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ORIGINAL RESEARCH |
From the Department of Gynecology, Martin-Luther-University, Halle (Saale), Germany.
Address reprint requests to: Heinz Koelbl, MD, Department of Gynecology, Martin-Luther-University Halle-Wittenberg, 06097 Halle (Saale), Germany; E-mail: heinz.koelbl{at}medizin.unihalle.de.
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ABSTRACT |
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 ABSTRACT MATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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METHODS: A full urogynecologic assessment including conventional urodynamic measurements and a clinical stress test were carried out. Computer-assisted virtual urethral pressure profile uses conventional urethral pressure profile measurements during stress, with the only change being that withdrawal of the catheter is stopped at distinct points along the whole urethra while the patient coughs. Cough-related changes of maximal urethral closure pressure, functional urethral length, and area under the urethral closure pressure curve were determined.
RESULTS: Sixty-one women were enrolled in our study: 30 symptom-free women (group A) were continent, and genuine stress incontinence was present in 31 patients (group B) complaining of urinary loss. Significant differences between group A and group B women were found for all parameters of computer-assisted virtual urethral pressure profile including maximal urethral closure pressure (91.59 ± 39.00 versus 20.70 ± 22.61 cm H2O; P < .001), functional urethral length (31.81 ± 9.02 versus 10.83 ± 10.76 mm; P < .001), and the area under the urethral closure pressure curve (2036 ± 1025.29 versus 253 ± 206.69 cm H2O x mm; P < .001).
CONCLUSION: Computer-assisted virtual urethral pressure profile is a new application of urethral pressure profile measurements during stress. Our data show significant differences between continent women and patients with genuine stress incontinence. Further studies are needed to assess the potential of computer-assisted virtual urethral pressure profile for diagnosing genuine stress incontinence.
In 1962, Enhörning introduced the urethral pressure profile as a new method into the field of urodynamics.1 Principles and algorithm of interpretation have not changed since then, even though electronic transducers and computer-assisted urodynamics have been introduced into clinical practice for registration and analysis of urethral pressure profile measurements. The procedure itself has been standardized by the International Continence Society requiring exact description of patient position, bladder volume, placement and direction of the transducer, and velocity of catheter withdrawal.2 However, urethral pressure profile measurements have distinct limits. A big overlap of urethral pressure profile measurements at rest between continent and stress incontinent women has been demonstrated previously, and thus the clinical validity of this procedure to assess genuine stress incontinence still remains a matter of debate.2,3 The term "hypotonic urethra" is defined when the urethral closure pressure (Pclo) does not exceed 20 cm H2O, but this is an arbitrary cutoff value. In these patients, an increased risk of recurrent genuine stress incontinence has been observed after anti-incontinence surgery, such as the Burch colposuspension.4
Urethral pressure profile measurements during stress are a matter of an even more controversial discussion. To date, exact identification of patients with genuine stress incontinence by conclusive evaluation of the urethral pressure profile during stress was impossible. Moreover, a sensitivity of 93.3% and specificity of 82.5% of the urethral pressure profile during stress have been observed in a previous study of 911 patients with clinically demonstrable genuine stress incontinence.5 A clinical stress test or pad test with direct vision of urinary loss through the urethra remains the gold standard so far.
Many factors may influence urethral pressure profile measurements during stress. Patient position, extent of the Valsalva or coughing maneuver, transducer position, and bladder volume are some of the many variables responsible for the outcome of the investigation. The force of the cough impulse and the resulting intravesical pressure (Pves) cannot be standardized unless simultaneous abdominal pressure is evaluated. Repetitive coughing may vary, and thus again influences the outcome of measurements. Moreover, movements of the pelvic floor with the urethra against the transurethral catheter carrying the measuring transducer may influence urethral pressure profile measurements contributing to reduced reproducibility.
As a consequence, urethral pressure profile measurements at rest and during stress are helpful to identify urethral occlusive forces either by extrinsic or intrinsic factors. However, without other tests, these techniques have remained unreliable to identify genuine stress incontinence.
Because of these findings, there definitely is a need for a more sensitive urodynamic method to assess the urethral competence mechanism in continent women and patients with genuine stress incontinence. We developed an alternative method for analysis of the urethral pressure profile under stress referred to as computer-assisted virtual urethral pressure profile. This method considers the aspects of the limited value of urethral pressure profile measurements during stress and takes advantage of the extensive mathematical possibilities of modern computer technology.
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MATERIALS AND METHODS |
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ABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Patients with genital prolapse, diabetes, neurologic disorders, residual bladder volumes (greater than 50 mL), urinary tract infections, or detrusor instabilities (increase in detrusor pressure to more than 15 cm H2O during filling cystometry, filling rate 90 mL per minute) were excluded from our study. Computer-assisted virtual urethral pressure profile uses the same parameters as those for conventional urethral pressure profile measurements during stress, with the only change being that withdrawal of the catheter is stopped at 3 mm increments on the catheter when the patient coughs.6 Three increasing and measurable forceful coughs at each catheter stop are requested (Figure 1
). As a consequence, three pairs of values of Pves and urethral pressure (Pura) are obtained, and Pura is determined by Pves. The value of Pves depends on the force of the cough impulse and is not reproducible. With the computer program Statgraphics (Manugistics Inc., Rockville, MD) and a self-produced software, a spline interpolation is performed. This is a mathematical method frequently used in modern techniques (eg, in medicine for calculation of computed tomography images).7–11 Virtual interim values are deduced from actually measured value pairs allowing to construct a graph containing all possible values of the independent variable (Pves in the presented model) and the corresponding ones for the dependent variable (Pura) within the span where a mathematical relationship exists in between the two. This allows selection of value pairs of Pves and Pura arbitrarily from those that have been measured as well as from those that have been calculated. The values of Pura to be expected with 0, 10, 20, 30, . . . , and 100 cm H2O of Pves can also be determined. This means that the "standardized cough impulses" have been created.
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).
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). In addition to functional urethral length and the maximal urethral closure pressure (Pclomax), the area under each curve is determined.
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Student t test for paired samples was used to compare the two groups. P < .05 was considered significant. All analyses were performed using the SPSS 8.0 Statistical Software package (SPSS Inc., Chicago, IL).
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RESULTS |
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. According to the results of our urogynecologic evaluation, we identified two groups of women. As was to be expected, no incontinence was present during urogynecologic investigation in 30 symptom-free women (group A). Genuine stress incontinence was present in 31 symptomatic patients (group B). No difference between group A and B patients was found for Pclo and for functional urethral length, measured during conventional urethral pressure profile at rest (Table 2).
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). Although in some incontinent women Pclomax may rise (two of 31) or functional urethral length does not shorten (five of 31), during computer-assisted virtual urethral pressure profile, the area under the urethral pressure profile curve always gets smaller with increasing Pves. |
DISCUSSION |
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Enhörning’s assumption that Pura must always exceed Pves to ascertain continence applies, strictly speaking, only for the undisturbed urethra.1 Registration under stress introduces additional methodological errors. The resting urethral pressure profile is taken as a baseline onto which the stress urethral pressure profile is being projected. Both parts of the resulting curve are then compared and analyzed mathematically to obtain transmission pressures. The two situations that are being compared—resting urethral pressure profile in between cough impulses and stress urethral pressure profile during coughing—are, however, completely different. Furthermore, it is impossible to standardize the rise of Pves during stress simulation. Relative movements in between the catheter and the urethra have an impact as well.13–15 Sequence and number of cough impulses are chosen arbitrarily. All this limits validity, accuracy, reliability, and reproducibility of the method.
How many cough impulses are needed to be evaluated? Which of these cough impulses are relevant for quantification—and even more basic identification—of incontinence? Why do several patients have a positive urethral closure pressure paralleling a positive clinical stress test under identical conditions? All these questions remain unanswered so far. On the other hand, we know that the urethral pressure profile under stress is well apt to evaluate urethral closure function.16 Only further refinement of the method and innovative interpretation of the results can lead to improvements. Computer-assisted virtual urethral pressure profile could bear such progress. All above listed methodological pitfalls are considered in this new method. In our study, the area under the curve seems to represent a highly significant parameter to confirm stress incontinence. This is a result of immediate relevance for urodynamic practice. However, the main advantage of computer-assisted virtual urethral pressure profile seems to be that new questions can be asked and answered. Especially when considering the paradigm of the urethral closure mechanism established by Papa Petros and Ulmsten,17,18 this opens aspects for further research.
Received June 12, 2001. Received in revised form September 13, 2001. Accepted September 24, 2001.
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REFERENCES |
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2. Abrams P, Blaivas JG, Stanton SL, Anderson JT. The standardization of terminology of lower urinary tract function recommended by the International Continence Society. Int Urogynecol J 1990;1:45–58.
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13. Schüssler B, Hesse U, Lentsch P, Anthuber C. Artefacts in urometry caused by marked genital prolapse. Neurourol Urodyn 1987;6:154–5.
14. Carey MP, Dwyer PL, Glenning PP. The sign of stress incontinence—Should we believe what we see? Aust N Z J Obstet Gynaecol 1997;37:436–9.[Medline]
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16. Eberhard J. Standardized measurement of urethral pressure with normal values in the diagnosis of stress incontinence. Geburtsh Frauenheilk 1986;46:145–50.
17. Papa Petros PE, Ulmsten U. An integral theory and its method for the diagnosis and management of female urinary incontinence. Scand J Urol Nephrol 1993;153:3–93.
18. Papa Petros PE, Ulmsten U. An anatomical classification—A new paradigm for management of urinary dysfunction in the female. Int Urogynecol J Pelvic Floor Dysfunct 1999;10:29–35.[Medline]
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