Repeated measurements of pulmonary function following spinal cord injury

Long-Term Pulmonary Function Postspinal Cord Injury

OBJECTIVE

To investigate mean values of pulmonary function tests (PFT) at specific time points to assess long-term progression in patients with spinal cord injury (SCI).

DESIGN

Retrospective cohort study from 1997-2022.

SETTING

National rehabilitation hospital, providing scheduled admission for potential SCI-related issues. Follow-up assessments are recommended annually, guiding the observation period into consecutive 1-year intervals.

PARTICIPANTS

This study included 1394 adult patients who were admitted at least twice to the National Rehabilitation Center between 1997 and 2022, selected from an initial pool of 1510. Overall, 116 patients were excluded owing to the absence of any PFT results.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Changes in PFT values over time, specifically assessing for a potential 2-phase pattern after injury. The hypothesis that PFT values would initially improve before declining was formulated based on existing literature.

RESULTS

Significant changes in pulmonary function were noted among 1394 adults with SCI. Forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) initially increased within the first 1-2 years after injury but declined to below baseline levels after 6 years. Pronounced changes occurred between <1 year and 1-2 years after injury (FVC: Δ=4.89, SE=0.87, P<.001; FEV1: Δ=4.28, SE=1.09, P=.002) and 1-2 years to >6 years (FVC: Δ= -5.83, SE=0.94, P<.001; FEV1: Δ= -6.49, SE=1.18, P<.001). No significant changes in the FEV1/FVC ratio. Motor completeness was significantly associated with the increase and decline phase, showing a steeper increase and less decline compared with the motor-incomplete group.

CONCLUSIONS

Pulmonary function in SCI initially increases but declines over time, falling below initial levels by 6 years. Further evaluation with more complete datasets is warranted to elucidate the factors influencing these changes.

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.

Efficacy of Wheelchair Skills Training Program in Enhancing Sitting Balance and Pulmonary Function in Chronic Tetraplegic Patients: A Randomized Controlled Study

Background and Objectives: This study aimed to evaluate the effectiveness of a wheelchair skills training program (WSTP) in improving sitting balance and pulmonary function in patients with chronic tetraplegia resulting from cervical spinal cord injury (cSCI). Materials and Methods: Twenty-four patients were randomly divided into WSTP and control groups. The WSTP group participated in the WSTP for eight weeks, while the control group underwent conventional physical therapy for the same eight-week period. Sitting balance was evaluated using the activity-based balance level evaluation (ABLE) scale, and pulmonary function was evaluated using forced vital capacity (FVC), forced expiratory volume in one second (FEV1), and peak expiratory flow (PEF). Results: The WSTP group showed significant improvements in both sitting balance and pulmonary function during the intervention period (p < 0.05), whereas the control group did not show any significant changes. A strong positive correlation was found between ABLE scores and all three pulmonary function parameters across all time points. Conclusions: Our results suggest that the WSTP significantly improves sitting balance and specific aspects of lung function in patients with tetraplegia.

Exoskeleton-assisted walking improves pulmonary function and walking parameters among individuals with spinal cord injury: a randomized controlled pilot study

BACKGROUND

Exoskeleton-assisted walking (EAW) is expected to improve the gait of spinal cord injury (SCI) individuals. However, few studies reported the changes of pulmonary function (PF) parameters after EAW trainings. Hence, we aimed to explore the effect of EAW on PF parameters, 6-min walk test (6MWT) and lower extremity motor score (LEMS) in individuals with SCI and to compare those with conventional trainings.

METHODS

In this prospective, single-center, single-blinded randomized controlled pilot study, 18 SCI participants were randomized into the EAW group (n = 9) and conventional group (n = 9) and received 16 sessions of 50-60 min training (4 days/week, 4 weeks). Pulmonary function parameters consisting of the forced vital capacity (FVC), forced expiratory volume in 1 s (FEV₁), forced expiratory flow (FEF), peak expiratory flow, and maximal voluntary ventilation, 6MWT with assisted devices and LEMS were reported pre- and post-training.

RESULTS

Values of FVC (p = 0.041), predicted FVC% (p = 0.012) and FEV₁ (p = 0.013) were significantly greater in EAW group (FVC: 3.8 ± 1.1 L; FVC% _pred = 94.1 ± 24.5%; FEV₁: 3.5 ± 1.0 L) compared with conventional group (FVC: 2.8 ± 0.8 L; FVC% _pred = 65.4 ± 17.6%; FEV₁: 2.4 ± 0.6 L) after training. Participants in EAW group completed 6MWT with median 17.3 m while wearing the exoskeleton. There was no difference in LEMS and no adverse event.

CONCLUSIONS

The current results suggest that EAW has potential benefits to facilitate PF parameters among individuals with lower thoracic neurological level of SCI compared with conventional trainings. Additionally, robotic exoskeleton helped walking.

TRIAL REGISTRATION

Registered on 22 May 2020 at Chinese Clinical Trial Registry (ChiCTR2000033166). http://www.chictr.org.cn/edit.aspx?pid=53920&htm=4 .

Predictors of respiratory complications in patients with C5-T5 spinal cord injuries

Study design

Retrospective chart audit.

Objectives

Describing the respiratory complications and their predictive factors in patients with acute traumatic spinal cord injuries at C5–T5 level during the initial hospitalization.

Setting

Hospital Vall d’Hebron, Barcelona.

Methods

Data from patients admitted in a reference unit with acute traumatic injuries involving levels C5–T5. Respiratory complications were defined as: acute respiratory failure, respiratory infection, atelectasis, non-hemothorax pleural effusion, pulmonary embolism or haemoptysis. Candidate predictors of these complications were demographic data, comorbidity, smoking, history of respiratory disease, the spinal cord injury characteristics (level and ASIA Impairment Scale) and thoracic trauma. A logistic regression model was created to determine associations between potential predictors and respiratory complications.

Results

We studied 174 patients with an age of 47.9 (19.7) years, mostly men (87%), with low comorbidity. Coexistent thoracic trauma was found in 24 (19%) patients with cervical and 35 (75%) with thoracic injuries (p < 0.001). Respiratory complications were frequent (53%) and were associated to longer hospital stay: 83.1 (61.3) and 45.3 (28.1) days in patients with and without respiratory complications (p < 0.001). The strongest predictors of respiratory complications were: previous respiratory disease (OR 5.4, 95% CI: 1.5–19.2), complete motor function impairment (AIS A–B) (OR 4.7, 95% CI: 2.4–9.5) and concurrent chest trauma (OR 3.73, 95% CI: 1.8–7.9).

Conclusions

Respiratory complications are common in traumatic spinal cord injuries between C5–T5. We identified previous respiratory disease, complete motor function impairment and the coexistence of thoracic trauma as predictors of respiratory complications. Identification of patients at risk might help clinicians to implement preventive strategies.

Spinal cord injury and diaphragm neuromotor control

Introduction: Neuromotor control of diaphragm muscle and the recovery of diaphragm activity following spinal cord injury have been narrowly focused on ventilation. By contrast, the understanding of neuromotor control for non-ventilatory expulsive/straining maneuvers (including coughing, defecation, and parturition) is relatively impoverished. This variety of behaviors are achieved via the recruitment of the diverse array of motor units that comprise the diaphragm muscle.Areas covered: The neuromotor control of ventilatory and non-ventilatory behaviors in health and in the context of spinal cord injury is explored. Particular attention is played to the neuroplasticity of phrenic motor neurons in various models of cervical spinal cord injury.Expert opinion: There is a remarkable paucity in our understanding of neuromotor control of maneuvers in spinal cord injury patients. Dysfunction of these expulsive/straining maneuvers reduces patient quality of life and contributes to severe morbidity and mortality. As spinal cord injury patient life expectancies continue to climb steadily, a nexus of spinal cord injury and age-associated comorbidities are likely to occur. While current research remains concerned only with the minutiae of ventilation, the major functional deficits of this clinical cohort will persist intractably. We posit some future research directions to avoid this scenario.

Improvement in Pulmonary Function with Short-term Rehabilitation Treatment in Spinal Cord Injury Patients

Cervical and upper thoracic spinal cord injury causes impairments in respiratory muscle performance, leading to variable degrees of pulmonary dysfunction and rendering deep breathing difficult for affected individuals. In this retrospective study, we investigated the effects of self-directed respiratory muscle training in this context by assessing pulmonary function relative to spinal cord injury characteristics. A total of 104 spinal cord injury patients (tetraplegia/paraplegia; 65/39, acute/subacute/chronic; 14/42/48) were admitted for short-term (4–8 weeks) in-patient clinical rehabilitation. Initial evaluation revealed a compromised pulmonary function with a percentage of predicted value of 62.0 and 57.5 in forced vital capacity in supine and forced vital capacity in sitting positions, respectively. Tetraplegic patients had more compromised pulmonary function compared with paraplegic patients. At follow-up evaluation, the percentage of predicted value of forced vital capacity in supine and sitting position improved overall on average by 11.7% and 12.7%, respectively. The peak cough flow improved by 22.7%. All assessed pulmonary function parameters improved significantly in all subgroups, with the greatest improvements found in patients with tetraplegia and subacute spinal cord injury. Therefore, short-term self-directed respiratory muscle training should be incorporated into all spinal cord injury rehabilitation regimens, especially for patients with tetraplegia and subacute spinal cord injury, as well as those with chronic spinal cord injury.

Plasticity Induced Recovery of Breathing Occurs at Chronic Stages after Cervical Contusion

Severe midcervical contusion injury causes profound deficits throughout the respiratory motor system that last from acute to chronic time points post-injury. We use chondroitinase ABC (ChABC) to digest chondroitin sulphate proteoglycans within the extracellular matrix (ECM) surrounding the respiratory system at both acute and chronic time points post-injury to explore whether augmentation of plasticity can recover normal motor function. We demonstrate that, regardless of time post-injury or treatment application, the lesion cavity remains consistent, showing little regeneration or neuroprotection within our model. Through electromyography (EMG) recordings of multiple inspiratory muscles, however, we show that application of the enzyme at chronic time points post-injury initiates the recovery of normal breathing in previously paralyzed respiratory muscles. This reduced the need for compensatory activity throughout the motor system. Application of ChABC at acute time points recovered only modest amounts of respiratory function. To further understand this effect, we assessed the anatomical mechanism of this recovery. Increased EMG activity in previously paralyzed muscles was brought about by activation of spared bulbospinal pathways through the site of injury and/or sprouting of spared serotonergic fibers from the contralateral side of the cord. Accordingly, we demonstrate that alterations to the ECM and augmentation of plasticity at chronic time points post-cervical contusion can cause functional recovery of the respiratory motor system and reveal mechanistic evidence of the pathways that govern this effect.

Evaluation of a clinical implementation of a respiratory muscle training group during spinal cord injury rehabilitation

STUDY DESIGN

Retrospective cohort study.

OBJECTIVE

To evaluate the clinical implementation of a respiratory muscle training group during rehabilitation of individuals with spinal cord injury.

SETTING

Spinal cord injury rehabilitation center.

METHODS

Individuals with complete or incomplete lesions during inpatient rehabilitation, level C4-T12.Ten or more training sessions of either an inspiratory or a combined in- and expiratory muscle training were performed in a group setting with respiratory function measurements before and after the training period.

RESULTS

Analysis of 79 persons. Inspiratory muscle training was performed for 7 weeks with a median of 3.1 training sessions per week. Median training intensity was at 33% of baseline PImax and 58 repetitions were performed per training session. Respiratory mucle strength parameters improved by 18-68% of baseline values and lung function parameters by 11-31% after inspiratory muscle training.The combined respiratory muscle training was performed for 13 weeks with a median of 2.8 sessions per week and 88 repetitions per training session. Median inspiratory training resistance was at 39% of baseline PImax and median expiratory training resistance was at 27% of baseline PEmax. Respiratory muscle strength parameters improved by 14-51% of baseline values and lung function parameters improved by 15-34% after the combined in- and expiratory muscle training.

CONCLUSION

Respiratory resistance training improved respiratory function of individuals with acute spinal cord injury. Even if the combined respiratory muscle training was performed with more repetitions per training and nearly twice as long, relative improvements of respiratory function parameters were comparable with isolated inspiratory muscle training.

Mid-cervical spinal cord contusion causes robust deficits in respiratory parameters and pattern variability

Mid-cervical spinal cord contusion disrupts both the pathways and motoneurons vital to the activity of inspiratory muscles. The present study was designed to determine if a rat contusion model could result in a measurable deficit to both ventilatory and respiratory motor function under “normal” breathing conditions at acute to chronic stages post trauma. Through whole body plethysmography and electromyography we assessed respiratory output from three days to twelve weeks after a cervical level 3 (C3) contusion. Contused animals showed significant deficits in both tidal and minute volumes which were sustained from acute to chronic time points. We also examined the degree to which the contusion injury impacted ventilatory pattern variability through assessment of Mutual Information and Sample Entropy. Mid-cervical contusion significantly and robustly decreased the variability of ventilatory patterns. The enduring deficit to the respiratory motor system caused by contusion was further confirmed through electromyography recordings in multiple respiratory muscles. When isolated via a lesion, these contused pathways were insufficient to maintain respiratory activity at all time points post injury. Collectively these data illustrate that, counter to the prevailing literature, a profound and lasting ventilatory and respiratory motor deficit may be modelled and measured through multiple physiological assessments at all time points after cervical contusion injury.

Spontaneous Functional Recovery in a Paralyzed Hemidiaphragm Following Upper Cervical Spinal Cord Injury in Adult Rats

Previous studies have shown that latent respiratory pathways can be activated by as phyxia or systemic theophylline administration to restore function to a hemidiaphragm paralyzed by C2 spinal cord hemisection in adult female rats. Based on this premise, electrophysiologic recording techniques were employed in the present investigation to first determine qualitatively whether latent respiratory pathways are activated spon taneously following prolonged post hemisection periods (4-16 weeks) without any therapeutic intervention. Our second objective in a separate group of hemisected an imals was to quantitate any documented functional recovery under the following stan dardized recording conditions: bilateral vagotomy, paralysis with pancuronium bro mide, artificial ventilation, and constant PCO2(maintained at 25 mmHg).

A center's experience: pulmonary function in spinal cord injury

Traumatic spinal cord injury (SCI) is associated with significant psychological and physical challenges. A multidisciplinary approach to management is essential to ensure recovery during the acute phase, and comprehensive rehabilitative strategies are necessary to foster independence and quality of life throughout the chronic phase of injury. Complications that beset these individuals are often a unique consequence of SCI, and knowledge of the effects of SCI upon organ systems is essential for appropriate management. According to the National SCI Statistical Center (NSCISC), as of 2010 there were an estimated 265,000 persons living with SCI in the United States, with approximately 12,000 incidence cases annually. Although life expectancy for newly injured individuals with SCI is markedly reduced, persons with chronic SCI are expected to live about as long as individuals without SCI; however, longevity varies inversely with level of injury. Since 2005, 56 % of persons with SCI are tetraplegic, and due to paralysis of respiratory muscles, these individuals may be especially prone to pulmonary complications, which remain a major cause of mortality among persons with chronic SCI. We at the VA Rehabilitation Research and Development Center of Excellence for the Medical Consequences of SCI at the James J. Peters VA Medical Center have devoted more than 25 years to the study of secondary medical conditions that complicate SCI. Herein, we review pulmonary research at the Center, both our past and future endeavors, which form an integral part of our multidisciplinary approach toward achieving a greater understanding of and improving care for veterans with SCI.

Early phrenic motor neuron loss and transient respiratory abnormalities after unilateral cervical spinal cord contusion

Contusion-type cervical spinal cord injury (SCI) is one of the most common forms of SCI observed in patients. In particular, injuries targeting the C3-C5 region affect the pool of phrenic motor neurons (PhMNs) that innervates the diaphragm, resulting in significant and often chronic respiratory dysfunction. Using a previously described rat model of unilateral midcervical C4 contusion with the Infinite Horizon Impactor, we have characterized the early time course of PhMN degeneration and consequent respiratory deficits following injury, as this knowledge is important for designing relevant treatment strategies targeting protection and plasticity of PhMN circuitry. PhMN loss (48% of the ipsilateral pool) occurred almost entirely during the first 24 h post-injury, resulting in persistent phrenic nerve axonal degeneration and denervation at the diaphragm neuromuscular junction (NMJ). Reduced diaphragm compound muscle action potential amplitudes following phrenic nerve stimulation were observed as early as the first day post-injury (30% of pre-injury maximum amplitude), with slow functional improvement over time that was associated with partial reinnervation at the diaphragm NMJ. Consistent with ipsilateral diaphragmatic compromise, the injury resulted in rapid, yet only transient, changes in overall ventilatory parameters measured via whole-body plethysmography, including increased respiratory rate, decreased tidal volume, and decreased peak inspiratory flow. Despite significant ipsilateral PhMN loss, the respiratory system has the capacity to quickly compensate for partially impaired hemidiaphragm function, suggesting that C4 hemicontusion in rats is a model of SCI that manifests subacute respiratory abnormalities. Collectively, these findings demonstrate significant and persistent diaphragm compromise in a clinically relevant model of midcervical contusion SCI; however, the therapeutic window for PhMN protection is restricted to early time points post-injury. On the contrary, preventing loss of innervation by PhMNs and/or inducing plasticity in spared PhMN axons at the diaphragm NMJ are relevant long-term targets.

Respiration following spinal cord injury: evidence for human neuroplasticity

Respiratory dysfunction is one of the most devastating consequences of cervical spinal cord injury (SCI) with impaired breathing being a leading cause of morbidity and mortality in this population. However, there is mounting experimental and clinical evidence for moderate spontaneous respiratory recovery, or "plasticity", after some spinal cord injuries. Pre-clinical models of respiratory dysfunction following SCI have demonstrated plasticity at neural and behavioral levels that result in progressive recovery of function. Temporal changes in respiration after human SCI have revealed some functional improvements suggesting plasticity paralleling that seen in experimental models-a concept that has been previously under-appreciated. While the extent of spontaneous recovery remains limited, it is possible that enhancing or facilitating neuroplastic mechanisms may have significant therapeutic potential. The next generation of treatment strategies for SCI and related respiratory dysfunction should aim to optimize these recovery processes of the injured spinal cord for lasting functional restoration.

Phonation after cervical spinal cord injury (CSCI): prospective case examinations of the acute and sub-acute stages of recovery

The aim of the investigation was to examine the changes in phonation and related quality-of-life in the acute and sub-acute stages of recovery post-cervical spinal cord injury (CSCI). A prospective examination of phonation was conducted using perceptual and instrumental measures of respiratory and laryngeal functioning alongside a quality-of-life rating scale. Change was present across measures for both cases at each time point. Overall, a general pattern of recovery was seen, although some areas deteriorated between 6-12 months. Severity of impairments, extent of change, and impact on quality-of-life differed between the cases. Measures varied in sensitivity to change in function. Phonation can be impaired following both complete and incomplete CSCI, with type and severity of impairment/s undergoing change throughout the acute and sub-acute period post-injury. Spontaneous physiological recovery does not necessarily result in improved phonation and/ or quality-of-life. Potential exists for targeted speech-language therapy in this population, throughout recovery, to best capitalize on the physical changes that are occurring and to maximize functional application of skills to improve quality- of-life. Further research is warranted to examine this recovery period on a larger scale.

Respiratory function following bilateral mid-cervical contusion injury in the adult rat

The consequences of spinal cord injury (SCI) are often viewed as the result of white matter damage. However, injuries occurring at any spinal level, especially in cervical and lumbar enlargement regions, also entail segmental neuronal loss. Yet, the contributions of gray matter injury and plasticity to functional outcomes are poorly understood. The present study addressed this issue by investigating changes in respiratory function following bilateral C(3)/C(4) contusion injuries at the level of the phrenic motoneuron (PhMN) pool which in the adult rat extends from C(3) to C(5/6) and provides innervation to the diaphragm. Despite extensive white and gray matter pathology associated with two magnitudes of injury severity, ventilation was relatively unaffected during both quiet breathing and respiratory challenge (hypercapnia). On the other hand, bilateral diaphragm EMG recordings revealed that the ability to increase diaphragm activity during respiratory challenge was substantially, and chronically, impaired. This deficit has not been seen following predominantly white matter lesions at higher cervical levels. Thus, the impact of gray matter damage relative to PhMNs and/or interneurons becomes evident during conditions associated with increased respiratory drive. Unaltered ventilatory behavior, despite significant deficits in diaphragm function, suggests compensatory neuroplasticity involving recruitment of other spinal respiratory networks which may entail remodeling of connections. Transynaptic tracing, using pseudorabies virus (PRV), revealed changes in PhMN-related interneuronal labeling rostral to the site of injury, thus offering insight into the potential anatomical reorganization and spinal plasticity following cervical contusion.

Cough following low thoracic hemisection in the cat

A function of the abdominal expiratory muscles is the generation of cough, a critical respiratory defense mechanism that is often disrupted following spinal cord injury. We assessed the effects of a lateral T9/10 hemisection on cough production at 4, 13 and 21 weeks post-injury in cats receiving extensive locomotor training. The magnitudes of esophageal pressure as well as of bilateral rectus abdominis electromyogram activity during cough were not significantly different from pre-injury values at all time points evaluated. The results show that despite considerable interruption of the descending pre-motor drive from the brainstem to the expiratory motoneuron pools, the cough motor system shows a significant function by 4 weeks following incomplete thoracic injury.

Pulmonary function and spinal cord injury

Injury to the cervical and upper thoracic spinal cord disrupts function of inspiratory and expiratory muscles, as reflected by reduction in spirometric and lung volume parameters and static mouth pressures. In association, subjects with tetraplegia have decreased chest wall and lung compliance, increased abdominal wall compliance, and rib cage stiffness with paradoxical chest wall movements, all of which contribute to an increase in the work of breathing. Expiratory muscle function is more compromised than inspiratory muscle function among subjects with tetraplegia and high paraplegia, which can result in ineffective cough and propensity to mucus retention and atelectasis. Subjects with tetraplegia also demonstrate heightened vagal activity with reduction in baseline airway caliber, findings attributed to loss of sympathetic innervation to the lungs. Significant increase in airway caliber following inhalation of ipratropium bromide, an anticholinergic agent, suggests that reduction in airway caliber is not due to acquired airway fibrosis stemming from repeated infections or to abnormal hysteresis secondary to chronic inability of subjects to inhale to predicted total lung capacity. Reduced baseline airway caliber possibly explains why subjects with tetraplegia exhibit airway hyperresponsiveness to methacholine and ultrasonically nebulized distilled water. While it has been well demonstrated that bilateral phrenic nerve pacing or stimulation through intramuscular diaphragmatic electrodes improves inspiratory muscle function, it remains unclear if inspiratory muscle training improves pulmonary function. Recent findings suggest that expiratory muscle training, electrical stimulation of expiratory muscles and administration of a long-acting beta(2)-agonist (salmeterol) improve physiological parameters and cough. It is unknown if baseline bronchoconstriction in tetraplegia contributes to respiratory symptoms, of if the chronic administration of a bronchodilator reduces the work of breathing and/or improves respiratory symptoms. Less is known regarding the benefits of treatment of obstructive sleep apnea, despite evidence indicating that the prevalence of this condition in persons with tetraplegia is far greater than that encountered in able-bodied individuals.

Cervical prephrenic interneurons in the normal and lesioned spinal cord of the adult rat

Although monosynaptic bulbospinal projections to phrenic motoneurons have been extensively described, little is known about the organization of phrenic premotor neurons in the adult rat spinal cord. Because interneurons may play an important role in normal breathing and recovery following spinal cord injury, the present study has used anterograde and transneuronal retrograde tracing to study their distribution and synaptic relations. Exclusive unilateral, first-order labeling of the phrenic motoneuron pool with pseudorabies virus demonstrated a substantial number of second-order, bilaterally distributed cervical interneurons predominantly in the dorsal horn and around the central canal. Combined transneuronal and anterograde tracing revealed ventral respiratory column projections to prephrenic interneurons, suggesting that some propriospinal relays exist between medullary neurons and the phrenic nucleus. Dual-labeling studies with pseudorabies virus recombinants also showed prephrenic interneurons integrated with either contralateral phrenic or intercostal motoneuron pools. The stability of interneuronal pseudorabies virus labeling patterns following lateral cervical hemisection was then addressed. Except for fewer infected contralateral interneurons at the level of the central canal, the number and distribution of phrenic-associated interneurons was not significantly altered 2 weeks posthemisection (i.e., the point at which the earliest postinjury recovery of phrenic activity has been reported). These results demonstrate a heterogeneous population of phrenic-related interneurons. Their connectivity and relative stability after cervical hemisection raise speculation for potentially diverse roles in modulating phrenic function normally and postinjury.

Respiratory neuroplasticity and cervical spinal cord injury: translational perspectives

Paralysis of the diaphragm is a severe consequence of cervical spinal cord injury. This condition can be experimentally modeled by lateralized, high cervical lesions that interrupt descending inspiratory drive to the corresponding phrenic nucleus. Although partial recovery of ipsilateral diaphragm function occurs over time, recent findings show persisting chronic deficits in ventilation and phrenic motoneuron activity. Some evidence suggests, however, that spontaneous recovery can be enhanced by modulating neural pathways to phrenic motoneurons via synaptic circuitries which appear more complex than previously envisioned. The present review highlights these and other recent experimental multidisciplinary findings pertaining to respiratory neuroplasticity in the rat. Translational considerations are also emphasized, with specific attention directed at the clinical and interpretational strengths of different lesion models and outcome measures.

Effect of spinal cord injury on the respiratory system: basic research and current clinical treatment options

Spinal cord injury (SCI) often leads to an impairment of the respiratory system. The more rostral the level of injury, the more likely the injury will affect ventilation. In fact, respiratory insufficiency is the number one cause of mortality and morbidity after SCI. This review highlights the progress that has been made in basic and clinical research, while noting the gaps in our knowledge. Basic research has focused on a hemisection injury model to examine methods aimed at improving respiratory function after SCI, but contusion injury models have also been used. Increasing synaptic plasticity, strengthening spared axonal pathways, and the disinhibition of phrenic motor neurons all result in the activation of a latent respiratory motor pathway that restores function to a previously paralyzed hemidiaphragm in animal models. Human clinical studies have revealed that respiratory function is negatively impacted by SCI. Respiratory muscle training regimens may improve inspiratory function after SCI, but more thorough and carefully designed studies are needed to adequately address this issue. Phrenic nerve and diaphragm pacing are options available to wean patients from standard mechanical ventilation. The techniques aimed at improving respiratory function in humans with SCI have both pros and cons, but having more options available to the clinician allows for more individualized treatment, resulting in better patient care. Despite significant progress in both basic and clinical research, there is still a significant gap in our understanding of the effect of SCI on the respiratory system.

Respiratory abnormalities resulting from midcervical spinal cord injury and their reversal by serotonin 1A agonists in conscious rats

Respiratory dysfunction after cervical spinal cord injury (SCI) has not been examined experimentally using conscious animals, although clinical SCI most frequently occurs in midcervical segments. Here, we report a C5 hemicontusion SCI model in rats with abnormalities that emulate human post-SCI pathophysiology, including spontaneous recovery processes. Post-C5 SCI rats demonstrated deficits in minute ventilation (Ve) responses to a 7% CO2 challenge that correlated significantly with lesion severities (no injury or 12.5, 25, or 50 mm x 10 g weight drop; New York University impactor; p < 0.001) and ipsilateral motor neuron loss (p = 0.016). Importantly, C5 SCI resulted in at least 4 weeks of respiratory abnormalities that ultimately recovered afterward. Because serotonin is involved in respiration-related neuroplasticity, we investigated the impact of activating 5-HT1A receptors on post-C5 SCI respiratory dysfunction. Treatment with the 5-HT1A agonist 8-hydroxy-2-(di-n-propylmino)tetralin (8-OH DPAT) (250 microg/kg, i.p.) restored hypercapnic Ve at 2 and 4 weeks after injury (i.e., approximately 39.2% increase vs post-SCI baseline; p < or = 0.033). Improvements in hypercapnic Ve response after single administration of 8-OH DPAT were dose dependent and lasted for approximately 4 h(p < or = 0.038 and p < or = 0.024, respectively). Treatment with another 5-HT1A receptor agonist, buspirone (1.5 mg/kg, i.p.), replicated the results, whereas pretreatment with a 5-HT1A-specific antagonist, 4-iodo-N-[2-[4(methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinyl-benzamide (3 mg/kg, i.p.) given 20 min before 8-OH DPAT negated the effect of 8-OH DPAT. These results imply a potential clinical use of 5-HT1A agonists for post-SCI respiratory disorders.

A longitudinal evaluation of sleep and breathing in the first year after cervical spinal cord injury

OBJECTIVES

To establish the incidence of sleep disordered breathing (SDB) after acute tetraplegia and to determine the relation between the Apnea-Hypopnea Index (AHI) score and the previously postulated predictors of SDB in tetraplegia.

DESIGN

Inception cohort. We performed full polysomnography immediately after acute tetraplegia and at 2, 4, 13, 26, and 52 weeks postinjury. Spirometry, maximum inspiratory and expiratory pressures, medication usage, and neck and abdominal girth were also assessed. Preinjury SDB was estimated using the multivariate apnea prediction equation.

SETTING

Acute care, subacute care, and community.

PARTICIPANTS

Consecutive sample with acute tetraplegia. Thirty subjects (25 men) were initially included. Thirteen completed 12 months of follow-up.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

SDB (AHI score >10 events/h) and respiratory function.

RESULTS

Three subjects (10%; 95% confidence interval [CI], 2%-28%) had probable SDB before injury. In the first 48 hours after injury, no subject had SDB. At 2 weeks, 60% (95% CI, 26%-88%) had SDB; at 4 weeks, 62% (95% CI, 38%-82%); at 13 weeks, 83% (95% CI, 61%-95%); at 26 weeks, 68% (95% CI, 44%-88%); and at 52 weeks, 62% (95% CI, 32%-86%). No consistent relation was found between the previously postulated predictors and SDB.

CONCLUSIONS

SDB is highly prevalent within 4 weeks of acute tetraplegia.

Effect of Spinal Cord Injury on the Respiratory System

There are >200,000 persons living with a spinal cord injury in the United States, with approximately 10,000 new cases of traumatic injury per year. Advances in the care of these patients have significantly reduced acute and long-term mortality rates, although life expectancy remains decreased. This article will review the alterations in respiratory mechanics resulting from a spinal cord injury and will examine the contribution of respiratory complications to morbidity and mortality associated with various types of spinal cord injury.

The crossed phrenic phenomenon: a model for plasticity in the respiratory pathways following spinal cord injury

Hemisection of the cervical spinal cord rostral to the level of the phrenic nucleus interrupts descending bulbospinal respiratory pathways, which results in a paralysis of the ipsilateral hemidiaphragm. In several mammalian species, functional recovery of the paretic hemidiaphragm can be achieved by transecting the contralateral phrenic nerve. The recovery of the paralyzed hemidiaphragm has been termed the "crossed phrenic phenomenon." The physiological basis for the crossed phrenic phenomenon is as follows: asphyxia induced by spinal hemisection and contralateral phrenicotomy increases central respiratory drive, which activates a latent crossed respiratory pathway. The uninjured, initially latent pathway mediates the hemidiaphragm recovery by descending into the spinal cord contralateral to the hemisection and then crossing the midline of the spinal cord before terminating on phrenic motoneurons ipsilateral and caudal to the hemisection. The purpose of this study is to review work conducted on the crossed phrenic phenomenon and to review closely related studies focusing particularly on the plasticity associated with the response. Because the review deals with recovery of respiratory muscles paralyzed by spinal cord injury, the clinical relevance of the reviewed studies is highlighted.

Can early extubation and intensive physiotherapy decrease length of stay of acute quadriplegic patients in intensive care? A retrospective case control study

BACKGROUND AND PURPOSE

Respiratory complications remain a major cause of morbidity and mortality in the acute quadriplegic patient population. The literature has suggested that early insertion of a tracheostomy facilitated pulmonary management and an earlier discharge from the intensive care unit (ICU). Recently, a change in practice has meant that these patients are considered for extubation and intensive physiotherapy treatment, including an overnight on-call service, rather than tracheostomy. The aim of the present retrospective, case-controlled study was to determine if either practice resulted in a difference in length of stay in intensive care and if an on-call physiotherapy service for these patients was cost effective.

METHOD

A case control design was used. Between April 1997 and November 1999, seven patients who did not require a tracheostomy were identified; case control subjects were matched for severity with seven patients who did receive a tracheostomy. Length of stay in intensive care and on the acute ward, days from injury to fixation and the overall number of respiratory physiotherapy and night physiotherapy treatments were recorded.

RESULTS

Five of the seven patients in the non-tracheostomy group received on-call overnight physiotherapy treatment, with an average of five sessions over a total of three nights. This group's length of stay in an ICU was significantly less than patients who were tracheostomized (p = 0.02). The overall number of physiotherapy treatments between the two groups was not significantly different.

CONCLUSIONS

The results of this study suggest that if extubation and intensive physiotherapy is undertaken for suitable patients, the length of stay in intensive care can be significantly reduced. This represents a considerable cost saving for ICUs and more than covers the added cost of providing an after hours on-call physiotherapy treatment service. A prospective evaluation is required to confirm these findings.

Lung mechanics in individuals with spinal cord injury: effects of injury level and posture

Individuals with spinal cord injury (SCI) exhibit reduced lung volumes and flow rates as a result of respiratory muscle weakness. These features have not, however, been investigated in relation to the combined effects of injury level and posture. Changes in forced vital capacity (FVC), forced expiratory volume in 1 s (FEV(1)), FEV(1)/FVC, forced expiratory flow at 50% vital capacity (FEF(50)), inspiratory capacity (IC), and expiratory reserve volume (ERV) were assessed by injury level in the seated and supine positions in 74 individuals with SCI. The main findings were 1) FVC, FEV(1), and IC increased with descending SCI level down to T(10), below which they tended to level off; 2) supine values of FVC and FEV(1) tended to be larger in the supine compared with the seated posture down to injury level T(1), caudad to which they were less than when seated; 3) IC increased proportionately more down to injury level L(1), below which it declined slightly and plateaued; 4) ERV was measurable even at high cervical injuries, was generally smaller in the supine position, reached peak values in both positions at T(10) injury level, and then rapidly declined at lower levels; 5) when subjects were separated according to current, former, and never smokers, only formerly smoking paraplegic individuals demonstrated spirometric values significantly less than paraplegic individuals who never smoked. Changes in spirometric measurements in SCI are dependent on injury level and posture. These findings support the concept that the increase in vital capacity in supine position is related to the effect of gravity on abdominal contents and increase in IC.

Basic fibroblast growth factor increases long-term survival of spinal motor neurons and improves respiratory function after experimental spinal cord injury

Acute focal injection of basic fibroblast growth factor (FGF2) protects ventral horn (VH) neurons from death after experimental contusive spinal cord injury (SCI) at T8. Because these neurons innervate respiratory muscles, we hypothesized that respiratory deficits resulting from SCI would be attenuated by FGF2 treatment. To test this hypothesis we used a head-out plethysmograph system to evaluate respiratory parameters in conscious rats before and at 24 hr and 7, 28, and 35 d after SCI. Two groups of rats (n = 8 per group) received either FGF2 (3 microg) beginning 5 min after injury or vehicle (VEH) solution alone. We found significantly increased respiratory rate and decreased tidal volume at 24 hr and 7 d after SCI in the VEH-treated group. Ventilatory response to breathing 5 or 7% CO(2) was also significantly reduced. Recovery took place over time. Respiration remained normal in the FGF2-treated group. At 35 d after injury, histological analyses were used to compare long-term neuron survival. FGF2 treatment doubled the survival of VH neurons adjacent to the injury site. Because the number of surviving VH neurons rostral to the injury epicenter was significantly correlated to the ventilatory response to CO(2), it is likely that the absence of respiratory deficits in FGF2-treated rats was caused by its neuroprotective effect. Our results demonstrate that FGF2 treatment prevents the respiratory deficits produced by thoracic SCI. Because FGF2 also reduced the loss of preganglionic sympathetic motoneurons after injury, this neurotrophic factor may have broad therapeutic potential for SCI.

Airway hyperresponsiveness to methacholine in subjects with spinal cord injury

Previously, we found that never-smokers with quadriplegia were hyperresponsive to aerosolized methacholine. To further explore the phenomenon, we compared responsiveness to methacholine in never-smokers with that of smokers and ex-smokers. We also evaluated responsiveness in subjects with high paraplegia (lesions at T-1 to T-6) or low paraplegia (lesions at T-7 and below). We found that smokers and ex-smokers with quadriplegia were hyperresponsive to methacholine (provocative concentration causing a 20% fall in FEV1 = 1.9 mg/mL), and that the response was comparable to that found in never-smokers, revealing that hyperresponsiveness among never-smokers cannot be attributed to preinjury airway hyperreactivity that precluded cigarette use. In contrast, subjects with low paraplegia were not hyperresponsive to methacholine. Among subjects with high paraplegia, the three subjects demonstrating airway hyperresponsiveness had significantly lower FEV1 (percent predicted). The findings support the hypothesis that airway hyperresponsiveness in subjects with quadriplegia represents loss of sympathetic innervation of the lung, thereby leaving intact unopposed bronchoconstrictor cholinergic activity. However, reduced lung volumes in these subjects also suggest the possibility that airway hyperresponsiveness is due to loss of ability to stretch airway smooth muscle by deep breathing.