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Invasive pressure flow studies (PFSs) in urodynamics are still the gold standard method
for objective classification of bladder outlet obstruction (BOO) in men with
lower urinary tract symptoms (LUTSs). It is able to delineate patients for successful
surgical approach [

The
risks of complications after conventional urodynamic study in men with BOO are
greater, and acute urinary retention, macroscopic hematuria, urinary tract
infection, and/or fever can occur in over 19% of the cases [

During
the past 14 years, many experts have raised minimal invasive possibilities as
substitutes [

Griffiths
et al. have previously described and validated a minimal invasive technique based on controlled inflation of a penile cuff during voiding [

Trying to
overcome these limitations, we developed, in association with the University’s
Biomedical Engineering Department, a urethral device capable of extracting from
the voiding patient measurements comparable to those achieved from invasive PFS
[

We have published before that applying logistic
regression fitting to the minimal invasive method utilizing this urethral
device was able to detect most patients with BOO [

The bladder outlet obstruction index (BOOI) was created
to classify men as obstructed, equivocal, or unobstructed based on invasive
urodynamic results of

These were plotted on an equation and the BOOI obtained could differentiate the
three groups by a nomogram analysis (ICS nomogram) [

Once logistic regression analysis has demonstrated 67% sensitivity and 79% specificity utilizing the novel intraurethral device to identify BOO [

After obtaining the Ethics Committee approval and a written informed consent, sequential invasive and minimal invasive PFSs were prospectively performed in men with clinical complaints of LUTS.

PFS was performed according to ICS good
urodynamic practice guidelines [

The minimal invasive urodynamic evaluation was
done using a urethral device [

Actual urethral device used in the noninvasive test.

After concluding the conventional urodynamic
assessment, the postvoid residual urine volume was measured. The bladder was
refilled with warm saline solution (

During voiding, the patient was instructed to
interrupt the flow with a digital maneuver that simply blocked the end of the
urethral device. Interrupted urine flow (Qinter) and isometric bladder pressure
(Piso) were registered using this technique. The rectal catheter used in the
conventional urodynamic assessment was maintained to record the Pabd. The Piso
was measured at the greatest pressure point after interrupted flow, and the
Qinter was considered the plateau: the greatest flow point resulted from the
impact of urine in the flow meter and was considered as interference [

These variables (Piso and Qinter) were
compared using the Pearson’s coefficient correlation test [

As only two
variables demonstrated predictive ability in a previous analysis including all
variables (isometric pressure, abdominal pressure, maximal flow, Qinter, and
postvoid residual urine volume) [

We tried to find a function of minimal invasive data to approximate (i.e., to classify), as closely as possible, the reference standard classification. This mathematical correlation was tested to determine substitute equivalents for an adapted Abrams-Griffiths equation worth for minimal invasive measures.

A
linear correlation between the minimal invasive

The

When we
substitute (

All computations were done with Statistical
Analysis Systems (SAS Institute, Cary,
NC), version 8.2 [

Fifty-one consecutive male patients with complaints of lower urinary tract symptoms were included in this study. Among these men, 46 (90%) were suitable for analysis, 5 (10%) were excluded due to involuntary high-amplitude detrusor contractions and low bladder compliance during the invasive test.

The
mean age was

The
mean international prostatic symptom score (IPSS) was

The mean postvoid residual urine volume was 48.9 mL (range: 0–250). The mean
values of the normal patients (45 mL, range: 0–110) were lower
than those of the equivocal patients (60 mL, range: 0–250) or
obstructed patients (65 mL, range: 0–140). The
comparison of the mean postvoid residual urine volume between the groups with
the different urodynamic diagnoses was not statistically significant (

The urethral devices used in the minimal invasive urodynamic evaluation did not cause pain during the procedure. Leakage occurred between the urethra and the device in 1 patient, and the examination was repeated.

Using invasive data, 21 (45.6%) were classified as obstructed, 15 (32.6%) as equivocal, and 10 (21.7%) as unobstructed; a total of 25 (54.4%) of equivocal/unobstructed. When Pabd was added to the statistical analysis, no additional patient was identified as obstructed.

Significant linear correlation was observed between invasive

This allowed for a mathematical substitution
of values on the Abrams-Griffiths original equation (

This
was the final equation for classification of BOO using the urethral device
test, and the result was denominated urethral device number (

The final
result (

Of the
21 men classified as obstructed by Abrams-Griffiths
equation (conventional invasive urodynamic), 13 were identified by the minimal invasive
diagnostic index (Table

Comparison between Abrams-Griffiths equation (conventional invasive urodynamic) and minimal invasive diagnostic index.

Minimal invasive diagnostic index | ||
---|---|---|

Conventional urodynamic | Normal and equivocal | Obstructed |

Normal and equivocal | 19 | 06 |

Obstructed | 08 | 13 |

This new
equation classified 27 (58.7%) of the patients as equivocal/unobstructed and 19
(41.3%) as obstructed. Sensitivity was 61.9%; specificity, 76%; PPV, 68.4%; NPV,
70.37%. Overall accuracy was
69.6% (Table

Measurements of accuracy for obstruction through the new method.

Measurement | % | 95% CI | |
---|---|---|---|

Sensitivity | 61.9 | 38.7; 81.1 | 19/21 |

Specificity | 76.0 | 54.5; 89.8 | 19/25 |

Positive predictive value | 68.4 | 43.5; 86.4 | 13/19 |

Negative predictive value | 70.4 | 49.7; 85.5 | 19/27 |

Accuracy | 69.6 | 54.1; 81.8 | 32/46 |

CI: confidence interval,

In order
to prove methodological equivalency, we tested the Pearson’s coefficient
correlation [

Linear correlation tested through the Pearson’s coefficient between the number of Abrams-Griffiths (BOOI:

This idea was original and the device was designed in our institution; therefore, this is the first report of this method.

The analysis
of the IPSS of the patients in this study did not identify patients with BOO.
However, none of the patients presented with an IPSS of 28 or greater, a score
that has a positive correlation with obstruction [

In this
study, no correlation was found between the postvoid residual urine volume and
BOO. Other studies have also failed to demonstrate this association [

The probability of a urinary infection from the use of the urethral device is low because it is introduced only up to the fossa navicularis, and it does not cause pain.

Other
techniques of noninvasive urodynamic evaluation have reported problems such as
elasticity in the condom catheter. Also, different types of material and different
sizes of the penile cuff can register a greater isometric pressure [

Because the
minimal invasive assessment was performed immediately after the conventional
assessment, a low variability was warranted as demonstrated before in the
second pressure/flow study of 192 patients with the diagnosis of BOO maintained
in 95.2% and reduced
only 6.9% in detrusor pressure at maximal urinary flow [

The results
obtained revealed 67% sensitivity and 79% specificity, applying a logistic
regression [

These results
are similar to those reported in other studies, in which the condom catheter
noninvasive urodynamic assessment was used to correctly diagnose 77% of the
patients who presented with obstruction [

The
noninvasive urodynamic study using a cuff also helped to separate the
obstructed from the unobstructed patients. The sensitivity and specificity rates
for the diagnosis of BOO in a study of 116 patients were 73% and 75%,
respectively [

Griffiths et al. obtained comparable results, which were actually useful for only two
thirds of the patients previously considered suitable for this method (i.e.,
two thirds of 54% from the total recruited men). This limited result could
probably be due to the method itself, which did not differ a lot from the
simple flow rate criterion, in addition to the inconvenience of wearing a
penile cuff, which restricted the overall evaluation [

The condom catheter and the penile cuff are
also not effective in identifying normal and equivocal patients [

Differently from what has been done so far [

Measures
obtained through the urethral device were comparable to the invasive
correspondents [

Taking
into account that data were obtained through different, though comparable,
methods, it was necessary to adequate parameters to use the standard
Abrams-Griffiths equation. The values of pressure and urinary flow measured
minimal invasive ultimately correlated to the invasive measures. This happens
because the minimal invasive method suffers external influences, such as
urethral compliance and abdominal pressure, which do not primarily affect the
direct measures achieved through invasive urodynamics [

When we
apply the minimal invasive diagnostic index (

The
urethral device test proved to be a promising substitute for invasive
evaluation of men presenting with LUTS after at least two different
methodologies and more than a hundred patients enrolled with over 70% accuracy
[

Primary results presented good correlation to the gold standard method, even though there is still much to improve. It is an easily performed, acceptable method located between the free simple flow rate criterion and PFS, and may represent a reasonable option for BOO diagnosis in the near future.

These
preliminary results need a greater number of men evaluated and the definition
of a final clinical use for its classification. It has not yet been proven if
the results could correlate with a good outcome after transurethral
prostatectomy. A prospective clinical study is under way to assess this new
method in relation to the outcome of elective prostatectomy [

Reis LO was awarded the Young Urology Talent Prize presenting this work in the XXXI Brazilian Urology Congress, Salvador, Bahia, Brazil, November, 2007 (Prêmio Jovem Talento da Urologia - pesquisa clínica).