- Email: [email protected]
EDITORIAL COMMENT
PRESSURE FLOW ANALYSIS MAY AID IN IDENTIFYING OUTFLOW OBSTRUCTION
continence surgery and other causes, and noted no significant differences in pressure flow values among the various obstructed groups. Cutoff values were then applied in 106 prospectively enrolled women with various lower urinary tract complaints. Approximately 20% of these patients had obstruction according to urodynamic criteria, although classic obstructive symptoms were present in a minority. Using cutoff values may help to identify women with obstruction who do not have overt symptoms, although not all who meet these criteria have an identifiable anatomical source. Dr. Barbara Foster assisted with the statistical analysis and Andrew Webb reviewed the manuscript.
1827
For these reasons it would have been better if clinical obstruction was defined not only by historical data, but also by low unintubated uroflowmetry and an adequate detrusor contraction, excluding women with no detrusor contractions. In addition, the authors should consider the effect of the urethral catheter on flow in the final conclusions. According to their criteria a woman with a detrusor pressure of 25 cm. water and an intubated urine flow of 10 cc per second would be considered to have obstruction even when the unintubated flow was 30 ml. per second with a normal shaped curve. Thus, to be clinically relevant I think that it is important to include unintubated uroflowmetry results as a parameter for defining urethral obstruction. Jerry G. Blaivas UroCenter of New York New York, New York
REFERENCES
1. Chassagne, S., Bernier, P. A., Haab, F. et al: Proposed cutoff values to define bladder outlet obstruction in women. Urology, 51: 408, 1998 2. Zimmern, P. E.: The role of voiding cystourethrography in the evaluation of the female lower urinary tract. Prob Urol, 5: 23, 1991 3. Griffiths, D., Hofner, K., van Mastrigt, R. et al: Standardization of terminology of lower urinary tract function: pressure-flow studies of voiding, urethral resistance, and urethral obstruction. Neurourol Urodyn, 16: 1, 1997 4. Griffiths, D.: Pressure-flow studies of micturition. Urol Clin North Am, 23: 279, 1996 5. Daneshgari, F., Zimmern, P. E. and Jacomides, L.: Magnetic resonance imaging detection of symptomatic noncommunicating intraurethral wall diverticula in women. J Urol, 161: 1259, 1999 6. Nurenberg, P. and Zimmern, P. E.: Role of MR imaging with transrectal coil in the evaluation of complex urethral abnormalities. AJR Am J Roentenol, 169: 1335, 1997 7. Nitti, V. W., Tu, L. M. and Gitlin, J.: Diagnosing bladder outlet obstruction in women. J Urol, 161: 1535, 1999 8. Fulford, S. C. V., Flynn, R., Barrington, J. et al: An assessment of the surgical outcome and urodynamic effects of the pubovaginal sling for stress incontinence and the associated urge syndrome. J Urol, 162: 135, 1999 9. Karram, M. M., Partoll, L., Bilotta, V. et al: Factors affecting detrusor contraction strength during voiding in women. Obstet Gynecol, 90: 723, 1997 10. Sorensen, S.: Urodynamic investigations and their reproducibility in healthy postmenopausal females. Scand J Urol Nephrol, suppl., 114: 42, 1988 EDITORIAL COMMENTS Until recently prostatic urethral obstruction and benign prostatic hyperplasia were considered near synonyms. With the advent of sophisticated video urodynamic studies and pressure flow analysis it soon became apparent that these terms are not synonymous and at least a third of patients previously thought to have prostatic obstruction have detrusor instability or impaired detrusor contractility as the main cause of symptoms. Currently the distinction between urethral obstruction and impaired detrusor contractility may only be made by the sophisticated analysis of detrusor pressure uroflowmetry studies. Until recently urethral obstruction in women was thought to be exceedingly rare. However, with the increasing use of detrusor pressure uroflowmetry it has become apparent that urethral obstruction in women is much more common than previously thought with recorded rates ranging from about 6% to 30% of those with lower urinary tract symptoms. These authors propose numeric cutoffs for detrusor pressure and synchronous intubated uroflowmetry for diagnosing ureteral obstruction in women. While I generally agree with their results, I take issue with some of their methodology. They defined clinical obstruction based on symptoms only and then compared the pressure flow characteristics of the clinically obstructed group to those of controls to arrive at the numeric cutoff for obstruction. I do not agree with this basic premise. If I agreed with that premise, there would be no need for urodynamics. Some patients with such symptoms have obstruction, some have impaired detrusor contractility, some have detrusor instability and some have voiding dysfunction. Furthermore, some women deny symptoms at all, particularly those with prolapse or after pelvic surgery, and yet may have obstruction.
The topic of obstruction in women is important and difficult to address adequately, partly because so few normal studies in healthy subjects are available for comparison (references 7 to 10 in article). In this study lacking normal subjects these authors chose as controls a group of women with stress incontinence and no other obvious abnormalities on standard examinations. There is no reason to suppose that these women void normally. In fact, they are just the group that one may suspect of voiding at abnormally low detrusor pressure because of sphincter abnormalities (reference 9 in article). Consequently although the authors carefully and conscientiously established cutoff criteria for distinguishing 2 groups of female patients, it is likely that these groups should not be labeled as unobstructed and obstructed, but as low and normal to high pressure voiders. In my opinion the authors have not identified cutoff criteria for obstruction. To be fair they, too, suggest that the cutoff values should not be rigidly applied but merely used to alert clinicians to perform a closer evaluation. If the control group comprises low pressure voiders, we would expect the obstructed group to be heterogeneous, and contain some normal and some genuinely obstructed cases. The obstructed group defined initially on nonurodynamic grounds was based on obstructive voiding complaints with other physical and radiographic findings that sometimes but not always indicate obstruction. It is now generally accepted that even in males the association of these symptoms with obstruction is so weak that they should be called voiding and not obstructive symptoms. Therefore, we should expect some women without obstruction in this group. Some would be expected to have impaired detrusor contractility rather than urethral obstruction. When cutoff criteria were applied prospectively to a group of 106 women with various complaints, 21 were identified with obstruction but only 5 with obstructive symptoms. At most 13 of the 21 patients had a history or diagnosis consistent with obstruction (table 3 in article). Even with every possible explanation considered in some there was no explicable source of obstruction that was identified urodynamically. Surely these cases were not really obstruction. The most common complaints in the 21 women with obstruction were suggestive of an overactive bladder and detrusor instability was observed in many. These findings confirm the common experience that women with an overactive bladder void at higher pressure than those with stress incontinence. However, which group has normal pressure? My opinion is that each group is heterogeneous. In this study about half of the stress incontinence group voided at abnormally low pressure, while a similar proportion of the obstruction group voided at abnormally high pressure and presumably had genuine obstruction. It difficult to define obstruction in women because of a fundamental conceptual problem. The concept of obstruction was developed for male patients before the days of urodynamics. Fortunately urodynamics confirm that voiding complaints in men are usually associated with obstruction, defined as high pressure, low flow voiding. Only in a minority of cases is the primary problem a defect of detrusor contractility. In women obstruction is much less common. If the conceptual scheme developed for men is applied to women, the relative importance of obstruction and impaired detrusor contractility should be reversed. Poor voiding should be initially associated with a defect of detrusor contractility. Only in a minority would urethral obstruction be the primary problem. I suggest that in future urodynamic studies of women with voiding complaints cutoff criteria initially be established for a weak detrusor contraction (low pressure, low flow voiding). One would expect an easily identifiable group with abnormally weak detrusors although
1828
PRESSURE FLOW ANALYSIS MAY AID IN IDENTIFYING OUTFLOW OBSTRUCTION
no strictly normal controls were available. After eliminating that group it may then be possible to seek the small minority with genuine urodynamic urethral obstruction based on clearly and abnormally elevated voiding detrusor pressure.
make. Although the proposed cutoff values may not be definitive for diagnosing obstruction, they help in our understanding of obstruction and should enlighten others to continue to work toward a more precise definition of obstruction in women.
Derek Griffiths Griffiths Urodynamics and Pro-Continence Consulting Edmonton, Alberta Canada
Victor W. Nitti Department of Urology New York University Medical Center New York, New York
Recently increased attention has been given to bladder outlet obstruction in women as many investigators realize that this phenomenon is probably more common than previously suspected. However, bladder outlet obstruction in women is not universally defined. In an attempt to clarify further the definition of bladder outlet obstruction in women these authors performed voiding pressure flow studies using cutoff values for defining obstruction. The cutoff values of maximum flow 11 ml. per second or less and detrusor pressure at maximum flow 21 cm. water or greater were previously defined in a cohort of 87 women with suspected obstruction based on the clinical grounds of symptoms, surgical history and physical examination (reference 1 in article). These cutoff values were then applied to a group of 106 consecutive women with various voiding complaints who underwent pressure flow testing. A total of 21 women (20%) met the urodynamic criteria for obstruction due to various types of anatomical obstruction. These authors were correct in pointing out that cutoff pressure flow values for identifying bladder outlet obstruction should only be used when combined with the overall clinical situation. However, it is not clear that the 21 patients diagnosed with obstruction met such clinical criteria for obstruction. They had various voiding complaints. One would wonder how clinically obstructed these cases were based on the low incidence of obstructive symptoms in this group. One must wonder is it then appropriate to apply cutoff values based on clinically obstructed cases in those without clinical obstruction. A difficulty defining bladder outlet obstruction in women is variable voiding patterns and urodynamic parameters in normal and abnormal voiding. This observation is evidenced by the large variation in voiding pressure and flow rate in the obstructed and unobstructed groups in this and other series (reference 7 in article). This large variation makes the diagnosis of obstruction difficult based on pressure flow criteria only. We have diagnosed bladder outlet obstruction based on video urodynamic criteria of radiographic evidence of obstruction between the bladder neck and the distal urethra during a sustained detrusor contraction (reference 7 in article). We did not use any cutoff values yet interestingly the mean values of maximum flow and detrusor pressure at maximum flow were similar to those of the authors. I am not convinced that cutoff values are completely applicable for diagnosing obstruction in women, at least as we understand the entity today. The authors appropriately stated in the discussion the limitation of using cutoff values and they also recognized the understanding that a rigidly enforced classification scheme for identifying women with obstruction may not be meaningful when based solely on urodynamics. Having said this, I believe that it is the intent of the authors not to apply cutoff values rigidly, but to alert clinicians to the possibility of obstruction. Another important consideration is that the cutoff values in this series apply only to anatomical causes of obstruction, for example a large cystocele, postoperative obstruction and periurethral fibrosis. In our experience functional obstruction, such as dysfunctional voiding or primary bladder neck obstruction, is more common in the population of women at large presenting with lower urinary tract symptoms. The cutoff values proposed in this study may not apply to such patients with functional obstruction and perhaps the video urodynamic criteria may be more useful in such patients. I wholeheartedly agree with the major points that the authors
REPLY BY AUTHORS These 3 insightful editorial comments highlight the controversy surrounding the issue of bladder outlet obstruction in women. This issue is far from settled and merits ongoing investigation. Blaivas points out appropriately that we relied on clinical obstructive symptoms to identify women with bladder outlet obstruction. The fallacy of relying on classic obstructive symptoms is demonstrated in the conclusion of the article, that is many women with pressure flow studies suggestive of obstruction will have atypical symptoms. Nonetheless, our goal was to derive cutoff values that might be useful to define bladder outlet obstruction similar to how the Abrams-Griffith nomogram was developed. Therefore, we had to rely solely on historical data to derive uroflow and pressure data since no universally accepted values currently exist. Additionally, while the presence of a urethral catheter could artificially lower maximum flow rate, our analysis of the 41 women who underwent nonintubated and intubated (with a 6Fr catheter) flow recordings demonstrated no consistent effect of the catheter. Still, since voided volumes were not rigidly standardized, although all were greater than 100 cc, one must concede that this issue is not resolved at least for women. Griffiths indicates that we relied on women with stress urinary incontinence as our control group to derive pressure flow values and that these women could arguably have lower than normal values for detrusor pressures (reference 9 in article). However, as noted several studies have demonstrated that our value for maximum detrusor pressure among women with stress urinary incontinence is fairly representative of normal detrusor contraction (references 7 to 10 in article). Nonetheless, only a study of age matched women without voiding complaints will adequately answer the question of who has normal and who has abnormal voiding pressures. Finally, Nitti cautions against applying these cutoff values to all women with voiding complaints to identify those who are obstructed. Moreover, he emphasizes the importance of considering dysfunctional voiding as a cause of functional obstruction in women. Indeed, this diagnosis was not considered in our study since women with evidence of electromyographic activity at the time of voiding were not included. Is it reasonable to assume that a woman is obstructed merely because she has a flow rate of 10 cc per second and a detrusor pressure of 25 cm. water? No, clearly other factors must be considered. Urodynamics alone cannot establish the diagnosis of obstruction in women as they may in most men. Results obtained from a careful history, properly validated symptom questionnaire1 and noninvasive flow rate can help predict urodynamic findings and establish the correct diagnosis. In this article we have demonstrated that women who might be obstructed from a variety of causes ranging from fairly acute (postoperative) to more insidious (cystocele) seem to have similar pressure flow values during voiding that differ significantly from women with no reason to be obstructed. We hope that future studies will further clarify the role of obstruction in women with lower urinary tract symptoms. 1. Lemack, G. E. and Zimmern, P. E.: Predictability of urodynamic findings based on the Urogenital Distress Inventory questionnaire. Urology, 54: 461, 1999
continence surgery and other causes, and noted no significant differences in pressure flow values among the various obstructed groups. Cutoff values were then applied in 106 prospectively enrolled women with various lower urinary tract complaints. Approximately 20% of these patients had obstruction according to urodynamic criteria, although classic obstructive symptoms were present in a minority. Using cutoff values may help to identify women with obstruction who do not have overt symptoms, although not all who meet these criteria have an identifiable anatomical source. Dr. Barbara Foster assisted with the statistical analysis and Andrew Webb reviewed the manuscript.
1827
For these reasons it would have been better if clinical obstruction was defined not only by historical data, but also by low unintubated uroflowmetry and an adequate detrusor contraction, excluding women with no detrusor contractions. In addition, the authors should consider the effect of the urethral catheter on flow in the final conclusions. According to their criteria a woman with a detrusor pressure of 25 cm. water and an intubated urine flow of 10 cc per second would be considered to have obstruction even when the unintubated flow was 30 ml. per second with a normal shaped curve. Thus, to be clinically relevant I think that it is important to include unintubated uroflowmetry results as a parameter for defining urethral obstruction. Jerry G. Blaivas UroCenter of New York New York, New York
REFERENCES
1. Chassagne, S., Bernier, P. A., Haab, F. et al: Proposed cutoff values to define bladder outlet obstruction in women. Urology, 51: 408, 1998 2. Zimmern, P. E.: The role of voiding cystourethrography in the evaluation of the female lower urinary tract. Prob Urol, 5: 23, 1991 3. Griffiths, D., Hofner, K., van Mastrigt, R. et al: Standardization of terminology of lower urinary tract function: pressure-flow studies of voiding, urethral resistance, and urethral obstruction. Neurourol Urodyn, 16: 1, 1997 4. Griffiths, D.: Pressure-flow studies of micturition. Urol Clin North Am, 23: 279, 1996 5. Daneshgari, F., Zimmern, P. E. and Jacomides, L.: Magnetic resonance imaging detection of symptomatic noncommunicating intraurethral wall diverticula in women. J Urol, 161: 1259, 1999 6. Nurenberg, P. and Zimmern, P. E.: Role of MR imaging with transrectal coil in the evaluation of complex urethral abnormalities. AJR Am J Roentenol, 169: 1335, 1997 7. Nitti, V. W., Tu, L. M. and Gitlin, J.: Diagnosing bladder outlet obstruction in women. J Urol, 161: 1535, 1999 8. Fulford, S. C. V., Flynn, R., Barrington, J. et al: An assessment of the surgical outcome and urodynamic effects of the pubovaginal sling for stress incontinence and the associated urge syndrome. J Urol, 162: 135, 1999 9. Karram, M. M., Partoll, L., Bilotta, V. et al: Factors affecting detrusor contraction strength during voiding in women. Obstet Gynecol, 90: 723, 1997 10. Sorensen, S.: Urodynamic investigations and their reproducibility in healthy postmenopausal females. Scand J Urol Nephrol, suppl., 114: 42, 1988 EDITORIAL COMMENTS Until recently prostatic urethral obstruction and benign prostatic hyperplasia were considered near synonyms. With the advent of sophisticated video urodynamic studies and pressure flow analysis it soon became apparent that these terms are not synonymous and at least a third of patients previously thought to have prostatic obstruction have detrusor instability or impaired detrusor contractility as the main cause of symptoms. Currently the distinction between urethral obstruction and impaired detrusor contractility may only be made by the sophisticated analysis of detrusor pressure uroflowmetry studies. Until recently urethral obstruction in women was thought to be exceedingly rare. However, with the increasing use of detrusor pressure uroflowmetry it has become apparent that urethral obstruction in women is much more common than previously thought with recorded rates ranging from about 6% to 30% of those with lower urinary tract symptoms. These authors propose numeric cutoffs for detrusor pressure and synchronous intubated uroflowmetry for diagnosing ureteral obstruction in women. While I generally agree with their results, I take issue with some of their methodology. They defined clinical obstruction based on symptoms only and then compared the pressure flow characteristics of the clinically obstructed group to those of controls to arrive at the numeric cutoff for obstruction. I do not agree with this basic premise. If I agreed with that premise, there would be no need for urodynamics. Some patients with such symptoms have obstruction, some have impaired detrusor contractility, some have detrusor instability and some have voiding dysfunction. Furthermore, some women deny symptoms at all, particularly those with prolapse or after pelvic surgery, and yet may have obstruction.
The topic of obstruction in women is important and difficult to address adequately, partly because so few normal studies in healthy subjects are available for comparison (references 7 to 10 in article). In this study lacking normal subjects these authors chose as controls a group of women with stress incontinence and no other obvious abnormalities on standard examinations. There is no reason to suppose that these women void normally. In fact, they are just the group that one may suspect of voiding at abnormally low detrusor pressure because of sphincter abnormalities (reference 9 in article). Consequently although the authors carefully and conscientiously established cutoff criteria for distinguishing 2 groups of female patients, it is likely that these groups should not be labeled as unobstructed and obstructed, but as low and normal to high pressure voiders. In my opinion the authors have not identified cutoff criteria for obstruction. To be fair they, too, suggest that the cutoff values should not be rigidly applied but merely used to alert clinicians to perform a closer evaluation. If the control group comprises low pressure voiders, we would expect the obstructed group to be heterogeneous, and contain some normal and some genuinely obstructed cases. The obstructed group defined initially on nonurodynamic grounds was based on obstructive voiding complaints with other physical and radiographic findings that sometimes but not always indicate obstruction. It is now generally accepted that even in males the association of these symptoms with obstruction is so weak that they should be called voiding and not obstructive symptoms. Therefore, we should expect some women without obstruction in this group. Some would be expected to have impaired detrusor contractility rather than urethral obstruction. When cutoff criteria were applied prospectively to a group of 106 women with various complaints, 21 were identified with obstruction but only 5 with obstructive symptoms. At most 13 of the 21 patients had a history or diagnosis consistent with obstruction (table 3 in article). Even with every possible explanation considered in some there was no explicable source of obstruction that was identified urodynamically. Surely these cases were not really obstruction. The most common complaints in the 21 women with obstruction were suggestive of an overactive bladder and detrusor instability was observed in many. These findings confirm the common experience that women with an overactive bladder void at higher pressure than those with stress incontinence. However, which group has normal pressure? My opinion is that each group is heterogeneous. In this study about half of the stress incontinence group voided at abnormally low pressure, while a similar proportion of the obstruction group voided at abnormally high pressure and presumably had genuine obstruction. It difficult to define obstruction in women because of a fundamental conceptual problem. The concept of obstruction was developed for male patients before the days of urodynamics. Fortunately urodynamics confirm that voiding complaints in men are usually associated with obstruction, defined as high pressure, low flow voiding. Only in a minority of cases is the primary problem a defect of detrusor contractility. In women obstruction is much less common. If the conceptual scheme developed for men is applied to women, the relative importance of obstruction and impaired detrusor contractility should be reversed. Poor voiding should be initially associated with a defect of detrusor contractility. Only in a minority would urethral obstruction be the primary problem. I suggest that in future urodynamic studies of women with voiding complaints cutoff criteria initially be established for a weak detrusor contraction (low pressure, low flow voiding). One would expect an easily identifiable group with abnormally weak detrusors although
1828
PRESSURE FLOW ANALYSIS MAY AID IN IDENTIFYING OUTFLOW OBSTRUCTION
no strictly normal controls were available. After eliminating that group it may then be possible to seek the small minority with genuine urodynamic urethral obstruction based on clearly and abnormally elevated voiding detrusor pressure.
make. Although the proposed cutoff values may not be definitive for diagnosing obstruction, they help in our understanding of obstruction and should enlighten others to continue to work toward a more precise definition of obstruction in women.
Derek Griffiths Griffiths Urodynamics and Pro-Continence Consulting Edmonton, Alberta Canada
Victor W. Nitti Department of Urology New York University Medical Center New York, New York
Recently increased attention has been given to bladder outlet obstruction in women as many investigators realize that this phenomenon is probably more common than previously suspected. However, bladder outlet obstruction in women is not universally defined. In an attempt to clarify further the definition of bladder outlet obstruction in women these authors performed voiding pressure flow studies using cutoff values for defining obstruction. The cutoff values of maximum flow 11 ml. per second or less and detrusor pressure at maximum flow 21 cm. water or greater were previously defined in a cohort of 87 women with suspected obstruction based on the clinical grounds of symptoms, surgical history and physical examination (reference 1 in article). These cutoff values were then applied to a group of 106 consecutive women with various voiding complaints who underwent pressure flow testing. A total of 21 women (20%) met the urodynamic criteria for obstruction due to various types of anatomical obstruction. These authors were correct in pointing out that cutoff pressure flow values for identifying bladder outlet obstruction should only be used when combined with the overall clinical situation. However, it is not clear that the 21 patients diagnosed with obstruction met such clinical criteria for obstruction. They had various voiding complaints. One would wonder how clinically obstructed these cases were based on the low incidence of obstructive symptoms in this group. One must wonder is it then appropriate to apply cutoff values based on clinically obstructed cases in those without clinical obstruction. A difficulty defining bladder outlet obstruction in women is variable voiding patterns and urodynamic parameters in normal and abnormal voiding. This observation is evidenced by the large variation in voiding pressure and flow rate in the obstructed and unobstructed groups in this and other series (reference 7 in article). This large variation makes the diagnosis of obstruction difficult based on pressure flow criteria only. We have diagnosed bladder outlet obstruction based on video urodynamic criteria of radiographic evidence of obstruction between the bladder neck and the distal urethra during a sustained detrusor contraction (reference 7 in article). We did not use any cutoff values yet interestingly the mean values of maximum flow and detrusor pressure at maximum flow were similar to those of the authors. I am not convinced that cutoff values are completely applicable for diagnosing obstruction in women, at least as we understand the entity today. The authors appropriately stated in the discussion the limitation of using cutoff values and they also recognized the understanding that a rigidly enforced classification scheme for identifying women with obstruction may not be meaningful when based solely on urodynamics. Having said this, I believe that it is the intent of the authors not to apply cutoff values rigidly, but to alert clinicians to the possibility of obstruction. Another important consideration is that the cutoff values in this series apply only to anatomical causes of obstruction, for example a large cystocele, postoperative obstruction and periurethral fibrosis. In our experience functional obstruction, such as dysfunctional voiding or primary bladder neck obstruction, is more common in the population of women at large presenting with lower urinary tract symptoms. The cutoff values proposed in this study may not apply to such patients with functional obstruction and perhaps the video urodynamic criteria may be more useful in such patients. I wholeheartedly agree with the major points that the authors
REPLY BY AUTHORS These 3 insightful editorial comments highlight the controversy surrounding the issue of bladder outlet obstruction in women. This issue is far from settled and merits ongoing investigation. Blaivas points out appropriately that we relied on clinical obstructive symptoms to identify women with bladder outlet obstruction. The fallacy of relying on classic obstructive symptoms is demonstrated in the conclusion of the article, that is many women with pressure flow studies suggestive of obstruction will have atypical symptoms. Nonetheless, our goal was to derive cutoff values that might be useful to define bladder outlet obstruction similar to how the Abrams-Griffith nomogram was developed. Therefore, we had to rely solely on historical data to derive uroflow and pressure data since no universally accepted values currently exist. Additionally, while the presence of a urethral catheter could artificially lower maximum flow rate, our analysis of the 41 women who underwent nonintubated and intubated (with a 6Fr catheter) flow recordings demonstrated no consistent effect of the catheter. Still, since voided volumes were not rigidly standardized, although all were greater than 100 cc, one must concede that this issue is not resolved at least for women. Griffiths indicates that we relied on women with stress urinary incontinence as our control group to derive pressure flow values and that these women could arguably have lower than normal values for detrusor pressures (reference 9 in article). However, as noted several studies have demonstrated that our value for maximum detrusor pressure among women with stress urinary incontinence is fairly representative of normal detrusor contraction (references 7 to 10 in article). Nonetheless, only a study of age matched women without voiding complaints will adequately answer the question of who has normal and who has abnormal voiding pressures. Finally, Nitti cautions against applying these cutoff values to all women with voiding complaints to identify those who are obstructed. Moreover, he emphasizes the importance of considering dysfunctional voiding as a cause of functional obstruction in women. Indeed, this diagnosis was not considered in our study since women with evidence of electromyographic activity at the time of voiding were not included. Is it reasonable to assume that a woman is obstructed merely because she has a flow rate of 10 cc per second and a detrusor pressure of 25 cm. water? No, clearly other factors must be considered. Urodynamics alone cannot establish the diagnosis of obstruction in women as they may in most men. Results obtained from a careful history, properly validated symptom questionnaire1 and noninvasive flow rate can help predict urodynamic findings and establish the correct diagnosis. In this article we have demonstrated that women who might be obstructed from a variety of causes ranging from fairly acute (postoperative) to more insidious (cystocele) seem to have similar pressure flow values during voiding that differ significantly from women with no reason to be obstructed. We hope that future studies will further clarify the role of obstruction in women with lower urinary tract symptoms. 1. Lemack, G. E. and Zimmern, P. E.: Predictability of urodynamic findings based on the Urogenital Distress Inventory questionnaire. Urology, 54: 461, 1999