Understanding the mechanisms of Abdominal Functional Electrical Stimulation in patients with a spinal cord injury

Intervention Electrical stimulation, the application of electrical pulses to a nerve, causes the associated muscle to contract, even when paralysed. For patients with a spinal cord injury, electrical stimulation of the abdominal muscles, termed Abdominal Functional Electrical Stimulation (Abdominal FES), has been shown to improve respiratory function. However, the mechanisms through which Abdominal FES improves respiratory function are poorly understood. In this study, 15 tetraplegic participants will be asked to attend an initial assessment session at Neuroscience Research Australia. During this assessment session, Abdominal FES will be applied via four electrodes placed on the stomach. During this time ultrasound and Electromyography (EMG) will be used to measure diaphragm excursion and activity, and abdominal muscle thickness, with and without Abdominal FES. The activity of the inspiratory muscles with and without Abdominal FES will be measured using intraoesophageal EMG electrodes mounted on a gastro-oesophageal catheter. The two pressure transducers on this catheter will be used to measure gastric pressure and oesophageal pressure with and without Abdominal FES. The total duration of the assessment session will be approximately 90 minutes, with Abdominal FES applied for approximately 25% of this time. Participants will then be asked to apply Abdominal FES at home for one hour per day, five days per week, for four weeks. They will be trained in how to use this technology by a rehabilitation physiotherapist with over 10 years experience. A training diary will be used to measure compliance. Participants will then return to Neuroscience Research Australia, where the aforementioned assessment session will be repeated. Abdominal FES parameters will be personalised to each patient. Stimulation current will be adjusted until a strong visible contraction of the abdominal muscles is observed.