Effect of Hypercapnia Treatment on Respiratory Recovery After Spinal Cord Injury

One of the most devastating consequences of cervical spinal cord injury (SCI) is damage to the phrenic motor network, controlling the diaphragm (primary muscle of breathing). Subsequent diaphragm paralysis or paresis results in life-threatening impairments in breathing and can necessitate a need for ventilator assistance. Respiratory and cardiovascular complications are the most common causes of death in the first year post-injury (51% combined). Thus, there is an urgent need to develop strategies for improving function for people with acute and chronic spinal cord injury. Currently, treatments for respiratory dysfunction in spinal cord injury patients are limited to mechanical devices or nerve pacing. Moreover, the proposed plan of studying respiratory muscle training in spinal cord injury patients is novel. However, it is based on animal and human studies that have shown with validity that respiratory muscle training using mild intermittent hypoxia improves respiratory function following SCI. However, the effect of intermittent hypoxia has shown to be dependent on the level of alveolar CO2 and may pose undesirable cardiovascular effects. Previous studies showed that respiratory recovery following SCI manifests by a delayed and partial restorative spontaneous plasticity. The current research project and future anticipated studies would set the base for developing innovative therapies that can stimulate respiratory plasticity hence recovery for this prevalent disorder.

The proposed pilot/feasibility study will test the effect of daily acute intermittent hypercapnia (dAIHc) in individuals with SCI. The objectives of this study are to (1) determine recruitment rates and test the feasibility of recruitment, (2) calculate withdrawal and dropout rates, (3) test the feasibility and tolerability and acceptability of the proposed intervention in an SCI population, (4) develop and refine a new respiratory training intervention using dAIHc paradigm (5) derive effect size estimates for clinical endpoints and their associated variability at the end of treatment to calculate an appropriate sample size for an adequately powered clinical trial. Compared to sham therapy, the central hypothesis is that the daily respiratory muscle training (dAIHc) approach is acceptable and feasible in patients with SCI and will strengthen respiratory muscles and reduce the severity of sleep-disordered breathing (SDB), and will improve daytime symptoms.

This study is highly innovative and the first of its kind in patients with SCI, as it seeks first to use a new set of rehabilitative exercises to improve ventilation and respiratory muscles strength; secondly, it aims to use controlled randomized design; finally, it will determine the role of respiratory muscle exercises in reducing the severity of sleep symptoms and daytime function in SCI. Each aim is independently testable and does not depend on the result of the other aims. The findings will likely apply to a broad range of other neuromuscular diseases (such as Multiple Sclerosis and Stroke). The team of this pilot project has the resources and IRB approval necessary to execute the project.

Inclusion criteria

• Adult patients with chronic SCI/D (>6 months post-injury)
• American Spinal Injury Association (ASIA) classification A-D who have evidence of SDB (excluding those with no evidence of a neurologic deficit based on ASIA classification)
• Able-bodied patients (without SCI/D0 who have OSA.

Exclusion criteria

• Receiving continuous mechanical ventilation (except PAP therapy which is considered usual treatment for SDB
• Severe congestive heart failure with ejection fraction <35%
• Recent health event that may affect sleep
• stroke
• acute myocardial infarction
• recent surgery
• hospitalization
• Alcohol or substance abuse (<90 days sobriety)
• Self-described as too ill to engage in study procedures
• Evidence of hypercapnia on spontaneous breathing (end-tidal CO2 >50 mmHg)
• Unable to provide self-consent for participation