment tools, rehabilitation strategies, approaches to ventilator liberation, and interventions to minimize post-intensive care syndrome are emphasized. The complex interrelationship between physical disability, cognitive dysfunction, and long-term patient-centered outcomes is explored. This review highlights the need for comprehensive, multidisciplinary approaches to mitigate morbidity and accelerate recovery.

Influence of blood lactate variations and passive exercise on cardiac responses

[Purpose] This study aimed to investigate cardiovascular responses, including heart rate (HR) and heart rate variability (HRV), to various hyperlactatemia-passive exercise interactions. [Participants and Methods] Nine healthy male participants performed upper limb passive cycling movement, and their HR and HRV were assessed while their blood lactate levels were manipulated by sustained handgrip exercise at control, 15% maximum voluntary contraction (MVC), and 30% MVC, followed by postexercise circulatory occlusion. [Results] HR and root mean squared standard difference (rMSSD) of HRV response remained constant at all blood lactate levels during passive exercise (HR: control, 75.8 ± 3.4 bpm; 15% MVC, 76.9 ± 2.7 bpm; and 30% MVC, 77.0 ± 3.7 bpm; rMSSD: control, 33.2 ± 6.9 ms; 15% MVC, 36.3 ± 7.3 ms; and 30% MVC, 37.3 ± 8.9 ms). [Conclusion] Manipulating metaboreflex activation did not significantly alter HR or HRV during passive exercise. These results suggest that, in healthy participants, the interactions between mechanical and metabolic stimuli do not affect HR and HRV responses, implying that passive exercise may be safely implemented.

Effects of Bed Rest on Physical Performance in Athletes: A Systematic and Narrative Review

BACKGROUND

Athletes can face scenarios in which they are confined to bed rest (e.g., due to injury or illness). Existing research in otherwise healthy individuals indicates that those entering bed rest with the greatest physical performance level might experience the greatest performance decrements, which indirectly suggests that athletes might be more susceptible to the detrimental consequences of bed rest than general populations. Therefore, a comprehensive understanding of the effects of bed rest might help guide the medical care of athletes during and following bed rest.

OBJECTIVE

This systematic and narrative review aimed to (1) establish the evidence for the effects of bed rest on physical performance in athletes; (2) discuss potential countermeasures to offset these negative consequences; and (3) identify the time-course of recovery following bed rest to guide return-to-sport rehabilitation.

METHODS

This review was performed using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Four databases were searched (SPORTDiscus, Web of Science, Scopus, and MEDLINE/PubMed) in October of 2022, and studies were included if they were peer-reviewed investigations, written in English, and investigated the effects of horizontal bed rest on changes in physical capacities and qualities in athletes (defined as Tier 3-5 participants). The reporting quality of the research was assessed using a modified version of the Downs & Black checklist. Furthermore, findings from studies that involved participants in Tiers 1-2 were presented and synthesized using a narrative approach.

RESULTS

Our systematic review of the literature using a rigorous criterion of 'athletes' revealed zero scientific publications. Nevertheless, as a by-product of our search, seven studies were identified that involved apparently healthy individuals who performed specific exercise training prior to bed rest.

CONCLUSIONS

Based on the limited evidence from studies involving non-athletes who were otherwise healthy prior to bed rest, we generally conclude that (1) bed rest rapidly (within 3 days) decreases upright endurance exercise performance, likely due to a rapid loss in plasma volume; whereas strength is reduced within 5 days, likely due to neural factors as well as muscle atrophy; (2) fluid/salt supplementation may be an effective countermeasure to protect against decrements in endurance performance during bed rest; while a broader array of potentially effective countermeasures exists, the efficacy of these countermeasures for previously exercise-trained individuals requires further study; and (3) athletes likely require at least 2-4 weeks of progressive rehabilitation following bed rest of ≤ 28 days, although the timeline of recovery might need to be extended depending on the underlying reason for bed rest (e.g., injury or illness). Despite these general conclusions from studies involving non-athletes, our primary conclusion is that substantial effort and research is still required to quantify the effects of bed rest on physical performance, identify effective countermeasures, and provide return-to-sport timelines in bona fide athletes.

TRIAL REGISTRATION NUMBER AND DATE OF REGISTRATION

Registration ID: osf.io/d3aew; Date: October 24, 2022.

Single fibre cytoarchitecture in ventilator-induced diaphragm dysfunction (VIDD) assessed by quantitative morphometry second harmonic generation imaging: Positive effects of BGP-15 chaperone co-inducer and VBP-15 dissociative corticosteroid treatment

Ventilator-induced diaphragm dysfunction (VIDD) is a common sequela of intensive care unit (ICU) treatment requiring mechanical ventilation (MV) and neuromuscular blockade (NMBA). It is characterised by diaphragm weakness, prolonged respirator weaning and adverse outcomes. Dissociative glucocorticoids (e.g., vamorolone, VBP-15) and chaperone co-inducers (e.g., BGP-15) previously showed positive effects in an ICU-rat model. In limb muscle critical illness myopathy, preferential myosin loss prevails, while myofibrillar protein post-translational modifications are more dominant in VIDD. It is not known whether the marked decline in specific force (force normalised to cross-sectional area) is a pure consequence of altered contractility signaling or whether diaphragm weakness also has a structural correlate through sterical remodeling of myofibrillar cytoarchitecture, how quickly it develops, and to which extent VBP-15 or BGP-15 may specifically recover myofibrillar geometry. To address these questions, we performed label-free multiphoton Second Harmonic Generation (SHG) imaging followed by quantitative morphometry in single diaphragm muscle fibres from healthy rats subjected to five or 10 days of MV + NMBA to simulate ICU treatment without underlying confounding pathology (like sepsis). Rats received daily treatment of either Prednisolone, VBP-15, BGP-15 or none. Myosin-II SHG signal intensities, fibre diameters (FD) as well as the parameters of myofibrillar angular parallelism (cosine angle sum, CAS) and in-register of adjacent myofibrils (Vernier density, VD) were computed from SHG images. ICU treatment caused a decline in FD at day 10 as well as a significant decline in CAS and VD from day 5. Vamorolone effectively recovered FD at day 10, while BGP-15 was more effective at day 5. BGP-15 was more effective than VBP-15 in recovering CAS at day 10 although not to control levels. In-register VD levels were restored at day 10 by both compounds. Our study is the first to provide quantitative insights into VIDD-related myofibrillar remodeling unravelled by SHG imaging, suggesting that both VBP-15 and BGP-15 can effectively ameliorate the structure-related dysfunction in VIDD.

Intensive Care Unit-Acquired Weakness in Patients With Acute Kidney Injury: A Contemporary Review

Acute kidney injury (AKI) and intensive care unit-acquired weakness (ICU-AW) are 2 frequent complications of critical illness that, until recently, have been considered unrelated processes. The adverse impact of AKI on ICU mortality is clear, but its relationship with muscle weakness-a major source of ICU morbidity-has not been fully elucidated. Furthermore, improving ICU survival rates have refocused the field of intensive care toward improving long-term functional outcomes of ICU survivors. We begin our review with the epidemiology of AKI in the ICU and of ICU-AW, highlighting emerging data suggesting that AKI and AKI treated with kidney replacement therapy (AKI-KRT) may independently contribute to the development of ICU-AW. We then delve into human and animal data exploring the pathophysiologic mechanisms linking AKI and acute KRT to muscle wasting, including altered amino acid and protein metabolism, inflammatory signaling, and deleterious removal of micronutrients by KRT. We next discuss the currently available interventions that may mitigate the risk of ICU-AW in patients with AKI and AKI-KRT. We conclude that additional studies are needed to better characterize the epidemiologic and pathophysiologic relationship between AKI, AKI-KRT, and ICU-AW and to prospectively test interventions to improve the long-term functional status and quality of life of AKI survivors.

Inhibition of DDX3X alleviates persistent inflammation, immune suppression and catabolism syndrome in a septic mice model

OBJECTIVE

DDX3X is involved in various pathological processes such as infection, immunity and cell death. This study aimed to investigate the effect of RK-33, a specific inhibitor of DDX3X, on the progression of sepsis to persistent inflammation, immune suppression and catabolism syndrome(PICS).

METHODS

The septic mice model was established using caecal ligation and perforation (CLP). The mice were randomly divided into four groups: sham group, sham + RK-33 group (20 mg/kg, intraperitoneal injection, once a day), CLP group and CLP + RK-33 group (20 mg/kg, intraperitoneal injection, once a day). The number of inflammatory cells in the peripheral blood, spleen and bone marrow was calculated, and inflammatory cytokines were detected using an enzyme-linked immunosorbent assay. The septic mice's body weight and skeletal muscle mass were measured, and skeletal muscle tissues were examined using eosin staining. Western blotting was performed to detect the expression levels of MuRF1, atrogin1 and NLRP3 in the skeletal muscle of septic mice. Additionally, reactive oxidative species, superoxide dismutase and malondialdehyde were measured using commercial kits.

RESULTS

RK-33 reduced inflammatory cell counts and cytokine levels in CLP mice, ameliorated the decline in CD4 and CD8 T cells and prevented the loss of body weight and skeletal muscle mass in septic mice. Additionally, RX-33 reduced oxidative stress in the skeletal muscle of septic mice.

CONCLUSION

In the established sepsis mouse model, RK-33 alleviated inflammation and oxidative stress, ameliorated CLP-induced immunosuppression and skeletal muscle atrophy and improved survival. These findings suggest that RK-33 could be a novel potential therapeutic agent for preventing the progression of sepsis to PICS.

Melatonin: A potential adjuvant therapy for septic myopathy

Septic myopathy, also known as ICU acquired weakness (ICU-AW), is a characteristic clinical symptom of patients with sepsis, mainly manifested as skeletal muscle weakness and muscular atrophy, which affects the respiratory and motor systems of patients, reduces the quality of life, and even threatens the survival of patients. Melatonin is one of the hormones secreted by the pineal gland. Previous studies have found that melatonin has anti-inflammatory, free radical scavenging, antioxidant stress, autophagic lysosome regulation, mitochondrial protection, and other multiple biological functions and plays a protective role in sepsis-related multiple organ dysfunction. Given the results of previous studies, we believe that melatonin may play an excellent regulatory role in the repair and regeneration of skeletal muscle atrophy in septic myopathy. Melatonin, as an over-the-counter drug, has the potential to be an early, complementary treatment for clinical trials. Based on previous research results, this article aims to critically discuss and review the effects of melatonin on sepsis and skeletal muscle depletion.

A prospective clinical study on the mechanisms underlying critical illness myopathy-A time-course approach

BACKGROUND

Critical illness myopathy (CIM) is a consequence of modern critical care resulting in general muscle wasting and paralyses of all limb and trunk muscles, resulting in prolonged weaning from the ventilator, intensive care unit (ICU) treatment and rehabilitation. CIM is associated with severe morbidity/mortality and significant negative socioeconomic consequences, which has become increasingly evident during the current COVID-19 pandemic, but underlying mechanisms remain elusive.

METHODS

Ten neuro-ICU patients exposed to long-term controlled mechanical ventilation were followed with repeated muscle biopsies, electrophysiology and plasma collection three times per week for up to 12 days. Single muscle fibre contractile recordings were conducted on the first and final biopsy, and a multiomics approach was taken to analyse gene and protein expression in muscle and plasma at all collection time points.

RESULTS

(i) A progressive preferential myosin loss, the hallmark of CIM, was observed in all neuro-ICU patients during the observation period (myosin:actin ratio decreased from 2.0 in the first to 0.9 in the final biopsy, P < 0.001). The myosin loss was coupled to a general transcriptional downregulation of myofibrillar proteins (P < 0.05; absolute fold change >2) and activation of protein degradation pathways (false discovery rate [FDR] <0.1), resulting in significant muscle fibre atrophy and loss in force generation capacity, which declined >65% during the 12 day observation period (muscle fibre cross-sectional area [CSA] and maximum single muscle fibre force normalized to CSA [specific force] declined 30% [P < 0.007] and 50% [P < 0.0001], respectively). (ii) Membrane excitability was not affected as indicated by the maintained compound muscle action potential amplitude upon supramaximal stimulation of upper and lower extremity motor nerves. (iii) Analyses of plasma revealed early activation of inflammatory and proinflammatory pathways (FDR < 0.1), as well as a redistribution of zinc ions from plasma.

CONCLUSIONS

The mechanical ventilation-induced lung injury with release of cytokines/chemokines and the complete mechanical silencing uniquely observed in immobilized ICU patients affecting skeletal muscle gene/protein expression are forwarded as the dominant factors triggering CIM.

Muscle size, strength, and physical function in response to augmented calorie delivery: A TARGET sub-study

PURPOSE

Augmented calories may attenuate muscle loss experienced in critical illness. This exploratory sub-study assessed the effect of augmented calorie delivery on muscle mass, strength, and function.

MATERIALS AND METHODS

Patients in The Augmented versus Routine approach to Giving Energy Trial (TARGET) randomised to 1.5 kcal/ml or 1.0 kcal/ml enteral formulae at a single-centre were included. Ultrasound-derived muscle layer thickness (MLT) at quadriceps, forearm and mid-upper arm, and handgrip strength, were measured weekly from baseline to hospital discharge, and 3- and 6-months. Physical function was assessed at 3- and 6-months using the 'get up and go' and 6-min walk tests. Data are mean ± SD.

RESULTS

Eighty patients were recruited (1.5 kcal: n = 38, 58 ± 14y, 60%M, APACHE II 20 ± 7; 1.0 kcal: n = 42, 54 ± 18y, 66%M, APACHE II 22 ± 10). The 1.5 kcal/ml group received more calories with no difference in quadriceps MLT at any timepoint including ICU discharge (primary outcome) (2.90 ± 1.27 vs 2.39 ± 1.06 cm; P = 0.141). Relationships were similar for all MLT measures, handgrip strength, and 6-min walk test. Patients in the 1.5 kcal/ml group had improved 'get up and go' test at 3-months (6.66 ± 1.33 vs. 9.11 ± 2.94 s; P = 0.014).

CONCLUSION

Augmented calorie delivery may not attenuate muscle loss or recovery of strength or function 6-months post-ICU, but this requires exploration in a larger trial.

Electrical stimulated GLUT4 signalling attenuates critical illness-associated muscle wasting

BACKGROUND

Critical illness myopathy (CIM) is a debilitating condition characterized by the preferential loss of the motor protein myosin. CIM is a by-product of critical care, attributed to impaired recovery, long-term complications, and mortality. CIM pathophysiology is complex, heterogeneous and remains incompletely understood; however, loss of mechanical stimuli contributes to critical illness-associated muscle atrophy and weakness. Passive mechanical loading and electrical stimulation (ES) therapies augment muscle mass and function. While having beneficial outcomes, the mechanistic underpinning of these therapies is less known. Therefore, here we aimed to assess the mechanism by which chronic supramaximal ES ameliorates CIM in a unique experimental rat model of critical care.

METHODS

Rats were subjected to 8 days of critical care conditions entailing deep sedation, controlled mechanical ventilation, and immobilization with and without direct soleus ES. Muscle size and function were assessed at the single cell level. RNAseq and western blotting were employed to understand the mechanisms driving ES muscle outcomes in CIM.

RESULTS

Following 8 days of controlled mechanical ventilation and immobilization, soleus muscle mass, myosin : actin ratio, and single muscle fibre maximum force normalized to cross-sectional area (CSA; specific force) were reduced by 40-50% (P < 0.0001). ES significantly reduced the loss of soleus muscle fibre CSA and myosin : actin ratio by approximately 30% (P < 0.05) yet failed to effect specific force. RNAseq pathway analysis revealed downregulation of insulin signalling in the soleus muscle following critical care, and GLUT4 trafficking was reduced by 55% leading to an 85% reduction of muscle glycogen content (P < 0.01). ES promoted phosphofructokinase and insulin signalling pathways to control levels (P < 0.05), consistent with the maintenance of GLUT4 translocation and glycogen levels. AMPK, but not AKT, signalling pathway was stimulated following ES, where the downstream target TBC1D4 increased 3 logFC (P = 0.029) and AMPK-specific P-TBC1D4 levels were increased approximately two-fold (P = 0.06). Reduction of muscle protein degradation rather than increased synthesis promoted soleus CSA, as ES reduced E3 ubiquitin proteins, Atrogin-1 (P = 0.006) and MuRF1 (P = 0.08) by approximately 50%, downstream of AMPK-FoxO3.

CONCLUSIONS

ES maintained GLUT4 translocation through increased AMPK-TBC1D4 signalling leading to improved muscle glucose homeostasis. Soleus CSA and myosin content was promoted through reduced protein degradation via AMPK-FoxO3 E3 ligases, Atrogin-1 and MuRF1. These results demonstrate chronic supramaximal ES reduces critical care associated muscle wasting, preserved glucose signalling, and reduced muscle protein degradation in CIM.

Acute and severe trabecular bone loss in a rat model of critical illness myopathy

Prolonged mechanical ventilation for critically ill patients with respiratory distress can result in severe muscle wasting with preferential loss of myosin. Systemic inflammation triggered by lung mechanical injury likely contributes to this myopathy, although the exact mechanisms are unknown. In this study, we hypothesized that muscle wasting following mechanical ventilation is accompanied by bone loss. The objective was to determine the rate, nature, and extent of bone loss in the femora of rats ventilated up to 10 days and to relate the bone changes to muscle deterioration. We have developed a rat model of ventilator-induced muscle wasting and established its feasibility and clinical validity. This model involves pharmacologic paralysis, parenteral nutrition, and continuous mechanical ventilation. We assessed the hindlimb muscle and bone of rats ventilated for 0, 2, 5, 8, and 10 days. Routine histology, microCT, and biomechanical evaluations were performed. Hindlimb muscles developed changes consistent with myopathy, whereas the femurs demonstrated a progressive decline in trabecular bone volume, mineral density, and microarchitecture beginning Day 8 of mechanical ventilation. Biomechanical testing showed a reduction in flexural strength and stiffness on Day 10. The bone changes correlated with the loss of muscle mass and myosin. These results demonstrate that mechanical ventilation leads to progressive trabecular bone loss parallel to muscle deterioration. The results of our study suggest that mechanically ventilated patients may be at risk of compromised bone integrity and muscle weakness, predisposing to post-ventilator falls and fractures, thereby warranting interventions to prevent progressive bone and muscle decline.

Passive motion of the lower extremities in sedated and ventilated patients in the ICU - a systematic review of early effects and replicability of Interventions

Early mobilization, which includes active / passive motion in bed along with mobilization out of bed, is recommended to prevent the development of intensive care unit acquired-weakness (ICU-AW) for patients with critical illness on the intensive care unit. To date, the impact of passive motion of the lower extremities in sedated and ventilated patients remains unclear. The aim of the study is to systematically review and summarize the currently available randomized controlled trials in English or German language on the impact of passive motion of the lower extremities in sedated and ventilated patients ≥ 18 years in the intensive care unit on musculature, inflammation and immune system and the development of intensive care unit-acquired weakness and to evaluate the replicability of interventions and the methodological quality of included studies. A systematic literature search was performed up to 20th February 2022 in the databases Medline, Embase, Cochrane Library, CINAHL and PEDro. The description of the intervention (TIDieR checklist) and the methodological quality (Downs and Black checklist) were assessed. Five studies were included in the qualitative syntheses. On average, the studies were rated with 6.8 out of 12 points according to the TIDieR checklist. For the methodological quality an average of 19.8 out of 27 points on the Downs and Black checklist was reported. The results of included studies indicated that muscle loss may be reduced by passive manual movement, passive cycling and passive motion on a continuous passive motion-unit. In addition, positive effects were reported on the reduction of nitrosative stress and the immune response. The impact on the development of ICU-AW remains unclear. In conclusion, passive movement show a slight tendency for beneficial changes on cellular level in sedated and ventilated patients in the ICU within the first days of admission, which may indicate a reduction of muscle wasting and could prevent the development of ICU-AW. Future randomized controlled trials should use larger samples, use complete intervention description, use a comparable set of outcome measures, use rigorous methodology and examine the effect of passive motion on the development of ICU-AW.

Metabolomic Profiling of Respiratory Muscles and Lung in Response to Long-Term Controlled Mechanical Ventilation

Critical illness myopathy (CIM) and ventilator-induced diaphragm dysfunction (VIDD) are characterized by severe muscle wasting, muscle paresis, and extubation failure with subsequent increased medical costs and mortality/morbidity rates in intensive care unit (ICU) patients. These negative effects in response to modern critical care have received increasing attention, especially during the current COVID-19 pandemic. Based on experimental and clinical studies from our group, it has been hypothesized that the ventilator-induced lung injury (VILI) and the release of factors systemically play a significant role in the pathogenesis of CIM and VIDD. Our previous experimental/clinical studies have focused on gene/protein expression and the effects on muscle structure and regulation of muscle contraction at the cell and motor protein levels. In the present study, we have extended our interest to alterations at the metabolomic level. An untargeted metabolomics approach was undertaken to study two respiratory muscles (diaphragm and intercostal muscle) and lung tissue in rats exposed to five days controlled mechanical ventilation (CMV). Metabolomic profiles in diaphragm, intercostal muscles and lung tissue were dramatically altered in response to CMV, most metabolites of which belongs to lipids and amino acids. Some metabolites may possess important biofunctions and play essential roles in the metabolic alterations, such as pyruvate, citrate, S-adenosylhomocysteine, alpha-ketoglutarate, glycerol, and cysteine. Metabolic pathway enrichment analysis identified pathway signatures of each tissue, such as decreased metabolites of dipeptides in diaphragm, increased metabolites of branch-chain amino acid metabolism and purine metabolism in intercostals, and increased metabolites of fatty acid metabolism in lung tissue. These metabolite alterations may be associated with an accelerated myofibrillar protein degradation in the two respiratory muscles, an active inflammatory response in all tissues, an attenuated energy production in two respiratory muscles, and enhanced energy production in lung. These results will lay the basis for future clinical studies in ICU patients and hopefully the discovery of biomarkers in early diagnosis and monitoring, as well as the identification of future therapeutic targets.

Understanding Brain-Skeletal Muscle Crosstalk Impacting Metabolism and Movement

Metabolism and movement, among the critical determinants in the survival and success of an organism, are tightly regulated by the brain and skeletal muscle. At the cellular level, mitochondria -that powers life, and myosin - the molecular motor of the cell, have both evolved to serve this purpose. Although independently, the skeletal muscle and brain have been intensively investigated for over a century, their coordinated involvement in metabolism and movement remains poorly understood. Therefore, a fundamental understanding of the coordinated involvement of the brain and skeletal muscle in metabolism and movement holds great promise in providing a window to a wide range of life processes and in the development of tools and approaches in disease detection and therapy. Recent developments in new tools, technologies and approaches, and advances in computing power and machine learning, provides for the first time the opportunity to establish a new field of study, the 'Science and Engineering of Metabolism and Movement'. This new field of study could provide substantial new insights and breakthrough into how metabolism and movement is governed at the systems level in an organism. The design and approach to accomplish this objective is briefly discussed in this article.

Upper Arm Muscular Echogenicity Predicts Intensive Care Unit-acquired Weakness in Critically Ill Patients

Objectives:

Methods:

Results:

Conclusions:

Efficacy of passive repetitive stretching of skeletal muscle on myofiber hypertrophy and genetic suppression on MAFbx, MuRF1, and myostatin

Skeletal muscles undergo adaptations in response to mechanical stimuli such as stretching. However, there is limited evidence regarding the hypertrophic effects of passive repetitive stretching in vivo. We examined the effect of passive repetitive stretching on skeletal muscle myofiber morphology, satellite cell content, and messenger RNA expression of myogenic regulatory factors and signaling molecules involved in muscle protein synthesis and degradation. The gastrocnemius muscles of mice were stretched 15 times/min by manual ankle dorsiflexion for 15 min, 5 days a week for 2 weeks. We found that passive repetitive stretching significantly increased myofiber cross-sectional area. In stretched gastrocnemius muscles, the messenger RNA expression of p70S6K and myogenin was upregulated, whereas MuRF1, MAFbx, myostatin, and 4E-BP1 were downregulated. The phosphorylation level of p70S6K was significantly increased in stretched muscles. The number of Pax7+ cells was unaffected. Passive repetitive stretching induces muscle hypertrophy by regulating signaling pathways involved in muscle protein turnover. These findings are applicable to clinical muscle strengthening and for the maintenance of skeletal muscle mass and function in patients who are unconscious or paralyzed.

Quality of life of COVID-19 critically ill survivors after ICU discharge: 90 days follow-up

PURPOSE

The onset of the coronavirus disease 19 (COVID-19) pandemic in Italy induced a dramatic increase in the need for intensive care unit (ICU) beds for a large proportion of patients affected by COVID-19-related acute respiratory distress syndrome (ARDS). The aim of the present study was to describe the health-related quality of life (HRQoL) at 90 days after ICU discharge in a cohort of COVID-19 patients undergoing invasive mechanical ventilation and to compare it with an age and sex-matched sample from the general Italian and Finnish populations. Moreover, the possible associations between clinical, demographic, social factors, and HRQoL were investigated.

METHODS

COVID-19 ARDS survivors from 16 participating ICUs were followed up until 90 days after ICU discharge and the HRQoL was evaluated with the 15D instrument. A parallel cohort of age and sex-matched Italian population from the same geographic areas was interviewed and a third group of matched Finnish population was extracted from the Finnish 2011 National Health survey. A linear regression analysis was performed to evaluate potential associations between the evaluated factors and HRQoL.

RESULTS

205 patients answered to the questionnaire. HRQoL of the COVID-19 ARDS patients was significantly lower than the matched populations in both physical and mental dimensions. Age, sex, number of comorbidities, ARDS class, duration of invasive mechanical ventilation, and occupational status were found to be significant determinants of the 90 days HRQoL. Clinical severity at ICU admission was poorly correlated to HRQoL.

CONCLUSION

COVID-19-related ARDS survivors at 90 days after ICU discharge present a significant reduction both on physical and psychological dimensions of HRQoL measured with the 15D instrument.

TRIAL REGISTRATION

NCT04411459.

A narrative review of skeletal muscle atrophy in critically ill children: pathogenesis and chronic sequelae

Muscle wasting is now recognized as a growing, debilitating problem in critically ill adults, resulting in long-term deficits in function and an impaired quality of life. Ultrasonography has demonstrated decreases in skeletal muscle size during pediatric critical illness, although variations exist. However, muscle protein turnover patterns during pediatric critical illness are unclear. Understanding muscle protein turnover during critical illness is important in guiding interventions to reduce muscle wasting. The aim of this review was to explore the possible protein synthesis and breakdown patterns in pediatric critical illness. Muscle protein turnover studies in critically ill children are lacking, with the exception of those with burn injuries. Children with burn injuries demonstrate an elevation in both muscle protein breakdown (MPB) and synthesis during critical illness. Extrapolations from animal models and whole-body protein turnover studies in children suggest that children may be more dependent on anabolic factors (e.g., nutrition and growth factors), and may experience greater muscle degradation in response to insults than adults. Yet, children, particularly the younger ones, are more responsive to anabolic agents, suggesting modifiable muscle wasting during critical illness. There is a lack of evidence for muscle wasting in critically ill children and its correlation with outcomes, possibly due to current available methods to study muscle protein turnover in children-most of which are invasive or tedious. In summary, children may experience muscle wasting during critical illness, which may be more reversible by the appropriate anabolic agents than adults. Age appears an important determinant of skeletal muscle turnover. Less invasive methods to study muscle protein turnover and associations with long-term outcome would strengthen the evidence for muscle wasting in critically ill children.

A national survey in United Arab Emirates on practice of passive range of motion by physiotherapists in intensive care unit

Background

Patients admitted to intensive care units (ICU) are at an increased risk of developing immobility related complications. Physiotherapists are challenged to employ preventive and rehabilitative strategies to combat these effects. Passive limb range of motion (PROM) exercises- a part of early mobilization-aid in maintaining joint range of motion and functional muscle strength and forms a part of treatment for patients in ICU. However, there is a lack of evidence on practice of PROM exercises on patients admitted to ICU in the United Arab Emirates (UAE). This study aimed at exploring practices regarding the same in UAE.

Methods

This survey, conducted from January 2021 to February 2021 in College of Physiotherapy, Sharjah University studied practice of physiotherapists in the intensive care units. Physiotherapists currently working in ICU completed an online questionnaire composed of forty-two questions about physiotherapy service provision, assessment and intervention in the intensive care units.

Results

33 physiotherapists completed the survey. 66.6% of respondents routinely assessed PROM for all the patients in ICU referred for physiotherapy. 84.8% of them assessed all the joints. More than half of the respondents (57.8%) reported that they administered PROM regularly to all the patients. According to 63.6% respondents, maintaining joint range of motion was the main reason for performing PROM. Responses pertaining to sets and repetitions of PROM were variable ranging from 1–6 sets and from 3 to 30 repetitions. Personal experience, resources/financial consideration and research findings were found to have influence on the practice.

Conclusions

PROM was found to be one of the frequently used mobilization techniques administered by physiotherapists in the intensive care units and was mostly performed after assessment. Maintaining joint range of motion was the main aim for performing PROM. Variability was found in the sets and repetitions of PROM administered. Various factors influenced the practice of PROM.

The impact of hindlimb disuse on sepsis-induced myopathy in mice

Sepsis induces a myopathy characterized by loss of muscle mass and weakness. Septic patients undergo prolonged periods of limb muscle disuse due to bed rest. The contribution of limb muscle disuse to the myopathy phenotype remains poorly described. To characterize sepsis-induced myopathy with hindlimb disuse, we combined the classic sepsis model via cecal ligation and puncture (CLP) with the disuse model of hindlimb suspension (HLS) in mice. Male C57bl/6j mice underwent CLP or SHAM surgeries. Four days after surgeries, mice underwent HLS or normal ambulation (NA) for 7 days. Soleus (SOL) and extensor digitorum longus (EDL) were dissected for in vitro muscle mechanics, morphological, and histological assessments. In SOL muscles, both CLP+NA and SHAM+HLS conditions elicited ~20% reduction in specific force (p < 0.05). When combined, CLP+HLS elicited ~35% decrease in specific force (p < 0.05). Loss of maximal specific force (~8%) was evident in EDL muscles only in CLP+HLS mice (p < 0.05). CLP+HLS reduced muscle fiber cross-sectional area (CSA) and mass in SOL (p < 0.05). In EDL muscles, CLP+HLS decreased absolute mass to a smaller extent (p < 0.05) with no changes in CSA. Immunohistochemistry revealed substantial myeloid cell infiltration (CD68+) in SOL, but not in EDL muscles, of CLP+HLS mice (p < 0.05). Combining CLP with HLS is a feasible model to study sepsis-induced myopathy in mice. Hindlimb disuse combined with sepsis induced muscle dysfunction and immune cell infiltration in a muscle dependent manner. These findings highlight the importance of rehabilitative interventions in septic hosts to prevent muscle disuse and help attenuate the myopathy.

Muscle atrophy in critically ill patients : a review of its cause, evaluation, and prevention

Critically ill patients exhibit prominent muscle atrophy, which occurs rapidly after ICU admission and leads to poor clinical outcomes. The extent of atrophy differs among muscles as follows: upper limb: 0.7%-2.4% per day, lower limb: 1.2%-3.0% per day, and diaphragm 1.1%-10.9% per day. This atrophy is caused by numerous risk factors such as inflammation, immobilization, nutrition, hyperglycemia, medication, and mechanical ventilation. Muscle atrophy should be monitored noninvasively by ultrasound at the bedside. Ultrasound can assess muscle mass in most patients, although physical assessment is limited to almost half of all critically ill patients due to impaired consciousness. Important strategies to prevent muscle atrophy are physical therapy and electrical muscular stimulation. Electrical muscular stimulation is especially effective for patients with limited physical therapy. Regarding diaphragm atrophy, mechanical ventilation should be adjusted to maintain spontaneous breathing and titrate inspiratory pressure. However, the sufficient timing and amount of nutritional intervention remain unclear. Further investigation is necessary to prevent muscle atrophy and improve long-term outcomes. J. Med. Invest. 67 : 1-10, February, 2020.

Pathophysiology and Treatment Strategies of Acute Myopathy and Muscle Wasting after Sepsis

Sepsis survivors experience a persistent myopathy characterized by skeletal muscle weakness, atrophy, and an inability to repair/regenerate damaged or dysfunctional myofibers. The origins and mechanisms of this persistent sepsis-induced myopathy are likely complex and multifactorial. Nevertheless, the pathobiology is thought to be triggered by the interaction between circulating pathogens and impaired muscle metabolic status. In addition, while in the hospital, septic patients often experience prolonged periods of physical inactivity due to bed rest, which may exacerbate the myopathy. Physical rehabilitation emerges as a potential tool to prevent the decline in physical function in septic patients. Currently, there is no consensus regarding effective rehabilitation strategies for sepsis-induced myopathy. The optimal timing to initiate the rehabilitation intervention currently lacks consensus as well. In this review, we summarize the evidence on the fundamental pathobiological mechanisms of sepsis-induced myopathy and discuss the recent evidence on in-hospital and post-discharge rehabilitation as well as other potential interventions that may prevent physical disability and death of sepsis survivors.

Impact of prolonged sepsis on neural and muscular components of muscle contractions in a mouse model

BACKGROUND

Prolonged critically ill patients frequently develop debilitating muscle weakness that can affect both peripheral nerves and skeletal muscle. In-depth knowledge on the temporal contribution of neural and muscular components to muscle weakness is currently incomplete.

METHODS

We used a fluid-resuscitated, antibiotic-treated, parenterally fed murine model of prolonged (5 days) sepsis-induced muscle weakness (caecal ligation and puncture; n = 148). Electromyography (EMG) measurements were performed in two nerve-muscle complexes, combined with histological analysis of neuromuscular junction denervation, axonal degeneration, and demyelination. In situ muscle force measurements distinguished neural from muscular contribution to reduced muscle force generation. In myofibres, imaging and biomechanics were combined to evaluate myofibrillar contractile calcium sensitivity, sarcomere organization, and fibre structural properties. Myosin and actin protein content and titin gene expression were measured on the whole muscle.

RESULTS

Five days of sepsis resulted in increased EMG latency (P = 0.006) and decreased EMG amplitude (P < 0.0001) in the dorsal caudal tail nerve-tail complex, whereas only EMG amplitude was affected in the sciatic nerve-gastrocnemius muscle complex (P < 0.0001). Myelin sheath abnormalities (P = 0.2), axonal degeneration (number of axons; P = 0.4), and neuromuscular junction denervation (P = 0.09) were largely absent in response to sepsis, but signs of axonal swelling [higher axon area (P < 0.0001) and g-ratio (P = 0.03)] were observed. A reduction in maximal muscle force was present after indirect nerve stimulation (P = 0.007) and after direct muscle stimulation (P = 0.03). The degree of force reduction was similar with both stimulations (P = 0.2), identifying skeletal muscle, but not peripheral nerves, as the main contributor to muscle weakness. Myofibrillar calcium sensitivity of the contractile apparatus was unaffected by sepsis (P ≥ 0.6), whereas septic myofibres displayed disorganized sarcomeres (P < 0.0001) and altered myofibre axial elasticity (P < 0.0001). Septic myofibres suffered from increased rupturing in a passive stretching protocol (25% more than control myofibres; P = 0.04), which was associated with impaired myofibre active force generation (P = 0.04), linking altered myofibre integrity to function. Sepsis also caused a reduction in muscle titin gene expression (P = 0.04) and myosin and actin protein content (P = 0.05), but not the myosin-to-actin ratio (P = 0.7).

CONCLUSIONS

Prolonged sepsis-induced muscle weakness may predominantly be related to a disruption in myofibrillar cytoarchitectural structure, rather than to neural abnormalities.

Pathophysiology and management of critical illness polyneuropathy and myopathy

Critical illness-associated weakness (CIAW) is an umbrella term used to describe a group of neuromuscular disorders caused by severe illness. It can be subdivided into three major classifications based on the component of the neuromuscular system (i.e. peripheral nerves or skeletal muscle or both) that are affected. This includes critical illness polyneuropathy (CIP), critical illness myopathy (CIM), and an overlap syndrome, critical illness polyneuromyopathy (CIPNM). It is a common complication observed in people with critical illness requiring intensive care unit (ICU) admission. Given CIAW is found in individuals experiencing grave illness, it can be challenging to study from a practical standpoint. However, over the past 2 decades, many insights into the pathophysiology of this condition have been made. Results from studies in both humans and animal models have found that a profound systemic inflammatory response and factors related to bioenergetic failure as well as microvascular, metabolic, and electrophysiological alterations underlie the development of CIAW. Current management strategies focus on early mobilization, achieving euglycemia, and nutritional optimization. Other interventions lack sufficient evidence, mainly due to a dearth of large trials. The goal of this Physiology in Medicine article is to highlight important aspects of the pathophysiology of these enigmatic conditions. It is hoped that improved understanding of the mechanisms underlying these disorders will lead to further study and new investigations for novel pharmacologic, nutritional, and exercise-based interventions to optimize patient outcomes.

Early detection of evolving critical illness myopathy with muscle velocity recovery cycles

OBJECTIVE

To investigate the sensitivity of muscle velocity recovery cycles (MVRCs) for detecting altered membrane properties in critically ill patients, and to compare this to conventional nerve conduction studies (NCS) and quantitative electromyography (qEMG).

METHODS

Twenty-four patients with intensive care unit acquired weakness (ICUAW) and 34 healthy subjects were prospectively recruited. In addition to NCS (median, ulnar, peroneal, tibial and sural nerves) and qEMG (biceps brachii, vastus medialis and anterior tibial muscles), MVRCs with frequency ramp were recorded from anterior tibial muscle.

RESULTS

MVRC and frequency ramp parameters showed abnormal muscle fiber membrane properties with up to 100% sensitivity and specificity. qEMG showed myopathy in 15 patients (63%) while polyneuropathy was seen in 3 (13%). Decreased compound muscle action potential (CMAP) amplitude (up to 58%) and absent F-waves (up to 75%) were frequent, but long duration CMAPs were only seen in one patient with severe myopathy.

CONCLUSIONS

Altered muscle fiber membrane properties can be detected in patients with ICUAW not yet fulfilling diagnostic criteria for critical illness myopathy (CIM). MVRCs may therefore serve as a tool for early detection of evolving CIM.

SIGNIFICANCE

CIM is often under-recognized by intensivists, and large-scale longitudinal studies are needed to determine its incidence and pathogenesis.

Impact of congenital diaphragmatic hernia on diaphragm muscle function in neonatal rats

Congenital diaphragmatic hernia (CDH) is characterized by incomplete partitioning of the thoracic and abdominal cavities by the diaphragm muscle (DIAm). The resulting in utero invasion of the abdominal viscera into the thoracic cavity leads to impaired fetal breathing movements, severe pulmonary hypoplasia, and pulmonary hypertension. We hypothesized that in a well-established rodent model of Nitrofen-induced CDH, DIAm isometric force generation, and DIAm fiber cross-sectional areas would be reduced compared with nonlesioned littermate and Control pups. In CDH and nonlesioned pups at embryonic day 21 or birth, DIAm isometric force responses to supramaximal field stimulation (200 mA, 0.5 ms duration pulses in 1-s duration trains at rates ranging from 10 to 100 Hz) was measured ex vivo. Further, DIAm fatigue was determined in response to 120 s of repetitive stimulation at 40 Hz in 330-ms duration trains repeated each second. The DIAm was then stretched to L_o, frozen, and fiber cross-sectional areas were measured in 10 μm transverse sections. In CDH pups, there was a marked reduction in DIAm-specific force and force following 120 s of fatiguing contraction. The cross-sectional area of DIAm fibers was also reduced in CDH pups compared with nonlesioned littermates and Control pups. These results show that CDH is associated with a dramatic weakening of the DIAm, which may contribute to poor survival despite various surgical efforts to repair the hernia and improve lung development.NEW & NOTEWORTHY There are notable respiratory deficits related to congenital diaphragmatic hernia (CDH), yet the contribution, if any, of frank diaphragm muscle weakness to CDH is unexplored. Here, we use the well-established Nitrofen teratogen model to induce CDH in rat pups, followed by diaphragm muscle contractility and morphological assessments. Our results show diaphragm muscle weakness in conjunction with reduced muscle fiber density and size, contributing to CDH morbidity.

An observational feasibility study - does early limb ergometry affect oxygen delivery and uptake in intubated critically ill patients - a comparison of two assessment methods

Background

Early rehabilitation can reduce ventilation duration and improve functional outcomes in critically ill patients. Upper limb strength is associated with ventilator weaning. Passive muscle loading may preserve muscle fibre function, help recover peripheral muscle strength and improve longer term, post-hospital discharge function capacity. The physiological effects of initiating rehabilitation soon after physiological stabilisation of these patients can be concerning for clinicians. This study investigated the feasibility of measuring metabolic demand and the safety and feasibility of early upper limb passive ergometry. An additional comparison of results, achieved from simultaneous application of the methods, is reported.

Methods

This was an observational feasibility study undertaken in an acute teaching hospital’s General Intensive Care Unit in the United Kingdom. Twelve haemodynamically stable, mechanically ventilated patients underwent 30 minutes of arm ergometry. Cardiovascular and respiratory parameters were monitored. A Friedman test identified changes in physiological parameters. A metabolic cart was attached to the ventilator to measure oxygen uptake. Oxygen uptake was concurrently calculated by the reverse Fick method, utilising cardiac output from the LiDCO™ and paired mixed venous and arterial samples. A comparison of the two methods was made. Data collection began 10 minutes before ergometry and continued to recovery. Paired mixed venous and arterial samples were taken every 10 minutes.

Results

Twelve patients were studied; 9 male, median age 55 years, range (27–82), median APACHE score 18.5, range (7–31), median fraction inspired oxygen 42.5%, range (28–60). Eight patients were receiving noradrenaline. Mean dose was 0.07 mcg/kg/min, range (0.01–0.15). Early ergometry was well tolerated. There were no clinically significant changes in respiratory, haemodynamic or metabolic variables pre ergometry to end recovery. There was no significant difference between the two methods of calculating VO₂ (p = 0.70).

Conclusions

We report the feasibility of using the reverse Fick method and indirect calorimetry to measure metabolic demand during early physical rehabilitation of critically ill patients. More research is needed to ascertain the most reliable method. Minimal change in metabolic demand supports the safety and feasibility of upper limb ergometry. These results will inform future study designs for further research into exercise response in critically ill patients.

Trial Registration

Clinicaltrials.gov No. NCT04383171. Registered on 06 May 2020 - Retrospectively registered. http://www.clinicaltrials.gov.

Nox2 signaling and muscle fiber remodeling are attenuated by losartan administration during skeletal muscle unloading

Reduced mechanical loading results in atrophy of skeletal muscle fibers. Increased reactive oxygen species (ROS) are causal in sarcolemmal dislocation of nNOS and FoxO3a activation. The Nox2 isoform of NADPH oxidase and mitochondria release ROS during disuse in skeletal muscle. Activation of the angiotensin II type 1 receptor (AT1R) can elicit Nox2 complex formation. The AT1R blocker losartan was used to test the hypothesis that AT1R activation drives Nox2 assembly, nNOS dislocation, FoxO3a activation, and thus alterations in morphology in the unloaded rat soleus. Male Fischer 344 rats were divided into four groups: ambulatory control (CON), ambulatory + losartan (40 mg kg^-1  day^-1 ) (CONL), 7 days of tail-traction hindlimb unloading (HU), and HU + losartan (HUL). Losartan attenuated unloading-induced loss of muscle fiber cross-sectional area (CSA) and fiber-type shift. Losartan mitigated unloading-induced elevation of ROS levels and upregulation of Nox2. Furthermore, AT1R blockade abrogated nNOS dislocation away from the sarcolemma and elevation of nuclear FoxO3a. We conclude that AT1R blockade attenuates disuse remodeling by inhibiting Nox2, thereby lessening nNOS dislocation and activation of FoxO3a.

Oxygen transport kinetics underpin rapid and robust diaphragm recovery following chronic spinal cord injury

Key points

Spinal treatment can restore diaphragm function in all animals 1 month following C2 hemisection induced paralysis. Greater recovery occurs the longer after injury the treatment is applied.

Through advanced assessment of muscle mechanics, innovative histology and oxygen tension modelling, we have comprehensively characterized in vivo diaphragm function and phenotype.

Muscle work loops reveal a significant deficit in diaphragm functional properties following chronic injury and paralysis, which are normalized following restored muscle activity caused by plasticity‐induced spinal reconnection.

Injury causes global and local alterations in diaphragm muscle vascular supply, limiting oxygen diffusion and disturbing function. Restoration of muscle activity reverses these alterations, restoring oxygen supply to the tissue and enabling recovery of muscle functional properties.

There remain metabolic deficits following restoration of diaphragm activity, probably explaining only partial functional recovery. We hypothesize that these deficits need to be resolved to restore complete respiratory motor function.

Abstract

Months after spinal cord injury (SCI), respiratory deficits remain the primary cause of morbidity and mortality for patients. It is possible to induce partial respiratory motor functional recovery in chronic SCI following 2 weeks of spinal neuroplasticity. However, the peripheral mechanisms underpinning this recovery are largely unknown, limiting development of new clinical treatments with potential for complete functional restoration. Utilizing a rat hemisection model, diaphragm function and paralysis was assessed and recovered at chronic time points following trauma through chondroitinase ABC induced neuroplasticity. We simulated the diaphragm's in vivo cyclical length change and activity patterns using the work loop technique at the same time as assessing global and local measures of the muscles histology to quantify changes in muscle phenotype, microvascular composition, and oxidative capacity following injury and recovery. These data were fed into a physiologically informed model of tissue oxygen transport. We demonstrate that hemidiaphragm paralysis causes muscle fibre hypertrophy, maintaining global oxygen supply, although it alters isolated muscle kinetics, limiting respiratory function. Treatment induced recovery of respiratory activity normalized these effects, increasing oxygen supply, restoring optimal diaphragm functional properties. However, metabolic demands of the diaphragm were significantly reduced following both injury and recovery, potentially limiting restoration of normal muscle performance. The mechanism of rapid respiratory muscle recovery following spinal trauma occurs through oxygen transport, metabolic demand and functional dynamics of striated muscle. Overall, these data support a systems‐wide approach to the treatment of SCI, and identify new targets to mediate complete respiratory recovery.

Spinal treatment can restore diaphragm function in all animals 1 month following C2 hemisection induced paralysis. Greater recovery occurs the longer after injury the treatment is applied.

Through advanced assessment of muscle mechanics, innovative histology and oxygen tension modelling, we have comprehensively characterized in vivo diaphragm function and phenotype.

Muscle work loops reveal a significant deficit in diaphragm functional properties following chronic injury and paralysis, which are normalized following restored muscle activity caused by plasticity‐induced spinal reconnection.

Injury causes global and local alterations in diaphragm muscle vascular supply, limiting oxygen diffusion and disturbing function. Restoration of muscle activity reverses these alterations, restoring oxygen supply to the tissue and enabling recovery of muscle functional properties.

There remain metabolic deficits following restoration of diaphragm activity, probably explaining only partial functional recovery. We hypothesize that these deficits need to be resolved to restore complete respiratory motor function.

Neurogenic vs. Myogenic Origin of Acquired Muscle Paralysis in Intensive Care Unit (ICU) Patients: Evaluation of Different Diagnostic Methods

Introduction. The acquired muscle paralysis associated with modern critical care can be of neurogenic or myogenic origin, yet the distinction between these origins is hampered by the precision of current diagnostic methods. This has resulted in the pooling of all acquired muscle paralyses, independent of their origin, into the term Intensive Care Unit Acquired Muscle Weakness (ICUAW). This is unfortunate since the acquired neuropathy (critical illness polyneuropathy, CIP) has a slower recovery than the myopathy (critical illness myopathy, CIM); therapies need to target underlying mechanisms and every patient deserves as accurate a diagnosis as possible. This study aims at evaluating different diagnostic methods in the diagnosis of CIP and CIM in critically ill, immobilized and mechanically ventilated intensive care unit (ICU) patients. Methods. ICU patients with acquired quadriplegia in response to critical care were included in the study. A total of 142 patients were examined with routine electrophysiological methods, together with biochemical analyses of myosin:actin (M:A) ratios of muscle biopsies. In addition, comparisons of evoked electromyographic (EMG) responses in direct vs. indirect muscle stimulation and histopathological analyses of muscle biopsies were performed in a subset of the patients. Results. ICU patients with quadriplegia were stratified into five groups based on the hallmark of CIM, i.e., preferential myosin loss (myosin:actin ratio, M:A) and classified as severe (M:A < 0.5; n = 12), moderate (0.5 ≤ M:A < 1; n = 40), mildly moderate (1 ≤ M:A < 1.5; n = 49), mild (1.5 ≤ M:A < 1.7; n = 24) and normal (1.7 ≤ M:A; n = 19). Identical M:A ratios were obtained in the small (4–15 mg) muscle samples, using a disposable semiautomatic microbiopsy needle instrument, and the larger (>80 mg) samples, obtained with a conchotome instrument. Compound muscle action potential (CMAP) duration was increased and amplitude decreased in patients with preferential myosin loss, but deviations from this relationship were observed in numerous patients, resulting in only weak correlations between CMAP properties and M:A. Advanced electrophysiological methods measuring refractoriness and comparing CMAP amplitude after indirect nerve vs. direct muscle stimulation are time consuming and did not increase precision compared with conventional electrophysiological measurements in the diagnosis of CIM. Low CMAP amplitude upon indirect vs. direct stimulation strongly suggest a neurogenic lesion, i.e., CIP, but this was rarely observed among the patients in this study. Histopathological diagnosis of CIM/CIP based on enzyme histochemical mATPase stainings were hampered by poor quantitative precision of myosin loss and the impact of pathological findings unrelated to acute quadriplegia. Conclusion. Conventional electrophysiological methods are valuable in identifying the peripheral origin of quadriplegia in ICU patients, but do not reliably separate between neurogenic vs. myogenic origins of paralysis. The hallmark of CIM, preferential myosin loss, can be reliably evaluated in the small samples obtained with the microbiopsy instrument. The major advantage of this method is that it is less invasive than conventional muscle biopsies, reducing the risk of bleeding in ICU patients, who are frequently receiving anticoagulant treatment, and it can be repeated multiple times during follow up for monitoring purposes.

Predictors of activities of daily living at discharge in elderly patients with heart failure with preserved ejection fraction

The purpose of this study was to clarify the predictive factors of activities of daily living (ADL) at discharge in elderly patients with heart failure with preserved ejection fraction (HFpEF). Participants were selected from among 598 consecutive hospitalized HF patients based on certain criteria. We investigated patient characteristics, and ADL with the motor and cognitive items of the Functional Independence Measure (FIM). We analyzed the data with the unpaired t test, Mann-Whitney U test, χ² test, logistic regression analysis, and receiver operating characteristic (ROC) curves. We included 154 patients for further analyses who were divided into the low ADL group (n = 75) and high ADL group (n = 79). There were significant differences between the two groups in age, long-term care insurance (LTCI) level, New York Heart Association class, creatinine level, albumin level, β-blocker, sitting, standing and walking exercise start days, length of hospital stay, and motor- and cognitive-FIM scores at admission and discharge (p < 0.05). The cutoff values of the ROC curves predicting ADL at discharge were LTCL: support level 2 (area under the curve [AUC]: 0.672, p < 0.001, sensitivity: 0.573, false-positive rate: 0.278); walking exercise start day: 4.5 days (AUC 0.694, p < 0.001, sensitivity: 0.609, false-positive rate: 0.299); motor FIM score: 34.5 points (AUC 0.710, p < 0.001, sensitivity: 0.633, false-positive rate: 0.280); and cognitive FIM score: 28.5 points (AUC 0.806, p < 0.001, sensitivity: 0.759, false-positive rate: 0.227). This study revealed several predictors of ADL at discharge and their associated cutoff values in elderly patients with HFpEF.

Intensive Care Unit-Acquired Weakness: Not just Another Muscle Atrophying Condition

Intensive care unit-acquired weakness (ICUAW) occurs in critically ill patients stemming from the critical illness itself, and results in sustained disability long after the ICU stay. Weakness can be attributed to muscle wasting, impaired contractility, neuropathy, and major pathways associated with muscle protein degradation such as the ubiquitin proteasome system and dysregulated autophagy. Furthermore, it is characterized by the preferential loss of myosin, a distinct feature of the condition. While many risk factors for ICUAW have been identified, effective interventions to offset these changes remain elusive. In addition, our understanding of the mechanisms underlying the long-term, sustained weakness observed in a subset of patients after discharge is minimal. Herein, we discuss the various proposed pathways involved in the pathophysiology of ICUAW, with a focus on the mechanisms underpinning skeletal muscle wasting and impaired contractility, and the animal models used to study them. Furthermore, we will explore the contributions of inflammation, steroid use, and paralysis to the development of ICUAW and how it pertains to those with the corona virus disease of 2019 (COVID-19). We then elaborate on interventions tested as a means to offset these decrements in muscle function that occur as a result of critical illness, and we propose new strategies to explore the molecular mechanisms of ICUAW, including serum-related biomarkers and 3D human skeletal muscle culture models.

The acute muscular response to passive movement and blood flow restriction

PURPOSE

To compare the acute effects of passive movement combined with blood flow restriction (PM + BFR) to passive movement (PM) or blood flow restriction alone (BFR).

METHODS

A total of 20 healthy participants completed: time control (TC), PM, BFR and PM + BFR (one per leg, over 2 days; randomized). For PM, a dynamometer moved the leg through 3 sets of 15 knee extensions/flexions (90° at 45°/second). For BFR, a cuff was inflated to 80% arterial occlusion pressure on the upper leg. Measurements consisted of anterior muscle thickness at 60% and 70% of the upper leg before and after (-0, -5 and -10 min) conditions, ratings of perceived effort and discomfort before conditions and after each set, and of the vastus lateralis during conditions. Data, presented as mean (SD), were compared using Bayesian RMANOVA, except for perceived effort and discomfort, which were compared using a Friedman's test (non-parametric).

RESULTS

60% (Δcm before-after-0: TC = 0.04 [0.09], PM = -0.01 [0.15], BFR = 0.00 [0.11], PM + BFR = 0.01 [0.22]) and 70% (Δcm before-after-0: TC = 0.01 [0.09], PM = -0.01 [0.15], BFR = 0.02 [0.11], PM + BFR = -0.03 [0.22]) muscle thickness did not change. Perceived effort was greater than TC following PM (p = .05) and PM + BFR (p = .001). Perceived discomfort was greater following BFR and PM + BFR compared to TC (all p ≤ .002) and PM (all p ≤ .010). Changes in deoxygenation (e.g. channel 1; ΔμM start set 1-end set 3: TC = 0.9 [1.2], PM = -1.2 [1.9], BFR = 10.3 [2.7], PM + BFR = 10.3 [3.0]) were generally greater with BFR and PM + BFR (BF_inclusion  = 1.210e + 13).

CONCLUSION

Acute muscular responses to PM + BFR are not augmented over the effect of BFR alone.

Gastrocnemius thickness by ultrasonography indicates the low skeletal muscle mass in Japanese elderly people

BACKGROUND

This study aimed to examine the relationship between gastrocnemius thickness by ultrasonography and the skeletal muscle mass in Japanese elderly people.

METHODS

The total of 195 healthy Japanese aged ≥65 years participated (average age, 72.4 ± 4.3y; male, n = 72). The skeletal muscle mass index (SMI) was measured using the bioelectrical impedance analysis (BIA) and the gastrocnemius thickness and collected echo intensity (CEI) were measured using ultrasonography. The low SMI was defined as <7.0 kg/m² in men and <5.7 kg/m² in women, and participants were classified into the low SMI and the normal group. Association of the gastrocnemius thickness with the low SMI was analyzed by the logistic regression analysis after adjusting age, gender, body mass index (BMI), physical performances and CEI. The cut-off value of gastrocnemius thickness to indicate the low SMI was calculated by a receiver operating characteristic curve analysis.

RESULTS

The low SMI rate was 16.9％ (n = 33). BMI was significantly lower (19.9 vs 22.5 kg/m²; p < 0.01), the gastrocnemius thickness lower (11.0 vs 13.3 mm; p < 0.01), and CEI higher (97.5 vs 87.0; p = 0.02) in the low SMI group than those in the normal group. The gastrocnemius thickness was independently associated with the low SMI (OR, 0.584; 95% CI, 0.416-0.818; p < 0.01). The cut-off value of gastrocnemius thickness was <11.6 mm (AUC, 0.83; sensitivity, 0.83; specificity, 0.73; p < 0.01).

CONCLUSION

Gastrocnemius thickness by ultrasonography was associated with low skeletal muscle mass, and the cut-off value to indicate the low skeletal muscle mass was revealed.

Efeitos do exercício passivo precoce em cicloergômetro na espessura muscular do quadríceps femoral de pacientes críticos: estudo-piloto randomizado controlado

RESUMO O objetivo deste estudo foi avaliar os efeitos do exercício passivo precoce em cicloergômetro na espessura muscular (EM) do quadríceps femoral (EMQ) de pacientes críticos admitidos em uma Unidade de Terapia Intensiva (UTI) de um hospital universitário terciário. O método utilizado foi um estudo-piloto randomizado controlado conduzido em uma amostra de 24 pacientes (51±18,11 anos, 16 do sexo masculino), com 24 a 48 horas de ventilação mecânica (VM), aleatoriamente divididos em dois grupos: grupo-controle (n=12), que recebeu a fisioterapia convencional; e grupo-intervenção (n=12), que recebeu o exercício passivo em cicloergômetro, uma vez ao dia, durante o período de sete dias do protocolo, em adição à fisioterapia convencional. A EMQ foi mensurada através da ultrassonografia. A primeira medida ultrassonográfica foi realizada entre as primeiras 48 horas de VM e a segunda ao término do protocolo. Não houve diferenças significativas na EMQ esquerda (27,29±5,86mm vs. 25,95±10,89mm; p=0,558) e direita (24,96±5,59mm vs 25,9±9,21mm; p=0,682) do grupo-controle e na EMQ esquerda (27,2±7,38mm vs 29,57±7,89mm; p=0,299) e direita (26,67±8,16mm vs 28,65±8,04mm; p=0,381) do grupo-intervenção. Na comparação entre os grupos, não houve alterações significativas em relação à EMQ esquerda (3,61±1,07mm; p=0,248) e a EMQ direita (2,75±0,85mm; p=0,738). Os resultados deste estudo-piloto demonstraram que a aplicação precoce do exercício passivo em cicloergômetro não promoveu mudanças significativas na espessura da camada muscular avaliada. No entanto, nossos achados sinalizam que a fisioterapia convencional foi capaz de preservar a EMQ de pacientes críticos admitidos em UTI.

Molecular regulation of skeletal muscle mass and the contribution of nitric oxide: A review

A variety of internal and external factors such as exercise, nutrition, inflammation, and cancer-associated cachexia affect the regulation of skeletal muscle mass. Because skeletal muscle functions as a crucial regulator of whole body metabolism, rather than just as a motor for locomotion, the enhancement and maintenance of muscle mass and function are required to maintain health and reduce the morbidity and mortality associated with diseases involving muscle wasting. Recent studies in this field have made tremendous progress; therefore, identification of the mechanisms that regulate skeletal muscle mass is necessary for the physical and nutritional management of both athletes and patients with muscle wasting disease. In this review, we present an overall picture of the interactions regulating skeletal muscle mass, particularly focusing on the insulin-like growth factor-I (IGF-I)/insulin-Akt-mammalian target of rapamycin (mTOR) pathway, skeletal muscle inactivity, and endurance and resistance exercise. We also discuss the contribution of nitric oxide (NO) to the regulation of skeletal muscle mass based on the current knowledge of the novel role of NO in these processes.

RNA-sequencing reveals altered skeletal muscle contraction, E3 ligases, autophagy, apoptosis, and chaperone expression in patients with critical illness myopathy

Background

Critical illness myopathy (CIM) is associated with severe skeletal muscle wasting and impaired function in intensive care unit (ICU) patients. The mechanisms underlying CIM remain incompletely understood. To elucidate the biological activities occurring at the transcriptional level in the skeletal muscle of ICU patients with CIM, the gene expression profiles, potential upstream regulators, and enrichment pathways were characterized using RNA sequencing (RNA-seq). We also compared the skeletal muscle gene signatures in ICU patients with CIM and genes perturbed by mechanical loading in one leg of the ICU patients, with an aim of reducing the loss of muscle function.

Methods

RNA-seq was used to assess gene expression changes in tibialis anterior skeletal muscle samples from seven critically ill, immobilized, and mechanically ventilated ICU patients with CIM and matched control subjects. We also examined skeletal muscle gene expression for both legs of six ICU patients with CIM, where one leg was mechanically loaded for 10 h/day for an average of 9 days.

Results

In total, 6257 of 17,221 detected genes were differentially expressed (84% upregulated; p < 0.05 and fold change ≥ 1.5) in skeletal muscle from ICU patients with CIM when compared to control subjects. The differentially expressed genes were highly associated with gene changes identified in patients with myopathy, sepsis, long-term inactivity, polymyositis, tumor, and repeat exercise resistance. Upstream regulator analysis revealed that the CIM signature could be a result of the activation of MYOD1, p38 MAPK, or treatment with dexamethasone. Passive mechanical loading only reversed expression of 0.74% of the affected genes (46 of 6257 genes).

Conclusions

RNA-seq analysis revealed that the marked muscle atrophy and weakness observed in ICU patients with CIM were associated with the altered expression of genes involved in muscle contraction, newly identified E3 ligases, autophagy and calpain systems, apoptosis, and chaperone expression. In addition, MYOD1, p38 MAPK, and dexamethasone were identified as potential upstream regulators of skeletal muscle gene expression in ICU patients with CIM. Mechanical loading only marginally affected the skeletal muscle transcriptome profiling of ICU patients diagnosed with CIM.

Electronic supplementary material

The online version of this article (10.1186/s13395-019-0194-1) contains supplementary material, which is available to authorized users.

Vamorolone treatment improves skeletal muscle outcome in a critical illness myopathy rat model

AIM

Critical illness myopathy (CIM) is a consequence of modern critical care, leading to skeletal muscle atrophy/paralysis with negative consequences for mortality/morbidity and health care costs. Glucocorticoids (GCs) have been proposed to trigger CIM. Here, we compare outcomes of two GCs, the commonly used prednisolone and the newly developed dissociative vamorolone in response to the intensive care unit (ICU) condition for 5 days, ie, sedation, immobilization, and mechanical ventilation.

METHODS

Rats were divided into a 0-day sham-operated control group, and three groups exposed to 5 days ICU condition during treatment with prednisolone (PRED) or vamorolone (VAM) or none of these GCs (ICU-group). Survival, body and muscle weights, cytokine concentrations, regulation of muscle contraction in single fast- and slow-twitch muscle fibres, myofibrillar protein expression and protein degradation pathways were studied.

RESULTS

Critical illness myopathy geno- and pheno-types were confirmed in the ICU group. However, VAM and PRED groups showed reduced atrophy/weakness than the ICU group, and muscle specific differences with more severe negative effects on fast-twitch muscle fibres in the PRED than the other groups.

CONCLUSION

These results show that vamorolone provides a GC intervention superior to typical GCs in improving CIM outcomes. Further, the findings do not support the notion that moderate-dose GC treatment represents a factor triggering CIM.

Addition of blood flow restriction to passive mobilization reduces the rate of muscle wasting in elderly patients in the intensive care unit: a within-patient randomized trial

OBJECTIVE:

To evaluate the addition of blood flow restriction to passive mobilization in patients in the intensive care unit.

DESIGN:

The study was a within-patient randomized trial.

SETTING:

Two intensive care units in Belém, from September to October 2017.

SUBJECTS:

In total, 34 coma patients admitted to the intensive care unit sector, and 20 patients fulfilled the study requirements.

INTERVENTIONS:

All participants received the passive mobilization protocol for lower limbs, and blood flow restriction was added only for one side in a concurrent fashion. Intervention lasted the entire patient's hospitalization time.

MAIN OUTCOME MEASUREMENT:

Thigh muscle thickness and circumference.

RESULTS:

In total, 34 subjects were enrolled in the study: 11 were excluded for exclusion criteria, 3 for death, and 20 completed the intervention (17 men and 3 women; mean age: 66 ± 4.3 years). Despite both groups presented atrophy, the atrophy rate was lower in blood flow restriction limb in relation to the control limb (-2.1 vs. -2.8 mm, respectively, in muscle thickness; P = 0.001). In addition, the blood flow restriction limb also had a smaller reduction in the thigh circumference than the control limb (-2.5 vs. -3.6 cm, respectively; P = 0.001).

CONCLUSION:

The use of blood flow restriction did not present adverse effects and seems to be a valid strategy to reduce the magnitude of the rate of muscle wasting that occurs in intensive care unit patients.

Influence of physical exercise on microRNAs in skeletal muscle regeneration, aging and diseases

Skeletal muscle is a dynamic tissue with remarkable plasticity and its growth and regeneration are highly organized, with the activation of specific transcription factors, proliferative pathways and cytokines. The decline of skeletal muscle tissue with age, is one of the most important causes of functional loss of independence in older adults. Maintaining skeletal muscle function throughout the lifespan is a prerequisite for good health and independent living.

Physical activity represents one of the most effective preventive agents for muscle decay in aging.

Several studies have underlined the importance of microRNAs (miRNAs) in the control of myogenesis and of skeletal muscle regeneration and function.

In this review, we reported an overview and recent advances about the role of miRNAs expressed in the skeletal muscle, miRNAs regulation by exercise in skeletal muscle, the consequences of different physical exercise training modalities in the skeletal muscle miRNA profile, their regulation under pathological conditions and the role of miRNAs in age-related muscle wasting.

Specific miRNAs appear to be involved in response to different types of exercise and therefore to play an important role in muscle fiber identity and myofiber gene expression in adults and elder population.

Understanding the roles and regulation of skeletal muscle miRNAs during muscle regeneration may result in new therapeutic approaches in aging or diseases with impaired muscle function or re-growth.

Muscle-specific differences in expression and phosphorylation of the Janus kinase 2/Signal Transducer and Activator of Transcription 3 following long-term mechanical ventilation and immobilization in rats

AIM

Muscle wasting is one of the factors most strongly predicting mortality and morbidity in critically ill intensive care unit (ICU). This muscle wasting affects both limb and respiratory muscles, but the understanding of underlying mechanisms and muscle-specific differences remains incomplete. This study aimed at investigating the temporal expression and phosphorylation of the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway in muscle wasting associated with the ICU condition to characterize the JAK/STAT proteins and the related changes leading or responding to their activation during exposure to the ICU condition.

METHODS

A novel experimental ICU model allowing long-term exposure to the ICU condition, immobilization and mechanical ventilation, was used in this study. Rats were pharmacologically paralysed by post-synaptic neuromuscular blockade and mechanically ventilated for durations varying between 6 hours and 14 days to study muscle-specific differences in the temporal activation of the JAK/STAT pathway in plantaris, intercostal and diaphragm muscles.

RESULTS

The JAK2/STAT3 pathway was significantly activated irrespective of muscle, but muscle-specific differences were observed in the temporal activation pattern between plantaris, intercostal and diaphragm muscles.

CONCLUSION

The JAK2/STAT3 pathway was differentially activated in plantaris, intercostal and diaphragm muscles in response to the ICU condition. Thus, JAK2/STAT3 inhibitors may provide an attractive pharmacological intervention strategy in immobilized ICU patients, but further experimental studies are required in the study of muscle-specific effects on muscle mass and function in response to both short- and long-term exposure to the ICU condition prior to the translation into clinical research and practice.

Exciting perspectives for Translational Myology in the Abstracts of the 2018Spring PaduaMuscleDays: Giovanni Salviati Memorial - Chapter III - Abstracts of March 16, 2018

Myologists working in Padua (Italy) were able to continue a half-century tradition of studies of skeletal muscles, that started with a research on fever, specifically if and how skeletal muscle contribute to it by burning bacterial toxin. Beside main publications in high-impact-factor journals by Padua myologists, I hope to convince readers (and myself) of the relevance of the editing Basic and Applied Myology (BAM), retitled from 2010 European Journal of Translational Myology (EJTM), of the institution of the Interdepartmental Research Center of Myology of the University of Padova (CIR-Myo), and of a long series of International Conferences organized in Euganei Hills and Padova, that is, the PaduaMuscleDays. The 2018Spring PaduaMuscleDays (2018SpPMD), were held in Euganei Hills and Padua (Italy), in March 14-17, and were dedicated to Giovanni Salviati. The main event of the “Giovanni Salviati Memorial”, was held in the Aula Guariento, Accademia Galileiana di Scienze, Lettere ed Arti of Padua to honor a beloved friend and excellent scientist 20 years after his premature passing. Using the words of Prof. Nicola Rizzuto, we all share his believe that Giovanni “will be remembered not only for his talent and originality as a biochemist, but also for his unassuming and humanistic personality, a rare quality in highly successful people like Giovanni. The best way to remember such a person is to gather pupils and colleagues, who shared with him the same scientific interests and ask them to discuss recent advances in their own fields, just as Giovanni have liked to do”. Since Giovanni’s friends sent many abstracts still influenced by their previous collaboration with him, all the Sessions of the 2018SpPMD reflect both to the research aims of Giovanni Salviati and the traditional topics of the PaduaMuscleDays, that is, basics and applications of physical, molecular and cellular strategies to maintain or recover functions of skeletal muscles. The translational researches summarized in the 2018SpPMD Abstracts are at the appropriate high level to attract approval of Ethical Committees, the interest of International Granting Agencies and approval for publication in top quality, international journals. The abstracts of the March 16, 2018 Padua Muscle Day are listed in this chapter III. All 2018SpPMD Abstracts are indexed at the end of the Chapter IV.

Activities of daily living at different levels of renal function in elderly hospitalized heart failure patients

BACKGROUND

Renal function (RF) and activities of daily living (ADL) are risk factors for heart failure (HF) patients.

AIMS

We evaluated differences in motor and cognitive ADL in relation to RF in elderly hospitalized HF patients.

METHODS

Participants were selected from 414 consecutive hospitalized HF patients based on certain criteria. We investigated patient characteristics including Functional Independence Measure (FIM) and estimated glomerular filtration rate (eGFR). Subjects were divided into three groups by RF level and analyzed with one-way ANOVA and Chi-square tests and two-way ANCOVA and multiple comparison tests.

RESULTS

Of the 414 patients, 165 met the inclusion criteria (high RF: 41, moderate RF: 84, low RF: 40). There were significant differences between the three groups in age, eGFR, hemoglobin level, mobility, cognitive function, and length of hospital stay (p < 0.05). Motor FIM showed an interaction between term and group, and cognitive FIM showed a main effect on the group (p < 0.05). In the multiple comparisons, motor FIM of all groups indicated significant recovery, but it was significantly lower after 1 week in the low RF versus moderate/high RF groups (p < 0.05). Cognitive FIM showed no significant recovery in the low RF group; the FIM score after 2 weeks was significantly lower than that in the moderate/high RF groups (p < 0.05).

CONCLUSIONS

In elderly hospitalized HF patients, the motor ADL recovery process in the low RF group was delayed compared to the high RF group. Cognitive ADL in hospitalized HF patients is difficult to recover, especially in those with low RF.

Weak by the machines: muscle motor protein dysfunction - a side effect of intensive care unit treatment

Intensive care interventions involve periods of mechanical ventilation, sedation and complete mechanical silencing of patients. Critical illness myopathy (CIM) is an ICU-acquired myopathy that is associated with limb muscle weakness, muscle atrophy, electrical silencing of muscle and motor proteinopathy. The hallmark of CIM is a preferential muscle myosin loss due to increased catabolic and reduced anabolic activity. The ubiquitin proteasome pathway plays an important role, apart from recently identified novel mechanisms affecting non-lysosomal protein degradation or autophagy. CIM is not reproduced by pure disuse atrophy, denervation atrophy, steroid-induced atrophy or septic myopathy, although combinations of high-dose steroids and denervation can mimic CIM. New animal models of critical illness and ICU treatment (i.e. mechanical ventilation and complete immobilization) provide novel insights regarding the time course of protein synthesis and degradation alterations, and the role of protective chaperone activities in the process of myosin loss. Altered mechano-signalling seems involved in triggering a major part of myosin loss in experimental CIM models, and passive loading of muscle potently ameliorates the CIM phenotype. We provide a systematic overview of similarities and distinct differences in the signalling pathways involved in triggering muscle atrophy in CIM and isolated trigger factors. As preferential myosin loss is mostly determined from biochemistry analyses providing no spatial resolution of myosin loss processes within myofibres, we also provide first results monitoring myosin signal intensities during experimental ICU intervention using multi-photon Second Harmonic Generation microscopy. Our results confirm that myosin loss is an evenly distributed process within myofibres rather than being confined to hot spots.