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Keywords:

  • magnetic stimulation;
  • overactive bladder;
  • pelvic floor

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. REFERENCES

OBJECTIVE

To evaluate the effect of magnetic stimulation of the pelvic floor (MSPF) on involuntary detrusor activity observed during natural filling, and on the overactive bladder symptom complex.

PATIENTS AND METHODS

Eighteen women with detrusor overactivity on conventional cystometry underwent ambulatory urodynamic monitoring over two filling cycles. Fluid intake was standardized, provocative manoeuvres applied at regular intervals and symptoms documented contemporaneously. During the second filling cycle MSPF was delivered whenever the detrusor pressure increased by> 5 cmH2O. The women were subsequently treated with MSPF for 6 weeks; their lower urinary tract symptoms were assessed before and after treatment.

RESULTS

Comparing the second (stimulated) cycle with the first (unstimulated) cycle, cystometric capacity was higher (373 vs 224 mL, P < 0.03). and involuntary detrusor activity of shorter duration (370 vs 427 s, P < 0.82) and lower amplitude (53 vs 63 cmH2O, P ≤ 0.05). All women tolerated the procedure comfortably, but nine found it too time-consuming and withdrew. In the nine women who completed treatment there was no consistent change in overactive bladder symptoms.

CONCLUSIONS

In this pilot study, MSPF during natural filling was associated with a decrease in the amplitude of involuntary detrusor contractions and a significant increase in cystometric capacity. However, MSPF had a variable effect on sensations of urgency, both acutely and after treatment, and currently there is no evidence to suggest that MSPF has an enduring effect on symptoms of the overactive bladder.


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. REFERENCES

Rapid magnetic stimulation can be used to deliver electrical energy to pelvic floor structures. This method may be more effective and more acceptable to patients than conventional electrical stimulation using intravaginal electrodes. Although the efficacy of intravaginal electrical stimulation has been established in research studies, its clinical application for treating detrusor overactivity has been limited by discomfort [1]. Reflex bladder inhibition by stimulating pudendal afferents is obtained at stimulation levels of two to three times the threshold intensity, and transvaginal electrical stimulation at such intensities is painful in unanaesthetized subjects. Relatively high currents have to be delivered via surface electrodes to achieve stimulation at depth because of volume-conductor effects. At these high currents pain receptors in the skin are also stimulated. Magnetic fields of the frequency used to cause neural stimulation penetrate all body tissues without attenuation, decreasing only as a function of distance [2].

Because current is induced in diffuse loops rather than passed directly through the skin, magnetic stimulation can activate proximal tissue, including pudendal afferents of the pelvic floor, at higher intensities and with less discomfort than electrical stimulation. There is some evidence that magnetic stimulation of the sacral nerve roots may suppress detrusor overactivity [3,4]. Craggs et al.[4] provoked detrusor contractions in individuals with idiopathic detrusor overactivity, by the rapid intravesical infusion of saline. Using a magnetic stimulator coil placed over the sacral nerve roots they were able to show a reduction in the duration and amplitude of provoked detrusor contractions. The optimal point of stimulation must be determined initially by eliciting specific motor responses, and this position must be carefully maintained throughout stimulation. This need for accurate positioning has limited the clinical application of sacral nerve root stimulation

Magnetic stimulation of the pelvic floor (MSPF) is more amenable to clinical application than is sacral nerve stimulation, as it is easily administered via a stimulating coil located in the seat of a chair. With instruction, patients can use perineal sensation to optimize their position over the coil, and stimulation may then continue without close supervision. Until recently such technology was cumbersome and stimulating coils were prone to overheating, as a consequence of which the duration of magnetic stimulation was restricted. Recent technological advances have provided equipment capable of delivering rapid MSPF for prolonged periods. Such technology was used by Yamanishi et al.[5], who reported an increase in cystometric capacity with MSPF during conventional cystometry with retrograde filling.

Thus the present study was designed to assess the acute effect of MSPF on spontaneous and provoked detrusor contractions, and symptoms of urgency and urge incontinence during natural-filling cystometry, and the symptomatic response to treatment with MSPF.

PATIENTS AND METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. REFERENCES

The study included 18 women with detrusor overactivity during conventional cystometry, negative urine microscopy and no evidence of other bladder pathology. Each patient had been previously treated with anticholinergic therapy and remained symptomatic. Any women who were still taking this therapy stopped medication for at least 2 weeks before investigation and during treatment. All women were offered prophylactic antibiotics at the start of the investigation to prevent UTI. The study was conducted with the informed consent of participating women and after peer review by the local ethics committee. Symptoms were documented at recruitment and after treatment using the Bristol Female LUTS questionnaire [6].

Ambulatory urodynamic monitoring (AUM) was undertaken with catheter-mounted microtip transducers (Gaeltec, Isle of Skye, UK) inserted into the bladder and rectum, and a solid-state recorder (UPS 2020, Medical Management Systems, MMS, the Netherlands). A portable computer was used to monitor the cystometric variables continuously throughout each fill/void cycle. Preliminary tests ex vivo showed that magnetic stimulation of the catheter-mounted transducers did not interfere with their normal functioning. The women received a 750-mL oral fluid load at the start of monitoring and further fluids at a volume equivalent to any voids. Throughout monitoring the women remained seated on a chair containing the magnetic stimulation coils, except when voiding. At regular intervals provocative manoeuvres, including listening to running water and cold-water hand-washing were performed. Women kept a contemporaneous diary of any symptoms experienced during monitoring. The residual volume of urine was estimated by ultrasonography at the beginning and end of each cycle. Pre-weighed pads were used to quantify any urinary leakage during each cycle.

At the end of each investigation, recorded data were downloaded to an personal computer and analysed in conjunction with the event diary, independently of the subject. Cystometric data were considered to be acceptable when the intravesical and abdominal pressure traces were ‘active’, showed good subtraction and were free from artefact and uninterpretable changes in baseline. Traces containing artefact that might mimic or mask true changes in detrusor pressure were excluded from analysis. The following variables were recorded for each cycle: the amplitude and duration of involuntary detrusor contractions during filling, the maximum bladder capacity, coincident symptoms and urinary leakage. The ‘area under the curve’ was calculated using the MMS software (Fig. 1).

image

Figure 1. Section from an AUM trace showing ‘area under the curve’ for detrusor pressure.

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Magnetic stimulation was delivered to the pelvic floor using a electromagnetic stimulator (Neocontrol®, Neotonus Inc., Marietta, GA, USA). A coil set in the seat of the chair provides rapid magnetic stimulation with a near-sinusoidal single-cycle pulse of magnetic field lasting 275 µs, delivered repetitively at 1–50 Hz. Figure 2 shows the spatial distribution of peak magnetic field measured above the seat surface.

image

Figure 2. The spatial distribution of peak magnetic field measured in a plane 2 mm above the Neotonus seat at 25% output.

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At the start of the second fill/void cycle immediately after the first void, a short trial period of magnetic stimulation was delivered to the pelvic floor. Women were instructed to position themselves on the seat with the perineum over the centre of the coil, and to identify the position in which they received the maximum amount of sensation between the vagina and the anus. Using increments of 10% of maximum output, the power was increased from 10% to the most comfortably tolerated, or 100%, whichever was lower. Having established the maximum tolerated intensity for each subject, this intensity was used for the remainder of the study. Magnetic stimulation was delivered at 10 Hz during the second fill cycle only, whenever the detrusor pressure increased from baseline by> 5 cmH2O. The periods during which the magnetic stimulator was active were automatically recorded on the data logger.

Women were subsequently treated by MSPF for two sessions per week for 6 weeks. Each session consisted of 10 min at 5 Hz, 5 min rest and 10 min at 50 Hz at the maximum tolerated power or 100% of output. Cystometric variables were compared for stimulated and unstimulated cycles using paired sample t-tests.

RESULTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. REFERENCES

Involuntary detrusor activity (IDA) was recorded during both cycles in eight of the 18 women and these women received MSPF during monitoring. One woman had IDA only in the first fill/void cycle and in five there was no IDA during monitoring. These women did not receive MSPF during monitoring. Four AUM investigations were uninterpretable because of transducer malfunction or artefact, and were excluded from analysis. Table 1 shows the characteristics of IDA and the paired sample t-tests comparing the two cycles in the eight women who received MPSF during monitoring.

Table 1.  Characteristics of involuntary detrusor activity and paired sample t-tests comparing stimulated and unstimulated cycles in the eight women in whom involuntary detrusor activity was detected in both cycles
VariableUnstimulatedStimulated * P
  • *

    paired sample t-tests;

  • † mean values.

Total duration of cycle, min  65  65 
Max. cystometric capacity, mL2243730.03
Max. rise in detrusor pressure, cmH2O  63  530.05
Total duration of IDA, s4273700.82
Area under curve, /min of fill (cmH2O s/min)196  790.17

Nine women completed the treatment course; five declined further treatment with MSPF and a further four withdrew after starting treatment. All nine stated that their main reason for withdrawing was the time involved in treatment. After treatment with MSPF the symptoms of urgency improved in eight of the nine women, whilst symptoms of frequency and nocturia improved in three and were unchanged in six. Urge incontinence improved in two women, worsened in one and was unchanged in six.

DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. REFERENCES

These findings on the effect of MSPF on IDA and overactive bladder symptoms during natural filling reflect those of Yamanishi et al.[5] using retrograde bladder filling, and show that cystometric variables improve with MSPF during natural filling. The artificial infusion of saline into the bladder during conventional cystometry may affect bladder activity [4,7]. Using natural instead of retrograde artificial filling ensures that any bladder activity during the study is representative of true detrusor function rather than the test conditions.

MSPF is thought to reduce or abolish detrusor overactivity, in the same way as does electrical stimulation. The ‘continence reflex’ by which pelvic floor muscle contraction results in reflex inhibition of the detrusor has been previously described. Lindstrom et al.[8] reported reflex bladder inhibition after intravaginal electrical stimulation in animal models, and identified the afferent pathway in the pudendal nerves. Detrusor inhibition with selective pudendal nerve stimulation was reported in patients with neurogenic detrusor overactivity [9]. Olney et al.[10] showed that the onset latency, amplitude, area and duration of responses during sensory and motor nerve conduction studies were similar whether elicited electrically or magnetically. It therefore seems reasonable to assume that MSPF acts on pudendal afferents in the same way as intravaginal electrical stimulation, resulting in detrusor inhibition via a spinal reflex arc. Bladder inhibition by intravaginal electrical stimulation is thought to depend on the frequency of stimulation, with the optimum effect at lower frequencies, but stimulation at frequencies of < 10 Hz is often associated with marked discomfort [1]. The most effective frequency for magnetic stimulation has yet to be clearly established. To date, studies evaluating MSPF have used higher frequencies designed to cause maximum pelvic floor contraction, sometimes using a range of frequencies to avoid the muscle fatigue caused by repeated stimulation at a constant frequency [5]. Thus we used 10 Hz for the initial assessment, and then a range of frequencies as described for the treatment sessions.

Although several studies suggested that magnetic stimulation is an effective treatment for urinary incontinence in general, few if any have addressed its effect on overactive bladder symptoms in particular [11,12]. In the present study the women who completed MSPF treatment reported no consistent change in overactive bladder symptoms. The acute improvement in urodynamic variables did not appear to be reflected in the symptoms experienced during stimulation or sustained after treatment. There is some evidence that cystometric capacity increases with repeated filling during static cystometry [13]. To our knowledge no similar work involving AUM has been published, but analysis of a cohort of 104 women undergoing AUM for a clinical trial in our centre showed that on average the second fill/void cycle was of lower capacity than the first, suggesting that the observed increase in cystometric capacity in the current study was not spurious and may indeed be attributable to the MSPF. The beneficial effect of intravaginal electrical stimulation and neuromodulation has been shown to have some persistent effect, suggesting that bladder reflexes have sufficient plasticity to allow remodelling. The amplitude and frequency of magnetic stimulation delivered in the present study may not have been optimal to drive this remodelling.

The present study design demanded that two entire fill/void cycles be interpretable to compare them accurately; consequently, the number of tests rejected for technical problems was unusually high (four of 18) [14]. More surprisingly, several women with detrusor overactivity confirmed on conventional urodynamics had no overactivity during prolonged periods of AUM, and had to be excluded. To ensure the two fill/void cycles were standardized, women had to remain seated throughout the study and this confinement and ‘laboratorization’ of subjects may account for the reduced incidence of detrusor overactivity in this study.

In conclusion, in this exploratory study, MSPF during natural bladder filling was associated with a decrease in the amplitude of involuntary detrusor contractions and a significant increase in cystometric capacity during prolonged cystometric monitoring. However, MSPF had a variable effect on overactive bladder symptoms, both acutely and after treatment, and at present there is no evidence to suggest that MSPF has an enduring effect on symptoms of the overactive bladder. Further work with more patients is required to evaluate whether there is any role for this method in treating detrusor overactivity.

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. REFERENCES
  • 1
    Fall M, Lindström S. Electrical stimulation. A physiologic approach to the treatment of urinary incontinence. Urol Clin North Am 1991; 18: 393407
  • 2
    Barker A. Magnetic stimulation of the human brain and peripheral nervous system: an introduction and the results of an initial clinical evaluation. Neurosurgery 1987; 20: 1009
  • 3
    Sheriff MK, Shah PJ, Fowler C, Mundy AR, Craggs MD. Neuromodulation of detrusor hyper-reflexia by functional magnetic stimulation of the sacral roots. Br J Urol 1996; 78: 3946
  • 4
    McFarlane JP, Foley SJ, De Winter P, Shah PJ, Craggs MD. Acute suppression of idiopathic detrusor instability with magnetic stimulation of the sacral nerve roots. Br J Urol 1997; 80: 73441
  • 5
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    Jackson S, Donovan J, Brookes S, Eckford S, Swithinbank L, Abrams P. The Bristol female lower urinary tract symptoms questionnaire. development and psychometric testing. Br J Urol 1996; 77: 80512
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    Radley SC, Rosario DJ, Chapple CR, Farkas AG. Conventional and ambulatory urodynamic findings in women with symptoms suggestive of bladder overactivity. J Urol 2001; 166: 22538
  • 8
    Lindström S, Fall M, Carlsson CA, Erlandson B. The neurophysiological basis of bladder inhibition in response to intravaginal electrical stimulation. J Urol 1983; 129: 40510
  • 9
    Vodusek D, Plevnik S, Vrtacnik P, Janez J. Detrusor inhibition on selective pudendal nerve stimulation in the perineum. Neurourol Urodynam 1988; 6: 38993
  • 10
    Olney RK, So YT, Goodin DS, Aminoff MJ. A comparison of magnetic and electrical stimulation of peripheral nerves. Muscle Nerve 1990; 13: 95763
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    Yamanishi T, Yasuda K, Sakakibara R, Hattori T, Ito H, Murakami S. Pelvic floor electrical stimulation in the treatment of stress incontinence: an investigational study and a placebo controlled double-blind trial. J Urol 1997; 158: 212731
  • 12
    Galloway NT, El-Galley RE, Sand PK, Appell RA, Russell HW, Carlan SJ. Extracorporeal magnetic innervation therapy for stress urinary incontinence. Urology 1999; 53: 110811
  • 13
    Brostrom S, Jennum P, Lose G. Short term reproducibility of cystometry and pressure/flow micturiton studies in healthy women. Int Urogynecol J Pelvic Floor Dysfunct 2001; 12: 63
  • 14
    Van Waalwijk van Doorn ES, Meier AH, Ambergen AW, Janknegt RA. Ambulatory urodynamics. extramural testing of the lower and upper urinary tract by holter monitoring of cystometrogram, uroflowmetry, and renal pelvic pressures. Urol Clin North Am 1996; 23: 34571
Abbreviations
MSPF

magnetic stimulation of the pelvic floor

AUM

ambulatory urodynamic monitoring

IDA

involuntary detrusor activity.