Tackling Brain and Muscle Dysfunction in Acute Respiratory Distress Syndrome Survivors: NHLBI Workshop Report.

Acute respiratory distress syndrome (ARDS) is associated with long-term impairments in brain and muscle function that significantly impact the quality of life of those who survive the acute illness. The mechanisms underlying these impairments are not yet well understood, and evidence-based interventions to minimize the burden on patients remain unproved. The NHLBI of the NIH assembled a workshop in April 2023 to review the state of the science regarding ARDS-associated brain and muscle dysfunction, to identify gaps in current knowledge, and to determine priorities for future investigation. The workshop included presentations by scientific leaders across the translational science spectrum and was open to the public as well as the scientific community. This report describes the themes discussed at the workshop as well as recommendations to advance the field toward the goal of improving the health and well-being of ARDS survivors.

Using Physiological Markers to Assess Comfort during Neuromuscular Electrical Stimulation Induced Muscle Contraction in a Virtually Guided Environment: Pilot Study for a Path toward Combating ICU-Acquired Weakness.

We assessed the feasibility of implementing a virtually guided Neuromuscular Electrical Stimulation (NMES) protocol over the tibialis anterior (TA) muscle while collecting heart rate (HR), Numeric Pain Rating Scale (NPRS), and quality of contraction (QoC) data. We investigated if HR, NPRS, and QoC differ ON and OFF the TA motor point and explored potential relationships between heart rate variability (HRV) and the NPRS. Twelve healthy adults participated in this cross-sectional study. Three NMES trials were delivered ON and OFF the TA motor point. HR, QoC, and NPRS data were collected. There was no significant difference in HRV ON and OFF the motor point (p > 0.05). The NPRS was significantly greater OFF the motor point (p < 0.05). The QoC was significantly different between motor point configurations (p < 0.05). There was no correlation between the NPRS and HRV (p > 0.05, r = -0.129). We recommend non-electrical methods of measuring muscle activity for future studies. The NPRS and QoC can be administered virtually. Time-domain HRV measures could increase the validity of the protocol. The variables should be explored further virtually to enhance the protocol before eventual ICU studies.

Utilization of the Rat Tibial Nerve Transection Model to Evaluate Cellular and Molecular Mechanisms Underpinning Denervation-Mediated Muscle Injury.

Peripheral nerve injury denervates muscle, resulting in muscle paralysis and atrophy. This is reversible if timely muscle reinnervation occurs. With delayed reinnervation, the muscle's reparative ability declines, and muscle-resident fibro-adipogenic progenitor cells (FAPs) proliferate and differentiate, inducing fibro-fatty muscle degradation and thereby physical disability. The mechanisms by which the peripheral nerve regulates FAPs expansion and differentiation are incompletely understood. Using the rat tibial neve transection model, we demonstrated an increased FAPs content and a changing FAPs phenotype, with an increased capacity for adipocyte and fibroblast differentiation, in gastrocnemius muscle post-denervation. The FAPs response was inhibited by immediate tibial nerve repair with muscle reinnervation via neuromuscular junctions (NMJs) and sensory organs (e.g., muscle spindles) or the sensory protection of muscle (where a pure sensory nerve is sutured to the distal tibial nerve stump) with reinnervation by muscle spindles alone. We found that both procedures reduced denervation-mediated increases in glial-cell-line-derived neurotrophic factor (GDNF) in muscle and that GDNF promoted FAPs adipogenic and fibrogenic differentiation in vitro. These results suggest that the peripheral nerve controls FAPs recruitment and differentiation via the modulation of muscle GDNF expression through NMJs and muscle spindles. GDNF can serve as a therapeutic target in the management of denervation-induced muscle injury.

Impact of COVID-19 on Tuberculosis Prevention and Treatment in Canada: A Multicenter Analysis of 10 833 Patients.

We assessed the COVID-19 pandemic's impact on treatment of latent tuberculosis, and of active tuberculosis, at 3 centers in Montreal and Toronto, using data from 10 833 patients (8685 with latent tuberculosis infection, 2148 with active tuberculosis). Observation periods prior to declarations of COVID-19 public health emergencies ranged from 219 to 744 weeks, and after declarations, from 28 to 33 weeks. In the latter period, reductions in latent tuberculosis infection treatment initiation rates ranged from 30% to 66%. At 2 centers, active tuberculosis treatment rates fell by 16% and 29%. In Canada, cornerstone measures for tuberculosis elimination weakened during the COVID-19 pandemic.

Comparison of quadriceps muscle size and quality in adults with cystic fibrosis with different severities of cystic fibrosis transmembrane conductance regulator protein dysfunction.

BACKGROUND: Cystic fibrosis (CF) is characterized by CF transmembrane conductance regulator (CFTR) dysfunction. CFTR protein is expressed in human skeletal muscle; however, its impact on skeletal muscle is unknown. The objectives of this study were to compare quadriceps muscle size and quality between adults with various severities of CFTR protein dysfunction. METHODS: We conducted a prospective, cross-sectional study comparing 34 adults with severe versus 18 with mild CFTR protein dysfunction, recruited from a specialized CF centre. Ultrasound images of rectus femoris cross-sectional area (RF-CSA) and quadriceps layer thickness for muscle size, and rectus femoris echogenicity (RF-ECHO) (muscle quality) were obtained. Multivariable linear regression models were developed using purposeful selection technique. RESULTS: People with severe CFTR protein dysfunction had larger RF-CSA by 3.22 cm2, 95% CI (1.03, 5.41) cm2, p=.0049], after adjusting for oral corticosteroid use and Pseudomonas aeruginosa colonization. However, a sensitivity analysis indicated that the result was influenced by the specific confounders being adjusted for in the model. We did not find any significant differences in quadriceps layer thickness or RF-ECHO between the two groups. CONCLUSION: We found no differential impact of the extent of diminished CFTR protein activity on quadriceps muscle size or quality in our study cohort. Based on these findings, CFTR mutation status cannot be used differentiate leg muscle size or quality in people with CF.

Epigenetic Profiling in Severe Sepsis: A Pilot Study of DNA Methylation Profiles in Critical Illness.

OBJECTIVES: Epigenetic alterations are an important regulator of gene expression in health and disease; however, epigenetic data in sepsis are lacking. To demonstrate proof of concept and estimate effect size, we performed the first epigenome-wide methylation analysis of whole blood DNA samples from a cohort of septic and nonseptic critically ill patients. DESIGN: A nested case-control study using genomic DNA isolated from whole blood from septic (n = 66) and nonseptic (n = 68) critically ill patients on "Day 1" of ICU admission. Methylation patterns were identified using Illumina 450K arrays with percent methylation expressed as ß values. After quality control, 134 participants and 414,818 autosomal cytosine-phosphate-guanine sites were used for epigenome-wide methylation analyses. SETTING: Tertiary care hospitals. SUBJECTS: Critically ill septic and nonseptic patients. INTERVENTIONS: Observational study. MEASUREMENTS AND MAIN RESULTS: A total of 668 differentially methylated regions corresponding to 443 genes were identified. Known sepsis-associated genes included complement component 3; angiopoietin 2; myeloperoxidase; lactoperoxidase; major histocompatibility complex, class I, A; major histocompatibility complex, class II, isotype DR ß I; major histocompatibility complex, class I, C; and major histocompatibility complex, class II, isotype DQ ß I. When compared with whole blood gene expression data from seven external datasets containing septic and nonseptic patients, 81% of the differentially methylated region-associated genes were differentially expressed in one or more datasets and 31% in three or more datasets. Functional analysis showed enrichment for antigen processing and presentation, methyltransferase activity, cell adhesion, and cell junctions. Analysis by weighted gene coexpression network analysis revealed DNA comethylation modules that were associated with clinical traits including severity of illness, need for vasopressors, and length of stay. CONCLUSIONS: DNA methylation marks may provide important causal and potentially biomarker information in critically ill patients with sepsis.

A machine learning-based clinical tool for diagnosing myopathy using multi-cohort microarray expression profiles.

BACKGROUND: Myopathies are a heterogenous collection of disorders characterized by dysfunction of skeletal muscle. In practice, myopathies are frequently encountered by physicians and precise diagnosis remains a challenge in primary care. Molecular expression profiles show promise for disease diagnosis in various pathologies. We propose a novel machine learning-based clinical tool for predicting muscle disease subtypes using multi-cohort microarray expression data. MATERIALS AND METHODS: Muscle tissue samples originating from 1260 patients with muscle weakness. Data was curated from 42 independent cohorts with expression profiles in public microarray gene expression repositories, which represent a broad range of patient ages and peripheral muscles. Cohorts were categorized into five muscle disease subtypes: immobility, inflammatory myopathies, intensive care unit acquired weakness (ICUAW), congenital, and chronic systemic disease. The data contains expression data on 34,099 genes. Data augmentation techniques were used to address class imbalances in the muscle disease subtypes. Support vector machine (SVM) models were trained on two-thirds of the 1260 samples based on the top selected gene signature using analysis of variance (ANOVA). The model was validated in the remaining samples using area under the receiver operator curve (AUC). Gene enrichment analysis was used to identify enriched biological functions in the gene signature. RESULTS: The AUC ranges from 0.611 to 0.649 in the observed imbalanced data. Overall, using the augmented data, chronic systemic disease was the best predicted class with AUC 0.872 (95% confidence interval (CI): 0.824-0.920). The least discriminated classes were ICUAW with AUC 0.777 (95% CI: 0.668-0.887) and immobility with AUC 0.789 (95% CI: 0.716-0.861). Disease-specific gene set enrichment results showed that the gene signature was enriched in biological processes including neural precursor cell proliferation for ICUAW and aerobic respiration for congenital (false discovery rate q-value < 0.001). CONCLUSION: Our results present a well-performing molecular classification tool with the selected gene markers for muscle disease classification. In practice, this tool addresses an important gap in the literature on myopathies and presents a potentially useful clinical tool for muscle disease subtype diagnosis.

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.

One-Year Outcomes in Caregivers of Critically Ill Patients.

BACKGROUND: Few resources are available to support caregivers of patients who have survived critical illness; consequently, the caregivers' own health may suffer. We studied caregiver and patient characteristics to determine which characteristics were associated with caregivers' health outcomes during the first year after patient discharge from an intensive care unit (ICU). METHODS: We prospectively enrolled 280 caregivers of patients who had received 7 or more days of mechanical ventilation in an ICU. Using hospital data and self-administered questionnaires, we collected information on caregiver and patient characteristics, including caregiver depressive symptoms, psychological well-being, health-related quality of life, sense of control over life, and effect of providing care on other activities. Assessments occurred 7 days and 3, 6, and 12 months after ICU discharge. RESULTS: The caregivers' mean age was 53 years, 70% were women, and 61% were caring for a spouse. A large percentage of caregivers (67% initially and 43% at 1 year) reported high levels of depressive symptoms. Depressive symptoms decreased at least partially with time in 84% of the caregivers but did not in 16%. Variables that were significantly associated with worse mental health outcomes in caregivers were younger age, greater effect of patient care on other activities, less social support, less sense of control over life, and less personal growth. No patient variables were consistently associated with caregiver outcomes over time. CONCLUSIONS: In this study, most caregivers of critically ill patients reported high levels of depressive symptoms, which commonly persisted up to 1 year and did not decrease in some caregivers. (Funded by the Canadian Institutes of Health Research and others; ClinicalTrials.gov number, NCT00896220.).

From skeletal muscle weakness to functional outcomes following critical illness: a translational biology perspective.

Intensive care unit acquired weakness (ICUAW) is now a well-known entity complicating critical illness. It increases mortality and in the critical illness survivor it is associated with physical disability, substantially increased health resource utilisation and healthcare costs. Skeletal muscle wasting is a key driver of ICUAW and physical functional outcomes in both the short and long term. To date, there is no intervention that can universally and consistently prevent muscle loss during critical illness, or enhance its recovery following intensive care unit discharge, to improve physical function. Clinical trials of early mobilisation or exercise training, or enhanced nutritional support have generated inconsistent results and we have no effective pharmacological interventions. This review will delineate our current understanding of the mechanisms underpinning the development and persistence of skeletal muscle loss and dysfunction in the critically ill individual, highlighting recent discoveries and clinical observations, and utilisation of this knowledge in the development of novel therapeutics.

Mechanisms of Chronic Muscle Wasting and Dysfunction after an Intensive Care Unit Stay. A Pilot Study.

RATIONALE: Critical illness survivors often experience permanent functional disability due to intensive care unit (ICU)-acquired weakness. The mechanisms responsible for long-term weakness persistence versus resolution are unknown. OBJECTIVES: To delineate cellular mechanisms underlying long-term weakness persistence in ICU survivors. METHODS: We conducted a nested, prospective study of critically ill patients mechanically ventilated for 7 days or longer. The patients were recruited from the RECOVER program and serially assessed over 6 months after ICU discharge. Twenty-seven of 82 patients consented to participate; 15 and 11 patients were assessed at 7 days and 6 months after ICU discharge, respectively. MEASUREMENTS AND MAIN RESULTS: We assessed motor functional capacity, quadriceps size, strength, and voluntary contractile capacity and performed electromyography, nerve conduction studies, and vastus lateralis biopsies for histologic, cellular, and molecular analyses. Strength and quadriceps cross-sectional areas were decreased 7 days after ICU discharge. Weakness persisted to 6 months and correlated with decreased function. Quadriceps atrophy resolved in 27% patients at 6 months. Muscle mass reconstitution did not correlate with resolution of weakness, owing to persistent impaired voluntary contractile capacity. Compared with Day 7, increased ubiquitin-proteasome system-mediated muscle proteolysis, inflammation, and decreased mitochondrial content all normalized at 6 months. Autophagy markers were normal at 6 months. Patients with sustained atrophy had decreased muscle progenitor (satellite) cell content. CONCLUSIONS: Long-term weakness in ICU survivors results from heterogeneous muscle pathophysiology with variable combinations of muscle atrophy and impaired contractile capacity. These findings are not explained by ongoing muscle proteolysis, inflammation, or diminished mitochondrial content. Sustained muscle atrophy is associated with decreased satellite cell content and compromised muscle regrowth, suggesting impaired regenerative capacity.

The RECOVER Program: Disability Risk Groups and 1-Year Outcome after 7 or More Days of Mechanical Ventilation.

RATIONALE: Disability risk groups and 1-year outcome after greater than or equal to 7 days of mechanical ventilation (MV) in medical/surgical intensive care unit (ICU) patients are unknown and may inform education, prognostication, rehabilitation, and study design. OBJECTIVES: To stratify patients for post-ICU disability and recovery to 1 year after critical illness. METHODS: We evaluated a multicenter cohort of 391 medical/surgical ICU patients who received greater than or equal to 1 week of MV at 7 days and 3, 6, and 12 months after ICU discharge. Disability risk groups were identified using recursive partitioning modeling. MEASUREMENTS AND MAIN RESULTS: The 7-day post-ICU Functional Independence Measure (FIM) determined the recovery trajectory to 1-year after ICU discharge and was an independent risk factor for 1-year mortality. The 7-day post-ICU FIM was predicted by age and ICU length of stay. By 2 weeks of MV, ICU patients could be stratified into four disability groups characterized by increasing risk for post ICU disability, ICU and post-ICU healthcare use, and disposition. Patients less than 42 years with ICU length of stay less than 2 weeks had the best function and fewest deaths at 1 year compared with patients greater than 66 years with ICU length of stay greater than 2 weeks who sustained the worst disability and 40% 1-year mortality. Depressive symptoms (17%) and post-traumatic stress disorder (18%) persisted at 1 year. CONCLUSIONS: ICU survivors of greater than or equal to 1 week of MV may be stratified into four disability groups based on age and ICU length of stay. These groups determine 1-year recovery and healthcare use and are independent of admitting diagnosis and illness severity. Clinical trial registered with www.clinicaltrials.gov (NCT 00896220).

PDLIM7 is a novel target of the ubiquitin ligase Nedd4-1 in skeletal muscle.

Skeletal muscle atrophy remains a complication occurring both as a natural response to muscle disuse and as a pathophysiological response to illness such as diabetes mellitus and nerve injury, such as traumatic muscle denervation. The ubiquitin-proteasome system (UPS) is the predominant proteolytic machinery responsible for atrophy of skeletal muscle, and Nedd4-1 (neural precursor cell-expressed developmentally down-regulated 4-1) is one of a series of E3 ubiquitin ligases identified to mediate inactivity-induced muscle wasting. Targets of Nedd4-1 mediated ubiquitination in skeletal muscle remain poorly understood. In the present study, we identified PDLIM7 (PDZ and LIM domain 7, Enigma), a member of the PDZ-LIM family of proteins, as a novel target of Nedd4-1 in skeletal muscle. The PDZ-LIM family of proteins is known to regulate muscle development and function. We show that Nedd4-1 expression in muscle atrophied by denervation is co-incident with a decrease in PDLIM7 and that PDLIM7 protein levels are stabilized in denervated muscle of Nedd4-1 skeletal muscle-specific knockout mice (SMS-KO). Exogenous PDLIM7 and Nedd4-1 transfected into human embryonic kidney (HEK)293 cells co-immunoprecipitate through binding between the PY motif of PDLIM7 and the second and third WW domains of Nedd4-1 and endogenous PDLIM7 and Nedd4-1 interact in the cytoplasm of differentiated C2C12 myotubes, leading to PDLIM7 ubiquitination. These results identify PDLIM7 as a bona fide skeletal muscle substrate of Nedd4-1 and suggest that this interaction may underlie the progression of skeletal muscle atrophy. This offers a novel therapeutic target that could be potentially used to attenuate muscle atrophy.

Neuromuscular Blocking Agent Cisatracurium Attenuates Lung Injury by Inhibition of Nicotinic Acetylcholine Receptor-α1.

BACKGROUND: Neuromuscular blocking agents (NMBAs) bind the nicotinic acetylcholine receptor α1 (nAChRα1) that also contributes to inflammatory signaling. Thus, the author hypothesized that the use of NMBA mitigates lung injury by improving ventilator synchrony and decreasing inflammatory responses. METHODS: Lung injury was induced by intratracheal instillation of hydrogen chloride in rats that were randomized to receive no NMBA with evidence of asynchronous ventilation (noNMBA/aSYNC, n = 10); no NMBA with synchronous ventilation (noNMBA/SYNC, n = 10); cisatracurium (CIS, n = 10); or pancuronium (PAN, n = 10). Mechanical ventilation was set at a tidal volume of 6 ml/kg and positive end-expiratory pressure 8 cm H2O for 3 h. Human lung epithelial, endothelial, and CD14⁺ cells were challenged with mechanical stretch, lipopolysaccharide, lung lavage fluids (bronchoalveolar lavage fluid), or plasma obtained from patients (n = 5) with acute respiratory distress syndrome, in the presence or absence of CIS or small-interfering RNA and small hairpin RNA to attenuate the cell expression of nAChRα1. RESULTS: The use of CIS and PAN improved respiratory compliance (7.2 ± 0.7 in noNMBA/aSYNC, 6.6 ± 0.5 in noNMBA/SYNC, 5.9 ± 0.3 in CIS, and 5.8 ± 0.4 cm H2O/l in PAN; P < 0.05), increased PaO2 (140 ± 54, 209 ± 46, 269 ± 31, and 269 ± 54 mmHg, respectively, P < 0.05), and decreased the plasma levels of tumor necrosis factor-α (509 ± 252 in noNMBA, 200 ± 74 in CIS, and 175 ± 84 pg/ml in PAN; P < 0.05) and interleukin-6 (5789 ± 79, 1608 ± 534, and 2290 ± 315 pg/ml, respectively; P < 0.05). The use of CIS and PAN or silencing the receptor nAChRα1 resulted in decreased cytokine release in the human cells in response to a variety of stimuli mentioned earlier. CONCLUSIONS: The use of NMBA is lung protective through its antiinflammatory properties by blocking the nAChRα1.

Skeletal muscle dysfunction in idiopathic pulmonary arterial hypertension.

Despite improvements in survival with disease-targeted therapies, the majority of patients with pulmonary arterial hypertension (PAH) have persistent exercise intolerance that results from impaired cardiac function and skeletal muscle dysfunction. Our intent was to understand the molecular mechanisms mediating skeletal muscle dysfunction in PAH. A total of 12 patients with PAH and 10 matched control subjects were assessed. Patients with PAH demonstrated diminished exercise capacity (lower oxygen uptake max, lower anaerobic threshold and higher minute ventilation/CO2) compared with control subjects. Quadriceps muscle cross-sectional area was significantly smaller in patients with PAH. The vastus lateralis muscle was biopsied to enable muscle fiber morphometric assessment and to determine expression levels/activation of proteins regulating (1) muscle mass, (2) mitochondria biogenesis and shaping machinery, and (3) excitation-contraction coupling. Patients with PAH demonstrated a decreased type I/type II muscle fiber ratio, with a smaller cross-sectional area in the type I fibers. Diminished AKT and p70S6 kinase phosphorylation, with increased atrogin-1 and muscle RING-finger protein-1 transcript levels, were evident in the PAH muscle, suggesting engagement of cellular signaling networks stimulating ubiquitin-proteasome-mediated proteolysis of muscle, with concurrent depression of networks mediating muscle hypertrophy. Although there were no differences in expression/activation of proteins associated with mitochondrial biogenesis or fission (MTCO2 [cytochrome C oxidase subunit II]/succinate dehydrogenase flavoprotein subunit A, mitochondrial transcription factor A, nuclear respiratory factor-1/dynamin-related protein 1 phosphorylation), protein levels of a positive regulator of mitochondrial fusion, Mitofusin2, were significantly lower in patients with PAH. Patients with PAH demonstrated increased phosphorylation of ryanodine receptor 1 receptors, suggesting that altered sarcoplasmic reticulum Ca(++) sequestration may impair excitation-contraction coupling in the PAH muscle. These data suggest that muscle dysfunction in PAH results from a combination of muscle atrophy and intrinsically impaired contractility.

Intensive care unit-acquired weakness: clinical phenotypes and molecular mechanisms.

Intensive care unit-acquired weakness (ICUAW) begins within hours of mechanical ventilation and may not be completely reversible over time. It represents a major functional morbidity of critical illness and is an important patient-centered outcome with clear implications for quality of life and resumption of prior work and lifestyle. There is heterogeneity in functional outcome related to ICUAW across various patient populations after an episode of critical illness. This state-of-the art review argues that this observed heterogeneity may represent a clinical spectrum of disability in which there are recognizable clinical phenotypes for outcome according to age, burden of comorbid illness, and ICU length of stay. It further argues that these functional outcomes are modified by mood, cognition, and caregiver physical and mental health. This proposed construct of clinical phenotypes will be used as a framework for a review of the current literature on the molecular biology of muscle and nerve injury. This translational approach for the development of models pairing clinical phenotypes for different functional outcomes after critical illness with molecular mechanism of injury may offer unique insights into the diagnosis and treatment of muscle and nerve lesions.

Lung-injured patients do not need a specialized rehabilitation program: ICUAW as a case study.

An episode of critical illness is transformative. Patients suffer important new nerve, brain, and muscle injury. The spectrum of morbidity varies according to individual risks, but prevalent disabilities transcend diagnostic groupings. In the context of intensive care unit-acquired weakness (ICUAW), each patient who enters the ICU will begin to degrade muscle through upregulation of different proteolytic pathways, and, although the inciting stimulus, or its magnitude, may differ somewhat across patients, the result is the same. This argues for an approach to rehabilitation that is etiologically neutral and based on an understanding of molecular pathophysiology that can be mapped to functional outcome and tailored to individual need.