In June, the FDA approved the NeuRx Diaphragm Pacing System (DPS)™ for spinal cord injury patients dependent on ventilators who cannot control their diaphragms. The electronic device is implanted in the diaphragm to stimulate the muscle, enabling certain spinal cord injury patients to breathe without a mechanical ventilator for at least four hours a day.
The FDA based its approval on data from a multicenter clinical trial, Electrical Activation of The Diaphragm for Ventilatory Assist, published this year in the Journal of Spinal Cord Medicine. Beginning in 2000, the investigators had implanted the device in 50 high-level spinal cord injury patients — those with C1-C3 tetraplegic injury — at hospitals in the US and Canada. The FDA granted approval under a Humanitarian Device Exemption, intended for devices that treat or diagnose conditions affecting fewer than 4,000 people a year.
Investigators reported that 90 percent of spinal cord injury patients who had been dependent on mechanical ventilation were able to use the device for over four continuous hours, and 70 percent for more than half of each day. At the time the data was submitted to the FDA, more than 50 percent of the patients had become completely free of reliance on mechanical ventilation and could use the DPS for 24 hours a day.
This long-term use depends on the level of injury and medical condition, patient age, motivation, and caregiver support, according to Ray Onders, MD, director of minimally invasive surgery at Case Western Reserve University School of Medicine in Cleveland, OH, and founder of the DPS device manufacturer Synapse Biomedial Inc.
The first patient has been using the DPS as his sole means of respiratory support for over seven years.
Through minimally invasive laparoscopic surgery, the electrodes are implanted near the phrenic nerves that control the diaphragm contractions and then attached through wires under the skin to a battery-powered pulse generator that stimulates contraction of the diaphragm. This contraction allows air to fill the lungs and thus imitates natural breathing, as opposed to forcing air in with a ventilator. The patient can turn on the stimulator when he or she chooses. Daily strengthening of the muscle is necessary to allow increasing amount of time off the ventilator.
Although the DPS does not cure paralysis of the diaphragm in patients with SCI, it does greatly enhance their quality of life, experts said, allowing them to travel and be more physically active, live at home instead of a ventilator ward, and reduce the cost of care. Normal speech patterns and the sense of smell and taste, which are often diminished in ventilator-dependent patients, return, and the risk of a serious complication such as pneumonia is greatly reduced.
Figure. The DPS uses...Image Tools
Eligible candidates must be at least 18 years old and have stable, high-level spinal cord injury with intact diaphragm muscle and peripheral nerves to the diaphragm, dependence on mechanical ventilation, and no control over the diaphragm. Patients with spinal cord injuries that result in damaged phrenic nerves do not qualify for the implant.
“The primary indications for the device implantation are similar to phrenic nerve pacer implants, which many neurologists are already familiar with,” said John McDonald, MD, PhD, associate professor of neurology at Johns Hopkins University School of Medicine and director of the International Center for Spinal Cord Injury at the Kennedy Krieger Institute. He added that the greatly shortened post-operative training time, compared to conventional phrenic nerve pacing, is an advance. The first patient Dr. McDonald recommended for the device was Christopher Reeves, and since then, he said, his center has referred five more patients for the DPS device, all of whom “have met with considerable success after implantation.”
Dr. McDonald, who was not involved with the trial, cited 2006 data from the National Spinal Cord Injury Statistical Center showing that an estimated 3,700 individuals are living with high C1-C3 tetraplegia spinal cord injury, with around 500 such new cases each year. A conservative estimate is that approximately half of these individuals will be eligible for the DPS device, he said, but “these numbers reflect only traumatic causes of SCI and there are an equal or greater number of non-traumatic causes of SCI that will prove to have similar benefits to diaphragmatic pacing including ALS, MS, and orthopedic-related spinal cord dysfunction.”
A cooperative group of medical centers trained to evaluate patients, perform the implantation procedure, and provide rehabilitative training has been established by the device's manufacturer Synapse in select areas such as Texas, Ohio, Georgia, and Colorado.
John R. Bach, MD, professor of neurosciences in the department of physical medicine and rehabilitation at the University of Medicine and Dentistry of New Jersey (UMDNJ), who was not involved in the study, said he would recommend the DPS only for complete C1-C2 level tetraplegics: those who cannot rotate their neck, breathe at all, use an intermittent abdominal pressure ventilator, or use a mouthpiece for ventilatory support. Other patients can use noninvasive ventilation around the clock and do not need a DPS device, which could cause deterioration of the phrenic nerves and diaphragm, he said.
“Even if using the DPS device for daytime support, the tracheostomy should be removed and the patient placed on nasal IPPV [intermittent positive pressure ventilation] for nocturnal ventilatory support,” he said. Dr. Bach also cautioned that as an “invasive sort of ventilator, it provides mechanical function and can fail suddenly like any ventilator.”
The device is only approved for use in spinal cord injury patients, but is currently being studied in a controlled clinical trial for ALS to determine if it can be used to delay the onset of respiratory failure and decrease or eliminate the need for mechanical ventilation.
• Onders RP, Elmo MJ, Dunkin B, et al. Diaphragm Pacing Stimulation (DPS) system for ventilatory support in tetraplegia complete worldwide results of a prospective FDA trial. J Spinal Cord Med 2008;31:223–224.
©2008 American Academy of Neurology