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Evaluation of Neuromuscular Electrical Stimulation in the Treatment of Genuine Stress Incontinence

Stephanie Knight Jo Laycock Dianne Naylor

Key Words Genuine stress incontinence, pelvic floor exercises, biofeedback, neuromuscular electrical stimulation, combination therapy

Summary Objectives: The purpose of this clinical trial was to evaluate the effectiveness of acute maximal clinic-based and chronic low- intensity home-based neuromuscular electrical stimulation in the treatment of genuine stress incontinence in women. For the purpose of this article these will be referred to as clinic and home treatments. As these treatments are often applied in combination with pelvic floor exercises and biofeedback, the two types of electrotherapy were evaluated within a combination therapy programme.

Study design: A prospective randomised controlled clinical trial was conducted, with 70 women aged 24-68, who had urodynamically proven genuine stress incontinence, referred for treatment in the department of urotherapy. The control group received a six-month treatment programme of pelvic floor exercises and biofeedback. The two treatment groups received, in addition, either home or clinic vaginal electrical stimulation. The primary outcome measures were the amount of urine loss determined by pad-testing, and the patients' subjective appraisal of their condition.

Results: A total of 57 women completed the trial and these sets of data were used for analysis to evaluate the effect of electrotherapy on subjects who received that treatment. Results were also evaluated on an intent-to-treat basis; 61% were subjectively greatly improved or cured, and 64% had a reduction in urine loss of 75% or more at pad-testing. There were no statistically significant differences in outcome measures between the three groups. However, the greatest percentage of subjects greatly improved or cured subjectively (80%) and by pad-test (8O%), were in the maximal stimulation group (n = 20). Subjects who received home stimulation had a lower success rate than either the clinic treatment or the control group.

Conclusions: Pelvic floor exercises and biofeedback alone are an effective treatment for genuine stress incontinence. Women with a long history of symptoms or previous ineffective incontinence surgery, may benefit from the addition of maximal vaginal stimulation. The addition of low intensity stimulation to a pelvic floor exercise programme appeared to have a detrimental influence on the women's progress.

Introduction Urinary incontinence is a widespread and debilitating problem, possibly affecting one quarter of all women. The most common form of incontinence is stress incontinence. Genuine stress incontinence (GSI), as defined by the International Continence Society (Abrams et aZ, 1990), can only be diagnosed by subtracted cystoinetry, to establish urine loss accompanying increased abdominal pressure, in the absence of any detrusor contraction.

Physiotherapists are considered to be experts in the rehabilitation of muscles in a wide variety of conditions. The pelvic floor muscles have not escaped attention as they may be atrophied due to a variety of causes, the most common factor being vaginal delivery a t childbirth (Thomas e t al , 1980). These muscles have been shown to be involved in the maintenance of continence in situations of increased intra-abdominal pressure (Deindl et al , 1991). Therefore weakened pelvic floor muscles may be assumed to predispose women t o an increased risk of developing GSI. It can be hypothesised that strengthening these muscles and developing an increased awareness of their activity may result in an improvement in continence.

Pelvic Floor Exercises and Biofeedback Pelvic floor exercises were described and advoc- ated as a cure for stress incontinence in the 1940s by an American gynaecologist (Kegel, 1948, 1951, 1956). Kegel (1956) reported a cure rate of 86% in women with stress incontinence. More recent studies have confirmed that diligently performed pelvic floor exercises lead to a reduction in incontinence. Lagro-Jansenn et a2 (1991) eonducted a controlled study, allocating 66 women with genuine stress incontinence into treatment and control groups. Following a three- month pelvic floor exercise programme 85% of the treatment group demonstrated subjective and objective improvement. None of the control subjects improved. However, the control group then went on to perform the same exercise regime, and 90% improved subjectively and objectively. An increase in pelvic floor strength and endurance, with a concurrent reduction in

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urine loss, has been demonstrated in a study by Ferguson et al(1990). Biofeedback is thought to enhance the effect of exercise, by making the subject more aware of pelvic floor muscle activity and encouraging greater muscular effort (Knight and Laycock, 1994). Burgio et al (19861, in a controlled trial of 27 women with GSI, demonstrated that after a four-week pelvic floor training programme the group receiving additional visual and auditory biofeedback reported a 79% improvement in their incontinence, significantly greater (p < 0.05) than their counterparts in the group receiving oral feedback during digital palpation (51% improvement). Pelvic floor exercises, with or without biofeedback, are often used in combination with some form of electrotherapy for the pelvic floor muscles. Two basic types of electrotherapy are described: maximal and low-intensity neuromuscular electrical stimulation.

Low-intensity Electrical Stimulation This type of stimulation is applied for several hours a day at low frequency and low current intensity. Stimulation is continued for several months (reported regimes range from 3-81 months) to allow for complete conversion of muscle fibre types. Skeletal muscle is composed of a mixture of muscle fibre types, type I (slow twitch) and type I1 (fast twitch) fibres, with a range of intermediate fibre types, the proportion varying in different muscles (Guyton, 1986). Pelvic floor muscle consists of a mixture of type I and type I1 fibres. In asymptomatic women the proportion of type I1 fibres has been found to be 33% (Gilpin et al, 1989). A high proportion of slow twitch fibres is necessary for continuous postural activity and fast twitch fibres are required for phasic activity in response to increases in intra-abdominal pressure. Fibre type composition demonstrates ‘plasticity’, and can be altered by imposing a different firing frequency on the motor units, either by activity or electrical stimulation. Low- intensity stimulation of muscles consisting of predominantly fast twitch (type 11) fibres at low frequencies (10 Hz) leads to conversion of fast to slow twitch (type I) fibres (Salmons and Henriksonn, 1981). Conversion of fast twitch to slow twitch fibres results in a muscle which is less susceptible to fatigue, but the reduction in fibre diameter may lead to a reduction in power. Alteration in the muscle’s contractile properties may require up to three months’ continuous stimulation (Salmons and Vrbova, 1969). Most devices used to supply low-intensity stimulation to the pelvic floor muscles produce

low frequency (10 Hz) currents. There is les! evidence for conversion of slow to fast twitcl fibres by electrical stimulation, and the inclusior of high frequency bursts of stimulation among lox frequency trains may be a rather simplistic, non. physiological approach (Kidd et al, 1989). Indeed some authors have suggested that low-intensity stimulation at any frequency will cause total conversion to slow twitch fibres, and may even lead to destruction of fast twitch fibres (Pette et al, 1975). In women with stress incontinence, it would be undesirable to compromise fast twitch fibres as their phasic activity helps to maintain continence during increases in intra-abdominal pressure.

Maximal Electrical Stimulation Electrical stimulation without instruction in pelvic floor exercise has proved effective in reducing incontinence (Laycock and Jerwood, 1993; Sand et al , 1995). Maximal vaginal stimulation is applied a t the highest tolerable current intensity for short periods (20 or 30 minutes). Different regimes have been described, ranging from 20-minute applications daily for four weeks (Plevnik et al, 1986), to twice-daily applications for 12 weeks (Sand et al, 19951, using home stimulation devices. When used in the treatment of GSI i t is desirable to produce a tetanic muscle contraction. A frequency of 30 Hz produces a tetanic contraction with minimal risk of undue muscle fatigue (Benton et nl, 1981), although frequencies of 20 Hz and 50 Hz have been successfully employed. The current must be delivered in trains of pulses, known as the duty cycle, in which the ‘off period must be equal to or greater than the ‘on’ period, to prevent fatigue of muscle fibres (Benton et al, 1981). In addition a pulse width of 200 microseconds produces excitation of muscle fibres at relatively low current intensity. This is more comfortable than shorter pulse widths, which may require current intensity high enough to be perceived as painful before a tetanic muscle contraction is produced.

The physiological basis of the success of this treatment is unknown but several theories have been proposed. The first hypothesis is that of muscle strengthening, with the assumption that the addition of electrical stimulation to an exercise programme will enhance muscle strength gains (Currier and Mann, 1983). Another theory is that of reversal of the recruitment order. The natural recruitment order begins with low firing frequency, type I, slow twitch muscle fibres, with type 11, fast twitch motor units being recruited later (Guyton, 1986). In electrically stimulated muscle recruitment is reversed, with type I1 fibres being recruited first (Sinacore et al, 1990). Targeting of the fast twitch fibres may enhance

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reflex phasic pelvic floor activity during increases in abdominal pressure (Vereecken et al , 1989).

Few clinical trials have been conducted to invest- igate the efficacy of electrical Stimulation in the treatment of GSI. Fall et al (1986) reported a 62% improvement or cure in women with mixed incontinence (n = 40), using low intensity stimulation (12 Hz) for at least three months. Sand et a1 (1995) conducted a randomised, double- blind, placebo-controlled trial of maximal pelvic floor stimulation in 52 women with GSI. The 35 patients who received maximal vaginal stimulation (50 Hz and 12.5 Hz simultaneously) demonstrated significant improvement in pelvic floor muscle strength and reduction in urine loss after 15 weeks. The control group using a sham device, issuing minimal current intensity, showed no such improvements. Neither of these studies included pelvic floor exercises in the treatment programme.

Aims of the Study The long-term success of pelvic floor exercises has been evaluated and appears to be a sensible first-line approach to the management of GSI (Mouritsen et a l , 1991; Bo and Talseth, 1996). Combination therapy with either maximal or low intensity electrical stimulation, although widely used by physiotherapists, has received little attention by investigators. The aim of the current clinical trial was to evaluate the effectiveness of clinic and home electrical stimulation, in combination with individually planned pelvic floor exercises and biofeedback, in the treatment of urodynamically proven GSI.

Methodology A prospective, randomised controlled clinical trial was conducted at Bradford Royal Infirmary between 1992 and 1996. Ethical committee permission was granted and all subjects gave written informed consent.

Subjects Seventy women aged 24-68 referred €or urotherapy were recruited for the study. An initial interview by a specialist continence physio- therapist determined the subjects’ suitability for the trial. Inclusion/exclusion criteria were applied at the interview where possible. A recent urine sample was sent to the micro- biology laboratory for urinalysis. Water-filled medium-flow cystometry was performed to establish a definite diagnosis of GSI, according to the specifications of the International Continence Society (Abrams et a l , 1990). Pelvic floor muscle assessment was carried out at the initial consultation.

Inclusion Criteria Female age 16-75

0 Sterile urine 0 Urodynamically proven GSI 0 Written informed consent 0 English speaking

Exclusion Criteria 0 Urinary tract infection

Unstable bladder 0 Unable to perform a voluntary pelvic floor contraction 0 Pregnancy 0 Breastfeeding

Pelvic malignancy Cardiac pacemaker

0 Diagnosed neurological conditions 0 Diabetes

0 Hormone replacement therapy started recently (less than three months)

Each patient was given a full explanation of the different treatments and gave written informed consent before being randomly allocated to one of the three treatment groups.

Randomisation A table of random numbers was used for randomisation and treatment groups were then sealed in consecutively numbered envelopes. Neither subject or examiner had prior knowledge of the treatment contained in the envelope.

Subject Grouping Group 1 (controls): The control group received intensive treatment with pelvic floor exercises and biofeedback.

Group 2 (home treatment): This group performed the same exercise regime as the control group, and in addition undertook low-intensity neuro- muscular stimulation at home.

Group 3 (clinic treatment): These women per- formed the same exercise regime as the control group, and also received acute maximal vaginal stimulation in a clinic.

Details of these treatment regimes are described later.

Equipment The Bradford Perineometer (Laycock and Jerwood, 1994) consisted of a water-filled vaginal probe connected via a pressure transducer to an oscilloscope screen (Datascope 2000). The graph

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obtained during a pelvic floor contraction was analysed by computer software.

In-clinic biofeedback PRS 900, InCare, USA (this equipment was suplied by Neen Healthcare, Norfolk, UK). The equipment consisted of an air- filled vaginal probe, connected via a pressure transducer to a computer monitor.

A single-user pelvic floor exerciser (PFX, Cardio Design, Australia) was issued to patients for home biofeedback. The equipment consisted of an air-filled blue latex vaginal probe connected by 400 mm tubing to a hand-held display unit. Pressure was indicated by a pointer against a scale from 1 to 12.

The home stimulation unit (DMI Ltd., Wigan, UK) consisted of a single-user vaginal electrode which connected to a small hand-held battery-operated stimulator unit.

The in-clinic stimulation equipment (VSI, Neen Healthcare, Norfolk, UK) utilised auto- claveable vaginal electrodes, connected to a mains operated stimulator.

Assessment and Investigations Baseline clinical data and patient characteristics, including pelvic floor assessment, were recorded on a standard pro forma.

Pre- and post-treatment tests included a frequency/volume chart, pad test, perineometry, subjective assessment of outcome, and compliance with treatment.

1. A seven day frequencylvolume chart was completed before the initial appointment, on completion of six months’ treatment, and for seven days before the 12-month follow-up appointment.

2. Pad-testing was carried out a t 75% of the maximum cystometric capacity as this has been proven to be accurate and reproducible (Janez et a l , 19851, and was chosen for its ease of application in the clinic. A standard series of provocative exercises were performed by the subject. Actual values of urine loss were recorded in grammes, and post-treatment values were translated into a percentage of the original loss (table 1). Table 1: Classification of pad-test results

Score Interpretation Post-treatment urine loss (“A of pre-treatment value)

1 Worse > 25

2 Same i 24

3 Slightly improved 25-74

4 Greatly improved 75 + 5 Cured < 2 g

3. Perineometry using the Bradford perineometer was carried out before and after treatment and at monthly intervals. Digital vaginal assessment before this test had established the ability to produce a correct pelvic floor contraction. Data were collected for ten seconds, during which the subject was instructed to attempt to maintain a maximum voluntary pelvic floor contraction. Information recorded included the maximum squeeze pressure generated (in cm H20), thought t o represent muscle strength. The subject was placed in a standardised half-lying position to obtain these readings, with the head and shoulders supported by three pillows, the legs arranged in an abducted position with a pillow placed underneath each knee.

4. Subjective assessment of symptoms was scored on a simple ordinal scale, after completion of six and 12 months’ treatment: 1 = worse, 2 = same, 3 = slightly improved, 4 = greatly improved, 5 = cured.

5. Compliance with the exercise programme, home biofeedback, and home stimulation protocol was assessed subjectively. The women were asked to estimate the percentage of the prescribed exercise/stimulation instructions that they had actually fulfilled.

Treatment Regimes Group I: Controls This group received individual instruction in a pelvic floor exercise regime lasting six months (Laycock, 1992). After digital vaginal assessment of pelvic floor muscle strength and endurance (with verbal consent for examination to proceed), each subject was issued with an individually tailored home pelvic floor exercise programme. Pelvic floor muscle strength was scored using a modified Oxford grading, after asking the subject to perform a maximal voluntary contraction on the examiner’s middle and index fingers (Laycock, 1992).

Modified Oxford Grading Score tor Pelvic Floor Muscles

0 Nil 3 Moderate 1 Flicker 4 Good 2 Weak 5 Strong

The subject was asked to hold the contraction for up to ten seconds. The number of repetitions was then recorded, with a four second rest between each contraction. The subject was then asked to perform repeated fast contractions, up t o a maximum of ten.

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This was recorded, as in the following examples:

Example Oxford Time Repetitions Fast grade held contractions

1 2 4 3 4 2 4 10 6 10

I

Example 1 is of a subject with weak pelvic floor muscles, able to perform three four-second contractions and four fast contractions. Example 2 is of a subject with strong muscles, who was able to perform six repetitions of a ten-second hold, and ten fast contractions. Subjects were instructed to perform their individual exercise programme six times daily. The regime was reviewed at each clinic visit and increased, if possible, to a maximum of ten ten-second holds.

Each subject was issued with a pelvic floor exerciser, the PFX (Cardio Design Pty, Australia), for home biofeedback, and instructed to perform one of the six daily exercise sessions using this device. In-clinic visual biofeedback with a computerised graphical display was performed weekly for the first month of treatment, then on alternate weeks for the remainder of the six- month programme (PRS 900 InCare, USA). The treatment received by the control group was considered to be a baseline exercise programme, and a n identical exercise regime was issued to the two treatment groups.

Group 2: Home treatment In addition t o the baseline exercise programme, this group was issued with battery-operated stimulation units and single-user vaginal electrodes (DMI, Wigan, UK). Subjects were instructed to use the stimulation overnight at low intensity for six months. The required current intensity was described to the subject as a barely perceptible tingling sensation. Use was discon- tinued during menstruation. The stimulator produced pre-set frequencies consisting of trains of 10 Hz, with the inclusion of occasional high frequency bursts a t 35 Hz, in an attempt to maintain fast twitch fibre activity. Pulse width was set at 200 microseconds and the duty cycle was maintained at five seconds onioff.

Group 3: Clinic treatment In addition to the baseline treatment, these women also received 16 30-minute clinic sessions of maximal vaginal electrical stimulation at 35 Hz, with a pulse width of 250 microseconds (VSI, Neen Healthcare, Norfolk, UK). The duty cycle was pre-set by the machine at five seconds onloff. Subjects were instructed to perform a voluntary contraction with the stimulation.

After completing six months’ intensive treatment, all women were instructed to perform their final pelvic floor exercise programme once a day, and use the PFX once a week. Subjects were then invited to attend a 12-month follow-up appoint- ment. Any patient who had undergone pelvic surgery, become pregnant, or started hormone replacement therapy in the intervening period was excluded from follow-up.

Statistical Analysis Statistical analysis was carried out using SPSS for Windows 6.1 version. As the majority of data were non-Gaussian normal (determined using the Kolgorov-Smirnoff one sample test), non- parametric tests were applied. The Kruskal- Wallis analysis of variance test was used for between-group analysis. If statistical significance was demonstrated, the Mann-Whitney U-test was used between pairs of groups to identify where these differences lay. The chi-square test was used to determine the significance of differences between two independent groups, if data were nominal or categorical. The Wilcoxon matched pairs signed rank test was used within groups to determine the significance of values for data before and after treatment. Statistical significance was taken at the 5% level (p < 0.05). As data were non-parametric, median values and their range are quoted. Correlation of variables, t o attempt to identify outcome predictors, was analysed using Spearmans rank correlation test for non-parametric data (Siege1 and Castellan, 1988).

Results Recruitment Seventy women with urodynamically proven GSI were recruited into the study. As shown in table 2, 13 of them (18.6%) failed to complete the six-month treatment programme. The highest drop-out rate in the home treatment group (24%) was not statistically significant. The 57 women who completed the full course of treatment were fairly evenly distributed: 18 in the control group, 19 in the home treatment group, and 20 in the clinic group. Analysis of the findings for these subjects evaluated the actual effect of the two

Table 2: Subject enrolment data

Control Home Clinic Total

Number enrolled 21 25 24 70

Failing to complete treatment 3 6 4 13

Drop-out rate (%) 14.3 24.0 16.7 18.6

Number at 6 months 18 19 20 57

Drop-outs from 6 to 12 months 3 3 0 6

Number at 12 months 15 16 20 51

~~~ ~ ~- ~~ ~~ ~ ~

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electrotherapies. Analysis of findings from all 70 recruits evaluated the outcome with intent to treat.

Subject Characteristics Subject characteristics were shown to be from an evenly matched population between the three groups for age, parity, body mass index, weight of heaviest baby delivered vaginally, duration of symptoms, menopausal status, perineal trauma and frequency of general exercise (Kruskal-Wallis test for analysis of variance). Factors which might predispose a subject to incontinence, such as cystitis, smoking, constipation and previous pelvic surgery, were also analysed to test that the samples produced evenly matched populations. There were no smokers in the control group, compared to 15.8% in the home treatment group, and 25% in the clinic treatment group. Statistical significance was demonstrated between the clinic and control groups (Mann Whitney, p = 0.03). These subjects smoked more than five cigarettes daily. In addition signif- icantly more subjects had undergone previous pelvic surgery in the clinic treatment group (45%) compared to the control group (ll%),

clinic treatment groups felt their condition had worsened, and only two subjects (10.5%) in the home treatment group were worse following treatment. The percentage of subjects reporting to be cured or greatly improved is shown in table 4a, both at six and 12 months. Statistical significance using a chi-square test was demonstrated between the home and clinic treatment groups both at six months (p = 0.034), and at 12 months (p = 0.009), the higher proportion of greatly improved or cured subjects being in the clinic treatment group. This high success rate is reduced if results are viewed with intention to treat, and these subjective data are shown in table 4b.

Table 4 Subjective outcome: Percentage of subjects reporting cure or great improvement

Assessment Control Home Clinic

(a) Subjects who completed treatment Six months (n = 18) (n = 19) (n = 20)

12 months (n = 14) (n = 15) (n = 20)

(b) Including subjects who failed to complete treatment Six months (n = 21) (n = 25) (n = 24)

56.0 47.3 80.0

66.7 43.8 85.0

47.6 36.0 66.7 - - Mann Whitney U-test, p = 0.02.

Objective Outcome Measures Baseline perineometric measurements were also Changes in Urine Loss from an evenly matched population. The home treatment group had higher starting values for all Pad test data were used as a n objective three pelvic floor parameters (table 3), although measurement of urine loss. The Kruskal-Wallis this was not statistically significant (Kruskal- test for analysis of variance was used to analyse Wallis test for analysis of variance). between-group differences in the percentage

Table 3: Baseline clinical data: Initial perineometric data*

Control Home Clinic n = 18 n = 79 n=20

Clinical data Median (range) Median (range) Median (range)

(a) Maximum pressure cm HzO 46.7 (16.7-83.0) 62.4 (14.9-131.1) 54.7 (2.8-152.1)

(b) Area cm H20/sec 324.8 (23.1 -701 .I) 500.2 (96.0-1 054.5) (320.6 (24.4-1224.7)

(c) Gradient cm H20/sec 68.2 (30.4-166.2) 96.0 (1 7.6-1 99.3) 81.1 (7.2-270)

* Using Bradford perineometer during a 10-second maximal contraction. (a) Maximum pressure during contraction thought to represent strength of the pelvic floor muscles. (b) Area = the area under the graph produced by a 10-second pelvic floor contraction thought to represent slow twitch fibre activity. (c) Gradient = the speed of the pelvic floor contraction thought to represent fast twitch fibre activity.

Subjective Outcome change in urine loss before and after treatment The subjects’ evaluation of their overall condition (table 5). There was no statistical evidence to following treatment was scored from 1 to 5 (see support any between-group differences. Within- above). None of the subjects in the control and group analysis to eliminate inter-patient

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Table 5: Objective analysis of urine loss: Between and within group analysis of pad-test results

Urine loss (pad-test)

~

Control Home Clinic (n = 18) (n = 19) (n = 20)

Median (range) Median (range) Median (range)

Initial (9) 13.1 (2.1-75.2) 9.8 (2.3-1 15.2) 20.8 (2.0-1 03.4) At six months (g) 0.8 (0.0-68.1) 2.9 (0.0-50.9) 1.5 (0.0-28.1) p value 0-6 months (Wilcoxon) 0.0012 0.0062 0.0003

YO difference

Six months 90.7 (-17.1-100.0) 76.5 (-580.3-100.0) 91.3 (-72.4-100.0)

Twelve months (n = 15) (n = 16) (n = 20)

100.0 (-8.1-100.0) 97.5 (-415.1-100.0) 100.0 (-67.5-100.0)

variation using the Wilcoxon matched pairs Pelvic Floor Characteristics signed rank test demonstrated a statistically significant reduction in urine loss in all three groups after six months’ treatment with the

using the Bradford perineometer, there was a statistically significant increase in all pelvic floor parameters, in all three groups, before and after

strongest evidence for improvement being again in the clinic treatment group (P = 0.0003)* At

treatment. Differences between the three groups were not found t o be statistically significant at

l2 months reduction in urine loss at pad-testing.

groups demonstrated a further either six or 12 months (Kruskal-Wallis test for analysis of variance) for strength, area or gradient

In table 5 it can be seen that all groups demonstrated a substantial percentage reduction in urine loss after six months treatment. The lowest percentage improvement was found to be in the home treatment group where the median reduction was 76.5% although this was not statistically significant using the Mann-Whitney U-test for analysis between pairs of groups. The percentage of patients objectively greatly improved or cured on pad testing is shown in table 6a. The lowest percentage was again in the home stimulation group, although this was not statistically significant. However, after 12 months these data appear very similar in each group. Data analysed ‘with intention to treat’ demonstrated a reduced success rate in all groups (table 6b).

Table 6: Objective evaluation of urine loss: Percentage of subjects greatly improved or cured at repeat pad-test*

Assessment Control Home Clinic ~~ ~

(a) Subjects who completed treatment

Six months (n = 18) (n = 19) (n = 20)

12 months (n = 14) (n = 15) (n = 20)

(b) Including subjects who failed to complete treatment Six months (n = 21) (n = 25) (n = 24)

72.3 52.6 80.0

73.3 81.3 84.2

61.9 40.0 66.6

* Greatly improved by pad-test was defined as 75% or more reduction in urine loss at repeat pad-test. A complete cure was defined as dry or urine loss of c 2 g

of the contraction. The percentage increase in maximum squeeze pressure (thought to represent pelvic floor strength) after six months’ treatment (table 7) was greatest in the maximal stimulation group, who demonstrated a 64.3% gain in muscle strength, compared to 40.8% in the control group, and only 32.7% in the home stimulation group. From six to 12 months, muscle strength continued t o increase in the control group (by a further 12.4%, statistical significance demonstrated, p = 0.01) and home treatment group (a further 14.4%). However, in the clinic treatment group there was a 19.9% decrease in pelvic floor strength in the six- t o 12-month review period, and this decrease was statistically significant (Wilcoxon matched pairs signed rank test, p = 0.004).

Table 7: Objective measurement of pelvic floor strength*: Percentage change from baseline data at six and 12 months

Control Home Clinic Median (range) Median (range) Median (range)

Six months (n = 18) (n 19) (n = 20)

12 months (n = 15) (n = 16) (n = 20)

p value

40.8 (-19.6-132.1) 32.7 (-8.3-368.6) 64.3 (-55.9-705.7)

53.2 (-22.9-137.0) 47.1 (-17.2-381.4) 44.4 (-43.2-433.3)

(Wilcoxon) 0.0125 ns 0.0040

* The maximum pressure generated during B ten-second voluntary contraction is thought to represent pelvic floor strength. t p value (Wilcoxon) indicates the statistical significance of the percentage change from six to 12 months.

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Frequency / volume Charts These were poorly completed. Sets of data were incomplete and were unsuitable for statistical analysis.

Compliance At the end of the six-month treatment period the lowest median percentage compliance, as estimated by the subjects, was in the home treatment group (72.5%), and the highest in the control group (90%). Compliance with the PFX instructions were lower, again the lowest score was in the home treatment group (47.5%), and the highest in the control group (75%). There were no statistically significant differences in compliance between the groups. Compliance with stimulation in the home treatment group was reported to be 77.5% of the prescribed treatment.

Correlation Between Subjective Outcome and Objective Markers Correlation analysis was performed using Spearmans rank correlation test for non- parametric data. There were too few markers showing a correlation with outcome variables to perform a regression analysis. The only group demonstrating a positive correlation between subjective and pad test outcome was the clinic group (p = 0.02). This group also had a significant positive correlation with the duration of incontinence symptoms; women with a longer history of incontinence demonstrated greater improvement. In both the home and clinic treatment groups, subjects with initially weaker pelvic floor muscle strength demonstrated a greater improvement than those with stronger muscles.

Discussion Subject Recruitment The higher proportion of drop-outs in the home treatment group may indicate that this treatment is unacceptable to some women. Reasons for dropping out of this group, before completion of treatment, were that the equipment was uncomfortable or obtrusive, and demanded too much time. Reasons for failure to complete treatment in the other groups were varied, and included factors such as inability to attend for treatment due to the demands of job and/or family. Subjects in the clinic treatment group who attended twice weekly appeared t o enjoy the more regular contact with the continence physiotherapist. Two subjects who dropped out in this group were unable to attend for frequent treatments owing t o difficulties with public transport. Daily treatment was not possible in the

clinic, and units for home use delivering maximal stimulation were not available for this study. Twice-weekly stimulation is common in physio- therapy, therefore it seemed realistic to use this treatment regime. It is acknowledged that a fairer comparison might have been made using a home stimulator for both the low intensity and maximal stimulation groups. Drop-outs from six to 12 months (control and home stimulation groups only) included subjects who had undergone hysterectomy, and those who failed to respond to follow-up appointments.

Randomisation Randomisation failed to produce an evenly matched population for two factors, with smoking and prior pelvic surgery being significantly higher in the clinic treatment group. Both these factors are poor predictors of a successful outcome (Bump and McClish, 1992; Bo et a l , 19901, and would produce a negative bias to the results for this group. However, as the clinic treatment group demonstrated the greatest improvement in all outcome measures, these factors may not be so influential as previously supposed.

Subjective and Objective Outcomes It was encouraging to demonstrate a significant reduction in symptoms both subjectively and a t pad test in all three groups. Of the subjects 67% were greatly improved or cured at pad-testing. The subjective outcome was statistically lower in the home treatment group than in the maximal stimulation group. Values for the home treatment group were also lower than in the control group. This may reflect the fact that subjects using the home stimulation unit found the treatment intrusive and demanding. Subjects in the clinic treatment group may have derived additional benefit from the increased patient /therapist time. A detailed quality-of- life questionnaire would have provided more useful information on the subjective effect of the different treatment regimes.

Pud-tests Pad-test results also demonstrated a greater improvement in the clinic treatment group than the home group and although not statistically significant, could indicate clinical significance. Pad test results for the home treatment group were also lower than in the control group. On this evidence it appears that the control group benefited more from careful instruction in pelvic floor exercises than they would have from the addition of low intensity stimulation. In fact the percentage of subjects who were clinically greatly improved or cured on pad-testing after six months’ treatment in the home treatment

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group (47.4% subjectively, 52.6% by pad-testing) is lower than in previously reported studies using pelvic floor exercises alone (Bo et al, 1989; Henalla et al , 1988).

Pelvic Floor Characteristics These improved significantly in all three groups but this did not correlate with either the subjective or objective outcome, indicating that factors other than pure strength gain must contribute to the reduction in symptoms. These may include improved support, brisker reflex activity and the ability to contract the muscles before and during, increases in abdominal pressure (‘bracing’). Miller et a1 (1996) found that 18 stress incontinent women were able to effect a statistically significant reduction in urine loss (p = 0.005) by a voluntary contraction of the pelvic floor muscles during a cough (the ‘knack‘), regardless of the initial strength of their pelvic floor muscles.

Compliance On reflection, asking the women to estimate their own compliance with the treatment regime provided a poor tool for the analysis. A more measureable tool would have been the use of an exercise diary. Alternatively, a recording device incorporated in the home stimulator would have provided indisputable evidence of the number of hours of use, but such equipment is costly and was not available for this study.

Correlation Analysis I t was disappointing to find too few predictor variables upon which to build a model for a treatment protocol. I t was unexpected to find no statistically significant correlation between the post-treatment improvement in pelvic floor strength and reduction in urine loss in any of the groups, since other studies have suggested that improved pelvic floor strength leads to a reduction in incontinence (Kegel, 1948; Wall and Davidson, 1992). In the current study, when the improvement in pelvic floor strength was analysed, it was found that subjects with weaker initial pelvic floor strength demonstrated a greater percentage improvement in both electrotherapy groups. Bo et a1 (1990) found that responders to pelvic floor exercises alone had stronger pelvic floor muscles on initial assessment. In the current study no such link was evident in the control group. The statistical evidence was a t its strongest in the clinic treatment group, suggesting that this may be the treatment of choice for subjects with very weak pelvic floor muscles. Subjects in the clinic treatment group also had the longest duration of symptoms at the outset of treatment, which had a significant positive correlation with the reduction

in urine loss at pad-testing. This suggests that acute neuromuscular stimulation may be the most appropriate treatment for subjects with a long history of incontinence.

Long-term Follow-up After 12 months subjects continued to improve both subjectively and objectively. This exceeds expectations as previous studies (Mouritsen et al , 1991) have indicated that improvement is maintained but not necessarily increased.

Proposed Explanation of Outcome The findings suggest that the addition of low frequency electrical stimulation to a carefully taught pelvic floor exercise programme could have had a detrimental effect on the clinical outcome. This may be due to the conversion of fast to slow twitch muscle fibres (Salmons and Vrbova, 1969). The inclusion of high frequency bursts may not have been effective in preventing deterioration of fast twitch fibres (essential for rapid phasic activity to maintain continence during rapid increases in intra-abdominal pressure); indeed there is some evidence to suggest that any stimulation a t low intensity converts all fibres to the slow twitch type I fibres (Pette, 1986). The overall improvement in symptoms in the home treatment group may have been hindered by the reduction in fast-twitch fibre activity.

However, from six t o 12 months, after home stimulation was discontinued, there was a large increase in the percentage of subjects cured or greatly improved at pad-test (52.6% at six months t o 81.3% at 12 months). This suggests that after the stimulation ceased there was a reversal of any effects of stimulation on muscle fibre composition (Brown et a l , 19891, enabling subjects to improve their symptoms by pelvic floor exercise alone. The apparently greater improvement in the clinic treatment group may have been due to an enhanced fast fibre activity, due to selective activation of fast twitch fibres, by the reversal of recruitment order (Sinacore et a l , 1990). As all the subjects in this study had proven GSI, in which incontinence is provoked by sudden increases in intra-abdominal pressure, a high level of restoration of fast-fibre activity would appear to be a logical approach to a reduction of incontinence. Although the greatest success was again in the clinic group at 12-month follow up, pelvic floor strength had significantly decreased in this group from six to 12 months. However as the improvement in continence was maintained, this suggests that the clinical outcome may have been due t o improved functioning and reflex activity of the muscles rather than purely a strength gain.

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Conclusions The findings of this study have demonstrated that correctly taught pelvic floor exercises, combined with biofeedback, are an effective treatment for the majority of patients with GSI. Even subjects with severe initial urine loss responded well to this treatment. However, for subjects presenting with very weak pelvic floor muscles, a long duration of symptoms and a history of ineffective pelvic surgery, the addition of acute maximal electrical stimulation to enhance the voluntary exercise programme may provide a better treatment outcome. Low intensity electrical stimulation appeared to confer no additional benefit to a conscientiously performed exercise programme, and may in fact have a detrimental influence on the recovery of patients with urodynamically proven GSI.

Recommendations It is recommended that all subjects referred for physiotherapy should receive careful instruction in a patient-specific programme of pelvic floor exercises. Emphasis should be placed on the importance of strict adherence to the exercise programme for several months before exploring other treatment options. Subjects with a long duration of symptoms, a history of previous ineffective incontinence surgery, or very weak pelvic floor muscles may benefit from acute maximal electrical stimulation at the outset of treatment. Low intensity stimulation is not considered advantageous for women suffering from GSI. Further clinical trials are necessary to confirm these recommendations.

Authors Stephanie Knight MPhil GradDipPhys MCSP was a research physiotherapist at Bradford Royal Infirmary conducting the above clinical trial, which formed the basis of her MPhil thesis. Jo Laycock PhD FCSP designed the research protocol and supervised the clinical trial. Retired urotherapy manager at Bradford Royal Infirmary, she now acts as a consultant urotherapist, and runs a private practice in the Lake District. Dianne Naylor GradDipPhys MCSP helped with the smooth running of the trial, and with data collection. She is a senior physiotherapist in the urotherapy department at Bradford Royal Infirmary. Action Research UK funded the clinical trial, including the cost of equipment, and a three-year Senior I post (S Knight). This article was received on December 10, 1996, and accepted on July 7, 1997.

Address for Correspondence Dr J Laycock, Pea Top Grange, Culgaith, Penrith, Cumbria CAI 0 1 QW.

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Binding CSP Periodicals A complete year’s issues for 1997 of both Physiotherapy and Physiotherapy Frontline can be bound in cloth covers with the title, volume and badge blocked in black on the spine and front cover.

The price for the 12 issues of Physiotherapy will be f 18.50 inclusive of return UK postage. Back numbers can be bound in the same way for f22, or without the badge or lettering for f 17.

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In either case, please send a complete set of issues with a cheque payable to ‘J R Harris’ or a postal order to the full amount to Mr J R Harris, Bookbinder, 191 Sandpit Lane, St Albans, Hertfordshire AL4 OBT. Please ensure they arrive by March 31, 1998, but note that the premises will be closed from January 19 to February 12 and parcels will not be accepted during that period. It is regretted that J R Harris cannot supply missing issues.

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