Mechanical ventilation reduces rat diaphragm blood flow and impairs oxygen delivery and uptake

Quantifying Diaphragm Blood Flow With Contrast-Enhanced Ultrasound in Humans

BACKGROUND

Despite the known interplay between blood flow and function, to our knowledge, there is currently no minimally invasive method to monitor diaphragm hemodynamics. We used contrast-enhanced ultrasound to quantify relative diaphragm blood flow (Q˙DIA) in humans and assessed the technique's efficacy and reliability during graded inspiratory pressure threshold loading. We hypothesized that: (1) Q˙DIA would linearly increase with pressure generation, and (2) that there would be good test-retest reliability and interanalyzer reproducibility.

RESEARCH QUESTION

Can we validate what is, to our knowledge, the first minimally invasive method to measure relative diaphragm blood flow in humans?

STUDY DESIGN AND METHODS

Quantitative contrast-enhanced ultrasound of the costal diaphragm was performed in healthy participants (10 male participants, 6 female participants; mean age 28 ± 5 years; BMI 22.8 ± 2.0 kg/m) during unloaded breathing and three stages of loaded breathing on two separate days. Gastric and esophageal balloon catheters measured transdiaphragmatic pressure. Ultrasonography was performed during a constant-rate IV infusion of lipid-stabilized microbubbles following each stage. Ultrasound images were acquired after a destruction-replenishment sequence and diaphragm specific time-intensity data were used to determine Q˙DIA by two individuals.

RESULTS

Transdiaphragmatic pressure for unloaded and each loading stage were 15.2 ± 0.8, 26.1 ± 0.8, 34.6 ± 0.8, and 40.0 ± 0.8 percentage of the maximum, respectively. Q˙DIA increased with each stage of loading (3.1 ± 3.1, 6.9 ± 3.6, 11.0 ± 4.9, and 13.5 ± 5.4 acoustic units/s; P < .0001). The linear relationship between diaphragmatic flow and pressure was reproducible from day to day. Q˙DIA had good to excellent test-retest reliability (0.86 [0.77, 0.92]; P < .0001) and excellent interanalyzer reproducibility (0.93 [0.90, 0.95]; P < .0001) with minimal bias.

INTERPRETATION

Relative Q˙DIA measurements had valid physiological underpinnings, were reliable day-to-day, and were reproducible analyzer-to-analyzer. This study indicated that contrast-enhanced ultrasound is a viable, minimally invasive method for assessing costal Q˙DIA in humans and may provide a tool to monitor diaphragm hemodynamics in clinical settings.

Different ethanol exposure durations affect cytochrome P450 2E1-mediated sevoflurane metabolism in rat liver

BACKGROUND

Chronic alcohol users often exhibit an increased minimum alveolar concentration (MAC) of sevoflurane, yet the specific mechanism remains unclear. It has been reported that ethanol exposure can upregulate the protein expression and enzyme activity of cytochrome P450 2E1 (CYP2E1). CYP2E1 is a key enzyme that converts 2-5% of sevoflurane into equimolar amounts of hexafluoroisopropanol (HFIP) and F-. This study aims to explore whether ethanol exposure could alter sevoflurane metabolism through CYP2E1 modulation, potentially explaining the increased MAC observed in alcohol users.

METHODS

Eighty adult male Sprague-Dawley (SD) rats were randomly divided into two groups and received either 50% ethanol (dose: 3 g/kg) or 0.9% saline twice daily by gavage. After 1, 2, 3, and 4 weeks of gavage, ten rats were randomly selected from each group to undergo 1-hour anesthesia with 2.3% sevoflurane. Blood samples were collected after anesthesia to measure the concentration of free HFIP using gas chromatography. Additionally, the left lobe tissue of the liver was collected for the analysis of CYP2E1 protein expression by Western blot and CYP2E1 enzyme activity by colorimetric assay. Correlations between these parameters were analyzed using Pearson's correlation.

RESULTS

In the ethanol group, CYP2E1 expression, activity, and the concentration of free HFIP were significantly higher at all time points compared to the control group (P < 0.05), except for protein expression in the first week (P > 0.05). Within-group comparisons indicated no significant changes in any of the parameters for the control group (P > 0.05). In the ethanol group, there was no difference in free HFIP concentration between the first and second weeks (P > 0.05), but a significant increase was observed in the third and fourth weeks (P < 0.01); protein expression and enzyme activity significantly varied over time, especially showing a notable increase from the first to the third and fourth weeks (P < 0.05). Correlation analysis revealed strong positive correlations between free HFIP concentration and CYP2E1 activity (r = 0.7898), free HFIP concentration and CYP2E1 expression (r = 0.8418), and CYP2E1 activity and expression (r = 0.8740), all with P < 0.001.

CONCLUSIONS

Ethanol exposure increased both the expression and enzymatic activity of CYP2E1, consequently enhancing the metabolism of sevoflurane.

Effects of aging on diaphragm hyperemia and blood flow distribution in male and female Fischer 344 rats

Aging is associated with inspiratory muscle dysfunction; however, the impact of aging on diaphragm blood flow (BF) regulation, and whether sex differences exist, is unknown. We tested the hypotheses in young animals that diaphragm BF and vascular conductance (VC) would be greater in females and that aging would decrease the diaphragm's ability to increase BF with contractions. Young (4-6 mo) and old (22-24 mo) Fischer 344 rats were divided into four groups: young female (YF, n = 7), young male (YM, n = 8), old female (OF, n = 9), and old male (OM, n = 9). Diaphragm BF (mL/min/100 g) and VC (mL/mmHg/min/100 g) were determined, via fluorescent microspheres, at rest and during 1 Hz contractions. In YF versus OF, aging blunted the increase in medial costal diaphragm BF (44 ± 5% vs. 16 ± 12%; P < 0.05) and VC (43 ± 7% vs. 21 ± 12%; P < 0.05). Similarly, in YM versus OM, aging blunted the increase in medial costal diaphragm BF (43 ± 6% vs. 24 ± 12%; P < 0.05) and VC (50 ± 6% vs. 34 ± 10%; P < 0.05). In female rats, age increased dorsal costal diaphragm BF, whereas in male rats, age increased crural diaphragm BF (P < 0.05). Compared with age-matched females, dorsal costal diaphragm BF was lower in YM and OM (P < 0.05). In conclusion, aging results in an inability to augment medial costal diaphragm BF and alters regional diaphragm BF distribution in response to muscular contractions. Furthermore, sex differences in regional diaphragm BF are present in young and old animals.NEW & NOTEWORTHY This is the first study, to our knowledge, to demonstrate that old age impairs the hyperemic response and alters blood flow distribution in the diaphragm of both female and male rats. In addition, this investigation provides novel evidence of sex differences in regional diaphragm blood flow distribution with contractions. The data presented herein suggest that aging compromises diaphragm vascular function and provides a potential mechanism for the diaphragm contractile dysfunction associated with old age.

Pulmonary hypertension impairs vasomotor function in rat diaphragm arterioles

Pulmonary hypertension (PH) is a chronic, progressive condition in which respiratory muscle dysfunction is a primary contributor to exercise intolerance and dyspnea in patients. Contractile function, blood flow distribution, and the hyperemic response are altered in the diaphragm with PH, and we sought to determine whether this may be attributed, in part, to impaired vasoreactivity of the resistance vasculature. We hypothesized that there would be blunted endothelium-dependent vasodilation and impaired myogenic responsiveness in arterioles from the diaphragm of PH rats. Female Sprague-Dawley rats were randomized into healthy control (HC, n = 9) and monocrotaline-induced PH rats (MCT, n = 9). Endothelium-dependent and -independent vasodilation and myogenic responses were assessed in first-order arterioles (1As) from the medial costal diaphragm in vitro. There was a significant reduction in endothelium-dependent (via acetylcholine; HC, 78 ± 15% vs. MCT, 47 ± 17%; P < 0.05) and -independent (via sodium nitroprusside; HC, 89 ± 10% vs. MCT, 66 ± 10%; P < 0.05) vasodilation in 1As from MCT rats. MCT-induced PH also diminished myogenic constriction (P < 0.05) but did not alter passive pressure responses. The diaphragmatic weakness, impaired hyperemia, and blood flow redistribution associated with PH may be due, in part, to diaphragm vascular dysfunction and thus compromised oxygen delivery which occurs through both endothelium-dependent and -independent mechanisms.

Pulmonary hypertension alters blood flow distribution and impairs the hyperemic response in the rat diaphragm

Pulmonary hypertension (PH) is characterized by pulmonary vascular remodeling, respiratory muscle and cardiac impairments, and exercise intolerance. Specifically, impaired gas exchange increases work of the diaphragm; however, compromised contractile function precludes the diaphragm from meeting the increased metabolic demand of chronic hyperventilation in PH. Given that muscle contractile function is in part, dependent upon adequate blood flow (Q ˙ ), diaphragmatic dysfunction may be predicated by an inability to match oxygen delivery with oxygen demand. We hypothesized that PH rats would demonstrate a decreased hyperemic response to contractions compared to healthy controls. Methods: Sprague-Dawley rats were randomized into healthy (HC, n = 7) or PH (n = 7) groups. PH rats were administered monocrotaline (MCT) while HC rats received vehicle. Disease progression was monitored via echocardiography. Regional and total diaphragm blood flow and vascular conductance at baseline and during 3 min of electrically-stimulated contractions were determined using fluorescent microspheres. Results: PH rats displayed morphometric and echocardiographic criteria for disease (i.e., acceleration time/ejection time, right ventricular hypertrophy). In all rats, total costal diaphragm Q ˙ increased during contractions and did not differ between groups. In HC rats, there was a greater increase in medial costal Q ˙ compared to PH rats (55% ± 3% vs. 44% ± 4%, p < 0.05), who demonstrated a redistribution of Q ˙ to the ventral costal region. Conclusion: These findings support a redistribution of regional diaphragm perfusion and an impaired medial costal hyperemic response in PH, suggesting that PH alters diaphragm vascular function and oxygen delivery, providing a potential mechanism for PH-induced diaphragm contractile dysfunction.

Research progress on the pathogenesis and treatment of ventilator-induced diaphragm dysfunction

Prolonged controlled mechanical ventilation (CMV) can cause diaphragm fiber atrophy and inspiratory muscle weakness, resulting in diaphragmatic contractile dysfunction, called ventilator-induced diaphragm dysfunction (VIDD). VIDD is associated with higher rates of in-hospital deaths, nosocomial pneumonia, difficulty weaning from ventilators, and increased costs. Currently, appropriate clinical strategies to prevent and treat VIDD are unavailable, necessitating the importance of exploring the mechanisms of VIDD and suitable treatment options to reduce the healthcare burden. Numerous animal studies have demonstrated that ventilator-induced diaphragm dysfunction is associated with oxidative stress, increased protein hydrolysis, disuse atrophy, and calcium ion disorders. Therefore, this article summarizes the molecular pathogenesis and treatment of ventilator-induced diaphragm dysfunction in recent years so that it can be better served clinically and is essential to reduce the duration of mechanical ventilation use, intensive care unit (ICU) length of stay, and the medical burden.

Low Intensity Respiratory Muscle Training in COVID-19 Patients after Invasive Mechanical Ventilation: A Retrospective Case-Series Study

Worldwide, healthcare systems had to respond to an exponential increase in COVID-19 patients with a noteworthy increment in intensive care units (ICU) admissions and invasive mechanical ventilation (IMV). The aim was to determine low intensity respiratory muscle training (RMT) effects in COVID-19 patients upon medical discharge and after an ICU stay with IMV. A retrospective case-series study was performed. Forty COVID-19 patients were enrolled and divided into twenty participants who received IMV during ICU stay (IMV group) and 20 participants who did not receive IMV nor an ICU stay (non-IMV group). Maximal expiratory pressure (PEmax), maximal inspiratory pressure (PImax), COPD assessment test (CAT) and Medical Research Council (MRC) dyspnea scale were collected at baseline and after 12 weeks of low intensity RMT. A greater MRC dyspnea score and lower PImax were shown at baseline in the IMV group versus the non-IMV group (p < 0.01). RMT effects on the total sample improved all outcome measurements (p < 0.05; d = 0.38−0.98). Intragroup comparisons after RMT improved PImax, CAT and MRC scores in the IMV group (p = 0.001; d = 0.94−1.09), but not for PImax in the non-IMV group (p > 0.05). Between-groups comparison after RMT only showed MRC dyspnea improvements (p = 0.020; d = 0.74) in the IMV group versus non-IMV group. Furthermore, PImax decrease was only predicted by the IMV presence (R2 = 0.378). Low intensity RMT may improve respiratory muscle strength, health related quality of life and dyspnea in COVID-19 patients. Especially, low intensity RMT could improve dyspnea level and maybe PImax in COVID-19 patients who received IMV in ICU.

Endoplasmic Reticulum Stress Contributes to Ventilator-Induced Diaphragm Atrophy and Weakness in Rats

Background: Accumulating evidence indicates that endoplasmic reticulum (ER) stress plays a critical role in the regulation of skeletal muscle mass. In recent years, much attention has been given to ventilator-induced diaphragm dysfunction (VIDD) because it strongly impacts the outcomes of critically ill patients. Current evidence suggests that the enhancement of oxidative stress is essential for the development of VIDD, but there are no data on the effects of ER stress on this pathological process.

Methods: VIDD was induced by volume-controlled mechanical ventilation (MV) for 12 h; Spontaneous breathing (SB, for 12 h) rats were used as controls. The ER stress inhibitor 4-phenylbutyrate (4-PBA), the antioxidant N-acetylcysteine (NAC), and the ER stress inducer tunicamycin (TUN) were given before the onset of MV or SB. Diaphragm function, oxidative stress, and ER stress in the diaphragms were measured at the end of the experiments.

Results: ER stress was markedly increased in diaphragms relative to that in SB after 12 h of MV (all p < 0.001). Inhibition of ER stress by 4-PBA downregulated the expression levels of proteolysis-related genes in skeletal muscle, including Atrogin-1 and MuRF-1, reduced myofiber atrophy, and improved diaphragm force-generating capacity in rats subjected to MV (all p < 0.01). In addition, mitochondrial reactive oxygen species (ROS) production and protein level of 4-HNE (4-hydroxynonenal) were decreased upon 4-PBA treatment in rats during MV (all p < 0.01). Interestingly, the 4-PBA treatment also markedly increased the expression of peroxisome proliferator-activated receptor-gamma co-activator-1alpha (PGC-1α) (p < 0.01), a master regulator for mitochondrial function and a strong antioxidant. However, the antioxidant NAC failed to reduce ER stress in the diaphragm during MV (p > 0.05). Finally, ER stress inducer TUN largely compromised diaphragm dysfunction in the absence of oxidative stress (all p < 0.01).

Conclusion: ER stress is induced by MV and the inhibition of ER stress alleviates oxidative stress in the diaphragm during MV. In addition, ER stress is responsible for diaphragm dysfunction in the absence of oxidative stress. Therefore, the inhibition of ER stress may be another promising therapeutic approach for the treatment of VIDD.

Supplemental oxygen administration during mechanical ventilation reduces diaphragm blood flow and oxygen delivery

During mechanical ventilation (MV), supplemental oxygen (O2) is commonly administered to critically ill patients to combat hypoxemia. Previous studies demonstrate that hyperoxia exacerbates MV-induced diaphragm oxidative stress and contractile dysfunction. Whereas normoxic MV (i.e., 21% O2) diminishes diaphragm perfusion and O2 delivery in the quiescent diaphragm, the effect of MV with 100% O2 is unknown. We tested the hypothesis that MV supplemented with hyperoxic gas (100% O2) would increase diaphragm vascular resistance and reduce diaphragmatic blood flow and O2 delivery to a greater extent than MV alone. Female Sprague-Dawley rats (4-6 mo) were randomly divided into two groups: 1) MV + 100% O2 followed by MV + 21% O2 (n = 9) or 2) MV + 21% O2 followed by MV + 100% O2 (n = 10). Diaphragmatic blood flow (mL/min/100 g) and vascular resistance were determined, via fluorescent microspheres, during spontaneous breathing (SB), MV + 100% O2, and MV + 21% O2. Compared with SB, total diaphragm vascular resistance was increased, and blood flow was decreased with both MV + 100% O2 and MV + 21% O2 (all P < 0.05). Medial costal diaphragmatic blood flow was lower with MV + 100% O2 (26 ± 6 mL/min/100 g) versus MV + 21% O2 (51 ± 15 mL/min/100 g; P < 0.05). Second, the addition of 100% O2 during normoxic MV exacerbated the MV-induced reductions in medial costal diaphragm perfusion (23 ± 7 vs. 51 ± 15 mL/min/100 g; P < 0.05) and O2 delivery (3.4 ± 0.2 vs. 6.4 ± 0.3 mL O2/min/100 g; P < 0.05). These data demonstrate that administration of supplemental 100% O2 during MV increases diaphragm vascular resistance and diminishes perfusion and O2 delivery to a significantly greater degree than normoxic MV. This suggests that prolonged bouts of MV (i.e., 6 h) with hyperoxia may accelerate MV-induced vascular dysfunction in the quiescent diaphragm and potentially exacerbate downstream contractile dysfunction.NEW & NOTEWORTHY This is the first study, to our knowledge, demonstrating that supplemental oxygen (i.e., 100% O2) during mechanical ventilation (MV) augments the MV-induced reductions in diaphragmatic blood flow and O2 delivery. The accelerated reduction in diaphragmatic blood flow with hyperoxic MV would be expected to potentiate MV-induced diaphragm vascular dysfunction and consequently, downstream contractile dysfunction. The data presented herein provide a putative mechanism for the exacerbated oxidative stress and diaphragm dysfunction reported with prolonged hyperoxic MV.

High-Intensity Inspiratory Muscle Training Improves Scalene and Sternocleidomastoid Muscle Oxygenation Parameters in Patients With Weaning Difficulties: A Randomized Controlled Trial

Background

Critically ill patients who have difficulties weaning from the mechanical ventilator are prone to develop respiratory muscle weakness. Inspiratory muscle training (IMT) can improve respiratory muscle strength. Whether IMT can improve scalene and sternocleidomastoid muscle oxygenation parameters is unknown.

Aim

To compare changes in muscle oxygenation parameters of scalene and sternocleidomastoid inspiratory muscles during a standardized task between patients with weaning difficulties who received either high-intensity IMT (intervention) or sham low-intensity IMT (control).

Method

Forty-one patients performed daily IMT sessions (4 sets, 6–10 breaths) until weaning success or for 28 consecutive days. The training load was progressively adjusted in the intervention group (n = 22) to the highest tolerable load, whilst the control group (n = 19) kept training at 10% of their baseline maximal inspiratory pressure (PImax). Breathing characteristics (i.e., work and power of breathing, PoB), respiratory muscle function [i.e., PImax and forced vital capacity (FVC)] were measured during a standardized loaded breathing task against a load of 30% of baseline PImax before and after the IMT period. In addition, during the same loaded breathing task, absolute mean and nadir changes from baseline in local scalene and sternocleidomastoid muscle oxygen saturation index (Δ%StiO2) (an index of oxygen extraction) and nadir Δ%StiO2 normalized for the PoB were measured by near-infrared spectroscopy.

Results

At post measures, only the intervention group improved mean PoB compared to pre measures (Pre: 0.42 ± 0.33 watts, Post: 0.63 ± 0.51watts, p-value &lt; 0.01). At post measures, both groups significantly improved nadir scalene muscles StiO2% normalized for the mean PoB (ΔStiOnadir%/watt) compared to pre measurements and the improvement was not significant different between groups (p-value = 0.40). However, at post measures, nadir sternocleidomastoid muscle StiO2% normalized for the mean PoB (ΔStiOnadir%/watt) was significantly greater improved in the intervention group (mean difference: +18.4, 95%CI: −1.4; 38.1) compared to the control group (mean difference: +3.7, 95%CI: −18.7; 26.0, between group p-value &lt; 0.01). Both groups significantly improved PImax (Intervention: +15 ± 13 cmH2O p-value &lt; 0.01, Control: +13 ± 15 cmH2O p-value &lt; 0.01). FVC only significantly improved in the intervention group (+0.33 ± 0.31 L p &lt; 0.01) report also change in control group.

Conclusion

This exploratory study suggests that high-intensity IMT induces greater improvements in scalene and sternocleidomastoid muscle oxygenation parameters attributed for oxygen delivery, utilization and oxygen saturation index compared to low-intensity IMT in patients with weaning difficulties.

Prolonged mechanical ventilation increases diaphragm arteriole circumferential stretch without changes in stress/stretch: Implications for the pathogenesis of ventilator-induced diaphragm dysfunction

INTRODUCTION

Prolonged mechanical ventilation (MV; ≥6 h) results in large, time-dependent reductions in diaphragmatic blood flow and shear stress. We tested the hypothesis that MV would impair the structural and material properties (ie, increased stress/stretch relation and/or circumferential stretch) of first-order arterioles (1A) from the medial costal diaphragm.

METHODS

Shear stress was estimated from isolated arterioles and prior blood flow data from the diaphragm during spontaneous breathing (SB) and prolonged MV (6 h MV). Thereafter, female Sprague-Dawley rats (~5 months) were randomly divided into two groups, SB (n = 6) and 6 h MV (n = 6). Following SB and 6 h MV, 1A medial costal diaphragm arterioles were isolated, cannulated, and subjected to stepwise (0-140 cmH2 O) increases in intraluminal pressure in calcium-free Ringer's solution. Inner diameter and wall thickness were measured at each pressure step and used to calculate wall:lumen ratio, Cauchy-stress, and circumferential stretch.

RESULTS

Compared to SB, there was a ~90% reduction in arteriolar shear stress with prolonged MV (9 ± 2 vs 78 ± 20 dynes/cm2 ; p ≤ .05). In the unloaded condition (0 cmH2 O), the arteriolar intraluminal diameter was reduced (37 ± 8 vs 79 ± 13 μm) and wall:lumen ratio was increased (120 ± 18 vs 46 ± 10%) compared to SB (p ≤ .05). There were no differences in the passive diameter responses or the circumferential stress/stretch relationship between groups (p > .05), but at each pressure step, circumferential stretch was increased with 6 h MV vs SB (p ≤ .05).

CONCLUSION

During prolonged MV, medial costal diaphragm arteriolar shear stress is severely diminished. Despite no change in the material behavior (stress/stretch), prolonged MV resulted in altered structural and mechanical properties (ie, elevated circumferential stretch) of medial costal diaphragm arterioles. This provides important novel mechanistic insights into the impaired diaphragm blood flow capacity and vascular dysfunction following prolonged MV.

Altered expression of microRNAs in the rat diaphragm in a model of ventilator-induced diaphragm dysfunction after controlled mechanical ventilation

BACKGROUND

Ventilator-induced diaphragm dysfunction (VIDD) is a common complication of life support by mechanical ventilation observed in critical patients in clinical practice and may predispose patients to severe complications such as ventilator-associated pneumonia or ventilator discontinuation failure. To date, the alterations in microRNA (miRNA) expression in the rat diaphragm in a VIDD model have not been elucidated. This study was designed to identify these alterations in expression.

RESULTS

Adult male Wistar rats received conventional controlled mechanical ventilation (CMV) or breathed spontaneously for 12 h. Then, their diaphragm tissues were collected for RNA extraction. The miRNA expression alterations in diaphragm tissue were investigated by high-throughput microRNA-sequencing (miRNA-seq). For targeted mRNA functional analysis, gene ontology (GO) analyses and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were subsequently conducted. qRT-PCR validation and luciferase reporter assays were performed. We successfully constructed a model of ventilator-induced diaphragm dysfunction and identified 38 significantly differentially expressed (DE) miRNAs, among which 22 miRNAs were upregulated and 16 were downregulated. GO analyses identified functional genes, and KEGG pathway analyses revealed the signaling pathways that were most highly correlated, which were the MAPK pathway, FoxO pathway and Autophagy-animal. Luciferase reporter assays showed that STAT3 was a direct target of both miR-92a-1-5p and miR-874-3p and that Trim63 was a direct target of miR-3571.

CONCLUSIONS

The current research supplied novel perspectives on miRNAs in the diaphragm, which may not only be implicated in diaphragm dysfunction pathogenesis but could also be considered as therapeutic targets in diaphragm dysfunction.

Application of bedside ultrasound in predicting the outcome of weaning from mechanical ventilation in elderly patients

BACKGROUND

With the increased ageing of society, more and more elderly people are admitted to the intensive care unit, How to accurately predict whether elderly patients can successfully wean from the ventilator is more complicated. Diaphragmatic excursion (DE) and diaphragm thickening fraction (DTF) were measured by bedside ultrasound to assess diaphragm function. The lung ultrasound score (LUS) and the rapid shallow breathing index (RBSI) were used as indices of diaphragm function to predict the outcome of weaning from mechanical ventilation. The aim of this study was to examine the clinical utility of these parameters in predicting extubation success.

METHODS

This prospective study included 101 consecutive elderly patients undergoing a trial of extubation in the ICU of Haidian Hospital between June 2017 and July 2020. Patients were divided into the successful weaning group (n = 69) and the failed weaning group (n = 32). Baseline characteristics, including RSBI, were recorded. Measurements of DE, DTF and LUS were made using ultrasound within 24 h before extubation.

RESULTS

Median DE was greater in patients with extubation success than in those with extubation failure (1.64 cm vs. 0.78 cm, p = 0.001). Patients with extubation success had a greater DTF than those with extubation failure (49.48% vs. 27.85%, p = 0.001). The areas under the receiver operating curves for the RSBI, LUS, DE and DFT were 0.680, 0.764, 0.831 and 0.881, respectively. The best cut-off values for predicting successful weaning were DTF ≥ 30%, DE ≥ 1.3 cm, LUS ≤ 11, and RSBI ≤ 102. The specificity of DTF (84%) in predicting weaning outcome was higher than that of RBSI (53%), that of LUS (55%), and that of DE (62%). The sensitivity of DTF (94%) was greater than that of RBSI (85%), that of LUS (71%), and that of DE (65%). The combination of RSBI, LUS, DE, and DTF showed the highest AUC (AUC = 0.919), with a sensitivity of 96% and a specificity of 89%.

CONCLUSIONS

DTF has higher sensitivity and specificity for the prediction of successful weaning in elderly patients than the other parameters examined. The combination of RSBI, LUS, DE and DFT performed well in predicting weaning outcome. This has potentially important clinical application and merits further evaluation.

Transcriptome profiling of the diaphragm in a controlled mechanical ventilation model reveals key genes involved in ventilator-induced diaphragmatic dysfunction

BACKGROUND

Ventilator-induced diaphragmatic dysfunction (VIDD) is associated with weaning difficulties, intensive care unit hospitalization (ICU), infant mortality, and poor long-term clinical outcomes. The expression patterns of long noncoding RNAs (lncRNAs) and mRNAs in the diaphragm in a rat controlled mechanical ventilation (CMV) model, however, remain to be investigated.

RESULTS

The diaphragms of five male Wistar rats in a CMV group and five control Wistar rats were used to explore lncRNA and mRNA expression profiles by RNA-sequencing (RNA-seq). Muscle force measurements and immunofluorescence (IF) staining were used to verify the successful establishment of the CMV model. A total of 906 differentially expressed (DE) lncRNAs and 2,139 DE mRNAs were found in the CMV group. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed to determine the biological functions or pathways of these DE mRNAs. Our results revealed that these DE mRNAs were related mainly related to complement and coagulation cascades, the PPAR signaling pathway, cholesterol metabolism, cytokine-cytokine receptor interaction, and the AMPK signaling pathway. Some DE lncRNAs and DE mRNAs determined by RNA-seq were validated by quantitative real-time polymerase chain reaction (qRT-PCR), which exhibited trends similar to those observed by RNA-sEq. Co-expression network analysis indicated that three selected muscle atrophy-related mRNAs (Myog, Trim63, and Fbxo32) were coexpressed with relatively newly discovered DE lncRNAs.

CONCLUSIONS

This study provides a novel perspective on the molecular mechanism of DE lncRNAs and mRNAs in a CMV model, and indicates that the inflammatory signaling pathway and lipid metabolism may play important roles in the pathophysiological mechanism and progression of VIDD.

Suppression of Hypoxia-Inducible Factor 1α by Low-Molecular-Weight Heparin Mitigates Ventilation-Induced Diaphragm Dysfunction in a Murine Endotoxemia Model

Mechanical ventilation (MV) is required to maintain life for patients with sepsis-related acute lung injury but can cause diaphragmatic myotrauma with muscle damage and weakness, known as ventilator-induced diaphragm dysfunction (VIDD). Hypoxia-inducible factor 1α (HIF-1α) plays a crucial role in inducing inflammation and apoptosis. Low-molecular-weight heparin (LMWH) was proven to have anti-inflammatory properties. However, HIF-1α and LMWH affect sepsis-related diaphragm injury has not been investigated. We hypothesized that LMWH would reduce endotoxin-augmented VIDD through HIF-1α. C57BL/6 mice, either wild-type or HIF-1α–deficient, were exposed to MV with or without endotoxemia for 8 h. Enoxaparin (4 mg/kg) was administered subcutaneously 30 min before MV. MV with endotoxemia aggravated VIDD, as demonstrated by increased interleukin-6 and macrophage inflammatory protein-2 levels, oxidative loads, and the expression of HIF-1α, calpain, caspase-3, atrogin-1, muscle ring finger-1, and microtubule-associated protein light chain 3-II. Disorganized myofibrils, disrupted mitochondria, increased numbers of autophagic and apoptotic mediators, substantial apoptosis of diaphragm muscle fibers, and decreased diaphragm function were also observed (p < 0.05). Endotoxin-exacerbated VIDD and myonuclear apoptosis were attenuated by pharmacologic inhibition by LMWH and in HIF-1α–deficient mice (p < 0.05). Our data indicate that enoxaparin reduces endotoxin-augmented MV-induced diaphragmatic injury, partially through HIF-1α pathway inhibition.

The role of vascular function on exercise capacity in health and disease

Three sentinel parameters of aerobic performance are the maximal oxygen uptake ( V ̇ O 2 max ), critical power (CP) and speed of the V ̇ O 2 kinetics following exercise onset. Of these, the latter is, perhaps, the cardinal test of integrated function along the O2 transport pathway from lungs to skeletal muscle mitochondria. Fast V ̇ O 2 kinetics demands that the cardiovascular system distributes exercise-induced blood flow elevations among and within those vascular beds subserving the contracting muscle(s). Ideally, this process must occur at least as rapidly as mitochondrial metabolism elevates V ̇ O 2 . Chronic disease and ageing create an O2 delivery (i.e. blood flow × arterial [O2 ], Q ̇ O 2 ) dependency that slows V ̇ O 2 kinetics, decreasing CP and V ̇ O 2 max , increasing the O2 deficit and sowing the seeds of exercise intolerance. Exercise training, in contrast, does the opposite. Within the context of these three parameters (see Graphical Abstract), this brief review examines the training-induced plasticity of key elements in the O2 transport pathway. It asks how structural and functional vascular adaptations accelerate and redistribute muscle Q ̇ O 2 and thus defend microvascular O2 partial pressures and capillary blood-myocyte O2 diffusion across a ∼100-fold range of muscle V ̇ O 2 values. Recent discoveries, especially in the muscle microcirculation and Q ̇ O 2 -to- V ̇ O 2 heterogeneity, are integrated with the O2 transport pathway to appreciate how local and systemic vascular control helps defend V ̇ O 2 kinetics and determine CP and V ̇ O 2 max in health and how vascular dysfunction in disease predicates exercise intolerance. Finally, the latest evidence that nitrate supplementation improves vascular and therefore aerobic function in health and disease is presented.

Effects of elevated positive end-expiratory pressure on diaphragmatic blood flow and vascular resistance during mechanical ventilation

Although mechanical ventilation (MV) is a life-saving intervention, prolonged MV can lead to deleterious effects on diaphragm function, including vascular incompetence and weaning failure. During MV, positive end-expiratory pressure (PEEP) is used to maintain small airway patency and mitigate alveolar damage. We tested the hypothesis that increased intrathoracic pressure with high levels of PEEP would increase diaphragm vascular resistance and decrease perfusion. Female Sprague-Dawley rats (~6 mo) were randomly divided into two groups receiving low PEEP (1 cmH₂O; n = 10) or high PEEP (9 cmH₂O; n = 9) during MV. Blood flow, via fluorescent microspheres, was determined during spontaneous breathing (SB), low-PEEP MV, high-PEEP MV, low-PEEP MV + surgical laparotomy (LAP), and high-PEEP MV + pneumothorax (PTX). Compared with SB, both low-PEEP MV and high-PEEP MV increased total diaphragm and medial costal vascular resistance (P ≤ 0.05) and reduced total and medial costal diaphragm blood flow (P ≤ 0.05). Also, during MV medial costal diaphragm vascular resistance was greater and blood flow lower with high-PEEP MV vs. low-PEEP MV (P ≤ 0.05). Diaphragm perfusion with high-PEEP MV+PTX and low-PEEP MV were not different (P > 0.05). The reduced total and medial costal diaphragmatic blood flow with low-PEEP MV appears to be independent of intrathoracic pressure changes and is attributed to increased vascular resistance and diaphragm quiescence. Mechanical compression of the diaphragm vasculature may play a role in the lower diaphragmatic blood flow at higher levels of PEEP. These reductions in blood flow to the quiescent diaphragm during MV could predispose critically ill patients to weaning complications.

NEW & NOTEWORTHY This is the first study, to our knowledge, demonstrating that mechanical ventilation, with low and high positive-end expiratory pressure (PEEP), increases vascular resistance and reduces total and regional diaphragm perfusion. The rapid reduction in diaphragm perfusion and increased vascular resistance may initiate a cascade of events that predispose the diaphragm to vascular and thus contractile dysfunction with prolonged mechanical ventilation.

Physiopathological mechanisms of diaphragmatic dysfunction associated with mechanical ventilation

Ventilator-induced diaphragm dysfunction (VIDD) is the loss of diaphragmatic muscle strength'related to of mechanical ventilation, noticed during the first day or 48hours after initiating controlled mechanical ventilation. This alteration has been related to disruption on the insulin growth factor/phosphoinositol 3-kinase/kinase B protein pathway (IGF/PI3K/AKT), in addition to an overexpression of FOXO, expression of NF-kB signaling, increase function of muscular ubiquitin ligase and activation of caspasa-3. VIDD has a negative impact on quality of life, duration of mechanical ventilation, and hospitalization stance and cost. More studies are necessary to understated the process and impact of VIDD. This is a narrative review of non-systematic literature, aiming to explain the molecular pathways involved in VIDD.

Sedation with midazolam worsens the diaphragm function than dexmedetomidine and propofol during mechanical ventilation in rats

BACKGROUND

Mechanical ventilation (MV) is identified as an independent contributor to diaphragmatic atrophy and contractile dysfunction. Appropriate sedation is also essential during MV, and anesthetics may have direct adverse effects on the diaphragm. However, there is a lack of research into the effects of different anesthetics on diaphragm function during MV.

OBJECTIVES

In the present study, we aim to examine the effect of midazolam, dexmedetomidine, and propofol on diaphragm function during MV.

DESIGN

Animal study.

SETTING

University research laboratory.

SUBJECTS

Male Wistar rats.

INTERVENTIONS

Animals were experienced 12 h of MV or spontaneous breathing (SB) with continuous anesthetics infusion. Diaphragm contractile properties, cross-sectional areas, microcirculation, oxidative stress, and proteolysis were examined.

MEASUREMENTS AND MAIN RESULTS

Diaphragmatic specific force was markedly reduced in the midazolam group compared with the dexmedetomidine (-60.4 ± 3.01%, p < 0.001) and propofol group (-58.3 ± 2.60%, p < 0.001) after MV. MV sedated with midazolam induced more atrophy of type II fibers compared with dexmedetomidine (-21.8 ± 2.11%, p = 0.0001) and propofol (-8.2 ± 1.53%, p = 0.003). No significant differences of these indices were found in the midazolam, dexmedetomidine, and propofol groups under SB condition (all p > 0.05, respectively). Twelve hours of MV resulted in a time dependent reduction in diaphragmatic functional capillary density (PB -25.1%, p = 0.0001; MZ -21.6%, p = 0.0003; DD -15.2%, p = 0.022; PP -24.8%, p = 0.0001, respectively), which did not occur in the gastrocnemius muscle. The diaphragmatic lipid peroxidation adducts 4-HNE and HIF-1α levels were significantly lower in dexmedetomidine group and propofol group compared to midazolam group (p < 0.05, respectively). Meanwhile, the catalase and SOD levels were also relatively lower (p < 0.05, respectively) in midazolam group compared to dexmedetomidine group and propofol group.

CONCLUSIONS

Twelve hours of mechanical ventilation during midazolam sedation led to a more severe diaphragm dysfunction than dexmedetomidine and propofol, possibly caused by its relative weaker antioxidant capacity.

Impaired diaphragm resistance vessel vasodilation with prolonged mechanical ventilation

Mechanical ventilation (MV) is a life-saving intervention, yet with prolonged MV (i.e., ≥6 h) there are time-dependent reductions in diaphragm blood flow and an impaired hyperemic response of unknown origin. Female Sprague-Dawley rats (4-8 mo, n = 118) were randomized into two groups; spontaneous breathing (SB) and 6-h (prolonged) MV. After MV or SB, vasodilation (flow-induced, endothelium-dependent and -independent agonists) and constriction (myogenic and α-adrenergic) responses were measured in first-order (1A) diaphragm resistance arterioles in vitro, and endothelial nitric oxide synthase (eNOS) mRNA expression was quantified. Following prolonged MV, there was a significant reduction in diaphragm arteriolar flow-induced (SB, 34.7 ± 3.8% vs. MV, 22.6 ± 2.0%; P ≤ 0.05), endothelium-dependent (via acetylcholine; SB, 64.3  ± 2.1% vs. MV, 36.4 ± 2.3%; P ≤ 0.05) and -independent (via sodium nitroprusside; SB, 65.0 ± 3.1% vs. MV, 46.0 ± 4.6%; P ≤ 0.05) vasodilation. Compared with SB, there was reduced eNOS mRNA expression (P ≤ 0.05). Prolonged MV diminished phenylephrine-induced vasoconstriction (SB, 37.3 ± 6.7% vs. MV, 19.0 ± 1.9%; P ≤ 0.05) but did not alter myogenic or passive pressure responses. The severe reductions in diaphragmatic blood flow at rest and during contractions, with prolonged MV, are associated with diaphragm vascular dysfunction which occurs through both endothelium-dependent and endothelium-independent mechanisms.NEW & NOTEWORTHY Following prolonged mechanical ventilation, vascular alterations occur through both endothelium-dependent and -independent pathways. This is the first study, to our knowledge, demonstrating that diaphragm arteriolar dysfunction occurs consequent to prolonged mechanical ventilation and likely contributes to the severe reductions in diaphragmatic blood flow and weaning difficulties.

Interactions between Cytosolic Phospholipase A2 Activation and Mitochondrial Reactive Oxygen Species Production in the Development of Ventilator-Induced Diaphragm Dysfunction

Cytosolic phospholipase A2 (cPLA2) has been reported to be critical for infection-induced mitochondrial reactive oxygen species (ROS) production and diaphragm dysfunction (DD). In the present study, we aim to investigate whether cPLA2 was involved in ventilator-induced diaphragm dysfunction (VIDD). Our results showed that mechanical ventilation (MV) induced cPLA2 activation in the diaphragm with excessive mitochondrial ROS generation and muscle weakness. Specific inhibition of cPLA2 with CDIBA resulted in decreased mitochondrial ROS levels and improved diaphragm forces. In addition, mitochondria-targeted antioxidant MitoTEMPO attenuated ventilator-induced mitochondrial oxidative stress and downregulated cPLA2 activation in vivo. Both CDIBA and MitoTEMPO were able to attenuate protein degradation, muscle atrophy, and weakness following prolonged MV. Furthermore, laser Doppler imaging showed that MV decreased diaphragm tissue perfusion and induced subsequent hypoxia. An in vitro study also demonstrated a positive association between cPLA2 activation and mitochondrial ROS generation in C2C12 cells cultured under hypoxic condition. Collectively, our study showed that cPLA2 activation positively interacts with mitochondrial ROS generation in the development of VIDD, and ventilator-induced diaphragm hypoxia serves as a possible contributor to this positive feedback loop.

The Signaling Network Resulting in Ventilator-induced Diaphragm Dysfunction

Mechanical ventilation (MV) is a life-saving measure for those incapable of adequately ventilating or oxygenating without assistance. Unfortunately, even brief periods of MV result in diaphragm weakness (i.e., ventilator-induced diaphragm dysfunction [VIDD]) that may render it difficult to wean the ventilator. Prolonged MV is associated with cascading complications and is a strong risk factor for death. Thus, prevention of VIDD may have a dramatic impact on mortality rates. Here, we summarize the current understanding of the pathogenic events underlying VIDD. Numerous alterations have been proven important in both human and animal MV diaphragm. These include protein degradation via the ubiquitin proteasome system, autophagy, apoptosis, and calpain activity-all causing diaphragm muscle fiber atrophy, altered energy supply via compromised oxidative phosphorylation and upregulation of glycolysis, and also mitochondrial dysfunction and oxidative stress. Mitochondrial oxidative stress in fact appears to be a central factor in each of these events. Recent studies by our group and others indicate that mitochondrial function is modulated by several signaling molecules, including Smad3, signal transducer and activator of transcription 3, and FoxO. MV rapidly activates Smad3 and signal transducer and activator of transcription 3, which upregulate mitochondrial oxidative stress. Additional roles may be played by angiotensin II and leaky ryanodine receptors causing elevated calcium levels. We present, here, a hypothetical scaffold for understanding the molecular pathogenesis of VIDD, which links together these elements. These pathways harbor several drug targets that could soon move toward testing in clinical trials. We hope that this review will shape a short list of the most promising candidates.

Activation of mammalian target of rapamycin induces lipid accumulation in the diaphragm of ventilated rats and hypoxia-treated C2C12 cells

BACKGROUND

Our previous study demonstrated that ventilators increase diaphragmatic lipid accumulation in rabbits, but their cellular mechanism is poorly understood. Mammalian target of rapamycin (mTOR) plays an important role in atherosclerosis in rat vascular smooth muscle cells. The present study investigated the role of mTOR pathway activation in the diaphragmatic muscle of ventilated rats and hypoxia-induced C2C12 cells.

MATERIALS AND METHODS

Male Sprague-Dawly rats were randomized into a control group (n = 8), controlled mechanical ventilation (CMV) group (n = 8), and CMV + Rapa group (n = 8). We evaluated the diaphragmatic contractility, lipid accumulation, and protein expression of the mTOR pathways. To explore the mechanism underlying ventilator-induced lipid accumulation, we observed protein expression of the mTOR and low-density lipoprotein receptor (LDLr) pathways in C2C12 cells under hypoxic and mTOR pathway inhibitor treatments.

RESULTS

Compared with the control group, there was a significant decrease in the peak twitch and peak tetanic forces in the CMV group (384.24 ± 70.39 versus 496.33 ± 78.64 g/cm², P < 0.05, and 869.24 ± 76.67 versus 1090.72 ± 118.91 g/cm², P < 0.05, respectively). There was a significant increase in peak twitch and peak tetanic forces in the CMV + Rapa group compared with that in the CMV group (501.81 ± 23.15 versus 384.24 ± 70.39 g/cm², P < 0.05, and 992.91 ± 88.99 versus 869.24 ± 76.67 g/cm², P < 0.05, respectively). In the CMV group, there were significant increases in lipid accumulation (0.086 ± 0.009 versus 0.005 ± 0.002, P < 0.05) and expression of mTOR in diaphragmatic fibers compared with those in the control group (P < 0.05). Rapamycin prevented lipid accumulation in rats of the CMV + Rapa group compared with that in the CMV group rats (0.024 ± 0.004 versus 0.086 ± 0.009, P < 0.05). Compared with the CMV group, there was a significant decrease in the phosphorylated protein expression levels of mTOR in rats of the CMV + Rapa group (P < 0.05). Hypoxic conditions activated the mTOR and LDLr pathways in C2C12 cells, which were correlated with an increase in expression of the mTOR and LDLr pathways compared with the control group (P < 0.05). In C2C12 cells treated with hypoxia + rapamycin, activation of the mTOR and LDLr pathways was blocked compared with C2C12 cells treated with hypoxia (P < 0.05).

CONCLUSIONS

These data suggest that CMV and hypoxia-induced activation of the mTOR pathway, resulting in lipid accumulation, and impaired the diaphragmatic contractile function. Therefore, pharmacologic agents that inhibit the mTOR pathway could potentially be useful for mitigating the diaphragmatic contractile dysfunction induced by mechanical ventilation.

[Functional respiratory imaging after neostigmine- or sugammadex-enhanced recovery from neuromuscular blockade in the anesthetised rat: a randomised controlled pilot study]

OBJECTIVES

Reductions in diaphragm activity are associated with the postoperative development of atelectasis. Neostigmine reversal is also associated with increased atelectasis. We assessed the effects of neostigmine, sugammadex, and spontaneous reversal on regional lung ventilation and airway flow.

METHODS

Six Sprague-Dawley rats were paralysed with rocuronium and mechanically ventilated until recovery of the train-of-four ratio to 0.5. We administered neostigmine (0.06mg.kg^-1), sugammadex (15mg.kg^-1), or saline (n=2 per group). Computed tomography scans were obtained during the breathing cycle. Three-dimensional models of lung lobes were generated using functional respiratory imaging technology, and lobar volumes were calculated during the breathing cycle. The diaphragmatic surface was segmented for the end-expiratory and end-inspiratory scans. The total change in volume was reported by the lung volume change from the end-expiratory scan to the end-inspiratory scan. Chest wall movement was defined as the lung volume change minus the volume change that resulted from diaphragm excursion.

RESULTS

The two rats that received neostigmine exhibited a smaller relative contribution of diaphragm movement to the total change in lung volume compared with the two rats that received sugammadex or saline (chest wall contribution (%): 26.69 and 25.55 for neostigmine; -2.77 and 15.98 for sugammadex; 18.82 and 10.30 for saline).

CONCLUSION

This pilot study in rats demonstrated an increased relative contribution of chest wall expansion after neostigmine compared with sugammadex or saline. This smaller relative contribution of diaphragm movement may be explained by a neostigmine-induced decrease in phrenic nerve activity or by remaining occupied acetylcholine receptors after neostigmine.

Diaphragm Thickness and Inspiratory Muscle Functions in Chronic Stroke Patients

Background

The aims of this study are to investigate the difference between the diaphragm thickness at end expiration and the thickness at total lung capacity (TLC), and to examine differences in inspiratory muscle function between stroke patients and healthy individuals.

Material/Methods

Forty-five stroke patients and 49 healthy volunteers were included in this study. Diaphragm thickness was measured at end expiration and at TLC by ultrasonography. The maximal inspiratory pressure (MIP), peak inspiratory flow (PIF), vital capacity (VC), and inspiratory muscle endurance (IME) were assess to evaluate inspiratory muscle function.

Results

In stroke patients, the diaphragm was significantly thinner on the affected side than the less affected side at end expiration and at TLC. The change between the thickness at end expiration and at TLC were also significant on both sides. Between groups, the difference in diaphragm thickness at end expiration was not significant, but at TLC, the diaphragms were significantly thicker in healthy individuals than on either side in stroke patients, and the change in diaphragm thickness was significantly greater for healthy individuals. Inspiratory muscle functions were also significantly greater in healthy individuals. MIP, PIF, and VC were positively correlated with the change in thickness in healthy individuals, and MIP was positively correlated with the change in thickness and IME in stroke patients.

Conclusions

Stroke patients showed decreases in the thickening ability of the diaphragm at TLC and in inspiratory muscle function. The change between the diaphragm thickness at end expiration and at TLC was positively correlated with MIP, PIF, and VC.

[Diaphragm dysfunction : Facts for clinicians]

Diaphragm function is crucial for patient outcome in the ICU setting and during the treatment period. The occurrence of an insufficiency of the respiratory pump, which is predominantly formed by the diaphragm, may result in intubation after failure of noninvasive ventilation. Especially patients suffering from chronic obstructive pulmonary disease are in danger of hypercapnic respiratory failure. Changes in biomechanical properties and fiber texture of the diaphragm are further cofactors directly leading to a need for intubation and mechanical ventilation. After intubation and the following inactivity the diaphragm is subject to profound pathophysiologic changes resulting in atrophy and dysfunction. Besides this inactivity-triggered mechanism (termed as ventilator-induced diaphragmatic dysfunction) multiple factors, comorbidities, pharmaceutical agents and additional hits during the ICU treatment, especially the occurrence of sepsis, influence diaphragm homeostasis and can lead to weaning failure. During the weaning process monitoring of diaphragm function can be done with invasive methods - ultrasound is increasingly established to monitor diaphragm contraction, but further and better powered studies are in need to prove its value as a diagnostic tool.

Kinetics of ventilation-induced changes in diaphragmatic metabolism by bilateral phrenic pacing in a piglet model

Perioperative necessity of deep sedation is inevitably associated with diaphragmatic inactivation. This study investigated 1) the feasibility of a new phrenic nerve stimulation method allowing early diaphragmatic activation even in deep sedation and, 2) metabolic changes within the diaphragm during mechanical ventilation compared to artificial activity. 12 piglets were separated into 2 groups. One group was mechanically ventilated for 12 hrs (CMV) and in the second group both phrenic nerves were stimulated via pacer wires inserted near the phrenic nerves to mimic spontaneous breathing (STIM). Lactate, pyruvate and glucose levels were measured continuously using microdialysis. Oxygen delivery and blood gases were measured during both conditions. Diaphragmatic stimulation generated sufficient tidal volumes in all STIM animals. Diaphragm lactate release increased in CMV transiently whereas in STIM lactate dropped during this same time point (2.6 vs. 0.9 mmol L^-1 after 5:20 hrs; p < 0.001). CMV increased diaphragmatic pyruvate (40 vs. 146 μmol L^-1 after 5:20 hrs between CMV and STIM; p < 0.0001), but not the lactate/pyruvate ratio. Diaphragmatic stimulation via regular electrodes is feasible to generate sufficient ventilation, even in deep sedation. Mechanical ventilation alters the metabolic state of the diaphragm, which might be one pathophysiologic origin of ventilator-induced diaphragmatic dysfunction. Occurrence of hypoxia was unlikely.

Ventilator-induced diaphragmatic dysfunction: what have we learned?

PURPOSE OF REVIEW

The purpose of the review is to summarize and discuss recent research regarding the role of mechanical ventilation in producing weakness and atrophy of the diaphragm in critically ill patients, an entity termed ventilator-induced diaphragmatic dysfunction (VIDD).

RECENT FINDINGS

Severe weakness of the diaphragm is frequent in mechanically ventilated patients, in whom it contributes to poor outcomes including increased mortality. Significant progress has been made in identifying the molecular mechanisms responsible for VIDD in animal models, and there is accumulating evidence for occurrence of the same cellular processes in the diaphragms of human patients undergoing prolonged mechanical ventilation.

SUMMARY

Recent research is pointing the way to novel pharmacologic therapies as well as nonpharmacologic methods for preventing VIDD. The next major challenge in the field will be to move these findings from the bench to the bedside in critically ill patients.

Dysfunction of respiratory muscles in critically ill patients on the intensive care unit

Muscular weakness and muscle wasting may often be observed in critically ill patients on intensive care units (ICUs) and may present as failure to wean from mechanical ventilation. Importantly, mounting data demonstrate that mechanical ventilation itself may induce progressive dysfunction of the main respiratory muscle, i.e. the diaphragm. The respective condition was termed 'ventilator-induced diaphragmatic dysfunction' (VIDD) and should be distinguished from peripheral muscular weakness as observed in 'ICU-acquired weakness (ICU-AW)'. Interestingly, VIDD and ICU-AW may often be observed in critically ill patients with, e.g. severe sepsis or septic shock, and recent data demonstrate that the pathophysiology of these conditions may overlap. VIDD may mainly be characterized on a histopathological level as disuse muscular atrophy, and data demonstrate increased proteolysis and decreased protein synthesis as important underlying pathomechanisms. However, atrophy alone does not explain the observed loss of muscular force. When, e.g. isolated muscle strips are examined and force is normalized for cross-sectional fibre area, the loss is disproportionally larger than would be expected by atrophy alone. Nevertheless, although the exact molecular pathways for the induction of proteolytic systems remain incompletely understood, data now suggest that VIDD may also be triggered by mechanisms including decreased diaphragmatic blood flow or increased oxidative stress. Here we provide a concise review on the available literature on respiratory muscle weakness and VIDD in the critically ill. Potential underlying pathomechanisms will be discussed before the background of current diagnostic options. Furthermore, we will elucidate and speculate on potential novel future therapeutic avenues.

Diaphragm Dysfunction in Mechanically Ventilated Patients

Muscle involvement is found in most critical patients admitted to the intensive care unit (ICU). Diaphragmatic muscle alteration, initially included in this category, has been differentiated in recent years, and a specific type of muscular dysfunction has been shown to occur in patients undergoing mechanical ventilation. We found this muscle dysfunction to appear in this subgroup of patients shortly after the start of mechanical ventilation, observing it to be mainly associated with certain control modes, and also with sepsis and/or multi-organ failure. Although the specific etiology of process is unknown, the muscle presents oxidative stress and mitochondrial changes. These cause changes in protein turnover, resulting in atrophy and impaired contractility, and leading to impaired functionality. The term 'ventilator-induced diaphragm dysfunction' was first coined by Vassilakopoulos et al. in 2004, and this phenomenon, along with injury cause by over-distention of the lung and barotrauma, represents a challenge in the daily life of ventilated patients. Diaphragmatic dysfunction affects prognosis by delaying extubation, prolonging hospital stay, and impairing the quality of life of these patients in the years following hospital discharge. Ultrasound, a non-invasive technique that is readily available in most ICUs, could be used to diagnose this condition promptly, thus preventing delays in starting rehabilitation and positively influencing prognosis in these patients.

Endotoxemia accelerates diaphragm dysfunction in ventilated rabbits

BACKGROUND

Ventilators may induce diaphragm dysfunction, and most of the septic population who are admitted to the intensive care unit require mechanical ventilation. However, there is no evidence that sepsis accelerates the onset of ventilator-induced diaphragm dysfunction or affects the microcirculation. Our study investigated whether lipopolysaccharide (LPS)-induced endotoxemia accelerated diaphragm dysfunction in ventilated rabbits by evaluating microcirculation, lipid accumulation, and diaphragm contractility.

METHODS

After anesthesia and tracheostomy, 25 invasively monitored and mechanically ventilated New Zealand white rabbits were randomized to control (n = 5), controlled mechanical ventilation (CMV) (n = 5), pressure support ventilation (PSV; n = 5), CMV or PSV with LPS-induced endotoxemia (CMV-LPS and PSV-LPS, respectively; n = 5 for each). Rabbits were anesthetized and ventilated for 24 h, except the control rabbits (30 min). Diaphragmatic contractility was evaluated using neuromechanical and neuroventilatory efficiency. We evaluated the following at the end of the protocol: (1) diaphragm microcirculation; (2) lipid accumulation; and (3) diaphragm muscular fibers structure.

RESULTS

Diaphragm contractility, microcirculation, lipid accumulation, and fiber structures were severely compromised in endotoxemic animals after 24 h compared to nonendotoxemic rabbits. Moreover, a slight but significant increase in lipid accumulation was observed in CMV and PSV groups compared with controls (P < 0.05).

CONCLUSIONS

Endotoxemia accelerates the diaphragm dysfunction process in ventilated rabbits, affects the microcirculation, and results in diaphragmatic lipid accumulation and contractility impairment.

Intra-aortic balloon pump combined with mechanical ventilation for treating patients aged > 60 years in cardiogenic shock: Retrospective analysis

Objective

To examine if mechanical ventilation with positive end-expiratory pressure (PEEP) combined with intra-aortic balloon pump (IABP) provided a better outcome than IABP alone for the treatment of cardiogenic shock after acute myocardial infarction in patients aged > 60 years.

Methods

This was a retrospective analysis of data from patients in cardiogenic shock, refractory to pharmacological therapy and treated at a geriatric coronary care unit.

Results

Sixty-two patients were eligible for study inclusion: 33 received IABP alone; 29 received IABP combined with mechanical ventilation. Patients in the IABP + mechanical ventilation group had lower mean arterial blood pressure (BP), systolic BP and partial pressure of oxygen compared with the IABP group, indicating worse cardiac and pulmonary function. In addition, higher rates of pulmonary infection and renal insufficiency were observed in the IABP + mechanical ventilation group than in the IABP group. A statistically significant improvement of left ventricular function before and after treatment was observed in the IABP + mechanical ventilation group, but not in the IABP group. Pulmonary infection and renal insufficiency were risk factors for all-cause in-hospital mortality; successful revascularization was a negative risk factor. There was no between-group difference in survival.

Conclusion

Mechanical ventilation with an appropriate level of PEEP appears to enhance the beneficial effects of IABP on left ventricular function for patients in cardiogenic shock.

High-Level Pressure Support Ventilation Attenuates Ventilator-Induced Diaphragm Dysfunction in Rabbits

BACKGROUND

The effects of different modes of mechanical ventilation in the same ventilatory support level on ventilator-induced diaphragm dysfunction onset were assessed in healthy rabbits.

METHODS

Twenty New Zealand rabbits were randomly assigned to 4 groups (n = 5 in each group). Group 1: no mechanical ventilation; group 2: controlled mechanical ventilation (CMV) for 24 hours; group 3: assist/control ventilation (A/C) mode for 24 hours; group 4: high-level pressure support ventilation (PSV) mode for 24 hours. Heart rate, mean arterial blood pressure, PH, partial pressure of arterial oxygen/fraction of inspired oxygen and partial pressure of arterial carbon dioxide were monitored and diaphragm electrical activity was analyzed in the 4 groups. Caspase-3 was evaluated by protein analysis and diaphragm ultra structure was assessed by electron microscopy.

RESULTS

The centroid frequency and the ratio of high frequency to low frequency were significantly reduced in the CMV, A/C and PSV groups (P < 0.001). The percent change in centroid frequency was significantly lower in the PSV group than in the CMV and A/C groups (P = 0.001 and P = 0.028, respectively). Electromyography of diaphragm integral amplitude decreased by 90% ± 1.48%, 67.8% ± 3.13% and 70.2% ± 4.72% in the CMV, A/C and PSV groups, respectively (P < 0.001). Caspase-3 protein activation was attenuated in the PSV group compared with the CMV and A/C groups (P = 0.035 and P = 0.033, respectively). Irregular swelling of mitochondria along with fractured and fuzzy cristae was observed in the CMV group, whereas mitochondrial cristae were dense and rich in the PSV group. The mitochondrial injury scores (Flameng scores) in the PSV group were the lowest among the 3 ventilatory groups (0.93 ± 0.09 in PSV versus 2.69 ± 0.05 in the CMV [P < 0.01] and PSV versus A/C groups [2.02 ± 0.08, P < 0.01]).

CONCLUSIONS

The diaphragm myoelectric activity was reduced in the PSV group, although excessive oxidative stress and ultra-structural changes of diaphragm were found. However, partial diaphragm electrical activity was retained and diaphragm injury was minimized using the PSV mode.

[Ventilator-induced diaphragm dysfunction : clinically relevant problem]

Mechanical ventilation is a life-saving intervention for patients with respiratory failure or during deep sedation. During continuous mandatory ventilation the diaphragm remains inactive, which activates pathophysiological cascades leading to a loss of contractile force and muscle mass (collectively referred to as ventilator-induced diaphragm dysfunction, VIDD). In contrast to peripheral skeletal muscles this process is rapid and develops after as little as 12 h and has a profound influence on weaning patients from mechanical ventilation as well as increased incidences of morbidity and mortality. In recent years, animal experiments have revealed pathophysiological mechanisms which have been confirmed in humans. One major mechanism is the mitochondrial generation of reactive oxygen species that have been shown to damage contractile proteins and facilitate protease activation. Besides atrophy due to inactivity, drug interactions can induce further muscle atrophy. Data from animal research concerning the influence of corticosteroids emphasize a dose-dependent influence on diaphragm atrophy and function although the clinical interpretation in intensive care patients (ICU) patients might be difficult. Levosimendan has also been proven to increase diaphragm contractile forces in humans which may prove to be helpful for patients experiencing difficult weaning. Additionally, antioxidant drugs that scavenge reactive oxygen species have been demonstrated to protect the diaphragm from VIDD in several animal studies. The translation of these drugs into the IUC setting might protect patients from VIDD and facilitate the weaning process.

Dynamic heterogeneity of exercising muscle blood flow and O2 utilization

Resolving the bases for different physiological functioning or exercise performance within a population is dependent on our understanding of control mechanisms. For example, when most young healthy individuals run or cycle at moderate intensities, oxygen uptake (VO2) kinetics are rapid and the amplitude of the VO2 response is not constrained by O2 delivery. For this to occur, muscle O2 delivery (i.e., blood flow × arterial O2 concentration) must be coordinated superbly with muscle O2 requirements (VO2), the efficacy of which may differ among muscles and distinct fiber types. When the O2 transport system succumbs to the predations of aging or disease (emphysema, heart failure, and type 2 diabetes), muscle O2 delivery and O2 delivery-VO2 matching and, therefore, muscle contractile function become impaired. This forces greater influence of the upstream O2 transport pathway on muscle aerobic energy production, and the O2 delivery-VO2 relationship(s) assumes increased importance. This review is the first of its kind to bring a broad range of available techniques, mostly state of the art, including computer modeling, radiolabeled microspheres, positron emission tomography, magnetic resonance imaging, near-infrared spectroscopy, and phosphorescence quenching to resolve the O2 delivery-VO2 relationships and inherent heterogeneities at the whole body, interorgan, muscular, intramuscular, and microvascular/myocyte levels. Emphasis is placed on the following: 1) intact humans and animals as these provide the platform essential for framing and interpreting subsequent investigations, 2) contemporary findings using novel technological approaches to elucidate O2 delivery-VO2 heterogeneities in humans, and 3) future directions for investigating how normal physiological responses can be explained by O2 delivery-VO2 heterogeneities and the impact of aging/disease on these processes.

Using a non-invasive assessment of lung injury in a murine model of acute lung injury

Arterial oxygen saturation has not been assessed sequentially in conscious mice as a direct consequence of an in vivo murine model of acute lung injury. Here, we report daily changes in arterial oxygen saturation and other cardiopulmonary parameters by using infrared pulse oximetry following intratracheal lipopolysaccharide (IT-LPS) for up to 9 days, and following IT-phosphate buffered saline up to 72 h as a control. We show that arterial oxygen saturation decreases, with maximal decline at 96 h post IT-LPS. Blood oxygen levels negatively correlate with 7 of 10 quantitative markers of murine lung injury, including neutrophilia and interleukin-6 expression. This identifies infrared pulse oximetry as a method to non-invasively monitor arterial oxygen saturation following direct LPS instillations.

Alterations in respiratory and limb muscle strength and size in patients with sepsis who are mechanically ventilated

BACKGROUND

Skeletal muscle wasting and weakness are common in patients with sepsis in the intensive care unit, although less is known about deficits in diaphragm and limb muscles when mechanical ventilation also is required.

OBJECTIVE

The objective of this study was to concurrently investigate relative differences in both thickness and strength of respiratory and peripheral muscles during routine care.

DESIGN

A prospective, cross-sectional study of 16 alert patients with sepsis and 16 people who were healthy (control group) was used.

METHODS

Assessment was made of the diaphragm, upper arm, forearm, and thigh muscle thicknesses with the use of ultrasound; respiratory muscle strength by means of maximal inspiratory pressure; and isometric handgrip, elbow flexion, and knee extension forces with the use of portable dynamometry. To describe relative changes, data also were normalized to fat-free body mass (FFM) measured by bioelectrical impedance spectroscopy.

RESULTS

Patients (9 men, 7 women; mean age=62 years, SD=17) were assessed after a median of 16 days (interquartile range=11-29) of intensive care unit admission. Patients' diaphragm thickness did not differ from that of the control group, even for a given FFM. When normalized to FFM, only the difference in patients' mid-thigh muscle size significantly deviated from that of the control group. Within the patient sample, all peripheral muscle groups were thinner compared with the diaphragm. Patients were significantly weaker than were the control group participants in all muscle groups, including for a given FFM. Within the critically ill group, limb weakness was greater than the already-significant respiratory muscle weakness.

LIMITATIONS

Volitional strength tests were applied such that successive measurements from earlier in the course of illness could not be reliably obtained.

CONCLUSIONS

When measured at bedside, survivors of sepsis and a period of mechanical ventilation may have respiratory muscle weakness without remarkable diaphragm wasting. Furthermore, deficits in peripheral muscle strength and size may exceed those in the diaphragm.

Prolonged mechanical ventilation alters the expression pattern of angio-neogenetic factors in a pre-clinical rat model

OBJECTIVE

Mechanical ventilation (MV) is a life saving intervention for patients with respiratory failure. Even after 6 hours of MV, diaphragm atrophy and dysfunction (collectively referred to as ventilator-induced diaphragmatic dysfunction, VIDD) occurs in concert with a blunted blood flow and oxygen delivery. The regulation of hypoxia sensitive factors (i.e. hypoxia inducible factor 1α, 2α (HIF-1α,-2α), vascular endothelial growth factor (VEGF)) and angio-neogenetic factors (angiopoietin 1-3, Ang) might contribute to reactive and compensatory alterations in diaphragm muscle.

METHODS

Male Wistar rats (n = 8) were ventilated for 24 hours or directly sacrificed (n = 8), diaphragm and mixed gastrocnemius muscle tissue was removed. Quantitative real time PCR and western blot analyses were performed to detect changes in angio-neogenetic factors and inflammatory markers. Tissues were stained using Isolectin (IB 4) to determine capillarity and calculate the capillary/fiber ratio.

RESULTS

MV resulted in up-regulation of Ang 2 and HIF-1α mRNA in both diaphragm and gastrocnemius, while VEGF mRNA was down-regulated in both tissues. HIF-2α mRNA was reduced in both tissues, while GLUT 4 mRNA was increased in gastrocnemius and reduced in diaphragm samples. Protein levels of VEGF, HIF-1α, -2α and 4 did not change significantly. Additionally, inflammatory cytokine mRNA (Interleukin (IL)-6, IL-1β and TNF α) were elevated in diaphragm tissue.

CONCLUSION

The results demonstrate that 24 hrs of MV and the associated limb disuse induce an up-regulation of angio-neogenetic factors that are connected to HIF-1α. Changes in HIF-1α expression may be due to several interactions occurring during MV.

Moderate and prolonged hypercapnic acidosis may protect against ventilator-induced diaphragmatic dysfunction in healthy piglet: an in vivo study

Introduction

Protective ventilation by using limited airway pressures and ventilation may result in moderate and prolonged hypercapnic acidosis, as often observed in critically ill patients. Because allowing moderate and prolonged hypercapnia may be considered protective measure for the lungs, we hypothesized that moderate and prolonged hypercapnic acidosis may protect the diaphragm against ventilator-induced diaphragmatic dysfunction (VIDD). The aim of our study was to evaluate the effects of moderate and prolonged (72 hours of mechanical ventilation) hypercapnic acidosis on in vivo diaphragmatic function.

Methods

Two groups of anesthetized piglets were ventilated during a 72-hour period. Piglets were assigned to the Normocapnia group (n = 6), ventilated in normocapnia, or to the Hypercapnia group (n = 6), ventilated with moderate hypercapnic acidosis (PaCO₂ from 55 to 70 mm Hg) during the 72-hour period of the study. Every 12 hours, we measured transdiaphragmatic pressure (Pdi) after bilateral, supramaximal transjugular stimulation of the two phrenic nerves to assess in vivo diaphragmatic contractile force. Pressure/frequency curves were drawn after stimulation from 20 to 120 Hz of the phrenic nerves. The protocol was approved by our institutional animal-care committee.

Results

Moderate and prolonged hypercapnic acidosis was well tolerated during the study period. The baseline pressure/frequency curves of the two groups were not significantly different (Pdi at 20 Hz, 32.7 ± 8.7 cm H₂O, versus 34.4 ± 8.4 cm H₂O; and at 120 Hz, 56.8 ± 8.7 cm H₂O versus 60.8 ± 5.7 cm H₂O, for Normocapnia and Hypercapnia groups, respectively). After 72 hours of ventilation, Pdi decreased by 25% of its baseline value in the Normocapnia group, whereas Pdi did not decrease in the Hypercapnia group.

Conclusions

Moderate and prolonged hypercapnic acidosis limited the occurrence of VIDD during controlled mechanical ventilation in a healthy piglet model. Consequences of moderate and prolonged hypercapnic acidosis should be better explored with further studies before being tested on patients.