Electrical Stimulation Could Improve Bladder Function in People with Spinal Cord Injury

Scientists using an advanced spinal stimulation technology enabled spinal cord- injured rats to empty their bladders more fully and in a timelier manner, according to research published this month in the journal PLos ONE. The promising results achieved in rats represent a significant step toward deployment of this novel approach in people with paraplegia, who often experience loss of bladder control, the researchers said.

The current study was prompted by earlier research in which the scientists’ electrical stimulation technology enabled four people with paraplegia to voluntarily stand for short periods of time and flex their toes, ankles and knees. In that study, V. Reggie Edgerton, Ph.D., at the University of California at Los Angeles and colleagues from the University of Louisville found improvement in the study subjects’ other impairments, including blood pressure control, body temperature regulation, bladder control and sexual function.

In the current study, Dr. Edgerton and his colleagues worked to identify specific stimulation protocols that allowed the rats to control bladder function – with the aim of eventually making this technology available in humans. This study was funded in part by the National Institute of Biomedical Imaging and Bioengineering, the National Institute of Neurological Disorders and Stroke, and the Christopher and Dana Reeve Foundation.

“This latest advancement provides further support for the value of electrical stimulation in communicating with the nervous system,” said Edelle Field-Fote, PT, Ph.D., director of spinal cord injury research at Shepherd Center in Atlanta. “Nerves ‘talk’ to each other through electrical signals, so electrical stimulation is a tool we can use to talk to nerves, as well.

“The neural circuits underlying control of bladder function reside in the lower end of the spinal cord and are very near the circuits that contribute to walking function,” she explained. “For this reason, it is possible that stimulation systems that are intended to promote walking may also promote improved bladder voiding, making both these areas of research important for further study."

Dr. Field-Fote noted that the electrical stimulation technology Dr. Edgerton and his colleagues are developing may also benefit people with quadriplegia.

In both the rat and human studies, researchers implanted an electrical epidural stimulator into the spine, allowing researchers to regulate the electrical stimulation. The amount of stimulation, known as electrical-enabling motor control (eEmc), can thus be modulated to determine the optimal level and duration to achieve the desired outcome, such as voluntary control of leg movement or bladder control. In addition, in humans who have sustained a spinal cord injury (SCI) and in rats with experimental spinal transections, a harness is used to suspend the participant, which enables him to voluntarily attempt a stepping motion on a treadmill while the implanted electrical stimulator is turned on. The harness setup allows subjects to “train,” or learn, to move their legs in conjunction with the electric stimulation of the spine. The combination of motor training and electrical stimulation has proven effective in restoring some function to limbs and organs previously thought to be permanently immobilized by the SCI.

In the current study – specifically aimed to determine whether eEmc might be used to regain control of bladder function – the UCLA group studied 10 rats with SCI that were trained daily for six weeks with eEmc stimulation of the spinal cord, and five rats that were untrained. The trained rats were induced to empty their bladders while stepping on a treadmill and receiving eEmc stimulation. The untrained rats had minimal to no ability to empty their bladders upon eEmc stimulation. This finding suggests the bladder response was enhanced by the additional sensory input to the spinal circuitry generated by treadmill training, researchers said.In a second test, trained rats with SCI were suspended in a harness, which allows the lower limbs to touch the ground. Saline solution was infused into the bladders of the rats using a catheter, and different levels of eEmc were applied to determine the amount of stimulation that optimized spontaneous emptying of the bladder. The most effective voiding was observed using a relatively low level of stimulation, with 90 to 95 percent of the volume of saline voided within 90 seconds.

The work succeeded in identifying specific spinal cord stimulation conditions that cause the bladder to empty within seconds. The results pave the way for potentially developing this technology for use in people with SCI to regain substantial control of bladder function, which is one of the highest priority health concerns of the approximately 1.3 million Americans with SCI, researchers said.

“We were surprised by how rapidly and completely stimulation induced voiding” Dr. Edgerton said. "There may be a way that when people have bladder problems, you can turn the stimulator on and they can release urine at will. This strategy may not completely restore this part of their lives to normal, but we are hopeful it could have a major impact in improving the quality of life and longevity of human patients."“It is gratifying to see the painstaking development of this breakthrough technology begin to show the potential to greatly improve the lives of paraplegics,” said Grace Peng, Ph.D., program director for rehabilitation engineering at the National Institute of Biomedical Imaging and Bioengineering (NIBIB). “This study of bladder control in the rat model lays the groundwork for translation to human SCI patients, with the potential to address a major daily challenge faced by these individuals.”