Perineal sound recording for diagnosis of bladder outlet obstruction

Abstract

Objectives: Elderly men are prone to developing lower urinary tract symptoms (LUTS) possibly caused by bladder outlet obstruction (BOO). The most frequently used method to diagnose this condition is an invasive and time-consuming pressure-flow study. We are developing a novel non-invasive method to diagnose BOO in men with LUTS based on perineal sound recording.

Methods: A biophysical model urethra was made from polyvinyl alcohol (PVA) cryogel with viscoelastic properties comparable to those of the male pig urethra. To this model different degrees of obstruction were applied and sound was recorded at different positions downstream of the obstruction. In a study in 16 healthy male volunteers the variability and repeatability of perineal sound recording was tested.

Results: In the model three parameters, derived from the frequency spectrum of the recorded sound (i.e., weighted average frequency, standard deviation and skewness) are uniquely related to the degree of obstruction (linear regression, P<0.001). The variability of perineal sound recording in healthy male volunteers was found to be smaller within volunteers than between volunteers (Kruskal-Wallis, P<0.001) and the repeatability was comparable to that of the maximum flow rate.

Conclusions: We conclude that perineal sound recordings are significantly different between volunteers. In combination with the unique relations found in the model-experiments these results increase the probability that perineal sound recording can be used as a simple and cheap non-invasive method to diagnose BOO. Clinical testing of this method is therefore strongly indicated.

Keywords: Bladder outlet obstruction; non-invasive urodynamics; perineal sound recording.

Figure 1

Cross-section of the lower urinary tract (a) and an example of a perineal sound recording in a volunteer (b)

Figure 2

Cross-sections of a PVA model urethra with a Y-shaped opening (a) and of the proximal part of the male pig urethra (b). We stained elastin, collagen (both dark grey) and muscle tissue (light grey) using elastin von Gieson staining. The lamina propria is surrounded by muscular tissue with a horseshoe-like shape. Panel b was reproduced from Urodinamica 16, 310–320, 2006, with kind permission from Editrice Kurtis.

Figure 3

Four parameters, i.e., the average amplitude of the sound and the weighted average frequency (f_c), standard deviation (σ), and skewness (γ₁) of its frequency spectrum, derived from a sound recording in a PVA model are plotted as a function of the degree of bladder outlet obstruction (BOOI). At each value of BOOI, the mean and standard error of the mean of 5 recordings at 12 distances downstream of the obstruction are shown. The critical BOOI-values are indicated by the dotted lines, unobstructed (Nobs) is defined by BOOI <20 and obstructed (Obs) is defined by BOOI >40 (1, 17). This figure is reproduced from IEEE Transactions on Biomedical Engineering, doi: 10.1109/TBME.2008.919131, © 2008 IEEE.

Figure 4

Example of a perineal sound recording in a male volunteer (reproduced from Neurourol. Urodyn., with kind permission of John Wiley and Sons, Inc.). In the example, the flow rate (a), perineal sound (b), and the frequency spectrum of the perineal noise (c) are plotted as a function of time. For each frequency (on the vertical axis) in the sound frequency spectrum red represents a high power and blue represents a low power. In the bottom, three panels the weighted average frequency (d), the standard deviation (e) and the skewness (f), derived from the sound frequency spectrum, are presented as a function of time.

Figure 5

Box-whisker plot of the three parameters, derived from the sound frequency spectra of each volunteer (reproduced from Neurourol. Urodyn., with kind permission of John Wiley and Sons, Inc.). The box represents the median value and the 25th and 75th percentile and the whiskers represent the highest and lowest value. Volunteers that were significantly different from three or more other volunteers (Dunn's test, P< 0.05) are marked with an asterisk. The number 1 identifies a volunteer that was significantly at the top end of the weighted average frequency and the standard deviation scale and at the bottom end of the skewness scale.