The assessment of a novel electrical stimulation waveform recently introduced for the treatment of overactive bladder

Feasibility of using a novel non-invasive ambulatory tibial nerve stimulation device for the home-based treatment of overactive bladder symptoms

Background

To evaluate safety, acceptability and pilot efficacy of transcutaneous low-frequency tibial nerve stimulation (TNS) using a novel device as home-based neuromodulation.

Methods

In this single-centre pilot study, 48 patients with overactive bladder (OAB) (24 with neurogenic and 24 with idiopathic OAB) were randomized to use a self-applicating ambulatory skin-adhering device stimulating transcutaneously the tibial nerve at 1 Hz for 30 minutes, either once daily or once weekly, for 12 weeks. Changes in OAB symptoms and QoL were measured at baseline, weeks 4, 8, and 12 using validated scoring instruments (ICIQ-OAB and ICIQ-LUTSqol), 3-day bladder diary and a Global Response Assessment (GRA) at week 12.

Results

Thirty-four patients completed the study (idiopathic n=15, neurogenic n=19). No significant adverse effects were noted. Patients found the device acceptable. Eighteen patients (53%) reported a moderate or marked improvement in symptoms from the GRA. Between baseline and week-12, ICIQ-OAB part A sub-scores improved from mean (SD) 9.3 (2.5) to 7.5 (3.1), and from 9.1 (1.9) to 5.9 (1.7) in the daily and the weekly arms, respectively. ICIQ-LUTSqol part A sub-scores improved from mean (SD) 51 (12.8) to 44.2 (13.1) and 44.9 (9.0) to 35.9 (8.8) in the daily and the weekly arms, respectively. Bladder diary mean 24-hour frequency episodes improved from 11.5 to 8.8 at week 12 for both arms.

Conclusions

This novel ambulatory transcutaneous TNS (TTNS) device is safe and acceptable for use in patients reporting OAB symptoms as a form of home-based neuromodulation. A larger study however is required to confirm clinical efficacy.

Nerve excitation using an amplitude-modulated signal with kilohertz-frequency carrier and non-zero offset

BACKGROUND

Incorporating kilohertz-frequency signals in transcutaneous electrical stimulation has been proposed as a means to overcome the impedance of the skin, thereby reaching deeper nerves. In particular, a transdermal amplitude modulated signal (TAMS), composed of a 210 kHz non-zero offset carrier modulated by rectangular pulses, was introduced recently for the treatment of overactive bladder. However, the contribution of the components of TAMS to nerve fiber activation has not been quantified.

METHODS

We conducted in vivo experiments and applied direct stimulation to the sciatic nerve of cats and rats. We measured electromyogram and compound action potential activity evoked by pulses, TAMS and modified versions of TAMS in which we varied the size of the carrier.

RESULTS

Nerve fiber activation using TAMS showed no difference with respect to activation with conventional pulse for carrier frequencies of 20 kHz and higher, regardless the relative amplitude of the carrier. For frequencies lower than 20 kHz, the offset needed to generate half of the maximal evoked response decreased significantly with respect to the pulse. Results of simulations in a computational model of nerve fiber stimulation using the same stimulation waveforms closely matched our experimental measurements.

CONCLUSION

Taken together, these results suggest that a TAMS with carrier frequencies >20 kHz does not offer any advantage over conventional pulses, even with larger amplitudes of the carrier, and this has implications for design of waveforms for efficient and effective transcutaneous stimulation.

Non-invasive transcutaneous electrical stimulation in the treatment of overactive bladder

We reviewed the literature on transcutaneous electrical nerve stimulation (TENS) used as a therapy for overactive bladder (OAB) symptoms, with a particular focus on: stimulation site, stimuli parameters, neural structures thought to be targeted, and the clinical and urodynamic outcomes achieved. The majority of studies used sacral or tibial nerve stimulation. The literature suggests that, whilst TENS therapy may have neuromodulation effects, patient are unlikely to benefit to a significant extent from a single application of TENS and indeed clear benefits from acute studies have not been reported. In long-term studies there were differences in the descriptions of stimulation intensity, strategy of the therapy, and positioning of the electrodes, as well as in the various symptoms and pathology of the patients. Additionally, most studies were uncontrolled and hence did not evaluate the placebo effect. Little is known about the underlying mechanism by which these therapies work and therefore exactly which structures need to be stimulated, and with what parameters. There is promising evidence for the efficacy of a transcutaneous stimulation approach, but adequate standardisation of stimulation criteria and outcome measures will be necessary to define the best way to administer this therapy and document its efficacy.

Volume conductor model of transcutaneous electrical stimulation with kilohertz signals

OBJECTIVE

Incorporating high-frequency components in transcutaneous electrical stimulation (TES) waveforms may make it possible to stimulate deeper nerve fibers since the impedance of tissue declines with increasing frequency. However, the mechanisms of high-frequency TES remain largely unexplored. We investigated the properties of TES with frequencies beyond those typically used in neural stimulation.

APPROACH

We implemented a multilayer volume conductor model including dispersion and capacitive effects, coupled to a cable model of a nerve fiber. We simulated voltage- and current-controlled transcutaneous stimulation, and quantified the effects of frequency on the distribution of potentials and fiber excitation. We also quantified the effects of a novel transdermal amplitude modulated signal (TAMS) consisting of a non-zero offset sinusoidal carrier modulated by a square-pulse train.

MAIN RESULTS

The model revealed that high-frequency signals generated larger potentials at depth than did low frequencies, but this did not translate into lower stimulation thresholds. Both TAMS and conventional rectangular pulses activated more superficial fibers in addition to the deeper, target fibers, and at no frequency did we observe an inversion of the strength-distance relationship. Current regulated stimulation was more strongly influenced by fiber depth, whereas voltage regulated stimulation was more strongly influenced by skin thickness. Finally, our model reproduced the threshold-frequency relationship of experimentally measured motor thresholds.

SIGNIFICANCE

The model may be used for prediction of motor thresholds in TES, and contributes to the understanding of high-frequency TES.

Maintenance of the therapeutic effect of two high-dosage antimuscarinics in the management of overactive bladder in elderly women

PURPOSE

To improve the long-term efficiency of the pharmacologic management of overactive bladder (OAB) in elderly women.

METHODS

The study comprised 229 women (mean age, 66.3 years; range, 65-77 years) with urodynamically and clinically confirmed OAB. All patients received the most effective treatment regimen based on the data obtained in the initial part of the study (trospium 60 mg/day + solifenacin 40 mg/day, for 6 weeks), and positive results similar to those in the first phase were obtained. They were then divided into four groups, based on the maintenance therapy: group A (59 women), trospium (60 mg/day) + solifenacin (40 mg/day) for 1 month; group B (51 women), electrical stimulation of the detrusor muscle for 1 month; group C (63 women), laser puncture for 1 month; group D (56 women), placebo. Maintenance therapy was administered 2.5 months after completion of primary treatment. The patients' condition was monitored through the OAB questionnaire for 1 year and by urodynamic examination at months 6 and 7 from the start of the study.

RESULTS

In group A, the clinical and urodynamic results achieved after the initial + main treatment phase (two high-dosage antimuscarinics of different generations, trospium and solifenacin, for a total of 2.5 months) were maintained for at least 7 months. Electrical stimulation of the urinary bladder as a method of maintenance therapy proved to be less effective. In groups C and D, deterioration in results was observed at 6-8 months, which led us to conclude that laser puncture was an inefficient method of maintenance therapy in elderly women with OAB.

CONCLUSIONS

Maintenance treatment of OAB in elderly women with a combination of high-dosage antimuscarinics is an effective method for reducing the risk of recurrence of the disease.