Hypothesis / aims of study
A pressure flow study has the gold standard for diagnosing bladder outflow obstruction (BOO) and other lower urinary tract dysfunctions. In storage phase of urodynamics, two frequent patterns shown by detrusor overactivity (DO), which are phasic DO and terminal DO. Phasic DO is defined by involuntary detrusor contractions of a characteristic wave form, which may or may not be voluntarily suppressed. Terminal DO is defined by a single involuntary detrusor contraction that cannot be suppressed, thus, causing DO incontinence. The combination of phasic and terminal DO is also common. Detrusor underactivity (DU) according to the International Continence Society (ICS) introduces low detrusor pressure or short detrusor contraction time, usually in combination with a low urine flow rate resulting in prolonged bladder emptying and/or failure to achieve complete bladder emptying within a normal time span (ref.1). The prevalence of DU is 9% to 23% in men and 12% to 45% in women. There is no report regarding the validity of pressure flow study parameters recorded during voiding subsequent to terminal DO.
In the current study, we focused female patients to avoid complexity of male composition of DU and BOO.
We investigated whether a valid diagnosis of lower urinary tract dysfunction could be established from pressure flow study analysis of a detrusor overactivity related voiding.
Study design, materials and methods
Women patients with neurogenic bladder who urodynamically proven DO have been analyzed. Multichannel urodynamic evaluations were performed for all patients. Urodynamic study was performed using a double lumen 6Fr transurethral catheter introduced into the bladder via the urethra. The 6Fr catheter served for infusing room temperature isotonic saline at 30 to 50 ml per minute and for measuring intravesical pressure. Abdominal pressure was measured by a 9Fr rectal balloon catheter inflated with 5 ml saline. The detrusor pressure was calculated by subtracting the intraabdominal pressure from the intravesical pressure electronically.
At pressure flow study for each subject we evaluated maximum flow rate (Qmax) (mL/second) and Pdet.Qmax (cm H2O) were considered. We defined two type of voiding in this study, DO related voiding; involuntary detrusor contraction accompanied by leakage was observed, even though the examiner had not instructed to void, resulting micturition or voiding after command micturition under DO has occurred and voluntary voiding; voiding voluntarily after command micturition and without terminal DO. To explore the difference between two types of voiding, we specifically focused on parameters of voiding phase. Statistical analyses were conducted with GraphPad Prism for Windows Ver. 6.01 (GraphPad Software, San Diego, CA, USA). Linear regression analysis is performed and compared.
The study comprised 22 women (mean age 62.0 ± 19.3 years, range 17-85) with a lower urinary tract symptoms. The causes are listed in Table 1. There were no significant differences in age between the two groups (70 vs.65). All patients showed DO on pressure flow study. In DO related voiding group, compared to voluntary voiding group, the following statistically significant differences were observed: Qmax was lower and Pdet.Qmax was higher (Figure 1). Moreover, in linear regression analysis (P/Q (Pdet.Qmax Qmax) plot), value of slope was reversed in positivity and negativity: DO related voiding y-intercept is 13.96 and slope is -0.1206, in voluntary voiding y-intercept is 11.08 and slope is 0.1504 (Figure 1).
Interpretation of results
During voiding phase, P/Q study simultaneously measures Pdet and flow rate. P/Q assessment is considered to be the gold standard for quantifying and grading BOO and differentiating between BOO and DU. This study demonstrates different pattern in P/Q plot between two types of voiding (DO related voiding and voluntary voiding). Although all patients have not apparent BOO anatomically, in P/Q plot, patients of DO related voiding have significantly high pressure/low flow pattern, which could be pretended outflow obstruction.
In previous reports (ref.2), male benign prostatic hyperplasia with BOO patients were analyzed in an analogous fashion, Pdet.Qmax showed a statistically significant increase in DO voiding (94 ± 37.7 (DO related voiding) vs. 75 ± 37.6 (voluntary voiding) cm H2O). And, 80% of this study patient again remained in the same diagnostic category of ICS nomogram. In our study, patients of DO related voiding have BOO pattern compared to patients of voluntary voiding (45.2 ± 23.2 (DO related voiding) vs. 18.1 ± 7.5 (voluntary voiding) cm H2O), even though we don’t have validated female nomogram. Moreover, under DO related voiding condition, it is difficult to detect DU from urodynamics parameters. Normal voluntary voiding is achieved through the initial relaxation of the urethral sphincter, followed by a sustained detrusor contraction that leads to complete bladder emptying within a normal time span. The inappropriate activities of the pelvic floor muscles and/or the urethral sphincter during voiding cause functional BOO. The increase in Pdet may have reflected the failure of relaxation of the striated sphincter with the subject still trying to postpone micturition under terminal DO or by changed pathways involved in lower urinary tract control and occur phenomenon like detrusor sphincter dyssynergia under terminal DO. In previous reports, DO would be associated with enhanced detrusor contraction strength. This has been attributed to DO related facilitation of bladder contractility. Terminal DO would be more due to alteration in detrusor function. However, this is only a hypothesis. Especially, patients with neurogenic bladder, accurate tools and a cooperative patient are required to obtain useful information from a pressure flow study. We would recommend that if a patient performed DO related voiding the test should be repeated to have voluntary voiding pattern, if possible. Moreover, from our results, we might have to adapt different nomogram for detecting BOO and DU under two types of voiding condition.