Med. & Biol. Eng. & Comput., 1977, 15, 155-167
Effects of functional electrical stimulation on the urethral closing muscles S. Plevnik
P. Suhel
Faculty for Electrical Engineering, University of Ljubljana, 61000 Ljubljana, TrEa~ka 25, Yugoslavia
S. Rakovec Medical Faculty, Department of Surgery, University of Ljubljana, 61000 Ljubljana, Vrazov trg 2, Yugoslavia
B. Kralj Hospital for Gynaecology & Obstetrics, 61000 Ljubljana, Njego,~eva 4, Yugoslavia
A b s t r a c t - - T h e importance of the selection of patients with urinary incontinence suitable for treatment with functional electrical stimulation ( f.e.s.) was tested. 40 patients with urinary incontinence of different kinds (mostly stress incontinence) were selected on the basis of urological, neurophysiological and urodynamic examinations. The positive response to optimal fe.s. was a criterion for urodynamic selection. Mechanicalproperties of the unstimulated and electrically stimulated urethral wall tissue in the functional part of the urethra were studied. The differences between the acute effects of different types of stimulation, namely monophasic and biphasic f.e.s, with vaginal or different types of anal plugs and mechanical stimulation produced by these plugs, were stated. An attempt was made to quantify the success of treatment with f.e.s. Besides the routine urological, neurophysiological and urodynamic methods, the investigative methods of measuring the urethre/ pressure profile (u.p.p.) and measuring the pressure at one point of the urethra, by means of Mikro- Tip pressure transducers, were used in our study. Errors due to the dimensions of the measuring device causing a nonphysiological dilatation of the urethra were considered in the method of measuring the u.p.p. Keywords--Electrical stimulation, Urethral pressure profile, Urinary incontinence
1. Introduction
THE IMPORTANCEof the correct selection of patients with urinary incontinence in whom a successful treatment with Functional Electrical Stimulation (f.e.s.) can be expected was indicated by GODEC and KRALJ (1976). The selection is made possible by means of routine urological and neurophysiological examinations and investigative urodynamic examinations, whose objectivity is highly related to the accuracy of the method applied. The basic parameter used as the criterion for the final urodynamic selection is response to f.e.s., i.e. an increase of the urethral pressure as the consequence of the application of f.e.s. In the literature, different authors have described more or less accurate methods for measuring urethral pressures. Basically, urethral pressures can be determined: (a) by measuring pressures at one point with the measuring sensor fixed in the functional part of the urethra (b) by measuring urethral pressure profiles (u.p.p.), in which case the measuring sensor is withdrawn from the bladder through the urethra at a constant rate. First received 20th October and in final form 2nd June 1976
Medical & Biological Engineering & Computing
The accuracy of measurements is affected by neurophysiological artefacts, errors due to the width of the measuring device causing nonphysiological dilatations of the urethra (PLEVNIK, 1976; ASMUSSEN and ULMSTEN, 1975) and unforeseeable displacements of the measuring sensor from the measuring point. Neurophysiological artefacts depend on the width of the measuring sensor and, for the urethral pressure profile, on its withdrawal rate (AsMUSSEN and ULMSTEN, 1975). The smaller the width of the measuring sensor and the rate of its movement, the smaller are the neurophysiological artefacts. The error due to nonphysiological dilatations of the urethra increases with the width of the measuring sensor, assuming that the electrically unstimulated tissue of the urethral walls has elastic properties. Displacement of the measuring sensor from the site of measurement can easily happen because of the uneven distribution of the urethral pressure; this can be partially prevented by selecting both a suitable shape of the measuring sensor and the method of measurement. When methods (a) and (b) are compared, it appears that in the latter case the neurophysiological artefacts are more pronounced than in the former (due to the withdrawal of the measuring sensor through the urethra), but they can be reduced
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considerably by means of a reduced withdrawal rate. The errors due to nonphysiological dilatations are in both cases probably equal. The errors due to the unforeseeable displacement of the measuring sensor are neglible in method (b), while, in method (a), they can be reduced to a certain extent by means of a suitably shaped measuring sensor so that the axial forces which may cause undefined movements of the sensor are minimised. A credible conclusion can be drawn from this preliminary discussion: urethral pressures can be more accurately determined by measuring u.p.p, than by measuring the pressure at one site of the urethra. F o r various reasons, however, method (a) cannot always be avoided. Accuracy in measuring urethral pressure is of great importance for determining the influence of f.e.s, on the urethral muscles, since it is relevant whether the recorded increase of pressure is due to f.e.s, or to a measuring error. In the majority of our experiments, urethral pressures were determined by measuring the u.p.p, and only in a few by measuring at one site in the urethra. The pressures were measured with Mikro-Tip pressure transducers (MILLARand BAKER,1973), as we assumed that the specific construction and very small dimensions of the measuring sensor would assure more accurate measurements than those obtained by other techniques. The basic purposes of the study were: (a) the evaluation and simplification of the method of measuring of the u.p.p. (as described by PLEVNIK, 1976) by means of Mikro-Tip pressure transducers, and the determination of the measuring errors due to nonphysiological dilatation of the urethra (b) the determination of the mechanical properties of unstimulated and electrically stimulated urethral-wall tissue (c) the determination of the acute effect of individual types of f.e.s., i.e. monophasic and biphasic f.e.s, with different types of stimulation plug, and the determination of the effect of mechanical stimulation of the individual stimulation plug
(d) the determination of the suitability of selection of patients with urinary incontinence to be treated with f.e.s. (e) an objective evaluation of the success of treatment with f.e.s, by means of measuring the u.p.p.
2. Materials, methods and experimental technique Preliminary urological, neurophysiological and urodynamic examinations of a group of 82 patients produced a group of 40 patients suitable for treatment with functional electrical stimulation (f.e.s.). The majority of these patients had stress incontinence; among them only patients with no significant anatomical changes were selected, with the exception of a small cystocele in three patients [patients 4, 11, 14 (see Table 2)], but no other pathological changes of the urinary pathways. A urodynamic and neurophysiologicat check revealed no neurological disorders or abnormalities of the detrusor. Previous training of the pelvic floor muscles had not been successful in these patients. Prior to our treatment four patients had had surgery; two twice [patients 8 and 19 (Table 2)] and two even five times [patients 3 and 9 (Table 2)], all without success. From 35 selected patients with stress incontinence 27 patients had severe, six had medium and two had mild degrees of incontinence. The degree of incontinence was in these cases defined as follows: severe was incontinence occurring at the slightest movement, the patient losing at least a quarter or more of the total volume of urine in erect position; medium was incontinence occurring in the case of an increased intra-abdominal pressure; mild was incontinence occurring only with a violently increased intraabdominal pressure. Three patients with severe nocturnal enuresis, not responding to previous conservative treatment, i.e. one patient with severe urge incontinence and one patient with incontinence of unknown origin (probably severe stress incontinence), were included in the group of selected patients. The final criterion of selection was a significant positive response of the urethral closing
Table I. First examination
Types of stimulation 1 2 3 4 5 6 7 8 9 10 156
(m.v.) monophasic f.e.s.; vaginal plug (b.v.) biphasic f.e.s.; vaginal plug (m.a.l.) monophasic f.e.s.; anal plug, large size (b.a.l.) biphasic f.e.s.; anal plug, large size (m.a.m.) monophasic f.e.s.; anal plug, medium size (b.a.m.) biphasic f.e.s.; anal plug, medium size (m.a.s.) monophasic f.e.s.; anal plug, small size (b.a.s.) biphasic f.e.s.; anal plug, small size (v.m.) vaginal plug, mechanical stimulation (a.m.l.) anal plug, large size; mechanical stimulation
Number of patients examined 20 23 28 32 18 17 18 21 15 23
Medical & Biological Engineering & Computing
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