Recovery Of Diaphragm Function Research Articles

PTEN inhibition promotes robust growth of bulbospinal respiratory axons and partial recovery of diaphragm function in a chronic model of cervical contusion spinal cord injury

High spinal cord injury (SCI) leads to persistent and debilitating compromise in respiratory function. Cervical SCI not only causes the death of phrenic motor neurons (PhMNs) that innervate the diaphragm, but also damages descending respiratory pathways originating in the rostral ventral respiratory group (rVRG) located in the brainstem, resulting in denervation and consequent silencing of spared PhMNs located caudal to injury. It is imperative to determine whether interventions targeting rVRG axon growth and respiratory neural circuit reconnection are efficacious in chronic cervical contusion SCI, given that the vast majority of individuals are chronically-injured and most cases of SCI involve contusion-type damage to the cervical region. We therefore employed a rat model of chronic cervical hemicontusion to test therapeutic manipulations aimed at reconstructing damaged rVRG-PhMN-diaphragm circuitry to achieve recovery of respiratory function. At a chronic time point post-injury, we systemically administered: an antagonist peptide directed against phosphatase and tensin homolog (PTEN), a central inhibitor of neuron-intrinsic axon growth potential; an antagonist peptide directed against receptor-type protein tyrosine phosphatase sigma (PTPσ), another important negative regulator of axon growth capacity; or a combination of these two peptides. PTEN antagonist peptide (PAP4) promoted partial recovery of diaphragm motor activity out to nine months post-injury (though this effect depended on the anesthetic regimen used during recording), while PTPσ peptide did not impact diaphragm function after cervical SCI. Furthermore, PAP4 promoted robust growth of descending bulbospinal rVRG axons caudal to the injury within the denervated portion of the PhMN pool, while PTPσ peptide did not affect rVRG axon growth at this location that is critical to control of diaphragmatic respiratory function. In conclusion, we find that, when PTEN inhibition is targeted at a chronic time point following cervical contusion, our non-invasive PAP4 strategy can successfully promote significant regrowth of damaged respiratory neural circuitry and also partial recovery of diaphragm motor function.

Comparison of the effects of neostigmine and sugammadex on postoperative residual curarization and postoperative pulmonary complications by means of diaphragm and lung ultrasonography: a study protocol for prospective double-blind randomized controlled trial

BackgroundPostoperative residual curarization (PORC) may be a potential risk factor of postoperative pulmonary complications (PPCs), and both of them will lead to adverse consequences on surgical patient recovery. The train-of-four ratio (TOFr) which is detected by acceleromyography of the adductor pollicis is thought as the gold standard for the measurement of PORC. However, diaphragm function recovery may differ from that of the peripheral muscles. Recent studies suggested that diaphragm ultrasonography may be useful to reveal the diaphragm function recovery, and similarly, lung ultrasound was reported for the assessment of PPCs in recent years as well. Sugammadex reversal of neuromuscular blockade is rapid and complete, and there appear to be fewer postoperative complications than with neostigmine. This study aims to compare the effects of neostigmine and sugammadex, on PORC and PPCs employing diaphragm and lung ultrasonography, respectively.Methods/designIn this prospective, double-blind, randomized controlled trial, patients of the American Society of Anesthesiologists Physical Status I–III, aged over 60, will be enrolled. They will be scheduled to undergo arthroplasty under general anesthesia. All patients will be allocated randomly into two groups, group NEO (neostigmine) and group SUG (sugammadex), using these two drugs for reversing rocuronium. The primary outcome of the study is the incidence of PPCs in the NEO and SUG groups. The secondary outcomes are the evaluation of diaphragm ultrasonography and lung ultrasound, performed by an independent sonographer before anesthesia, and at 10 min and 30 min after extubation in the post-anesthesia care unit, respectively.DiscussionElimination of PORC is a priority at the emergence of anesthesia, and it may be associated with reducing postoperative complications like PPCs. Sugammadex was reported to be superior to reverse neuromuscular blockade than neostigmine. Theoretically, complete recovery of neuromuscular function should be indicated by TOFr > 0.9. However, the diaphragm function recovery may not be the same matter, which probably harms pulmonary function. The hypothesis will be proposed that sugammadex is more beneficial than neostigmine to reduce the incidence of PPCs and strongly favorable for the recovery of diaphragm function in our study setting.Trial registrationClinicalTrials.gov NCT05040490. Registered on 3 September 2021

Ampakine CX717 Stimulates Diaphragm Activity following Mid‐cervical Spinal Contusion Injury

Cervical spinal cord injuries result in significant respiratory compromise and there is a need to develop therapies to counter respiratory insufficiency in this patient population. Ampakines are positive allosteric modulators of AMPA receptors, and can stimulate breathing during states of hypoventilation, such as following opioid overdose or in neuromuscular disorders. Our laboratory has previously shown that acute treatment with ampakine CX717 can stimulate phrenic activity in spinally injured animals under urethane anesthesia. Recently, we extended these findings by showing that a low dose of CX717 was sufficient to enhance diaphragm electromyography (EMG) activity and tidal volume in unanaesthetized animals with a C2 hemisection injury. The next step in the translational pathway, and the goal of the current study, was to test the efficacy of ampakines in a model of contusion injury that is more similar to the injuries typically experienced by humans. The C4 contusion injury used in the current study results in direct phrenic motor neuron loss and significant damage of the spinal pathways innervating respiratory motor pools. This model is also associated with strong spontaneous recovery of diaphragm function, such that pronounced deficits are likely to be detected only in the initial week following injury. Animals were implanted with in‐dwelling bilateral diaphragm EMG electrodes and ventilation was measured using whole body plethysmography. At 4 and 14 days following a 150 kDy C4 unilateral contusion injury (C4Ct), male and female rats were given a single intravenous bolus of CX717 (5 mg/kg, n=4) or vehicle (2‐hydroxypropyl‐beta‐cyclodextrin; HPCD; n=4). At the 4‐day time point, infusion of CX717 increased peak diaphragm EMG (recorded ipsilateral to C4Ct) by 40‐50% when compared to vehicle group. Respiratory rate was also elevated in the CX717 group by 80% post‐infusion, indicating a likely supraspinal mechanism of the impact of ampakines. In the CX717 group, tidal volume was increased by 25±13% during infusion, 20±16% at 5 min post infusion and returned to baseline levels by 15 mins post CX717 infusion. There was no change in tidal volume in the vehicle group. During an acute respiratory challenge with hypoxia (10% O2), CX717 treated animals were able to increase diaphragm EMG (100±15%) to a greater extent as compared to vehicle (50 ± 23%, P=0.004). Similarly, during a combined hypoxia‐hypercapnia challenge (10% O2, 7% CO2), CX717 treated animals displayed an increased diaphragm EMG response (200±44%) compared to vehicle (100 ± 55%, P=0.0144). In contrast to the 4‐day data, there was no discernable impact of ampakines on baseline or challenged breathing at 14 days post C4Ct. This is perhaps not surprising because prior work establishes that in this injury model, robust compensation has occurred after 2 weeks, and deficits in diaphragm activation are difficult to detect. In summary, our data indicate that low dose, low impact ampakine treatment can increase diaphragm muscle output at an acute timepoint following mid‐cervical contusion type injuries. These studies pave the path for future experiments to test if ampakine treatment can be combined with rehabilitation techniques to further enhance the therapeutic effect of ampakines in this injury model.

Tissue Engineering for the Diaphragm and its Various Therapeutic Possibilities – A Systematic Review

AbstractDiaphragmatic impairments exhibit high morbidity as well as mortality while current treatment options remain unsatisfactory. Tissue engineering (TE) approaches have explored the generation of an optimal biocompatible scaffold for diaphragmatic repair through tissue decellularization or de novo construction, with or without the addition of cells. The authors conducted a systematic review on the current state of the art in diaphragmatic tissue engineering (DTE) and found 24 articles eligible for final synthesis. The included approaches studied decellularization‐based graft generation (9) and de novo bioscaffold construction (9). Three studies focused on in vitro host‐scaffold interaction with synthesized, recellularized grafts (2) and decellularized extracellular matrix scaffolds (1). Another three studies investigated evaluation tools for decellularization efficacy. Among all studies, recellularization is performed in both decellularization‐based (4) and de novo generated scaffolds (4). De novo constructed biocomposites as well as decellularized and recellularized scaffolds induced pro‐regenerative remodeling and recovery of diaphragmatic function in all examined animal models. Potential therapeutic applications comprise substance defects requiring patch repair, such as congenital diaphragmatic hernia, and functional diseases demanding an entire organ transplant, like muscular dystrophies or dysfunction after prolonged artificial respiration.

Respiratory axon regeneration in the chronically injured spinal cord

Promoting the combination of robust regeneration of damaged axons and synaptic reconnection of these growing axon populations with appropriate neuronal targets represents a major therapeutic goal following spinal cord injury (SCI). A key impediment to achieving this important aim includes an intrinsic inability of neurons to extend axons in adult CNS, particularly in the context of the chronically-injured spinal cord. We tested whether an inhibitory peptide directed against phosphatase and tensin homolog (PTEN: a central inhibitor of neuron-intrinsic axon growth potential) could restore inspiratory diaphragm function by reconnecting critical respiratory neural circuitry in a rat model of chronic cervical level 2 (C2) hemisection SCI. We found that systemic delivery of PTEN antagonist peptide 4 (PAP4) starting at 8 weeks after C2 hemisection promoted substantial, long-distance regeneration of injured bulbospinal rostral Ventral Respiratory Group (rVRG) axons into and through the lesion and back toward phrenic motor neurons (PhMNs) located in intact caudal C3-C5 spinal cord. Despite this robust rVRG axon regeneration, PAP4 stimulated only minimal recovery of diaphragm function. Furthermore, re-lesion through the hemisection site completely removed PAP4-induced functional improvement, demonstrating that axon regeneration through the lesion was responsible for this partial functional recovery. Interestingly, there was minimal formation of putative excitatory monosynaptic connections between regrowing rVRG axons and PhMN targets, suggesting that (1) limited rVRG-PhMN synaptic reconnectivity was responsible at least in part for the lack of a significant functional effect, (2) chronically-injured spinal cord presents an obstacle to achieving synaptogenesis between regenerating axons and post-synaptic targets, and (3) addressing this challenge is a potentially-powerful strategy to enhance therapeutic efficacy in the chronic SCI setting. In conclusion, our study demonstrates a non-invasive and transient pharmacological approach in chronic SCI to repair the critically-important neural circuitry controlling diaphragmatic respiratory function, but also sheds light on obstacles to circuit plasticity presented by the chronically-injured spinal cord.

Diaphragm Pacing in Lung Transplant Patients: To Identify and Treat Diaphragm Function Abnormalities

Purpose Lung disease and transplantation can lead to diaphragm dysfunction (DD). Phrenic neuropathy in lung transplants increases morbidity. Diaphragm pacing (DP) improves nerve recovery and prevents ventilator induced diaphragm dysfunction (VIDD). The FDA authorized temporary DP to decrease the burden of mechanical ventilators (MV) during the COVID-19 pandemic. We report the largest experience of DP in lung transplantation. Methods This is a retrospective analysis of an IRB approved prospective, non-randomized interventional experience at a single institution with two DP systems. A chronic DP system was laparoscopically implanted in those with identified (either pre or post-transplant) phrenic nerve injury. Post implantation, diaphragm stimulation ensued and results evaluated radiographically and with diaphragm electromyography (dEMG). Transplant recipients had the temporary DP system implanted percutaneously via their chest incision. Diaphragm activity was monitored with the electrodes and stimulation applied for MV weaning. Results 8 patients utilized DP with no device adverse events. 3 patients with DD, 6 months average post-transplant, had chronic DP implanted. All had evidence of subsequent recovery of diaphragm function. 1 patient had DP pre-transplant for unilateral DD with subsequent diaphragm recovery. At time of unilateral transplant on contralateral side a phrenic nerve injury was identified. DP was used during the recovery. 4 patients underwent implantation of temporary DP electrodes during lung transplant. 2 patients had bilateral dEMG identified post-operatively with uneventful recovery and removal of electrodes. 2 patient had no dEMG activity or movement bilaterally post-operatively. Retrospectively this was a pre-operative condition. 1 recovered diaphragm function at 2 weeks with DP therapy. The 2nd is still undergoing DP. 3 patients with phrenic nerve dysfunction post operatively also had intercostal nerve cryoanalgesia which decreases external intercostal muscles use for respiration. These 3 patients had prolonged ventilation difficulties. Conclusion DP was safely used in lung transplantation in identifying and improving recovery of phrenic nerve injuries and preventing VIDD. Intercostal nerve cryoanalgesia should not be used if there is DD. DP should be considered in all lung transplants for improved outcomes.

LAR inhibitory peptide promotes recovery of diaphragm function and multiple forms of respiratory neural circuit plasticity after cervical spinal cord injury

Chondroitin sulfate proteoglycans (CSPGs), up-regulated in and around the lesion after traumatic spinal cord injury (SCI), are key extracellular matrix inhibitory molecules that limit axon growth and consequent recovery of function. CSPG-mediated inhibition occurs via interactions with axonal receptors, including leukocyte common antigen- related (LAR) phosphatase. We tested the effects of a novel LAR inhibitory peptide in rats after hemisection at cervical level 2, a SCI model in which bulbospinal inspiratory neural circuitry originating in the medullary rostral ventral respiratory group (rVRG) becomes disconnected from phrenic motor neuron (PhMN) targets in cervical spinal cord, resulting in persistent partial-to-complete diaphragm paralysis. LAR peptide was delivered by a soaked gelfoam, which was placed directly over the injury site immediately after C2 hemisection and replaced at 1 week post-injury. Axotomized rVRG axons originating in ipsilateral medulla or spared rVRG fibers originating in contralateral medulla were separately assessed by anterograde tracing via AAV2-mCherry injection into rVRG. At 8 weeks post-hemisection, LAR peptide significantly improved ipsilateral hemidiaphragm function, as assessed in vivo with electromyography recordings. LAR peptide promoted robust regeneration of ipsilateral-originating rVRG axons into and through the lesion site and into intact caudal spinal cord to reach PhMNs located at C3-C5 levels. Furthermore, regenerating rVRG axons re-established putative monosynaptic connections with their PhMNs targets. In addition, LAR peptide stimulated robust sprouting of both modulatory serotonergic axons and contralateral-originating rVRG fibers within the PhMN pool ipsilateral/caudal to the hemisection. Our study demonstrates that targeting LAR-based axon growth inhibition promotes multiple forms of respiratory neural circuit plasticity and provides a new peptide-based therapeutic strategy to ameliorate the devastating respiratory consequences of SCI.

AAV2-BDNF promotes respiratory axon plasticity and recovery of diaphragm function following spinal cord injury.

More than half of spinal cord injury (SCI) cases occur in the cervical region, leading to respiratory dysfunction due to damaged neural circuitry that controls critically important muscles such as the diaphragm. The C3-C5 spinal cord is the location of phrenic motor neurons (PhMNs) that are responsible for diaphragm activation; PhMNs receive bulbospinal excitatory drive predominately from supraspinal neurons of the rostral ventral respiratory group (rVRG). Cervical SCI results in rVRG axon damage, PhMN denervation, and consequent partial-to-complete paralysis of hemidiaphragm. In a rat model of C2 hemisection SCI, we expressed the axon guidance molecule, brain-derived neurotrophic factor (BDNF), selectively at the location of PhMNs (ipsilateral to lesion) to promote directed growth of rVRG axons toward PhMN targets by performing intraspinal injections of adeno-associated virus serotype 2 (AAV2)-BDNF vector. AAV2-BDNF promoted significant functional diaphragm recovery, as assessed by in vivo electromyography. Within the PhMN pool ipsilateral to injury, AAV2-BDNF robustly increased sprouting of both spared contralateral-originating rVRG axons and serotonergic fibers. Furthermore, AAV2-BDNF significantly increased numbers of putative monosynaptic connections between PhMNs and these sprouting rVRG and serotonergic axons. These findings show that targeting circuit plasticity mechanisms involving the enhancement of synaptic inputs from spared axon populations is a powerful strategy for restoring respiratory function post-SCI.-Charsar, B. A., Brinton, M. A., Locke, K., Chen, A. Y., Ghosh, B., Urban, M. W., Komaravolu, S., Krishnamurthy, K., Smit, R., Pasinelli, P., Wright, M. C., Smith, G. M., Lepore, A. C. AAV2-BDNF promotes respiratory axon plasticity and recovery of diaphragm function following spinal cord injury.

P4385Diaphragm dysfunction following cardiac surgery: role of ultrasound imaging for initial and follow-up assessment during cardiac rehabilitation

Abstract Background Diaphragm dysfunction is a common complication of cardiac surgery, often underdiagnosed. Ultrasonography (US) is a promising technique for diaphragmatic assessment. Few trials have been conducted using US after heart surgery and no clear data exist on the recovery of diaphragm function after cardiovascular rehabilitation (CR). Purpose The aim of this study is to evaluate post-cardiac surgery diaphragm dysfunction using US and to assess the impact of an inpatient CR programme on its functional recovery. Methods In a single-centre prospective cohort study 97 consecutive patients hospitalised in our CR Unit were enrolled. 14 patients underwent aortic valve replacement, 38 mitral valve repair or replacement, 14 coronary artery bypass grafting (CABG), 22 combined surgery, and 9 other surgical interventions. We performed diaphragm US at admission and after 10 rehabilitative sessions. The following parameters were assessed: thickening fraction (TF) in B-mode on the right intercostal projections, and excursion, time of inspiration, time of a respiratory cycle and contraction velocity in M-mode on right anterior subcostal projections. Results After cardiac surgery, the incidence of diaphragm dysfunction and paralysis were 60% and 1%, respectively. Patients with TF <20% at admission showed a significant improvement in TF (13.30%, IQR 8.69–17.39 vs 27.27%, IQR 21.05–31.58; p<0.001), excursion (1.67cm, IQR 1.3–2.1 vs 2.23cm, IQR 1.9–2.7; p<0.001), time of inspiration (0.9s, IQR 0.9–1.07 vs 1.01s, IQR 0.87–1.13; p=0.005), time of a respiratory cycle (2.67s, IQR 2.38–3.05 vs 3.07s, IQR 2.68–3.35; p<0.001) and velocity (1.81cm/s, IQR 1.14–2.33 vs 2.24cm/s, IQR 1.92–2.76; p<0.001). On the contrary, in patients with a TF>20%, no additional improvement was observed. In both groups, there was a significant improvement in the parameters of physical performance. In particular, in the group with a TF<20%, the distance covered during the 6MWT (300m, IQR 205–370 vs 555m, IQR 450–612; p<0.001) and the energy cost of physical activity (2.60, IQR 2.13–2.92 vs 4.09, IQR 3.44–4.50; p<0.001) increased while the perception of exertion (Borg Scale 11, IQR 11–13 vs 13, IQR 12–13; p=0.011) was reduced. At the 10th day assessment, 51.5% of the total population had a recovery of diaphragm function, whilst 48.5% had a failure of recovery (TF relative change between admission and discharge <60%). The multivariate analysis identified CABG as an independent predictor of failure of diaphragm recovery (OR 5.44; CI 1.10–26.84, p=0.037). Conclusion US might be a valuable part of routine clinical practice for initial and follow-up assessment of patients after open-heart surgery. CR showed to be an effective strategy to improve diaphragm parameters in patients with post-surgical dysfunction. Progressive evaluation of diaphragm function may drive personalised rehabilitation programmes.

Protein Tyrosine Phosphatase σ Inhibitory Peptide Promotes Recovery of Diaphragm Function and Sprouting of Bulbospinal Respiratory Axons after Cervical Spinal Cord Injury.

Damage to respiratory neural circuitry and consequent loss of diaphragm function is a major cause of morbidity and mortality after cervical spinal cord injury (SCI). Upon SCI, inspiratory signals originating in the medullary rostral ventral respiratory group (rVRG) become disrupted from their phrenic motor neuron (PhMN) targets, resulting in diaphragm paralysis. Limited growth of both damaged and spared axon populations occurs after central nervous system trauma attributed, in part, to expression of various growth inhibitory molecules, some that act through direct interaction with the protein tyrosine phosphatase sigma (PTPσ) receptor located on axons. In the rat model of C2 hemisection SCI, we aimed to block PTPσ signaling to investigate potential mechanisms of axon plasticity and respiratory recovery using a small molecule peptide mimetic that inhibits PTPσ. The peptide was soaked into a biocompatible gelfoam and placed directly over the injury site immediately after hemisection and replaced with a freshly soaked piece 1 week post-SCI. At 8 weeks post-hemisection, PTPσ peptide significantly improved ipsilateral hemidiaphragm function, as assessed in vivo with electromyography recordings. PTPσ peptide did not promote regeneration of axotomized rVRG fibers originating in ipsilateral medulla, as assessed by tracing after adeno-associated virus serotype 2/mCherry injection into the rVRG. Conversely, PTPσ peptide stimulated robust sprouting of contralateral-originating rVRG fibers and serotonergic axons within the PhMN pool ipsilateral to hemisection. Further, relesion through the hemisection did not compromise diaphragm recovery, suggesting that PTPσ peptide-induced restoration of function was attributed to plasticity of spared axon pathways descending in contralateral spinal cord. These data demonstrate that inhibition of PTPσ signaling can promote significant recovery of diaphragm function after SCI by stimulating plasticity of critical axon populations spared by the injury and consequently enhancing descending excitatory input to PhMNs.

Astrocyte progenitor transplantation promotes regeneration of bulbospinal respiratory axons, recovery of diaphragm function, and a reduced macrophage response following cervical spinal cord injury.

Stem/progenitor cell transplantation delivery of astrocytes is a potentially powerful strategy for spinal cord injury (SCI). Axon extension into SCI lesions that occur spontaneously or in response to experimental manipulations is often observed along endogenous astrocyte "bridges," suggesting that augmenting this response via astrocyte lineage transplantation can enhance axon regrowth. Given the importance of respiratory dysfunction post-SCI, we transplanted glial-restricted precursors (GRPs)-a class of lineage-restricted astrocyte progenitors-into the C2 hemisection model and evaluated effects on diaphragm function and the growth response of descending rostral ventral respiratory group (rVRG) axons that innervate phrenic motor neurons (PhMNs). GRPs survived long term and efficiently differentiated into astrocytes in injured spinal cord. GRPs promoted significant recovery of diaphragm electromyography amplitudes and stimulated robust regeneration of injured rVRG axons. Although rVRG fibers extended across the lesion, no regrowing axons re-entered caudal spinal cord to reinnervate PhMNs, suggesting that this regeneration response-although impressive-was not responsible for recovery. Within ipsilateral C3-5 ventral horn (PhMN location), GRPs induced substantial sprouting of spared fibers originating in contralateral rVRG and 5-HT axons that are important for regulating PhMN excitability; this sprouting was likely involved in functional effects of GRPs. Finally, GRPs reduced the macrophage response (which plays a key role in inducing axon retraction and limiting regrowth) both within the hemisection and at intact caudal spinal cord surrounding PhMNs. These findings demonstrate that astrocyte progenitor transplantation promotes significant plasticity of rVRG-PhMN circuitry and restoration of diaphragm function and suggest that these effects may be in part through immunomodulation.

Cell-type specific expression of constitutively-active Rheb promotes regeneration of bulbospinal respiratory axons following cervical SCI

Damage to respiratory neural circuitry and consequent loss of diaphragm function is a major cause of morbidity and mortality in individuals suffering from traumatic cervical spinal cord injury (SCI). Repair of CNS axons after SCI remains a therapeutic challenge, despite current efforts. SCI disrupts inspiratory signals originating in the rostral ventral respiratory group (rVRG) of the medulla from their phrenic motor neuron (PhMN) targets, resulting in loss of diaphragm function. Using a rat model of cervical hemisection SCI, we aimed to restore rVRG-PhMN-diaphragm circuitry by stimulating regeneration of injured rVRG axons via targeted induction of Rheb (ras homolog enriched in brain), a signaling molecule that regulates neuronal-intrinsic axon growth potential. Following C2 hemisection, we performed intra-rVRG injection of an adeno-associated virus serotype-2 (AAV2) vector that drives expression of a constitutively-active form of Rheb (cRheb). rVRG neuron-specific cRheb expression robustly increased mTOR pathway activity within the transduced rVRG neuron population ipsilateral to the hemisection, as assessed by levels of phosphorylated ribosomal S6 kinase. By co-injecting our novel AAV2-mCherry/WGA anterograde/trans-synaptic axonal tracer into rVRG, we found that cRheb expression promoted regeneration of injured rVRG axons into the lesion site, while we observed no rVRG axon regrowth with AAV2-GFP control. AAV2-cRheb also significantly reduced rVRG axonal dieback within the intact spinal cord rostral to the lesion. However, cRheb expression did not promote any recovery of ipsilateral hemi-diaphragm function, as assessed by inspiratory electromyography (EMG) burst amplitudes. This lack of functional recovery was likely because regrowing rVRG fibers did not extend back into the caudal spinal cord to synaptically reinnervate PhMNs that we retrogradely-labeled with cholera toxin B from the ipsilateral hemi-diaphragm. Our findings demonstrate that enhancing neuronal-intrinsic axon growth capacity can promote regeneration of injured bulbospinal respiratory axons after SCI, but this strategy may need to be combined with other manipulations to achieve reconnection of damaged neural circuitry and ultimately recovery of diaphragm function.

Evaluation of diaphragmatic function in mechanically ventilated children: An ultrasound study.

BackgroundThe recovery of diaphragmatic function is vital for successful extubation from mechanical ventilation. Recent studies have detected diaphragm atrophy in ventilated adults by using ultrasound, but no similar report has been conducted in children. In the current study, we hypothesized that mechanically ventilated children may also develop diaphragm atrophy and diaphragmatic dysfunction.Materials and methodsChildren who were admitted to the pediatric intensive care unit and were newly intubated for mechanical ventilation were enrolled into this prospective case–control study. Diaphragm ultrasound assessments were performed daily to evaluate diaphragmatic function in the enrolled children until their discharge from the pediatric intensive care unit. Diaphragm thickness and the diaphragmatic thickening fraction (DTF) were measured through these assessments.ResultsA total of 31 patients were enrolled, and overall, 1389 ultrasound assessments were performed. Immediately after intubation, the initial diaphragm thickness and DTF were measured to be 1.94 ± 0.44 mm and 25.85% ± 3.29%, respectively. In the first 24 hours of mechanical ventilation, diaphragm thickness and the DTF decreased substantially and decreased gradually thereafter. After extubation, the DTF was significantly different between the successful and failed extubation groups (P < 0.001), and a DTF value of <17% was associated with extubation failure.ConclusionsDiaphragm ultrasound is a noninvasive method for measuring diaphragmatic function in mechanically ventilated children. In this study, significant diaphragm atrophy and a decreased DTF were observed within 24 hours of mechanical ventilation. The recovery of diaphragm thickness and the DTF may be a potential predictor of successful extubation from mechanical ventilation.

Nanoconjugate-bound adenosine A1 receptor antagonist enhances recovery of breathing following acute cervical spinal cord injury

Respiratory complications in patients with spinal cord injury (SCI) are common and can have a negative impact on the quality of patients' lives. Previously, we found that intradiaphragmatic administration of the nanoconjugate-bound A1 adenosine receptor antagonist, 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) induced recovery of diaphragm function following SCI in rats. When administered immediately following the injury, recovery was observed as early as 3days following SCI and it persisted until the end of the study, 28days after the drug delivery. The recovery was observed using diaphragmatic electromyography (EMG) as well as phrenic nerve recordings; both of which were conducted under anesthetized conditions. Confounding effects of anesthetic may make data interpretation complex in terms of the impact on overall ventilatory function and clinical relevance. The objective of the present study was to test the hypothesis that intradiaphragmatic administration of nanoconjugate-bound DPCPX, enhances recovery of ventilation following SCI in the unanesthetized rat. To that end, Sprague-Dawley rats underwent C2 spinal cord hemisection (C2Hx) on day 0 and received either: (i) 0.15μg/kg of nanoconjugate-bound DPCPX or (ii) vehicle control (50μl distilled water). To assess ventilation, unrestrained whole body plethysmography (WBP) was performed on day 0 (immediately before the surgery) and 3, 7, 14, 21 and 28days following the SCI. Frequency, tidal volume, and minute ventilation data were analyzed in two minute bins while the animal was calm and awake. We found that a single administration of the nanoconjugate-bound A1 adenosine receptor antagonist facilitated recovery of tidal volume and minute ventilation following SCI. Furthermore, the treatment attenuated SCI-associated increases in respiratory frequency. Taken together, this study suggests that the previously observed DPCPX nanoconjugate-induced recovery in diaphragmatic and phrenic motor outputs may translate to a clinically meaningful improvement in ventilatory function in patients with SCI.

Prolonged Diaphragm Weakness in Acute Lung Injury UL1TR000117, HL112085, HL113494

Acquired skeletal muscle weakness, a devastating complication of critical illness, affects both limb and respiratory muscles. Diaphragm weakness is especially important, persisting for days to weeks, prolonging duration of mechanical ventilation and increasing in‐hospital mortality. Currently no animal model of critical illness replicates the sustained diaphragm weakness observed in patients. We sought to establish an animal model that parallels the severity and duration of diaphragm weakness observed in critically ill patients using male C57BL6 mice (n=50) treated with a single intratracheal injection of lipopolysaccharide (IT‐LPS) which induces acute lung injury (ALI). We first measured diaphragm specific force in mice treated with varying doses of IT‐LPS at several time points to determine the dose that would produce sustained diaphragm injury. We then examined diaphragm force‐frequency relationships in mice treated with 30,000 EU/gm of IT‐LPS. ALI invoked significant loss in animal body weight and hypothermia. In addition, ALI markedly reduced diaphragm specific force generation which persisted at Day 10 (150 Hz force averaged 26.4±0.5,17.7±1.7, 15.6±1.9, 15.9±1.8, 15.7±12.1, and 16.7±2.1 N/cm2 for controls, Day 1, Day 2, Day 4, Day 7, and Day 10 groups, respectively, p&lt;0.001). This is the first study to show that a clinically relevant animal model of critical illness, acute lung injury, induces diaphragm weakness in a pattern and time course that parallels data obtained from human studies. We speculate that this model may prove useful for determining the mechanistic basis for prolonged respiratory muscle weakness as well as the pathways required for recovery of diaphragm function in critically ill patients.

Recovery of Diaphragm Function following Mechanical Ventilation in a Rodent Model

BackgroundMechanical ventilation (MV) induces diaphragmatic muscle fiber atrophy and contractile dysfunction (ventilator induced diaphragmatic dysfunction, VIDD). It is unknown how rapidly diaphragm muscle recovers from VIDD once spontaneous breathing is restored. We hypothesized that following extubation, the return to voluntary breathing would restore diaphragm muscle fiber size and contractile function using an established rodent model.MethodsFollowing 12 hours of MV, animals were either euthanized or, after full wake up, extubated and returned to voluntary breathing for 12 hours or 24 hours. Acutely euthanized animals served as controls (each n = 8/group). Diaphragmatic contractility, fiber size, protease activation, and biomarkers of oxidative damage in the diaphragm were assessed.Results12 hours of MV induced VIDD. Compared to controls diaphragm contractility remained significantly depressed at 12 h after extubation but rebounded at 24 h to near control levels. Diaphragmatic levels of oxidized proteins were significantly elevated after MV (p = 0.002) and normalized at 24 hours after extubation.ConclusionsThese findings indicate that diaphragm recovery from VIDD, as indexed by fiber size and contractile properties, returns to near control levels within 24 hours after returning to spontaneous breathing. Besides the down-regulation of proteolytic pathways and oxidative stress at 24 hours after extubation further repairing mechanisms have to be determined.

Idiopathic Diaphragmatic Paralysis: Bell’s Palsy of the Diaphragm?

Idiopathic diaphragm paralysis is probably more common and responsible for more morbidity than generally appreciated. Bell's palsy, or idiopathic paralysis of the seventh cranial nerve, may be seen as an analogous condition. The roles of zoster sine herpete and herpes simplex have increasingly been recognized in Bell's palsy, and there are some data to suggest that antiviral therapy is a useful adjunct to steroid therapy. Thus, we postulated that antiviral therapy might have a positive impact on the course of acute idiopathic diaphragm paralysis which is likely related to viral infection. Three consecutive patients with subacute onset of symptomatic idiopathic hemidiaphragm paralysis were empirically treated with valacyclovir, 1,000 mg twice daily for 1 week. Prior to therapy, diaphragmatic function was assessed via pulmonary function testing and two-dimensional B-mode ultrasound, with testing repeated 1 month later. Diaphragmatic function pre- and post-treatment was compared to that of a historical control group of 16 untreated patients. All three subjects demonstrated ultrasound recovery of diaphragm function 4-6 weeks following treatment with valacyclovir. This recovery was accompanied by improvements in maximum inspiratory pressure (PI(max)) and vital capacity (VC). In contrast, in the untreated cohort, diaphragm recovery occurred in only 11 subjects, taking an average of 14.9 +/- 6.1 months (mean +/- SD). The results of this small, preliminary study suggest that antiviral therapy with valacyclovir may be helpful in the treatment of idiopathic diaphragm paralysis induced by a viral infection.

The effect of bi-level positive airway pressure mechanical ventilation on gas exchange during general anaesthesia

Atelectasis may occur and ventilation-perfusion mismatch may increase during general anaesthesia with neuromuscular paralysis and mechanical ventilation, though preservation of some intermittent muscle contraction might mitigate this process. There is still no ideal manoeuvre to minimize such mismatch or atelectasis. Bi-level positive airway pressure (BiPAP) ventilation adjusts to extra breaths and improves gas exchange during recovery of diaphragm function after neuromuscular paralysis. We hypothesize that BiPAP ventilation may limit the development of pulmonary shunt and may improve ventilation-perfusion mismatch when compared with standard IPPV, with or without PEEP when neuromuscular paralysis has been used during surgery. Twenty ventilated patients either on BiPAP or IPPV with or without PEEP were studied randomly using the multiple inert gas elimination technique (MIGET) at 60 and 120 min after rocuronium at induction and after 60 min. Non-invasive cardiac output (NICO) monitoring and plasma concentrations of rocuronium were measured. We compared the data of MIGET, gas exchange, haemodynamic variables and pulmonary mechanics measurements between the different ventilatory modes. Intrapulmonary shunt (blood flow to V(A)/Q < 0.005) did not increase at 60 min of anaesthesia in any of the different ventilation modes compared with the shunt value before anaesthesia. Log standard deviation of perfusion increased in IPPV, with and without PEEP groups, compared with the baseline (P< 0.05) but did not increase in the BiPAP group. BiPAP ventilation generated a higher level of Pa(O2)than IPPV with or without PEEP (P<0.05). BiPAP ventilation was beneficial in decreasing ventilation-perfusion mismatch and improving oxygenation when compared with conventional IPPV (with or without PEEP).

Phrenic nerve injury associated with high free right internal mammary artery harvesting

Background The right phrenic nerve is at risk of injury during high mobilization of the right internal mammary artery (RIMA). The incidence and implications of this injury have not been previously defined. Methods Prospectively collected data on all patients who underwent RIMA harvesting between January 1995 and February 2002 were analyzed. Thirty-one patients with right phrenic nerve injury were identified and the medical charts reviewed. Phrenic nerve injury was diagnosed when a postoperative chest roentgenogram showed the right hemidiaphragm to be two or more intercostal spaces higher than the left, or transection of the nerve was seen intraoperatively. Investigations included fluoroscopy and spirometry in upright and supine positions. Diaphragm plication was offered for symptom control. Subsequent follow-up was undertaken to determine the incidence of spontaneous recovery of diaphragm function and the benefits of diaphragm plication. Results Seven hundred and eighty-three patients underwent high mobilization of the RIMA with proximal detachment for use as a free graft. Thirty-one patients with right hemidiaphragm dysfunction were identified in the postoperative period providing an injury incidence of 4% (confidence interval, 2.6% to 5.3%). Of these, 12 patients underwent diaphragm plication (4 early and 8 late), 14 patients achieved spontaneous recovery, and 5 patients were lost to follow-up. The supine to upright forced vital capacity ratios at the time of phrenic nerve dysfunction, after diaphragm plication, and after spontaneous recovery were 0.79, 0.90, and 0.96 respectively. Conclusions The incidence of phrenic nerve injury associated with high RIMA harvesting was 4% but spontaneous recovery may be anticipated in two thirds (14 of 22) of patients in whom the injury is identified postoperatively. High RIMA harvesting should be used with caution in patients with preoperative pulmonary dysfunction in whom phrenic nerve injury would be poorly tolerated.

Bilateral diaphragm paralysis following lung transplantation and cardiac surgery in a 17-year-old

Bilateral diaphragm paralysis is a rare complication of lung transplantation. This report describes the development of chronic respiratory failure due to bilateral diaphragm paralysis following bilateral lung transplantation and closure of a patent foramen ovale. This patient required prolonged mechanical ventilation post-operatively; however, he eventually had adequate recovery of diaphragm function to wean from mechanical ventilation.