- Email: [email protected]
profilometry pressure transmission ratio determinations in stress-incontinent and stress-continent subjects
Dynamic urethral pressure I profilometry pressure transmission ratio determinations in stress-incontinent and stress-continent subjects Richard C. Bump, MD,a.b William E. Copeland, Jr., MD,b W. Glenn Hurt, MD," and J. Andrew Fantl, MD• Richmond, Virginia, and Columbus, Ohio Bladder-to-urethra pressure transmission ratios were calculated in each quarter (designated Q1 through Q4) of the dynamic urethral pressure profile in 110 subjects. Thirty-seven subjects had genuine stress urinary incontinence, whereas 73 were stress continent. Subjects with genuine stress incontinence had significantly lower mean (±SO) pressure transmission ratios in all four urethral quarters compared with stress-continent subjects: 71% ± 14% versus 94% ± 38% for 01 (p = 0.004), 69% ± 16% versus 101% ± 42% for Q2 (p = 0.00001), 79% ± 19% versus 113% ± 46% for Q3 (p = 0.0001), and 90% ± 22% versus 117% ± 36% for Q4 (p = 0.001). A pressure transmission ratio value <90% in the proximal half of the dynamic profile had a sensitivity of 97%, a specificity of 56%, an abnormal predictive value of 53%, and a normal predictive value of 97%. Calculation of pressure transmission ratios, as opposed to declaring the stress profile positive or negative based on whole urethra/bladder pressure equalization with stress, enhances the utility of the dynamic urethral pressure profile and allows quantification of one of the several variable in the equation of stress urinary incontinence. (AM J OssTET GYNECOL 1988;159:749-55.)
Key words: Pressure transmission, dynamic profile, stress incontinence
The symptom of stress urinary incontinence represents the involuntary and objectionable loss of urine from the urethra coincident with a physical action that causes an abrupt increase in intraabdominal pressure. However, the description of this symptom may not accurately reflect the pathophysiology of the individual patient's lower urinary tract dysfunction. For this reason, the International Continence Society has precisely defined the condition of genuine stress incontinence as the involuntary loss of urine that occurs when the intravesical pressure exceeds the maximum urethral pressure, in the absence of a detrusor contraction.' As emphasized by Hilton and Stanton; there are many interrelated variables in the complex equation of stress incontinence in women. These include the amplitude and stability of resting intraluminal urethral pressure, the level and stability of bladder pressure, the magnitude of intraabdominal pressure variations, the active stress response of urethral pressure, and anatomic and
From the Department of Obstetrics and Gynecology, The Medical College of Virginia/Virginia Commonwealth University," Richmond, and the Department of Obstetrics and Gynecology, The Ohio State University College of Medicine,b Columbus. Presented as Official Guest at the Fiftieth Annual Meeting of the South Atlantic Association of Obstetricians and Gynecologists, Palm Beach, Florida, january 10-13, 1988. Reprint requests: Dr. R. C. Bump, The Medical College of Virginia Hospitals, Box 34 MCV Station, Richmond, VA 23298.
neuromuscular determinants of pressure transmission to the bladder and urethra. Dynamic urethral pressure profilometry is a urodynamic technique that has been widely adopted to objectively demonstrate and document the International Continence Society diagnostic criteria for genuine stress incontinence. 2•6 The dynamic urethral pressure profile is accomplished while the patient coughs repeatedly during catheter withdrawal. It is interpreted by looking for pressure equalization between the bladder and the urethra in the absence of a detrusor contraction. Implicit in several previous studies is the concept that the dynamic profile virtually always shows pressure equalization throughout the urethra in every patient with genuine stress incontinence, and that it is thus a highly sensitive and specific test. 7 · 8 Two recent reports, however, have challenged the clinical accuracy of the dynamic profile in the diagnosis of genuine stress incontinence. 9 • 10 These have shown that, although the pressure equalization interpretation criterion is highly specific (92% to 100%) and has a high abnormal test predictive value (82% to 100%), it is insensitive (31% to 50%) and has a low normal test predictive value (52% to 58%). Richardson 9 emphasizes the diagnostic limitations of the dynamic profile imposed by this low preoperative sensitivity and also cautions against use of the test as the sole verification criterion for success of therapy.
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PTR(%)
tlp,,
=~
X 100
Calculated at C, C', C", C"'
AB = Functional Urethral Length C,C',C",C"' = Cough Spike Locations
AC/AB x 100 = } AC'/AB X 100 = AC"/AB X 100 AC"'/AB x 100
= =
Ps = Bladder Pressure Pu = Urethral Pressure
% of FUL with: 1 - 25 % = Ql 26-50% = Q2 51- 75% = Q3 76-100% = Q4
Puc = Urethral Closure Pressure PASD
=Abdominal Pressure
Fig. 1. Calculation of pressure transmission ratios and quarters of urethra from the dynamic urethral pressure profile. PTR, Pressure transmission ratio; FUL, functional urethral length.
It is possible, however, that the diagnostic inaccuracy of the dynamic profile is due to the interpretation criterion rather than to an inherent limitation of the technique per se. Some authors have looked at a quantitative interpretation rather than the qualitative pressure equalization interpretation of the dynamic profile. They have determined the efficiency with which intraabdominal pressure increases are transmitted to the bladder and urethra by calculating a bladder-to-urethra pressure transmission ratio at the instant of stress. 2 • 6 To date, there has been no evaluation of the utility and reliability of pressure transmission ratios calculated from dynamic profilometric data in the diagnosis of genuine stress incontinence. The purpose of the current study was to compare pressure transmission ratios, calculated from standardized dynamic urethral pressure profiles, in stress-continent and stress-incontinent women, all of whom had symptoms of lower urinary tract dysfunction. Furthermore, we attempted to determine a critical cutoff value for pressure transmission ratio and calculate its diagnostic accuracy in establishing or excluding the diagnosis of genuine stress incontinence in such a population.
Methods The study population represents 110 consecutive patients who came to the first author (R. C. B.) for evaluation of symptoms of lower urinary tract dysfunction at the Gynecologic Urodynamic Laboratory at either The Medical College of Virginia Hospitals (n = 73) or The Ohio State University Hospitals (n = 37). The women ranged in age from 19 to 77 years. All had negative (<100 cfu/ml) bacterial urine cultures before urodynamic evaluation and none had pyuria on the day of evaluation. A urologic history was obtained by use of a standardized questionnaire with extensive interview supplementation, after which a complete genito-
urinary physical examination and neurologic evaluation were performed. All subjects underwent a standardized urodynamic evaluation that included the following: simple uroftowmetry with postvoid residual urine volume measurement, retrograde provocative urethrocystometry, passive urethral pressure profilometry, urethroscopy, resting and stressed urethral axis determinations (Q-tip cotton swab test), direct visualization for fluid loss, and dynamic urethral pressure profilometry. Selected subjects also underwent external urethral sphincter electromyography and complex uroftowmetry. Dynamic urethral pressure profilometry was performed with the subject in a modified lithotomy, 45degree upright position, after retrograde infusion of 300 ml of normal saline solution at room temperature. Profiles were recorded by an 8-Fr dual-sensor microtip transducer catheter (Millar Instruments, Houston, Texas) with the urethral sensor toward the 3 o'clock position. The urethral transducer was withdn~wn from the bladder to the external urethral meatus at a speed of 0.5 mm/sec by a mechanical puller. The puller was positioned such that the direction of withdrawal was as close as possible to the axis of the urethra. The bladder pressure, abdominal pressure (rectal or vaginal), urethral pressure, and electronically subtracted urethral closure pressure were recorded on a multichannel urodynamic recorder with paper speed matched to the catheter withdrawal speed. During withdrawal the subject was asked to cough on command with maximum effort. An attempt was made to time cough commands so that a cough spike would be generated in each quarter of the functional urethral length. The pressure scale of the urodynamic recorder was set to capture the entire amplitude of each cough spike. The pressure transmission ratio for each cough was calculated by dividing the amplitude of the urethral
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pressure spike by the amplitude of the corresponding bladder pressure spike and multiplying the quotient by 100. The location of each cough spike was converted into a percentage of the urethral length by dividing the distance of the cough spike from the urodynamic bladder neck by the total functional urethral length and multiplying the quotient by 100. For purposes of analysis, cough spikes were assigned locations in the first, second, third, or fourth quarter of the urethra (designated Q1 through Q4 respectively). These measurements and calculations are demonstrated in Fig. 1. Genuine stress urinary incontinence was diagnosed in any subject who complained of the symptom of stress incontinence and who either had observable leakage produced by stress without concurrently demonstrable detrusor instability during urodynamic testing or who had a positive direct visualization test in the total absence of detrusor instability during immediately prior urethrocystometry. The result of the dynamic urethral pressure profile was not considered in making the diagnosis. Except as already noted, measurements and terms conform to the recommendations of the International Continence Society.' Data were analyzed for significance with the X2 test with the Yates correction or with a standard two-tailed t test. Sensitivity (fraction of subjects with genuine stress incontinence who have abnormal pressure transmission ratios), specificity (fraction of subjects with stress continence who have normal pressure transmission ratios), abnormal predictive value (fraction of subjects with abnormal pressure transmission ratios who have genuine stress incontinence), and normal predictive value (fraction of subjects with normal pressure transmission ratios who are stress continent) were determined by standard formulas.
Results Thirty-seven (34%) of the 110 subjects met the urodynamic criteria for genuine stress urinary incontinence. One subject with genuine stress incontinence had concurrent detrusor instability. Seventythree (66%) subjects did not meet the urodynamic criteria for genuine stress incontinence and are designated as stress continent. Of this group, 16 had detrusor instability, 16 had sensory urgency I urethral instability, 13 had symptoms and physical findings consistent with genuine stress incontinence but without loss observed during the testing session, 11 had thirddegree uterine or vaginal vault prolapse, and 17 had no filling phase urodynamic abnormality. Five subjects in the stress-continent group but none in the stressincontinent group had previously undergone a retropubic urethropexy. For some analyses, the stresscontinent group was divided into two subgroups; subgroup 1 included 57 subjects who neither had se-
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Table I. Comparison of stress-continent and stress-incontinent subjects Stress incontinent Stress continent (n = 37) (n = 73) p Value
Age (yr) Range Mean± SD Weight Range± SD Mean± SD Parity Range Mean± SD Hypoestrogenic
26-77 49 ± 12
19-77 46 ± 14
NS
102-253 178 ± 45
110-280 170 ± 38
NS
0-9 3.1 ± 2.0 14 (38%)
0-7 2.5 ± 1.7 20 (27%)
NS NS
vere prolapse nor had undergone prior urethropexy, whereas subgroup 2 included 16 stress-continent subjects with either severe prolapse (n = 11) or prior urethropexy (n = 5). This subgrouping was made because it is felt that subgroup 2 might have a unique stress continence mechanism, characterized by markedly elevated pressure transmission ratios, that might unduly bias pressure transmission ratio differences between subjects with genuine stress incontinence and those who were stress continent. The age, weight, parity, and hormonal status of the two groups are compared in Table I. Subjects were considered hypoestrogenic if they were postmenopausal or castrate, not receiving estrogen replacement, and had clinical evidence of vaginal atrophy. There were no significant differences between the groups with respect to any of these variables. Table II compares the results of passive urethral pressure profilometry and urethral axial mobility testing between the genuine stress incontinence group and the stress-continent group and subgroups. Whereas urethral length measurements showed no significant differences, maximum urethral closure pressure, and both axial mobility measurements did show significant differences. The genuine stress incontinence group had significantly lower pressure transmission ratios throughout the urethra compared with the stress-continent group (Table Ill). These differences remained significant when both stress-continent subgroups were compared separately with the genuine stress incontinence group. Table IV demonstrates that subjects with genuine stress incontinence were significantly more likely than stresscontinent subjects to have a pressure transmission ratio <90% in all quarters of the urethra. These differences were still highly significant when the genuine stress incontinence group was compared separately with the stress-continent subgroups. Although it was not uncommon for stress-continent subjects to have a pressure transmission ratio <90%, it was exceptionally uncommon for a subject with genuine stress incontinence not
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Table II. Comparison of passive urethral pressure profile and urethral axis testing Q-tip cotton swab
Stress incontinent p vs SC group p vs SC subgroup 1* p vs SC subgroup 2t Stress continent Subgroup 1* Subgroup 2t
N
FUL (em)
MUCP (em H 20)
Stress (degrees)
37
2.8 ± 0.6 NS NS NS 2.7 ± 0.5 2.9 ± 0.6 2.4 ± 0.6
52± 17 0.003 0.001 NS 67 ± 26 70 ± 27 59± 25
48 ± 26 0.001 0.0009 NS 30 ± 26 28 ± 25 34 ± 32
73 57 16
I
Excursion (degrees) 39 ± 22 0.0003 0.002 0.0008 23 ± 19 25 ± 19 17 ± 16
Data are the mean ± SD. FUL, Functional urethral length; MUCP, maximum urethral closed pressure; SC, stress continent. *Stress continent without severe prolapse or prior urethropexy. tStress continent with severe prolapse or prior retropubic urethropexy.
Table III. Comparison of pressure transmission ratios Pressure transmission ratio
Stress incontinent p vs SC group p vs SC subgroup 1* p vs SC subgroup 2t Stress continent Subgroup 1* Subgroup 2t
N
Ql (%)
37
71 ± 14 0.004 0.05 <0.0001 94 ± 38 84 ± 30 123 ± 42
73 57 16
I
Q2 (%) 69 ± 16 0.0001 0.0007 <0.0001 101 ± 42 90 ± 32 145 ± 44
I
Q3 (%) 79 ± 19 0.0001 0.0003 <0.0001 113 ± 46 103 ± 32 149 ± 63
l
Q4 (%) 90 ± 22 0.001 0.005 0.0005 117 ± 36 112 ± 33 134 ± 42
Data are the mean ± SD. SC, Stress continent. *Stress continent without severe prolapse or prior urethropexy. tStress continent with severe prolapse or prior retropubic urethropexy.
to have a pressure transmission ratio <90% (1 of 37) in the proximal three quarters of the urethra. Overall, the finding of a PTR <90% in the proximal half of the dynamic profile had a sensitivity of 97%, a specificity of 56%, an abnormal predictive value of 53%, and a normal predictive value of 98%, with a genuine stress incontinence prevalence rate of 34%. If stress-continent subgroup 2 subjects are eliminated from analysis, the sensitivity remains 97%, the specificity drops to 47%, and the abnormal and normal predictive values are essentially unchanged at 55% and 96%, respectively. Table V compares the diagnostic accuracy of a pressure transmission ratio <90% with that of a resting maximum urethral closure pressure <50 em H 20 and a Qtip cotton swab excursion >30 degrees in our study population. If 13 stress-continent subjects who had a strong history for stress incontinence, a stable detrusor on urethrocystometric examination, and an abnormal Q-tip cotton swab test but who did not demonstrate observable loss with stress during the single testing session were included in the genuine stress incontinence group, all of the differences in pressure transmission
ratios discussed in the preceding paragraph became even more significant. Furthermore, values for sensitivity, specificity, abnormal predictive value, and normal predictive value improved to 98%, 68%, 72%, and 98%, respectively.
Comment We have demonstrated that women with genuine stress urinary incontinence have significantly lower pressure transmission ratios calculated from a standardized dynamic urethral pressure profile than do stress-continent women with other types of lower urinary tract dysfunction. This finding is in agreement with the observations regarding pressure transmission to the bladder and urethra first made by Enhorning, 11 observations that many other authors have confirmed in the intervening 25 years. 2 • •-6 • 12 It also extends the observations made by Hilton and Stanton 2 in their 1983 report. They noted significant differences in pressure transmission ratios between subjects with genuine stress incontinence and a normal control population specifically recruited to exclude all types oflower urinary tract dysfunction. It is important to know that subjects with
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Table IV. Significance of pressure transmission ratios* <90% PTR <90%
In Ql p vs GSI In Q2 p vs GSI In Q3 p vs GSI In Q4 p vs GSI
group group group group
GSI group
SC group
SC subgroup 1
SC subgroup 2
24/26
21150 0.0001 26/68 <0.00001 21/70 <0.00001 8/42 0.01
19/37 0.002 26/54 <0.00001 20/54 0.0009 7/33 0.03
2/13 <0.00001 0114 <0.00001 l/ 16 <0.00001 l/9 NS
34/36 27/36 14/27
PTR, Pressure transmission ratio; GSI, genuine stress incontinence; SC, stress continence. *Not every subject had pressure transmission ratio determined in every quarter.
genuine stress incontinence differ significantly from stress-continent subjects with other types of dysfunction, because this is precisely the type of population that seeks out the urogynecologist for evaluation and treatment. Because our study population is an unselected consecutive series specifically seeking urogynecologic evaluation, it is valid to use our data to establish a tentative critical cutoff value for the pressure transmission ratio and to evaluate its diagnostic accuracy. Our critical cutoff value for pressure transmission ratio was determined after a comparison between 60%, 70%, 80%, and 90% revealed that 90% yielded the best diagnostic accuracy for our study popultion. Although this retrospective determination of diagnostic accuracy for a test value is the only way to arrive at a tentative critical value, prospective confirmation by ourselves and others is essential. The 90% value can be measured with confidence in its precision. It is consistent with the 95% cutoff suggested by Hilton and Stanton2 and the "< 100%'' reported by Beisland et a!. 12 When we compared the 90% pressure transmission ratio to a 50 em H 20 resting maximum urethral closure pressure and a 30-degree urethral axial excursion in our study population (Table V), we found that the latter two parameters were much less sensitive and had a much lower normal predictive value while having similar specificities and abnormal predictive values. If we compare the 90% pressure transmission ratio with the pressure equalization criterion of Richardson, 9 we see that the former is more sensitive (97% versus 31% to 41 %) and has a better normal predictive value (98% versus 57% to 58%), but is less specific (56% versus 92% to 93%) and has a lower abnormal predictive value (53% versus 82% to 86%). These differences reflect the fact that subjects with genuine stress incontinence virtually always have pressure transmission ratios <90% in the inner half of the urethra, but so do many stresscontinent subjects. In contrast, subjects with pressure equalization throughout the dynamic profile virtually always have genuine stress incontinence, but many subjects with genuine stress incontinence do not have whole urethra pressure equalization. Pressure trans-
Table V. Comparison of predicitve powers of critical cutoff values for pressure transmission ratio, maximum urethral closure pressure, and Q-tip cotton swab excursion in the diagnosis of stress incontinence Q-tip cotton Proximal half urethra PTR MUCP <50 swab excursion >30 degrees em H 20 <90%
Sensitivity Specificity Abnormal predictive value Normal predictive value
97% 56% 53%
38% 70% 39%
70% 66% 51%
98%
69%
81%
PTR, pressure transmission ratio; MUCP, maximum urethral closure pressure.
mission is but one variable in the equation of stress incontinence. If other variables such as maximum urethral closure pressure or the magnitude of intraabdominal pressure variations are favorable, continence can be maintained in the face of inefficient pressure transmission. Furthermore, it must be recognized that, like all laboratory testing procedures, the dynamic profile is confining and sets limits on some variables that may result in pressure equalization under other, less confining, circumstances. There are two potential biases in this study that we tried to assess. One was the inclusion of 16 subjects in the stress-continent group who had third-degree uterovaginal prolapse or who had had a previous successful retropubic urethropexy. These conditions likely share a unique stress continence mechanism that is typified by exaggerated pressure transmission ratios, 13• 14 a fact that would tend to overestimate differences between the genuine-stress-incontinent and stress-continent groups. When these 16 subjects were eliminated from analysis, the pressure transmission ratio differences between the groups remained significant and the diagnostic accuracy of the 90% cutoff value was essentially unchanged. The second potential bias was the inclusion of 13 subjects in the stress-continent group who had
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strong histories for pure genuine stress incontinence, a stable detrusor on urethrocystometric examination, and an abnormal Q-tip cotton swab test but who did not demonstrate observable loss with stress during the single testing session. It is likely that many of these subjects would have genuine stress incontinence under less confining circumstances, and their inclusion in the stress-continent group could bias results in either direction depending on whether their pressure transmission ratios were more like the other stress-continent subjects or more like subjects with genuine stress incontinence. Inclusion of these I3 subjects in the genuine stress incontinence group made all pressure transmission ratio differences between the genuine-stressincontinent and stress-continent groups more significant and improved the diagnostic accuracy of the 90% pressure transmission ratio cutoff value. We conclude that finding pressure transmission ratios >90% in the proximal urethra makes the diagnosis of genuine stress incontinence extremely unlikely. Although the finding of a pressure transmission ratio <90% does not establish the diagnosis of genuine stress incontinence, it does support that diagnosis in consort with other historic, physical, and urodynamic evidence. Finally, the pressure transmission ratio may become a useful urodynamic tool to quantify the severity of the transmission defect in an individual patient and to quantify the effects of surgical efforts to correct her stress incontinence. REFERENCES I. Committee on Standardisation of terminology, Hald T, chairman. The standardisation of terminology of lower urinary tract function. Glasgow: International Continence Society, 1984. 2. Hilton P, Stanton SL. Urethral pressure measurement by microtransducer: the results in symptom-free women and in those with genuine stress incontinence. Br 1 Obstet Gynaecol 1983;90:919-33. 3. Asmussen M, Ulmsten U. Simultaneous urethrocystometry and urethral pressure profile measurement with a new technique. Acta Obstet Gynecol Scand 1975;54: 385-6. 4. Bunne G, Obrink A. Urethral closure pressure with stress. A comparison between stress incontinent and continent women. Urol Res 1978;6:127-34. 5. Henriksson L, Andersson K-E, Ulmsten U. The urethral pressure profile in continent and stress incontinent women. Scand J Urol Nephrol 1979;13:5-10. 6. Fossberg E, Beisland HO. Incompetent urethral closure mechanism in females: experimental and clinical studies with special reference to diagnosis and classification. Urol Int 1982;37:34-41. 7. Bergman A, McCarthy TA. Urodynamic changes after successful operation for stress urinary incontinence. AM j 0BSTET GYNECOL 1983;147:325-6. 8. Bhatia NN, Ostergard DR. Urodynamics in women with stress urinary incontinence. Obstet Gynecol 1982;60: 552-9. 9. Richardson DA. Value of the cough pressure profile in the evaluation of patients with stress incontinence. AM 1 0BSTET GYNECOL 1986;155:808-11.
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10. Fant!JA, Hurt WG, Bump RC, Dunn lJ, Choi SC. Urethral axis and sphincteric function. AMJ OBSTET GYNECOL 1986;155:554-8. II. Enhorning G. Simultaneous recording of the intravesical and intraurethral pressure. Act Chir Scand 1961; 276(suppl): 1-68. 12. Beisland HO, Fossberg E, SanderS. Urodynamic studies before and after retropubic urethropexy for stress incontinence in females. Surg Gynecol Obstet 1982; 155:333-6. 13. Richardson DA, Bent AE, Ostergard DR. The effect of uterovaginal prolapse on urethrovesical pressure dynamics. AM j 0BSTET GYNECOL 1983;146:901-5. 14. Hertogs K, Stanton SL. Mechanism of urinary continence after colposuspension: barrier studies. Br J Obstet Gynaecoll985;92:ll84-8.
Discussion DR. WILLIS E. LANIER, Atlanta, Georgia (Official Guest). Urethral pressure profilometry measurements have been made and evaluated by various authors. However, the report by Dr. Bump and coworkers has taken a unique approach and has used these measurements as an adjunct to other evaluations, to help understand a given patient's lower urinary tract problem and perhaps help to predict the outcome of a surgical correction. Although other authors have not felt that the dynamic profile data should be used as the only criteria for successful surgery, these authors suggest that the associated inaccuracy may be due to the interpretation rather than to the technique itself. The purposes of the report-to compare pressure transmission ratios calculated from standardized dynamic urethral pressure profiles in stress-continent and stress-incontinent women, all of whom had symptoms of lower urinary tract dysfunctions, and to determine a critical cutoff value for pressure transmission ratios and calculate its diagnostic accuracy-were clearly stated. Their selection of patients was straightforward and did not seem skewed due to the fact that they used II 0 consecutive patients who sought evaluation of lower urinary tract dysfunction. They were careful to watch the groups for age, weight, parity, and anestrogenicity and were explicit in the definitions of the groups for genuine stress incontinence and stress continence, including a detailed urodynamic evaluation of each of the subjects. The report gives exact details of how the dynamic urethral pressure profilometric examination was carefully and meticulously performed and how the data were interpreted for the various quarters of the urethra. Careful correction for variables was carried out in the evaluation of the results. Their values for sensitivity, specificity, abnormal predictive value, and normal predictive value are discussed fairly. The authors list two potential biases: inclusion of subjects in the stress-continent group who had third-degree uterovaginal prolapse or who had had a previous successful retropubic urethropexy, and the inclusion of I3 subjects in the stress-continent group who had strong histories for pure genuine stress incontinence, a stable detrusor on urethrocystometric examination, and an
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abnormal Q-tip cotton swab test but who did not demonstrate loss with stress during the single testing session. Although the procedure has poor abnormal predictive value, the conclusion that a pressure transmission ratio <90% in the proximal half of the urethra does not establish the diagnosis of genuine stress incontinence, but that in co~unction with other urodynamic evaluations it may help in determining the degree of a patient's problem and possibly the response to surgery, gives us reason to consider this modality in the evaluation of our patients before surgery. An extension of this study to compare preoperative and postoperative values of this technique might help us to understand how and why certain procedures actually work. DR. FRANK C. GREISS, Winston-Salem, North Carolina. I remember coming up through the ranks and having an excellent summation in what was then known about continence- I guess that information is now 30 to 35 years old. I think there was little clear understanding of bladder function then. We have become tremendously more sophisticated over the subsequent three or four generations, but as I listened to this report, I was a little unclear as to what real progress we have made. Dr. Henry Thiede' last year gave an excellent presentation, but had no real measure of what fraction of patients that have incontinence had been filtered out and what fraction he was seeing for further evaluation. When do you think the fancy examination methods of today are necessary for the evaluation of the incontinent patient? REFERENCE 1. Thiede HA. U rogynecology: comments and caveats. AM J 0BSTET GYNECOL 1987;157:563.
DR. BuMP (Closing). Dr. Greiss, I usually spend about 3 hours answering that question. I think we have made
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755
some progress. If you look at the success of continence surgical procedures, there is a distressing failure rate, even in the best of hands, of 10% to 15%. There is a distressing complication rate (mainly urgency instability syndromes) in another 10% to 15% of subjects in carefully done studies. When we start out to cure stress incontinence, we may end up with only 50% to 60% of the patients happy with the effects of their surgery. The people who I think need to be studied are certainly people who have obvious symptoms of instabilitybedwetting, urgency incontinence, and the like. I think another important group we are beginning to appreciate are elderly patients. I do not know what "elderly" is, but certainly if a patient appears to be elderly, I think she needs to undergo thorough study. Patients with previous failed continence surgery also deserve sophisticated studies. Pressure transmission allows us to quantitate the functional effects of anatomic defects. I think the woman who has a pressure transmission ratio of 95%, has a closure pressure of only 15 to 20 em H 2 0, and loses urine when she coughs has stress incontinence by the strict definition of the term. Nonetheless, she is much different than the woman who has a 70 em H 20 closure pressure and only transmits pressure at 30% efficiency. The problem in the latter patient is very easy to cure surgically. It is the condition in the former patient that is very difficult to cure surgically without creating obstructive symptoms and voiding dysfunction afterward. The main aim of this report was to substantiate the validity of the pressure transmission value in the type of patients who come to see us. Stuart Stanton has documented this in an incontinent patient versus a normal asymptomatic control, but I do not evaluate any normal asymptomatic controls. We think that the pressure transmission ratio is valid in that circumstance, and now we are using it to evaluate the effects of our surgery. It seems to be very promising in this respect.
Key words: Pressure transmission, dynamic profile, stress incontinence
The symptom of stress urinary incontinence represents the involuntary and objectionable loss of urine from the urethra coincident with a physical action that causes an abrupt increase in intraabdominal pressure. However, the description of this symptom may not accurately reflect the pathophysiology of the individual patient's lower urinary tract dysfunction. For this reason, the International Continence Society has precisely defined the condition of genuine stress incontinence as the involuntary loss of urine that occurs when the intravesical pressure exceeds the maximum urethral pressure, in the absence of a detrusor contraction.' As emphasized by Hilton and Stanton; there are many interrelated variables in the complex equation of stress incontinence in women. These include the amplitude and stability of resting intraluminal urethral pressure, the level and stability of bladder pressure, the magnitude of intraabdominal pressure variations, the active stress response of urethral pressure, and anatomic and
From the Department of Obstetrics and Gynecology, The Medical College of Virginia/Virginia Commonwealth University," Richmond, and the Department of Obstetrics and Gynecology, The Ohio State University College of Medicine,b Columbus. Presented as Official Guest at the Fiftieth Annual Meeting of the South Atlantic Association of Obstetricians and Gynecologists, Palm Beach, Florida, january 10-13, 1988. Reprint requests: Dr. R. C. Bump, The Medical College of Virginia Hospitals, Box 34 MCV Station, Richmond, VA 23298.
neuromuscular determinants of pressure transmission to the bladder and urethra. Dynamic urethral pressure profilometry is a urodynamic technique that has been widely adopted to objectively demonstrate and document the International Continence Society diagnostic criteria for genuine stress incontinence. 2•6 The dynamic urethral pressure profile is accomplished while the patient coughs repeatedly during catheter withdrawal. It is interpreted by looking for pressure equalization between the bladder and the urethra in the absence of a detrusor contraction. Implicit in several previous studies is the concept that the dynamic profile virtually always shows pressure equalization throughout the urethra in every patient with genuine stress incontinence, and that it is thus a highly sensitive and specific test. 7 · 8 Two recent reports, however, have challenged the clinical accuracy of the dynamic profile in the diagnosis of genuine stress incontinence. 9 • 10 These have shown that, although the pressure equalization interpretation criterion is highly specific (92% to 100%) and has a high abnormal test predictive value (82% to 100%), it is insensitive (31% to 50%) and has a low normal test predictive value (52% to 58%). Richardson 9 emphasizes the diagnostic limitations of the dynamic profile imposed by this low preoperative sensitivity and also cautions against use of the test as the sole verification criterion for success of therapy.
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PTR(%)
tlp,,
=~
X 100
Calculated at C, C', C", C"'
AB = Functional Urethral Length C,C',C",C"' = Cough Spike Locations
AC/AB x 100 = } AC'/AB X 100 = AC"/AB X 100 AC"'/AB x 100
= =
Ps = Bladder Pressure Pu = Urethral Pressure
% of FUL with: 1 - 25 % = Ql 26-50% = Q2 51- 75% = Q3 76-100% = Q4
Puc = Urethral Closure Pressure PASD
=Abdominal Pressure
Fig. 1. Calculation of pressure transmission ratios and quarters of urethra from the dynamic urethral pressure profile. PTR, Pressure transmission ratio; FUL, functional urethral length.
It is possible, however, that the diagnostic inaccuracy of the dynamic profile is due to the interpretation criterion rather than to an inherent limitation of the technique per se. Some authors have looked at a quantitative interpretation rather than the qualitative pressure equalization interpretation of the dynamic profile. They have determined the efficiency with which intraabdominal pressure increases are transmitted to the bladder and urethra by calculating a bladder-to-urethra pressure transmission ratio at the instant of stress. 2 • 6 To date, there has been no evaluation of the utility and reliability of pressure transmission ratios calculated from dynamic profilometric data in the diagnosis of genuine stress incontinence. The purpose of the current study was to compare pressure transmission ratios, calculated from standardized dynamic urethral pressure profiles, in stress-continent and stress-incontinent women, all of whom had symptoms of lower urinary tract dysfunction. Furthermore, we attempted to determine a critical cutoff value for pressure transmission ratio and calculate its diagnostic accuracy in establishing or excluding the diagnosis of genuine stress incontinence in such a population.
Methods The study population represents 110 consecutive patients who came to the first author (R. C. B.) for evaluation of symptoms of lower urinary tract dysfunction at the Gynecologic Urodynamic Laboratory at either The Medical College of Virginia Hospitals (n = 73) or The Ohio State University Hospitals (n = 37). The women ranged in age from 19 to 77 years. All had negative (<100 cfu/ml) bacterial urine cultures before urodynamic evaluation and none had pyuria on the day of evaluation. A urologic history was obtained by use of a standardized questionnaire with extensive interview supplementation, after which a complete genito-
urinary physical examination and neurologic evaluation were performed. All subjects underwent a standardized urodynamic evaluation that included the following: simple uroftowmetry with postvoid residual urine volume measurement, retrograde provocative urethrocystometry, passive urethral pressure profilometry, urethroscopy, resting and stressed urethral axis determinations (Q-tip cotton swab test), direct visualization for fluid loss, and dynamic urethral pressure profilometry. Selected subjects also underwent external urethral sphincter electromyography and complex uroftowmetry. Dynamic urethral pressure profilometry was performed with the subject in a modified lithotomy, 45degree upright position, after retrograde infusion of 300 ml of normal saline solution at room temperature. Profiles were recorded by an 8-Fr dual-sensor microtip transducer catheter (Millar Instruments, Houston, Texas) with the urethral sensor toward the 3 o'clock position. The urethral transducer was withdn~wn from the bladder to the external urethral meatus at a speed of 0.5 mm/sec by a mechanical puller. The puller was positioned such that the direction of withdrawal was as close as possible to the axis of the urethra. The bladder pressure, abdominal pressure (rectal or vaginal), urethral pressure, and electronically subtracted urethral closure pressure were recorded on a multichannel urodynamic recorder with paper speed matched to the catheter withdrawal speed. During withdrawal the subject was asked to cough on command with maximum effort. An attempt was made to time cough commands so that a cough spike would be generated in each quarter of the functional urethral length. The pressure scale of the urodynamic recorder was set to capture the entire amplitude of each cough spike. The pressure transmission ratio for each cough was calculated by dividing the amplitude of the urethral
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pressure spike by the amplitude of the corresponding bladder pressure spike and multiplying the quotient by 100. The location of each cough spike was converted into a percentage of the urethral length by dividing the distance of the cough spike from the urodynamic bladder neck by the total functional urethral length and multiplying the quotient by 100. For purposes of analysis, cough spikes were assigned locations in the first, second, third, or fourth quarter of the urethra (designated Q1 through Q4 respectively). These measurements and calculations are demonstrated in Fig. 1. Genuine stress urinary incontinence was diagnosed in any subject who complained of the symptom of stress incontinence and who either had observable leakage produced by stress without concurrently demonstrable detrusor instability during urodynamic testing or who had a positive direct visualization test in the total absence of detrusor instability during immediately prior urethrocystometry. The result of the dynamic urethral pressure profile was not considered in making the diagnosis. Except as already noted, measurements and terms conform to the recommendations of the International Continence Society.' Data were analyzed for significance with the X2 test with the Yates correction or with a standard two-tailed t test. Sensitivity (fraction of subjects with genuine stress incontinence who have abnormal pressure transmission ratios), specificity (fraction of subjects with stress continence who have normal pressure transmission ratios), abnormal predictive value (fraction of subjects with abnormal pressure transmission ratios who have genuine stress incontinence), and normal predictive value (fraction of subjects with normal pressure transmission ratios who are stress continent) were determined by standard formulas.
Results Thirty-seven (34%) of the 110 subjects met the urodynamic criteria for genuine stress urinary incontinence. One subject with genuine stress incontinence had concurrent detrusor instability. Seventythree (66%) subjects did not meet the urodynamic criteria for genuine stress incontinence and are designated as stress continent. Of this group, 16 had detrusor instability, 16 had sensory urgency I urethral instability, 13 had symptoms and physical findings consistent with genuine stress incontinence but without loss observed during the testing session, 11 had thirddegree uterine or vaginal vault prolapse, and 17 had no filling phase urodynamic abnormality. Five subjects in the stress-continent group but none in the stressincontinent group had previously undergone a retropubic urethropexy. For some analyses, the stresscontinent group was divided into two subgroups; subgroup 1 included 57 subjects who neither had se-
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Table I. Comparison of stress-continent and stress-incontinent subjects Stress incontinent Stress continent (n = 37) (n = 73) p Value
Age (yr) Range Mean± SD Weight Range± SD Mean± SD Parity Range Mean± SD Hypoestrogenic
26-77 49 ± 12
19-77 46 ± 14
NS
102-253 178 ± 45
110-280 170 ± 38
NS
0-9 3.1 ± 2.0 14 (38%)
0-7 2.5 ± 1.7 20 (27%)
NS NS
vere prolapse nor had undergone prior urethropexy, whereas subgroup 2 included 16 stress-continent subjects with either severe prolapse (n = 11) or prior urethropexy (n = 5). This subgrouping was made because it is felt that subgroup 2 might have a unique stress continence mechanism, characterized by markedly elevated pressure transmission ratios, that might unduly bias pressure transmission ratio differences between subjects with genuine stress incontinence and those who were stress continent. The age, weight, parity, and hormonal status of the two groups are compared in Table I. Subjects were considered hypoestrogenic if they were postmenopausal or castrate, not receiving estrogen replacement, and had clinical evidence of vaginal atrophy. There were no significant differences between the groups with respect to any of these variables. Table II compares the results of passive urethral pressure profilometry and urethral axial mobility testing between the genuine stress incontinence group and the stress-continent group and subgroups. Whereas urethral length measurements showed no significant differences, maximum urethral closure pressure, and both axial mobility measurements did show significant differences. The genuine stress incontinence group had significantly lower pressure transmission ratios throughout the urethra compared with the stress-continent group (Table Ill). These differences remained significant when both stress-continent subgroups were compared separately with the genuine stress incontinence group. Table IV demonstrates that subjects with genuine stress incontinence were significantly more likely than stresscontinent subjects to have a pressure transmission ratio <90% in all quarters of the urethra. These differences were still highly significant when the genuine stress incontinence group was compared separately with the stress-continent subgroups. Although it was not uncommon for stress-continent subjects to have a pressure transmission ratio <90%, it was exceptionally uncommon for a subject with genuine stress incontinence not
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September 1988 Am J Obstet Gynecol
Table II. Comparison of passive urethral pressure profile and urethral axis testing Q-tip cotton swab
Stress incontinent p vs SC group p vs SC subgroup 1* p vs SC subgroup 2t Stress continent Subgroup 1* Subgroup 2t
N
FUL (em)
MUCP (em H 20)
Stress (degrees)
37
2.8 ± 0.6 NS NS NS 2.7 ± 0.5 2.9 ± 0.6 2.4 ± 0.6
52± 17 0.003 0.001 NS 67 ± 26 70 ± 27 59± 25
48 ± 26 0.001 0.0009 NS 30 ± 26 28 ± 25 34 ± 32
73 57 16
I
Excursion (degrees) 39 ± 22 0.0003 0.002 0.0008 23 ± 19 25 ± 19 17 ± 16
Data are the mean ± SD. FUL, Functional urethral length; MUCP, maximum urethral closed pressure; SC, stress continent. *Stress continent without severe prolapse or prior urethropexy. tStress continent with severe prolapse or prior retropubic urethropexy.
Table III. Comparison of pressure transmission ratios Pressure transmission ratio
Stress incontinent p vs SC group p vs SC subgroup 1* p vs SC subgroup 2t Stress continent Subgroup 1* Subgroup 2t
N
Ql (%)
37
71 ± 14 0.004 0.05 <0.0001 94 ± 38 84 ± 30 123 ± 42
73 57 16
I
Q2 (%) 69 ± 16 0.0001 0.0007 <0.0001 101 ± 42 90 ± 32 145 ± 44
I
Q3 (%) 79 ± 19 0.0001 0.0003 <0.0001 113 ± 46 103 ± 32 149 ± 63
l
Q4 (%) 90 ± 22 0.001 0.005 0.0005 117 ± 36 112 ± 33 134 ± 42
Data are the mean ± SD. SC, Stress continent. *Stress continent without severe prolapse or prior urethropexy. tStress continent with severe prolapse or prior retropubic urethropexy.
to have a pressure transmission ratio <90% (1 of 37) in the proximal three quarters of the urethra. Overall, the finding of a PTR <90% in the proximal half of the dynamic profile had a sensitivity of 97%, a specificity of 56%, an abnormal predictive value of 53%, and a normal predictive value of 98%, with a genuine stress incontinence prevalence rate of 34%. If stress-continent subgroup 2 subjects are eliminated from analysis, the sensitivity remains 97%, the specificity drops to 47%, and the abnormal and normal predictive values are essentially unchanged at 55% and 96%, respectively. Table V compares the diagnostic accuracy of a pressure transmission ratio <90% with that of a resting maximum urethral closure pressure <50 em H 20 and a Qtip cotton swab excursion >30 degrees in our study population. If 13 stress-continent subjects who had a strong history for stress incontinence, a stable detrusor on urethrocystometric examination, and an abnormal Q-tip cotton swab test but who did not demonstrate observable loss with stress during the single testing session were included in the genuine stress incontinence group, all of the differences in pressure transmission
ratios discussed in the preceding paragraph became even more significant. Furthermore, values for sensitivity, specificity, abnormal predictive value, and normal predictive value improved to 98%, 68%, 72%, and 98%, respectively.
Comment We have demonstrated that women with genuine stress urinary incontinence have significantly lower pressure transmission ratios calculated from a standardized dynamic urethral pressure profile than do stress-continent women with other types of lower urinary tract dysfunction. This finding is in agreement with the observations regarding pressure transmission to the bladder and urethra first made by Enhorning, 11 observations that many other authors have confirmed in the intervening 25 years. 2 • •-6 • 12 It also extends the observations made by Hilton and Stanton 2 in their 1983 report. They noted significant differences in pressure transmission ratios between subjects with genuine stress incontinence and a normal control population specifically recruited to exclude all types oflower urinary tract dysfunction. It is important to know that subjects with
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Table IV. Significance of pressure transmission ratios* <90% PTR <90%
In Ql p vs GSI In Q2 p vs GSI In Q3 p vs GSI In Q4 p vs GSI
group group group group
GSI group
SC group
SC subgroup 1
SC subgroup 2
24/26
21150 0.0001 26/68 <0.00001 21/70 <0.00001 8/42 0.01
19/37 0.002 26/54 <0.00001 20/54 0.0009 7/33 0.03
2/13 <0.00001 0114 <0.00001 l/ 16 <0.00001 l/9 NS
34/36 27/36 14/27
PTR, Pressure transmission ratio; GSI, genuine stress incontinence; SC, stress continence. *Not every subject had pressure transmission ratio determined in every quarter.
genuine stress incontinence differ significantly from stress-continent subjects with other types of dysfunction, because this is precisely the type of population that seeks out the urogynecologist for evaluation and treatment. Because our study population is an unselected consecutive series specifically seeking urogynecologic evaluation, it is valid to use our data to establish a tentative critical cutoff value for the pressure transmission ratio and to evaluate its diagnostic accuracy. Our critical cutoff value for pressure transmission ratio was determined after a comparison between 60%, 70%, 80%, and 90% revealed that 90% yielded the best diagnostic accuracy for our study popultion. Although this retrospective determination of diagnostic accuracy for a test value is the only way to arrive at a tentative critical value, prospective confirmation by ourselves and others is essential. The 90% value can be measured with confidence in its precision. It is consistent with the 95% cutoff suggested by Hilton and Stanton2 and the "< 100%'' reported by Beisland et a!. 12 When we compared the 90% pressure transmission ratio to a 50 em H 20 resting maximum urethral closure pressure and a 30-degree urethral axial excursion in our study population (Table V), we found that the latter two parameters were much less sensitive and had a much lower normal predictive value while having similar specificities and abnormal predictive values. If we compare the 90% pressure transmission ratio with the pressure equalization criterion of Richardson, 9 we see that the former is more sensitive (97% versus 31% to 41 %) and has a better normal predictive value (98% versus 57% to 58%), but is less specific (56% versus 92% to 93%) and has a lower abnormal predictive value (53% versus 82% to 86%). These differences reflect the fact that subjects with genuine stress incontinence virtually always have pressure transmission ratios <90% in the inner half of the urethra, but so do many stresscontinent subjects. In contrast, subjects with pressure equalization throughout the dynamic profile virtually always have genuine stress incontinence, but many subjects with genuine stress incontinence do not have whole urethra pressure equalization. Pressure trans-
Table V. Comparison of predicitve powers of critical cutoff values for pressure transmission ratio, maximum urethral closure pressure, and Q-tip cotton swab excursion in the diagnosis of stress incontinence Q-tip cotton Proximal half urethra PTR MUCP <50 swab excursion >30 degrees em H 20 <90%
Sensitivity Specificity Abnormal predictive value Normal predictive value
97% 56% 53%
38% 70% 39%
70% 66% 51%
98%
69%
81%
PTR, pressure transmission ratio; MUCP, maximum urethral closure pressure.
mission is but one variable in the equation of stress incontinence. If other variables such as maximum urethral closure pressure or the magnitude of intraabdominal pressure variations are favorable, continence can be maintained in the face of inefficient pressure transmission. Furthermore, it must be recognized that, like all laboratory testing procedures, the dynamic profile is confining and sets limits on some variables that may result in pressure equalization under other, less confining, circumstances. There are two potential biases in this study that we tried to assess. One was the inclusion of 16 subjects in the stress-continent group who had third-degree uterovaginal prolapse or who had had a previous successful retropubic urethropexy. These conditions likely share a unique stress continence mechanism that is typified by exaggerated pressure transmission ratios, 13• 14 a fact that would tend to overestimate differences between the genuine-stress-incontinent and stress-continent groups. When these 16 subjects were eliminated from analysis, the pressure transmission ratio differences between the groups remained significant and the diagnostic accuracy of the 90% cutoff value was essentially unchanged. The second potential bias was the inclusion of 13 subjects in the stress-continent group who had
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Bump et al.
strong histories for pure genuine stress incontinence, a stable detrusor on urethrocystometric examination, and an abnormal Q-tip cotton swab test but who did not demonstrate observable loss with stress during the single testing session. It is likely that many of these subjects would have genuine stress incontinence under less confining circumstances, and their inclusion in the stress-continent group could bias results in either direction depending on whether their pressure transmission ratios were more like the other stress-continent subjects or more like subjects with genuine stress incontinence. Inclusion of these I3 subjects in the genuine stress incontinence group made all pressure transmission ratio differences between the genuine-stressincontinent and stress-continent groups more significant and improved the diagnostic accuracy of the 90% pressure transmission ratio cutoff value. We conclude that finding pressure transmission ratios >90% in the proximal urethra makes the diagnosis of genuine stress incontinence extremely unlikely. Although the finding of a pressure transmission ratio <90% does not establish the diagnosis of genuine stress incontinence, it does support that diagnosis in consort with other historic, physical, and urodynamic evidence. Finally, the pressure transmission ratio may become a useful urodynamic tool to quantify the severity of the transmission defect in an individual patient and to quantify the effects of surgical efforts to correct her stress incontinence. REFERENCES I. Committee on Standardisation of terminology, Hald T, chairman. The standardisation of terminology of lower urinary tract function. Glasgow: International Continence Society, 1984. 2. Hilton P, Stanton SL. Urethral pressure measurement by microtransducer: the results in symptom-free women and in those with genuine stress incontinence. Br 1 Obstet Gynaecol 1983;90:919-33. 3. Asmussen M, Ulmsten U. Simultaneous urethrocystometry and urethral pressure profile measurement with a new technique. Acta Obstet Gynecol Scand 1975;54: 385-6. 4. Bunne G, Obrink A. Urethral closure pressure with stress. A comparison between stress incontinent and continent women. Urol Res 1978;6:127-34. 5. Henriksson L, Andersson K-E, Ulmsten U. The urethral pressure profile in continent and stress incontinent women. Scand J Urol Nephrol 1979;13:5-10. 6. Fossberg E, Beisland HO. Incompetent urethral closure mechanism in females: experimental and clinical studies with special reference to diagnosis and classification. Urol Int 1982;37:34-41. 7. Bergman A, McCarthy TA. Urodynamic changes after successful operation for stress urinary incontinence. AM j 0BSTET GYNECOL 1983;147:325-6. 8. Bhatia NN, Ostergard DR. Urodynamics in women with stress urinary incontinence. Obstet Gynecol 1982;60: 552-9. 9. Richardson DA. Value of the cough pressure profile in the evaluation of patients with stress incontinence. AM 1 0BSTET GYNECOL 1986;155:808-11.
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10. Fant!JA, Hurt WG, Bump RC, Dunn lJ, Choi SC. Urethral axis and sphincteric function. AMJ OBSTET GYNECOL 1986;155:554-8. II. Enhorning G. Simultaneous recording of the intravesical and intraurethral pressure. Act Chir Scand 1961; 276(suppl): 1-68. 12. Beisland HO, Fossberg E, SanderS. Urodynamic studies before and after retropubic urethropexy for stress incontinence in females. Surg Gynecol Obstet 1982; 155:333-6. 13. Richardson DA, Bent AE, Ostergard DR. The effect of uterovaginal prolapse on urethrovesical pressure dynamics. AM j 0BSTET GYNECOL 1983;146:901-5. 14. Hertogs K, Stanton SL. Mechanism of urinary continence after colposuspension: barrier studies. Br J Obstet Gynaecoll985;92:ll84-8.
Discussion DR. WILLIS E. LANIER, Atlanta, Georgia (Official Guest). Urethral pressure profilometry measurements have been made and evaluated by various authors. However, the report by Dr. Bump and coworkers has taken a unique approach and has used these measurements as an adjunct to other evaluations, to help understand a given patient's lower urinary tract problem and perhaps help to predict the outcome of a surgical correction. Although other authors have not felt that the dynamic profile data should be used as the only criteria for successful surgery, these authors suggest that the associated inaccuracy may be due to the interpretation rather than to the technique itself. The purposes of the report-to compare pressure transmission ratios calculated from standardized dynamic urethral pressure profiles in stress-continent and stress-incontinent women, all of whom had symptoms of lower urinary tract dysfunctions, and to determine a critical cutoff value for pressure transmission ratios and calculate its diagnostic accuracy-were clearly stated. Their selection of patients was straightforward and did not seem skewed due to the fact that they used II 0 consecutive patients who sought evaluation of lower urinary tract dysfunction. They were careful to watch the groups for age, weight, parity, and anestrogenicity and were explicit in the definitions of the groups for genuine stress incontinence and stress continence, including a detailed urodynamic evaluation of each of the subjects. The report gives exact details of how the dynamic urethral pressure profilometric examination was carefully and meticulously performed and how the data were interpreted for the various quarters of the urethra. Careful correction for variables was carried out in the evaluation of the results. Their values for sensitivity, specificity, abnormal predictive value, and normal predictive value are discussed fairly. The authors list two potential biases: inclusion of subjects in the stress-continent group who had third-degree uterovaginal prolapse or who had had a previous successful retropubic urethropexy, and the inclusion of I3 subjects in the stress-continent group who had strong histories for pure genuine stress incontinence, a stable detrusor on urethrocystometric examination, and an
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abnormal Q-tip cotton swab test but who did not demonstrate loss with stress during the single testing session. Although the procedure has poor abnormal predictive value, the conclusion that a pressure transmission ratio <90% in the proximal half of the urethra does not establish the diagnosis of genuine stress incontinence, but that in co~unction with other urodynamic evaluations it may help in determining the degree of a patient's problem and possibly the response to surgery, gives us reason to consider this modality in the evaluation of our patients before surgery. An extension of this study to compare preoperative and postoperative values of this technique might help us to understand how and why certain procedures actually work. DR. FRANK C. GREISS, Winston-Salem, North Carolina. I remember coming up through the ranks and having an excellent summation in what was then known about continence- I guess that information is now 30 to 35 years old. I think there was little clear understanding of bladder function then. We have become tremendously more sophisticated over the subsequent three or four generations, but as I listened to this report, I was a little unclear as to what real progress we have made. Dr. Henry Thiede' last year gave an excellent presentation, but had no real measure of what fraction of patients that have incontinence had been filtered out and what fraction he was seeing for further evaluation. When do you think the fancy examination methods of today are necessary for the evaluation of the incontinent patient? REFERENCE 1. Thiede HA. U rogynecology: comments and caveats. AM J 0BSTET GYNECOL 1987;157:563.
DR. BuMP (Closing). Dr. Greiss, I usually spend about 3 hours answering that question. I think we have made
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755
some progress. If you look at the success of continence surgical procedures, there is a distressing failure rate, even in the best of hands, of 10% to 15%. There is a distressing complication rate (mainly urgency instability syndromes) in another 10% to 15% of subjects in carefully done studies. When we start out to cure stress incontinence, we may end up with only 50% to 60% of the patients happy with the effects of their surgery. The people who I think need to be studied are certainly people who have obvious symptoms of instabilitybedwetting, urgency incontinence, and the like. I think another important group we are beginning to appreciate are elderly patients. I do not know what "elderly" is, but certainly if a patient appears to be elderly, I think she needs to undergo thorough study. Patients with previous failed continence surgery also deserve sophisticated studies. Pressure transmission allows us to quantitate the functional effects of anatomic defects. I think the woman who has a pressure transmission ratio of 95%, has a closure pressure of only 15 to 20 em H 2 0, and loses urine when she coughs has stress incontinence by the strict definition of the term. Nonetheless, she is much different than the woman who has a 70 em H 20 closure pressure and only transmits pressure at 30% efficiency. The problem in the latter patient is very easy to cure surgically. It is the condition in the former patient that is very difficult to cure surgically without creating obstructive symptoms and voiding dysfunction afterward. The main aim of this report was to substantiate the validity of the pressure transmission value in the type of patients who come to see us. Stuart Stanton has documented this in an incontinent patient versus a normal asymptomatic control, but I do not evaluate any normal asymptomatic controls. We think that the pressure transmission ratio is valid in that circumstance, and now we are using it to evaluate the effects of our surgery. It seems to be very promising in this respect.