16. Bross, S., Schumacher, S., Scheepe, J. R. et al: Smooth musclefatigue due to repeated urinary bladder neurostimulation: anin vivo study. Neurourol Urodynam, 18: 41, 1999

17. Shoukry, M. S. and Ghoniem, G. M.: Effect of time interval andoverdistension on repeated urodynamic studies. J Urol, 147: 185,1992

EDITORIAL COMMENT

The authors analyze again the reproducibility of pressure flowstudies, which is the prerequisite for acceptance of the measurementroutine for patients with lower urinary tract symptoms and bladderoutlet obstruction. Overall, there is little short-term variability foran invasive measurement without anesthesia. However, the authorsdetermine a significant decrease in relevant voiding pressure valuesfrom measurement 1 to 3, and in principle these results were con-firmed by Rosier and Hansen et al (references 4 and 5 in article). Atshort-term repeat measurement Rosier et al reported that variationsof maximum flow rate were not significant and values for detrusorpressure at maximum flow rate were significant lower. The appro-priate detrusor pressure at maximum flow rate was less than 15 cm.water in 80% of the patients. Overall, rarely were the intra-individual fluctuations great enough to effect a change in the gradeof obstruction on the Schafter nomogram. Hansen et al found similarresults with a systematic variation in detrusor pressure at maximumflow rate and a lack of statistically significant systematic variationsin maximum flow rate in 22 patients.

Apparently, it appears to be physiological that the values of void-ing pressures decrease on repeated studies without a significantvariation of maximum flow rate being observed. However, in contrastto previous publications, the authors report a decrease in maximumflow rate but information on concrete values of the decrease or itssignificance is lacking. It would be important to attempt to explainthe cause of the decrease in voiding parameters on repeated meas-urements. Generally, a decrease in pressure values (mainly detrusorpressure at maximum flow rate as the most accepted obstructionvalue) without relevant maximum flow rate changes indicates a lessobstructed second voiding.

The discussion by the authors that “bladder fatigue,” as observedby Bross et al during quick repetition of electrostimulation (reference16 in article) or detrusor over distention (reference 17 in article)1 isnot likely the cause of the decrease in voiding pressures withoutmaximum flow rate variation. In the case of electrostimulation theconditions for initiation and quality of detrusor contraction are to-tally different. Bladder over distention is only evident when a sig-nificantly higher filled volume is used during the second or thirdfilling of the bladder. In the article by Rosier et al the filled volumesdid not vary significantly during the second repeat measurement buteven so detrusor pressure at maximum flow rate was significantlylower. Furthermore, the authors provide no data for bladder fatigue

during a significant reduction of detrusor contractility. A second butcoarse method is the variation of the detrusor pressure at maximumflow rate point on the Schafer nomogram into an area of lowerdetrusor contractility. In view of the pressure values published thisfact is also not convincing. The only explanation remaining is thevariation of the grade of obstruction, which the authors present inthe reduction of Abrams/Griffiths number and urethral resistancealgorithm, which is in agreement with others (references 4 to 6 inarticle).

The reproducibility of urodynamic measurements becomes a deci-sive question when they are the basis for diagnosis and therapeuticdecision. Complete relaxation of the urethral muscles is a precondi-tion for the diagnosis of mechanical obstruction, as unfavorableinvestigation conditions (unfavorable position of the patient duringvoiding or disturbance during investigation) make complete relax-ation of the sphincter muscles and, thus, detection of the mechanicalresistance (resistance remaining after complete relaxation of theurethral muscles) impossible. Therefore, measurements should berepeated in any case to achieve relaxation of the urethral musclesduring voiding. Each investigation showing the lowest value of me-chanical obstruction is considered correct during repeated meas-urement, independent of the type of analysis or classification con-cept. In principle the lowest detrusor pressure at maximum flow ratevalue registered on repeated measurements is valid, if only singlepoints of the pressure flow plot are used for classification. If duringmultiple measurements equal maximum flow rate values are regis-tered, the investigation with the lowest detrusor pressure duringmaximum flow rate should be used. The same procedure applies forminimal voiding pressure.

Klaus HofnerDepartment of UrologyHannover Medical SchoolHannover, Germany

1. Bross, S., Schumacher, S., Scheepe, J. R. et al: Effects of acuteurinary bladder overdistension on bladder response duringsacral neurostimulation. Eur Urol, 36: 354, 1999

REPLY BY AUTHORS

We found a decrease in bladder outlet obstruction at short-termretesting, which did not result in improved flow rate because repeatvoids were performed with a lower detrusor pressure. We used thesomewhat simplistic term bladder fatigue for this phenomenon.However, the decrease in detrusor pressure at repeat voiding mightalso have been a result of adaptation of the detrusor to a lower levelof bladder outlet obstruction, and it might have been more appropri-ate for us to use a more generic term.

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