Heinz Koelbl led the peer-review process as the Associate Editor responsible for the paper.
The impact of tension-free vaginal tape on the urethral closure function: Mechanism of action
Article first published online: 8 NOV 2013
© 2013 Wiley Periodicals, Inc.
Neurourology and Urodynamics
Volume 34, Issue 1, pages 50–54, January 2015
How to Cite
Saaby, M.-L., Klarskov, N. and Lose, G. (2015), The impact of tension-free vaginal tape on the urethral closure function: Mechanism of action. Neurourol. Urodyn., 34: 50–54. doi: 10.1002/nau.22513
Conflict of interest: Gunnar Lose—Research cooperation with Coloplast under grant from Advanced Technology Foundation.
- Issue published online: 12 DEC 2014
- Article first published online: 8 NOV 2013
- Manuscript Accepted: 25 SEP 2013
- Manuscript Received: 27 JUN 2013
- closure function;
- closure mechanism;
- intra-abdominal pressure increase;
- pressure reflectometry;
- tension-free vaginal tape;
- urinary incontinence;
To investigate if the tension-free vaginal tape (TVT) works by increasing the abdominal to urethral pressure impact ratio (APIR).
Twenty one women with urodynamically proven stress urinary incontinence (SUI) were assessed by ICIQ-SF, pad-weighing test, incontinence diary and Urethral Pressure Reflectometry (UPR) before and after TVT. UPR was conducted during resting and increased intra-abdominal pressure (PAbd) by straining. Related values of PAbd and urethral opening pressure (Po) were plotted into an abdomino-urethral pressuregram. Linear regression of the values was conducted, and the slope of the line was found. The slope expresses the ratio of pressure increase in the urethra compared to the pressure increase in the abdomen and was called APIR.
The urethral opening pressure at rest (Po-rest) was unchanged after TVT, while APIR increased in all women (from 0.7 to 1.4, P < 0.0001).
The TVT seems to strengthen the urethral closure function by increasing the APIR while Po-rest is unchanged regardless of the type of pre-operative dysfunction. This confirms the theory of TVT's mechanism of action being mid-urethral support. Neurourol. Urodynam. 34:50–54, 2015. © 2013 Wiley Periodicals, Inc.
Stress urinary incontinence (SUI) occurs when the bladder pressure exceeds the urethral pressure on effort or exertion or on sneezing or coughing and depends on the efficiency of the urethral closure function and the pressure to which it is subjected.
The urethral closure mechanism has been described anatomically consisting of a sphincteric unit and a support system.
Urodynamically, the urethral closure function has been characterized by means of the permanent and the adjunctive closure forces. The permanent closure forces, primarily generated by the urethral sphincteric unit, can be assessed by the resting urethral opening pressure (Po-rest).[4, 5] The adjunctive closure forces superposed during intra-abdominal pressure increase, suggested primarily to be generated by the support system, has previously been measured as the “pressure transmission ratio (PTR).”[6-10] However, the PTR has very poor reproducibility and has never shown to be clinical relevant. The term is, in addition, confusing as pressure does not transmit. Therefore a new method for measuring the adjunctive closure forces has been developed. The method is called the abdominal to urethral pressure impact ratio (APIR). APIR expresses the ratio of pressure increase in the high pressure zone of urethra (HPZ) compared to the increase in intra-abdominal pressure and is measured with Urethral Pressure Reflectometry (UPR).
The dysfunctional basis of SUI is suggested principally to be urethral sphincter deficiency and/or urethral hypermobility (due to deterioration of urethral support). Correspondingly, recent results have shown that Po-rest and APIR differ statistically significantly between SUI and continent women, and the urethral closure function can be insufficient due to deteriorated Po-rest and/or APIR.
The impact of TVT on the urethral opening pressure during intra-abdominal pressure increase is ambiguous. MUCP has shown to be unchanged after TVT,[7-9, 13] hence the empirically shown effect of TVT might be caused by increased APIR subsequent to the urethral support, which could explain the mechanism of action behind the procedure.
The aim of this study was to investigate if the TVT works by increasing the APIR.
MATERIALS AND METHODS
Women with bothersome urodynamically proven SUI and scheduled for TVT were consecutively recruited via the outpatient clinic.
Subjects were excluded if they had pelvic organ prolapse (POP) stage 2 or greater, previous surgery for SUI or POP, hysterectomy within the last year before enrolment, detrusor overactivity on filling cystometry, intake of anti-muscarinic drugs within the last 3 months, overt neurological diseases, signs of lower urinary tract infection on urine dipstick, or were pregnant.
In addition to the UPR measurements, the pre- and postoperative assessment included a comprehensive medical history, the International Consultation on Incontinence Questionnaire Short Form (ICIQ-SF), pelvic examination, uroflowmetry, measurement of post-void residual urine volume (PVR), cough stress test, urine analysis, pad-weighing test (2 × 24 hr), bladder diary (2 days), incontinence episode diary (7 days), and 3D and 4D ultrasound. Cystometry was performed at enrolment if not previously conducted within the 3 months before enrolment.
Cough stress test (five forceful coughs) was carried out in the standing position after insertion of 150 ml of saline to the bladder via a catheter (10 F).
Filling cystometry (Duet Logic, Mediwatch, Rugby, UK or MMS Solar Gold, MEQ, Enschede, The Netherlands) was undertaken using two 5 F transurethral catheters, one for filling the bladder and one for pressure measurements, and a fluid filled rectal catheter for measurement of abdominal pressure. With the patient seated, saline was infused at a medium filling rate (50 ml/min), and the diagnosis of urodynamic stress incontinence was based on the detection of urinary leakage during coughing in the absence of detrusor activity.
The 2-day bladder diary included records of incontinence episodes, liquid intake, the time of micturitions and voided volumes.
In the 7-day incontinence diary, the patient noted every incontinence episode in seven consecutive days.
3D and 4D perineal ultrasound (Voluson E8, GE Medical Systems, Zipf, Austria) was used as biofeedback to ensure straining without voluntary contraction of the pelvic floor muscles.
The UPR Measurements
The UPR equipment consists of a computer with an integrated pressure recorder which via a PVC tube is connected to a probe (containing an acoustic transmitter and a microphone), a 12 ml syringe and a polyurethane bag. The technique enables simultaneous measurement of pressure and cross-sectional area in the entire length of the urethra by use of the very thin and highly flexible polyurethane bag. It is reproducible, meets the requirements of investigation in a collapsible tube such as the urethra, and avoids the common artifacts encountered with conventional catheters. The urethral opening pressure can be obtained at a specific site of the urethra, for example the HPZ. The UPR enables measurement within 7 sec opposed to conventional techniques which require several minutes. This faster technique allows assessment during resting, squeezing and increased intra-abdominal pressure by straining (bearing down).
With the woman supine the polyurethane bag was inserted in the urethra as earlier described. Air was injected into the bag by the syringe thereby increasing the pressure and distending the bag. The cross-sectional area within the bag, and thus the urethra, was measured continuously with acoustic reflectometry, and the pressure needed just to open the collapsed urethra, the opening pressure (Po), was obtained. We only evaluated measurements from the HPZ of the urethra, defined as the position in the urethra where the cross-sectional area was smallest.
Measurements at rest
The woman was instructed to relax. The pressure in the polyurethane bag was raised from 0 cm H2O to 200 cm H2O within approximately 7 sec and the resting urethral opening pressure (Po-rest) was measured. Hereafter the pressure was decreased to 0 cm H2O.
Measurements during increased intra-abdominal pressure
The woman was instructed to increase the intra-abdominal pressure by straining 10 times at different intensities and keep the pressure for 7 sec. At each strain the pressure in the bag was raised from 0 cm H2O to 200 cm H2O within 7 sec and the urethral opening pressure measured. Hereafter the pressure was decreased to 0 cm H2O.
The abdominal pressure (PAbd) was simultaneously measured with an air filled catheter (T-dock, Wenonah, NJ) in the rectum.
The related values of Po and PAbd at the 10 different abdominal pressures were recorded and plotted into a HPZ abdomino-urethral pressuregram (Fig. 1). Linear regression of the values was conducted, and the slope of the line was found. The slope expresses the APIR. An APIR of 1 means that the pressure in the HPZ of the urethra increases exactly as much as the increase in the abdominal pressure. An APIR <1 means that the abdominal pressure increases more than the pressure in the HPZ, thus the subject will become incontinent if the abdominal pressure increases enough. The actual abdominal pressure at which the subject becomes incontinent depends on the Po-rest and the APIR. An APIR >1 means that the pressure in the HPZ increases more than the abdominal pressure and in this case the subject will not be stress incontinent even at very high abdominal pressures.
The TVT procedure (Gynecare, Division of Ethicon and Johnson & Johnson, Somerville, NJ) was carried out under local anesthesia with no concomitant surgical procedures using the technique described by Ulmsten et al.
Subjective “Cure” was defined as no reported stress incontinence on ICIQ-SF, “improvement” as ≥50% decrease in post-operative ICIQ-SF score, and “failure” as ≤50% decrease in post-operative score.
Objective “Cure” was defined as negative stress test and <5 g leakage on pad test, “improvement” as negative stress test and ≥5 g leakage on the pad test, and “failure” as leakage on stress test.
Prior to the study, power calculations showed that 21 patients were needed (power: 90%, two sided P-value 0.05) to detect a 10% difference in APIR.
Statistical analyses including the linear regressions were performed using the Microsoft Excel software (2007) (Microsoft, Redmond, WA). Data were tested with paired t-test, and statistical significance was determined at P ≤ 0.05.
The study was approved by The Committees on Biomedical Research Ethics for the Capital Region of Denmark (H-B-2008-002), and informed consent was obtained from all participants.
Included in the study were 22 patients who all gave informed consent and met for follow up measurement. One patient was excluded from analysis because of poor UPR tracing. Median age of the remaining 21 patients was 54 years (range: 38–69 years), median parity was 2 (range: 1–3), and median body mass index (BMI) was 28 (range: 20–36). All patients had delivered vaginally only, except one who had had no vaginal deliveries but one caesarean section. Two patients had undergone hysterectomy several years before study inclusion, and not on POP indication. 11 women were post menopausal. Topical estrogen therapy was established in four patients before surgical treatment was considered and continued throughout the study.
Median follow-up time was 167 days (range: 84–401 days). Median time between preoperative measurement and TVT was 49 days (range: 0–115 days).
Objectively and subjectively, all were cured of SUI, but four patients reported de novo urge incontinence. The number of incontinence episodes, ICIQ-SF-score, stress test and pad test all changed significantly after surgery (Table I).
|N = 21||Before TVT||After TVT||P-Value|
|Pad test (24 hr, g)||45.5||0.1||0.002|
|Incontinence (7 days, episodes)||24.6||0.4||<0.0001|
|Positive stress test (n)||21||0||<0.0001|
|Po-rest (cm H2O)||42 (8)||43 (9)||0.77|
|APIR||0.7 (0.2)||1.4 (0.4)||<0.0001|
Mean Po-rest was unchanged after TVT (42 cm H2O before, 43 cm H2O after, P = 0.77).
The combination of Po-rest and APIR before and after the TVT is shown in Figure 3.
Mean Po-rest was unchanged after TVT indicating that TVT has no effect on the permanent closure forces, which is consistent with previous reports of MUCP[7-9, 13] and with biomechanical statements.
APIR increased in all patients after TVT indicating that TVT strengthens the adjunctive closure forces. Previously the urethral pressure during intra-abdominal pressure increase has been assessed by PTR. Some investigators found an increased PTR after TVT,[6-8] while others did not.[9, 10] The heterogeneous results are not surprising as PTR has low reproducibility.
Regarding the adjunctive closure forces, Zacharin suggested “the suspensory mechanism” (a ligamentous complex including the pubo-urethral ligament) to limit the urethral mobility during stress-events by acting as a central fulcrum between the bladder and the external urethral meatus. Hence, when the bladder descends caudally during intra-abdominal pressure increases the urethra is subsequently compressed at its mid-point. Accordingly, dysfunctional mid-urethral support is supposed to cause decreased mid-urethral compression during stress and subsequently insufficient mid-urethral pressure increase (equivalent to APIR). Recently, dysfunctional mid-urethral support and subsequent mid-urethral hyper-mobility has been reported to be strongly associated to SUI.[19, 20]
The increase in APIR to values >1 means that the pressure increase in the urethra is more than 100% of the pressure increase in the abdomen. This can be explained by a muscle contraction or by a passive gearing of the abdominal pressure, for example, a kink of the urethra.[12, 18] Kinking of the urethra after TVT due to decreased mid-urethral mobility has been revealed by ultrasound and MR in several reports.[6, 19-23]
SUI is due to low Po-rest or low APIR or a combination. However, TVT has no effect on Po-rest but increases APIR to levels of continent subjects or higher, thus TVT restores continence by an enhanced APIR which is then able to compensate for the low Po-rest. This is visualized in the scatter gram of related values of Po-rest and APIR before and after TVT (Fig. 3) which reveals a mere upward movement of the patients after TVT and not a diagonal movement towards the values of continent women.
In search for predictive factors for TVT failure, some investigators found a low urethral pressure predictive of failure,[8, 13, 24, 25] while others did not.[9, 22] Numerous found low urethral mobility to be predictive.[13, 22-25] To our knowledge there are no reports on PTR as predicting factor of failure after TVT.
In this study, we could not clarify the role of Po-rest or APIR as predicting factors because of lack of failures and the small study population. However, it does seem plausible that a certain low level of APIR could provide better effect of TVT.
The knowledge of the urethral dysfunction being caused by a decreased Po-rest or APIR, and of TVT's ability to induce increased APIR might improve gynecologists in tailoring the optimal treatment for a specific patient; however studies are needed on how other anti-incontinence treatments achieve a strengthened urethral closure function.
Some limitations of this study are acknowledged. First, we measured urethral opening pressure during intra-abdominal pressure increase by straining well aware that leakage often occurs during faster pressure increases such as coughs. However, the urethral closure mechanism is very complex and so far our technique does not allow reliable measurement during such complicated stress events as a cough. Second, results were shown for measurement in the supine position.
The UPR equipment provided advantages compared to conventional techniques: the polyurethane bag ensured luminal pressure measurement, measured the entire length of the urethra simultaneously, was highly flexible and allowed kinking of the urethra. Hence the technique met the requirements of measurements in a collapsible tube and avoided the artifacts commonly encountered with conventional techniques.
APIR increased in all patients after TVT while Po-rest was unchanged regardless of the type of pre-operative dysfunction.
The results indicate that the TVT improves the urethral closure function predominantly by increasing the APIR. This supports the concept of characterizing the urethral closure function by the permanent closure forces, Po-rest, and adjunctive closure forces, APIR. In addition, the results confirm the theory of TVT's mechanism of action being mid-urethral support.
- 3Dynamic testing. In: Abrams P, Cardozo L, Khoury S, Wein A, ediors. Incontinence. 3rd edition. Plymouth, UK: Health Publications; 2005. p. 585–675., , , et al.
- 5Urethral pressure reflectometry during intra-abdominal pressure increase-an improved technique to characterize the urethral closure function in continent and stress urinary incontinent women. Neurourol Urodyn 2013; 32:1103–8., , .