The goal of this clinical trial is to learn if abdominal functional electrical stimulation (FES) using the VentFree Respiratory Muscle Stimulator improves cough strength in adults with a new spinal cord injury (SCI). It will also learn about the safety of abdominal FES in this population. The main questions it aims to answer are:

Does abdominal FES improve cough peak flow (a measure of cough strength) compared to cough training alone? Does abdominal FES reduce the number of respiratory complications (such as pneumonia or atelectasis)? What medical problems do participants have when receiving abdominal FES?

Researchers will compare abdominal FES (active treatment) to supervised cough training without stimulation (control) to see if abdominal FES improves cough function after spinal cord injury.

Participants will:

Receive abdominal FES or perform supervised cough training 5 days per week for up to 6 weeks during inpatient rehabilitation Have cough strength and breathing function measured at the start of the study and every week during treatment Complete quality of life and bowel function questionnaires at multiple time points Have a follow-up visit or phone call 4 weeks after completing treatment

Spinal cord injury (SCI) at the cervical or high thoracic level impairs the abdominal and intercostal muscles, reducing expiratory muscle strength and cough effectiveness. An impaired cough leads to secretion retention and respiratory complications, which are the leading cause of morbidity and mortality in the first year following SCI. Current standard-of-care techniques such as manually assisted coughing and mechanical insufflation-exsufflation can augment assisted cough but do not directly improve a patient's voluntary, unassisted cough function.

Abdominal functional electrical stimulation (FES) uses transcutaneous neuromuscular electrical stimulation (NMES) applied to the abdominal wall muscles in synchrony with the expiratory phase of breathing. This approach can recruit the abdominal muscles in the absence of voluntary or automatic muscle activation, making it particularly suited for use after SCI. Prior investigator-initiated studies and pilot randomized controlled trials have demonstrated that abdominal FES is safe and feasible in this population, and that repeated training with abdominal FES can produce longitudinal improvements in respiratory function including cough peak flow (CPF), forced vital capacity (FVC), and peak expiratory flow (PEF).

This is a prospective, randomized, single-blind (observer-blinded), multicenter superiority trial enrolling adults with a new non-progressive SCI at neurological levels C1-T5 (AIS A-C) who are in the inpatient rehabilitation phase of care and have a CPF below 160 L/min. Approximately 150 participants will be enrolled at up to 20 sites in North America and randomized 1:1 to active treatment or control. Randomization is stratified by site and injury level.

Participants in the active group receive abdominal FES during 3 sets of 10 coughs followed by 30 minutes of quiet breathing, 5 days per week, for up to 6 weeks or until hospital discharge. Stimulation is delivered at 30 Hz / 350 µs during quiet breathing and 50 Hz / 400 µs during coughing, with amplitude titrated to achieve a strong visible abdominal wall contraction. Participants in the control group perform 3 sets of 10 supervised volitional coughs per day, 5 days per week, for the same duration, with no active stimulation.

The primary endpoint is CPF measured 4 weeks post-randomization. Secondary endpoints include additional respiratory function measures (FVC, FEV1, PEF, MIP, MEP), effectiveness of cough (proportion achieving CPF >160 L/min), respiratory complications, bowel function (Neurogenic Bowel Dysfunction Score), quality of life (SF-36ww), global impression of benefit, and mortality. All respiratory function measurements follow ATS/ERS guidelines. Outcome assessors and radiographers are blinded to treatment allocation.

The sample size of 150 participants (75 per group) provides 90% power to detect a 42 L/min between-group difference in CPF improvement from baseline, assuming a standard deviation of 72 L/min and a one-sided significance level of 0.025, with 15% attrition allowance.

Inclusion Criteria:

1. Adults (≥ 22 years of age) admitted to rehabilitation with a new SCI.
2. New non-progressive SCI occurring in the past 3 to 8 weeks.
3. Neurological level of injury of C1-T5.
4. American Spinal Injuries Association Impairment Scale A to C.
5. CPF of <160 L/min (Note: A CPF of <270 L/min has been shown to be associated with decreased secretion clearance and increased respiratory complications, while a CPF of <160 L/min has been shown to lead to an ineffective cough).
6. Not dependent on mechanical ventilation (people dependent on mechanical ventilation are at greatly increased risk of respiratory complications and are excluded due to this heterogeneity).
7. Able to sit upright.
8. Expected to remain in rehabilitation for at least another 3 weeks.

Exclusion Criteria:

1. Respiratory complications in previous 24 hours (screening out iatrogenic complications).

2. Chronic respiratory disease.

3. No contraction of the abdominal wall muscles in response to abdominal NMES.

4. Open abdominal surgery ≤ 4 weeks prior to enrollment.

5. Have yet to undergo spinal surgery to stabilize injury, where required.

6. Body mass index >40 kg/m2.

7. Pacemaker (external or internal) or implanted electronic device (e.g., a defibrillator).

8. Known or expected to be pregnant.

9. Placed on a palliative/supportive care only pathway.

10. Receiving any of the following as standard of care:

    • Abdominal FES
    • Inspiratory or Expiratory muscle training
    • Transcutaneous or implanted thoracolumbar spinal stimulation

11. Participating in any of the following:

    • A study with the same or similar primary endpoint
    • A study investigating electrical stimulation or respiratory muscle therapy
    • Any study in which the investigator determines may interfere with the results of this study

12. Unable or unwilling to comply with protocol requirements, including assessments, tests, and follow-up visits including facial or dental trauma.

13. Any other medical condition which in the opinion of the Investigator will make participation medically unsafe or interfere with the study results.

14. Unable to provide informed consent.

15. Unwilling to provide informed consent.