Studies Suggest ‘Bladder Pacemaker’ for People With Spinal Cord Injury
DURHAM, N.C. -- Biomedical engineers at Duke University's Pratt School of Engineering have demonstrated for the first time that stimulating a specific nerve in the pelvis triggers the process that causes urine to begin flowing out from the bladder, refuting conventional thinking that "bladder emptying" requires signals from the brain.
Their research, carried out with animals, could lead to a "bladder pacemaker" to restore bladder control for the more than 200,000 Americans living with spinal cord injury (SCI) or disease-related spinal cord problems.
Neural engineer Warren Grill and biomedical engineering doctoral candidate Joseph Boggs found that applying small electrical currents to the pudendal nerve triggered coordinated contraction of the bladder and relaxation of the urethral sphincter, which controls the bladder's outlet. The electrical stimulation emptied 65 percent of the bladder's volume.
In contrast, the bladder overfills without such intervention, triggering spastic contractions that empty only about 32 percent of the volume. The urethral sphincter frequently closes, blocking the flow of urine and forcing the urine back up toward the kidneys. This backup causes the chronic urinary tract infections and kidney problems that typically plague people with SCI.
What's surprising and encouraging about the findings, said the researchers, is that electrically stimulating the pudendal nerve caused the urethral sphincter to function normally and to efficiently empty the bladder.
Boggs, Grill and biomedical engineers Brian Wenzel and Kenneth Gustafson at Case Western Reserve University in Ohio published the findings in the Journal of Neurophysiology. The paper is now available online and will be published later in 2005. The research was sponsored by the National Institutes of Health and the Whitaker Graduate Student Fellowship program.
The researchers used cats in their studies because cats, like humans, empty their bladders through coordinated bladder and urethral sphincter activity. NIH animal care and experimental procedures were followed and approved by the Institutional Animal Care and Use Committee of Case Western Reserve University, where the studies took place.
Until now, most bladder control research has focused on treating incontinence, a major cause of health problems such as urinary tract and kidney infections, and of skin degradation. Other research teams have reported that electrical pulses with low frequencies, about 2 to 20 cycles per second, help control incontinence by calming involuntary bladder contractions, while higher-frequency pulses do not help.
The new research demonstrates that the higher-frequency pulses fail to control incontinence because they trigger bladder contractions. The team found that frequencies in the range of 20 to 40 cycles per second work best for bladder emptying.
"It was a surprise that no one had figured this out yet. But now that we understand the whole picture, we can pursue an engineered solution to help people restore bladder control," Boggs said.
"With this new understanding of the function of the pudendal nerve and the beneficial application of both high- and low-frequency pulses in controlling bladder emptying and incontinence, it should be possible for us to create a 'bladder pacemaker' analogous to a heart pacemaker," said Grill, who previously (in 2004) published preliminary human research that supports his optimism in extrapolating from the new studies with cats. Those earlier studies showed that a similar reflex in bladder contraction exists in people with SCI.
In January 2005, the National Institutes of Health awarded Grill a 5-year, $1.8 million grant to develop a system to sense involuntary bladder contractions and trigger a calming low-frequency electrical signal. The project also seeks to enable patients to generate a high-frequency signal on demand so they can empty their bladders at will.
"More control over bladder function could significantly improve quality of life, such as by allowing people the simple freedom of going to the movies without worrying about an accident," Boggs said.
"Our objective is to complete clinical testing and be able to put bladder control implants in humans by the year 2010," said Grill, who plans to carry out human experiments at Duke to follow up the research with cats.
Today, people with SCI typically manage their bladders with catheters or an implanted device that empties the bladder by stimulating sacral nerves at the base of the spine. However, implanting this "Vocare device" requires doctors to cut sensory nerves and insert electrodes into the spine. Many patients are reluctant to do this because of concerns about losing bowel control or sexual function such as erection in men and lubrication in women.
"Our goal is to create a system that performs as well as existing technology, but that is less invasive to install and preserves as much of the person's remaining function as possible," Grill said.
He envisions a simple system with an electrode on the pudendal nerve attached to an electrical signal stimulator placed in the abdomen. The bladder pacemaker operation would be optimized by a doctor and then run by the patient using a wireless control device.
Grill is a founding partner in NDI Medical Company, which has exclusive license to the selective stimulation patent relevant to this research. NDI Medical is also the U.S. distributor of the Vocare device.