Long-term change in respiratory function following spinal cord injury

Changes in respiratory structure and function after traumatic cervical spinal cord injury: observations from spinal cord and brain

Respiratory difficulties and mortality following severe cervical spinal cord injury (CSCI) result primarily from malfunctions of respiratory pathways and the paralyzed diaphragm. Nonetheless, individuals with CSCI can experience partial recovery of respiratory function through respiratory neuroplasticity. For decades, researchers have revealed the potential mechanism of respiratory nerve plasticity after CSCI, and have made progress in tissue healing and functional recovery. While most existing studies on respiratory plasticity after spinal cord injuries have focused on the cervical spinal cord, there is a paucity of research on respiratory-related brain structures following such injuries. Given the interconnectedness of the spinal cord and the brain, traumatic changes to the former can also impact the latter. Consequently, are there other potential therapeutic targets to consider? This review introduces the anatomy and physiology of typical respiratory centers, explores alterations in respiratory function following spinal cord injuries, and delves into the structural foundations of modified respiratory function in patients with CSCI. Additionally, we propose that magnetic resonance neuroimaging holds promise in the study of respiratory function post-CSCI. By studying respiratory plasticity in the brain and spinal cord after CSCI, we hope to guide future clinical work.

Inflammation and Oxidative Stress as Common Mechanisms of Pulmonary, Autonomic and Musculoskeletal Dysfunction after Spinal Cord Injury

Simple Summary

When a spinal cord injury occurs, the neurons that regulate our voluntary movements, those involved in environment and somatic perception and those that regulate vegetative functions are affected. Once neuronal damage is established, the cells of other tissues are also affected in their functions, altering the interaction between organs and altering the proper functioning of the organism. Multiple studies in animal models, as well as in humans, have recognized as factors involved in organ damage the imbalance between the formation of highly reactive molecules called pro-oxidants and defensive mechanisms called antioxidants. Closely associated with this phenomenon, the inflammatory response is also pathologically activated. In this narrative review, we have analyzed the information involving these pathological processes at the level of the lung, the autonomic nervous system and the skeletal musculature after spinal cord injury. Knowing the abnormal functioning mechanisms that occur after a spinal cord injury not only offers a better understanding of the organic events but also offers future possibilities for therapeutic interventions that may benefit the thousands of patients suffering this pathology.

Abstract

One of the etiopathogenic factors frequently associated with generalized organ damage after spinal cord injury corresponds to the imbalance of the redox state and inflammation, particularly of the respiratory, autonomic and musculoskeletal systems. Our goal in this review was to gain a better understanding of this phenomenon by reviewing both animal and human studies. At the respiratory level, the presence of tissue damage is notable in situations that require increased ventilation due to lower thoracic distensibility and alveolar inflammation caused by higher levels of leptin as a result of increased fatty tissue. Increased airway reactivity, due to loss of sympathetic innervation, and levels of nitric oxide in exhaled air that are similar to those seen in asthmatic patients have also been reported. In addition, the loss of autonomic control efficiency leads to an uncontrolled release of catecholamines and glucocorticoids that induce immunosuppression, as well as a predisposition to autoimmune reactions. Simultaneously, blood pressure regulation is altered with vascular damage and atherogenesis associated with oxidative damage. At the muscular level, chronically elevated levels of prooxidants and lipoperoxidation associated with myofibrillar atrophy are described, with no reduction or reversibility of this process through antioxidant supplementation.

Inspiratory Muscle Performance and Anthropometric Measures-Novel Assessments Related to Pulmonary Function in People with Spinal Cord Injury: A Pilot Study

OBJECTIVE

To investigate the feasibility and validity of using the novel axillary:umbilical (A:U) ratio and sustained maximal inspiratory pressure (SMIP) as supplementary measures in the assessment of respiratory function in people with spinal cord injury.

DESIGN

Pilot study with a single day of data collection. All measurements were taken with participants in their personal wheelchairs to best represent normal functioning and positioning for each individual.

SETTING

Research institution.

PARTICIPANTS

A convenience sample of 30 community dwelling volunteers with chronic spinal cord injury (C2-T12, American Spinal Injury Association Impairment Scale A-D) participated.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Participants underwent anthropometric measurements (trunk height, abdominal circumference, axillary circumference) and assessment of inspiratory muscle performance, incluidng maximal inspiratory pressure, SMIP, and inspiratory duration, as well as standard pulmonary function tests.

RESULTS

The A:U ratio and SMIP were recorded for all participants. The SMIP was significantly related to more respiratory performance measures than the maximal inspiratory pressure (P<.05) and the A:U ratio was significantly related to more respiratory performance measures than any other anthropometric measure (P<.05). Additionally, an A:U ratio cutoff point detected individuals with a peak expiratory flow ≥ 80% of their predicted value with a sensitivity and specificity of 85.7% and 91.3%, respectively (area under the curve: 0.92).

CONCLUSIONS

It is feasible to capture the A:U Ratio and SMIP in individuals with spinal cord injury. Further, the strong significant relationships of SMIP and the A:U ratio to respiratory performance measures suggests their clinical importance in the pulmonary assessment and risk stratification of people with chronic spinal cord injury.

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.

Respiratory function and respiratory complications in spinal cord injury: protocol for a prospective, multicentre cohort study in high-income countries

INTRODUCTION

Pneumonia is one of the leading complications and causes of death after a spinal cord injury (SCI). After a cervical or thoracic lesion, impairment of the respiratory muscles decreases respiratory function, which increases the risk of respiratory complications. Pneumonia substantially reduces patient's quality of life, may prolong inpatient rehabilitation time, increase healthcare costs or at worse, lead to early death. Respiratory function and coughing can be improved through various interventions after SCI, but the available evidence as to which aspect of respiratory care should be optimised is inconclusive. Furthermore, ability of respiratory function parameters to predict pneumonia risk is insufficiently established. This paper details the protocol for a large-scale, multicentre research project that aims to evaluate the ability of parameters of respiratory function to predict and understand variation in inpatient risk of pneumonia in SCI.

METHODS AND ANALYSIS

RESCOM, a prospective cohort study, began recruitment in October 2016 across 10 SCI rehabilitation centres from Australia, Austria, Germany, the Netherlands and Switzerland. Inpatients with acute SCI, with complete or incomplete cervical or thoracic lesions, 18 years or older and not/no more dependent on 24-hour mechanical ventilation within the first 3 months after injury are eligible for inclusion. The target sample size is 500 participants. The primary outcome is an occurrence of pneumonia; secondary outcomes include pneumonia-related mortality and quality of life. We will use the longitudinal data for prognostic models on inpatient pneumonia risk factors.

ETHICS AND DISSEMINATION

The study has been reviewed and approved by all local ethics committees of all participating centres. Study results will be disseminated to the scientific community through peer-reviewed journals and conference presentations, to the SCI community, other stakeholders and via social media, newsletters and engagement activities.

TRIAL REGISTRATION DETAILS

ClinicalTrials.gov NCT02891096.

Pharmacological disinhibition enhances paced breathing following complete spinal cord injury in rats

Respiratory dysfunction is one of the most devastating and life-threatening deficits that occurs following cervical spinal cord injury (SCI). Assisted breathing with mechanical ventilators is a necessary part of care for many cervical injured individuals, but it is also associated with increased risk of secondary complications such as infection, muscle atrophy and maladaptive plasticity. Pre-clinical studies with epidural stimulation (EDS) have identified it as an alternative/additional method to support adequate lung ventilation without mechanical assistance. The full potential of EDS, however, may be limited by spinal inhibitory mechanisms within the injured spinal cord. The goal of the present work is to assess the potential improvement for EDS in combination with pharmacological disinhibition of spinal circuits following complete high cervical SCI. All experiments were performed in decerebrate, unanesthetized, non-paralyzed (n = 13) and paralyzed (n = 8) adult Sprague-Dawley rats 6 h following a complete C1 transection. The combination of high-frequency EDS (HF-EDS) at the C4 spinal segment with intrathecal delivery of GABA and glycine receptors antagonists (GABAzine and strychnine, respectively) resulted in significantly increased phrenic motor output, tidal volume and amplitude of diaphragm electrical activity compared to HF-EDS alone. Thus, it appears that spinal fast inhibitory mechanisms limit phrenic motor output and present a new neuropharmacological target to improve paced breathing in individuals with cervical SCI.

A Review of Different Stimulation Methods for Functional Reconstruction and Comparison of Respiratory Function after Cervical Spinal Cord Injury

Background

Spinal cord injury (SCI) is a common severe trauma in clinic, hundreds of thousands of people suffer from which every year in the world. In terms of injury location, cervical spinal cord injury (CSCI) has the greatest impact. After cervical spinal cord injury, the lack of innervated muscles is not enough to provide ventilation and other activities to complete the respiratory function. In addition to the decline of respiratory capacity, respiratory complications also have a serious impact on the life of patients. The most commonly used assisted breathing and cough equipment is the ventilator, but in recent years, the functional electrical stimulation method is being used gradually and widely.

Methods

About hundred related academic papers are cited for data analysis. They all have the following characteristics: (1) basic conditions of patients were reported, (2) patients had received nerve or muscle stimulation and the basic parameters, and (3) the results were evaluated based on some indicators.

Results

The papers mentioned above are classified as four kinds of stimulation methods: muscle electric/magnetic stimulation, spinal dural electric stimulation, intraspinal microstimulation, and infrared light stimulation. This paper describes the stimulation principle and application experiment. Finally, this paper will compare the indexes and effects of typical stimulation methods, as well as the two auxiliary methods: training and operation.

Conclusions

Although there is limited evidence for the treatment of respiratory failure by nerve or muscle stimulation after cervical spinal cord injury, the two techniques seem to be safe and effective. At the same time, light stimulation is gradually applied to clinical medicine with its strong advantages and becomes the development trend of nerve stimulation in the future.

Influence of early extensive posterior decompression on hyponatremia and cardiopulmonary dysfunction after severe traumatic cervical spinal cord injury: A clinical observational study

Retrospective single institution observational study.The aim of the present study was to analyze the influence of early extensive posterior decompression on complications in patients with severe traumatic cervical spinal cord injury (tcSCI).Cervical SCI is associated with a high prevalence of hyponatremia and cardiopulmonary dysfunction. However, very few studies have focused on this exploration to reduce the incidence of SCI early complications.We reviewed the medical records of consecutive patients undergoing extensive posterior decompression within 24 h for severe tcSCI (American Spinal Injury Association Impairment Scale [AIS] A to C) admitted between January 2009 and January 2018. The data collected retrospectively included age, gender, mechanism, and level of SCI, AIS grade, fracture or dislocation, electrolyte, and cardiopulmonary complications.Of the 97 enrolled patients, the baseline AIS grade was AIS A in 14, AIS B in 31, and AIS C in 52. Improvement of at least two AIS grades was found in 26 (26.8%), and improvement of at least one grade was found in 80.4% of patients at discharge. Twenty-nine (29.9%) patients had mild hyponatremia, 8 (8.2%) had moderate hyponatremia, and 3 (3.1%) had severe hyponatremia during hospitalization. The incidences of hyponatremia, hypotension, and tracheotomy were 41.2%, 13.4%, and 6.2%, respectively. The mean forced vital capacity (FVC) on admission and at discharge was 1.34 ± 0.46 L and 2.21 ± 0.41 L (P < .0001), respectively. Five patients developed pneumonia.Our results suggest that early expansive posterior decompression significantly reduces the incidence of hyponatremia, hypotension, and tracheotomy by promoting recovery of spinal cord function after severe tcSCI.

Development and validation of models to predict respiratory function in persons with long-term spinal cord injury

STUDY DESIGN

Multicenter, cross-sectional study.

OBJECTIVES

To validate previously developed respiratory function prediction models for persons with long-term spinal cord injury (SCI) and if necessary develop and validate new models.

SETTING

Ten SCI rehabilitation centers.

METHODS

Five respiratory function parameters were measured in adults with chronic, traumatic, motor complete SCI (C4-T12). First, the models published in 2012 were validated using Bland-Altman plots. Then, new models were calculated using 80% of the dataset by multiple regression analysis with the candidate predictors gender, age, height, weight, time post injury (TPI), lesion level, and smoking. In a third step, the new models were validated using the other 20% of the dataset by Bland-Altman plots.

RESULTS

In total 613 participants were included. For persons with long-term SCI, the 2012 models were poorly predictive, especially for respiratory muscle strength (R2 = 0.4). Significant predictors for all respiratory function parameters in the new models (R2 = 0.7-0.8) were lesion level, gender and weight. Small effects on single outcome parameters were observed for TPI and age whereas smoking had no effect. For the new models the mean differences between measured and predicted values for respiratory muscle strength were 4.0 ± 36.0 cm H₂O and for lung function parameters -0.5 ± 1.2 L (FVC), -0.3 ± 0.9 L (FEV1) and -0.5 ± 2.0 L/s (PEF).

CONCLUSION

We did not find better models for lung function in long-term SCI but those for respiratory muscle strength showed better accuracy.

SPONSORSHIP

The content of this publication was developed under grant from Wings for Life, grant number WFL-CH-017/14.

Respiratory problems and management in people with spinal cord injury

Spinal cord injury (SCI) is characterised by profound respiratory compromise secondary to the level of loss of motor, sensory and autonomic control associated with the injury. This review aims to detail these anatomical and physiological changes after SCI, and outline their impact on respiratory function. Injury-related impairments in strength substantially alter pulmonary mechanics, which in turn affect respiratory management and care. Options for treatments must therefore be considered in light of these limitations.

KEY POINTS

Respiratory impairment following spinal cord injury (SCI) is more severe in high cervical injuries, and is characterised by low lung volumes and a weak cough secondary to respiratory muscle weakness.Autonomic dysfunction and early-onset sleep disordered breathing compound this respiratory compromise.The mainstays of management following acute high cervical SCI are tracheostomy and ventilation, with noninvasive ventilation and assisted coughing techniques being important in lower cervical and thoracic level injuries.Prompt investigation to ascertain the extent of the SCI and associated injuries, and appropriate subsequent management are important to improve outcomes.

EDUCATIONAL AIMS

To describe the anatomical and physiological changes after SCI and their impact on respiratory function.To describe the changes in respiratory mechanics seen in cervical SCI and how these changes affect treatments.To discuss the relationship between injury level and respiratory compromise following SCI, and describe those at increased risk of respiratory complications.To present the current treatment options available and their supporting evidence.