X ray image showing spinal column with electrode array and implanted stimulation device

On March 19, the University of Louisville announced the results of a study showing the normalization of blood pressure with epidural stimulation in people with spinal cord injury.

The study follows on previous research at Kentucky Spinal Cord Injury Research Center in collaboration with V. Reggie Edgerton at UCLA, and the Mayo Clinic, which has shown that epidural stimulation, when combined with activity-based training, can produce functional recovery of voluntary movement below the level of injury, along with improved bladder, bowel and sexual function. Much interest has been focused on the motor-recovery aspect of epi-stim, but for those with spinal cord injuries, alleviation of secondary symptoms could be just as important for daily living.

According to Stephanie Putnam, one of the research participants, “[Low blood pressure] prevented me from participating in activities, from talking on the phone, from sitting at a table and eating food. I had trouble breathing, trouble swallowing, trouble carrying on a conversation. I was passing out periodically — six or more times a day. Then I would have to tilt back in the chair for two hours.”

This blood pressure specific study, which was led by Dr. Susan Harkema in conjunction with the KSCIRC, involved four participants with chronic motor-complete cervical-level spinal cord injury who experienced persistent low resting blood pressure. As with previous epidural stimulation studies, researchers implanted an epidural stimulation device made by Medtronics and FDA approved for pain (with off-label approval for functional rehabilitation purposes) and connected it to an electrode array positioned on the dorsal epidural surface of the spine.

Doctors then adjusted the device configuration — pulse frequency, voltage, and electrode activation — for each subject to target cardiovascular response and raise resting blood pressure. Once optimal configurations were determined, all four participants were able to maintain an elevated resting blood pressure while the stimulator was turned on. Blood pressure dropped back to baseline when the device was turned off.

The study noted that, “Individuals reported physical changes during these sessions including: 1. a feeling of alertness or heightened awareness; 2. increased ability to project their voice and carry on conversations; 3. increased capacity to breathe and cough; and 4. overall improved sense of well-being.”

Different configurations are required to produce different functional outcomes — that is, activating motor functions require different device settings than those needed to raise blood pressure — and Harkema says that right now, the research is somewhat limited by the use of an epidural stimulation device designed for pain alleviation.

“We don’t fully know that answer … can you do more than one thing at once?” she says. “The technology is going to have to change. You would have to have stimulators that are able to deliver more than one configuration at a time.”

Another important and unresolved question is whether the epidural stimulation can retrain the spinal cord and nervous system to eventually maintain functional improvement even with the stimulator turned off.

Harkema and the team at the KSIRC plan to pursue these questions and continue to push the boundaries of functional recovery in spinal cord injury with a much larger epidural stimulation study involving 36 participants. While no exact timeline is set, the team hopes to begin implanting the devices in participants this summer.

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