1
no strictly normal controls were available. After eliminating that group it may then be possible to seek the small minority with gen- uine urodynamic urethral obstruction based on clearly and abnor- mally elevated voiding detrusor pressure. Derek Griffiths Griffiths Urodynamics and Pro-Continence Consulting Edmonton, Alberta Canada Recently increased attention has been given to bladder outlet obstruction in women as many investigators realize that this phe- nomenon is probably more common than previously suspected. How- ever, 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 ana- tomical 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 situa- tion. However, it is not clear that the 21 patients diagnosed with obstruction met such clinical criteria for obstruction. They had var- ious 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 vari- able voiding patterns and urodynamic parameters in normal and abnormal voiding. This observation is evidenced by the large varia- tion in voiding pressure and flow rate in the obstructed and unob- structed 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 ob- struction based on video urodynamic criteria of radiographic evi- dence 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 under- standing 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 void- ing 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 make. Although the proposed cutoff values may not be definitive for diagnosing obstruction, they help in our understanding of obstruc- tion and should enlighten others to continue to work toward a more precise definition of obstruction in women. Victor W. Nitti Department of Urology New York University Medical Center New York, New York 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 symp- toms 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. None- theless, 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 his- torical 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 intu- bated (with a 6Fr catheter) flow recordings demonstrated no consis- tent effect of the catheter. Still, since voided volumes were not rigidly standardized, although all were greater than 100 cc, one must con- cede 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 dysfunc- tional 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 consid- ered. Urodynamics alone cannot establish the diagnosis of obstruc- tion in women as they may in most men. Results obtained from a careful history, properly validated symptom questionnaire 1 and non- invasive flow rate can help predict urodynamic findings and estab- lish 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 signifi- cantly 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 question- naire. Urology, 54: 461, 1999 PRESSURE FLOW ANALYSIS MAY AID IN IDENTIFYING OUTFLOW OBSTRUCTION 1828

REPLY BY AUTHORS

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no strictly normal controls were available. After eliminating thatgroup it may then be possible to seek the small minority with gen-uine urodynamic urethral obstruction based on clearly and abnor-mally elevated voiding detrusor pressure.

Derek GriffithsGriffiths Urodynamics and Pro-Continence ConsultingEdmonton, AlbertaCanada

Recently increased attention has been given to bladder outletobstruction in women as many investigators realize that this phe-nomenon is probably more common than previously suspected. How-ever, bladder outlet obstruction in women is not universally defined.In an attempt to clarify further the definition of bladder outletobstruction in women these authors performed voiding pressure flowstudies using cutoff values for defining obstruction. The cutoff valuesof maximum flow 11 ml. per second or less and detrusor pressure atmaximum flow 21 cm. water or greater were previously defined in acohort of 87 women with suspected obstruction based on the clinicalgrounds of symptoms, surgical history and physical examination(reference 1 in article). These cutoff values were then applied to agroup of 106 consecutive women with various voiding complaintswho underwent pressure flow testing. A total of 21 women (20%) metthe urodynamic criteria for obstruction due to various types of ana-tomical obstruction. These authors were correct in pointing out thatcutoff pressure flow values for identifying bladder outlet obstructionshould only be used when combined with the overall clinical situa-tion. However, it is not clear that the 21 patients diagnosed withobstruction met such clinical criteria for obstruction. They had var-ious voiding complaints. One would wonder how clinically obstructedthese cases were based on the low incidence of obstructive symptomsin this group. One must wonder is it then appropriate to apply cutoffvalues based on clinically obstructed cases in those without clinicalobstruction.

A difficulty defining bladder outlet obstruction in women is vari-able voiding patterns and urodynamic parameters in normal andabnormal voiding. This observation is evidenced by the large varia-tion in voiding pressure and flow rate in the obstructed and unob-structed groups in this and other series (reference 7 in article). Thislarge variation makes the diagnosis of obstruction difficult based onpressure flow criteria only. We have diagnosed bladder outlet ob-struction based on video urodynamic criteria of radiographic evi-dence of obstruction between the bladder neck and the distal urethraduring a sustained detrusor contraction (reference 7 in article). Wedid not use any cutoff values yet interestingly the mean values ofmaximum flow and detrusor pressure at maximum flow were similarto those of the authors.

I am not convinced that cutoff values are completely applicable fordiagnosing obstruction in women, at least as we understand theentity today. The authors appropriately stated in the discussion thelimitation of using cutoff values and they also recognized the under-standing that a rigidly enforced classification scheme for identifyingwomen with obstruction may not be meaningful when based solely onurodynamics. Having said this, I believe that it is the intent of theauthors not to apply cutoff values rigidly, but to alert clinicians to thepossibility of obstruction.

Another important consideration is that the cutoff values in thisseries apply only to anatomical causes of obstruction, for example alarge cystocele, postoperative obstruction and periurethral fibrosis.In our experience functional obstruction, such as dysfunctional void-ing or primary bladder neck obstruction, is more common in thepopulation of women at large presenting with lower urinary tractsymptoms. The cutoff values proposed in this study may not apply tosuch patients with functional obstruction and perhaps the videourodynamic criteria may be more useful in such patients.

I wholeheartedly agree with the major points that the authors

make. Although the proposed cutoff values may not be definitive fordiagnosing obstruction, they help in our understanding of obstruc-tion and should enlighten others to continue to work toward a moreprecise definition of obstruction in women.

Victor W. NittiDepartment of UrologyNew York University Medical CenterNew York, New York

REPLY BY AUTHORS

These 3 insightful editorial comments highlight the controversysurrounding the issue of bladder outlet obstruction in women. Thisissue is far from settled and merits ongoing investigation. Blaivaspoints out appropriately that we relied on clinical obstructive symp-toms to identify women with bladder outlet obstruction. The fallacyof relying on classic obstructive symptoms is demonstrated in theconclusion of the article, that is many women with pressure flowstudies suggestive of obstruction will have atypical symptoms. None-theless, our goal was to derive cutoff values that might be useful todefine bladder outlet obstruction similar to how the Abrams-Griffithnomogram was developed. Therefore, we had to rely solely on his-torical data to derive uroflow and pressure data since no universallyaccepted values currently exist. Additionally, while the presence of aurethral catheter could artificially lower maximum flow rate, ouranalysis of the 41 women who underwent nonintubated and intu-bated (with a 6Fr catheter) flow recordings demonstrated no consis-tent effect of the catheter. Still, since voided volumes were not rigidlystandardized, although all were greater than 100 cc, one must con-cede that this issue is not resolved at least for women.

Griffiths indicates that we relied on women with stress urinaryincontinence as our control group to derive pressure flow values andthat these women could arguably have lower than normal values fordetrusor pressures (reference 9 in article). However, as noted severalstudies have demonstrated that our value for maximum detrusorpressure among women with stress urinary incontinence is fairlyrepresentative of normal detrusor contraction (references 7 to 10 inarticle). Nonetheless, only a study of age matched women withoutvoiding complaints will adequately answer the question of who hasnormal and who has abnormal voiding pressures.

Finally, Nitti cautions against applying these cutoff values to allwomen with voiding complaints to identify those who are obstructed.Moreover, he emphasizes the importance of considering dysfunc-tional voiding as a cause of functional obstruction in women. Indeed,this diagnosis was not considered in our study since women withevidence of electromyographic activity at the time of voiding were notincluded.

Is it reasonable to assume that a woman is obstructed merelybecause she has a flow rate of 10 cc per second and a detrusorpressure of 25 cm. water? No, clearly other factors must be consid-ered. Urodynamics alone cannot establish the diagnosis of obstruc-tion in women as they may in most men. Results obtained from acareful history, properly validated symptom questionnaire1 and non-invasive flow rate can help predict urodynamic findings and estab-lish the correct diagnosis. In this article we have demonstrated thatwomen who might be obstructed from a variety of causes rangingfrom fairly acute (postoperative) to more insidious (cystocele) seem tohave similar pressure flow values during voiding that differ signifi-cantly from women with no reason to be obstructed. We hope thatfuture studies will further clarify the role of obstruction in womenwith lower urinary tract symptoms.

1. Lemack, G. E. and Zimmern, P. E.: Predictability of urodynamicfindings based on the Urogenital Distress Inventory question-naire. Urology, 54: 461, 1999

PRESSURE FLOW ANALYSIS MAY AID IN IDENTIFYING OUTFLOW OBSTRUCTION1828