Hypothesis / aims of study
Lower urinary tract (LUT) symptoms are one of the major causes of visits to the pediatric urologist, affecting 2 to 25% of the population. Patients with LUT symptoms may present with overactive bladder (OAB) or dysfunctional voiding (DV). Investigation for LUT dysfunction should be non-invasive and, as proposed by ICCS, should include clinical history, voiding diary, bladder ultrasound with post void residual evaluation, and uroflowmetry. Uroflowmetry is an important adjunct to the evaluation and management of Bowel and Bladder Dysfunction. Uroflowmetry collects important voiding information based on flow parameters. Additionally, Qmax Flow Index (FI) and Qave FI can be calculated and have been shown to be a reproducible and better measure of voiding efficacy. When associated with pelvic floor EMG (PFEMG), it can also help to evaluate sphincter contraction during voiding. Identification of external sphincter activity and prolonged lag times are useful in helping make a diagnosis and directing therapy. In a recent survey, we found that 45% of health professionals never use EMG when doing uroflowmetry. This study aims to evaluate if activity of pelvic floor will have a discernible effect on flow parameters even in normal bell curves that were smooth without interruptions or evidence of staccato patterns.
Study design, materials and methods
Of total of 4133 uroflow curves 362 female and 87 male curves were selected for evaluation. Inclusion criteria were age between 12 to 20 years with a flow curve classified as smooth bell shape, with FI Qmax ranging from 0.741 to 1.330, based on previous defined criteria for bell curves using FI (1), voided volume greater than 50 ml, post-voided residual (PVR) less than 20 ml, a bladder volume not greater than 115% of estimated bladder capacity, which was established as 400 ml, and a reliable quality EMG signal.
Curves that fell in the flow index criteria of bells but did not have the appearance of a bell were eliminated. All curves included in the study were considered to have a bell shape with no interruption by two-experienced pediatric urologists and were evaluated for PFEMG activity. Pelvic floor activity was demonstrated in 256 female and 31 male curves and composed the study groups. The other 106 and 56 flows from females and males, respectively, comprised the control groups of ideal normal voiders without PFEMG activity (Fig 1).
All uroflowmetries had been performed in a private room using Laborie flowmeter (Toronto, Canada). A pair of electrodes was placed in the perineum, 1 to 3 cm laterally to anus, on either side and connected to the EMG unit, the patient was asked to free void.
Data from all flow parameters (Qmax, Qave, Time to Qmax, percentile of void to Qmax, acceleration, voiding time, voided volume, post voided residual (PVR), total bladder capacity (TBC), Qmax FI, and Qave FI) were evaluated and compared between those with and without activity on PFEMG.
Parametric variables were compared using t-test and nonparametric ones with Mann-Whitney analysis. A confidence interval of 95% with a p<0.05 was considered for statistical significance.
Mean ages were similar for females without PFEMG activity (14.53 ± 2.43 yo) and with PFEMG activity (14.22 ± 2.10 yo) (p=0.224) and males without PFEMG activity (15.38 ± 2.83 yo) and with PFEMG activity (15.65 ± 2.44 yo) (p=0.570) with and without PFEMG activity.
For females, those with PFEMG activity presented lower Qave (10.2 ± 3.6) than those without PFEMG activity (11.9 ± 3.8) (p<0.001). Voided volume and TBC were also lower in those with PFEMG activity (168.4 ± 84.9 and 176.0 ± 86.2, respectively) than those with no activity (192.6 ± 92.2 and 200.7 ± 93.4, respectively) (p=0.018 and p=0.018, respectively). Acceleration was higher in those with PFEMG activity (4.2 ± 2.1 vs. 3.8 ± 2.3) (p=0.039). All other flow parameters were similar between study and control groups. Patients with relaxed pelvic floor during voiding presented a lower Qmax FI (p<0.001) and a higher Qave FI were similar (p=0.011) when compared to those with activity on PFEMG (Table 1).
For males adolescents, no differences were seen in all flow parameters (table 1).
Interpretation of results
A bell shape curve that has no interruption in its trace is considered to be the graphic demonstration of a normal void, therefore, if pelvic floor activity is not investigated, a person who presents with a smooth bell curve is considered to void totally normal. We have demonstrated that it is possible to void with a normal appearing bell curve on visual inspection and by flow index criteria and have evidence of elevated pelvic floor activity. This pelvic floor activity does produce a discernible difference in flow characteristics in females. The lower average flow rate is due to a lower bladder volume at which these patients are voiding. We had a concomitant reduction in average flow velocity, which is directly proportional to the voided volume as well as TBC. This confirms the relationship between volume and flow rates and further establishes the benefit of using a flow index which is volume agnostic. In males we did not see a difference in the flow parameters that are routinely measured. This difference between the males and females may be related to the nature of the two urethras. The male urethra with its greater tortuosity and greater energy dissipation may account for the unmeasureable differences between flows that have active and inactive EMG’s.(2) It is also possible that the smaller number of male cases may just not be robust enough to identify a difference in the male flows especially if the differences are small.
Attempts have been made to establish nomograms to interpret uroflow in children and adults. Significant differences in Qmax and Qave have been demonstrated for normal females that are pre and post-menopausal, with a Qave in pre-menopausal women of 12 ml/sec and 10.2 ml/sec in post-menopausal women.(3) These findings are comparable when we look at young women that void with a non-relaxed pelvic floor and compare them to post-menopausal ones (Qavg=10.23 ml/sec).
The reduction in the bladder volume can be multifactorial; it could be related to increased outlet resistance leading to bladder wall thickening thereby reducing volume by increasing irritability. Or, it can be associated with sensory processing of bladder fullness that is commonly aberrant in patients with LUTS.
We cannot comment on patients with fractionated flow rates that fall within the normal boundaries of a bell flow index in this study since the study was not setup to address this issue.