An Evaluation of Voiding Cystometry as a Diagnostic Test for Bladder Outlet Obstruction

THE

J OUR)l".AL

OF UROLOGY

Vol. 92, No. 5 November 1964 Copyright© 1964 by The Williams & Wilkins Co. Printed in U.S.A.

AN EVALUATION OF VOIDING CYSTOMETRY AS A DIAGNOSTIC TEST FOR BLADDER OUTLET OBSTRUCTION JOHN P. DONOHUE

GUY W. LEADBETTER, JR.

AND

From the Massach1.tsetts General Hospital, Boston, M~assachusetts

Are voiding pressure studies necessary or even helpful in evaluating bladder outlet obstruction? In an effort to answer this question, the voiding cystometrograms of 250 patients at the Massachusetts General Hospital kwe been reviewed. We hope to learn at least two things: 1) what is the normal range of voiding cystometry and 2) how do normal voiding cystometric studies differ from those in patients with proven bladder neck obstruction. Prior to Dr. Bodo von Garrelts' 1 classic studies of voiding cystometry in 1956 and 1957, water manometry was the only means used for recording bladder pressures. Von Garrelts employed a more sensitive system whereby pressure changes were transduced into electrical equivalents, amplified, and recorded by a photokymograph. Despite these electronic recording systems now used at many centers, cystometry by this method remains a relatively cumbersome and elaborate technique. METHODS AND MATERIALS

A total of 250 patients, private and ward, was evaluated with voiding cystometry at the Massachusetts General Hospital from October 30, 1961 to May 30, 1963; 188 were female and 62 were male. The age range was 1 to 67 years with the majority between 3 and 12 years. A complete history, physical examination, hemogram, urinalysis and urine culture were obtained on each patient. The majority had a voiding cine cystogram immediately after the cystometric study and all but a few patients had an endoscopic examination of the bladder, bladder neck, and urethra. The equipment used was a standard Sanborn Accepted for publication July 10, 1964. Read at annual meeting of American Urological Association, Inc., Pittsburgh, Pennsylvania, May 11-14, 1964. 1 Von Garrelts, B.: Analysis of micturition: A new method of recording the voiding of the bladder. Acta chir. Scand., 112: 326-340, 1956. Von Garrelts, B.: Intravesical pressure and urinary flow during micturition in normal subjects. Acta chir. Scand., 114: 49-66, 1957.

recording polygraph with amplifier, strain gauge, and a pressure transducer (fig. 1). A polyethylene catheter (luminal dian1eter 0.9 mm.) was used to record intravesical pressure per urethram. The following technique was used. Each patient was asked to void and was then catheterized using a small rubber coude catheter (6-14F) together with the recording polyethylene catheter. Care was taken to insert the polyethylene catheter at least 2 to 4 cm. beyond the bladder neck; its outer end was taped to the labia and thigh and connected to the strain gauge tubing.* With the patient seated on a bedpan, zero level of the transducer was set at the upper level of the symphysis pubis (fig. 2). After determination of residual urine, the bladder was filled through the rubber catheter at a rate of about 22 cc/min. with normal saline around 37C. During filling the maximum filling pressure and the onset of spontaneous contractions were recorded. When the patient reported fullness or desire to void, the rubber catheter was removed and the patient allowed to void around the polyethylene catheter. Prior to voiding, the patient was reminded not to strain either in starting or stopping the urinary stream. The recording was continued until the post-voiding pressure returned to the initial pre-voiding level. Each subject had at least three voidings recorded with every pressure study, and the most relaxed one was selected for study. Most patients had followup voiding. pressure studies after corrective surgery, or necessary medical treatment. The artifacts produced by abdominal straining can easily be recognized while a tracing is in progress; but in order to reduce the artifacts to a minimum * The technique of using a small urethral catheter for recording voiding pressures may be questioned. In order to determine if recordings could be as accurate via a urethral catheter as via a suprapubic one, 2 patients early in this study had voiding pressure recorded via a 14F suprapubic catheter as well as by a urethral polyethylene catheter (luminal size 0.9 mm.). Tracings were identical. Hence, a suprapubic recording catheter was considered to be of no advantage and was abandoned.

464

VOIDING CYSTOMETRY AS TEST FOR BLADDER OUTLET OBSTRUCTION

465

Fm, L Equipment used for catheterizing patient for cystometry

filling pressure (mm, Hg,), spontaneous contractions (mm. Hg.), amount voided (ml.), residual urine (ml.), voiding time (sec.), voiding rate''' (ml./sec.), maximum voiding pressure (mm. Hg.), and resistance factor (maximum_ voiding pressure) (ml. voided per second) RESULTS

Patients were divided into three group.s: 1) Normal, 29 patients: Aside from enuresis, all had a normal urological history. All had normal excretory urograms. Kone had eviclence of infected urine by microscopic examination or culture. Almost all of these patients had voiding cine cystograms and endoscopy, and each study was normal. 2) Bladder neck obstruction, 44 patients: A history indicative of urinary tract abnormality Fm. 2. Patient, nurse and equipment in setting for voiding cystometry,

and to produce consistent recordings, a registered nurse, trained specifically for this work, was used as a technician. In this way, recordings were reproducible and internally consistent in her hands. Cystometric parameters tested were maximum

* Voiding or flow rate was recorded by a stopwatch and measuring cylinder, and the amount voided in ml. was divided by the voiding time in seconds. Our method gave only an average value of urine flow in ml./sec. A balanced strain gauge in a urine collecting cylinder can measure the maximum urine flow rate, considered by some 2 to be a key factor in assessing outlet obstruction. 2 Gleason, D. M. and Lattimer, J. K.: Personal communication.

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Fm. 3. Each clot represents a patient. The 3 patient groups are normal, bladder neck obstruction (ENO), and all others combined (AOC), Relatively wide range of normal values appears strikingly similar to range of values in both obstructed groups, ENO and AOC,

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468

DONOHUE AND LEADBETTER

TABLE 1. Results of chi square (x 2) tests With Grouping*

No Grouping Category

Amount voided Residual urine Max. filling pressure Spontaneous contractions Time of voiding Voiding rate (cc/sec.) Max. voiding pressure Resistance factor

x'

DF

p

One group

x'

DF

p

Sig.

22.9229 13.0603 19.6105 50.8407 11.8205 19.9756 21.4989 30.6869

26 24 20 42 20

.625 .960 .500 .10 .500 .200 .992 .750

350+ 125+ 25+ 55+ 60+ 25+ 65+ 11+

8.030 11.094 14.892 13.066 10.071 15.170 18.127 23.192

14 10 10 22 12 10 26 20

.87 .364 .48 .920 .609 .135 .850 .275

No No No No No No No No

16

40 38

x' = Chi square DF = Degrees of freedom

P = Probability of obtaining x' under the null hypothesis One Group everything above stated level in that category was taken as 1 group Formula:

x' =

(Observed - Expected) 2 Expected

* Biostatisticians 3 have suggested the use of grouping to make the chi square test more accurate.

(frequency, dysuria, pyuria, or fever) was elicited from each patient. Most patients had bacteriuria and half had residual urine. The presence of bladder neck obstruction was diagnosed preoperatively by cine cystography and panendoscopy, and was confirmed at surgery in all patients. The corrective surgical technique was anterior Y-V plasty, excision of the obstructing tissue posteriorly, or both combined, as indicated in each instance. The bladder neck obstructions associated with ureteral reflux were not included in this group because voiding pressure rises may be dissipated during ureteral reflux which acts as a pressure "escape valve." 3) All others, 177 patients: These were abnormal in at least one respect. Many had infected urine, residual urine or persistent pyuria. Those with urethral stenosis were treated by dilation and a few by urethral meatotomy. Aside from some of the patients in this group who had ureteral reflux with bladder neck obstruction, none had open surgery. It became immediately apparent, after collecting the data, that the range of results was strikingly similar between the normal group and the two abnormal groups. This is graphically illustrated in figures 3 and 4. 3 Cochran, W. G.: Some methods for strengthening the common chi square tests. Biometrics, 10: 417-451, 1954.

To determine whether a significant difference did exist between the three patient groups, our data were analyzed in all eight cystometry categories by four calculations: 1) chi square (X2) testing, 2) calculation of the median, mode, mean and standard deviation from the mean, 3) statistical testing of the mean, and 4) analysis of variance. (See tables 1 to 4 with keys and footnotes.) Analysis by chi square testing revealed no significant difference in the frequency of case distribution within the three groups of any category. Statistical testing on the means, together with analysis of variance, showed a statistically significant difference between the means of the normal groups as opposed to the obstructed groups in the categories of spontaneous contractions, duration of voiding, voiding rate in ml. per second, residual urine, maximum voiding pressure, and resistance factor, but no difference for voided urine volmne or maxinium filling pressure. Interpretation of these analyses means that there was no significant difference as regards the frequency of case distribution within each group, but there was a significant difference in the statistical 1neans between the 3 groups in six of 8 categories. DISCUSSION

This study demonstrates a wide range of results for voiding cystometry in the normal subject. Results from patients in the two obstructed

VOIDING CYSTOJ\IIETRY AS TEST FOR BLADDER OUTLET OBSTRUCTION TABLE

Cystometric Category

2. Summary of statistics Factor

I Normal

others IIBNO All combined ---

1. Amount voided 2. Residual urine

Median Mode Mean S* Median Mode Mean

150 150 158.62 114.24 0 0

3 .12 2.79 10 10 12.59 5.28 25 30 27.5

s 3. Maximum filling pressure

Median Mode Mean

4. Spontane-

Median Mode Mean

ous contractions

s

s

17 .16

5. Time of voiding

Median Mode Mean

6. cc per second

Median Mode Mean

7. Maximum voiding pressure

Median Mode Mean

8. Resistance factor

Median Mode Mean

20 10 18.27 12.55 10 10 10.16 4.74 35 25 37.83 8.97 4 2 4 93 5.26

s

s

s

Is *S

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100 100 156.82 123.27 25 25 23.96 40.70 10 10 12.27 4.24 30 20 30.45 22.94 20 10 25.81 19.55 5

5 8.29 5.99 40 30 46.28 20.14 6 4 7.09 4.54

100 100 155.97 121.92 25 0 34.59 54.07 10 10 13.63 6.54 30 20 35.12 28.36 20 10 21.74 17.07 10 10 8.86 6.33 40 30 45.38 17.89 5 4 6.64 5.68

standard deviation.

groups overlap the normal range significantly enough to wa.na.nt our questioning the practical value of voiding pressure studies in the evaluation of patients suspected of having bladder neck obstruction. The original hope for voiding cystometry was that it might be a. specific test for ma.king a. diagnosis of bladder neck obstruction. Data. presented indicate that a. high voiding pressure is not a. sine qua non of bladder neck obstruction; and that it would be a. mistake to regard a. high voiding pressure (as some have, even in the presence of other normal studies) as the basis for doing a. bladder neck revision in a. child. As expected, nonna.l subjects did not have significant residua.I urine but 1na.ny patients with obstruction did. The significant difference in spon-

469

ta.neons contractions between groups 1 a.ncl 2 may be due to the presence of more active bladder infection in group 3 and, therefore, more irritable bladders with earlier contractions in that group. One n1ight expect an obstructed bladder neck to let urine out at a. somewhat slower than normal rate a.ncl, statistically, there was a significant difference between groups 1 and 2 for duration of voiding and voiding rate in cc/sec. (table 4). ·Finally we expected that a. bladder obstructed at its outlet would respond with higher than normal voiding pressures, thereby increasing the resistance factor. Indeed, there was a. statistical difference between the means of nornial and obstructed data.. Yet half of the obstructed patients ha.cl voiding pressures within normal range. The 90 per cent R factor overlap on figure 4 is misleading because of the large standard deviation. For convenience, if R factor 5 is selected as a ceiling, 72.5 per cent (21/29) normal cases, 45.5 per cent (20 /44) bladder neck obstruction cases, and 54.8 per cent (97 /177) all other cases had an R factor of 5 or under. Therefore, half of the obstructed cases ha.cl R factors in the normal range. Leaders in the field of cystometry have likewise noted a wide normal range. 4 Some clinicians have felt that voiding cystometry could become a. helpful tool for establishing the diagnosis of bladder outlet obstruction;5 others have not. 6 This large series affords a. chance to compare adequately large groups of completely documented normal a.ncl obstructed patients. Most important is the fact that the frequency of distribution is much the same in both normal and obstructed groups. This in no way is contradicted by the fact that in 6 categories, there i.s a significant difference between the mean of the normal groups as opposed to the obstructed ones. This suggests that the grouping was correct and the data. internally consistent. But these calculations allow only a. statistical comparison. Yet, as the chi square test shows in any individual case, it is almost impossible to accurately predict from cystometry data. into what patient group (1, 2 or 3) he or she will fall. Therefore, as a diagnostic test 4 Zinner, N. R. and Paquin, A. J., Jr.: Clinical urodyna.mics I: Studies of intra.vesical pressure in normal human female subjects. J. Urol., 90: 719-730, 1963. 5 Murphy, J. J. and Schoenberg, H. W.: Observations on intra.vesical pressure changes during micturition. J. Urol., 84: 106-110, 1960. 6 Weyrauch, H. lVI., Lucia, E. L. and Howard, J.: The failure of the cystometrogra.m as a. diagnostic test. J. UroL, 51: 191-209, 1944.

470

DONOHUE AND LEADBETTER

TABLE 3. Test on means Category

Groups Examined

z

1. Amount voided

Normal vs. ENO (II) ENO (II) vs. AOC (III) Normal (I) vs. AOC (III) Normal vs. ENO ENO vs. AOC Normal vs. AOC Normal vs. ENO ENO vs. AOC Normal vs. AOC Normal vs. ENO ENO vs. AOC Normal vs. AOC Normal vs. BNO ENO vs. AOC Normal vs. AOC Normal vs. ENO

.064 .139 .116 2.495 1.114 6.568 .269 1.698 .963 .612 1.132 1.928 1.989 1.348 1.291 1.505

ENO vs. AOC Normal vs. AOC Normal vs. ENO ENO vs. AOC Normal vs. AOC Normal vs. ENO ENO vs. AOC Normal vs. AOC

0.547 1.310 2.458 0.269 3.629 1.817 0.815 1.601

2. Residual urine

3. Maximum filling pressure 4. Spontaneous contractions 5. Time of voiding 6. Cc voided/sec.

7. Maximum voiding pressure 8. Resistance factor

Formula:

- -/s

Z = (X, - X2)

---'-2 N,

a Level

1 1 1

.5255 .4745 .5553 .4447 .5462 .4538 .0063 .132 .0001 .367 .045 .168 .270 .129 .027 .023 .089 .098 .066 .292 .095 .007 .394 .0001 .035 .208 .054

Significant Difference

No No No Yes No Yes No Yes No No No Yes Yes No No No, but almost No No Yes No Yes Yes No Yes

S,' + -=-N2

Z = N(0,1)

X = Means S 2 = Variance S = Standard deviation

N = Number of cases Z = Standardized form to test difference between means a = Significance level

to determine if bladder neck obstruction exists in a given patient, voiding cystometry by our method is of little practical value. Nevertheless, cystometry is still of value in special cases of bladder dysfunction. On the basis of this study, pediatricians should not feel that a voiding pressure study is an essential part of the diagnostic investigation for all children with repeated episodes of urinary tract infection and suspected bladder neck obstruction. Although cystometry may be an adjunct in our own experience, we have found that an excretory urogram, a good voiding cine cystogram, bougie

a boule calibration of the bladder neck and urethra and panendoscopy have been the most helpful studies in confirming the diagnosis of bladder neck obstruction. Our present esti1nates of a resistance factor do not take into account the turbulence of urethral flow, as noted by Paquin and Pierce. To provide better correlation between pressure and flow measurements, Paquin7 suggests incorporating velocity pressure drop as well as friction pressure 7 Ritter, R. C., Zinner, N. R. and Paquin, A. J., Jr.: Clinical urodynamics II: Analysis of pressureflow relations in the normal female urethra. J. Urol., 91: 161-165, 1964.

VOIDING CYSTOMETRY AS TEST FOR BLADDER OUTLET OBSTRUCTION

TABLE 4. Results of analysis of variance between groups I, II, III Category

F

DF

--

1. Amount voided 2. Residual urine 3. Maximum filling pressure 4. Spontaneous contractions 5. Time of voiding 6. Cc per second 7. Maximum voiding pressure 8. Resistance factor

Significant Difference ----a Level

.0056 2,271 >.50 3.320 2,162 > .05 1.138 2,253 .25

No Yes No

5.544

2,256 >.005

Yes

3.107 9.910 1.688

2,236 .05 2,226 > .005 2,269 .025

Yes Yes No

3.930

2,243

Yes

.025

Formula:

'I:, 1n/t;' - 'I:,nx' K

F=-------

Liixi/ - LJnJXl n - k

Mean Square Between Groups Mean Square Within Groups DF = Kin - K

X = Over-all mean for the three groups X; = Mean for the Jth Group. J = 1, 2, 3 X;; = Measurement on the 0th item in Jth group N = Total number of cases N; = Total number of cases in Jth group K = Number of groups = 3 L = Sum F = Ratio of variance between groups to variance within groups DF = Degrees of freedom drop into a physically more correct resistance factor, which then 111.ight more accurately indicate outlet obstruction. Pierce8 has emphasized the need to incorporate physical hydraulic principle::, in making resistance to flow measurements, and the fallacy of basing judgments relative to the bladder outlet on the flow rate or voiding pressure alone. Gleason and Lattimer 9 report that a differential strain gauge can erase abdominal straining from. intravesical pressure 8 Pierce, J. JVI., Jr., Braun, E., Sniderman, A. J. and Lewis, H. Y.: The concept of resistance to

flow applied to the lower urinary tract. Surg., Gynec. & Obst., 116: 217-222, 1963. 9 Gleason, D. M. and Lattimer, J. K.: The interpretation of voiding pressure. J. Urol., 91: 156160, 1964.

471

measurements, and a pressure curve of pure detrusor contraction is said to result. A combination of these improvements may produce more characteristic obstructed versus normal tracings. Time and sin1ilar statistical analysis will yield the answer. Finally, there is a wide range of normal in almost every facet of human function and behavior. In assessing the human bladder outlet by cystometry, there are many variables in health and disease (such as patient anxiety, bladder infection or decompensation, ureteral reflux to mention a few) which may influence the result. In order to prove the diagnostic value of cystometry, three factors must exist: 1) There must be a large retrospective study to insure correct grouping, with enough normal subjects to allow comparison of obstructed versus normal groups. 2) If computers are used to process data, the specifications of the program must be correct. 3) One's data should be independently analyzed by biostatisticians. Until such analysis of other methods and data are available, cystometry by our method must be regarded a questionable adjuvant at best, and, for practical purposes, we shall rely on the other diagnostic acids mentioned above for assessment of the bladder outlet. SUMMARY

The experience with voiding cystometry in 250 cases at Massachusetts General Hospital has been reviewed. In order to determine the range of normal, and how cystometry differs from normal in subjects with proven bladder neck obstruction, the patients were divided into three groups: 1) 29 normal subjects, 2) 44 patients with proven bladder neck obstruction and 3) 177 patients who, for the most part, were children with infected urine who did not undergo open surgery but who were treated medically and with urethral dilation for early to moderate outlet obstruction. Data for each patient group were compared and analyzed in eight cystometry parameters. Chi square testing for each parameter showed there was no significant difference in case distribution within the three patient groups. Statistical tests on the means together with analysis of variance for each parameter showed there was a statistically significant difference between the means of the normal group (No. 1) as opposed to obstructed groups (Nos. 2 and 3) for the parameters of spontaneous contractions, duration of

472

DONOHUE AND LEADBETTER

voiding, voiding rates, residual urine, maximum voiding pressure and resistance factor. These results demonstrate the wide range of normal in voiding cystometry and, conversely, the large percentage of measurements from obstructed patients which overlaps the normal range. Inherent problems in interpreting cystometric data, and current improvements in theory and technique are mentioned. As a diagnostic test therefore, to determine if bladder outlet obstruction exists in a given patient, voiding cystometry by our method is nonspecific and has been of little practical value. We wish to thank Mrs. Andrea Pollack, R.N., and Mrs. Nancy Spear, R.N., for performing the

cystometric studies meticulously for more than 4 years. Their charm disarmed the many apprehensive children studied and made obtaining the best possible results a reality. Also, to Miss Toby Kraus, M.A., M.G.H. biostatistician from Harvard University, we extend thanks for invaluable assistance in statistical analysis of our data. Finally, we are grateful to Miss Alice Danforth for preparation of the manuscript. REFERENCES BRUNK, H. D.: Mathematical Statistics. New York: Ginn and Co., 1960. BENNETT, C. A. AND FRANKLIN, N. L.: Statistical Analysis in Chemistry and the Chemical Industry. New York: John Wiley and Sons, Inc., 1954. ScHEFFE, H.: The Analysis of Variance. New York: John Wiley and Sons, Inc., 1959.