- Email: [email protected]
Voiding dynamics in women: a comparison of pressure-flow studies between asymptomatic and incontinent women
ADULT UROLOGY
VOIDING DYNAMICS IN WOMEN: A COMPARISON OF PRESSURE-FLOW STUDIES BETWEEN ASYMPTOMATIC AND INCONTINENT WOMEN GARY E. LEMACK, ADAM G. BASEMAN,
AND
PHILIPPE E. ZIMMERN
ABSTRACT Objectives. To define the normative values for pressure-flow studies in asymptomatic women and to compare them with the values in women with stress incontinence. Methods. Asymptomatic women between the ages of 30 and 70 years were recruited from the community to undergo urodynamic studies (UDSs). Only women with no or minimal symptoms on the Urogenital Distress Inventory Questionnaire, minimal pelvic organ prolapse, and no previous surgery for incontinence were included. The results of the pressure-flow studies were compared with the values from women evaluated for stress urinary incontinence (SUI) between December 1998 and August 2000. Results. Twenty asymptomatic women (mean age 41.7 years) met the inclusion criteria of the 59 who applied. Their pressure-flow data were compared with that of 40 women with symptoms of pure SUI selected from the 415 who underwent UDSs during this period, 16 of whom were found to have SUI during the UDS. The average maximal flow was 17.2 ⫾ 6.7 mL/s in the control population and 22.0 ⫾ 6.8 mL/s among women with genuine SUI during the UDS (P ⫽ 0.039). The detrusor pressure at the maximal flow averaged 24 ⫾ 10 cm H2O and 16.0 ⫾ 8.6 cm H2O for the control and SUI groups, respectively (P ⫽ 0.016). The voided volumes were somewhat higher for the SUI group (330 versus 419 mL, P ⫽ 0.041). Conclusions. These findings confirm the normative pressure-flow data in women and suggest that women with stress incontinence void at a lower detrusor pressure. A chronically reduced outlet resistance during bladder filling, which likely contributes to SUI, also appears to affect the voiding phase in stress-incontinent women. UROLOGY 59: 42–46, 2002. © 2002, Elsevier Science Inc.
A
s our understanding of the physiology of voiding in women continues to grow, new questions have emerged. Among these questions is the issue of the pressure-flow relationship during micturition. Although it is well recognized that many women will void to completion with nearly imperceptible increases in detrusor pressure, most women will be shown to have a notable rise in pressure with the onset of voiding. Still, a consensus of what can be considered normal voiding in women remains elusive. This issue has been further highlighted by the recent recognition that bladder outlet obstruction (BOO) in women may be more common than was From the Department of Urology, University of Texas Southwestern Medical Center, Dallas, Texas Reprint requests: Gary E. Lemack, M.D., Department of Urology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-9110 Submitted: June 20, 2001, accepted (with revisions): August 23, 2001
42
© 2002, ELSEVIER SCIENCE INC. ALL RIGHTS RESERVED
once appreciated. Recent evidence suggests that as many as 20% of women presenting to a tertiary referral center for the evaluation of lower urinary tract symptoms may have obstruction, depending on the criteria used to define BOO.1–3 All studies used to define BOO in women have relied on the populations of women in their urodynamic database, which do not represent asymptomatic controls. Often, these women either have other urologic complaints such as overactive bladder types of symptoms or stress urinary incontinence (SUI). The issue has been raised as to whether these populations truly represent control groups against which the symptomatic group should be considered.4 Specifically, it has been suggested that incontinent women may void with lower voiding pressures than do continent women. The rationale for this explanation is that the detrusor contraction strength in women with SUI may be, in part, related to the urethral resistance. Many women with 0090-4295/02/$22.00 PII S0090-4295(01)01462-5
SUI may have a lower outlet resistance and, therefore, might be expected to void at lower pressures. Other factors such as increasing age, altered hormonal milieu, and pelvic floor dysfunction have also been theorized to affect detrusor contraction strength, although the available studies in small cohorts of women have not noted a dramatic difference in the voiding dynamics between premenopausal and postmenopausal women.5,6 The current study was undertaken to determine the pressureflow relationship during voiding in a group of volunteers rigidly defined as having no lower urinary tract complaints. This group was then compared with a group of women with symptoms of pure SUI found to have genuine SUI on urodynamic studies (UDSs) to determine whether the voiding dynamics differed in the two populations. MATERIAL AND METHODS This study was reviewed and approved by the institutional review board of the University of Texas Southwestern Medical Center. Women aged 30 to 70 years were recruited from the local community and invited to participate in a study of voiding function. After responding to local advertisements asking for women with few or no difficulties with urination, volunteers were screened for inclusion on the basis of a telephone interview. All women completed the short form of the Urogenital Distress Inventory7 (six questions scored from 0 to 3), and any woman responding greater than 1 (“a little bit”) to any of the six questions posed in this questionnaire was excluded. Any woman with previous surgery for incontinence or prolapse was also excluded. The details of the procedures to be performed were explained to the participants and they were told they would be examined on the day of the study. If a large cystocele was found to be present at the examination (Baden classification 2 or higher, that is, an anterior bulge extending beyond the introitus with straining), they were informed that they would be excluded from participation, but would be given partial compensation. On the day of the study, the volunteers were examined for prolapse, and then a 6F dual-lumen urethral catheter, a 9F rectal catheter, and surface electromyographic electrodes were placed on the perineum on each side of the anus. The postvoid residual volume was determined, the transducers were zeroed to atmosphere before the introduction of the catheters, and a “two fill and void” study was carried out. Technical considerations were given to using the smallest urethral catheter possible to minimize any possible direct obstructive effect, placing electromyographic patches to ensure relaxation during voiding, and determining the true intravesical pressure by zeroing to gravity, per the current International Continence Society recommendations.8 The bladder filling was begun at 50 mL/min, and the baseline intravesical pressure was recorded. The volume at the first sensation to void was recorded, and graded Valsalva and cough maneuvers were carried out at 250 mL to assess for SUI. The detrusor pressure was monitored throughout the filling for instability, which was defined as any rise in the detrusor pressure associated with the perception of urgency. The maximal capacity was recorded, as was the maximal flow rate, the detrusor pressure at the maximal flow (pdetQmax), and the voided volume. All participants were given a single dose of quinolone at the conclusion of the study. Volunteers were compensated for their participation. For both groups, each study was carried out once and then UROLOGY 59 (1), 2002
immediately repeated. The value for the volume at the first sensation from the first study was used for each group for comparison. The maximal flow rate and detrusor pressure at that flow rate were recorded for each study. The maximal capacities and volumes voided during those studies were also recorded. For comparison with the SUI group, the maximal flow rate of the two studies, its associated detrusor pressure, and the voided volume were used. Patients who voided less than 100 mL were not included. The comparison group of women with SUI was accrued from our database of all women who had undergone UDSs during December 1998 to August 2000 for a variety of voiding complaints (n ⫽ 415). Their charts were reviewed, and only the patients with a chief complaint of SUI were included. Patients with mixed incontinence were included only if SUI clearly predominated. Patients with any degree of prolapse greater than a grade 2 cystocele were excluded. Additionally, patients with any history of previous bladder or urethral surgery were excluded. This left 40 patients with SUI assessable for inclusion. Each of these patients also underwent a “two fill and void” technique at the time of testing, exactly as for the group of asymptomatic women, and the maximal flow and associated detrusor pressure and voided volume were used for comparison with the control group. They were then stratified according to the presence or absence of genuine SUI during the UDS. A statistical software program (SigmaStat) was used to analyze the data. Where data assumed a normal distribution, t tests were used to compare the results between the incontinent and control groups and to analyze for trends in parity, age, and hormonal status within each group. For data not assuming a normal distribution, a Mann-Whitney U test was used. The chi-square test was used to compare the categorical data where appropriate.
RESULTS A total of 59 women responded to the advertisements, 27 of whom did not qualify on the basis of either a response to the questionnaire or a history of previous bladder surgery. Ten of the remaining women elected not to participate after the procedure was described in more detail, and two terminated the study while it was in progress. Twenty asymptomatic women therefore completed the study. Their mean age was 41.7 years (range 30 to 55). Twelve of the women were premenopausal, four were postmenopausal but receiving hormone replacement, and four were postmenopausal and not receiving hormonal replacement. The comparative data for the incontinent group is reported in Table I. During the filling portion of the UDS, 3 of the 20 women in the control group and 4 of the 40 women with SUI developed detrusor instability during the study. No control patients leaked with either a graded Valsalva or cough maneuver. Of the 40 women with a chief complaint of SUI, 16 leaked with the Valsalva or cough maneuver during the UDS. The average maximal intubated flow rate for the control group was 17.2 ⫾ 6.7 mL/s and for the entire SUI group was 20.1 ⫾ 7.0 mL/s (P ⫽ 0.128; Fig. 1). Among women found to have SUI during 43
TABLE I. Baseline characteristics of control (asymptomatic) and stress incontinent groups
Mean age (yr) Median parity (n) Premenopausal or taking HRT (%)
Control
Symptomatic with SUI on UDSs
Symptomatic with No SUI on UDSs
41.7 (30–55) 1.5 (0–4) 80
53.9 (36–67)* 2.0 (0–6) 81.3
47.9 (31–68)* 2.0 (0–5)* 54.2
KEY: SUI ⫽ stress urinary incontinence; UDSs ⫽ urodynamic studies; HRT ⫽ hormonal replacement therapy. Data in parentheses are the range. * P ⬍0.05 compared with controls.
FIGURE 1. Box and whiskers plot of maximal flow rate in control patients, those with SUI on UDSs, and those with symptoms of SUI, although none demonstrated SUI on UDSs. Patients with SUI on UDSs had significantly greater flow rates compared with controls.
the UDS (genuine SUI), however, the average maximal flow rate was 22.0 ⫾ 6.8 mL/s, a difference that was significant compared with the controls (P ⫽ 0.041). Those who reported stress incontinence but were not found to have genuine SUI on the UDS had a maximal flow rate of 18.8 mL/s (P ⫽ 0.43). The mean pdetQmax was 24 ⫾ 10 cm H2O for the control group, 16.0 ⫾ 8.6 cm H2O for the women found to have genuine SUI (P ⫽ 0.016), and 18.8 ⫾ 10.7 cm H2O for symptomatic women without SUI during the UDS (P ⫽ 0.106; Fig. 2). The voided volume was somewhat larger for the SUI group (330 ⫾ 109 mL and 406 ⫾ 178 mL, respectively, although this difference was not statistically significant [P ⫽ 0.084]). The voided volume was also higher among women verified to have SUI during the UDS (420 mL, P ⫽ 0.041). No differences were found in the maximal flow rate, detrusor pressure, or voided volume between the group of incontinent women who had SUI during the UDS and those who did not. The mean postvoid residual volume for both groups was less than 50 mL (26 mL and 8.4 mL for the continent and incontinent groups, respectively). One control patient demonstrated significant sphincteric dyssynergic activity during the voiding portion of the 44
FIGURE 2. Box and whiskers plot of pdetQmax in control patients, those with SUI on UDSs, and those with symptoms of SUI, although none demonstrated SUI on UDSs. Patients with SUI on UDSs had significantly lower pdetQmax than did controls.
first study, and the second study was used for pressure-flow analysis. Within each group (SUI and control), no differences were found in the bladder capacity, maximal flow rate, or pdetQmax when stratifying by hormonal status, age, or parity. These data indicate that an impact of each of these factors on the urodynamic results seems unlikely, even though overall, the incontinent women were older and of greater parity than were the controls. COMMENT The role of the pressure-flow studies in evaluating lower urinary tract symptoms in women continues to evolve. Like men, many of the same symptoms are shared by different etiologies. For example, the symptom of urgency and frequency may be a manifestation of overactive bladder, carcinoma in situ, interstitial cystitis, BOO, and probably several other etiologies that are ill defined. Pressure-flow studies performed during UDSs may aid in discriminating some of these possibilities, and several investigators have speculated on the role of UDSs in identifying women who are potentially obstructed.1 UROLOGY 59 (1), 2002
Most of these studies have relied on women presumed to be nonobstructed as their control group, against whom the obstructed group was compared.1,2 One such comparison was with a group of women with stress incontinence, among whom statistically significant differences in flow rate and pdetQmax were noted in comparison with the obstructed group. An important point to consider is whether incontinent women should be used as controls with regard to their voiding dynamics. Perhaps chronically reduced outlet resistance, which may be present in many of these women, alters the pressure at which they void and the corresponding flow rate. Karram and colleagues9 noted reduced voiding pressure in 70 women with SUI compared with a group of 30 asymptomatic women (20 versus 12 cm H2O). In their study, however, the groups were not well matched. It is possible that other factors, such as age, menopausal status, and parity, which were significantly different between the groups, might have independently affected the results, regardless of their continence status, although within each group, these factors did not appear to affect the voiding pressure. Moreover, the means of defining the control groups was not explained. The findings of the current study, in which the control group was rigidly defined, agree with those of Karram et al.9 in noting a significantly lower voiding pressure among women evaluated for SUI than in the normal controls. These data suggest that chronically reduced outlet resistance during filling (accounting for episodes of SUI) also may affect the voiding phase during prolonged periods. This conclusion is particularly supported by the finding that, compared with our control group, the pressure-flow values were not statistically different among women who reported SUI, although had none during the UDS, whereas the women with genuine SUI on the UDS had significantly higher flow and lower detrusor pressure. Bhatia and colleagues10 performed UDSs before and after incontinence operations (modified Burch and modified Pereyra) and noted several women who voided with very low voiding pressures before the procedure who regained a “normal” contraction postoperatively. They theorized that patients with SUI are able to void with lower pressures owing to a decreased urethral resistance and that with an increase in resistance after surgery the detrusor contraction strength rebounds appropriately. Others have evaluated pressure-flow studies in women presumed to be asymptomatic. Sorensen et al.5,6 found no significant differences between the pressure-flow parameters in 10 premenopausal and 12 postmenopausal women, although the maximal urethral closure pressure was higher in the premenopausal group. Wyndaele11 noted a UROLOGY 59 (1), 2002
wide range of cystometric and pressure-flow findings in a small group of young asymptomatic women (n ⫽ 10) and cautioned avoidance of overinterpretation of unusual urodynamic findings. None of these studies carefully documented the mechanism by which the lack of symptoms was gauged. This is not a trivial issue, because in the present study, 59 women responded to an advertisement specifically seeking women with no voiding problems, and yet nearly one half were excluded because of the presence of moderate voiding symptoms as determined by the Urogenital Distress Inventory. Thus, for the purposes of identifying a truly asymptomatic group for comparison with other populations, strict entry criteria are required. The shortcomings of the present study are well recognized. The women with SUI were older, had had more pregnancies, and were more likely to be postmenopausal than were the group of controls. It is possible that aging alone, or hormonal fluxes induced by the menopausal status, could affect the detrusor strength and therefore lower the voiding pressures. Still, within each group, these factors did not appear to play a significant role on the basis of our statistical analysis results. Overall, although the numbers within each group were fairly limited, both the SUI and control groups represented a very strictly defined homogenous population of women, narrowed down from a much larger pool. Finally, the incontinent women voided with larger volumes, which could clearly affect the maximal flow rate during the UDSs. It is unclear, however, that a higher voided volume would naturally result in a significantly reduced detrusor pressure, as was noted in the incontinent group. Future work will focus on expanding our control group to include older women to overcome these shortcomings. CONCLUSIONS During UDSs, women found to have SUI void with a significantly lower detrusor pressure and higher flow rate than a continent group of women without any voiding complaints. These data suggest that reduced outlet resistance does affect the detrusor contraction required to complete bladder emptying in women with stress incontinence. When comparing a control group with symptomatic groups, it is important to use a rigidly defined control population of women without incontinence or lower urinary tract symptoms to establish normative values. Future development of a BOO nomogram in women may only be possible if the normative values have been clearly defined. 45
REFERENCES 1. Lemack GE, and Zimmern PE: Pressure-flow analysis can aid in identifying women with outflow obstruction. J Urol 163: 1823–1828, 2000. 2. Blaivas JG, and Groutz A: Bladder outlet obstruction nomogram for women with lower urinary tract symptomatology. Neurourol Urodyn 19: 553–564, 2000. 3. Nitti VW, Tu LM, and Gitlin J: Diagnosing bladder outlet obstruction in women. J Urol 161: 1535–1540, 1999. 4. Griffiths D: Editorial comment: Pressure-flow analysis can aid in identifying women with outflow obstruction. J Urol 163: 1829, 2000. 5. Sorensen S: Urodynamic investigations and their reproducibility in healthy postmenopausal females. Scand J Urol Nephrol Suppl 114: 42– 46, 1988. 6. Sorensen S, Knudsen UB, Kirkeby HJ, et al: Urodynamic investigations in healthy fertile females during the menstrual cycle. Scand J Urol Nephrol Suppl 114: 28 –34, 1988.
46
7. Uebersax JS, Wyman FF, Shumaker SA, et al: Short forms to assess life quality and symptom distress for urinary incontinence in women: the incontinence impact questionnaire and urogenital distress inventory. Neurourol Urodyn 14: 131–139, 1995. 8. Abrams P, Griffiths D, Liao L, et al: The urodynamic assessment of lower urinary tract symptoms, in Denis L, Griffiths K, Khoury S, et al (Eds): Fourth International Consultation on Benign Prostatic Hyperplasia. Plymouth, UK, Plymbridge Distributors, 1998, vol 4, pp 229 –281. 9. Karram MM, Partoll L, Bilotta V, et al: Factors affecting detrusor contraction strength during voiding in women. Obstet Gynecol 90: 73–76, 1997. 10. Bhatia NN, Bergman A, and Karram M: Changes in urethral resistance after surgery for stress incontinence. Urology 34: 200 –204, 1989. 11. Wyndaele J-J: Normality in urodynamics studied in healthy adults. J Urol 161: 899 –902, 1999.
UROLOGY 59 (1), 2002
VOIDING DYNAMICS IN WOMEN: A COMPARISON OF PRESSURE-FLOW STUDIES BETWEEN ASYMPTOMATIC AND INCONTINENT WOMEN GARY E. LEMACK, ADAM G. BASEMAN,
AND
PHILIPPE E. ZIMMERN
ABSTRACT Objectives. To define the normative values for pressure-flow studies in asymptomatic women and to compare them with the values in women with stress incontinence. Methods. Asymptomatic women between the ages of 30 and 70 years were recruited from the community to undergo urodynamic studies (UDSs). Only women with no or minimal symptoms on the Urogenital Distress Inventory Questionnaire, minimal pelvic organ prolapse, and no previous surgery for incontinence were included. The results of the pressure-flow studies were compared with the values from women evaluated for stress urinary incontinence (SUI) between December 1998 and August 2000. Results. Twenty asymptomatic women (mean age 41.7 years) met the inclusion criteria of the 59 who applied. Their pressure-flow data were compared with that of 40 women with symptoms of pure SUI selected from the 415 who underwent UDSs during this period, 16 of whom were found to have SUI during the UDS. The average maximal flow was 17.2 ⫾ 6.7 mL/s in the control population and 22.0 ⫾ 6.8 mL/s among women with genuine SUI during the UDS (P ⫽ 0.039). The detrusor pressure at the maximal flow averaged 24 ⫾ 10 cm H2O and 16.0 ⫾ 8.6 cm H2O for the control and SUI groups, respectively (P ⫽ 0.016). The voided volumes were somewhat higher for the SUI group (330 versus 419 mL, P ⫽ 0.041). Conclusions. These findings confirm the normative pressure-flow data in women and suggest that women with stress incontinence void at a lower detrusor pressure. A chronically reduced outlet resistance during bladder filling, which likely contributes to SUI, also appears to affect the voiding phase in stress-incontinent women. UROLOGY 59: 42–46, 2002. © 2002, Elsevier Science Inc.
A
s our understanding of the physiology of voiding in women continues to grow, new questions have emerged. Among these questions is the issue of the pressure-flow relationship during micturition. Although it is well recognized that many women will void to completion with nearly imperceptible increases in detrusor pressure, most women will be shown to have a notable rise in pressure with the onset of voiding. Still, a consensus of what can be considered normal voiding in women remains elusive. This issue has been further highlighted by the recent recognition that bladder outlet obstruction (BOO) in women may be more common than was From the Department of Urology, University of Texas Southwestern Medical Center, Dallas, Texas Reprint requests: Gary E. Lemack, M.D., Department of Urology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-9110 Submitted: June 20, 2001, accepted (with revisions): August 23, 2001
42
© 2002, ELSEVIER SCIENCE INC. ALL RIGHTS RESERVED
once appreciated. Recent evidence suggests that as many as 20% of women presenting to a tertiary referral center for the evaluation of lower urinary tract symptoms may have obstruction, depending on the criteria used to define BOO.1–3 All studies used to define BOO in women have relied on the populations of women in their urodynamic database, which do not represent asymptomatic controls. Often, these women either have other urologic complaints such as overactive bladder types of symptoms or stress urinary incontinence (SUI). The issue has been raised as to whether these populations truly represent control groups against which the symptomatic group should be considered.4 Specifically, it has been suggested that incontinent women may void with lower voiding pressures than do continent women. The rationale for this explanation is that the detrusor contraction strength in women with SUI may be, in part, related to the urethral resistance. Many women with 0090-4295/02/$22.00 PII S0090-4295(01)01462-5
SUI may have a lower outlet resistance and, therefore, might be expected to void at lower pressures. Other factors such as increasing age, altered hormonal milieu, and pelvic floor dysfunction have also been theorized to affect detrusor contraction strength, although the available studies in small cohorts of women have not noted a dramatic difference in the voiding dynamics between premenopausal and postmenopausal women.5,6 The current study was undertaken to determine the pressureflow relationship during voiding in a group of volunteers rigidly defined as having no lower urinary tract complaints. This group was then compared with a group of women with symptoms of pure SUI found to have genuine SUI on urodynamic studies (UDSs) to determine whether the voiding dynamics differed in the two populations. MATERIAL AND METHODS This study was reviewed and approved by the institutional review board of the University of Texas Southwestern Medical Center. Women aged 30 to 70 years were recruited from the local community and invited to participate in a study of voiding function. After responding to local advertisements asking for women with few or no difficulties with urination, volunteers were screened for inclusion on the basis of a telephone interview. All women completed the short form of the Urogenital Distress Inventory7 (six questions scored from 0 to 3), and any woman responding greater than 1 (“a little bit”) to any of the six questions posed in this questionnaire was excluded. Any woman with previous surgery for incontinence or prolapse was also excluded. The details of the procedures to be performed were explained to the participants and they were told they would be examined on the day of the study. If a large cystocele was found to be present at the examination (Baden classification 2 or higher, that is, an anterior bulge extending beyond the introitus with straining), they were informed that they would be excluded from participation, but would be given partial compensation. On the day of the study, the volunteers were examined for prolapse, and then a 6F dual-lumen urethral catheter, a 9F rectal catheter, and surface electromyographic electrodes were placed on the perineum on each side of the anus. The postvoid residual volume was determined, the transducers were zeroed to atmosphere before the introduction of the catheters, and a “two fill and void” study was carried out. Technical considerations were given to using the smallest urethral catheter possible to minimize any possible direct obstructive effect, placing electromyographic patches to ensure relaxation during voiding, and determining the true intravesical pressure by zeroing to gravity, per the current International Continence Society recommendations.8 The bladder filling was begun at 50 mL/min, and the baseline intravesical pressure was recorded. The volume at the first sensation to void was recorded, and graded Valsalva and cough maneuvers were carried out at 250 mL to assess for SUI. The detrusor pressure was monitored throughout the filling for instability, which was defined as any rise in the detrusor pressure associated with the perception of urgency. The maximal capacity was recorded, as was the maximal flow rate, the detrusor pressure at the maximal flow (pdetQmax), and the voided volume. All participants were given a single dose of quinolone at the conclusion of the study. Volunteers were compensated for their participation. For both groups, each study was carried out once and then UROLOGY 59 (1), 2002
immediately repeated. The value for the volume at the first sensation from the first study was used for each group for comparison. The maximal flow rate and detrusor pressure at that flow rate were recorded for each study. The maximal capacities and volumes voided during those studies were also recorded. For comparison with the SUI group, the maximal flow rate of the two studies, its associated detrusor pressure, and the voided volume were used. Patients who voided less than 100 mL were not included. The comparison group of women with SUI was accrued from our database of all women who had undergone UDSs during December 1998 to August 2000 for a variety of voiding complaints (n ⫽ 415). Their charts were reviewed, and only the patients with a chief complaint of SUI were included. Patients with mixed incontinence were included only if SUI clearly predominated. Patients with any degree of prolapse greater than a grade 2 cystocele were excluded. Additionally, patients with any history of previous bladder or urethral surgery were excluded. This left 40 patients with SUI assessable for inclusion. Each of these patients also underwent a “two fill and void” technique at the time of testing, exactly as for the group of asymptomatic women, and the maximal flow and associated detrusor pressure and voided volume were used for comparison with the control group. They were then stratified according to the presence or absence of genuine SUI during the UDS. A statistical software program (SigmaStat) was used to analyze the data. Where data assumed a normal distribution, t tests were used to compare the results between the incontinent and control groups and to analyze for trends in parity, age, and hormonal status within each group. For data not assuming a normal distribution, a Mann-Whitney U test was used. The chi-square test was used to compare the categorical data where appropriate.
RESULTS A total of 59 women responded to the advertisements, 27 of whom did not qualify on the basis of either a response to the questionnaire or a history of previous bladder surgery. Ten of the remaining women elected not to participate after the procedure was described in more detail, and two terminated the study while it was in progress. Twenty asymptomatic women therefore completed the study. Their mean age was 41.7 years (range 30 to 55). Twelve of the women were premenopausal, four were postmenopausal but receiving hormone replacement, and four were postmenopausal and not receiving hormonal replacement. The comparative data for the incontinent group is reported in Table I. During the filling portion of the UDS, 3 of the 20 women in the control group and 4 of the 40 women with SUI developed detrusor instability during the study. No control patients leaked with either a graded Valsalva or cough maneuver. Of the 40 women with a chief complaint of SUI, 16 leaked with the Valsalva or cough maneuver during the UDS. The average maximal intubated flow rate for the control group was 17.2 ⫾ 6.7 mL/s and for the entire SUI group was 20.1 ⫾ 7.0 mL/s (P ⫽ 0.128; Fig. 1). Among women found to have SUI during 43
TABLE I. Baseline characteristics of control (asymptomatic) and stress incontinent groups
Mean age (yr) Median parity (n) Premenopausal or taking HRT (%)
Control
Symptomatic with SUI on UDSs
Symptomatic with No SUI on UDSs
41.7 (30–55) 1.5 (0–4) 80
53.9 (36–67)* 2.0 (0–6) 81.3
47.9 (31–68)* 2.0 (0–5)* 54.2
KEY: SUI ⫽ stress urinary incontinence; UDSs ⫽ urodynamic studies; HRT ⫽ hormonal replacement therapy. Data in parentheses are the range. * P ⬍0.05 compared with controls.
FIGURE 1. Box and whiskers plot of maximal flow rate in control patients, those with SUI on UDSs, and those with symptoms of SUI, although none demonstrated SUI on UDSs. Patients with SUI on UDSs had significantly greater flow rates compared with controls.
the UDS (genuine SUI), however, the average maximal flow rate was 22.0 ⫾ 6.8 mL/s, a difference that was significant compared with the controls (P ⫽ 0.041). Those who reported stress incontinence but were not found to have genuine SUI on the UDS had a maximal flow rate of 18.8 mL/s (P ⫽ 0.43). The mean pdetQmax was 24 ⫾ 10 cm H2O for the control group, 16.0 ⫾ 8.6 cm H2O for the women found to have genuine SUI (P ⫽ 0.016), and 18.8 ⫾ 10.7 cm H2O for symptomatic women without SUI during the UDS (P ⫽ 0.106; Fig. 2). The voided volume was somewhat larger for the SUI group (330 ⫾ 109 mL and 406 ⫾ 178 mL, respectively, although this difference was not statistically significant [P ⫽ 0.084]). The voided volume was also higher among women verified to have SUI during the UDS (420 mL, P ⫽ 0.041). No differences were found in the maximal flow rate, detrusor pressure, or voided volume between the group of incontinent women who had SUI during the UDS and those who did not. The mean postvoid residual volume for both groups was less than 50 mL (26 mL and 8.4 mL for the continent and incontinent groups, respectively). One control patient demonstrated significant sphincteric dyssynergic activity during the voiding portion of the 44
FIGURE 2. Box and whiskers plot of pdetQmax in control patients, those with SUI on UDSs, and those with symptoms of SUI, although none demonstrated SUI on UDSs. Patients with SUI on UDSs had significantly lower pdetQmax than did controls.
first study, and the second study was used for pressure-flow analysis. Within each group (SUI and control), no differences were found in the bladder capacity, maximal flow rate, or pdetQmax when stratifying by hormonal status, age, or parity. These data indicate that an impact of each of these factors on the urodynamic results seems unlikely, even though overall, the incontinent women were older and of greater parity than were the controls. COMMENT The role of the pressure-flow studies in evaluating lower urinary tract symptoms in women continues to evolve. Like men, many of the same symptoms are shared by different etiologies. For example, the symptom of urgency and frequency may be a manifestation of overactive bladder, carcinoma in situ, interstitial cystitis, BOO, and probably several other etiologies that are ill defined. Pressure-flow studies performed during UDSs may aid in discriminating some of these possibilities, and several investigators have speculated on the role of UDSs in identifying women who are potentially obstructed.1 UROLOGY 59 (1), 2002
Most of these studies have relied on women presumed to be nonobstructed as their control group, against whom the obstructed group was compared.1,2 One such comparison was with a group of women with stress incontinence, among whom statistically significant differences in flow rate and pdetQmax were noted in comparison with the obstructed group. An important point to consider is whether incontinent women should be used as controls with regard to their voiding dynamics. Perhaps chronically reduced outlet resistance, which may be present in many of these women, alters the pressure at which they void and the corresponding flow rate. Karram and colleagues9 noted reduced voiding pressure in 70 women with SUI compared with a group of 30 asymptomatic women (20 versus 12 cm H2O). In their study, however, the groups were not well matched. It is possible that other factors, such as age, menopausal status, and parity, which were significantly different between the groups, might have independently affected the results, regardless of their continence status, although within each group, these factors did not appear to affect the voiding pressure. Moreover, the means of defining the control groups was not explained. The findings of the current study, in which the control group was rigidly defined, agree with those of Karram et al.9 in noting a significantly lower voiding pressure among women evaluated for SUI than in the normal controls. These data suggest that chronically reduced outlet resistance during filling (accounting for episodes of SUI) also may affect the voiding phase during prolonged periods. This conclusion is particularly supported by the finding that, compared with our control group, the pressure-flow values were not statistically different among women who reported SUI, although had none during the UDS, whereas the women with genuine SUI on the UDS had significantly higher flow and lower detrusor pressure. Bhatia and colleagues10 performed UDSs before and after incontinence operations (modified Burch and modified Pereyra) and noted several women who voided with very low voiding pressures before the procedure who regained a “normal” contraction postoperatively. They theorized that patients with SUI are able to void with lower pressures owing to a decreased urethral resistance and that with an increase in resistance after surgery the detrusor contraction strength rebounds appropriately. Others have evaluated pressure-flow studies in women presumed to be asymptomatic. Sorensen et al.5,6 found no significant differences between the pressure-flow parameters in 10 premenopausal and 12 postmenopausal women, although the maximal urethral closure pressure was higher in the premenopausal group. Wyndaele11 noted a UROLOGY 59 (1), 2002
wide range of cystometric and pressure-flow findings in a small group of young asymptomatic women (n ⫽ 10) and cautioned avoidance of overinterpretation of unusual urodynamic findings. None of these studies carefully documented the mechanism by which the lack of symptoms was gauged. This is not a trivial issue, because in the present study, 59 women responded to an advertisement specifically seeking women with no voiding problems, and yet nearly one half were excluded because of the presence of moderate voiding symptoms as determined by the Urogenital Distress Inventory. Thus, for the purposes of identifying a truly asymptomatic group for comparison with other populations, strict entry criteria are required. The shortcomings of the present study are well recognized. The women with SUI were older, had had more pregnancies, and were more likely to be postmenopausal than were the group of controls. It is possible that aging alone, or hormonal fluxes induced by the menopausal status, could affect the detrusor strength and therefore lower the voiding pressures. Still, within each group, these factors did not appear to play a significant role on the basis of our statistical analysis results. Overall, although the numbers within each group were fairly limited, both the SUI and control groups represented a very strictly defined homogenous population of women, narrowed down from a much larger pool. Finally, the incontinent women voided with larger volumes, which could clearly affect the maximal flow rate during the UDSs. It is unclear, however, that a higher voided volume would naturally result in a significantly reduced detrusor pressure, as was noted in the incontinent group. Future work will focus on expanding our control group to include older women to overcome these shortcomings. CONCLUSIONS During UDSs, women found to have SUI void with a significantly lower detrusor pressure and higher flow rate than a continent group of women without any voiding complaints. These data suggest that reduced outlet resistance does affect the detrusor contraction required to complete bladder emptying in women with stress incontinence. When comparing a control group with symptomatic groups, it is important to use a rigidly defined control population of women without incontinence or lower urinary tract symptoms to establish normative values. Future development of a BOO nomogram in women may only be possible if the normative values have been clearly defined. 45
REFERENCES 1. Lemack GE, and Zimmern PE: Pressure-flow analysis can aid in identifying women with outflow obstruction. J Urol 163: 1823–1828, 2000. 2. Blaivas JG, and Groutz A: Bladder outlet obstruction nomogram for women with lower urinary tract symptomatology. Neurourol Urodyn 19: 553–564, 2000. 3. Nitti VW, Tu LM, and Gitlin J: Diagnosing bladder outlet obstruction in women. J Urol 161: 1535–1540, 1999. 4. Griffiths D: Editorial comment: Pressure-flow analysis can aid in identifying women with outflow obstruction. J Urol 163: 1829, 2000. 5. Sorensen S: Urodynamic investigations and their reproducibility in healthy postmenopausal females. Scand J Urol Nephrol Suppl 114: 42– 46, 1988. 6. Sorensen S, Knudsen UB, Kirkeby HJ, et al: Urodynamic investigations in healthy fertile females during the menstrual cycle. Scand J Urol Nephrol Suppl 114: 28 –34, 1988.
46
7. Uebersax JS, Wyman FF, Shumaker SA, et al: Short forms to assess life quality and symptom distress for urinary incontinence in women: the incontinence impact questionnaire and urogenital distress inventory. Neurourol Urodyn 14: 131–139, 1995. 8. Abrams P, Griffiths D, Liao L, et al: The urodynamic assessment of lower urinary tract symptoms, in Denis L, Griffiths K, Khoury S, et al (Eds): Fourth International Consultation on Benign Prostatic Hyperplasia. Plymouth, UK, Plymbridge Distributors, 1998, vol 4, pp 229 –281. 9. Karram MM, Partoll L, Bilotta V, et al: Factors affecting detrusor contraction strength during voiding in women. Obstet Gynecol 90: 73–76, 1997. 10. Bhatia NN, Bergman A, and Karram M: Changes in urethral resistance after surgery for stress incontinence. Urology 34: 200 –204, 1989. 11. Wyndaele J-J: Normality in urodynamics studied in healthy adults. J Urol 161: 899 –902, 1999.
UROLOGY 59 (1), 2002