Browsing by Subject "electrical stimulation"

Spinal cord injury (SCI) and other neurological diseases and disorders can cause urinary dysfunction that can cause serious health problems and reduce an individual's quality of life. Current methods for treating urinary dysfunction have major limitations or provide inadequate improvement in urinary symptoms. Pudendal nerve stimulation is a potential means of restoring control of bladder function in persons with neurological disease or spinal cord injury. Bladder contraction and relaxation can be evoked by pudendal afferent stimulation, and peripheral pudendal afferent branches may be ideal targets for a bladder control neural prosthesis. This dissertation investigates control of bladder function by selective activation of pudendal afferents.

This study investigated the ability to improve both urinary continence and micturition by both direct and minimally-invasive electrical stimulation of selected pudendal afferents in α-chloralose anesthetized male cats. Direct stimulation of the pudendal afferents in the dorsal nerve of the penis (DNP), percutaneous DNP stimulation, and intraurethral stimulation were used to investigate the bladder response to selective activation of pudendal afferents. Finite element modeling of the cat lower urinary tract was used to investigate the impact of intraurethral stimulation location and intraurethral electrode configuration on activation of pudendal afferents. Also, the impact of pharmacological and surgical block of sympathetic activity to the bladder on the bladder reflexes evoked by DNP stimulation was investigated to determine the role of the sympathetic bladder innervation on the mechanism of bladder activation by pudendal afferent stimulation.

The DNP is an ideal target for restoring urinary function because stimulation at low frequencies (5-10 Hz) improves urinary continence, while stimulation at high frequencies (33-40 Hz) improves urinary voiding. Intraurethral stimulation is a valid method for clinical investigation of the ability to evoke bladder inhibition and activation via selective activation of the DNP or cranial sensory branch (CSN) of the pudendal nerve. In the cat, intraurethral stimulation can activate the bladder via two distinct neural pathways, a supraspinal pathway reflex activated by the CSN and a spinal reflex activated by the DNP. Finite element modeling revealed the importance of urethral location for selective pudendal afferent activation by intraurethral stimulation. Finally, the sympathetic bladder pathway does not play a significant role in the mechanism mediating bladder activation by DNP stimulation. These findings imply that selective pudendal afferent stimulation is a promising approach for restoring control of bladder function to individuals with SCI or other neurological disorders.

Modulation of neural activity with electrical stimulation is a widespread therapy for treating neurological disorders and diseases. Two notable applications that have had striking clinical success are deep brain stimulation (DBS) for the treatment of movement disorders (e.g., Parkinson's disease) and spinal cord stimulation (SCS) for the treatment of chronic low back and limb pain. In these therapies, the battery life of the stimulators is much less than the required duration of treatment, requiring patients to undergo repeated battery replacement surgeries, which are costly and obligate them to incur repeatedly the risks associated with surgery. Further, deviations in lead position of 2-3 mm can preclude some or all potential clinical benefits, and in some cases, generate side-effects by stimulation of non-target regions. Therefore, despite the success of DBS and SCS, their efficiency and ability to activate target neural elements over non-target elements, termed selectivity, are inadequate and need improvement.

We combined computational models of volume conduction in the brain and spine with cable models of neurons to design novel electrode configurations for efficient and selective electrical stimulation of nervous tissue. We measured the efficiency and selectivity of prototype electrode designs in vitro and in vivo. Stimulation efficiency was increased by increasing electrode area and/or perimeter, but the effect of increasing perimeter was not as pronounced as increasing area. Cylindrical electrodes with aspect (height to diameter) ratios of > 5 were the most efficient for stimulating neural elements oriented perpendicular to the axis of the electrode, whereas electrodes with aspect ratios of < 2 were the most efficient for stimulating parallel neural elements.

Stimulation selectivity was increased by combining two or more electrodes in multipolar configurations. Asymmetric bipolar configurations were optimal for activating parallel axons over perpendicular axons; arrays of cathodes with short interelectrode spacing were optimal for activating perpendicular axons over parallel axons; anodes displaced from the center of the target region were optimal for selectively activating terminating axons over passing axons; and symmetric tripolar configurations were optimal for activating neural elements based on their proximity to the electrode. The performance of the efficient and selective designs was not be explained solely by differences in their electrical properties, suggesting that field-shaping effects from changing electrode geometry and polarity can be as large as or larger than the effects of decreasing electrode impedance.

Advancing our understanding of the features of electrode geometry that are important for increasing stimulation efficiency and selectivity facilitates the design of the next generation of stimulation electrodes for the brain and spinal cord. Increased stimulation efficiency will increase the battery life of IPGs, increase the recharge interval of rechargeable IPGs, and potentially reduce stimulator volume. Greater selectivity may improve the success rate of DBS and SCS by mitigating the sensitivity of clinical outcomes to malpositioning of the electrode.

This dissertation is about the first substantial restoration of human sense using a medical intervention. In particular, the development of the modern cochlear implant (CI) is described, with a focus on sound processors for CIs. As of October 2015, more than 460 thousand persons had each received a single CI on one side or bilateral CIs for both sides. More than 75 percent of users of the present-day devices use the telephone routinely, including conversations with previously unknown persons and with varying and unpredictable topics. That ability is a long trip indeed from severe or worse losses in hearing. The sound processors, in conjunction with multiple sites of highly-controlled electrical stimulation in the cochlea, made the trip possible.

Many methods and techniques were used in the described research, including but not limited to those of signal processing, electrical engineering, neuroscience, speech science, and hearing science. In addition, the results were the products of collaborative efforts, beginning in the late 1970s. For example, our teams at the Duke University Medical Center and the Research Triangle Institute worked closely with investigators at 27 other universities worldwide.

The most important outcome from the research was unprecedented levels of speech reception for users of CIs, which moved a previously experimental treatment into the mainstream of clinical practice.