The effect of vaginal distension on the female urinary bladder and urethral sphincters

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1 Acta Obstetricia et Gynecologica. 2007; 86: ORIGINAL ARTICLE The effect of vaginal distension on the female urinary bladder and urethral sphincters AHMED SHAFIK 1, OLFAT EL SIBAI 2, ALI A. SHAFIK 1 & ISMAIL A. SHAFIK 1 1 Department of Surgery and Experimental Research, Faculty of Medicine, Cairo University, Cairo, Egypt, and 2 Department of Surgery, Faculty of Medicine, Menoufia University, Shebin El-Kom, Egypt Abstract Aims. A mention of effect of vaginal distension, as induced by penile thrusting at coitus, on urinary bladder (UB) and urethral sphincters could not be traced in literature. We investigated the hypothesis that, upon vaginal distension, UB undergoes inhibited activity, while external and internal urethral sphincters (IUS) exhibit increased activity in order to guard against urine leakage during coitus. Methods. Response of UB and external and IUS to vaginal balloon distension was recorded in 28 healthy women (age years). A vaginal condom was inflated with air in increments of 50 up to 200 ml, and vesical pressure as well as electromyographic (EMG) activity of external and IUS were registered. The test was repeated after separate anaesthetisation of vagina, UB and external and IUS. Results. On vaginal distension, vesical pressure was reduced in the ratio of expansion of vaginal volume up to a certain capacity, beyond which vesical pressure ceased to decline when distending volume was augmented. Similarly, IUS EMG activity increased progressively on incrementally added vaginal distension up to 150-ml distension, beyond which any further vaginal distension did not produce an additional increase of EMG activity; the external urethral sphincter (EUS) EMG activity showed no response. Vaginal distension, while the vagina, UB and external and IUS had been separately anaesthetised, produced no significant change. Conclusion. Vaginal balloon distension seems to effect vesical wall relaxation and increase IUS tone. This appears to provide a mechanism that prevents urine leak during coitus. Vesical and IUS response to vaginal distension are suggested to be mediated through a reflex we term vagino-vesicosphincteric reflex, which seems to be evoked by vaginal distension during penile thrusting. The reflex may prove of diagnostic significance in sexual disorders. Key words: Electromyography, penile thrusting, coitus, sexual intercourse Introduction Many of the physiological mechanisms involved in the female sexual act seem to have an effect on the nearby pelvic organs. The effect of vaginal distension on some of these organs during penile thrusting at coitus is not exactly known. The structures that are close to the vagina and may be affected by penile buffeting of the vagina at coitus include: the urinary bladder (UB), urethra, rectum, and anal canal. A previous study has shown that penile buffeting of the vagina during coitus affects rectal wall relaxation and increases the internal anal sphincter tone (1). This effect seems to be mediated through the vaginoanorectal reflex, to provide a mechanism that prevents faecal leakage and soiling during coitus. An earlier study demonstrated that vaginal distension produced a vesical pressure decrease, but an increase in urethral pressure; this response appears to be evoked by the vagino-vesicourethral reflex (2). The sexual act seems to be affected by several factors, including sensory and physiological stimuli as well as local and reflex actions (38). The role played by the parasympathetic and sympathetic innervations in the sexual act is still a matter of speculation (9). The sensory signals from the genital region are assumed to be mediated to the sacral segments of the spinal cord through the pudendal nerve and sacral plexus before they are transmitted to the cerebrum (4,9). Local reflexes integrated in the sacral and lumbar spinal cord may also share in sexual reactions (1014). Correspondence: Ahmed Shafik, 2 Talaat Harb Street, Cairo 11121, Egypt. shafik@ahmedshafik.com (Received 14 July 2007; accepted 23 August 2007) ISSN print/issn online # 2007 Taylor & Francis DOI: /

2 The effect of vaginal distension 1399 Sexual stimulation not only produces reflex changes in the female external and internal reproductive organs, but also extragenital reactions (9,15 19). Thus, the pelvic floor muscles have been demonstrated to respond to stimulation of the cervix uteri and clitoris through reflex reactions (7,8,15 19). The receptors in the genital organs, with axons running in the pudendal nerve to the sacral cord (S2 4), seem to initiate the extragenital responses. However, a mention of the effect of vaginal distension as that induced by penile thrusting of the vagina at coitus, on the UB and urethral sphincters, could not be traced in the literature. The current study investigated the hypothesis that upon vaginal distension, the UB activity is inhibited while the external (EUS) and internal (IUS) urethral sphincters exhibit increased activity. This hypothesis was investigated in the current study. Material and methods Subjects The study comprised 28 healthy women volunteers (mean age: SD years, range: 27 40). Eighteen women were multiparous and 10 nulliparous. All were married and sexually active, had regular menses, and no gynaecologic complaint in the past or at the time of enrolment. The multiparous women had undergone normal vaginal deliveries with episiotomy which healed without complications. Physical examination, including neurologic and gynaecologic assessment, was normal. Informed consent was given by each woman on receipt of information on the nature of the study and her role in it. The study was approved by the Cairo University Faculty of Medicine Review Board and Ethics Committee. Methods The response of the UB, EUS, and IUS to vaginal distension was examined. The woman was placed supine with the knee and hip joints flexed and thighs abducted. A condom (London Rubber Industries Ltd, London, UK), tied to the distal part of a 16 F catheter with multiple side holes, was introduced 45 cm into the vagina. The response of the EUS to vaginal distension was recorded by a concentric electromyographic (EMG) needle electrode (Type 13L49, Disa, Copenhagen, Denmark), 30 mm long and 0.65 mm in diameter. The needle electrode was introduced through the vaginal mucosa on one side of the external urethral orifice to a depth of approximately 1.25 cm to lie in the EUS. The EMG response of the IUS was recorded by means of a surface electrode mounted on an indwelling urethral catheter. The catheter was introduced into the UB per urethra and was then pulled backward gradually until the electrode lay opposite the IUS as gauged by fluoroscopy. A ground electrode was applied to the thigh. The response of the EUS and IUS to vaginal distension was displayed on the oscilloscope of a standard EMG apparatus (Type MES, Medelec, Woking, UK). Films of the motor unit action potentials (MUAPs) including frequency, amplitude, and conduction velocity were taken on light sensitive paper (Linagraph type 1898; Kodak, Rochester, NY) from which measurements of the MUAPs and latency of the reflex were made. The EMG signals were, in addition, stored on an FM tape recorder (type 7758A; Hewlett Packard, Waltham, MA, USA) for further analysis as required. The correct position of the needle electrode was checked by the burst of activity heard from the loudspeaker and visualised on the oscilloscopic screen of the electromyograph as soon as the needle had entered the muscle. The normality of the myoelectric activity of the urethral sphincters was controlled in all of the subjects prior to the test by stimulating the concerned muscles and recording its activity. All subjects showed normal EMG activity of the EUS and IUS. The vaginal condom was inflated with air, in increments of 50 ml, up to 200 ml, and the EMG of the EUS and IUS as well as the UB pressure were recorded. The EMG apparatus was switched on at the end of balloon inflation. The speed of balloon inflation was not considered as EMG recording was performed, only at the end of balloon filling. The latency of the response was measured from the stimulus (vaginal distension) to the first deflection of the action potentials (AP) complex registered from the urethral sphincter electrodes. In order to examine whether vesical and urethral sphincteric response to vaginal distension was a direct or a reflex action, the vagina was anaesthetised with lidocaine gel in 19 of the 28 studied women who consented to do the test; lidocaine gel is used for local anaesthetisation of epithelial tissues (20). The response of the vesical pressure, the EUS and the IUS EMG to vaginal distension, as mentioned above, was then recorded after 20 min, and again 3 h later when the anaesthetic effect had disappeared. The test was repeated in the same woman after painting the vagina with bland gel (K-Y, Johnson & Johnson, Boston, MA, USA). The following day, the EUS and IUS were anaesthetised by infiltrating the muscle bundles around the needle electrode with

3 1400 A. Shafik et al. 2 ml of 1% lidocaine with a 20-gauge needle introduced into the sphincter in the same manner as the needle electrode. The UB was also anaesthetised by means of instilling an anaesthetic solution, composed of 20 ml of 2% lidocaine with 50 ml of normal saline, into the UB through a 10 F catheter. The response of the individually anaesthetised EUS, IUS, and UB to vaginal balloon distension was recorded after 20 min and after 3 h, when the anaesthetic effect had waned. The test was repeated after saline infiltration of the EUS and IUS, and after saline instillation into the UB. To ensure reproducibility of the results, the aforementioned recordings were repeated at least twice in the individual woman, and the mean value was calculated. The independent sample t-test (pooled or Student s t- test) was used to assess the statistical significance based on data obtained from independent samples. All results were expressed as mean9 standard deviation. Differences were considered significant with a p-value of B0.05. Results No complications occurred during or after the performance of the tests, and all the women were evaluable. The basal UB pressure recorded a mean of SD cmh 2 O (Table I) which was in accord with the value of normal control women in our laboratory. The EUS recorded mean basal MUAPs of mv (range: ) (Figure 1). The IUS at rest basal registered regular and negatively deflected monophasic slow waves (SWs) (Figure 2), which had a mean frequency of cm/min, an amplitude of mv, and a conduction velocity of cm/sec (Figure 2, Table II). Fast activity spikes or APs followed or were superimposed on the SWs and represented by negative deflections (Figure 2). They occurred randomly and did not follow each SW. Table I. Vesical pressure response to vaginal balloon distension in increments of ml of air. Vesical pressure (cmh 2 O) Vaginal distension (ml) Mean Range 0 (basal) * * ** ** Values are mean9sd. *p B0.05. **p B0.01. Upon vaginal balloon distension, the EUS did not exhibit a significant change in the EMG activity up to 200 ml distension (p 0.05) (Figure 1). Meanwhile, the IUS recorded a progressive increase of the EMG activity upon incremental vaginal distension up to 150 ml, but ceased increasing with further vaginal distension (Figure 2, Table II). The UB, upon vaginal balloon distension, recorded diminished pressure in the ratio of vaginal volume expansion (Table I). However, additional vaginal distension beyond 150 ml did not raise the pressure further (Table I). The latency of the response is depicted in Table II. It was dependent on the volume of vaginal distension; it decreased with increasing vaginal distension (Table II), but ceased decreasing when the vaginal distension rose beyond a volume of 150 ml. Effect of vaginal distension on the anaesthetised vagina, EUS, IUS, and the UB. Vaginal balloon distension did not effect a significant change (p 0.05) in the vesical pressure or the EUS and IUS EMG activity, when the test was performed 20 min following individual vesical, EUS, and IUS anaesthetisation. Three hours later, when the anaesthetic effect had waned, all vesical pressure, and the EUS and IUS EMG activity responded to vaginal balloon distension similar to the response obtained before anaesthetisation with no significant difference (p 0.05). The response of the aforementioned variables to vaginal distension when normal saline was used instead of lidocaine was similar to that without saline testing with no significant difference (p 0.05). The UB, EUS, and IUS reacted similarly, as reported above, when the vagina was anaesthetised or painted with bland gel. Thus, 20 min after vaginal anaesthetisation, the vesical pressure and the EUS and IUS EMG activity did not respond to vaginal balloon distension, whereas 3 h later, the response was similar to that before anaesthetisation. The results of the aforementioned recordings were reproducible with no significant difference (p0.05) when the test was repeated on the same woman. Discussion The current study seems to identify the response of the UB and urethral sphincters during coitus. Penile thrusting during coitus presumably effects vaginal distension. The vagina is in close contact with the urethra and the lower part of the posterior vesical wall (21). We speculate that during penile thrusting at coitus, the urethra and the lower part of the posterior bladder wall are repeatedly buffeted with a

4 The effect of vaginal distension 1401 Figure 1. Electromyographic activity of the external urethral sphincter at rest (a), upon vaginal balloon distension with 50 (b), 100 (c), 150 (d), and 200 (e) of air. possible vesical stimulation and contraction. Vesical contraction with reflex IAS relaxation during coitus, and the resulting possible urine leakage, may psychologically and functionally disturb and interrupt the sexual act, and lead to coitus interruption; IAS relaxation may be associated with urine leakage (22). However, it appears that a protective mechanism occurs during coitus that prevents urine leakage. The inflated condom seems to simulate the erected penis during coitus. The lowering of the vesical pressure during vaginal balloon distension presumably denotes vesical wall relaxation, which would prevent the vesical wall from contracting as a result of vesical stimulation induced by penile thrusting at coitus. Vesical wall relaxation appears also to allow for the uninterrupted accommodation of urine in the UB during the sexual act. The associated increase of the IUS EMG activity seems to indicate an increased IUS tone. The tightening of the IUS at coitus by its increased tone presumably effects firm closure of the IUS and prevents urine leakage. The increased IUS tone combined with vesical relaxation appear to provide a protective mechanism against urine leakage during penile thrusting at coitus. Urine leakage during coitus would be awkward for both partners. Patients with ill-functioning urethral sphincters from neurogenic or traumatic causes commonly complain about urine Figure 2. Electromyographic activity of the internal urethral sphincter at rest (a), upon vaginal balloon distension with 50 (b), 100 (c), 150 (d), and 200 ml (e) of air.

5 1402 A. Shafik et al. Table II. Electromyographic activity of the internal urethral sphincter upon vesical balloon distension in increments of ml of air. Frequency (cpm) Amplitude (mv) Conduction velocity (cm/s) Latency (ms) Vaginal distension (ml) Mean Range Mean Range Mean Range Mean Range 0 (basal) * * * * * * ** *** *** *** * *** *** *** * 1722 Values are mean9sd. Cpm, cycles per minute. *p B0.05. **p ***p B0.01. leakage during coitus which interrupts the sexual act. Concern may be raised regarding the concept that penile thrusting equates with vaginal distension. During penile thrusting, the penis pushes its way into the vagina affecting its distension. Therefore, at coitus there is repeated vaginal distension resulting from repeated penile thrusting. The current findings postulate the existence of a hitherto unrecognised relationship between vaginal balloon distension, on the one hand, and the UB and IUS on the other hand. The vesical pressure decrease and the increased IUS EMG upon vaginal distension affirm the hypothesis of the possible involvement of a reflex that we term vagino-vesicosphincteric reflex (VVSR). The constancy of this relationship is manifest from reproducibility, and its reflex nature is evidenced by its absence during individual anaesthetisation of the assumed two arms of the reflex arc, namely the vagina and the IUS with the UB. Lidocaine anaesthetisation blocks the C and A a-fibres which are responsible for pain and reflex activity (23,24). We suggest that this reflex is evoked on vaginal distension by the penis during coitus to prevent urine leakage. As already mentioned, it is suggested that bladder relaxation and increased tonus of urethral sphincters would act to prevent urine leakage during coitus. It may be argued that this action would only be useful if the reflex was maintained. However, it needs to be considered here that coitus involves repeated penile thrusting of the vagina with repeated vaginal distension during the period of coitus. The VVSR is, hence, repeatedly initiated by repeated vaginal distension, especially as the vesical musculature and the IUS consist of smooth muscle fibres which do not fatigue easily. The VVSR may prove of diagnostic significance in sexual act disorders. The diagnostic procedures for the diagnosis of these disorders are apparently scarce (19,25). Changes in the response of the vesical pressure or the IUS EMG to vaginal distension might indicate a defect in the reflex pathway, such as damage to the urethral sphincters or vesical musculature, or nerve damage from a disease of the spinal cord, spinal nerve roots or peripheral nerves, or from a cord lesion. The VVSR may be incorporated as an investigative tool in the diagnosis of micturition sexual disorders, provided further studies are performed. It may be argued that the VVSR represents the bulbocavernosus reflex (BCR). However, the mode of action of the two reflexes is completely different. The BCR comprised of perineal muscles contraction on manual compression of the glans clitoris (25). Meanwhile, the VVSR functions to effect vesical relaxation and IUS contraction on vaginal distension. It needs to be mentioned that investigators seeking a non-pharmacological treatment for chronic urine incontinence, have studied related mechanisms. Intravaginal electrical stimulation was found to effect bladder inhibition and urethral closure, and was suggested to be used with some success as a treatment for urine incontinence due to detrusor instability, stress incontinence and lower motor lesions (2628). However, a recent study has questioned the effectiveness of intravaginal electrical stimulation in the treatment of mixed urinary incontinence (29). A possible limitation of the study is the question of whether the inflated condom is a suitable and adequate simulator of penile thrusting. Meanwhile, vaginal distension occurs during and is an essential part of penile thrusting, and the rationale of the study was to investigate the effect of vaginal distension on the vesical pressure and the EUS and IUS EMG activity. In conclusion, vaginal distension by the inflated condom, which presumably simulates the erect penis, seems to effect vesical wall relaxation and an

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