INSTRUMENTATION FOR MINIMALLY INVASIVE

MEASUREMENT OF VESICAL PRESSURE IN MEN

João Carlos Martins de Almeida

School of Electrical and Computer Engineering, University of Campinas, Campinas, Brazil

Center for Biomedical Engineering, University of Campinas, Campinas, Brazil

Rodrigo Horikawa Watanabe

School of Electrical and Computer Engineering, University of Campinas, Campinas, Brazil

David Jacques Cohen, Carlos Arturo Levi D′Ancona

Division of Urology of School of Medical Sciences, University of Campinas, Campinas, SP, Brazil

José Wilson Magalhães Bassani

School of Electrical and Computer Engineering, University of Campinas, Campinas, Brazil

Center for Biomedical Engineering, University of Campinas, Campinas, Brazil

Keywords: Urodynamics, Prostate, Vesical pressure, Instrumentation.

Abstract: Urodynamic assessment is important to evaluate bladder outlet obstruction (BOO), but the procedure is

invasive, expensive and time-consuming, and is not free of complications (e. g. macroscopic hematuria,

fever). In a previous work, we reported a new method developed for measuring vesical static pressure

during urodynamic exams by using a device named urethral connector (UC). Clinical tests indicated that the

new method is comparable to the conventional standard procedure with clear advantages. In this work, we

describe improvements made on the UC, which confer greater autonomy and portability to the whole

measurement system. We also report the results of clinical tests.

1 INTRODUCTION

Lower urinary tract symptoms (LUTS) are very

common in elderly patients (Gomes et al., 2004).

Many of these symptoms are related to bladder

outlet obstruction (BOO) due to benign prostatic

hyperplasia (BPH), which afflicts approximately

50% of men above 60 years-old (Power &

Fitzpatrick, 2004). About 35% of the patients

undergoing prostate surgery due to LUTS will not

benefit from it because they do not have obstruction.

Urodynamic assessment is the gold standard

procedure (GSM) for detecting BOO; however, the

procedure is invasive, expensive and time-

consuming (Gomes et al., 2004).

Along the years, other methods have been

proposed for minimally invasive urodynamic

assessment (Pel & van Mastrigt, 1999; Griffiths et

al., 2002; Parsons et al., 2009), each of them with

advantages and disadvantages. As previously

reported (D’Ancona et al., 2008), we have

developed a new method (MUC, Method of the

Urethral Conector) for minimally invasive

measurement of the static bladder pressure. This

variable, as well as void flow, have been used to

categorize patients as non-obstructed, equivocal or

obstructed (van Mastrigt et al., 2009; Clarkson et al.,

2008; Harding et al., 2009). We have developed a

relatively simple device named urethral connector

(UC), which was tested clinically, and proved to be

easy to use, while allowing detection of BOO in men

189

Martins de Almeida J., Horikawa Watanabe R., Jacques Cohen D., Levi D’Ancona C. and Magalhães Bassani J..

INSTRUMENTATION FOR MINIMALLY INVASIVE MEASUREMENT OF VESICAL PRESSURE IN MEN.

DOI: 10.5220/0003152601890193

In Proceedings of the International Conference on Biomedical Electronics and Devices (BIODEVICES-2011), pages 189-193

ISBN: 978-989-8425-37-9

 2011 SCITEPRESS (Science and Technology Publications, Lda.)

(D’Ancona et al., 2008).

Here we describe improvements made on the

UC, as to confer autonomy and portability to the

device and measurement system, and report clinical

tests.

2 METHODOLOGY

2.1 Instrumentation

The UC is a device made of polyvinyl carbon and

polytetrafluoroethylene, with a conic inlet tube (A in

Figure 1) designed to fit the urethral meatus and

fossa navicularis, as to avoid leakage during voiding

through the device. In the present device a built-in

pressure transducer (B in Figure 1, MPX2300DT1,

30 μV/mmHg, Freescale Semiconductor, Austin,

TX, USA) was included for measurement of the

urine edge pressure on the outflow line. The output

signal of the transducer was amplified (custom-made

amplifier with variable gain and offset) and fed to a

computer via NI USB-6215 interface (National

Instruments, Austin, TX, USA). A Labview

program was used for data acquisition and

processing.

Figure 1: Urethral connector. (A), conic tube designed to

fit the urethral meatus and fossa navicularis. (B) contains a

pressure transducer for measuring vesical pressure.

For the transducer calibration, the amplifier

offset and gain were adjusted so that when no

pressure was applied to the transducer, the output

voltage is zero, and application of 200 cmH

results in an output of 5 V. Transducer calibration

was performed with a pneumatic transducer tester

(DPM-IB, Bio-Tek Instruments, Winooski) in the

range of 0 to 200 cmH

O. This pressure range has

been adopted by other investigators to test their

minimally invasive methods (Griffiths et al., 2002).

Dynamic tests of the UC were performed using a

setup in which pressure gradient was generated by

gravity, and the reference pressure values were

obtained by manometry (Figure 2). These data were

useful for determining part of the UC clinical

procedure, as discussed further.

Figure 2: Setup used for bench-tests with the urethral

connector. In dynamic tests, the UC was occluded so that

the steady-state static pressure could be measured.

2.2 Clinical Tests

All the procedures were approved by the Committee

for Ethics in Clinical Research of the University of

Campinas (Protocol #1017/2008). The new system

was tested successfully in 6 patients (66 ± 2 years

old) with complaints of LUTS, after signature of a

consent form. Patients underwent both the

conventional and the minimally invasive (using the

UC) urodynamic tests. Prior to the conventional

urodynamic test, free flow uroflowmetry was also

performed. Urine flow parameters, such as flow

duration, time to reach maximum rate, maximum

and average flow, and released urine volume were

measured using a commercially available equipment

(Urolite, Dynamed, São Paulo) in all patients during

free uroflowmetry, GSM and MUC. For comparison

between methods, we selected the parameters flow

duration, maximum flow rate and urine volume.

The conventional urodynamic exam was

performed using 6F and 8F urethral catheters, for

measurement of vesical pressure and infusion of

saline solution (37°C; 50 ml/min), respectively. The

abdominal pressure was measured using a 6F rectal

catheter. After reaching the maximal cystometric

capacity and just before miction, the 8F catheter was

removed, and the patient was oriented to empty his

bladder. Urine flow, as well as vesical and

abdominal pressures, were recorded with the Urolite

equipment (Dynamed, São Paulo). Then saline

solution was infused again until the maximal

cystometric capacity was reached, and both urethral

catheters were removed. The patient was instructed

to introduce a previously sterilized UC (standard

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ethylene oxide sterilization) into the urethra and to

urinate through it. During miction, the UC outlet

was manually occluded by the patient for a short

period, allowing pressure recording by the

developed system. Two alternatives were used:

either the patient closed the UC outlet with his

gloved finger, or a small flexible tube was connected

to the output, allowing the patient to pinch it to

produce a brief occlusion. For both methods (i.e.,

GSM and MUC), the patient was instructed to avoid

straining. After the procedure, the patients answered

a brief questionary about the exam. Data obtained

from clinical tests were computed using the software

Prism (Graphpad Software, San Diego, CA, USA).

3 RESULTS

Figure 3 shows the transducer calibration curve.

Voltage output values (y-axis) were measured (10

replicates) for 9 different pressure levels (x-axis).

Data were fit by linear regression (a = 0.024; b =

0.032; R

= 0.999; values are expressed as mean ±

standard error.

0 50 100 150 200 250

Pressure applied (cmH

Amplifier output voltage (V)

Figure 3: Calibration curve of the transducer. Applying 9

different pressure levels (x-axis) on the transducer, the

output voltage (y-axis) of the circuit was measured. Data

are means ± SEM (N= 10). SEM values are 0.005-0.012

V, and thus not apparent in the figure.

Some dynamic tests were performed aiming at

simulating aspects of the clinical procedure using the

UC. The device was occluded in the following ways:

instantaneously, as by an on-off solenoid valve, and

gradually. The signals recorded are shown in Figures

4 and 5, respectively.

5 6 7 8 9 10

100

125

Occlusion

Time

(

)

Pressure (cmH

Figure 4: Simulation of aspects of the clinical procedure

with instantaneous occlusion of the UC during continuous

flow and constant pressure. The time to reach the

maximum pressure was lower than 100ms. The initial

abrupt pressure change is the hydraulic shock.

0.0 2.5 5.0 7.5 10.0

Occlusion

Time

(

)

Pressure (cmH

Figure 5: Simulation of a clinical procedure with gradual

occlusion of the UC during continuous flow and constant

pressure. The steady-state static pressure is not

significantly different from that obtained as in Figure 4.

Pressure rise time was about 300 ms.

Figure 6 illustrates the pressure recorded during

a clinical procedure using the UC. The approximate

moment of the UC occlusions is indicated by an

arrow.

With the UC method, the maximum steady-state

pressure value during an occlusion is considered as

the value that best reflects the bladder contraction

capability. In the conventional method, this pressure

value is best measured at the maximal flow rate. The

comparison of vesical pressure values recorded with

both methods is shown in Figure 7. There was

significant correlation between the measurements

obtained with the two methods (Pearson r = 0.89; R

= 0.802; P < 0.015; a = 2.00 ± 0.49, b = -37.00 ±

36.78), although absolute values could differ as

much as 30%.

INSTRUMENTATION FOR MINIMALLY INVASIVE MEASUREMENT OF VESICAL PRESSURE IN MEN

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17.5 20.0 22.5 25.0 27.5

-50

100

150

Time (s)

Pressure (cmH

Figure 6: Pressure recorded during a clinical procedure

using the UC. Arrows indicate the approximate moments

of the UC occlusion. The steady-state static pressure after

occlusion was ~122 cmH2O in this case.

0 25 50 75 100 125 150

100

125

150

175

200

Vesical Pressure GSM (cmH

Vesical Pressure MUC (cmH

Figure 7: Regression line representing comparison of

pooled data obtained from six patients using GSM and

MUC.

Table 1 summarizes data obtained from

uroflowmetry. Statistical differences between the

two methods were not observed for flow duration,

maximum flow rate and urine volume (P > 0.05;

Student´s t test; Table 1).

Table 1: Uroflowmetry data (values are expressed as mean

± standard error, N = 6). The last line shows the P values

obtained from the t test for comparison of the two

methods.

Procedure

Flow duration

(s)

Maximum

flow rate

(ml/s)

Urine

volume (ml)

GSM 67.5 ± 12.9 6.7 ± 1.2 194.2 ± 39.3

MUC 72.9 ± 9.1 8.5 ± 1.5 199.5 ± 43.8

P 0.400 0.442 0.844

4 DISCUSSION

The results from the bench tests have shown that the

amplifier output is linear and reproducible (r

0.999). Dynamic bench tests showed that it is

possible to implement gradual occlusion of the UC

(Figure 5) and that this seems to be the best

approach for measuring the steady-state static

pressure without causing hydraulic shock (see

Figure 4), which results from abrupt flow

interruption and may cause discomfort to the patient

and/or damage to his urinary system.

As shown in Figure 6, in a typical clinical test

using the UC, as the outflow is interrupted, pressure

rises quickly to a steady-state value. This patient

shows a clearly elevated bladder pressure that

indicates there is some kind of disturbance in low

urinary tract. In elderly patients, this disturbance is

likely to be due to prostate enlargement. In this case,

the patient was diagnosed as obstructed, according

to the conventional method.

The steady-state static pressure recorded by

using the UC is not expected to be identical to the

pressure measured at the maximum flow as in GSM.

However, a positive correlation between these

pressures was observed (Figure 7), which indicates

that MUC is also sensitive at detecting alterations of

vesical pressure. Nevertheless, control reference

pressure values recorded with the UC in healthy

patients are still to be determined.

Flow is also a parameter used for diagnosis of

infravesical obstruction. The absence of significant

differences in the flow values measured with GSM

and MUC is an indication that the UC seems not to

impose a significant additional resistance to urine

flow. It should be observed that both methods were

applied at the same maximum cystometric capacity.

Other non-invasive methods for measuring

bladder pressure are currently available (Pel & van

Mastrigt, 1999; Griffiths et al., 2002). We believe

that the present solution, allows more comfort to the

patient during examination, as patients reported no

pain or discomfort during clinical tests.

Nevertheless, MUC showed to be at least as

sensitive as GSM in the detection of alterations of

vesical pressure. Further studies in equivocal and

healthy subjects are being planned so that control

reference values for vesical pressure may be

determined.

5 CONCLUSIONS

The developed device and measuring system is

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portable, reliable and robust, allowing measurement

of the static bladder pressure during voiding. The

clinical results indicate that the MUC may be a

promising minimally invasive alternative for clinical

evaluation of vesical pressure.

REFERENCES

Clarkson, B., Robson, W., Griffiths, C., McArdle, F.,

Drinnan, M., Pickard, R. 2008. Multisite evaluation of

noninvasive bladder pressure flow recording using the

penile cuff device: assessment of test-retest agreement.

The Journal of Urology. 180: 2515-2521.

D’Ancona, C. A. L., Bassani, J. W. M., Querne, F. A. O.,

Carvalho, J., Oliveira, R. R. M., Netto Junior, N. R.

2008. New method for minimally invasive urodynamic

assessment in men with lower urinary tract symptoms.

Urology. 71: 75-78.

Gomes, C. M., Arap, S., Trigo-Rocha, F. E. 2004. Voiding

dysfunction and urodynamic abnormalities in elderly

patients. Revista do Hospital das Clínicas da

Faculdade de Ciências Médicas da Universidade de

São Paulo. 59: 206-215.

Griffiths, C. J., Rix, D., MacDonald, A. M., Drinnan, M.

J., Pickard, R. S., Ramsden, P. D. 2002. Noninvasive

measurement of bladder pressure by controlled

inflation of a penile cuff. The Journal of Urology. 167:

1344-1347.

Harding, C., Robson, W., Drinnan, M., McIntosh, S.,

Sajeel, M., Griffiths, C., Pickard, R. 2009. The penile

cuff test: A clinically useful non-invasive urodynamic

investigation to diagnose men with lower urinary tract

symptoms. Indian Journal of Urology. 25: 116-121.

Parsons, B. A., Bright, E., Shaban, A. M., Whitehouse, A.,

Drake, M. J. 2009. The role of invasive and non-

invasive urodynamics in male voiding lower urinary

tract symptoms. World Journal of Urology.

Pel, J. J. M., van Mastrigt, R. 1999. Non-invasive

measurement of bladder pressure using an external

catheter. Neurourology and Urodynamics. 18: 455-

475.

Power, R. E., Fitzpatrick, J. M. Medical treatment of BPH:

an update on results. 2004. European Urology Update

series. 2: 6-14.

van Mastrigt, R., Pel, J. J. M., Huang Foen Chung, J. W.

N. C., de Zeeuw, S. 2009. Development and

application of the condom catheter method for non-

invasive measurement of bladder pressure. Indian

Journal of Urology. 25: 99-104.

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