Complete Restoration of Respiratory Muscle Function in Three Subjects With Spinal Cord Injury: Pilot Interventional Clinical Trial

Unintentionally intentional: unintended effects of spinal stimulation as a platform for multi-modal neurorehabilitation after spinal cord injury

Electrical stimulation of spinal neurons has emerged as a valuable tool to enhance rehabilitation after spinal cord injury. In separate parameterizations, it has shown promise for improving voluntary movement, reducing symptoms of autonomic dysreflexia, improving functions mediated by muscles of the pelvic floor (e.g., bowel, bladder, and sexual function), reducing spasms and spasticity, and decreasing neuropathic pain, among others. This diverse set of actions is related both to the density of sensorimotor neural networks in the spinal cord and to the intrinsic ability of electrical stimulation to modulate neural transmission in multiple spinal networks simultaneously. It also suggests that certain spinal stimulation parameterizations may be capable of providing multi-modal therapeutic benefits, which would directly address the complex, multi-faceted rehabilitation goals of people living with spinal cord injury. This review is intended to identify and characterize reports of spinal stimulation-based therapies specifically designed to provide multi-modal benefits and those that report relevant unintended effects of spinal stimulation paradigms parameterized to enhance a single consequence of spinal cord injury.

Impact of the cough stimulation system on the care burden and life quality of caregivers of tetraplegics

OBJECTIVES

To determine caregiver burden and quality of life of primary family caregivers of participants with cervical SCI before and after use of the cough stimulation system (CSS).

DESIGN

Prospective assessment at four timepoints via questionnaire responses.

SETTING

Out-patient hospital, United States.

PARTICIPANTS

15 primary family caregivers of participants with cervical SCI completed questionnaires including a respiratory care burden index (n = 15) and a commonly employed caregiver burden inventory (n = 9), before and at the 6-month, 1-year and 2-year timepoints following use of the CSS.

RESULTS

SCI participants had significant clinical improvements in terms of restoration of an effective cough and ability to manage airway secretions with use of the CSS. Restoration of expiratory muscle function with use of the CSS also resulted in less caregivers (CG) stress, greater control of their participants' breathing problems, and improvement in quality of life. Results of the caregiver burden inventory demonstrated marked reductions in caregiver burden in development items, physical health and social relationship. Overall caregiver burden fell from 43.4 ± 13.8 pre-implant to 32.4 ± 7.9 (P = 0.06), 31.7 ± 10.5 (P = 0.05), and 26.5 ± 9.3 (P = 0.01) at the 6-month, 1-year and 2-year timepoints.

CONCLUSION

Use of the CSS by cervical SCI participants results in restoration of an effective cough with significant clinical benefits. While caregiver burden is very high in primary family caregivers, they derive marked improvement in caregiver burden and quality of life with implementation of this device.Trial registration: ClinicalTrials.gov identifier: NCT00116337.Trial registration: ClinicalTrials.gov identifier: NCT01659541.

Effects of restoration of cough via spinal cord stimulation on subject quality of life

Objectives

To determine participant quality of life before and after use of the cough stimulation system (Cough System).

Design

Prospective assessment of life quality at 4 timepoints via questionnaire responses.

Setting

Out-patient hospital, United States.

Participants

28 subjects with spinal cord injury (SCI) completed life quality assessment questionnaires before and at the 28- 40- and 52-week timepoints following use of the Cough System.

Results

Each subject demonstrated significant clinical improvements in terms of restoration of an effective cough and ability to manage airway secretions with use of the Cough System. Positive airway pressures and peak expiratory airflows approached values associated with a normal cough. Related to cough/secretion management, use of this system also resulted less interference with family life and daily activities, less financial difficulties, less requirement for caregiver assistance, less stress, less embarrassment and greater control of their breathing problems (p < 0.01), for each comparison). There also significant improvements in that their overall health and quality of life (p < 0.01, for each comparison). Subjects also reported greater ease in breathing, restored ability to sneeze and enhanced mobility. The incidence of acute respiratory tract infections fell from 1.3 ± 0.3 to 0.2 ± 0.1 events/subject year (p < 0.01). Ten subjects developed mild hemodynamic effects consistent with autonomic dysreflexia that abated completely with continued use of the Cough System. Some subjects experienced mild leg jerks during SCS, which were well tolerated and abated completely with reduction in stimulus amplitude, No subjects reported bowel or bladder leakage.

Conclusion

Use of the Cough System by SCI subjects is a safe and efficacious method which significantly improves life quality and has the potential to reduce the mortality and morbidity associated with SCI.

Epidural electrical stimulation of the cervical spinal cord opposes opioid-induced respiratory depression

Opioid overdose suppresses brainstem respiratory circuits, causes apnoea and may result in death. Epidural electrical stimulation (EES) at the cervical spinal cord facilitated motor activity in rodents and humans, and we hypothesized that EES of the cervical spinal cord could antagonize opioid-induced respiratory depression in humans. Eighteen patients requiring surgical access to the dorsal surface of the spinal cord between C2 and C7 received EES or sham stimulation for up to 90 s at 5 or 30 Hz during complete (OFF-State) or partial suppression (ON-State) of respiration induced by remifentanil. During the ON-State, 30 Hz EES at C4 and 5 Hz EES at C3/4 increased tidal volume and decreased the end-tidal carbon dioxide level compared to pre-stimulation control levels. EES of 5 Hz at C5 and C7 increased respiratory frequency compared to pre-stimulation control levels. In the OFF-State, 30 Hz cervical EES at C3/4 terminated apnoea and induced rhythmic breathing. In cadaveric tissue obtained from a brain bank, more neurons expressed both the neurokinin 1 receptor (NK1R) and somatostatin (SST) in the cervical spinal levels responsive to EES (C3/4, C6 and C7) compared to a region non-responsive to EES (C2). Thus, the capacity of cervical EES to oppose opioid depression of respiration may be mediated by NK1R+/SST+ neurons in the dorsal cervical spinal cord. This study provides proof of principle that cervical EES may provide a novel therapeutic approach to augment respiratory activity when the neural function of the central respiratory circuits is compromised by opioids or other pathological conditions. KEY POINTS: Epidural electrical stimulation (EES) using an implanted spinal cord stimulator (SCS) is an FDA-approved method to manage chronic pain. We tested the hypothesis that cervical EES facilitates respiration during administration of opioids in 18 human subjects who were treated with low-dose remifentanil that suppressed respiration (ON-State) or high-dose remifentanil that completely inhibited breathing (OFF-State) during the course of cervical surgery. Dorsal cervical EES of the spinal cord augmented the respiratory tidal volume or increased the respiratory frequency, and the response to EES varied as a function of the stimulation frequency (5 or 30 Hz) and the cervical level stimulated (C2-C7). Short, continuous cervical EES restored a cyclic breathing pattern (eupnoea) in the OFF-State, suggesting that cervical EES reversed the opioid-induced respiratory depression. These findings add to our understanding of respiratory pattern modulation and suggest a novel mechanism to oppose the respiratory depression caused by opioids.

Comparison of disc and wire electrodes to restore cough via lower thoracic spinal cord stimulation

OBJECTIVE

To compare the safety and effectiveness of wire (WE) vs. disc (DE) electrodes to restore cough in subjects with spinal cord injury (SCI).

DESIGN

Clinical trials assessing the effectiveness and clinical outcomes associated with two electrode systems to activate the expiratory muscles.

SETTING

Inpatient hospital setting for DE or WE electrode insertion; outpatient evaluation of cough efficacy and instructions for home use.

PARTICIPANTS

Twenty-nine subjects with SCI; 17 participants with DE and 12 with WE implants.

INTERVENTION

Surgical implantation of WE or DE to restore cough. Daily application of spinal cord stimulation (SCS) at home.

MAIN OUTCOME MEASURE(S)

Airway pressure (P) and peak airflow (F) generation achieved with SCS; clinical parameters including ease in raising secretions, incidence of acute respiratory tract infections (RTI) and side effects.

RESULTS

P and F achieved with DE and WE were not significantly different. For example, at total lung capacity (TLC) with participant effort, P was 128 ± 12 cmH2O and 118 ± 14 cmH2O, with DE and WE, respectively. The degree of difficulty in raising secretions improved markedly in both groups. The incidence of RTI per year fell from 1.3 ± 0.3 and 1.3 ± 0.5-0.3 ± 0.1 and 0.1 ± 0.1 for DE and WE groups, respectively (P < 0.01 for both when compared to pre-implant values and NS between DE and WE groups). The only significant side effect i.e. short-term autonomic dysreflexia was also similar between groups.

CONCLUSIONS

The results of this investigation indicate that both DE and WE result in comparable degrees of expiratory muscle activation, clinical benefits and side effects. Importantly, SCS to restore cough can be achieved with use of WE which can be placed using minimally invasive techniques and associated reduction in cost, surgical time and overall risk.Trial registration: ClinicalTrials.gov identifier: NCT00116337., NCT01659541, FDA IDE: G980267.

The phrenic neuromuscular system

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

Comparison of wire and disc electrodes to electrically activate the inspiratory muscles in dogs

OBJECTIVE

To compare the effectiveness of wire versus disc electrodes to activate the inspiratory muscles via high frequency spinal cord stimulation.

DESIGN

Animal study.

SETTING

Research laboratory.

ANIMALS

Dogs (n = 5) INTERVENTIONS: In separate trials, spinal cord stimulation (SCS) was applied via disc (DE) and two parallel wire electrodes (WE) on the ventral epidural space at the T2-T3 spinal region.

MAIN OUTCOME MEASURE(S)

Airway pressure (P) and inspired volume (V) generation following stimulation with DE and WE were compared. Given our previous success with (DE), outcome variables with this electrode were used as our gold standard to which all comparisons were made.

RESULTS

Two configurations of WE using monopolar stimulation (MS) resulted in P and V that were similar to those generated with MS with DE. For example, MS with parallel WE connected together to function as a common cathode (Y-connection) and a 2-channel system (separate cathodes with a remote ground), resulted in P that were 91 ± 6 and 92 ± 4%, respectively, of those achieved with DE (NS for both). Bipolar stimulation with parallel WE using a Y-connection and with a 2-channel system, resulted in P that were 96 ± 4 and 94 ± 4%, of the P achieved with DE (NS for both).

CONCLUSION(S)

These results suggest that specific configurations of WE, which can be placed via minimally invasive techniques, provide comparable activation of the inspiratory muscles compared to DE and may be a useful technique to restore ventilatory support in persons with spinal cord injury.

Effectiveness of oral motor respiratory exercise and vocal intonation therapy on respiratory function and vocal quality in patients with spinal cord injury: a randomized controlled trial

Singing, as a method of combining respiratory function exercise and vocal intonation therapy, provides a new direction for respiratory function exercise in patients with spinal cord injury. This randomized controlled trial investigated the effects of oral motor respiratory exercise and vocal intonation therapy on respiratory function and vocal quality in patients with spinal cord injury. Among 31 included patients with spinal cord injury, 18 completed the treatment. These 18 patients were randomly assigned to undergo music therapy (intervention group, 30 min/d, 5 times a week, for a total of 12 weeks; n = 9, 7 males and 2 females; 30.33 ± 11.74 years old) or normal respiratory training (control group, n = 9; 8 males and 1 female; 34.78 ± 11.13 years old). Both patient groups received routine treatment concurrently. Before and at 6 and 12 weeks after intervention, a standard respiratory function test, a voice test, the St. George's Respiratory Questionnaire, and a quality of life questionnaire were administered. The results showed that the inspiratory capacity, forced expiratory volume in 1 second, forced vital capacity, maximal mid-expiratory flow rate, sing-loud pressure level, and sustained note length were significantly increased in the intervention group compared with the control group. The St. George's Respiratory Questionnaire and quality of life results of patients in the intervention group were significantly superior to those in the control group. These findings suggest that oral motor respiratory exercise and vocal intonation therapy, as respiratory training methods in music therapy, are effective and valuable for improving respiratory dysfunction and vocal quality in patients with spinal cord injury. This study was approved by the Ethics Committee of China Rehabilitation Research Center (approval No. 2019-78-1) on May 27, 2019 and was registered with the Chinese Clinical Trial Registry (registration number: ChiCTR1900026922) on October 26, 2019.

Effects of Lower Thoracic Spinal Cord Stimulation on Bowel Management in Individuals With Spinal Cord Injury

OBJECTIVE

To systematically determine whether use of the spinal cord stimulation (SCS) system to restore cough may improve bowel management (BM) in individuals with spinal cord injury (SCI).

DESIGN

Experimental studies (clinical trial).

SETTING

Inpatient hospital setting for electrode insertion; outpatient setting for measurement of respiratory pressures; home setting for application of SCS.

PARTICIPANTS

Participants (N=5) with cervical SCI.

INTERVENTION

A fully implantable SCS cough system was surgically placed in each subject. SCS was applied at home, 2-3 times/d, on a chronic basis, every time bowel regimen was performed and as needed for secretion management. Stimulus parameters were set at values resulting in near maximum airway pressure generation, which was used as an index of expiratory muscle strength. Participants also used SCS during their bowel routine.

MAIN OUTCOME MEASURES

Airway pressure generation achieved with SCS. Weekly completion of Bowel Routine Log including BM time, mechanical measures, and medications used.

RESULTS

Mean pressure during spontaneous efforts was 30±8 cmH₂O. After a period of reconditioning, SCS resulted in pressure of 146±21 cmH₂O. The time required for BM routines was reduced from 118±34 minutes to 18±2 minutes (P<.05) and was directly related to the magnitude of pressure development during SCS. Mechanical methods for BM were completely eliminated in 4 patients. No patients experienced fecal incontinence as result of SCS. Each participant also reported marked overall improvement associated with BM.

CONCLUSIONS

Our results of this pilot study suggest that SCS to restore cough may be a useful method to improve BM and life quality for both patients with SCI and their caregivers. Our results indicate that the improvement in BM is secondary to restoration of intra-abdominal pressure development.

Restoration of cough via spinal cord stimulation improves pulmonary function in tetraplegics

Background: Spinal cord injury (SCI) results in significant loss in pulmonary function secondary to respiratory muscle paralysis. Retention of secretions and atelectasis and, recurrent respiratory tract infections may also impact pulmonary function. Objective: To determine whether usage of lower thoracic spinal cord stimulation (SCS) to restore cough may improve spontaneous pulmonary function in individuals with chronic SCI. Design/Methods: 10 tetraplegics utilized SCS system on a regular daily basis. Spontaneous inspiratory capacity (IC), maximum inspiratory pressure (MIP) and maximum expiratory pressure (MEP) were measured at baseline prior to usage of the device and repeated every 4-5 weeks over a 20-week period. Maximum airway pressure generation (P) during SCS (40 V, 50 Hz, 0.2 ms) at total lung capacity (TLC) with subject maximal expiratory effort, at the same timepoints were determined, as well. Results: Following daily use of SCS, mean IC improved from 1636 ± 229 to 1932 ± 239 ml (127 ± 8% of baseline values) after 20 weeks (P < 0.05). Mean MIP increased from 40 ± 7, to 50 ± 8 cmH2O (127 ± 6% of baseline values) after 20 weeks, respectively (P < 0.05). MEP also improved from 27 ± 3.7 to 33 ± 5 (127 ± 14% of baseline values) (NS). During SCS, P increased from baseline in all participants from mean 87 ± 8 cmH2O to 117 ± 14 cmH2O at weeks 20, during TLC with subject maximal expiratory effort, respectively (P < 0.05). Each subject stated that they experienced much greater ease in raising secretions with use of SCS. Conclusion: Our findings indicate that use of SCS not only improves expiratory muscle function to restore cough but also results in improvement inspiratory function, as well.

Neural engineering: the process, applications, and its role in the future of medicine

OBJECTIVE

Recent advances in neural engineering have restored mobility to people with paralysis, relieved symptoms of movement disorders, reduced chronic pain, restored the sense of hearing, and provided sensory perception to individuals with sensory deficits.

APPROACH

This progress was enabled by the team-based, interdisciplinary approaches used by neural engineers. Neural engineers have advanced clinical frontiers by leveraging tools and discoveries in quantitative and biological sciences and through collaborations between engineering, science, and medicine. The movement toward bioelectronic medicines, where neuromodulation aims to supplement or replace pharmaceuticals to treat chronic medical conditions such as high blood pressure, diabetes and psychiatric disorders is a prime example of a new frontier made possible by neural engineering. Although one of the major goals in neural engineering is to develop technology for clinical applications, this technology may also offer unique opportunities to gain insight into how biological systems operate.

MAIN RESULTS

Despite significant technological progress, a number of ethical and strategic questions remain unexplored. Addressing these questions will accelerate technology development to address unmet needs. The future of these devices extends far beyond treatment of neurological impairments, including potential human augmentation applications. Our task, as neural engineers, is to push technology forward at the intersection of disciplines, while responsibly considering the readiness to transition this technology outside of the laboratory to consumer products.

SIGNIFICANCE

This article aims to highlight the current state of the neural engineering field, its links with other engineering and science disciplines, and the challenges and opportunities ahead. The goal of this article is to foster new ideas for innovative applications in neurotechnology.