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

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