Paralysis or the loss of mobility are among the most pressing and clear consequences of a spinal cord injury. But many patients also face lesser-known complications that can disrupt their daily lives in other ways.
One of the most common problems is orthostatic hypotension, or not being able to maintain a stable blood pressure when switching positions between sitting, standing, or lying down. In the short term, this can lead to dizziness or fainting. In the long term, it can increase risk of heart attack or stroke, which are both leading causes of death for those who have suffered a spinal cord injury.
But researchers with the University of Calgary and the Swiss Federal Institute of Technology have devised a potential solution: a neuroprosthetic device that can replicate the natural physiological process to sustain blood pressure while changing positions. Just a few centimeters in length, the implanted device imitates the body’s baroreflex, stimulating the spine to trigger neural responses that affect blood pressure. Such devices are already used to treat several types of pain unrelated to spinal cord injuries, but this is the first time it’s been used to address orthostatic hypotension.
“Before our technology, there were practically no viable options,” said Aaron Phillips, a researcher at the University of Calgary and author of a new paper published Wednesday in Nature about the device.
When unencumbered, the body can regulate blood pressure on its own. Active muscles help to continue pumping blood to the heart and brain. But a spinal cord injury essentially severs the connection between the reflexive neurons that sense blood pressure and the sympathetic nervous system that adjusts accordingly.
For people with orthostatic hypotension, even moving between bed and one’s wheelchair, or sitting up to eat breakfast, can pose a risk. Episodes of dizziness or lost consciousness from a sudden drop in blood pressure are common, occurring up to 11 times per day for some. The degree of the problem likely depends on the severity and the location of the spinal injury, said Edelle Field-Fote, who leads spinal cord injury research at the Shepherd Center in Atlanta and was not involved in the study.
Patients who experience these blood pressure issues often have to manage the problem with compression bands wrapped around their muscles or medication. But Phillips argues those are largely ineffective and come with their own array of side effects. While his team’s device requires surgery for implantation, the existing use of similar devices means it is a minimally invasive and common procedure.
Phillips likens the new device to a thermostat, with the body as its home. It regulates internal blood pressure and when it senses a drop, activates sensory neurons that can send signals to sympathetic neurons in order to keep the pressure steady.
The device, a self-regulating closed loop system, was first tested successfully in rats and then in monkeys. In 2019, the researchers were able to implant the device in a patient with a chronic spinal cord injury and a debilitating case of orthostatic hypotension. The patient, a 38-year-old male, has been able to stop taking blood pressure medication and no longer uses compression bandages.
Experts were impressed with the team’s ability to identify the specific neural circuits in the spinal cord that were needed to affect blood pressure.
“There is beautiful physiological and neurobiological work,” said Patrice Guyenet of the University of Virginia, who peer-reviewed the paper and wrote an accompanying perspective piece. “It’s a tour de force.”
If it proves safe and effective in further studies, the device could even provide hope for other symptoms. Field-Fote said that when used by patients with spinal cord injuries, similar devices already approved to treat pain have shown improvements in bladder function as secondary effects.
Phillips, who first came up with the idea for the device in 2016, is now working with his colleagues to plan clinical trials to further test safety and efficacy of the device, with the support of Defense Advanced Research Projects Agency and Onward Healthcare. They hope to have the therapy available to patients within the next five years, though there are significant research and regulatory milestones to meet before such a device could make its way to the market.
“When you know someone with an acute injury, you know that there are many things beyond walking function that are important to them that need to be addressed,” said Field-Fote. “And it’s very exciting to see a group addressing these other problems that don’t get as much attention, but can make a big difference to somebody’s life.”