Ventilator-induced diaphragm dysfunction: cause and effect

Higher protein intake may benefit in patients with prolonged mechanical ventilation

Background

Patients with prolonged mechanical ventilation (PMV) is usually associated with muscle wasting and diaphragm weakness, resulting in high medical costs and mortality. Adequate energy and protein intake were beneficial in sarcopenia patients. We aimed to investigate the impact of protein intake in weaning parameters in patients with PMV.

Materials and methods

We enrolled patients with PMV (mechanical ventilation ≥6 h/day for ≥21 days) from a respiratory care center (RCC) of a tertiary medical center from December 2020 to October 2022, and classified them into weaning success and weaning failure groups. The patients' characteristics, nutrition records, weaning parameters and outcomes were analyzed.

Results

A total of 289 patients were included (mean age 73.5 years). Of the 289 patients, 149 were weaned successfully and 140 were not. The average protein intake was higher in the weaning success group than in the weaning failure group (1.22 ± 0.320 versus 0.99 ± 0.332 g/kg/day, p < 0.001). No significant differences were noted in the average calorie intake and whey protein intake between the two groups. RSBI <90 breaths/min/L (OR = 2.38, p = 0.045), serum albumin at 4th week ≥3 g/dL (OR = 2.89, p = 0.027), daily protein intake ≥1.01 g/kg/day (OR = 8.10, p < 0.001), PaO2/FiO2 (PF) ratio ≥ 300 (OR = 2.56, p = 0.027) were independent predictors for weaning from ventilator. Weak positive correlations were found between average protein intake with PF ratio (r = 0.1576, p = 0.0227) and PaO2 (r = 0.13359, p = 0.0497).

Conclusion

Daily protein intake had positively correlated with PF ratio and had independently benefit for weaning in patients with PMV.

Ventilator-induced diaphragm dysfunction: phenomenology and mechanism(s) of pathogenesis

Mechanical ventilation (MV) is used to support ventilation and pulmonary gas exchange in patients during critical illness and surgery. Although MV is a life-saving intervention for patients in respiratory failure, an unintended side-effect of MV is the rapid development of diaphragmatic atrophy and contractile dysfunction. This MV-induced diaphragmatic weakness is labelled as 'ventilator-induced diaphragm dysfunction' (VIDD). VIDD is an important clinical problem because diaphragmatic weakness is a risk factor for the failure to wean patients from MV. Indeed, the inability to remove patients from ventilator support results in prolonged hospitalization and increased morbidity and mortality. The pathogenesis of VIDD has been extensively investigated, revealing that increased mitochondrial production of reactive oxygen species within diaphragm muscle fibres promotes a cascade of redox-regulated signalling events leading to both accelerated proteolysis and depressed protein synthesis. Together, these events promote the rapid development of diaphragmatic atrophy and contractile dysfunction. This review highlights the MV-induced changes in the structure/function of diaphragm muscle and discusses the cell-signalling mechanisms responsible for the pathogenesis of VIDD. This report concludes with a discussion of potential therapeutic opportunities to prevent VIDD and suggestions for future research in this exciting field.

Effectiveness of abdominal sandbag training in enhancing diaphragm muscle function and exercise tolerance in patients with chronic respiratory failure

BACKGROUND

Chronic respiratory failure is a common cause of ventilator dependence in the intensive care unit (ICU). The causes of chronic respiratory failure include primary disease or complications, such as ICU-acquired weakness. Traditional practice requires patients to remain immobile and bedridden; however, recent evidence suggests that early adequate exercise promotes recovery without increasing risks. In this study, we explored the efficacy of planned progressive abdominal sandbag training in promoting the successful withdrawal of patients with chronic respiratory failure from mechanical ventilation.

METHODS

This study was conducted between April 2019 and November 2020. Patients were recruited and divided into two groups: abdominal sandbag training group and control group (no training). The training group participated in a 3-month daily pulmonary rehabilitation program, which involved a 30-min session of progressive sandbag loading on the upper abdomen as a form of diaphragmatic resistant exercise. The pressure support level of the ventilator was adjusted to maintain a tidal volume of 8 mL/kg. To investigate the effect of abdominal sandbag training on patients with chronic respiratory failure, we compared tidal volume, shallow breathing index, maximum respiratory pressure, and diaphragm characteristics between the training and control groups.

RESULTS

This study included 31 patients; of them, 17 (54.8 %) received abdominal sandbag training and 14 (45.2 %) did not. No significant between-group difference was found in baseline characteristics. Compared with the control group, the training group exhibited considerable improvements in ventilation-related parameters (p < 0.001): the tidal volume markedly increased (p = 0.012), rapid shallow breathing index declined (p = 0.016), and maximum respiratory pressure increased (p < 0.001) in the training group. The diaphragm motion value (p = 0.048) and diaphragm thickness (p = 0.041) were greater in the training group than in the control group. Nine patients (52.9 %) in the training group were removed from the ventilator compared with 1 (7.1 %) in the control group (p = 0.008).

CONCLUSION

Abdominal sandbag training may be beneficial for patients dependent on a ventilator. The training improves the function of the diaphragm muscle, thereby increasing tidal volume and reducing the respiratory rate and rapid shallow breathing index, thus facilitating withdrawal from ventilation. This training approach may also improve the thickness and motion of the diaphragm and the rate of ventilator detachment.

Respiratory muscle dysfunction in acute and chronic respiratory failure: how to diagnose and how to treat?

Assessing and treating respiratory muscle dysfunction is crucial for patients with both acute and chronic respiratory failure. Respiratory muscle dysfunction can contribute to the onset of respiratory failure and may also worsen due to interventions aimed at treatment. Evaluating respiratory muscle function is particularly valuable for diagnosing, phenotyping and assessing treatment efficacy in these patients. This review outlines established methods, such as measuring respiratory pressures, and explores novel techniques, including respiratory muscle neurophysiology assessments using electromyography and imaging with ultrasound.Additionally, we review various treatment strategies designed to support and alleviate the burden on overworked respiratory muscles or to enhance their capacity through training interventions. These strategies range from invasive and noninvasive mechanical ventilation approaches to specialised respiratory muscle training programmes. By summarising both established techniques and recent methodological advancements, this review aims to provide a comprehensive overview of the tools available in clinical practice for evaluating and treating respiratory muscle dysfunction. Our goal is to present a clear understanding of the current capabilities and limitations of these diagnostic and therapeutic approaches. Integrating advanced diagnostic methods and innovative treatment strategies should help improve patient management and outcomes. This comprehensive review serves as a resource for clinicians, equipping them with the necessary knowledge to effectively diagnose and treat respiratory muscle dysfunction in both acute and chronic respiratory failure scenarios.

The role of zinc and matrix metalloproteinases in myofibrillar protein degradation in critical illness myopathy

Due to an unexpected activation of different zinc (Zn) transporters in a recent prospective clinical study, we have revisited the role of Zn homeostasis and the activation of matrix metalloproteinases (MMPs) in skeletal muscle exposed to the intensive care unit (ICU) condition (immobilization and mechanical ventilation). ICU patients exposed to 12 days ICU condition were followed longitudinally with six repeated muscle biopsies while they showed a progressive preferential myosin loss, i.e., the hallmark of Critical Illness Myopathy (CIM), in parallel with the activation of Zn-transporters. In this study, we have revisited the expression of Zn-transporters and the activation of MMPs in clinical as well as in experimental studies using an established ICU model. MMPs are a group Zn-dependent endopeptidases which do not only target and cleave extracellular proteins but also intracellular proteins including multiple sarcomeric proteins. MMP-9 is of specific interest since the hallmark of CIM, the preferential myosin loss, has also been reported in dilated cardiomyopathy and coupled to MMP-9 activation. Transcriptional activation of Zn-transporters was observed in both clinical and experimental studies as well as the activation of MMPs, in particular MMP-9, in various limb and respiratory muscles in response to long-term exposure to the ICU condition. The activation of Zn-transporters was paralleled by increased Zn levels in skeletal muscle which in turn showed a negative linear correlation with the preferential myosin loss associated with CIM, offering a potential intervention strategy. Thus, activation of Zn-transporters, increased intramuscular Zn levels, and activation of the Zn-dependent MMPs are forwarded as a probable mechanism involved in CIM pathophysiology. These effects were confirmed in different rat strains subjected to a model of CIM and exacerbated by old age. This is of specific interest since old age and muscle wasting are the two factors most strongly associated with ICU mortality.

Diaphragm atrophy during invasive mechanical ventilation is related to extubation failure in preterm infants: An ultrasound study

Background

Diaphragm dysfunction is associated with poor outcomes in critically ill patients. Ventilator‐induced diaphragmatic dysfunction (VIDD), including diaphragm atrophy (DA), is poorly studied in newborns. We aimed to assess VIDD and its associations in newborns.

Methods

Single‐center prospective study. Diaphragm thickness was measured at end‐inspiration (TDI) and end‐expiration (TDE) on the right midaxillary line. DA was defined as decrease in TDE ≥ 10%. Daily measurements were recorded in preterm newborns on invasive mechanical ventilation (IMV) for ≥2 days. Clinical characteristics of patients and extubation failure were recorded. Univariate analysis, logistic regression, and mixed models were performed to describe VIDD and associated factors.

Results

We studied 17 patients (median gestational age 270/7 weeks) and 22 IMV cycles (median duration 9 days). Median TDE decreased from 0.118 cm (interquartile range [IQR] 0.094–0.165) on the first IMV day to 0.104 cm (IQR 0.083–0.120) on the last IMV day (p = .092). DA occurred in 11 IMV cycles (50%) from 10 infants early during IMV (median: second IMV day). Mean airway pressure (MAP) and lung ultrasound score (LUS) on the first IMV day were significantly higher in patients who developed DA. DA was more frequent in patients with extubation failure than in those with extubation success within 7 days (83.3 vs. 33.3%, p = .038).

Conclusions

DA, significantly associated with extubation failure, occurred in 58.8% of the study infants on IMV. Higher MAP and LUS at IMV start were associated with DA. Our results suggest a potential role of diaphragm ultrasound to assess DA and predict extubation failure in clinical practice.

Risk factors for prolonged mechanical ventilation in critically ill patients with influenza-related acute respiratory distress syndrome

BACKGROUND

Patients with influenza-related acute respiratory distress syndrome (ARDS) are critically ill and require mechanical ventilation (MV) support. Prolonged mechanical ventilation (PMV) is often seen in these cases and the optimal management strategy is not established. This study aimed to investigate risk factors for PMV and factors related to weaning failure in these patients.

METHODS

This retrospective cohort study was conducted by eight medical centers in Taiwan. All patients in the intensive care unit with virology-proven influenza-related ARDS requiring invasive MV from January 1 to March 31, 2016, were included. Demographic data, critical illness data and clinical outcomes were collected and analyzed. PMV is defined as mechanical ventilation use for more than 21 days.

RESULTS

There were 263 patients with influenza-related ARDS requiring invasive MV enrolled during the study period. Seventy-eight patients had PMV. The final weaning rate was 68.8% during 60 days of observation. The mortality rate in PMV group was 39.7%. Risk factors for PMV were body mass index (BMI) > 25 (kg/m2) [odds ratio (OR) 2.087; 95% confidence interval (CI) 1.006-4.329], extracorporeal membrane oxygenation (ECMO) use (OR 6.181; 95% CI 2.338-16.336), combined bacterial pneumonia (OR 4.115; 95% CI 2.002-8.456) and neuromuscular blockade use over 48 h (OR 2.8; 95% CI 1.334-5.879). In addition, risk factors for weaning failure in PMV patients were ECMO (OR 5.05; 95% CI 1.75-14.58) use and bacteremia (OR 3.91; 95% CI 1.20-12.69).

CONCLUSIONS

Patients with influenza-related ARDS and PMV have a high mortality rate. Risk factors for PMV include BMI > 25, ECMO use, combined bacterial pneumonia and neuromuscular blockade use over 48 h. In addition, ECMO use and bacteremia predict unsuccessful weaning in PMV patients.

Temporary diaphragm pacing for patients at risk of prolonged mechanical ventilation after extensive aortic repair

Objective

Prolonged mechanical ventilation (MV) after extensive aortic reconstructive surgery is common. Studies have demonstrated that diaphragm pacing (DP) improves lung function in patients with unilateral diaphragm paralysis. The goal of this study is to determine whether this technology can be applied to complex aortic repair to reduce prolonged MV and other respiratory sequelae.

Methods

A retrospective review was performed of patients who underwent temporary DP after extensive aortic reconstructive surgery between 2019 and 2022. The primary end point was prolonged MV incidence. Other measured end points included diaphragm electromyography improvement, length of hospitalization, duration of intensive care unit stay, and reintubation rates.

Results

Fourteen patients deemed at high risk of prolonged MV based on their smoking and respiratory history underwent DP after extensive aortic repair. The mean age was 70.2 years. The indications for aortic repair were a thoracoabdominal aortic aneurysm (n = 8, including 2 ruptured, 2 symptomatic, and 1 mycotic), a perivisceral aneurysm (n = 4), and a perivisceral coral reef aorta (n = 2). All patients had a significant smoking history (active or former) or other risk factors for ventilator-induced diaphragmatic dysfunction and prolonged MV. The mean total duration of MV postoperatively was 31.9 hours (range, 8.1-76.5 hours). The total average pacing duration was 4.4 days. Two patients required prolonged MV, with an average of 75.4 hours. Two patients required reintubation. No complications related to DP wire placement or removal occurred.

Conclusions

DP is safe and feasible for patients at high risk of pulmonary insufficiency after extensive aortic reconstructive surgery.

Electrical stimulation mitigates muscle degradation shift in gene expressions during 12-h mechanical ventilation

Ventilator-induced diaphragm dysfunction (VIDD), a dysfunction of the diaphragm muscle caused by prolonged mechanical ventilation (MV), is an important factor that hinders successful weaning from ventilation. We evaluated the effects of electrical stimulation of the diaphragm muscle (pulsed current with off-time intervals) on genetic changes during 12 h of MV (E-V12). Rats were divided into four groups: control, 12-h MV, sham operation, and E-V12 groups. Transcriptome analysis using an RNA microarray revealed that 12-h MV caused upregulation of genes promoting muscle atrophy and downregulation of genes facilitating muscle synthesis, suggesting that 12-h MV is a reasonable method for establishing a VIDD rat model. Of the genes upregulated by 12-h MV, 18 genes were not affected by the sham operation but were downregulated by E-V12. These included genes related to catabolic processes, inflammatory cytokines, and skeletal muscle homeostasis. Of the genes downregulated by 12-h MV, 6 genes were not affected by the sham operation but were upregulated by E-V12. These included genes related to oxygen transport and mitochondrial respiration. These results suggested that 12-h MV shifted gene expression in the diaphragm muscle toward muscle degradation and that electrical stimulation counteracted this shift by suppressing catabolic processes and increasing mitochondrial respiration.

Aberrant mitochondrial dynamics contributes to diaphragmatic weakness induced by mechanical ventilation

In critical care patients, the ""temporary inactivity of the diaphragm caused by mechanical ventilation (MV) triggers a series of events leading to diaphragmatic dysfunction and atrophy, commonly known as ventilator-induced diaphragm dysfunction (VIDD). While mitochondrial dysfunction related to oxidative stress is recognized as a crucial factor in VIDD, the exact molecular mechanism remains poorly understood. In this study, we observe that 6 h of MV triggers aberrant mitochondrial dynamics, resulting in a reduction in mitochondrial size and interaction, associated with increased expression of dynamin-related protein 1 (DRP1). This effect can be prevented by P110, a molecule that inhibits the recruitment of DRP1 to the mitochondrial membrane. Furthermore, isolated mitochondria from the diaphragms of ventilated patients exhibited increased production of reactive oxygen species (ROS). These mitochondrial changes were associated with the rapid oxidation of type 1 ryanodine receptor (RyR1) and a decrease in the stabilizing subunit calstabin 1. Subsequently, we observed that the sarcoplasmic reticulum (SR) in the ventilated diaphragms showed increased calcium leakage and reduced contractile function. Importantly, the mitochondrial fission inhibitor P110 effectively prevented all of these alterations. Taken together, the results of our study illustrate that MV leads, in the diaphragm, to both mitochondrial fragmentation and dysfunction, linked to the up-/down-regulation of 320 proteins, as assessed through global comprehensive quantitative proteomics analysis, primarily associated with mitochondrial function. These outcomes underscore the significance of developing compounds aimed at modulating the balance between mitochondrial fission and fusion as potential interventions to mitigate VIDD in human patients.

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.

Effects of aerobic exercise on cardiac function and gene expression of NADPH oxidases in diaphragm muscle of rats with aortic stenosis-induced heart failure

We evaluated the influence of aerobic physical exercise (EX) on gene-encoding proteins associated with oxidative stress in diaphragm muscle of rats with aortic stenosis-induced heart failure (HF). Wistar male rats were divided into four groups: Control sedentary (C); Control exercise (C-Ex); Sedentary aortic stenosis (AS); Aortic stenosis exercise (AS-Ex). Exercised rats trained 5 times a week for 10 weeks on a treadmill. Statistical analysis was performed by ANOVA or Kruskal-Wallis test. In the final echocardiogram, animals with aortic stenosis subjected to exercise demonstrated improvement in systolic function compared to the sedentary aortic stenosis group. In diaphragm muscle, the activity of antioxidant enzymes, malondialdehyde malondialdehyde concentration, protein carbonylation, and protein expression of p65 and its inhibitor IκB did not differ between groups. Alterations in gene expression of sources that generate reactive species of oxygen were observed in AS-Ex group, which showed decreased mRNA abundance of NOX2 and NOX4 compared to the aortic stenosis group (p < 0.05). We concluded that aerobic exercise has a positive impact during heart failure, ameliorating systolic dysfunction and biomarkers of oxidative stress in diaphragm muscle of rats with aortic stenosis-induced heart failure.

Diaphragm stimulation elicits phrenic afferent-induced neuromuscular plasticity

We hypothesized that activation of phrenic afferents induces diaphragm motor plasticity. In anesthetized and spontaneously breathing rats we delivered 40 Hz, low threshold (twitch and 1.5X twitch threshold), inspiratory-triggered stimulation to the left hemidiaphragm for 30 min to activate ipsilateral phrenic afferents. Diaphragm amplitude ipsilateral and contralateral to stimulation were increased for 60 min following both currents compared to time controls not receiving stimulation. Diaphragm stimulation was repeated in laminectomy controls or following a unilateral C3-C6 dorsal rhizotomy to eliminate phrenic afferent volleys. Laminectomy controls expressed neuromuscular plasticity post-stimulation. In contrast, ipsilateral and contralateral diaphragm amplitude following dorsal rhizotomy was lower than laminectomy controls and no different than time controls, suggesting diaphragm motor plasticity was not induced post-rhizotomy. Our results indicate that diaphragm stimulation induces a novel form of plasticity in the phrenic motor system which requires phrenic afferent activation. Respiratory motor plasticity elicited by diaphragm stimulation may have value as a therapeutic strategy to improve diaphragm output in neuromuscular conditions.

Small-Molecule Inhibition of MuRF1 Prevents Early Disuse-Induced Diaphragmatic Dysfunction and Atrophy

In clinical conditions such as diaphragm paralysis or mechanical ventilation, disuse-induced diaphragmatic dysfunction (DIDD) is a condition that poses a threat to life. MuRF1 is a key E3-ligase involved in regulating skeletal muscle mass, function, and metabolism, which contributes to the onset of DIDD. We investigated if the small-molecule mediated inhibition of MuRF1 activity (MyoMed-205) protects against early DIDD after 12 h of unilateral diaphragm denervation. Wistar rats were used in this study to determine the compound's acute toxicity and optimal dosage. For potential DIDD treatment efficacy, diaphragm contractile function and fiber cross-sectional area (CSA) were evaluated. Western blotting investigated potential mechanisms underlying MyoMed-205's effects in early DIDD. Our results indicate 50 mg/kg bw MyoMed-205 as a suitable dosage to prevent early diaphragmatic contractile dysfunction and atrophy following 12 h of denervation without detectable signs of acute toxicity. Mechanistically, treatment did not affect disuse-induced oxidative stress (4-HNE) increase, whereas phosphorylation of (ser632) HDAC4 was normalized. MyoMed-205 also mitigated FoxO1 activation, inhibited MuRF2, and increased phospho (ser473) Akt protein levels. These findings may suggest that MuRF1 activity significantly contributes to early DIDD pathophysiology. Novel strategies targeting MuRF1 (e.g., MyoMed-205) have potential therapeutic applications for treating early DIDD.

Treatment with levosimendan in an experimental model of early ventilator-induced diaphragmatic dysfunction

Introduction

Mechanical ventilation (MV) is a life-saving approach in critically ill patients. However, it may affect the diaphragmatic structure and function, beyond the lungs. Levosimendan is a calcium sensitizer widely used in clinics to improve cardiac contractility in acute heart failure patients. In vitro studies have demonstrated that levosimendan increased force-generating capacity of the diaphragm in chronic obstructive pulmonary disease patients. Thus the aim of this study was to evaluate the effects of levosimendan administration in an animal model of ventilator-induced diaphragmatic dysfunction (VIDD) on muscle contraction and diaphragm muscle cell viability.

Methods

Sprague-Dawley rats underwent prolonged MV (5 hours). VIDD+Levo group received a starting bolus of levosimendan immediately after intratracheal intubation and then an intravenous infusion of levosimendan throughout the study. Diaphragms were collected for ex vivo contractility measurement (with electric stimulation), histological analysis and Western blot analysis. Healthy rats were used as the control.

Results

Levosimendan treatment maintained an adequate mean arterial pressure during the entire experimental protocol, preserved levels of autophagy-related proteins (LC3BI and LC3BII) and the muscular cell diameter demonstrated by histological analysis. Levosimendan did not affect the diaphragmatic contraction or the levels of proteins involved in the protein degradation (atrogin).

Conclusions

Our data suggest that levosimendan preserves muscular cell structure (cross-sectional area) and muscle autophagy after 5 hours of MV in a rat model of VIDD. However, levosimendan did not improve diaphragm contractile efficiency.

Intensive Care Unit Acquired Weakness Is Associated with Rapid Changes to Skeletal Muscle Proteostasis

Intensive care unit (ICU)-acquired weakness is a frequent consequence of critical illness that impacts both the limb and respiratory muscles. The cause of ICU-acquired weakness is multifactorial, but both prolonged limb muscle inactivity and mechanical ventilation are risk factors for muscle wasting, which predisposes ICU patients to both short-term complications and long-term disabilities resulting from muscle weakness. Unfortunately, the current research does not provide a detailed understanding of the cellular etiology of ICU-acquired weakness, and no standard treatment exists. Therefore, improving knowledge of the mechanisms promoting muscle atrophy in critically ill patients is essential to developing therapeutic strategies to protect against ICU-induced skeletal muscle wasting. To advance our understanding of the mechanism(s) responsible for ICU-acquired weakness, we tested the hypothesis that ICU-induced muscle inactivity promotes a rapid decrease in anabolic signaling/protein synthesis and accelerates proteolysis in both limb and respiratory muscles. To investigate ICU-induced changes in skeletal muscle proteostasis, adult Sprague Dawley rats were anesthetized and mechanically ventilated for 12 h to simulate ICU care. Measurements of anabolic signaling, protein synthesis, and proteolytic activity in the limb muscles (plantaris and soleus) and respiratory muscles (parasternal and intercostal) revealed ICU-induced reductions in both anabolic signaling (i.e., AKT/mTOR pathway) and muscle protein synthesis. Moreover, simulated ICU care resulted in increased biomarkers of accelerated proteolysis in both limb and respiratory muscles. These novel findings reveal that disturbances in limb and respiratory muscle proteostasis occur rapidly during ICU-induced muscle inactivity, irrespective of the muscle function or muscle fiber type.

The effects of external diaphragmatic pacing on diaphragm function and weaning outcomes of critically ill patients with mechanical ventilation: a prospective randomized study

BACKGROUND

Diaphragmatic pacing can improve diaphragm function, which is beneficial for the prognosis of patients treated with prolonged mechanical ventilation (MV). While most previous studies have focused on the role of implanted diaphragm pacing (IDP), our study is the first to examine the effects of external diaphragmatic pacing (EDP) in mechanically ventilated patients. Specifically, the effect of EDP on diaphragm function, the success rate of weaning, the duration of MV (DMV), and the intensive care unit (ICU) length of stay (ILOS) were assessed.

METHODS

From September 2019 to December 2020, a total of 51 mechanically ventilated patients in the ICU of the Sun Yat-sen Memorial Hospital, Sun Yat-sen University were enrolled and randomly divided into an EDP group of 27 patients and a control group of 24 patients. The control group received routine treatment, and the EDP group received EDP treatment in addition to routine treatment. The diaphragm excursion (DE), diaphragm thickening fraction (DTF), DMV, ILOS, and average survival time were recorded to evaluate efficacy.

RESULTS

Patients treated with EDP had increased DE [exp(B) =1.86, 95% CI: 1.39 to 2.50, P<0.001] and DTF [exp(B) =1.35, 95% CI: 1.05 to 1.76, P=0.022], shortened weaning time (P=0.026) and prolonged average survival time (P<0.001) compared to patients who did not receive EDP therapy. Especially in cases with difficult weaning, the improvement of DE and DTF in the EDP treatment group was more obvious than that in the control group (P=0.013 and P=0.032). Moreover, the DTF upon attempted spontaneous breathing trial (SBT) was negatively correlated with the fraction of inspired oxygen (FiO2) [r=-0.54; 95% confidence interval (CI): -0.77 to -0.19; P=0.004], the arterial partial pressure of oxygen (PaO2) (r=-0.58; 95% CI: -0.79 to -0.25; P=0.001), the PaO2/FiO2 ratio (r=-0.52; 95% CI: -0.75 to -0.16; P=0.006), and the serum lactate concentration (Lac) (r=-0.39; 95% CI: -0.68 to 0.003; P=0.046).

CONCLUSIONS

EDP treatment can effectively reduce the DMV and prolong the average survival time of mechanically ventilated patients.

TRIAL REGISTRATION

Chinese Clinical Trial Registry ChiCTR1900024096.

Identification of the co-differentially expressed hub genes involved in the endogenous protective mechanism against ventilator-induced diaphragm dysfunction

BACKGROUND

In intensive care units (ICU), mechanical ventilation (MV) is commonly applied to save patients' lives. However, ventilator-induced diaphragm dysfunction (VIDD) can complicate treatment by hindering weaning in critically ill patients and worsening outcomes. The goal of this study was to identify potential genes involved in the endogenous protective mechanism against VIDD.

METHODS

Twelve adult male rabbits were assigned to either an MV group or a control group under the same anesthetic conditions. Immunostaining and quantitative morphometry were used to assess diaphragm atrophy, while RNA-seq was used to investigate molecular differences between the groups. Additionally, core module and hub genes were analyzed using WGCNA, and co-differentially expressed hub genes were subsequently discovered by overlapping the differentially expressed genes (DEGs) with the hub genes from WGCNA. The identified genes were validated by western blotting (WB) and quantitative real-time polymerase chain reaction (qRT-PCR).

RESULTS

After a VIDD model was successfully built, 1276 DEGs were found between the MV and control groups. The turquoise and yellow modules were identified as the core modules, and Trim63, Fbxo32, Uchl1, Tmprss13, and Cst3 were identified as the five co-differentially expressed hub genes. After the two atrophy-related genes (Trim63 and Fbxo32) were excluded, the levels of the remaining three genes/proteins (Uchl1/UCHL1, Tmprss13/TMPRSS13, and Cst3/CST3) were found to be significantly elevated in the MV group (P < 0.05), suggesting the existence of a potential antiproteasomal, antiapoptotic, and antiautophagic mechanism against diaphragm dysfunction.

CONCLUSION

The current research helps to reveal a potentially important endogenous protective mechanism that could serve as a novel therapeutic target against VIDD.

A bibliometric and visualized analysis of early mobilization in intensive care unit from 2000 to 2021

Background

Early mobilization in the intensive care unit (ICU) is a hotspot. This study aims to provide a bibliometric perspective of the progress in this field.

Methods

We extracted publications on ICU early mobilization published in the Web of Science Core Collection database from 2000 to 2021. VOSviewer was used to construct co-occurrence and co-citation relationships for authors, references, and keywords; Citespace was used to visualize knowledge mapping of subject categories, countries, and keywords with the strongest citation bursts.

Results

A total of 4,570 publications were analyzed, with a steady increase in publications in the field of ICU early mobilization. From a macro perspective, research on ICU early mobilization involves multidisciplinary involvement, including critical care medicine, neurology, and nursing; as for the meso perspective, the United States is the major contributor. Needham DM and Schweickert WD are the key researchers in this field. Moreover, the core journal is Critical Care Medicine, with the most publications and citations. The microscopic level, dominated by references and keywords, illustrates that the hotspot and frontier of research on ICU early mobilization focus on ICU-acquired weakness, delirium, the prognosis of critical illness, and severe COVID-19.

Conclusion

This study presents a research landscape of ICU early mobilization from different perspectives. These findings will contribute to a better understanding of the current state of research in critical care medicine and provide the available information for future research ideas.

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.

Activation of Calpain Contributes to Mechanical Ventilation-Induced Depression of Protein Synthesis in Diaphragm Muscle

Mechanical ventilation (MV) is a clinical tool that provides respiratory support to patients unable to maintain adequate alveolar ventilation on their own. Although MV is often a life-saving intervention in critically ill patients, an undesired side-effect of prolonged MV is the rapid occurrence of diaphragmatic atrophy due to accelerated proteolysis and depressed protein synthesis. Investigations into the mechanism(s) responsible for MV-induced diaphragmatic atrophy reveal that activation of the calcium-activated protease, calpain, plays a key role in accelerating proteolysis in diaphragm muscle fibers. Moreover, active calpain has been reported to block signaling events that promote protein synthesis (i.e., inhibition of mammalian target of rapamycin (mTOR) activation). While this finding suggests that active calpain can depress muscle protein synthesis, this postulate has not been experimentally verified. Therefore, we tested the hypothesis that active calpain plays a key role in the MV-induced depression of both anabolic signaling events and protein synthesis in the diaphragm muscle. MV-induced activation of calpain in diaphragm muscle fibers was prevented by transgene overexpression of calpastatin, an endogenous inhibitor of calpain. Our findings indicate that overexpression of calpastatin averts MV-induced activation of calpain in diaphragm fibers and rescues the MV-induced depression of protein synthesis in the diaphragm muscle. Surprisingly, deterrence of calpain activation did not impede the MV-induced inhibition of key anabolic signaling events including mTOR activation. However, blockade of calpain activation prevented the calpain-induced cleavage of glutaminyl-tRNA synthetase in diaphragm fibers; this finding is potentially important because aminoacyl-tRNA synthetases play a central role in protein synthesis. Regardless of the mechanism(s) responsible for calpain’s depression of protein synthesis, these results provide the first evidence that active calpain plays an important role in promoting the MV-induced depression of protein synthesis within diaphragm fibers.

The phrenic neuromuscular system

The phrenic neuromuscular system consists of the phrenic motor nucleus in the mid-cervical spinal cord, the phrenic nerve, and the diaphragm muscle. This motor system helps sustain breathing throughout life, while also contributing to posture, coughing, swallowing, and speaking. The phrenic nerve contains primarily efferent phrenic axons and afferent axons from diaphragm sensory receptors but is also a conduit for autonomic fibers. On a breath-by-breath basis, rhythmic (inspiratory) depolarization of phrenic motoneurons occurs due to excitatory bulbospinal synaptic pathways. Further, a complex propriospinal network innervates phrenic motoneurons and may serve to coordinate postural, locomotor, and respiratory movements. The phrenic neuromuscular system is impacted in a wide range of neuromuscular diseases and injuries. Contemporary research is focused on understanding how neuromuscular plasticity occurs in the phrenic neuromuscular system and using this information to optimize treatments and rehabilitation strategies to improve breathing and related behaviors.

Different Tidal Volumes May Jeopardize Pulmonary Redox and Inflammatory Status in Healthy Rats Undergoing Mechanical Ventilation

Mechanical ventilation (MV) is essential for the treatment of critical patients since it may provide a desired gas exchange. However, MV itself can trigger ventilator-associated lung injury in patients. We hypothesized that the mechanisms of lung injury through redox imbalance might also be associated with pulmonary inflammatory status, which has not been so far described. We tested it by delivering different tidal volumes to normal lungs undergoing MV. Healthy Wistar rats were divided into spontaneously breathing animals (control group, CG), and rats were submitted to MV (controlled ventilation mode) with tidal volumes of 4 mL/kg (MVG4), 8 mL/kg (MVG8), or 12 mL/kg (MVG12), zero end-expiratory pressure (ZEEP), and normoxia (FiO₂ = 21%) for 1 hour. After ventilation and euthanasia, arterial blood, bronchoalveolar lavage fluid (BALF), and lungs were collected for subsequent analysis. MVG12 presented lower PaCO₂ and bicarbonate content in the arterial blood than CG, MVG4, and MVG8. Neutrophil influx in BALF and MPO activity in lung tissue homogenate were significantly higher in MVG12 than in CG. The levels of CCL5, TNF-α, IL-1, and IL-6 in lung tissue homogenate were higher in MVG12 than in CG and MVG4. In the lung parenchyma, the lipid peroxidation was more important in MVG12 than in CG, MVG4, and MVG8, while there was more protein oxidation in MVG12 than in CG and MVG4. The stereological analysis confirmed the histological pulmonary changes in MVG12. The association of controlled mode ventilation and high tidal volume, without PEEP and normoxia, impaired pulmonary histoarchitecture and triggered redox imbalance and lung inflammation in healthy adult rats.

Risk factors for prolonged intensive care unit stays in patients after cardiac surgery with cardiopulmonary bypass: A retrospective observational study

Objectives

Patients after cardiac surgery with cardiopulmonary bypass (CPB) require a stay in the ICU postoperatively. This study aimed to investigate the incidence of prolonged length of stay (LOS) in the ICU after cardiac surgery with CPB and identify associated risk factors.

Methods

The current investigation was an observational, retrospective study that included 395 ICU patients who underwent cardiac surgery with CPB at a tertiary hospital in Guangzhou from June 2015 to June 2017. Data were obtained from the hospital database. Binary logistic regression modeling was used to analyze risk factors for prolonged ICU LOS.

Results

Of 395 patients, 137 (34.7%) had a prolonged ICU LOS (>72.0 h), and the median ICU LOS was 50.9 h. Several variables were found associated with prolonged ICU LOS: duration of CPB, prolonged mechanical ventilation and non-invasive assisted ventilation use, PaO₂/FiO₂ ratios within 6 h after surgery, type of surgery, red blood cell infusion during surgery, postoperative atrial arrhythmia, postoperative ventricular arrhythmia (all P < 0.05).

Conclusions

These findings are clinically relevant for identifying patients with an estimated prolonged ICU LOS, enabling clinicians to facilitate earlier intervention to reduce the risk and prevent resulting delayed recovery.

Respiratory Training and Plasticity After Cervical Spinal Cord Injury

While spinal cord injuries (SCIs) result in a vast array of functional deficits, many of which are life threatening, the majority of SCIs are anatomically incomplete. Spared neural pathways contribute to functional and anatomical neuroplasticity that can occur spontaneously, or can be harnessed using rehabilitative, electrophysiological, or pharmacological strategies. With a focus on respiratory networks that are affected by cervical level SCI, the present review summarizes how non-invasive respiratory treatments can be used to harness this neuroplastic potential and enhance long-term recovery. Specific attention is given to "respiratory training" strategies currently used clinically (e.g., strength training) and those being developed through pre-clinical and early clinical testing [e.g., intermittent chemical stimulation via altering inhaled oxygen (hypoxia) or carbon dioxide stimulation]. Consideration is also given to the effect of training on non-respiratory (e.g., locomotor) networks. This review highlights advances in this area of pre-clinical and translational research, with insight into future directions for enhancing plasticity and improving functional outcomes after SCI.

Mitoquinone mesylate (MitoQ) prevents sepsis-induced diaphragm dysfunction

Sepsis-induced diaphragm dysfunction is a major contributor to respiratory failure in mechanically ventilated patients. There are no pharmacological treatments for this syndrome, but studies suggest that diaphragm weakness is linked to mitochondrial free radical generation. We hypothesized that administration of mitoquinone mesylate (MitoQ), a mitochondrially targeted free radical scavenger, would prevent sepsis-induced diaphragm dysfunction. We compared diaphragm function in 4 groups of male mice: 1) sham-operated controls treated with saline (0.3 mL ip), 2) sham-operated treated with MitoQ (3.5 mg/kg/day given intraperitoneally in saline), 3) cecal ligation puncture (CLP) mice treated with saline, and 4) CLP mice treated with MitoQ. Forty-eight hours after surgery, we assessed diaphragm force generation, myosin heavy chain content, state 3 mitochondrial oxygen consumption (OCR), and aconitase activity. We also determined effects of MitoQ in female mice with CLP sepsis and in mice with endotoxin-induced sepsis. CLP decreased diaphragm specific force generation and MitoQ prevented these decrements (e.g. maximal force averaged 30.2 ± 1.3, 28.0 ± 1.3, 12.8 ± 1.9, and 30.0 ± 1.0 N/cm² for sham, sham + MitoQ, CLP, and CLP + MitoQ groups, respectively, P < 0.001). CLP also reduced diaphragm mitochondrial OCR and aconitase activity; MitoQ blocked both effects. Similar responses were observed in female mice and in endotoxin-induced sepsis. Moreover, delayed MitoQ treatment (by 6 h) was as effective as immediate treatment. These data indicate that MitoQ prevents sepsis-induced diaphragm dysfunction, preserving force generation. MitoQ may be a useful therapeutic agent to preserve diaphragm function in critically ill patients with sepsis.NEW & NOTEWORTHY This is the first study to show that mitoquinone mesylate (MitoQ), a mitochondrially targeted antioxidant, treats sepsis-induced skeletal muscle dysfunction. This biopharmaceutical agent is without known side effects and is currently being used by healthy individuals and in clinical trials in patients with various diseases. When taken together, our results suggest that MitoQ has the potential to be immediately translated into treatment for sepsis-induced skeletal muscle dysfunction.

Diaphragm Pacing and a Model for Respiratory Rehabilitation After Spinal Cord Injury

BACKGROUND AND PURPOSE

Cervical spinal cord injury (CSCI) can cause severe respiratory impairment. Although mechanical ventilation (MV) is a lifesaving standard of care for these patients, it is associated with diaphragm atrophy and dysfunction. Diaphragm pacing (DP) is a strategy now used acutely to promote MV weaning and to combat the associated negative effects. Initial reports indicate that DP also may promote neuromuscular plasticity and lead to improvements in spontaneous diaphragm activation and respiratory function. These outcomes suggest the need for reevaluation of respiratory rehabilitation for patients with CSCI using DP and consideration of new rehabilitation models for these patients and their unique care needs.

SUMMARY OF KEY POINTS

This article discusses the rationale for consideration of DP as a rehabilitative strategy, particularly when used in combination with established respiratory interventions. In addition, a model of respiratory rehabilitation and recovery (RRR) is presented, providing a framework for rehabilitation and consideration of DP as an adjuvant rehabilitation approach. The model promotes goals such as respiratory recovery and independence, and lifelong respiratory health, via interdisciplinary care, respiratory training, quantitative measurement, and use of adjuvant strategies such as DP. Application of the model is demonstrated through a description of an inpatient rehabilitation program that applies model components to patients with CSCI who require DP.

RECOMMENDATIONS FOR CLINICAL PRACTICE

As DP use increases for patients with acute CSCI, so does the need and opportunity to advance rehabilitation approaches for these patients. This perspective article is a critical step in addressing this need and motivating the advancement of rehabilitation strategies for CSCI patients. (See Video Abstract, Supplemental Digital Content, available at: http://links.lww.com/JNPT/A348).

Non-intubated spontaneous ventilation in video-assisted thoracoscopic surgery: a meta-analysis

It remains unclear whether non-intubated video-assisted thoracoscopic surgery (VATS) is comparable or advantageous compared with conventional intubated VATS. Thus, we systematically assessed the feasibility and safety of non-intubated VATS compared with intubated VATS perioperatively for the treatment of different thoracic diseases. An extensive search of literature databases was conducted. Perioperative outcomes were compared between 2 types of operations. The time trend of the overall results was evaluated through a cumulative meta-analysis. Subgroup analyses of different thoracic diseases and study types were examined. Twenty-seven studies including 2537 patients were included in the analysis. A total of 1283 patients underwent non-intubated VATS; intubated VATS was performed on the other 1254 patients. Overall, the non-intubated VATS group had fewer postoperative overall complications [odds ratios (OR) 0.505; P < 0.001]; shorter postoperative fasting times [standardized mean difference (SMD) -2.653; P < 0.001]; shorter hospital stays (SMD -0.581; P < 0.001); shorter operative times (SMD -0.174; P = 0.041); shorter anaesthesia times (SMD -0.710; P < 0.001) and a lower mortality rate (OR 0.123; P = 0.020). Non-intubated VATS may be a safe and feasible alternative to intubated VATS and provide a more rapid postoperative rehabilitation time than conventional intubated VATS.

Hydrogen sulfide donor protects against mechanical ventilation-induced atrophy and contractile dysfunction in the rat diaphragm

Mechanical ventilation (MV) is a clinical tool providing adequate alveolar ventilation in patients that require respiratory support. Although a life-saving intervention for critically ill patients, prolonged MV results in the rapid development of inspiratory muscle weakness due to both diaphragmatic atrophy and contractile dysfunction; collectively known as "ventilator-induced diaphragm dysfunction" (VIDD). VIDD is a severe clinical problem because diaphragmatic weakness is a risk factor for difficulties in weaning patients from MV. Currently, no standard treatment to prevent VIDD exists. Nonetheless, growing evidence reveals that hydrogen sulfide (H₂ S) possesses cytoprotective properties capable of protecting skeletal muscles against several hallmarks of VIDD, including oxidative damage, accelerated proteolysis, and mitochondrial damage. Therefore, we used an established animal model of MV to test the hypothesis that treatment with sodium sulfide (H₂ S donor) will defend against VIDD. Our results confirm that sodium sulfide was sufficient to protect the diaphragm against both MV-induced fiber atrophy and contractile dysfunction. H₂ S prevents MV-induced damage to diaphragmatic mitochondria as evidenced by protection against mitochondrial uncoupling. Moreover, treatment with sodium sulfide prevented the MV-induced activation of the proteases, calpain, and caspase-3 in the diaphragm. Taken together, these results support the hypothesis that treatment with a H₂ S donor protects the diaphragm against VIDD. These outcomes provide the first evidence that H₂ S has therapeutic potential to protect against MV-induced diaphragm weakness and to reduce difficulties in weaning patients from the ventilator. Study Highlights WHAT IS THE CURRENT KNOWLEDGE ON THE TOPIC? Mechanical ventilation (MV) results in diaphragm atrophy and contractile dysfunction, known as ventilator-induced diaphragm dysfunction (VIDD). VIDD is important because diaphragm weakness is a risk factor for problems in weaning patients from MV. Currently, no accepted treatment exists to protect against VIDD. Growing evidence reveals that hydrogen sulfide (H₂ S) donors protect skeletal muscle against ischemia-reperfusion-induced injury. Nonetheless, it is unknown if treatment with a H₂ S donor can protect against VIDD. WHAT QUESTION DID THIS STUDY ADDRESS? Can treatment with an H₂ S donor protect against VIDD? WHAT DOES THIS STUDY ADD TO OUR KNOWLEDGE? This study provides the first evidence that treatment with a H₂ S donor protects against VIDD. HOW MIGHT THIS CHANGE CLINICAL PHARMACOLOGY OR TRANSLATIONAL SCIENCE? These new findings provide the basis for further exploration of H₂ S donors as a therapy to prevent VIDD and reduce the risk of problems in weaning patients from MV.

Late Ventilator-Induced Diaphragmatic Dysfunction After Extubation

OBJECTIVES

Mechanical ventilation is associated with primary diaphragmatic dysfunction, also termed ventilator-induced diaphragmatic dysfunction. Studies evaluating diaphragmatic function recovery after extubation are lacking. We evaluated early and late recoveries from ventilator-induced diaphragmatic dysfunction in a mouse model.

DESIGN

Experimental randomized study.

SETTING

Research laboratory.

SUBJECTS

C57/BL6 mice.

INTERVENTIONS

Six groups of C57/BL6 mice. Mice were ventilated for 6 hours and then euthanatized immediately (n = 18), or 1 (n = 18) or 10 days after extubation with (n = 5) and without S107 (n = 16) treatment. Mice euthanatized immediately after 6 hours of anesthesia (n = 15) or after 6 hours of anesthesia and 10 days of recovery (n = 5) served as controls.

MEASUREMENTS AND MAIN RESULTS

For each group, diaphragm force production, posttranslational modification of ryanodine receptor, oxidative stress, proteolysis, and cross-sectional areas were evaluated. After 6 hours of mechanical ventilation, diaphragm force production was decreased by 25-30%, restored to the control levels 1 day after extubation, and secondarily decreased by 20% 10 days after extubation compared with controls. Ryanodine receptor was protein kinase A-hyperphosphorylated, S-nitrosylated, oxidized, and depleted of its stabilizing subunit calstabin-1 6 hours after the onset of the mechanical ventilation, 1 and 10 days after extubation. Post extubation treatment with S107, a Rycal drug that stabilizes the ryanodine complex, did reverse the loss of diaphragmatic force associated with mechanical ventilation. Total protein oxidation was restored to the control levels 1 day after extubation. Markers of proteolysis including calpain 1 and calpain 2 remained activated 10 days after extubation without significant changes in cross-sectional areas.

CONCLUSIONS

We report that mechanical ventilation is associated with a late diaphragmatic dysfunction related to a structural alteration of the ryanodine complex that is reversed with the S107 treatment.

Angiotensin 1-7 protects against ventilator-induced diaphragm dysfunction

Mechanical ventilation (MV) is a life‐saving instrument used to provide ventilatory support for critically ill patients and patients undergoing surgery. Unfortunately, an unintended consequence of prolonged MV is the development of inspiratory weakness due to both diaphragmatic atrophy and contractile dysfunction; this syndrome is labeled ventilator‐induced diaphragm dysfunction (VIDD). VIDD is clinically important because diaphragmatic weakness is an important contributor to problems in weaning patients from MV. Investigations into the pathogenesis of VIDD reveal that oxidative stress is essential for the rapid development of VIDD as redox disturbances in diaphragm fibers promote accelerated proteolysis. Currently, no standard treatment exists to prevent VIDD and, therefore, developing a strategy to avert VIDD is vital. Guided by evidence indicating that activation of the classical axis of the renin‐angiotensin system (RAS) in diaphragm fibers promotes oxidative stress and VIDD, we hypothesized that activation of the nonclassical RAS signaling pathway via angiotensin 1‐7 (Ang1‐7) will protect against VIDD. Using an established animal model of prolonged MV, our results disclose that infusion of Ang1‐7 protects the diaphragm against MV‐induced contractile dysfunction and fiber atrophy in both fast and slow muscle fibers. Further, Ang1‐7 shielded diaphragm fibers against MV‐induced mitochondrial damage, oxidative stress, and protease activation. Collectively, these results reveal that treatment with Ang1‐7 protects against VIDD, in part, due to diminishing oxidative stress and protease activation. These important findings provide robust evidence that Ang1‐7 has the therapeutic potential to protect against VIDD by preventing MV‐induced contractile dysfunction and atrophy of both slow and fast muscle fibers.

Developing new drugs that activate the protective arm of the renin-angiotensin system as a potential treatment for respiratory failure in COVID-19 patients

COVID-19, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has reached pandemic proportions with negative impacts on global health, the world economy and human society. The clinical picture of COVID-19, and the fact that Angiotensin converting enzyme 2 (ACE2) is a receptor of SARS-CoV-2, suggests that SARS-CoV-2 infection induces an imbalance in the renin–angiotensin system (RAS). We review clinical strategies that are attempting to rebalance the RAS in COVID-19 patients by using ACE inhibitors, angiotensin receptor blockers, or agonists of angiotensin-II receptor type 2 or Mas receptor (MasR). We also propose that the new MasR activator BIO101, a pharmaceutical grade formulation of 20-hydroxyecdysone that has anti-inflammatory, anti-fibrotic and cardioprotective properties, could restore RAS balance and improve the health of COVID-19 patients who have severe pneumonia.

Sonographic evaluation of diaphragmatic thickness and excursion as a predictor for successful extubation in mechanically ventilated preterm infants

Sonographic assessment of diaphragmatic thickness and excursion has been found to be an accurate tool in predicting successful extubation of adult patients from invasive mechanical ventilation. We aimed to evaluate the accuracy of sonographic assessment of diaphragmatic thickness and excursion in predicting successful extubation of preterm infants from invasive conventional mechanical ventilation. Preterm infants less than 32 weeks gestation who required invasive conventional mechanical ventilation were evaluated by diaphragmatic sonography within 1 h of their planned extubation. Infants were classified into successful or failed extubation groups based on their ability to stay off invasive mechanical ventilation for 72 h after extubation. Inspiratory and expiratory thickness plus excursion of the right and left hemidiaphragm as well as diaphragmatic thickening fraction (DTF) measures were compared between groups. We included 43 eligible infants, of whom 34 infants succeeded and 9 infants failed extubation. Infants in the successful extubation group had a significantly higher expiratory thickness of the right and left hemidiaphragm, excursion of the right and left hemidiaphragm, inspiratory thickness of the left hemidiaphragm, and DTF of the left hemidiaphragm compared with infants who failed extubation. The receiver-operating characteristic curves showed that excursion of the right and left hemidiaphragm has the highest significant accuracy in predicting successful extubation of preterm infants among all diaphragmatic parameters (AUC is 0.98 and 0.96, respectively; p value < 0.001 for both).Conclusion: We conclude that diaphragmatic excursion is a useful indicator for successful extubation of preterm infants from mechanical ventilation. What is Known: • Invasive mechanical ventilation induces ventilator induced diaphragmatic dysfunction (VIDD) particularly when used for long time. • Assessment of diaphragmatic dimensions and functional activity has been a valuable tool in predicting successful extubation of adult patients from invasive mechanical ventilation. What is New: • Sonographic assessment of diaphragmatic dimensions can be used to predict successful extubation of preterm infants from mechanical ventilation. • Sonographic assessment of diaphragmatic excursion shows the highest sensitivity and specificity in predicting successful extubation of preterm infants.

Disturbances in Calcium Homeostasis Promotes Skeletal Muscle Atrophy: Lessons From Ventilator-Induced Diaphragm Wasting

Mechanical ventilation (MV) is often a life-saving intervention for patients in respiratory failure. Unfortunately, a common and undesired consequence of prolonged MV is the development of diaphragmatic atrophy and contractile dysfunction. This MV-induced diaphragmatic weakness is commonly labeled “ventilator-induced diaphragm dysfunction” (VIDD). VIDD is an important clinical problem because diaphragmatic weakness is a major risk factor for the failure to wean patients from MV; this inability to remove patients from ventilator support results in prolonged hospitalization and increased morbidity and mortality. Although several processes contribute to the development of VIDD, it is clear that oxidative stress leading to the rapid activation of proteases is a primary contributor. While all major proteolytic systems likely contribute to VIDD, emerging evidence reveals that activation of the calcium-activated protease calpain plays a required role. This review highlights the signaling pathways leading to VIDD with a focus on the cellular events that promote increased cytosolic calcium levels and the subsequent activation of calpain within diaphragm muscle fibers. In particular, we discuss the emerging evidence that increased mitochondrial production of reactive oxygen species promotes oxidation of the ryanodine receptor/calcium release channel, resulting in calcium release from the sarcoplasmic reticulum, accelerated proteolysis, and VIDD. We conclude with a discussion of important and unanswered questions associated with disturbances in calcium homeostasis in diaphragm muscle fibers during prolonged MV.

Comparative Efficacy of Angiotensin II Type 1 Receptor Blockers Against Ventilator-Induced Diaphragm Dysfunction in Rats

Mechanical ventilation (MV) is a life‐saving intervention for many critically ill patients. Unfortunately, prolonged MV results in the rapid development of inspiratory muscle weakness due to diaphragmatic atrophy and contractile dysfunction (termed ventilator‐induced diaphragm dysfunction (VIDD)). Although VIDD is a major risk factor for problems in weaning patients from MV, a standard therapy to prevent VIDD does not exist. However, emerging evidence suggests that pharmacological blockade of angiotensin II type 1 receptors (AT1Rs) protects against VIDD. Nonetheless, the essential characteristics of AT1R blockers (ARBs) required to protect against VIDD remain unclear. To determine the traits of ARBs that are vital for protection against VIDD, we compared the efficacy of two clinically relevant ARBs, irbesartan and olmesartan; these ARBs differ in molecular structure and effects on AT1Rs. Specifically, olmesartan blocks both angiotensin II (AngII) binding and mechanical activation of AT1Rs, whereas irbesartan prevents only AngII binding to AT1Rs. Using a well‐established preclinical model of prolonged MV, we tested the hypothesis that compared with irbesartan, olmesartan provides greater protection against VIDD. Our results reveal that irbesartan does not protect against VIDD whereas olmesartan defends against both MV‐induced diaphragmatic atrophy and contractile dysfunction. These findings support the hypothesis that olmesartan is superior to irbesartan in protecting against VIDD and are consistent with the concept that blockade of mechanical activation of AT1Rs is a required property of ARBs to shield against VIDD. These important findings provide a foundation for future clinical trials to evaluate ARBs as a therapy to protect against VIDD.

The effects of different ventilatory modes in female adult rats submitted to mechanical ventilation

This study aimed to analyze the effects of volume-controlled ventilation (VCV) and pressure-controlled ventilation (PCV) modes in female Wistar rats. 18 Wistar female adult rats were divided into three groups: control (CG), pressure-controlled ventilation (PCVG), and volume-controlled ventilation (VCVG). PCVG and VCVG were submitted to MV for one hour with a tidal volume (TV) of 8 mL/Kg, respiratory rate of 80 breaths/min, and positive end-expiratory pressure of 0 cmH₂O. At the end of the experiment, all animals were euthanized. The neutrophils and lymphocytes influx to lung were higher in VCVG and PCVG compared to CG. The activities of superoxide dismutase, catalase and myeloperoxidase were higher in PCVG compared to CG. There was an increase in lipid peroxidation and protein oxidation in PCVG compared to CG. The levels of CCL3 and CCL5 were higher in PCVG compared to CG. In conclusions, the PCV mode promoted structural changes in the lung parenchyma, redox imbalance and inflammation in healthy adult female rats submitted to MV.

SARS-CoV-2/Renin-Angiotensin System: Deciphering the Clues for a Couple with Potentially Harmful Effects on Skeletal Muscle

Severe acute respiratory syndrome coronavirus (SARS-CoV-2) has produced significant health emergencies worldwide, resulting in the declaration by the World Health Organization of the coronavirus disease 2019 (COVID-19) pandemic. Acute respiratory syndrome seems to be the most common manifestation of COVID-19. A high proportion of patients require intensive care unit admission and mechanical ventilation (MV) to survive. It has been well established that angiotensin-converting enzyme type 2 (ACE2) is the primary cellular receptor for SARS-CoV-2. ACE2 belongs to the renin–angiotensin system (RAS), composed of several peptides, such as angiotensin II (Ang II) and angiotensin (1-7) (Ang-(1-7)). Both peptides regulate muscle mass and function. It has been described that SARS-CoV-2 infection, by direct and indirect mechanisms, affects a broad range of organ systems. In the skeletal muscle, through unbalanced RAS activity, SARS-CoV-2 could induce severe consequences such as loss of muscle mass, strength, and physical function, which will delay and interfere with the recovery process of patients with COVID-19. This article discusses the relationship between RAS, SARS-CoV-2, skeletal muscle, and the potentially harmful consequences for skeletal muscle in patients currently infected with and recovering from COVID-19.

Redox Control of Proteolysis During Inactivity-Induced Skeletal Muscle Atrophy

Significance: Skeletal muscles play essential roles in key body functions including breathing, locomotion, and glucose homeostasis; therefore, maintaining healthy skeletal muscles is important. Prolonged periods of muscle inactivity (e.g., bed rest, mechanical ventilation, or limb immobilization) result in skeletal muscle atrophy and weakness. Recent Advances: Disuse skeletal muscle atrophy occurs due to both accelerated proteolysis and decreased protein synthesis with proteolysis playing a leading role in some types of inactivity-induced atrophy. Although all major proteolytic systems are involved in inactivity-induced proteolysis in skeletal muscles, growing evidence indicates that both calpain and autophagy play an important role. Regulation of proteolysis in skeletal muscle is under complex control, but it is established that activation of both calpain and autophagy is directly linked to oxidative stress. Critical Issues: In this review, we highlight the experimental evidence that supports a cause and effect link between reactive oxygen species (ROS) and activation of both calpain and autophagy in skeletal muscle fibers during prolonged inactivity. We also review the sources of oxidant production in muscle fibers during inactivity-induced atrophy, and provide a detailed discussion on how ROS activates both calpain and autophagy during disuse muscle wasting. Future Directions: Future studies are required to delineate the specific mechanisms by which ROS activates both calpain and autophagy in skeletal muscles during prolonged periods of contractile inactivity. This knowledge is essential to develop the most effective strategies to protect against disuse muscle atrophy. Antioxid. Redox Signal. 33, 559-569.

Ultrasonographic assessment of parasternal intercostal muscles during mechanical ventilation

Although mechanical ventilation is a lifesaving treatment, abundant evidence indicates that its prolonged use (1 week or more) promotes respiratory muscle weakness due to both contractile dysfunction and atrophy. Along with the diaphragm, the intercostal muscles are one of the most important groups of respiratory muscles. In recent years, muscular ultrasound has become a useful bedside tool for the clinician to identify patients with respiratory muscle dysfunction related to critical illness and/or invasive mechanical ventilation. Images obtained over the course of illness can document changes in muscle dimension and can be used to estimate changes in function. Recent evidence suggests the clinical usefulness of ultrasound imaging in the assessment of intercostal muscle function. In this narrative review, we summarize the current literature on ultrasound imaging of the parasternal intercostal muscles as used to assess the extent of muscle activation and muscle weakness and its potential impact during discontinuation of mechanical ventilation. In addition, we proposed a practical flowchart based on recent evidence and experience of our group that can be applied during the weaning phase. This approach integrates multiple predictive parameters of weaning success with respiratory muscle ultrasound.

A prospective observational study on critically ill children with diaphragmatic dysfunction: clinical outcomes and risk factors

Background

Diaphragmatic dysfunction (DD) has a great negative impact on clinical outcomes, and it is a well-recognized complication in adult patients with critical illness. However, DD is largely unexplored in the critically ill pediatric population. The aim of this study was to identify risk factors associated with DD, and to investigate the effects of DD on clinical outcomes among critically ill children.

Methods

Diaphragmatic function was assessed by diaphragm ultrasound. According to the result of diaphragmatic ultrasound, all enrolled subjects were categorized into the DD group (n = 24) and the non-DD group (n = 46). Collection of sample characteristics in both groups include age, sex, height, weight, primary diagnosis, complications, laboratory findings, medications, ventilatory time and clinical outcomes.

Results

The incidence of DD in this PICU was 34.3%. The level of CRP at discharge (P = 0.003) in the DD group was higher than the non-DD group, and duration of elevated C-reactive protein (CRP) (P < 0.001), sedative days (P = 0.008) and ventilatory treatment time (P < 0.001) in the DD group was significantly longer than the non-DD group. Ventilatory treatment time and duration of elevated CRP were independently risk factors associated with DD. Patients in the DD group had longer PICU length of stay, higher rate of weaning or extubation failure and higher mortality.

Conclusion

DD is associated with poorer clinical outcomes in critically ill childern, which include a longer PICU length of stay, higher rate of weaning or extubation failure and a higher mortality. The ventilatory treatment time and duration of elevated CRP are main risk factors of DD in critically ill children.

Trial registration

Current Controlled Trials ChiCTR1800020196, Registered 01 Dec 2018.

Difference in electromyographic activity between the trapezius muscle and other neck accessory muscles under an increase in inspiratory resistive loading in the supine position

The activity of the trapezius muscle is reportedly higher than that of other neck accessory muscles under a condition of increased inspiratory pressure in the standing position. The present study aimed to compare the activity of the trapezius muscle with those of the scalene and sternocleidomastoid muscles under a condition of increased inspiratory pressure in the supine position. This study included 40 subjects, and the muscle activity was measured using surface electromyography. Regarding the results, there was a significant difference in the muscle activity between the trapezius muscle and the scalene and sternocleidomastoid muscles (p = 0.003) in both men and women. Post-hoc analysis showed significant differences between trapezius and the other muscles. Moreover, there was no difference between the scalene and sternocleidomastoid muscles (p = 0.596). The increase in the change in electromyography activity of the muscle is greater in the trapezius muscle than in other muscles when the level of inspiratory pressure increases in the supine position.

Human and Rodent Skeletal Muscles Express Angiotensin II Type 1 Receptors

Abundant evidence reveals that activation of the renin-angiotensin system promotes skeletal muscle atrophy in several conditions including congestive heart failure, chronic kidney disease, and prolonged mechanical ventilation. However, controversy exists about whether circulating angiotensin II (AngII) promotes skeletal muscle atrophy by direct or indirect effects; the centerpiece of this debate is the issue of whether skeletal muscle fibers express AngII type 1 receptors (AT1Rs). While some investigators assert that skeletal muscle expresses AT1Rs, others argue that skeletal muscle fibers do not contain AT1Rs. These discordant findings in the literature are likely the result of study design flaws and additional research using a rigorous experimental approach is required to resolve this issue. We tested the hypothesis that AT1Rs are expressed in both human and rat skeletal muscle fibers. Our premise was tested using a rigorous, multi-technique experimental design. First, we established both the location and abundance of AT1Rs on human and rat skeletal muscle fibers by means of an AngII ligand-binding assay. Second, using a new and highly selective AT1R antibody, we carried out Western blotting and determined the abundance of AT1R protein within isolated single muscle fibers from humans and rats. Finally, we confirmed the presence of AT1R mRNA in isolated single muscle fibers from rats. Our results support the hypothesis that AT1Rs are present in both human and rat skeletal muscle fibers. Moreover, our experiments provide the first evidence that AT1Rs are more abundant in fast, type II muscle fibers as compared with slow, type I fibers. Together, these discoveries provide the foundation for an improved understanding of the mechanism(s) responsible for AngII-induced skeletal muscle atrophy.

Sigh maneuver protects healthy lungs during mechanical ventilation in adult Wistar rats

Mechanical ventilation (MV) is a tool used for the treatment of patients with acute or chronic respiratory failure. However, MV is a non-physiological resource, and it can cause metabolic disorders such as release of pro-inflammatory cytokines and production of reactive oxygen species. In clinical setting, maneuvers such as sigh, are used to protect the lungs. Thus, this study aimed to evaluate the effects of sigh on oxidative stress and lung inflammation in healthy adult Wistar rats submitted to MV. Male Wistar rats were divided into four groups: control (CG), mechanical ventilation (MVG), MV set at 20 sighs/h (MVG20), and MV set at 40 sighs/h (MVG40). The MVG, MVG20, and MVG40 were submitted to MV for 1 h. After the protocol, all animals were euthanized and the blood, bronchoalveolar lavage fluid, and lungs were collected for subsequent analysis. In the arterial blood, MVG40 presented higher partial pressure of oxygen and lower partial pressure of carbon dioxide compared to control. The levels of bicarbonate in MVG20 were lower compared to CG. The neutrophil influx in bronchoalveolar lavage fluid was higher in the MVG compared to CG and MVG40. In the lung parenchyma, the lipid peroxidation was higher in MVG compared to CG, MVG20, and MVG40. Superoxide dismutase and catalase activity were higher in MVG compared to CG, MVG20, and MVG40. The levels of IL-1, IL-6, and TNF in the lung homogenate were higher in MVG compared to CG, MVG20, and MVG40. The use of sigh plays a protective role as it reduced redox imbalance and pulmonary inflammation caused by MV.

Physical Activity Intolerance and Cardiorespiratory Dysfunction in Patients with Moderate-to-Severe Traumatic Brain Injury

Moderate-to-severe traumatic brain injury (TBI) is a chronic health condition with multi-systemic effects. Survivors face significant long-term functional limitations, including physical activity intolerance and disordered sleep. Persistent cardiorespiratory dysfunction is a potentially modifiable yet often overlooked major contributor to the alarmingly high long-term morbidity and mortality rates in these patients. This narrative review was developed through systematic and non-systematic searches for research relating cardiorespiratory function to moderate-to-severe TBI. The literature reveals patients who have survived moderate-to-severe TBI have ~ 25-35% reduction in maximal aerobic capacity 6-18 months post-injury, resting pulmonary capacity parameters that are reduced 25-40% for weeks to years post-injury, increased sedentary behavior, and elevated risk of cardiorespiratory-related morbidity and mortality. Synthesis of data from other patient populations reveals that cardiorespiratory dysfunction is likely a consequence of ventilator-induced diaphragmatic dysfunction (VIDD), which is not currently addressed in TBI management. Thus, cardiopulmonary exercise testing should be routinely performed in this patient population and those with cardiorespiratory deficits should be further evaluated for diaphragmatic dysfunction. Lack of targeted treatment for underlying cardiorespiratory dysfunction, including VIDD, likely contributes to physical activity intolerance and poor functional outcomes in these patients. Interventional studies have demonstrated that short-term exercise training programs are effective in patients with moderate-to-severe TBI, though improvement is variable. Inspiratory muscle training is beneficial in other patient populations with diaphragmatic dysfunction, and may be valuable for patients with TBI who have been mechanically ventilated. Thus, clinicians with expertise in cardiorespiratory fitness assessment and exercise training interventions should be included in patient management for individuals with moderate-to-severe TBI.

Temporary Transvenous Diaphragmatic Neurostimulation in Prolonged Mechanically Ventilated Patients: A Feasibility Trial (RESCUE 1)

Prolonged mechanical ventilation promotes diaphragmatic atrophy and weaning difficulty. The study uses a novel device containing a transvenous phrenic nerve stimulating catheter (Lungpacer IntraVenous Electrode Catheter) to stimulate the diaphragm in ventilated patients. We set out to determine the feasibility of temporary transvenous diaphragmatic neurostimulation using this device.

DESIGN

Multicenter, prospective open-label single group feasibility study.

SETTING

ICUs of tertiary care hospitals.

PATIENTS

Adults on mechanical ventilation for greater than or equal to 7 days that had failed two weaning trials.

INTERVENTIONS

Stimulation catheter insertion and transvenous diaphragmatic neurostimulation therapy up to tid, along with standard of care.

MEASUREMENTS AND MAIN RESULTS

Primary outcomes were successful insertion and removal of the catheter and safe application of transvenous diaphragmatic neurostimulation. Change in maximal inspiratory pressure and rapid shallow breathing index were also evaluated. Eleven patients met all entry criteria with a mean mechanical ventilation duration of 19.7 days; nine underwent successful catheter insertion. All nine had successful mapping of one or both phrenic nerves, demonstrated diaphragmatic contractions during therapy, and underwent successful catheter removal. Seven of nine met successful weaning criteria. Mean maximal inspiratory pressure increased by 105% in those successfully weaned (mean change 19.7 ± 17.9 cm H2O; p = 0.03), while mean rapid shallow breathing index improved by 44% (mean change -63.5 ± 64.4; p = 0.04).

CONCLUSIONS

The transvenous diaphragmatic neurostimulation system is a feasible and safe therapy to stimulate the phrenic nerves and induce diaphragmatic contractions. Randomized clinical trials are underway to compare it to standard-of-care therapy for mechanical ventilation weaning.

SS31, a mitochondrially targeted antioxidant, prevents sepsis-induced reductions in diaphragm strength and endurance

Sepsis-induced diaphragm dysfunction contributes to respiratory failure and mortality in critical illness. There are no treatments for this form of diaphragm weakness. Studies show that sepsis-induced muscle dysfunction is triggered by enhanced mitochondrial free radical generation. We tested the hypothesis that SS31, a mitochondrially targeted antioxidant, would attenuate sepsis-induced diaphragm dysfunction. Four groups of mice were studied: 1) sham-operated controls, 2) sham-operated+SS31 (10 mg·kg-1·day-1), 3) cecal ligation puncture (CLP), and 4) CLP+SS31. Forty-eight hours postoperatively, diaphragm strips with attached phrenic nerves were isolated, and the following were assessed: muscle-field-stimulated force-frequency curves, nerve-stimulated force-frequency curves, and muscle fatigue. We also measured calpain activity, 20S proteasomal activity, myosin heavy chain (MHC) levels, mitochondrial function, and aconitase activity, an index of mitochondrial superoxide generation. Sepsis markedly reduced diaphragm force generation; SS31 prevented these decrements. Diaphragm-specific force generation averaged 30.2 ± 1.4, 9.4 ± 1.8, 25.5 ± 2.3, and 27.9 ± 0.6 N/cm2 for sham, CLP, sham+SS31, and CLP+SS31 groups (P < 0.001). Similarly, with phrenic nerve stimulation, CLP depressed diaphragm force generation, effects prevented by SS31. During endurance trials, force was significantly reduced with CLP, and SS31 prevented these reductions (P < 0.001). Sepsis also increased diaphragm calpain activity, increased 20S proteasomal activity, decreased MHC levels, reduced mitochondrial function (state 3 rates and ATP generation), and reduced aconitase activity; SS31 prevented each of these sepsis-induced alterations (P ≤ 0.017 for all indices). SS31 prevents sepsis-induced diaphragm dysfunction, preserving force generation, endurance, and mitochondrial function. Compounds with similar mechanisms of action may be useful therapeutically to preserve diaphragm function in patients who are septic and critically ill.NEW & NOTEWORTHY Sepsis-induced diaphragm dysfunction is a major contributor to mortality and morbidity in patients with critical illness in intensive care units. Currently, there is no proven pharmacological treatment for this problem. This study provides the novel finding that administration of SS31, a mitochondrially targeted antioxidant, preserves diaphragm myosin heavy chain content and mitochondrial function, thereby preventing diaphragm weakness and fatigue in sepsis.

Oxidants Regulated Diaphragm Proteolysis during Mechanical Ventilation in Rats

WHAT WE ALREADY KNOW ABOUT THIS TOPIC

Diaphragm dysfunction and atrophy develop during controlled mechanical ventilation. Although oxidative stress injures muscle during controlled mechanical ventilation, it is unclear whether it causes autophagy or fiber atrophy.

WHAT THIS ARTICLE TELLS US THAT IS NEW

Pretreatment of rats undergoing 24 h of mechanical ventilation with N-acetylcysteine prevents decreases in diaphragm contractility, inhibits the autophagy and proteasome pathways, but has no influence on the development of diaphragm fiber atrophy.

BACKGROUND

Diaphragm dysfunction and atrophy develop during prolonged controlled mechanical ventilation. Fiber atrophy has been attributed to activation of the proteasome and autophagy proteolytic pathways. Oxidative stress activates the proteasome during controlled mechanical ventilation, but it is unclear whether it also activates autophagy. This study investigated whether pretreatment with the antioxidant N-acetylcysteine affects controlled mechanical ventilation-induced diaphragm contractile dysfunction, fiber atrophy, and proteasomal and autophagic pathway activation. The study also explored whether proteolytic pathway activity during controlled mechanical ventilation is mediated by microRNAs that negatively regulate ubiquitin E3 ligases and autophagy-related genes.

METHODS

Three groups of adult male rats were studied (n = 10 per group). The animals in the first group were anesthetized and allowed to spontaneously breathe. Animals in the second group were pretreated with saline before undergoing controlled mechanical ventilation for 24 h. The animals in the third group were pretreated with N-acetylcysteine (150 mg/kg) before undergoing controlled mechanical ventilation for 24 h. Diaphragm contractility and activation of the proteasome and autophagy pathways were measured. Expressions of microRNAs that negatively regulate ubiquitin E3 ligases and autophagy-related genes were measured with quantitative polymerase chain reaction.

RESULTS

Controlled mechanical ventilation decreased diaphragm twitch force from 428 ± 104 g/cm (mean ± SD) to 313 ± 50 g/cm and tetanic force from 2,491 ± 411 g/cm to 1,618 ± 177 g/cm. Controlled mechanical ventilation also decreased diaphragm fiber size, increased expression of several autophagy genes, and augmented Atrogin-1, MuRF1, and Nedd4 expressions by 36-, 41-, and 8-fold, respectively. Controlled mechanical ventilation decreased the expressions of six microRNAs (miR-20a, miR-106b, miR-376, miR-101a, miR-204, and miR-93) that regulate autophagy genes. Pretreatment with N-acetylcysteine prevented diaphragm contractile dysfunction, attenuated protein ubiquitination, and downregulated E3 ligase and autophagy gene expression. It also reversed controlled mechanical ventilation-induced microRNA expression decreases. N-Acetylcysteine pretreatment had no affect on fiber atrophy.

CONCLUSIONS

Prolonged controlled mechanical ventilation activates the proteasome and autophagy pathways in the diaphragm through oxidative stress. Pathway activation is accomplished, in part, through inhibition of microRNAs that negatively regulate autophagy-related genes.

Lung-protective ventilation worsens ventilator-induced diaphragm atrophy and weakness

Background

Lung–protective ventilation (LPV) has been found to minimize the risk of ventilator–induced lung injury (VILI). However, whether LPV is able to diminish ventilator–induced diaphragm dysfunction (VIDD) remains unknown. This study was designed to test the hypothesis that LPV protects the diaphragm against VIDD.

Methods

Adult male Wistar rats received either conventional mechanical (tidal volume [V_T]: 10 ml/kg, positive end–expiratory pressure [PEEP]: 2 cm H₂O; CV group) or lung-protective (V_T: 5 ml/kg, PEEP: 10 cm H₂O; LPV group) ventilation for 12 h. Then, diaphragms and lungs were collected for biochemical and histological analyses. Transcriptome sequencing (RNA–seq) was performed to determine the differentially expressed genes in the diaphragms between groups.

Results

Our results suggested that LPV was associated with diminished pulmonary injuries and reduced oxidative stress compared with the effects of the CV strategy in rats. However, animals that received LPV showed increased protein degradation, decreased cross–sectional areas (CSAs) of myofibers, and reduced forces of the diaphragm compared with the same parameters in animals receiving CV (p < 0.05). In addition, the LPV group showed a higher level of oxidative stress in the diaphragm than the CV group (p < 0.05). Moreover, RNA–seq and western blots revealed that the peroxisome proliferator–activated receptor γ coactivator–1alpha (PGC–1α), a powerful reactive oxygen species (ROS) inhibitor, was significantly downregulated in the LPV group compared with its expression in the CV group (p < 0.05).

Conclusions

Compared with the CV strategy, the LPV strategy did not protect the diaphragm against VIDD in rats. In contrast, the LPV strategy worsened VIDD by inducing oxidative stress together with the downregulation of PGC–1α in the diaphragm. However, further studies are required to determine the roles of PGC–1α in ventilator-induced diaphragmatic oxidative stress.

Hemorrhagic Shock Sensitized the Diaphragm to Ventilator-Induced Dysfunction through the Activation of IL-6/JAK/STAT Signaling-Mediated Autophagy in Rats

Mechanical ventilation (MV) is a major life support technique for the management of trauma-associated hemorrhagic shock (HS). Ventilator-induced diaphragm dysfunction (VIDD), one of the most common complications of MV, has been well demonstrated in animal and human studies. However, few data are available concerning the effects of MV on diaphragm function in HS victims. In the present study, we found diaphragm muscle atrophy and weakness in HS but not in healthy animals after 4 hours of MV. The inhibition of autophagy resulted in reduced muscle fiber atrophy and improved forces. In addition, we observed diaphragmatic interleukin- (IL-) 6 overexpression and activation of its downstream signaling JAK/STAT in HS animals after MV, and either the neutralization of IL-6 or the inhibition of the JAK/STAT pathway attenuated autophagy, diaphragm atrophy, and weakness. Importantly, treatment with nonselective antioxidant exerted no protective effects against VIDD in HS animals. In addition, in vitro study showed that exogenous IL-6 was able to induce activation of JAK/STAT signaling and to increase autophagy in C2C12 cells. Moreover, the inhibition of JAK/STAT signaling abolished IL-6-induced cell autophagy. Together, our results suggested that HS sensitized the diaphragm to ventilator-induced atrophy and weakness through the activation of IL-6/JAK/STAT signaling-mediated autophagy in rats.

Evaluation of diaphragm ultrasound in predicting extubation outcome in mechanically ventilated patients with COPD

Background

To explore the value of the right hemi-diaphragmatic excursion (DE) and its variation in predicting extubation outcome in mechanically ventilated patients with COPD.

Methods

All included patients with COPD received mechanical ventilation (MV) and were ready to wean from MV. After patients passed the 30 min spontaneous breathing trail (SBT), extubation was considered to be feasible, and the right DE measured by ultrasound at 0 min, 5 min, and 30 min of SBT were named as DE₀, DE₅, and DE₃₀, respectively.

Results

Twenty-five patients succeeded extubation; 12 patients failed. The area under receiver operator characteristic curve (AUC_ROC) of DE₃₀ and ΔDE₃₀₋₅ (the variation between 30 and 5 min) were 0.762 and 0.835; a cutoff value of DE₃₀ > 1.72 cm and ΔDE₃₀₋₅ > 0.16 cm were associated with a successful extubation with a sensitivity of 76% and 84%, a specificity of 75% and 83.3%, respectively. The predictive probability equation of the DE₃₀ plus ∆DE₃₀₋₅ was P = 1/[1 + e^{−(−5.625+17.689×∆DE}₃₀₋₅^+1.802×DE₃₀⁾], a cutoff value of P > 0.626 was associated with a successful extubation with the AUC_ROC of 0.867, a sensitivity of 92%, and a specificity of 83.3%.

Conclusion

The combination of DE₃₀ and ∆DE₃₀₋₅ could improve the predictive value and could be used as the predictor of extubation outcome in mechanically ventilated patients with COPD.