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Urethral pressure profile
URETHRAL
PRESSURE
PROFILE
Standardization of Technique and Study of Reproducibility M. A. GHONEIM,
M.D.
J. L. ROITEMBOURG J. FRETIN,
M.D.
J. G. SUSSET,
M.D.
From the Department of Urology, University of Sherbrooke, Sherbrooke, Quebec, Canada
ABSTRACT - The diff erent methods utilized for measurement of urethral resistance were critically reviewed. Using dogs, experiments were done to standardize the pressure profile measurement. A catheter with eight side holes measuring 0.34 mm. each was found to give the best results. The various parameters which can influence the procedure were analyzed. Strict specijcations are proposed to be utilized fw such a procedure.
The need for an accurate and a reproducible method to measure urethral resistance is obvious. Its use for a better understanding of the mechanism of voiding or for the study of such urologic problems as stress incontinence is invaluable. The following approaches were utilized to achieve this goal. Simultaneous measurements of the intravesical pressure and urine flow rate provided the basis for calculation of urethral resistance to flow. l-5 However, this approach suffers from several disadvantages: (1) A suprapubic puncture is necessary for filling of the bladder and recording the intravesical pressure during voiding; and (2) a measurement of the total urethral resistance is provided, but the site or length of obstruction cannot be defined. Measurement of pressure exerted by the urethra is carried out by measuring the pressure transmitted from a balloon situated in the urethra. The technique was perfected by Enhorning’ who measured the intraurethral pressure at consecutive points in the urethra 0.5 cm. apart. Tanagho, Meyers, and Smith’ used a catheter with three channels and recorded the intravesiCal, proximal urethral, and mid-urethral pres-
632
sures simultaneously. Donker, Ivanovici, and Noach* used an arrangement similar to that of Enhorninga6 The catheter was withdrawn to the outside at a constant rate using a mechanical device, thus a complete profile of the urethral pressure was recorded. Although fluid-filled balloons provide a fairly accurate method for measuring the pressure exerted in the urethra, it would appear that they have the disadvantage of measuring pressure over a finite length of the urethra, equivalent to the length of the balloon rather than pressure at consecutive points. Bonney in 1923s reported a study in which he determined the pressure required to force liquid up the urethra into the bladder. The liquid was injected through an open end catheter. HartlelO modified the system by injecting air instead of liquid and observing the pressure with a blood pressure manometer. More recently, similar techniques have been described by Kleeman and Chutte,ll and Herr, Silber, and Martini’ The pressure within the urethra varies from one portion to another. With the methods previously described, only the greatest pressure of any segment of the urethra could be determined.
UROLOGY
/ MAY 1975 / VOLUME
V, NUMBER 5
FIGURE 1. (A) Diagram of apparatus: (1) infusion pump; (2) mechanical withdrawing device; (3) device for measurement of displacement; (4) three-way connector; (5) pressure transducer; (6) ampli$er; (7) filter; (8) catheter; and (9) X-Y recorder. (B) Mechanical withdrawing device. Hollow plexiglass tube isfixed to end of traveler support to prevent kinking of catheter. Note also that triangular metal piece is in constant contact with resistance wire.
D A
::
f
II II
!I I’
I____________
-IL9 I’
-_____
II0
II
,______-_
I___
4
1’
II
FIGURE2. (A) Diagram of design of metal piece. (B) Metal piece with eight side holes mounted on catheter.
\
A
I-
I
II’ ;t
I i I
However, if a catheter is gradually withdrawn from the urethra, it is possible to determine the resistance of different parts of the urethra to hydrostatic pressure. Lapides et al. l3 used a water manometer filled with fluid, which was allowed to discharge through a 16 F whistle-tipped catheter opening into the urethra. When the height of the water column was equal to the wall pressure, flow ceased and the level was maintained and recorded. This procedure was repeated at several points along the length of the urethra so that a crude pressure profile could be plotted. Toesi improved the procedure by using pressure transducer for measurement of the urethral resistance to flow. Brown and Wickham15 proposed the following modifications: (1) a pump to provide a constant flow of fluid through the catheter; (2) a mechanical device to withdraw the catheter to the exterior at a constant rate; and (3) a special catheter with multiple side holes situated 5 to 6 cm. from its closed tip. This technique allows the measurement of pressure at consecutive points along the whole length of the urethra; the size of these points is equal to the diameter of the side holes in the catheter. Harrison and Constable16 carried the technique a step farther by introducing the catheter position transducer and recording the pressure on an X-Y recorder. The modification allows (1) accurate and noninterfering method for measurement of the urethral length; (2) superimposition of the profile for precise comparison; and (3) accurate localization of any specific site in the urethra to be studied. We have elected to use the technique described by Brown and Wickham15 and modified by Harrison and Constable16 because of several advantages previously discussed. The objectives of this study are to characterize precisely the various parameters which can influence this procedure as well as to define the reproducibility of urethral pressure profile measurements. Material The general arrangement of the apparatus is presented in Figure 1A and the mechanical withdrawing device in Figure lB.* The catheter was *Manufacturers involved: Type 7545-1, Cole-Parmer Inst. Co., Chicago, Illinois; Type 6215A, Hewlett, Packard, Massachusetts; Type 71100, Braun, Melsungen, Germany; Type M. P. L. S. 125, Kulite Semi-conductor Producers, Inc., New Jersey; Type 119, Accudata Bridge Amplifier, Honeywell, Denver, Colorado; Type 7004B, Hewlett, Packard, Massachusetts; U.S. Catheters and Instrument Corp., New York; Sherwood, Missouri; Heyer-Schulte Corp., Goleta, California.
634
mechanically withdrawn from the urethra at a constant speed. The device consists of a traveler which moves forward or backward over a motordriven endless screw. An electronic switch controls the speed and direction of displacement of this motor. A triangular metal piece was fixed to the side of the traveler so its tip was in constant contact with a resistance wire. A power supply delivers a constant tension to this wire. The electric potential which appears at this triangular piece will be proportional to the position of the traveler. A constant speed pump fitted with a 50 cc. syringe was used to infuse the catheter. The catheter was relayed by a three-way connector fixed on the traveler to the infusion pump and to a pressure transducer. The signal from the transducer was amplified and then filtered by a 1 Hz. frequency cut-off RC network filter. The amplified, filtered signal was fed to the Y input of the X-Y recorder. The X input received variations in electric tension appearing at the triangular metal piece. Accordingly, the variation in pressure (Y input) and the displacement of the catheter (X input) were simultaneously recorded. In our initial studies, catheters made from 8 F rigid polyethylene tubes were used. Three prototypes were tested: a catheter with one side hole, one with two holes, a third with four holes. In all these models the holes measured 1 mm. in diameter each and were situated 5 cm. from the close tip of the catheter. However, our preliminary results dictated a change of this design. Special metal pieces with four, six, or eight side holes were made (Fig. 2A). In the design of these pieces it was planned that the total surface area of the holes should be equal to the surface area of a circle 1 mm. in diameter. These metal pieces were mounted on 8 F catheters made from three different materials: rigid polyethylene, semirigid polyethylene, and silicone (Fig. 2B). Female mongrel dogs weighing 12 to 15 Kg. were used. A total of 9 dogs were used in fifteen experiments. Method The dogs were anesthetized with intravenous pentobarbitol (Nembutal) (25 mg. per kilogram). Additional doses were given as required. The trachea was intubated, and the dogs were allowed to breathe air. An episiotomy was performed to allow easy access to the urethra. The bladder was catheterized and emptied at the start of the experiment and before each set of measurements.
UROLOGY
/ MAY 1975 I
VOLUME
V, NUMBER 5
mn
H!
100
FIGURE 3. (A) Catheter with one side hole. Variations in pressure profile with axial rotation through 360 degrees. Method of calculation of error demonstrated on graph. (B) Variations of profile, with increasing number of side holes; (a) catheter with one hole; (b) catheter with two holes; and (c) catheter with four holes.
The hydraulic system was filled with water to get rid of all air bubbles. The zero of the system was adjusted to the atmospheric pressure. The gain of the X input was adjusted so that a displacement of 1 cm. by the traveler would correspond to 1 inch on the graphic paper. The different catheters were tested following a rigid protocol. Five consecutive curves were recorded on the same graph to allow the study of the intrinsic reproducibility. Then the catheter was rotated for 90 degrees and a profile was recorded. With each complete rotation (360 degrees) four curves were recorded on the same graph. This procedure was repeated three times. This allows the study of errors in reproducibility due to axial rotation of the catheter. Using the catheter which gave the best results in terms of reproducibility, further experiments were carried out to study the influence of the following parameters: (1) Speed of catheter withdrawal: four consecutive pressure profiles were recorded on the same graph, using different speeds of withdrawals (5, 10, 20, and 40 cm. per minute). (2) Influence of flow rate: four consecutive pressure profiles were recorded using different flow rates (1, 2, 5, and 10 cc. per minute). (3) Reproducibility with time: under the same experimental conditions, consecutive curves were recorded every hour for four hours. (4) Influence of respiration: variations in the intra-abdominal pressure with respiration were studied by simultaneous recording of the intrarectal pressure (using a balloon) and the urethral pressure profile. (5) Influence ofvesical distention: the bladder was completely emptied, and a urethral profile was recorded. Fifty-cc. increments of saline were injected into the bladder via a urethral catheter; a profile was recorded after each additional fill.
For evaluation of the different catheters, we have defined a criterion of quality (Q), which is expressed as: Q = D/2M x 100, where D = the amount of dispersion in the curve at a given point, and M = the arithmetic mean of the different pressure values at the same point. The rate was always calculated at the point of maximal dispersion. Obviously, the best catheter should be the one with the smallest intrinsic error. Moreover, the difference between the intrinsic and rotational errors should be minimal. Results Our initial trials, using a catheter with one side hole measuring 1 mm. in diameter, revealed that a good pressure amplitude could be obtained. However, the reproducibility with axial rotation was extremely poor (Fig. 3A). Increasing the number of the side holes improved the rotational error, but the pressure amplitudes were reduced (Fig. 3B). Accordingly a conclusion was made that the number of side holes should be increased to reduce the rotational error, but the total surface area of the holes should be kept equal to that of a hole 1 mm. in diameter to maintain the pressure amplitude. Since the accurate construction of such fine holes in the conventional catheter material was difficult at least by our available means, the special metal pieces with four, six, and eight holes were designed and tested (Fig. 4). The results of the calculated error of the different catheters are given in Figure 5, which clearly demonstrate that the catheter with eight side holes provided the best results. Catheters constructed from rigid materials gave an excellent pressure amplitude. Nevertheless, it was observed that they traumatize and
mmlig
not influence the amplitude or quality of the profile. Over a period of four hours the error in reproducibility was in a range of k 5 per cent (Fig. 6). Changes in the intra-abdominal pressure with respiration can change the amplitude of the profile in a range of + 4 per cent. It was consistently observed that by increasing the vesical volume the amplitude of the profile was also increased.
t
Comment Al 0
.
1
.
b
5
cm
mmHgA
20 .
The technique employed does not provide a measurement of an absolute pressure. It measures variations in resistance presented by the urethral wall to the flow output from the holes (variations in head loss). Accordingly, strict and well-standardized specifications of the system are mandatory to give the measurement a quantitative meaning and to allow comparison of results. I t x Error JO-
:: :: :: . .
:: :: :: I-:: ii
20 t
B
0
5
c
cm
:: ..
::
I 10
:: 4:
a... ,. . .
::
:::: . .
mm** . . ??* mm** --
0
FIGURE
5.
. .
. . . . .m . . . . . .
0
Average intrinsic and rotational errors
fm differ-ent catheters.
Variations with axial rotation: (A) catheFIGURE 4. ter with four holes; (B) catheter with six holes; and (C) catheter with eight holes. deform the urethra. Catheters made of a softer material gave a smaller pressure amplitude but have the advantage of being less traumatic and noninterfering. Under the same experimental conditions, the speed of withdrawal of the catheter from the urethra did not influence the amplitude or quality of the profile, and variations in the flow rate did
636
FIGURE
6.
UROLOGY
Reproducibility of profile with time.
/ MAY 1975 I
VOLUME
V, NUMBER 5
Previous studies revealed that the catheter size is not critical so long as catheters of a size ranging between 8 to 12F are used. 15*17,16 We have chosen an 8 F catheter to minimize the chances of trauma and irritation to the urethral wall. Although very critical, specifications of the size and number of the side holes are lacking. Brown and Wickham,15 Harrison and Constable,16 and Edwards and Malvern’* used a special profile cannula with several side holes (two to four). Griffith,l’ and Glen and Rowanlg used catheters with two side holes only. However, in all the aforementioned studies the size of the holes was not defined. Gleason et ~1.~’ used a single side hole measuring 1 mm. in diameter. We agree that such a hole permits greater resolution of the profile, yet the rotational error is unacceptable. Axial rotations of such a catheter limited to 2 15 degrees have produced an error of about 40 per cent. Increasing the number of holes will permit recording of the resultant pressures exerted by the different points on the urethral wall at a given plane. A catheter with eight holes, measuring 0.34 mm. in diameter each, will give a good pressure amplitude with a minimal rotational error. The number of the side holes was limited to eight, since the rotational error had dropped and became virtually equal to the intrinsic one. The intrinsic error in our system was very similar to that reported by Griffithl’ (+ 5 per cent), but errors due to rotation were not mentioned in his study. A factor which can contribute to this error is variation in the intra-abdominal pressure with respiration. Changes in the intra-abdominal pressure do influence the intraurethral pressure.*l We have simultaneously recorded the intraabdominal pressure (by a rectal balloon) and the urethral pressure profile. This study has shown that respiratory movements can influence the amplitude of the profile within a * 4 per cent range. The speed of catheter withdrawal and rate of flow of fluid in the catheter did not significantly influence the profile measurements. These findings are in agreement with those of Edwards and Malvern. l6 Department of Urology Central University Hospital Sherbrooke Quebec, Canada (DR. GHONEIM) ACKNOWLEDGMENT. We express our gratitude to Mr. Daniel Dutartre who suggested and designed the metal pieces with multiple side holes.
UROLOGY
/
MAY 1975 / VOLUME V, NUMBER 5
References 1. GLEASON, D. M., and LATTIMER, J. K.: The pressure flow study: the method of measuring bladder neck resistance, J. Urol. 87: 844 (1962). 2. RITTER, R. C., ZINNER, N. R., and PAQUIN, A. J., JR. : Clinical urodynamics. II. Analysis of pressure flow relations in the normal female urethra, ibid. 91: 161 (1964). 3. SMITH, J. C.: Some theoretical aspects of urethral resistance, Invest. Urol. 1: 477 (1964). 4. SUSSET, J. G., RABINOVITCH, H. H., ROSARIO, F., and of urethral resisMACKINNON, K. J.: Measurement tance, J. Urol. 96: 746 (1966). 5. BACKMAN, K.: Micturition in normal women, Acta Chir. &and. 132: 413 (1966). 6. ENHORNING, G.: Simultaneous recording of intervesical and intraurethral pressure, Acta Chir. Stand. (Suppl.) 276: 1 (1961). 7. TANAGHO, E. A., MEYERS, F. H., and SMITH, D. R.: Urethral resistance: its components and implications. I. Smooth muscle components, Invest. Urol. 7: 136 (1969). 8. DONKER, P. J,, IVANOVICI, F., and NOACH, E. L. : Analysis of the urethral pressure profile by means of electromyography and administration of drugs, Br. J. Urol. 44: 180 (1972). 9. BONNEY, V.: On diurnal incontinence of urine in women, J. Obstet. Gynaecol. Br. Commonw. 30: 358 (1923). 10. HARTLE, H.: Die mnktionelle Harninkontinenz der Frau, Stuttgart, Ferdinand Enke Verlag, 1953. 11. KLEEMAN, F. J., and CHUTTE, R. : A plan for the evaluation of patients with bladder dysfunction and the use of pudendal neurectomy in selected cases, J. Urol. 97: 1029 (1967). 12. HERR, H. W., SJLBER, I., and MARTIN, D. C.: Bedside sphincterometry, Urology 4: 57 (1974). 13. LAPIDES, J., et aE. : Further observations on the kinetics of the urethrovesical sphincter, J. Urol. 84: 86 (1960). 14. TOES, H. A.: Intraurethral and intravesical pressures in normal and stress incontinent women, Obstet. Gynecol. 29: 613 (1967). 15. BROWN, M., and WICKHAM, J. E. A.: The urethral pressure profile, Br. J. Ural. 41: 211 (1969). 16. HARRISON, N. W., and CONSTABLE, A. R.: Urethral pressure measurement. A modified technique, ibid. 42: 229 (1970). 17. GRIFFITHS, D. J. : The mechanics of the urethra and of micturition, ibid. 45: 497 (1973). 18. EDWARDS, L., and MALVERN, J.: The urethral pressure profile: theoretical considerations and clinical applications, ibid. 46: 325 (1974). 19. GLEN, E. S., and ROWAN, D.: Continuous flow cystometry and urethral pressure profile measurement with monitored intravesical pressure, Urol. Res. 1: 97 (1973). 20. GLEASON, D. M., REILLY, R. J., BOTTACCINI, M. R., and PIERCE, M. J.: The urethral continence zone, and its relation to stress incontinence, J. Ural. 112: 81 (1974). 21. GF&ER, P., LARUENT, G., and TANAGHO, E. A.: Effeet of abdominal pressure rise on the urethral profile. An experimental study on dogs, Invest. Urol. 12: 57 (1974).
637
PRESSURE
PROFILE
Standardization of Technique and Study of Reproducibility M. A. GHONEIM,
M.D.
J. L. ROITEMBOURG J. FRETIN,
M.D.
J. G. SUSSET,
M.D.
From the Department of Urology, University of Sherbrooke, Sherbrooke, Quebec, Canada
ABSTRACT - The diff erent methods utilized for measurement of urethral resistance were critically reviewed. Using dogs, experiments were done to standardize the pressure profile measurement. A catheter with eight side holes measuring 0.34 mm. each was found to give the best results. The various parameters which can influence the procedure were analyzed. Strict specijcations are proposed to be utilized fw such a procedure.
The need for an accurate and a reproducible method to measure urethral resistance is obvious. Its use for a better understanding of the mechanism of voiding or for the study of such urologic problems as stress incontinence is invaluable. The following approaches were utilized to achieve this goal. Simultaneous measurements of the intravesical pressure and urine flow rate provided the basis for calculation of urethral resistance to flow. l-5 However, this approach suffers from several disadvantages: (1) A suprapubic puncture is necessary for filling of the bladder and recording the intravesical pressure during voiding; and (2) a measurement of the total urethral resistance is provided, but the site or length of obstruction cannot be defined. Measurement of pressure exerted by the urethra is carried out by measuring the pressure transmitted from a balloon situated in the urethra. The technique was perfected by Enhorning’ who measured the intraurethral pressure at consecutive points in the urethra 0.5 cm. apart. Tanagho, Meyers, and Smith’ used a catheter with three channels and recorded the intravesiCal, proximal urethral, and mid-urethral pres-
632
sures simultaneously. Donker, Ivanovici, and Noach* used an arrangement similar to that of Enhorninga6 The catheter was withdrawn to the outside at a constant rate using a mechanical device, thus a complete profile of the urethral pressure was recorded. Although fluid-filled balloons provide a fairly accurate method for measuring the pressure exerted in the urethra, it would appear that they have the disadvantage of measuring pressure over a finite length of the urethra, equivalent to the length of the balloon rather than pressure at consecutive points. Bonney in 1923s reported a study in which he determined the pressure required to force liquid up the urethra into the bladder. The liquid was injected through an open end catheter. HartlelO modified the system by injecting air instead of liquid and observing the pressure with a blood pressure manometer. More recently, similar techniques have been described by Kleeman and Chutte,ll and Herr, Silber, and Martini’ The pressure within the urethra varies from one portion to another. With the methods previously described, only the greatest pressure of any segment of the urethra could be determined.
UROLOGY
/ MAY 1975 / VOLUME
V, NUMBER 5
FIGURE 1. (A) Diagram of apparatus: (1) infusion pump; (2) mechanical withdrawing device; (3) device for measurement of displacement; (4) three-way connector; (5) pressure transducer; (6) ampli$er; (7) filter; (8) catheter; and (9) X-Y recorder. (B) Mechanical withdrawing device. Hollow plexiglass tube isfixed to end of traveler support to prevent kinking of catheter. Note also that triangular metal piece is in constant contact with resistance wire.
D A
::
f
II II
!I I’
I____________
-IL9 I’
-_____
II0
II
,______-_
I___
4
1’
II
FIGURE2. (A) Diagram of design of metal piece. (B) Metal piece with eight side holes mounted on catheter.
\
A
I-
I
II’ ;t
I i I
However, if a catheter is gradually withdrawn from the urethra, it is possible to determine the resistance of different parts of the urethra to hydrostatic pressure. Lapides et al. l3 used a water manometer filled with fluid, which was allowed to discharge through a 16 F whistle-tipped catheter opening into the urethra. When the height of the water column was equal to the wall pressure, flow ceased and the level was maintained and recorded. This procedure was repeated at several points along the length of the urethra so that a crude pressure profile could be plotted. Toesi improved the procedure by using pressure transducer for measurement of the urethral resistance to flow. Brown and Wickham15 proposed the following modifications: (1) a pump to provide a constant flow of fluid through the catheter; (2) a mechanical device to withdraw the catheter to the exterior at a constant rate; and (3) a special catheter with multiple side holes situated 5 to 6 cm. from its closed tip. This technique allows the measurement of pressure at consecutive points along the whole length of the urethra; the size of these points is equal to the diameter of the side holes in the catheter. Harrison and Constable16 carried the technique a step farther by introducing the catheter position transducer and recording the pressure on an X-Y recorder. The modification allows (1) accurate and noninterfering method for measurement of the urethral length; (2) superimposition of the profile for precise comparison; and (3) accurate localization of any specific site in the urethra to be studied. We have elected to use the technique described by Brown and Wickham15 and modified by Harrison and Constable16 because of several advantages previously discussed. The objectives of this study are to characterize precisely the various parameters which can influence this procedure as well as to define the reproducibility of urethral pressure profile measurements. Material The general arrangement of the apparatus is presented in Figure 1A and the mechanical withdrawing device in Figure lB.* The catheter was *Manufacturers involved: Type 7545-1, Cole-Parmer Inst. Co., Chicago, Illinois; Type 6215A, Hewlett, Packard, Massachusetts; Type 71100, Braun, Melsungen, Germany; Type M. P. L. S. 125, Kulite Semi-conductor Producers, Inc., New Jersey; Type 119, Accudata Bridge Amplifier, Honeywell, Denver, Colorado; Type 7004B, Hewlett, Packard, Massachusetts; U.S. Catheters and Instrument Corp., New York; Sherwood, Missouri; Heyer-Schulte Corp., Goleta, California.
634
mechanically withdrawn from the urethra at a constant speed. The device consists of a traveler which moves forward or backward over a motordriven endless screw. An electronic switch controls the speed and direction of displacement of this motor. A triangular metal piece was fixed to the side of the traveler so its tip was in constant contact with a resistance wire. A power supply delivers a constant tension to this wire. The electric potential which appears at this triangular piece will be proportional to the position of the traveler. A constant speed pump fitted with a 50 cc. syringe was used to infuse the catheter. The catheter was relayed by a three-way connector fixed on the traveler to the infusion pump and to a pressure transducer. The signal from the transducer was amplified and then filtered by a 1 Hz. frequency cut-off RC network filter. The amplified, filtered signal was fed to the Y input of the X-Y recorder. The X input received variations in electric tension appearing at the triangular metal piece. Accordingly, the variation in pressure (Y input) and the displacement of the catheter (X input) were simultaneously recorded. In our initial studies, catheters made from 8 F rigid polyethylene tubes were used. Three prototypes were tested: a catheter with one side hole, one with two holes, a third with four holes. In all these models the holes measured 1 mm. in diameter each and were situated 5 cm. from the close tip of the catheter. However, our preliminary results dictated a change of this design. Special metal pieces with four, six, or eight side holes were made (Fig. 2A). In the design of these pieces it was planned that the total surface area of the holes should be equal to the surface area of a circle 1 mm. in diameter. These metal pieces were mounted on 8 F catheters made from three different materials: rigid polyethylene, semirigid polyethylene, and silicone (Fig. 2B). Female mongrel dogs weighing 12 to 15 Kg. were used. A total of 9 dogs were used in fifteen experiments. Method The dogs were anesthetized with intravenous pentobarbitol (Nembutal) (25 mg. per kilogram). Additional doses were given as required. The trachea was intubated, and the dogs were allowed to breathe air. An episiotomy was performed to allow easy access to the urethra. The bladder was catheterized and emptied at the start of the experiment and before each set of measurements.
UROLOGY
/ MAY 1975 I
VOLUME
V, NUMBER 5
mn
H!
100
FIGURE 3. (A) Catheter with one side hole. Variations in pressure profile with axial rotation through 360 degrees. Method of calculation of error demonstrated on graph. (B) Variations of profile, with increasing number of side holes; (a) catheter with one hole; (b) catheter with two holes; and (c) catheter with four holes.
The hydraulic system was filled with water to get rid of all air bubbles. The zero of the system was adjusted to the atmospheric pressure. The gain of the X input was adjusted so that a displacement of 1 cm. by the traveler would correspond to 1 inch on the graphic paper. The different catheters were tested following a rigid protocol. Five consecutive curves were recorded on the same graph to allow the study of the intrinsic reproducibility. Then the catheter was rotated for 90 degrees and a profile was recorded. With each complete rotation (360 degrees) four curves were recorded on the same graph. This procedure was repeated three times. This allows the study of errors in reproducibility due to axial rotation of the catheter. Using the catheter which gave the best results in terms of reproducibility, further experiments were carried out to study the influence of the following parameters: (1) Speed of catheter withdrawal: four consecutive pressure profiles were recorded on the same graph, using different speeds of withdrawals (5, 10, 20, and 40 cm. per minute). (2) Influence of flow rate: four consecutive pressure profiles were recorded using different flow rates (1, 2, 5, and 10 cc. per minute). (3) Reproducibility with time: under the same experimental conditions, consecutive curves were recorded every hour for four hours. (4) Influence of respiration: variations in the intra-abdominal pressure with respiration were studied by simultaneous recording of the intrarectal pressure (using a balloon) and the urethral pressure profile. (5) Influence ofvesical distention: the bladder was completely emptied, and a urethral profile was recorded. Fifty-cc. increments of saline were injected into the bladder via a urethral catheter; a profile was recorded after each additional fill.
For evaluation of the different catheters, we have defined a criterion of quality (Q), which is expressed as: Q = D/2M x 100, where D = the amount of dispersion in the curve at a given point, and M = the arithmetic mean of the different pressure values at the same point. The rate was always calculated at the point of maximal dispersion. Obviously, the best catheter should be the one with the smallest intrinsic error. Moreover, the difference between the intrinsic and rotational errors should be minimal. Results Our initial trials, using a catheter with one side hole measuring 1 mm. in diameter, revealed that a good pressure amplitude could be obtained. However, the reproducibility with axial rotation was extremely poor (Fig. 3A). Increasing the number of the side holes improved the rotational error, but the pressure amplitudes were reduced (Fig. 3B). Accordingly a conclusion was made that the number of side holes should be increased to reduce the rotational error, but the total surface area of the holes should be kept equal to that of a hole 1 mm. in diameter to maintain the pressure amplitude. Since the accurate construction of such fine holes in the conventional catheter material was difficult at least by our available means, the special metal pieces with four, six, and eight holes were designed and tested (Fig. 4). The results of the calculated error of the different catheters are given in Figure 5, which clearly demonstrate that the catheter with eight side holes provided the best results. Catheters constructed from rigid materials gave an excellent pressure amplitude. Nevertheless, it was observed that they traumatize and
mmlig
not influence the amplitude or quality of the profile. Over a period of four hours the error in reproducibility was in a range of k 5 per cent (Fig. 6). Changes in the intra-abdominal pressure with respiration can change the amplitude of the profile in a range of + 4 per cent. It was consistently observed that by increasing the vesical volume the amplitude of the profile was also increased.
t
Comment Al 0
.
1
.
b
5
cm
mmHgA
20 .
The technique employed does not provide a measurement of an absolute pressure. It measures variations in resistance presented by the urethral wall to the flow output from the holes (variations in head loss). Accordingly, strict and well-standardized specifications of the system are mandatory to give the measurement a quantitative meaning and to allow comparison of results. I t x Error JO-
:: :: :: . .
:: :: :: I-:: ii
20 t
B
0
5
c
cm
:: ..
::
I 10
:: 4:
a... ,. . .
::
:::: . .
mm** . . ??* mm** --
0
FIGURE
5.
. .
. . . . .m . . . . . .
0
Average intrinsic and rotational errors
fm differ-ent catheters.
Variations with axial rotation: (A) catheFIGURE 4. ter with four holes; (B) catheter with six holes; and (C) catheter with eight holes. deform the urethra. Catheters made of a softer material gave a smaller pressure amplitude but have the advantage of being less traumatic and noninterfering. Under the same experimental conditions, the speed of withdrawal of the catheter from the urethra did not influence the amplitude or quality of the profile, and variations in the flow rate did
636
FIGURE
6.
UROLOGY
Reproducibility of profile with time.
/ MAY 1975 I
VOLUME
V, NUMBER 5
Previous studies revealed that the catheter size is not critical so long as catheters of a size ranging between 8 to 12F are used. 15*17,16 We have chosen an 8 F catheter to minimize the chances of trauma and irritation to the urethral wall. Although very critical, specifications of the size and number of the side holes are lacking. Brown and Wickham,15 Harrison and Constable,16 and Edwards and Malvern’* used a special profile cannula with several side holes (two to four). Griffith,l’ and Glen and Rowanlg used catheters with two side holes only. However, in all the aforementioned studies the size of the holes was not defined. Gleason et ~1.~’ used a single side hole measuring 1 mm. in diameter. We agree that such a hole permits greater resolution of the profile, yet the rotational error is unacceptable. Axial rotations of such a catheter limited to 2 15 degrees have produced an error of about 40 per cent. Increasing the number of holes will permit recording of the resultant pressures exerted by the different points on the urethral wall at a given plane. A catheter with eight holes, measuring 0.34 mm. in diameter each, will give a good pressure amplitude with a minimal rotational error. The number of the side holes was limited to eight, since the rotational error had dropped and became virtually equal to the intrinsic one. The intrinsic error in our system was very similar to that reported by Griffithl’ (+ 5 per cent), but errors due to rotation were not mentioned in his study. A factor which can contribute to this error is variation in the intra-abdominal pressure with respiration. Changes in the intra-abdominal pressure do influence the intraurethral pressure.*l We have simultaneously recorded the intraabdominal pressure (by a rectal balloon) and the urethral pressure profile. This study has shown that respiratory movements can influence the amplitude of the profile within a * 4 per cent range. The speed of catheter withdrawal and rate of flow of fluid in the catheter did not significantly influence the profile measurements. These findings are in agreement with those of Edwards and Malvern. l6 Department of Urology Central University Hospital Sherbrooke Quebec, Canada (DR. GHONEIM) ACKNOWLEDGMENT. We express our gratitude to Mr. Daniel Dutartre who suggested and designed the metal pieces with multiple side holes.
UROLOGY
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MAY 1975 / VOLUME V, NUMBER 5
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