Novel Natural Fill Telemetric Pressure Flow Study of Discomfortand Bladder Outlet Obstruction

Hyoun-Joong Kong, Sunmee Park, Tack Lee, Ji Youl Lee, Hee Chan Kimand Seung-June Oh*From the Interdisciplinary Program, Biomedical Engineering Major, Graduate School (HJK, SP), Departments of Biomedical Engineering (HCK)and Urology (SJO), College of Medicine and Institute of Medical and Biological Engineering, Medical Research Center (HCK), Seoul NationalUniversity, Seoul, and Departments of Urology, Inha University College of Medicine (TL), Incheon and College of Medicine,Catholic University of Korea (JYL), Bucheon, Korea

Purpose: We evaluated the accuracy of natural fill telemetric pressure flow studyperformed in a private room, and assessed patient discomfort and experienceafter the procedure compared to those of standard pressure flow study.Materials and Methods: In 58 patients with lower urinary tract symptoms/benign prostatic hyperplasia free uroflowmetry, and natural fill telemetric andstandard pressure flow studies were prospectively performed. Immediately aftereach step patients were asked to rate the experience in terms of pain, embar-rassment, bother, boredom and repeat testing. Subjective items and objectiveurodynamic parameters were compared among the 3 tests.Results: Maximum urine flow on natural fill telemetric pressure flow study wasnot different from that on free uroflowmetry. In contrast, maximum flow, detru-sor pressure at maximum flow and bladder contractility index on the standardpressure flow study were significantly lower than on the natural fill pressure flowstudy. However, the bladder outlet obstruction index was not significantly dif-ferent between the 2 studies, and the bladder outlet obstruction and bladdercontractility indexes correlated well. There were also no differences in bother andembarrassment scores. However, natural fill telemetric pressure flow study wassuperior in terms of pain and boredom scores. Patients were more willing toundergo repeat natural fill telemetric pressure flow study than standard pressureflow study. Time to complete the test was significantly shorter for the natural fillstudy than for the standard study.Conclusions: Flow rate differences between pressure flow studies and free uro-flowmetry are not due to mechanical obstruction by the catheter but to otherfactors, such as the bladder filling method. Objective parameters on the naturalfill telemetric pressure flow study correlated with standard pressure flow studyfindings. The natural fill telemetric pressure flow study shortened the timeneeded for the test and may decrease the discomfort of the standard pressure flowstudy.

Key Words: prostate, prostatic hyperplasia, urinary bladder neck obstruction,

Abbreviations

and Acronyms

BCI � bladder contractility indexBOO � bladder outlet obstructionBOOI � BOO indexBPH � benign prostatic hyperplasiaICS � International ContinenceSocietyNFT-PFS � natural fill telemetricPFSPabd � abdominal pressurePC � personal computerPdet � detrusor pressurePdetQmax � Pdet at QmaxPFS � pressure flow studyPves � vesical pressurePVR � post-void residual urineQmax � maximum urinary flowrateS-PFS � standard PFS

Submitted for publication December 23, 2008.Study received Seoul National University Hos-

pital institutional review board approval.Supported by Research Foundation Grant

KUA-2006-HCMC060TO38 funded by the KoreanUrological Association.

* Correspondence: Department of Urology,Seoul National University Hospital, Yeongeon-dong, Jongno-gu, Seoul, Korea 110-744 (tele-phone: �82-2-2072-2406; FAX: �82-2-742-4665;

urodynamics, pain

topic see page 766.

A significant proportion of patientswith low urinary flow rate in the oldermale population have detrusor under- activity or BOO. PFS is considered

0022-5347/09/1822-0601/0THE JOURNAL OF UROLOGY®

Copyright © 2009 by AMERICAN UROLOGICAL ASSOCIATION

the gold standard for diagnosing BOOin patients with BPH.1 However, gen-eral urologists are confronted with

several limitations in its application

Vol. 182, 601-606, August 2009Printed in U.S.A.

DOI:10.1016/j.juro.2009.04.030

e-mail: sjo@snu.ac.kr).

For another article on a related

www.jurology.com 601

NATURAL FILL TELEMETRIC PRESSURE FLOW STUDY602

in patients with BPH. The procedure is invasive andtime-consuming. It is usually performed in an openlaboratory space where patients wear pressure linesconnected to a urodynamic machine during the pro-cedure. Therefore, it not only causes significant dis-comfort but also usually does not guarantee patientprivacy. Also, it may not reflect the actual voidingpattern since it is usually done after nonphysiologi-cal bladder filling during cystometry. To overcomethese problems several noninvasive urodynamic mea-surement methods have been designed.2–4 However,none of these newer methods are universally acceptedas a replacement for S-PFS.

We designed a telemetric wireless PFS device todiagnose BOO, decrease patient discomfort and pro-vide privacy during testing. We also modified theS-PFS method so that the procedure could be per-formed without artificial bladder filling, ie with nat-ural physiological filling of urine. The telemetricdevice was designed to transmit real-time pressureand flow signals to a laptop computer using Blue-tooth® technology. To our knowledge this wirelessnatural fill PFS method has not been previouslydescribed. We evaluated the accuracy of NFT-PFS toassess patient discomfort and the general experi-ence after NFT-PFS compared to after S-PFS.

MATERIALS AND METHODS

A prospective study was performed on an outpatient basisbetween May 2007 and March 2008. This study was ap-proved by the Seoul National University Hospital institu-tional review board and informed consent was obtainedfrom all patients. Study inclusion criteria were agegreater than 50 years, complaints of lower urinary tractsymptoms suggestive of BPH and the ability to read in-formed consent. Study exclusion criteria included activeurinary tract infection, bladder stones, previous urinarysurgery or any genitourinary malignancy and any ure-

A B

Figure 1. Wireless portable pressure (A) and flow (B) measur

thral abnormality such as urethral stricture or congenitalurethral anomaly.

To perform telemetric urodynamic monitoring we de-veloped a new NFT-PFS system composed of custom-madepressure and flow measurement devices. For the pressuremeasurement device Pves and Pabd were acquiredthrough a 6Fr fluid filled double lumen catheter and a 5Frrectal balloon catheter, and converted into electrical sig-nals with 2 disposable pressure transducers. Analog Pvesand Pabd signals were sampled at 25 Hz with a 24 bitanalog-to-digital converter and transmitted to the masterlaptop computer using a Bluetooth Parani-ESD100 trans-ceiver (Sena Technologies, Seoul, Korea). Overall deviceoperation was controlled by a low power consuming mi-crocontroller unit. The whole device was portable enoughto hang on the waist (fig. 1). For the flow measurementdevice the flow volume signal was sensed with a load celltransducer. It was also sampled at 25 Hz and wirelesslytransmitted to the laptop computer. Except for the trans-ducer the device had the same analog-to-digital converter,Bluetooth transceiver and microcontroller unit as thepressure measurement device. The resolution of the pres-sure and flow sensing devices was 25 �V/mm Hg and 1�V/gm, respectively.

The PC program was developed to acquire, plot andanalyze Pabd, Pves and flow volume data transmitted tothe Bluetooth module embedded in the laptop computer.Flow rate was determined as the first derivative of flowvolume data, which was smoothed with a moving averagefilter5 to suppress the effect of locally, rapid high fre-quency components or noise caused by load cell transducersensitivity. The size of the averaging window was 3 timesthe device sampling frequency, ie 25 Hz. SimultaneouslyPdet was calculated by subtracting Pabd from Pves with-out a filtering method. After pressure and flow data ac-quisition was completed the ICS nomogram, voided vol-ume, and opening, closure and maximum Pdet wereextracted from Pdet and flow data (fig. 2).

To measure pressure and flow volume accurately thepressure and flow volume calibration functions were in-cluded in the PC program. Pves and Pabd were accurately

C

ement devices, and device placement for NFT-PFS (C)

repre

NATURAL FILL TELEMETRIC PRESSURE FLOW STUDY 603

adjusted using a water column and a 100 cm ruler, andflow volume was calibrated with a poise that had the sameweight as 300 ml water. When the same water pressureand weight were applied to the conventional Solar S-PFSsystem (Medical Measurement Systems, Enschede, TheNetherlands), resulting pressure and volume values werethe same as with the NFT-PFS system.

The study procedure involved 3 steps. After a patientunderwent free uroflowmetry at visit 1 PVR volume wassubsequently measured on ultrasound. The patient wasinstructed to visit the clinic again while holding urine forthe next examination (step 1—free uroflowmetry). At thenext visit NFT-PFS was done in patients with a bladdervolume of more than 150 ml on ultrasound. Urodynamicand rectal catheters connected to the pressure measure-ment device were inserted into the proper place, as instandard filling cystometry. The patient was asked to voidwith the flowmeter alone in a private room while wearingthe pressure measurement device on the waist. Pves, Pabdand flow data were monitored with the master laptopcomputer outside the room in wireless fashion (step2—NFT-PFS). Subsequent procedures, including fillingcystometry and S-PFS, were performed in standard ICSfashion (step 3—S-PFS), as previously described.6 A singledose of antibiotic medication was prescribed after the pro-cedure (fig. 3). Immediately after each step patients wereasked to rate the experience at each step of the proce-dure in terms of pain, embarrassment, bother, boredomand undergoing repeat testing. The examiner also ratedpain and patient compliance for each step. Subjectiveanswers were given using a 10-point visual analog

Figure 2. PC program and

scale.

Subjective items, such as patient or examiner rated dis-comfort, and objective urodynamic parameters, includingtime to complete the test, voided volume, Qmax, PdetQmax,BOOI and BCI, were compared among the 3 tests. Allterminology conforms to ICS standards.1 Data are shownas the mean � SD and p �0.05 was considered statisti-cally significant.

RESULTS

A total of 58 patients with a mean age of 65.1 � 7.4years participated in this study. Average prostatevolume on transrectal ultrasound was 35.6 � 18.1ml. Mean International Prostate Symptom Scoresymptom and quality of life scores were 16.5 � 8.0and 4.1 � 1.2, respectively (table 1).

Patients reported that free uroflowmetry was bet-ter than the other 2 tests. Bother and embarrass-ment scores were not different between S-PFS andNFT-PFS but the NFT-PFS was superior in terms ofpain and boredom scores. Patients were more will-ing to repeat NFT-PFS if necessary than S-PFS. Theexaminer also reported that patients were more tol-erant of NFT-PFS than of S-PFS. Time to completethe test was significantly shorter for NFT-PFS thanfor S-PFS. Qmax on NFT-PFS was not differentfrom Qmax on free uroflowmetry. In contrast, Qmax,PdetQmax and BCI on S-PFS were significantlylower than on NFT-PFS (table 2). However, BOOI

sentative NFT-PFS results

was not significantly different on S-PFS vs NFT-

Study

NATURAL FILL TELEMETRIC PRESSURE FLOW STUDY604

PFS. BOOI and BCI correlated well in the 2 studies(Pearson’s correlation coefficient � 0.76, p �0.001and 0.680, p �0.001, respectively, fig. 4).

DISCUSSION

Pressure flow studies are important in patients witha low urinary flow rate to differentiate BOO frompoor detrusor contractility.7 However, such testingis not widely done by urologists in clinical practice.There have been many attempts to develop nonin-vasive urodynamic tests and nonurodynamic meth-ods, such as prostate volume, bladder wall thick-ness, bladder weight and intravesical prostaticprotrusion. However, these tests are not consideredsufficient to diagnose bladder outlet obstruction.The only current gold standard test that is univer-sally accepted is PFS.1

The NFT-PFS method in this study is a novel testthat applies 2 concepts. 1) We used wireless technol-ogy, which allows the patient to void in a privatespace. Privacy should be maximally guaranteed inthe laboratory environment, where the patient is

Figure 3.

Table 1. Baseline patient characteristics

Mean � SD International Prostate Symptom Score:Storage symptom 7.1 � 3.9Voiding symptom 9.9 � 5.4

Mean � SD serum PSA (ng/ml) 1.9 � 2.1Mean � SD prostate transitional zone vol (ml) 14.6 � 13.6Standard fill cystometry:

Mean � SD max cystometric capacity (ml) 410.4 � 123.2

No. involuntary detrusor contraction (%) 9 (15.8)

actually voiding, so that cortical inhibition affectsthe result minimally. The laboratory environmentshould be patient friendly, ie the patient must berelaxed and the environment should be private.2) We adopted the natural fill concept, which en-ables the patient to void voluntarily with naturalsensations on uroflowmetry. Natural sensations arenot influenced by artificial bladder filling. Therefore,information on patient flow on NFT-PFS is closelyassociated with information on free uroflowmetry.We found significant differences in S-PFS and NFT-PFS outcome parameters.

Following ICS guidelines8 S-PFS is performed afterartificial fill cystometry. Flow results on subsequentPFSs are different from those of free uroflowmetry.This was confirmed by ambulatory urodynamic studyresults, which also reflect natural filling.9 Klevmarksuggested that bladder behavior is different duringartificial and natural filling, and argued that artifi-cial filling decreases detrusor contractility.10,11 Wealso confirmed that after artificial filling there aredifferences during subsequent bladder emptying.There was also a significant difference in PVR be-tween free uroflowmetry and natural filling PFS.Since post-void residual urine is an aspect of detru-sor contractility, this presumably indicates that de-trusor contractility is slightly lower during a studywith vs without a catheter, although this cannot beassessed directly because BCI cannot be measuredon free uroflowmetry. S-PFS was subsequently per-formed after filling cystometry. S-PFS is performedunder the influence of artificial, nonphysiological,

protocol

rapid bladder filling. Since we used the same 6Fr

NATURAL FILL TELEMETRIC PRESSURE FLOW STUDY 605

caliber urodynamic catheter, we believe that thefilling rate was the main factor in the differencebetween the 2 PFS results. However, the cause of

Table 2. Urodynamic results

Mean � SD Free Uroflowmetry

Voided vol (ml) 237.9 � 172.0PVR (ml) 49.7 � 95.8Bladder capacity at volitional void (ml)* 287.6 � 202.4Qmax (ml/sec) 13.2 � 6.5PdetQmax (cm H2O) Not applicablePressure (cm H2O):

Open Not applicableClosed Not applicable

Slope Not applicableBOOI Not applicableBCI Not applicablePt rated:†

Pain 0.15 � 0.78Embarrassment 0.44 � 1.34Bother 0.05 � 0.30Boredom 0.25 � 1.17Repeat test 9.16 � 2.21

Time to complete test (mins) 4.05 � 2.78Examiner rated:†

Pain 0.04 � 0.27Compliance 9.73 � 0.78

* Voided volume plus post-void residual volume.† Ten-point visual analog scale.

1075.0050.0025.000.00-25.00

Standard PFS

80.00

60.00

40.00

20.00

0.00

-20.00

Tel

emet

ric

PFS

r=0.76, p<0.00

16140.00120.00100.0080.0060.0040.0020.00

Standard PFS

250.00

200.00

150.00

100.00

50.00

Tel

emet

ric

PFS

r=0.68, p<0.00

Figure 4. NFT-PFS and S-PFS urodynamic parameters, including

and 0.68, p �0.001, respectively).

the major differences may be cortical inhibition. De-trusor contractility may also be decreased by thelack of privacy during conventional PFS, in addition

Value NFT-PFS Mean � SD S-PFS Mean � SD p Value

0.511 279.6 � 153.4 355.6 � 157.8 �0.0010.016 94.4 � 85.2 127.0 � 96.2 0.0050.020 375.3 � 183.6 482.7 � 144.5 0.0010.952 14.0 � 7.1 9.8 � 4.5 �0.001

50.8 � 18.3 44.2 � 17.5 0.001

44.6 � 23.1 44.4 � 19.2 0.82026.4 � 11.9 27.4 � 12.3 0.559

2.7 � 1.1 3.3 � 1.5 0.03322.0 � 22.4 22.8 � 21.4 0.328

120.7 � 40.3 93.2 � 24.4 �0.001

0.001 3.16 � 1.82 3.72 � 2.14 0.0280.001 1.79 � 2.15 2.07 � 2.20 0.0660.001 0.77 � 1.53 0.95 � 1.65 0.5150.001 1.34 � 1.97 3.00 � 2.66 �0.0010.009 8.20 � 3.00 7.49 � 3.31 0.0250.001 12.98 � 6.24 25.84 � 6.92 �0.001

0.001 2.68 � 1.45 3.47 � 1.55 �0.0010.001 7.80 � 1.55 7.25 � 1.88 �0.001

p=0.328

100.0080.0060.0040.0020.000.00-20.00

Mean

5.00

0.00

-5.00

-10.00

-15.00

-20.00

Diff

eren

ce

200.00150.00100.0050.00

Mean

0.75

0.50

0.25

0.00

-0.25

-0.50

-0.75

Diff

eren

ce

p<0.001

(A) and BCI (B) (Pearson’s correlation coefficient 0.76, p �0.001

p

��

�

�

��

0.00

1

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1

BOOI

NATURAL FILL TELEMETRIC PRESSURE FLOW STUDY606

to artificial bladder filling. Currently it is not clearwhich factor had a major influence on the difference.Further study with a prospective design using arti-ficial bladder filling with vs without privacy mayconfirm this.

In this context it might be difficult to match no-mograms from S-PFS and NFT-PFS with a singlestandard ICS nomogram. The standard nomogrammay not represent studies done with this technique,given these differences in flow and pressure values.We compared outcomes based on the assumptionthat the 2 studies are based on the same principle.To obtain the highest quality results we believe thatPFS should reflect the actual patient physiologicalvoiding pattern. To accurately determine BOO theurinary flow reflecting natural physiological fillingis desirable. A new BOO nomogram for natural fill-ing conditions should be established before wide-spread application of NFT-PFS in clinical practice.It would be advantageous to perform NFT-PFS toshow that actual clinical treatment outcomes wereimproved by better patient diagnosis and selectionusing natural filling.

Bother and embarrassment scores were not dif-ferent for S-PFS and NFT-PFS in this study, whichmay have been due to the sequence of the proce-dures. Catheters for Pves and Pabd were inserted

just before NFT-PFS and thereafter no further cath-

REFERENCES

1998; 160: 1792. Saunders 2001; pp 900 –93

eter reinsertion was necessary for S-PFS. Thismight have caused significant bias in favor of S-PFSin terms of the patient rating. Since patients with avolume of less than 150 ml in the bladder had to waitfor the bladder to fill further for the telemetricstudy, the actual time to complete the telemetric testmight have been longer in some patients. SinceNFT-PFS can provide a better study environmentfor patients and requires less time to complete, itcan be used in patients with lower urinary tractsymptoms/BPH in an office based practice.

CONCLUSIONS

Our results show that flow rate differences betweenPFS types and free uroflowmetry are not due tomechanical obstruction by the catheter but to otherfactors, such as the bladder filling method before thestudy. Objective parameters of this novel NFT-PFSmethod correlate with those of standard PFS andmay also decrease patient discomfort due to PFS.Time needed to perform NFT-PFS was less thanthat for S-PFS.

ACKNOWLEDGMENTS

Soojin Hwang, Jin-Young Kim, Kwi Shik Kim andSang-A Byun provided support. Professor Ja Hyeon

Ku assisted with statistics.

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