Sub-study to Spinal Cord Stimulation to Restore Cough

Patients with cervical and thoracic spinal cord injuries often have paralysis of a major portion of their expiratory muscles - the muscles responsible for coughing - and therefore, lack a normal cough mechanism. Consequently, most of these patients suffer from a markedly reduced ability to clear airway secretions, a factor which contributes to the development of recurrent respiratory tract infections such as pneumonia and bronchitis. In fact, pneumonia is a major cause of death in this patient population. In a recent clinical trial, we have shown that the expiratory muscles can be electrically activated by spinal cord stimulation (SCS), a technique which involves the surgical placement of disc electrodes on the surface of the spinal cord. This method is successful in achieving an effective means of expiratory muscle activation, as demonstrated by the generation of large airway pressures and peak airflow rates. Importantly, SCS facilitates secretion removal, reduces the need for caregiver support, reduces the incidence of respiratory tract infections and improves life quality. This method therefore has the potential to reduce health care costs and improve survival in spinal cord injured subjects. The purpose of this trial is to directly compare activation of the expiratory muscles using wire electrodes, which can be inserted percutaneously through a needle, with the previously employed disc electrodes. In this trial, researchers will study 6 adults (18-70 years old) with spinal injuries (T5 level or higher), at least 12 months following the date of injury. After an evaluation including medical history, a brief physical examination, and initial testing, each participant will undergo a surgical procedure to implant small electrodes (metal discs) over the surface of the spinal cord on the lower back to stimulate the expiratory muscles and restore cough. Prior to permanent implantation of this system, wire and disc electrodes will be compared by assessing the degree of expiratory muscle activation with each electrode type. The disc electrodes will then be permanently implanted, allowing the participant to have use of a fully functioning stimulation system to restore an effective cough.

The participant will have wire electrodes temporarily placed - by a routine surgical procedure - over the surface of the spinal cord on the lower back. These electrodes will be activated in the operating room and the degree of muscle activation assessed. The wire electrodes will then be removed. Small, disc electrodes will then be permanently implanted to stimulate expiratory muscles and restore cough. These electrodes are activated using an external control unit.

The participant will have wire electrodes temporarily placed - by a routine surgical procedure - over the surface of the spinal cord on the lower back. These electrodes will be activated in the operating room and the degree of muscle activation assessed. The wire electrodes will then be removed. Small, disc electrodes will then be permanently implanted to stimulate expiratory muscles and restore cough. These electrodes are activated using an external control unit.

The expiratory muscle stimulator consists of three small electrodes (metal discs) implanted over the surface of their spinal cords on the lower back to stimulate the expiratory muscles and restore cough. These electrodes are connected to an implanted receiver in the abdomen or chest wall. The device is activated through an external antenna connected to an external control box.

The Effects of Electrical Spinal Cord Stimulation (SCS) on Airway Pressure Generation While Using Temporarily Placed Parallel Wire Leads and Implanted Disc Electrodes

The effects of SCS with temporarily placed parallel wire leads and then with permanently implanted disc electrodes on airway pressure generation in each participant was evaluated in the operating room. The wire electrodes were temporarily placed (immediately prior to placement of disc electrodes as part of the current clinical trial) over the surface of the spinal cord on the lower back. These electrodes were activated, and the degree of expiratory muscle activation were assessed. The wire electrodes were then removed. Small, disc electrodes were then permanently implanted to stimulate expiratory muscles and restore cough. All measurements were repeated. Since SCS with the disc electrode leads, when applied in clinical trials, resulted in airway pressure generation that approximated pressures generated with a normal maximum cough, airway pressure generation achieved during SCS with these leads served as our gold standard to which all comparisons were made.

Inclusion Criteria: Stable spinal cord injury T5 level or higher Expiratory muscle weakness Exclusion Criteria: Significant cardiovascular disease Active lung disease Brain disease Scoliosis, chest wall deformity, or marked obesity

DiMarco AF, Kowalski KE, Geertman RT, Hromyak DR. Spinal cord stimulation: a new method to produce an effective cough in patients with spinal cord injury. Am J Respir Crit Care Med. 2006 Jun 15;173(12):1386-9. doi: 10.1164/rccm.200601-097CR. Epub 2006 Mar 16.

DiMarco AF, Kowalski KE, Geertman RT, Hromyak DR. Lower thoracic spinal cord stimulation to restore cough in patients with spinal cord injury: results of a National Institutes of Health-sponsored clinical trial. Part I: methodology and effectiveness of expiratory muscle activation. Arch Phys Med Rehabil. 2009 May;90(5):717-25. doi: 10.1016/j.apmr.2008.11.013.

DiMarco AF, Kowalski KE, Geertman RT, Hromyak DR, Frost FS, Creasey GH, Nemunaitis GA. Lower thoracic spinal cord stimulation to restore cough in patients with spinal cord injury: results of a National Institutes of Health-Sponsored clinical trial. Part II: clinical outcomes. Arch Phys Med Rehabil. 2009 May;90(5):726-32. doi: 10.1016/j.apmr.2008.11.014.