Dr GA Digesu, Via Bottalico 59, Bari 70124, Italy.
Objective This study determines whether the retrograde urethral retro-resistance pressure (URP) measurement discriminates between urodynamic diagnoses in a group of women.
Design A prospective observational study.
Setting Urogynaecology units of three tertiary referral teaching hospitals.
Population Women with lower urinary tract symptoms.
Methods Consecutive women attending the urodynamic clinics of three tertiary referral teaching hospitals were studied using a validated urinary symptom questionnaire, URP measurement and urodynamic evaluation between February and July 2004. The URP mean values were compared with urinary symptoms and urodynamic diagnoses, using the independent t test correction for multiple measurements.
Main outcome measures Retrograde URP, urodynamic diagnoses and urinary symptoms.
Results One hundred and eighty-five women were recruited. Women with urodynamic stress incontinence (USI) have significantly lower URP than women with competent urethral sphincters (P < 0.05, independent t test). Women with mixed urodynamic incontinence had values of URP intermediate between women with detrusor overactivity (DOA) and those with USI. In the mixed group, URP mean values were not significantly different from those with DOA and competent sphincters or USI (P > 0.05, independent t test). There was no significant difference between mean URP values and different urinary symptoms (P > 0.05, independent t test).
Conclusions There are significantly different URP measurements between women with DOA and those with USI. However, the URP is not a diagnostic tool.
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The existing tests to assess the urethral function of patients with lower urinary tract function are poor. They include urethral pressure profilometry,1 leak point pressures,2,3 pressure flow studies4–7 and ultrasound assessment of the urethral sphincter.8,9 All these techniques, apart from ultrasound assessment (which requires expert personnel and specialised equipment) require catheterisation that carries attendant morbidity,10–19 including urinary tract infections20–26 and pain or dysuria.22,23 The presence of a urethral catheter or transducer is inherently non-physiological and may affect interpretation of the test result.
Retrograde urethral pressure measurement has been previously described as a useful method to assess urethral function.27–29 Ulmsten recently revived this concept and introduced the term urethral retro-resistance pressure (URP). The URP is defined as the pressure required to achieve and maintain an open urethral sphincter at rest and is obtained by the infusion of sterile fluid along the urethra into the bladder.30 The technique avoids catheterisation and may produce fewer artefacts and be less uncomfortable for the patient. However, the data on the usefulness of this test are limited. A recent study in women with stress urinary incontinence demonstrated a significant correlation between URP and incontinence severity, suggesting that this parameter was a useful diagnostic tool to measure urethral function.30 The reliability and reproducibility of the measurement have been demonstrated in asymptomatic women.31 However, the role of URP in routine urodynamic practice is still unclear. There are no data that look at URP measurement in an unselected population, and the relationship of URP to different urodynamic diagnoses has never been evaluated. Therefore, the aim of our study was to assess whether the URP measurement discriminates between urodynamic diagnoses.
Local ethical committee approval was obtained at each centre and each woman signed an informed consent form to the study. Women referred to tertiary urogynaecology clinics with lower urinary tract symptoms were eligible to participate. Women with neurogenic detrusor overactivity (DOA), previous continence procedures, bladder outlet obstruction and infection were excluded from the study. On referral all women were sent a validated urinary symptom questionnaire32 and a frequency volume chart, which they completed prior to their first appointment. All women underwent a clinical evaluation including complete history, vaginal examination and were investigated with saline cystometry using a standard protocol. Each woman was asked to attend for urodynamic studies with a comfortably full bladder. Uroflowmetry was performed with the woman voiding in private and recorded with a gravimetric flow-meter, urinalysis was then performed. Women with positive urine analysis were excluded and a midstream urine sample (MSU) was sent for microscopy, culture and sensitivity. Following uroflowmetry, the post-micturition residual was measured using a transabdominal ultrasound scan.33 The URP was then measured with woman relaxed in a supine position and an empty bladder by placing a 5-mm cone-shaped plug into the external urethral meatus as previously described by Slack et al.30 The device infused sterile fluid in a retrograde fashion through the urethra at a controlled rate of 1 mL/second (Monitorr, Gynecare, Ethichon, Somerville, New Jersey, USA). The pressure required to open the urethral sphincter is displayed on a screen and the URP measurement is recorded once the pressure stabilised as shown by a plateau on the screen. The test was repeated three times in each woman and the device automatically calculated the mean value.
Finally, saline cystometry was performed by a second investigator blinded to the URP measurement. A 12F (French gauge) urethral filling catheter was inserted and the post-micturition residual measured. Fluid filled catheters of 3.5F (French gauge) and 4.5F were used to measure the intravesical and rectal pressures. With the patient supine, the bladder was filled with room temperature saline solution at 100 mL/min until the women developed a strong desire to void or 600 mL had been infused into the bladder. Then the filling line was removed and provocative manoeuvres were carried out in a standing position: listening to running water, washing hands in cold water and asking the woman to cough with maximum effort. Finally, the woman was seated to void in private to perform a pressure-flow study.
Direct visualisation of involuntary urine loss in the absence of a detrusor contraction was required to make a diagnosis of urodynamic stress incontinence (USI). DOA was diagnosed if spontaneous or provoked involuntary detrusor contractions were seen during the filling phase. Where both DOA and USI were present the woman was deemed to have mixed incontinence. All terms, definitions are in accordance with the International Continence Society (ICS).18
Means and standard deviation for URP were established using an ANOVA test and these URP mean values were compared with symptoms as well as different urodynamic diagnoses, using the independent t test. This test was used to compare parametrically distributed continuous data, and statistical significance was assigned to a P value of less than 0.05. The 12.0 SPSS v 12.0 software (SPSS, Chicago, Illinois, USA) was used for the statistical analysis.
One hundred and eighty-five women were investigated between February and July 2004. The demographic characteristics of these women are shown in 1Table 1. Twenty-one women (11%) had positive urine culture before cystometry, and 17 women (9%) developed UTI after the urodynamic investigation. Seventy women (38%) had urinary frequency of at least 8/24 hours; 120 (65%) complained of urgency; 110 (60%) had urge incontinence; 133 (72%) had stress incontinence; 86 (46%) had mixed incontinence; and 71 (38%) had prolapse symptoms.
Table 1. Demographic characteristics. Values are presented as mean [SD] or median (range)
Total patients (no.)
Body mass index
Premenopausal, n (%)
Postmenopausal, n (%)
Years since menopause
The urodynamic diagnoses obtained and the mean URP measurement for women with each diagnosis are shown in 1, 2Table 2 and Fig. 1. All URP data were normally distributed (Kolmogorov-Smirnov test, P < 0.05). There were significant differences in URP measurements among women with different diagnoses, with mean URP higher in women with DOA and lower in women with USI. There was no significant difference between mean URP values and different urinary symptoms (3Table 3).
Table 2. URP and urodynamic diagnosis. URP data are mean [SD] and are expressed in cm/H2O. Significant differences between mixed urodynamic incontinence and USI, DOA and USI, normal urodynamic study and USI P < 0.05, independent t test
Mixed urodynamic incontinence
Normal urodynamic study
Table 3. Comparison between URP and different urinary symptoms. URP mean [SD] are expressed in cm/H2O
Our study is the first to examine URP in women with different urinary symptoms and urodynamic diagnoses. Our data showed that URP measurements are significantly lower in women with USI than those who have DOA and competent urethral sphincters, suggesting a reduced urethral outlet resistance. This is consistent with previous studies that have shown lower opening detrusor pressures during voiding in women with USI.34 Women with DOA had URP values significantly higher than those with USI and this is consistent with the increased volume of striated muscle found to encircle the urethra imaged with 3D volume ultrasound,35 which leads to increased detrusor pressure during voiding.34
Conventional tests such as urethral pressure profilometry, leak point pressures and urodynamics are of limited use for assessment of urethral function.14,15,36–38 The concept of retrograde urethral pressure has been explored previously.27–29,39 Urethral competence is related in part to efficient urethral coaptation, which is related to the physiological properties of the urethral mucosa and submucosa. The urethral lumen is kept closed by a combination of passive, intramural and periurethral forces. The active closure forces have been investigated by measuring the tissue resistance to rapid dilatation of the urethra. In the storage phase, the ‘critical pressure’ required to overcome urethral resistance is greater than the sustained urethral resistance to constant flow,40 this is consistent with an active mechanism producing increasing closure with bladder filling.
A difference in urethral closure pressure has been found following manual inflation of a urethral balloon and this difference is higher in continent women rather than women with stress incontinence.41 Thind et al.42 measured the urethral response to rapid balloon dilations. They found that there was an initial stress relaxation effect with a peak pressure followed by a pressure decay over a few seconds. Rapid urethral dilations were performed by a balloon mounted on a double tip transducer catheter for simultaneous measurement of pressure in the urethral and the bladder. The peak pressure response to dilatations represents the bladder pressure required to open the specific urethral segment. All along the urethra the increase in pressure response was statistically significant with increasing rate and size of dilatation. These findings were thought to be due to the integrated response of the urethra to stretching of its anatomic structures.42 The URP decreases with increasing age and with years after the menopause, which are known risk factors associated with declining urethral function.30
Although urodynamics remains the ‘gold standard’ test43 in the assessment and management of women with LUTS, particularly prior to continence surgery to exclude DOA or voiding difficulties, the URP appears to be useful tool for the evaluation of urethral function at rest, but it is poor in its diagnostic discrimination. This test is useful for a scientific evaluation of the urethra as it measures different aspects of the urethral function at rest from the urethral pressure profile.
Although the URP cannot replace urodynamic studies prior to surgery, assessing the urethral function with URP may be considered before initiating conservative therapies such as physiotherapy. This measurement could direct treatment and predict the outcome of continence surgery, although further work is required in the evaluation of this new investigation and its clinical role in the assessment of the incontinent patient.▮