The Role Of Sensory Dysfunction In Idiopathic Underactive Bladder

BackgroundUnderactive bladder (UAB) is a common lower urinary tract dysfunction. The main clinical manifestations include decreased and/or interrupted urinary stream, micturition hesitancy, feeling of incomplete bladder emptying and urinary retention. The etiology and pathogenesis of UAB is still unclear. There are a variety of factors that can lead to UAB:urinary tract obstruction (such as benign prostatic hyperplasia), diabetes, aging, spinal cord or peripheral nerve Injury, central diseases such as Parkinson’s disease, stroke etc. Currently, since the underling pathophysiological mechanisms were not identified, there are no effective drugs for the treatment of UAB. Although muscle and efferent factors is considered to be the important reasons for UAB, studies in old animals as well as idiopathic UAB patients (in neurologically intact unobstructed patients) indicated detrusor contractility was not reduced. Activation of bladder sensory afferents was the first step for initiation of voiding reflex, the accomplishment of a normal voiding depends on continous sensory inputs from the bladder and uretha. In our study, we hypothesize that the dysfunction of bladder sensory function may lead to the development of idiopathic UAB.ObjectiveTo explore the role of bladder sensory function in the development of idiopathic UAB, we compared the volume threshold, pressure threshold and the voiding functions of idiopathic UAB patients with those of other three groups including OAB, increased sensation (IS) as well as stress urinary incontinence (SUI).MethodsComputer-urodynamic tests were performed by the experienced investigator in line with the ICS Good Urodynamic Practices standards. We first did the free uroflowmetry measurement and recorded the maximum urinary flow rate (Qmax). Then pressure-flow measurements were conducted, the post void residual (PVR) urine volume was measured immediately after bladder catherizaion. Volume and pressure threshold was recorded at four sensation points:first sensation of bladder filling (FS), the first desire to void (FD), strong desire to void (SD) and maximum bladder volume (MBV). The bladder wall stress (WS), a bladder sensory afferent strength index, was calculated with the formula:WS= pressure* volume. Voiding parameters were recorded:maximum urinary flow rate (Qmax), the detrusor pressure at Qmax (Pdet@Qmax) and bladder urination efficiency (BVE). Bladder contraction index (BCI) was used to measure detrusor contractility and was calculated with the following formula:BCI= Pdet@Qmax+5 Qmax. Bladder outlet obstruction index (BOO I) was also measured for each patient with the formula:BOOI= Pdet@Qmax-2Qmax. Obstructive disease and neurogenic disease and/or injury were ruled out when screening idiopathic UAB patients. The screening criteria:for men:BCI< 100, BOOI< 20, BVE<90%; for women:detrusor pressure at maximum urinary flow rate (Pdet@Qmax)< 20 cmH20, maximum urinary flow rate Qmax< 15, BVE< 90%. We screened 552 urine dynamics measurements, and obtained 85 cases including 20 cases of UAB,22 cases of DO,27 cases of SUI as well as 16 cases of IS patients. We compared the volume threshold, the pressure threshold and the wall stress at FS, FD, SD and MBV in the four groups, we also compared voiding parameters including Qmax from free uroflowmetry, postvoid residual urine (PVR), BVE, and Watt index at Qmax. Data were analyzed with SPSS 19.0.ResultsEighty-five urodynamic measurements were analyzed for comparison. UAB patients were older than patients in other groups and a linear correlation was found between age and the incidence of UAB. The UAB group was predominantly male versus the other groups. UAB had higher volume thresholds than other three groups at first sensation (FS) of bladder filling. UAB group also showed greater pressure thresholds than SUI group (P< 0.0083) at FS, FD, SD and MBV, but compared with IS group, the difference was found only at FS, however, there were no statistically significant differences compared with DO group. UAB demonstrated higher wall stress than IS and SUI. UAB group did not show significant difference of the Watts factor at Qmax except with DO group. Regarding the voiding function, UAB patients had a smaller voided volumes and a higher PVR than other groups.ConclusionsIncidence of idiopathic UAB increased with aging.Impairement of either volume or pressure sensory function may play important roles in the development of idiopathic UAB. This diminished sensitivity to bladder volume or pressure may be mediated by dysfunction in central or peripheral processing of afferent information. Premature termination of the micturition reflex due to impaired afferent inputs may be the reason for the failure to empty bladder efficiently. Identification of the underling molecular mechanisms of the diminished sensitivity either at peripheral or central site will promote the development of effective treatment approches for UAB.