Evaluation of a suture electrode for direct bladder stimulation in a lower motor neuron lesioned animal model

Can we improve techniques and patients' selection for nerve stimulation suitable for lower urinary tract dysfunctions? ICI-RS 2023

AIMS

Lower urinary tract dysfunctions (LUTD) are very common and, importantly, affect patients' quality of life (QoL). LUTD can range from urinary retention to urgency incontinence and includes a variety of symptoms. Nerve stimulation (NS) is an accepted widespread treatment with documented success for LUTD and is used widely. The aim of this review is to report the results of the discussion about how to improve the outcomes of NS for LUTD treatment.

METHODS

During its 2023 meeting in Bristol, the International Consultation on Incontinence Research Society discussed a literature review, and there was an expert consensus discussion focused on the emerging awareness of NS suitable for LUTD.

RESULTS

The consensus discussed how to improve techniques and patients' selection in NS, and high-priority research questions were identified.

CONCLUSIONS

Technique improvement, device programming, and patient selection are the goals of the current approach to NS. The conditional nerve stimulation with minimally invasive wireless systems and tailored algorithms hold promise for improving NS for LUTD, particularly for patients with neurogenic bladder who represent the new extended population to be treated.

Wireless, Fully Implantable and Expandable Electronic System for Bidirectional Electrical Neuromodulation of the Urinary Bladder

Current standard clinical options for patients with detrusor underactivity (DUA) or underactive bladder─the inability to release urine naturally─include the use of medications, voiding techniques, and intermittent catheterization, for which the patient inserts a tube directly into the urethra to eliminate urine. Although those are life-saving techniques, there are still unfavorable side effects, including urinary tract infection (UTI), urethritis, irritation, and discomfort. Here, we report a wireless, fully implantable, and expandable electronic complex that enables elaborate management of abnormal bladder function via seamless integrations with the urinary bladder. Such electronics can not only record multiple physiological parameters simultaneously but also provide direct electrical stimulation based on a feedback control system. Uniform distribution of multiple stimulation electrodes via mesh-type geometry realizes low-impedance characteristics, which improves voiding/urination efficiency at the desired times. In vivo evaluations using live, free-moving animal models demonstrate system-level functionality.

A New Electrode Design for Direct Bladder Wall Stimulation: A Pilot Minipig Study with Chronic Testing

(1) Aims: To test a newly designed helical-wire hook electrode implanted in the bladder wall to induce contraction and promote voiding. (2) Methods: In three minipigs with a created lesion of the sacral spinal cord, four electrodes were implanted in the bladder wall, ventral to the trigone. Stimulation tests were conducted initially in conscious pigs, and later after general anesthesia. (3) Results: Electrical stimulation in the conscious animals on postoperative days 4 and 7 at 40 Hz was limited to 10 mA, because of abdominal, leg, and anal contractions with animal discomfort; bladder contractions were not induced. Electrical stimulation on postoperative days 9 and 28 at 60 mA under anesthesia induced sustained vesical wall contractions with bladder pressure variations, but without voiding. Simultaneous abdominal contractions occurred, with strong leg and anal contractions. Subsequent stimulation with a single set of electrodes or at 20 Hz induced less vesical pressure response. At autopsy, the electrodes had not migrated, and extraction forces were high, at 7.9 ± 0.9 Newtons (n = 12). (4) Conclusions: Our 28-day study has confirmed the utility of the new electrode design, preventing migration from the bladder wall and making it suitable for long-term electrode implants.

Ultracompliant Carbon Nanotube Direct Bladder Device

The bladder, stomach, intestines, heart, and lungs all move dynamically to achieve their purpose. A long-term implantable device that can attach onto an organ, sense its movement, and deliver current to modify the organ function would be useful in many therapeutic applications. The bladder, for example, can suffer from incomplete contractions that result in urinary retention with patients requiring catheterization. Those affected may benefit from a combination of a strain sensor and electrical stimulator to better control bladder emptying. The materials and design of such a device made from thin layer carbon nanotube (CNT) and Ecoflex 00-50 are described and demonstrate its function with in vivo feline bladders. During bench-top characterization, the resistive and capacitive sensors exhibit stability throughout 5000 stretching cycles under physiology conditions. In vivo measurements with piezoresistive devices show a high correlation between sensor resistance and volume. Stimulation driven from platinum-silicone composite electrodes successfully induce bladder contraction. A method for reliable connection and packaging of medical grade wire to the CNT device is also presented. This work is an important step toward the translation of low-durometer elastomers, stretchable CNT percolation, and platinum-silicone composite, which are ideal for large-strain bioelectric applications to sense or modulate dynamic organ states.

Closed-loop stimulation of the pelvic nerve for optimal micturition

OBJECTIVE

Neural stimulation to restore bladder function has traditionally relied on open-loop approaches that used pre-set parameters, which do not adapt to suboptimal outcomes. The goal of this study was to examine the effectiveness of a novel closed-loop stimulation paradigm for improving micturition or bladder voiding.

APPROACH

We compared the voiding efficiency obtained with this closed-loop framework against open-loop stimulation paradigms in anesthetized rats. The bladder pressures that preceded voiding, and the minimum current amplitudes for stimulating the pelvic nerves to evoke bladder contractions, were first calibrated for each animal. An automated closed-loop system was used to initiate voiding upon bladder fullness, adapt the stimulation current by using real-time bladder pressure changes to classify voiding outcomes, and halt stimulation when the bladder had been emptied or when the safe stimulation limit was reached.

MAIN RESULTS

In vivo testing demonstrated that the closed-loop system achieved high voiding efficiency or VE (75.7%  ±  3.07%, mean  ±  standard error of the mean) and outperformed open-loop systems with either conserved number of stimulation epochs (63.2%  ±  4.90% VE) or conserved charge injected (32.0%  ±  1.70% VE). Post-hoc analyses suggest that the classification algorithm can be further improved with data from additional closed-loop experiments.

SIGNIFICANCE

This novel approach may be applied to an implantable device for treating underactive bladder (<60% VE), especially in cases where under- or over-stimulation of the nerve is a concern.

A Mini-Invasive Long-Term Bladder Urine Pressure Measurement ASIC and System

A mini-invasive system for long-term bladder urine pressure measurement system is presented. Not only is the design cost reduced, but also the reliability is enhanced by using a 1-atm canceling sensing instrumentation amplifier (IA). Because the urine pressure inside the bladder does not vary drastically, both the sleeping and working modes are required in order to save the battery power for long-term observation. The IA amplifies the signal sensed by the pressure sensor, which is then fed into the following analog-to-digital converter. Owing to the intrinsic 1-atm pressure existing inside the bladder, the IA must be able to cancel such a pressure from the signal picked up by the pressure sensor to keep the required linearity and the resolution for pressure measurement of the bladder urine. The pressure range of the proposed system is found out to be 14.7~19.7 Psi, which covers the range of all of the known unusual bladder syndromes or complications.

Control of urinary bladder function with devices: successes and failures

The management of urinary tract dysfunction is crucial for the health and well-being of people with spinal cord injury. Devices, specifically catheters, play an important role in the daily regime of bladder management for most people with spinal cord injury. However, the high incidence of complications associated with the use of catheters, and the fact that the spinal segments involved in lower urinary tract control remain intact in most cord-injured people, continue to motivate research into devices that could harness the nervous system to provide greater control over lower urinary tract function. Mechanical devices discussed in this review include catheters, artificial urethral sphincters, urethral stents and intraurethral pumps. Additionally, many attempts to restore control of the lower urinary tract with electrical stimulation have been made. Stimulation sites have included: inside the bladder, bladder wall, thigh, pelvic floor, dorsal penile nerve, pelvic nerve, tibial nerve, sacral roots, sacral nerves and spinal cord. Catheters and sacral root stimulators are two techniques whose efficacy is well established. Some approaches have proven less successful and others are still in the development stage. Modifications to sacral root stimulation including posterior root stimulation, anodal blockade and high-frequency blockade as well as new techniques including intraspinal microstimulation, urethral afferent stimulation and injectable microstimulators are also discussed. No single device has yet restored the control and function of the lower urinary tract to the pre-injury state, but new techniques are bringing this possibility closer to reality.

Artificial autonomic reflexes: using functional electrical stimulation to mimic bladder reflexes after injury or disease

Autonomic reflexes controlling bladder storage (continence) and emptying (micturition) involve spinal and supraspinal nerve pathways, with complex mechanisms coordinating smooth muscle activity of the lower urinary tract with voluntary muscle activity of the external urethral sphincter (EUS). These reflexes can be severely disrupted by various diseases and by neurotrauma, particularly spinal cord injury (SCI). Functional electrical stimulation (FES) refers to a group of techniques that involve application of low levels of electrical current to artificially induce or modify nerve activation or muscle contraction, in order to restore function, improve health or rectify physiological dysfunction. Various types of FES have been developed specifically for improving bladder function and while successful for many urological patients, still require substantial refinement for use after spinal cord injury. Improved knowledge of the neural circuitry and physiology of human bladder reflexes, and the mechanisms by which various types of FES alter spinal outflow, is urgently required. Following spinal cord injury, physical and chemical changes occur within peripheral, spinal and supraspinal components of bladder reflex circuitry. Better understanding of this plasticity may determine the most suitable methods of FES at particular times after injury, or may lead to new FES approaches that exploit this remodeling or perhaps even influence the plasticity. Advances in studies of the neuroanatomy, neurophysiology and plasticity of lumbosacral nerve circuits will provide many further opportunities to improve FES approaches, and will provide "artificial autonomic reflexes" that much more closely resemble the original, healthy neuronal regulatory mechanisms.

Evaluation of a suture electrode for direct bladder stimulation in a lower motor neuron lesioned animal model

The purpose of this study was to evaluate a "suture" type electrode for direct bladder stimulation in an animal model of a lower motor neuron lesion. During an initial surgery, five male cats were instrumented under anesthesia using multistranded, 316 LVM, stainless-steel, wire electrodes implanted on the bladder wall serosa above the trigone area. Electrodes were constructed with a needle attached to the end that was removed after suturing the electrode in place. Additional instrumentation included urinary bladder catheters (tubes) for pressure recording and filling, and hook type electrodes for leg and pelvic floor electromyography recording. Chronic bladder filling and stimulation studies were conducted in tethered animals three to four weeks following surgery. To test these electrodes in a spinal cord injury model, a lower motor neuron lesion was performed including the sacral cord and complete nerve roots at L6 and below. These animals were evaluated during weeks 3 and 10 after injury. Direct bladder stimulation induced active contractions and voiding both before and after spinal cord injury. Effective stimulation parameters consisted of 40 pulses per s, 300 micros to 1 ms pulse duration, a stimulation period from 3 to 4 s, and a stimulation current from 10 to 40 mA. Fluoroscopy revealed an open membranous urethra during stimulation and following stimulation. A small diameter penile urethra was observed to limit flow. Postmortem evaluation of the suture electrode revealed no abnormalities such as corrosion, migration into the bladder lumen or displacement. These findings indicate that suture electrodes are suitable and effective for short-term implantation in the lower motor neuron animal model.