Clinical epidemiology suggests an association of detrusor overactivity (DO) with bladder outflow obstruction (BOO) in men with prostate enlargement.(1) Urethral (partial) ligation, to cause BOO, is applied to elicit DO in laboratory animal studies.(2) Very sparse research is however published, regarding clinical quantification of cystometry filling abnormalities with BOO -grades based on pressure flow (p/Q) analysis. BOO is much more prevalent in men but also women can have higher bladder outflow resistance. The cut-off value for clinically relevant BOO in women is not precisely determined, however the urodynamical concept of BOO, being an increase of detrusor pressure against a reduced flowrate during micturition, is undisputed. By consequence, bladder outflow resistance can be ranked or graded on a continuum from very low to very high. We have graded BOO identically in both gender. This study aimed to explore graded BOO in association with cystometry filling sensation and volume parameters to further unveil whether BOO could be one of the fundamental causes of DO in the human.

Urodynamic studies of 4842 persons (34.0% ♀) referred with signs and symptoms of lower urinary tract dysfunction were re-evaluated. Age ranged from 17-103 (♂ 67,8y; ♀59,5y). All patients had voided >100mL during the p/Q test and reported the voiding to be (almost) as usual. Filling cystometry has been ICS standard with double lumen fluid filled pressure measurement and ICS standard questioning of sensation landmark; First sensation of Filling (FSF), First Desire to void (FDV) and Strong Desire to void (SDV). No patient had urinary tract infection or relevant neurologic abnormalities, based on history and clinical (saddle region) exam. Patients were grouped by grade of BOO on the basis of the linearized passive urethral resistance relation (LinPURR) graph; from 0 to 6. Grade 2 equals ICS ‘equivocal’ zone.

The table shows the results per LinPURR (BOO grading) class up to 3. Only few women had LinPURR>3 (not shown due to space constraints): 

The graphs show that the pressures at the 3 sensation landmarks increase with every LinPURR group. Volumes at every sensation were usually (significantly) smaller per LinPURR group when women and men were compared but pressure differences were (t-tested up to grade 3, because of too low (female) sample number for grades>3) not significantly different between men and women:

This cross sectional analysis showed that in men but also in women standardized sensation mean volumes decrease and pressures increase in association with an increasing grade of bladder outflow obstruction. Women have bladder filling sensation at consistently lower volumes when compared to men, per bladder outflow obstruction grade group, however alterations in filling pressures are not significantly different up to intermediate grade of bladder outflow obstruction. This can suggest that in both gender an increase of bladder outflow resistance leads to a an increased likelihood of detrusor overactivity in the filling phase. Based on laboratory animal observations and (smooth) muscle physiology, this may be regarded as a clinical confirmation of the origin of one of the fundamental pathways to the development of detrusor overactivity.

This analysis suggests that higher grade of bladder outflow resistance is associated with an increased likelihood of detrusor overactivity in the filling phase on the basis of the observation that in men but also in women standardized sensation mean volumes decrease and pressures increase with increasing grade of bladder outflow obstruction.

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Zhang NZ, Ma L, Zhang JB, Chen J. Improved model for the establishment and evaluation of detrusor overactivity in female Wistar rats. Int Braz J Urol. 2014  May-Jun;40(3):414-21; discussion 422. doi: 10.1590/S1677-5538.IBJU.2014.03.17. PubMed PMID: 25010309.