Functional Electrical Stimulation for Production of Artificial Cough

The purpose of the present study is to assess the utility of abdominal muscle stimulation to provide large positive airway pressures and expiratory airflow thus simulating cough. Restoration of cough in spinal cord injured patients may reduce the incidence of respiratory complications such as atelectasis, respiratory tract infections and respiratory failure.

Cough is a complex defensive respiratory reflex mechanism necessary for the clearance of respiratory secretions and foreign materials. In patients with chronic bronchitis, previous investigations have found that the cough mechanism is the most effective measure to enhance mucous clearance from the lung. Patients with cervical and thoracic spinal cord injuries have suffered a loss of the major portion of their expiratory muscles. Consequently, they are unable to generate significant positive intrathoracic airway pressures or airflow and have a markedly increased risk of developing pulmonary infections. Mechanical methods have been developed to enhance cough production. However, these have resulted in only marginal increases in airway pressure. Preliminary studies in our laboratory in animal experiments and those of others in humans have suggested that the abdominal muscles can be stimulated directly by surface electrodes. The purpose of the present study, therefore, is to assess the utility of abdominal muscle stimulation in quadriplegics and paraplegics to simulate cough. A range of stimulus parameters and electrode locations will be assessed to determine optimal stimulus paradigms. Airway pressure and expiratory airflow will be used as indices of cough effectiveness. If successful, abdominal muscle stimulation may be a useful tool to restore cough and hopefully reduce the incidence of respiratory complications such as atelectasis and infection in spinal cord injured patients.

Surface electrodes currently used for peripheral muscle stimulation by other groups will be applied to the abdominal wall and over the posterior lower thoracic rib cage. Between two and three pairs (anodic and cathodic) of electrodes will be used in combination to activate the expiratory muscles. Electrodes will be positioned at various points over the abdominal wall and the posterior thoracic rib cage to ascertain optimal placement for airway pressure and expiratory airflow generation. The electrical stimulators to be used (EMPI and NeuroMedic) are powered by 9-volt batteries. These stimulators are currently in clinical use to stimulate other skeletal muscles and are known to be quite safe.

Inclusion Criteria: Patients with cervical or thoracic spinal cord injury Exclusion Criteria: Significant cardiovascular disease Active lung disease Pacemaker or other metallic implant Legally incompetent