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Mural Tension in Vesical Disorders and Ureteral Reflux
THE JOURNAL OF UROLOGY
, Vol. 91, No. 1
i Copyright © ·
January 1964 1964 hy The Williams & Wilkins Co. Printed in U.S.A.
MURAL TENSION IN VESICAL DISORDERS AND URETERAL REFLUX FRANK HINMAN, JR.
AND
EARL R. MILLER
From the Division of Urology and the Department of Radiology, University of California School of Medicine, San Francisco 22, Cal.
of tension to pressure at increasing volumes is shown graphically in figure 2, B. Stress (S), the force upon the unit area of the bladder wall, may be looked upon as tension in two dimensions. It is defined as the product of pressure and volume, S = PV; where S is expressed in relative units as gm. F /cm2 •
Studies of vesical physiology usually consider the bladder only as an active neuromuscular, reflex organ. Yet part of its function arises from its purely physical, elastic properties. 1 • 2 Current research in vesical physiology has concentrated on measurement of intravesical pressure, vesical volume and rate of flow during micturition, -'"'Llu""'---- overlooking the stresses which volume and pressure place on the bladder wall itself. Mural tension, a measure of the stress placed upon the wall of the bladder during filling and emptying, is the key to an understanding of the opening of the vesical neck in normal and abnormal micturition and provides the link between the vesical neck and the ureteral orifice. The present studies deal with elasticity in 4""=c.u~"'------' normal vesical filling, including the implications of "accommodation," with neuromuscular tension at the vesical orifice during micturition, in addition to changes in tension with prostatic obstruction and urinary retention, and the role of . tension at the trigone and vesical neck in pre: venting ureteral reflux. 1
NORMAL CYSTOMETROGRA.M CORRELATING 2.00 PRESSURE (P) MURAL TENSION (T) ANO MURAL STRESS (S=PV.
0
1
t
ZTO
I
'i'
-. = MURAL STRESS o---o
=
X····X
= PIUSSUR.E
I
I
I
MURAL TENSION
I I
I
I I
I
I I I
I
,' ~ p' i:
ELASTIC PROPERTIES OF THE BLADDER (PASSIVE MURAL TENSION)
/I
Normal vesical filling. Bladder pressure rises , very little, if at all, during the major portion of · filling. The flat, phase II portion on the cystometrogram illustrates this (fig. 1). Yet the tension : in the wall rises progressively, since the volume : is increasing. The mathematical derivation of the formula for bladder tension, T = P · yV · .312, where T is mural tension in gm. F /cm., P - I is intravesical pressure in cm. H20 and V is : volume in cc, is shown in figure 2, A. The relation
Read at annual meeting of American Association of Genito-Urinary Surgeons, Chicago, Ill., . May 8-10, 1963. Supported in part by a grant from the Research Committee of American Urological Association, : Inc., and in part by Grant C-9440 from the United : States Public Health Service. 1 Tang, P-C and Ruch, T. C.: Non-neurogenic _,,=~; ____ ,: basis of bladder tonus. Amer. J. Physiol., 181: 249, 1955. 2 Brody, D. A. and Quigley, J. P.: Some physical factors in receptive relaxation. Fed. Proc., 6: 82, 1947. .
_,,,-
20
.o-,-.0-'.o"
.:
__ x
- ___ .,..~--1<----x-----*----x··0 l.oa~--'---'---L--L__ 0
100
200
300
400
500
cc FIG. 1. Normal cystometrogram (X) of 24-yearold man free of urologic disorder. Note typical flat "phase II" extending from 50 to 400 cc. Calculation of mural tension (0), an expression of passive elastic properties of bladder wall, shows it to rise continuously throughout filling (since tension is function of pressure and volume). Calculated stress (solid dots) rises even more steeply. VOLUME IN
From figure 1, it is seen that in this representative, normal patient, the intravesical pressure rose little if at all during most of filling. The tension started slightly lower than did the pressure and rose progressively as the volume increased. As the elastic limits of the bladder were reached, pressure rose but mural tension increased even more rapidly, although a voiding reflex was absent. 33
34
HINMAN AND MILLER
A
T T I
r
T= PR 2
- P·W.
. 312.
BLADDER WALL TENSION vs PRESSURE AT VARIOUS VOLUMES
r
~
150
t
--·-r:~;
14c hi Jf¥-;;-~::-=~;~:ff*+>'f-*>"'J,
------·- +-t_.-1_-
Ii
..
~ liq
!co
100
~
.••• i-{-Tl'!.7: ~!ri~fj~,jz:~~12~1'."f~~..,.'?1'~~----lf-i
..
(
!
.l+--fr~hl'-n'!Ml(7":j.',,!W.'!'----h-"-'-t-::~
60
0
200 IILADDE.R
Fm. 2. A, if bladder is represented as a sphere, force required to hold halves together at edge of imaginary coronal line equals force pushing halves apart, so that: intravesical pressure (P) times area of coronal surface against which it works (1rR 2) equals force or tension (T) times length of coronal line which holds halves together (21rR); or P ·1rR• = T · 21rR. To re-express this in terms of tension, T = PR/2. Since radius is related to volume, tension equals pressure times the cube root of the volume times a factor, .312, (T = P~y· .. 312, and is expressed in gm. force/cm.). B, graphic representation of relation of tension to volume and pressure.
MURAL TENSION IN VESICAL DISORDERS AND URETERAL REFLUX
35
RELATION OF MURAL STRESS TO PRESSURE AND VOIDING RATE FILL
VOID
1qooo
r,
I \ II
300
V incc
200
\
.. I I
0 40
MURAL STRESS (PV)
1
~,' ,
'\
gm F/cm'2
\
''
5,000
,
\
'
'~:~:::~>< /- - -\~-,-,·. . . . . . . ..
p
in cmH 2 0
',
II
100
STRESS (PV)
'\
I I
20
._._.,,,--...............................
0:
'
0
~ 2 MIN.------l,iE--f2 SEC.~:
Fm. 3. Relation of mural stress to pressure and ·ct· t A bl dd · · re1!11aints relativelyh constant but mural stress rise:, 0to 1~e~~h :· pe~k !t s~~:; !P:~rJr~grast~~s~1rh:ss:r c mes o approac zero at end of detrusor contraction. · n eStress, being directly related to both volume and pressure, shows an even steeper curve, as would be expected. The relation between pressure, volume and stress during filling and voiding is shown in figure 3. Vesical "tone." Osborne's studies of the filling of rubber balloons with air 3 show that the pressure rises slowly at first, then progresses to a peak, then falls to a plateau as overfilling occurs. He could not show the fall after the peak in excised aninlal bladders, but Lawson and Tomlinson4 did, using living dogs with acute retention. We were unable to fill the dog's bladder in situ sufficiently to demonstrate a decline in pressure after the peak had been passed. Our own experiments with sequential filling and emptying of the dog's bladder show that the period of "accommodation" occurs whether the animal is alive or dead. The same phenomenon of "accommodation" is seen in the denervated bladder in spinal shock. Since it occurs without nerve supply, "accommodation" is a physical, not a reflex, characteristic of the detrusor. The increase in pressure after the "accommodation" 3 Osborne, W. A.: The elasticity of rubber balloons and hollow viscera. Proc. Roy. Soc. London (B), 81: 485, 1909. • 4 Lawson, J. ~. and Tomlinson, W. B.: Observat10ns on dynamics of acute urinary retention in dog. J. Urol., 66: 678, 1951.
phase is more abrupt in the living than in the dead bladder, indicating beginning of reflex activity. NEUROMUSCULAR PROPERTIES OF THE BLADDER (ACTIVE MURAL TENSION)
Mural tension during voiding. Mural tension may be increased by active contraction of the detrusor as well as during the passive filling just discussed. If one postulates that the detrusor muscle has its origin and insertion in the posterior urethra (fig. 4), the effect of its contraction will be to draw open the vesical neck much as will squeezing a half-filled toy balloon. Tension, as a force in the wall of the bladder, is a more realistic indication of the forces involved in opening the neck than is pressure alone, and it may be demonstrated by the following analysis that this tension at the vesical neck promotes its function. It is a common observation that the rate of micturition is higher as vesical volume increases. This relationship was analysed in the normal male by von Garrelts who observed that even though voiding pressure was independent of bladder volume, the rate of voiding was related to the volume of fluid in the bladder at the start of micturition. From this he concluded that urethral resistance is lower when the voided volume is large than when it is small.
HINMAN AND MILLER
36
Fm. 6. Frame of cine study shows abnormal detrusor contraction with "waist" above trigone. In such a case, mural tension is not transmitted in normal way to vesical neck.
Fm. 4. Simplified diagram of relation between forces of detrusor contraction (active mural tension) and intravesical pressure. Contraction of detrusor around its contents pulls open vesical neck. 40
80
8
30 0
ti
~
00 000
u u 2.0
~ ~
•
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.... 00
0
~ II
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00
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/
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/"·
24
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16 o
8
0 0
100
200 VOLUME
300
400
0
(cc)
Fm. 5. Voiding rate (closed dots) and mural tension (open circles) in normal male subjects at varying volumes, assuming constant intravesical pressure of 32 cm H20. Close correlation between two curves suggests causal relationship (rate data from von Garrelts 5). We can help explain this phenomenon by relating volume, pressure and rate to mural tension. The greater the mural tension, which is dependent upon both volume and pressure, the larger the volume in the bladder at the start of voiding. For example, in a bladder containing 200 cc and having a normal micturition pressure of 32 cm. H20, the mural tension is 57.5 gm. F /cm. At double the volume, but with the same normal micturition pressure, the tension is 73.5 cm. F/cm,
Von Garrelts 5 published data on voiding rate and bladder volume from 59 recordings of micturition in 47 young men. If these data are related to mural tension (fig. 5), the voiding rate and mural tension rise in parallel as the volume increases. This correlation agrees with the concept that mural tension is the force which opens the neck of the bladder and not positional disposition o± the fibers in the full bladder, or other static condition. The greater the force, the wider the opening. Disorganization of the detrusor in the region of the vesical neck, caused by congenital malformation or disease, may prevent transmission of mural tension to the walls of the posterior urethra and thus interfere with the normal reduction of urethral resistance which accompanies the proper opening of the bladder neck (fig. 6). These interrelationships will become even more pertinent when we discuss vesicoureteral reflux. Analysis was made of 47 records selected from patients whose intravesical pressure and voiding rates were recorded simultaneously at the University of California Medical Center. Twentyfour were from girls with recurrent infection, seven from boys principally with vesical neck obstruction, and 16 from adult patients with various lower tract disorders. Mural tension was plotted first against maximal voiding rate. As figure 7, A shows, poor correlation is obtained (in contrast to the good correlation in normal male patients seen in figure 5). This is interpreted as evidence that varying degrees of disturbance of the vesical neck opening mechanism exist in these patients. Further, a plot of tension against urethral resistance (fig. 7, B) also shows poor correlation, presumably for the same reason. 5 von Garrelts, B.: Micturition in normal male. Acta chir. scand., 114: 197, 1957 (fig. 7).
37
MURAL TENSION IN VESICAL DISORDERS AND URETERAL REFLUX
B
A
olso
~o
~
~
•= BOY$ (7)
{>
GIRLS WITH RECURRENT x=ADULTS (/6) INFECTION (24)
!
0=
•=BOY$
30
o=61Rl$ WITH RECURRENT INFECTION
X
. "
" 00 0
" 0 a,
0
""
00
"=ADl/LTS
oo><>
)(
)( 00
0
"
"' 0
to
.
.
"
X
•
"
~ )(
" 0 '---'---'--------"--------'--0 50 too 200 300
T (gm F/cm)
X
0
0 0
.$al< o ~ iio oX• O
0
0
.
100
T
"
"
200
(gmF/cm)
. Fm: 7. A, relation of mura_l tensi?n to yoiding rate in t~ree groups of patients: girls with recurrent mfect10n; boys, and adults with various disorders. Correlat10n is minimal. . B, relation of mural tension to urethral resistance in three groups of patients. Only slight correlation 1s observed. PROSTATIC OBSTRUCTION AND ACUTE URINARY RETENTION
distended bladders had lost them. The pressure and tension curves obtained from the patient with the largest bladder during withdrawal of fluid and replacement show a decline during refilling (fig. 8, B). Hence overfilling alters the elastic tension of the wall, decreasing the forces available for opening the neck. The result is retention.
Prostatic hypertrophy, because the adenoma is growing in the vesical neck, interferes with the ability of the detrusor to open the internal sphincter. The result is delayed opening (producing hesitancy) and premature closure, as the detrusor continues to contract (causing dribbling and residual urine). The extreme example of inability to open the bladder neck occurs in acute urinary retention. Bladder pressure determinations were made on a series of such patients during withdrawal of fluid and refilling the bladder. These are reported in a separate communication. 6 It was found that both pressure and tension fell rapidly during decompression. Both rose even more rapidly during refilling. If the bladder were small (less than 1000 cc) the rise was greater than if it were large (over 1000 cc) (fig. 8, A). This finding suggests that the smaller bladders had retained more of their elastic properties, whereas larger, over-
Mural tension increases during filling of the bladder and during micturition not only in the vesical wall itself, but also in the trigonal structures, which make up a part of the vesical neck mechanism and continue upward to attach to the terminal ureter. Dissection of the ureter and trigone (well shown by Uhlenhuth and Hunter 7 and more recently brought into focus by Tanagho 8) has shown that the trigonal muscle is a continuation of the ureter into the posterior urethra and that W aldeyer's sheath, after encircling the distal ureter, also
6 Osius, T. G. and Hinman, F., Jr.: The dynamics of acute urinary retention: A manometric, radiographic and clinical study. J. Urol., 90: 702, 1963.
7 Uhlenhuth, E. and Hunter, deW. T.: Problems in the Anatomy of the Pelvis. Philadelphia: J.B. Lippincott Co., 1953. 8 Tanagho, E.: Personal communication.
VESICOURETERAL REFLUX
38
HINMAN AND MILLER
VOLUME IN CC
200
DECOMPRESS/ON
REFILLING
A 150 TENSION (CmHaO) . _ _ LARGE BLADD.ERS
100
(>IOOOcc)
o-----o SMALL BLADDERS (/000 cc OR LESS)
50
_.,a-·-----· 0-
----0-------0-_
,.O} PRESSURE
_.-----_._.--. (gmF/cmJ
o"=-_
_.___,L___.......___,__,__ _J__-1....,_ _ _ _ _ __ OP - 5 -15 -100 +5 +85 +100
B 100
1800cc VOLUME
80
DECOMPRESSION
REFILLING
60 40
20
-ts -too +s
+85
+100
Fm. 8. A, acute urinary retention: relation of pressure and tension on withdrawing 100 cc fluid and replacing it in smaller and large bladders. B, effect on pressure of withdrawal and refilling very overdistended bladder of 1800 cc volume, showing loss of elasticity. passes through the vesical neck (fig. 9). Thus, the distal ureter is functionally and anatomically related to the vesical neck. Any disorder of this system (congenital
malformation, neurologic disease, or acquired disorder) will prevent normal transmission of mural tension from the bladder neck to the intravesical and intramural ureter. In these
MURAL TENSION IN VESICAL DISORDERS AND URETERAL REFLUX
39
ureteral orifices in position if the trigone and vesical neck were relaxed through defective innervation, disease or congenital abnormality. Moreover, abnormalities of these continuous structures would not only allow reflux of urine into the ureter, but also render less efficient the mechanism which opens the vesical neck. SUMMARY AND CONCLUSIONS MIDDLE CIRCULAR MUSCLE.
Ol/TER LONGITUDINAL MUSCLE
Frn. 9. Schematic cross-section of_ureter, trigone and ves1cal_ neck showmg how tension on trigonal and retrotngonal muscles will hold ureteral orifice m mtravesical position (from data of Tanagho 8 ).
disorders, the ureteral orifice is less fixed. Under various conditions it rises and becomes more extravesical so that it loses the essential ingredients of the submucosal tunnel and the muscular backing required for competency. Thus it permits reflux of urine from the bladder to the ureter. In a previous communication 9 it was reported that most ureters in children with recurrent infections permitted reflux at low bladder pressures and low vesical volumes ("low pressure reflux"). In these cases mural tension is low. l\!J:ural tension, as we have noted, is a more accurate and sensitive indicator of the forces acting on the vesical neck than is either pressure or volume alone and was calculated for those cases which refluxed only during filling (fig. 10, A.). :.\foral tension is relatively low at the time of "low pressure reflux" compared to the almost 3 times higher value at the time of void when reflux did not occur (fig. 10, B). Since the tension is so low (27 .6 gm. F /cm. at reflux compared to 75.6 gm. F /cm. at the time of voiding (fig. 10, B)), it would be less likely to hold the , '_Hinman, F., Jr., JVIiller, E. R., Hutch, J. A., C~amey, M. D., Cox, C. E., Goodfriend, R. B. and:JVIarshall, S.: Low pressure reflux: Relation of vesicoureteral reflux to intravesical pressure. J. Urol., 88: 758, 1962.
Passive intrinsic elasticity and active neuromuscular contraction are the two complementary functions of the bladder wall. The elastic structure of the bladder wall is passively stretched during a major part of filling of the bladder without a rise in intravesical pressure. This vesical "accorn.modation" or tone is the reflection of the purely physical elastic properties of the wall in its maintenance of constant, low intravesical pressure during bladder filling, even though mural tension, resulting from increasing stretch of the wall, is rising steadily. The development of high mural tension helps explain the high rate of voiding from a full bladder, since tension is highest in the wall of the bladder with the largest volume. It is felt that the higher tension of the bladder wall opens the bladder neck more widely which decreases urethral resistance on voiding. Graphically, mural tension has the same relation to voided volume as does the rate of flow. An analysis of recordings of intravesical pressure and micturition flow rates in 47 patients with various urologic disorders indicated only slight correlation between mural tension and both rate of voiding or calculated urethral resistance in contrast to the good correlation in normal subjects. This disparity reflects the varying degrees of vesical neck abnormality encountered in the patients. Patients with prostatic hypertrophy have hesitancy and dribbling with residual urine, because the action of tension at the vesical neck is blocked by the obstructing adenoma, which delays opening and hastens closure. In patients with acute retention, mural tension during refilling after withdrawal of urine was greater in smaller than in large bladders. This suggests that overstretching damages elastic activity in the bladder. Mural tension acts on the trigone, a structure continuous with the ureter, holding the ureteral
40
HINMAN AND MILLER
A MURAL TENSION AND MURAL STRESS WITH LOW PRESSURE REFLUX. (43 URETERS IN 25 PATIENTS)
REFLI/X
VOLUME
.,.,.,.,.,.it~fliii;;·'·'·'·'·'·'·· 17.B cn,H,,0
2X
VOID
REFLI/X
PRESSURE ·····················i!ii,,i!ij~····.....···········....-. 27.0gmF/cm
MURAL TONE
2.2. X
VOID
REFLI/X
·.·.·.·.·.·.·)*id.J1ii¢1fh:"-l'.i.·.·.·.·.U.U.U.U.U.U.U.U.U.U.U.U.U}.i.U
2.7X VOID
4.4X
MURAL STRESS
(PV)
VOID
B RELATIOM OF MURAL TENSION TO REFLUX AND VOIDING WITH LOW PRESSURE REFLUX. 100
~
MEAN VOWME AT REFLUX (122 cc}
~ 80
i
,t.
MEAN VOLUME AT VOID (240cc}
•
..._. 60
~
::S
Cl)
::!
~ !
r
• •
40
20 0
•
MEAN PRESSURE AT REFLUX (17.(J cm Hao) •
~MEA;;;;;ESSURE AT VOID (!19 cm H20}
••./ . .. i --•••• --.----.,----------------1-------. ---------. . . ----. -----------
.-
0
50
.: '
100
150
200
• •
250
300
350
400
VOLUME (cc) FIG. 10. A, comparison of volume, pressure, mural tension and mural stress at time of reflux, and at. time of voiding when reflux did not occur, in 43 instances of low pressure reflux in 25 patients. Note low mural tone (tension) associated with reflux. B, graph shows pressure, volume and tension in 47 ureters which refluxed only during filling and not dnring voiding.
orifice in a non-refluxing position during filling and voiding. Tension was low at the time of "low pressure" reflux in 43 ureters, none of which refluxed at high pressures, suggesting that the abnormal trigone-ureter complex in these cases required greater than usual tension to maintain
integrity against reflux. Thus, abnormalities of the trigonal muscle, Waldeyer's sheath and the underlying bladder wall in these children lessen the tension on the trigone and vesical neck and lead to reflux at low pressure, as well as to abnormalities of voiding.
, Vol. 91, No. 1
i Copyright © ·
January 1964 1964 hy The Williams & Wilkins Co. Printed in U.S.A.
MURAL TENSION IN VESICAL DISORDERS AND URETERAL REFLUX FRANK HINMAN, JR.
AND
EARL R. MILLER
From the Division of Urology and the Department of Radiology, University of California School of Medicine, San Francisco 22, Cal.
of tension to pressure at increasing volumes is shown graphically in figure 2, B. Stress (S), the force upon the unit area of the bladder wall, may be looked upon as tension in two dimensions. It is defined as the product of pressure and volume, S = PV; where S is expressed in relative units as gm. F /cm2 •
Studies of vesical physiology usually consider the bladder only as an active neuromuscular, reflex organ. Yet part of its function arises from its purely physical, elastic properties. 1 • 2 Current research in vesical physiology has concentrated on measurement of intravesical pressure, vesical volume and rate of flow during micturition, -'"'Llu""'---- overlooking the stresses which volume and pressure place on the bladder wall itself. Mural tension, a measure of the stress placed upon the wall of the bladder during filling and emptying, is the key to an understanding of the opening of the vesical neck in normal and abnormal micturition and provides the link between the vesical neck and the ureteral orifice. The present studies deal with elasticity in 4""=c.u~"'------' normal vesical filling, including the implications of "accommodation," with neuromuscular tension at the vesical orifice during micturition, in addition to changes in tension with prostatic obstruction and urinary retention, and the role of . tension at the trigone and vesical neck in pre: venting ureteral reflux. 1
NORMAL CYSTOMETROGRA.M CORRELATING 2.00 PRESSURE (P) MURAL TENSION (T) ANO MURAL STRESS (S=PV.
0
1
t
ZTO
I
'i'
-. = MURAL STRESS o---o
=
X····X
= PIUSSUR.E
I
I
I
MURAL TENSION
I I
I
I I
I
I I I
I
,' ~ p' i:
ELASTIC PROPERTIES OF THE BLADDER (PASSIVE MURAL TENSION)
/I
Normal vesical filling. Bladder pressure rises , very little, if at all, during the major portion of · filling. The flat, phase II portion on the cystometrogram illustrates this (fig. 1). Yet the tension : in the wall rises progressively, since the volume : is increasing. The mathematical derivation of the formula for bladder tension, T = P · yV · .312, where T is mural tension in gm. F /cm., P - I is intravesical pressure in cm. H20 and V is : volume in cc, is shown in figure 2, A. The relation
Read at annual meeting of American Association of Genito-Urinary Surgeons, Chicago, Ill., . May 8-10, 1963. Supported in part by a grant from the Research Committee of American Urological Association, : Inc., and in part by Grant C-9440 from the United : States Public Health Service. 1 Tang, P-C and Ruch, T. C.: Non-neurogenic _,,=~; ____ ,: basis of bladder tonus. Amer. J. Physiol., 181: 249, 1955. 2 Brody, D. A. and Quigley, J. P.: Some physical factors in receptive relaxation. Fed. Proc., 6: 82, 1947. .
_,,,-
20
.o-,-.0-'.o"
.:
__ x
- ___ .,..~--1<----x-----*----x··0 l.oa~--'---'---L--L__ 0
100
200
300
400
500
cc FIG. 1. Normal cystometrogram (X) of 24-yearold man free of urologic disorder. Note typical flat "phase II" extending from 50 to 400 cc. Calculation of mural tension (0), an expression of passive elastic properties of bladder wall, shows it to rise continuously throughout filling (since tension is function of pressure and volume). Calculated stress (solid dots) rises even more steeply. VOLUME IN
From figure 1, it is seen that in this representative, normal patient, the intravesical pressure rose little if at all during most of filling. The tension started slightly lower than did the pressure and rose progressively as the volume increased. As the elastic limits of the bladder were reached, pressure rose but mural tension increased even more rapidly, although a voiding reflex was absent. 33
34
HINMAN AND MILLER
A
T T I
r
T= PR 2
- P·W.
. 312.
BLADDER WALL TENSION vs PRESSURE AT VARIOUS VOLUMES
r
~
150
t
--·-r:~;
14c hi Jf¥-;;-~::-=~;~:ff*+>'f-*>"'J,
------·- +-t_.-1_-
Ii
..
~ liq
!co
100
~
.••• i-{-Tl'!.7: ~!ri~fj~,jz:~~12~1'."f~~..,.'?1'~~----lf-i
..
(
!
.l+--fr~hl'-n'!Ml(7":j.',,!W.'!'----h-"-'-t-::~
60
0
200 IILADDE.R
Fm. 2. A, if bladder is represented as a sphere, force required to hold halves together at edge of imaginary coronal line equals force pushing halves apart, so that: intravesical pressure (P) times area of coronal surface against which it works (1rR 2) equals force or tension (T) times length of coronal line which holds halves together (21rR); or P ·1rR• = T · 21rR. To re-express this in terms of tension, T = PR/2. Since radius is related to volume, tension equals pressure times the cube root of the volume times a factor, .312, (T = P~y· .. 312, and is expressed in gm. force/cm.). B, graphic representation of relation of tension to volume and pressure.
MURAL TENSION IN VESICAL DISORDERS AND URETERAL REFLUX
35
RELATION OF MURAL STRESS TO PRESSURE AND VOIDING RATE FILL
VOID
1qooo
r,
I \ II
300
V incc
200
\
.. I I
0 40
MURAL STRESS (PV)
1
~,' ,
'\
gm F/cm'2
\
''
5,000
,
\
'
'~:~:::~>< /- - -\~-,-,·. . . . . . . ..
p
in cmH 2 0
',
II
100
STRESS (PV)
'\
I I
20
._._.,,,--...............................
0:
'
0
~ 2 MIN.------l,iE--f2 SEC.~:
Fm. 3. Relation of mural stress to pressure and ·ct· t A bl dd · · re1!11aints relativelyh constant but mural stress rise:, 0to 1~e~~h :· pe~k !t s~~:; !P:~rJr~grast~~s~1rh:ss:r c mes o approac zero at end of detrusor contraction. · n eStress, being directly related to both volume and pressure, shows an even steeper curve, as would be expected. The relation between pressure, volume and stress during filling and voiding is shown in figure 3. Vesical "tone." Osborne's studies of the filling of rubber balloons with air 3 show that the pressure rises slowly at first, then progresses to a peak, then falls to a plateau as overfilling occurs. He could not show the fall after the peak in excised aninlal bladders, but Lawson and Tomlinson4 did, using living dogs with acute retention. We were unable to fill the dog's bladder in situ sufficiently to demonstrate a decline in pressure after the peak had been passed. Our own experiments with sequential filling and emptying of the dog's bladder show that the period of "accommodation" occurs whether the animal is alive or dead. The same phenomenon of "accommodation" is seen in the denervated bladder in spinal shock. Since it occurs without nerve supply, "accommodation" is a physical, not a reflex, characteristic of the detrusor. The increase in pressure after the "accommodation" 3 Osborne, W. A.: The elasticity of rubber balloons and hollow viscera. Proc. Roy. Soc. London (B), 81: 485, 1909. • 4 Lawson, J. ~. and Tomlinson, W. B.: Observat10ns on dynamics of acute urinary retention in dog. J. Urol., 66: 678, 1951.
phase is more abrupt in the living than in the dead bladder, indicating beginning of reflex activity. NEUROMUSCULAR PROPERTIES OF THE BLADDER (ACTIVE MURAL TENSION)
Mural tension during voiding. Mural tension may be increased by active contraction of the detrusor as well as during the passive filling just discussed. If one postulates that the detrusor muscle has its origin and insertion in the posterior urethra (fig. 4), the effect of its contraction will be to draw open the vesical neck much as will squeezing a half-filled toy balloon. Tension, as a force in the wall of the bladder, is a more realistic indication of the forces involved in opening the neck than is pressure alone, and it may be demonstrated by the following analysis that this tension at the vesical neck promotes its function. It is a common observation that the rate of micturition is higher as vesical volume increases. This relationship was analysed in the normal male by von Garrelts who observed that even though voiding pressure was independent of bladder volume, the rate of voiding was related to the volume of fluid in the bladder at the start of micturition. From this he concluded that urethral resistance is lower when the voided volume is large than when it is small.
HINMAN AND MILLER
36
Fm. 6. Frame of cine study shows abnormal detrusor contraction with "waist" above trigone. In such a case, mural tension is not transmitted in normal way to vesical neck.
Fm. 4. Simplified diagram of relation between forces of detrusor contraction (active mural tension) and intravesical pressure. Contraction of detrusor around its contents pulls open vesical neck. 40
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300
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Fm. 5. Voiding rate (closed dots) and mural tension (open circles) in normal male subjects at varying volumes, assuming constant intravesical pressure of 32 cm H20. Close correlation between two curves suggests causal relationship (rate data from von Garrelts 5). We can help explain this phenomenon by relating volume, pressure and rate to mural tension. The greater the mural tension, which is dependent upon both volume and pressure, the larger the volume in the bladder at the start of voiding. For example, in a bladder containing 200 cc and having a normal micturition pressure of 32 cm. H20, the mural tension is 57.5 gm. F /cm. At double the volume, but with the same normal micturition pressure, the tension is 73.5 cm. F/cm,
Von Garrelts 5 published data on voiding rate and bladder volume from 59 recordings of micturition in 47 young men. If these data are related to mural tension (fig. 5), the voiding rate and mural tension rise in parallel as the volume increases. This correlation agrees with the concept that mural tension is the force which opens the neck of the bladder and not positional disposition o± the fibers in the full bladder, or other static condition. The greater the force, the wider the opening. Disorganization of the detrusor in the region of the vesical neck, caused by congenital malformation or disease, may prevent transmission of mural tension to the walls of the posterior urethra and thus interfere with the normal reduction of urethral resistance which accompanies the proper opening of the bladder neck (fig. 6). These interrelationships will become even more pertinent when we discuss vesicoureteral reflux. Analysis was made of 47 records selected from patients whose intravesical pressure and voiding rates were recorded simultaneously at the University of California Medical Center. Twentyfour were from girls with recurrent infection, seven from boys principally with vesical neck obstruction, and 16 from adult patients with various lower tract disorders. Mural tension was plotted first against maximal voiding rate. As figure 7, A shows, poor correlation is obtained (in contrast to the good correlation in normal male patients seen in figure 5). This is interpreted as evidence that varying degrees of disturbance of the vesical neck opening mechanism exist in these patients. Further, a plot of tension against urethral resistance (fig. 7, B) also shows poor correlation, presumably for the same reason. 5 von Garrelts, B.: Micturition in normal male. Acta chir. scand., 114: 197, 1957 (fig. 7).
37
MURAL TENSION IN VESICAL DISORDERS AND URETERAL REFLUX
B
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. Fm: 7. A, relation of mura_l tensi?n to yoiding rate in t~ree groups of patients: girls with recurrent mfect10n; boys, and adults with various disorders. Correlat10n is minimal. . B, relation of mural tension to urethral resistance in three groups of patients. Only slight correlation 1s observed. PROSTATIC OBSTRUCTION AND ACUTE URINARY RETENTION
distended bladders had lost them. The pressure and tension curves obtained from the patient with the largest bladder during withdrawal of fluid and replacement show a decline during refilling (fig. 8, B). Hence overfilling alters the elastic tension of the wall, decreasing the forces available for opening the neck. The result is retention.
Prostatic hypertrophy, because the adenoma is growing in the vesical neck, interferes with the ability of the detrusor to open the internal sphincter. The result is delayed opening (producing hesitancy) and premature closure, as the detrusor continues to contract (causing dribbling and residual urine). The extreme example of inability to open the bladder neck occurs in acute urinary retention. Bladder pressure determinations were made on a series of such patients during withdrawal of fluid and refilling the bladder. These are reported in a separate communication. 6 It was found that both pressure and tension fell rapidly during decompression. Both rose even more rapidly during refilling. If the bladder were small (less than 1000 cc) the rise was greater than if it were large (over 1000 cc) (fig. 8, A). This finding suggests that the smaller bladders had retained more of their elastic properties, whereas larger, over-
Mural tension increases during filling of the bladder and during micturition not only in the vesical wall itself, but also in the trigonal structures, which make up a part of the vesical neck mechanism and continue upward to attach to the terminal ureter. Dissection of the ureter and trigone (well shown by Uhlenhuth and Hunter 7 and more recently brought into focus by Tanagho 8) has shown that the trigonal muscle is a continuation of the ureter into the posterior urethra and that W aldeyer's sheath, after encircling the distal ureter, also
6 Osius, T. G. and Hinman, F., Jr.: The dynamics of acute urinary retention: A manometric, radiographic and clinical study. J. Urol., 90: 702, 1963.
7 Uhlenhuth, E. and Hunter, deW. T.: Problems in the Anatomy of the Pelvis. Philadelphia: J.B. Lippincott Co., 1953. 8 Tanagho, E.: Personal communication.
VESICOURETERAL REFLUX
38
HINMAN AND MILLER
VOLUME IN CC
200
DECOMPRESS/ON
REFILLING
A 150 TENSION (CmHaO) . _ _ LARGE BLADD.ERS
100
(>IOOOcc)
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B 100
1800cc VOLUME
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Fm. 8. A, acute urinary retention: relation of pressure and tension on withdrawing 100 cc fluid and replacing it in smaller and large bladders. B, effect on pressure of withdrawal and refilling very overdistended bladder of 1800 cc volume, showing loss of elasticity. passes through the vesical neck (fig. 9). Thus, the distal ureter is functionally and anatomically related to the vesical neck. Any disorder of this system (congenital
malformation, neurologic disease, or acquired disorder) will prevent normal transmission of mural tension from the bladder neck to the intravesical and intramural ureter. In these
MURAL TENSION IN VESICAL DISORDERS AND URETERAL REFLUX
39
ureteral orifices in position if the trigone and vesical neck were relaxed through defective innervation, disease or congenital abnormality. Moreover, abnormalities of these continuous structures would not only allow reflux of urine into the ureter, but also render less efficient the mechanism which opens the vesical neck. SUMMARY AND CONCLUSIONS MIDDLE CIRCULAR MUSCLE.
Ol/TER LONGITUDINAL MUSCLE
Frn. 9. Schematic cross-section of_ureter, trigone and ves1cal_ neck showmg how tension on trigonal and retrotngonal muscles will hold ureteral orifice m mtravesical position (from data of Tanagho 8 ).
disorders, the ureteral orifice is less fixed. Under various conditions it rises and becomes more extravesical so that it loses the essential ingredients of the submucosal tunnel and the muscular backing required for competency. Thus it permits reflux of urine from the bladder to the ureter. In a previous communication 9 it was reported that most ureters in children with recurrent infections permitted reflux at low bladder pressures and low vesical volumes ("low pressure reflux"). In these cases mural tension is low. l\!J:ural tension, as we have noted, is a more accurate and sensitive indicator of the forces acting on the vesical neck than is either pressure or volume alone and was calculated for those cases which refluxed only during filling (fig. 10, A.). :.\foral tension is relatively low at the time of "low pressure reflux" compared to the almost 3 times higher value at the time of void when reflux did not occur (fig. 10, B). Since the tension is so low (27 .6 gm. F /cm. at reflux compared to 75.6 gm. F /cm. at the time of voiding (fig. 10, B)), it would be less likely to hold the , '_Hinman, F., Jr., JVIiller, E. R., Hutch, J. A., C~amey, M. D., Cox, C. E., Goodfriend, R. B. and:JVIarshall, S.: Low pressure reflux: Relation of vesicoureteral reflux to intravesical pressure. J. Urol., 88: 758, 1962.
Passive intrinsic elasticity and active neuromuscular contraction are the two complementary functions of the bladder wall. The elastic structure of the bladder wall is passively stretched during a major part of filling of the bladder without a rise in intravesical pressure. This vesical "accorn.modation" or tone is the reflection of the purely physical elastic properties of the wall in its maintenance of constant, low intravesical pressure during bladder filling, even though mural tension, resulting from increasing stretch of the wall, is rising steadily. The development of high mural tension helps explain the high rate of voiding from a full bladder, since tension is highest in the wall of the bladder with the largest volume. It is felt that the higher tension of the bladder wall opens the bladder neck more widely which decreases urethral resistance on voiding. Graphically, mural tension has the same relation to voided volume as does the rate of flow. An analysis of recordings of intravesical pressure and micturition flow rates in 47 patients with various urologic disorders indicated only slight correlation between mural tension and both rate of voiding or calculated urethral resistance in contrast to the good correlation in normal subjects. This disparity reflects the varying degrees of vesical neck abnormality encountered in the patients. Patients with prostatic hypertrophy have hesitancy and dribbling with residual urine, because the action of tension at the vesical neck is blocked by the obstructing adenoma, which delays opening and hastens closure. In patients with acute retention, mural tension during refilling after withdrawal of urine was greater in smaller than in large bladders. This suggests that overstretching damages elastic activity in the bladder. Mural tension acts on the trigone, a structure continuous with the ureter, holding the ureteral
40
HINMAN AND MILLER
A MURAL TENSION AND MURAL STRESS WITH LOW PRESSURE REFLUX. (43 URETERS IN 25 PATIENTS)
REFLI/X
VOLUME
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100
150
200
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250
300
350
400
VOLUME (cc) FIG. 10. A, comparison of volume, pressure, mural tension and mural stress at time of reflux, and at. time of voiding when reflux did not occur, in 43 instances of low pressure reflux in 25 patients. Note low mural tone (tension) associated with reflux. B, graph shows pressure, volume and tension in 47 ureters which refluxed only during filling and not dnring voiding.
orifice in a non-refluxing position during filling and voiding. Tension was low at the time of "low pressure" reflux in 43 ureters, none of which refluxed at high pressures, suggesting that the abnormal trigone-ureter complex in these cases required greater than usual tension to maintain
integrity against reflux. Thus, abnormalities of the trigonal muscle, Waldeyer's sheath and the underlying bladder wall in these children lessen the tension on the trigone and vesical neck and lead to reflux at low pressure, as well as to abnormalities of voiding.