Effects Of Bladder Outlet Obstruction On Detrusor Biomechanical Properties

Background and ObjectiveBladder outlet obstruction is not an unusual disease with any obstruction between bladder outlet and urethral orifice. Besides the voiding difficulties, it may induce urinary bladder structural and functional change. By influencing the reservoir and voiding function, upper urinary tract damage and even end stage renal disease ( ESRD) may occur. The urinary tract damage persists after obstruction relieved. Thus it is critical to early diagnose and to treat BOO, and to thoroughly acknowledge its impaction on urinary bladder. Biomechanics is one branch of biophysics which applies mechanical principle and method to carry out the quantitative studies on mechanical problems in the living things. The effect of BOO on urinary bladder and detrusor muscles comes from increasing bladder outlet resistance, increasing intravesical pressure, and overwhelming stretching stimulation beyond normal physical limit on detrusor muscles. Thus the pathophysiology of BOO is a kind of typical biomechanical process and it changed the biomechanical characters of urinary bladder. According to these biomechanical changes, we could not only have thoroughly idea of the urinary impaction of BOO, but also diagnose and treat BOO timely to rescue the bladder function and to avoid the ESRD. Thus researching the BOO induced biomechanical changes of urinary bladder has both theoretical and clinical meanings. In this study, we establish a stable and repeatable experimental BOO rat model and to figure out the BOO impaction on bladder compliance and detrusor contraction function.Materials and MethodsTo establish a stable animal model of bladder outlet obstruction(BOO) by partialligation of the bladder neck of male Wistar rats forming , a urethra stricture by laying a trochar at outside of bladder neck.The rats were divided into false group,BOO 6 weeks group(BOO6W)and BOO 12 weeks group(BOO12W) by time.The cystomety was performed in BOO6W and the rats was divided into detrusor instability(DI) group and destrusor stability (DS) group on the basis of destrusor stability,one with DI and another without DI.The active contraction of detrusor muscle stripes to Carbachol was recorded with transfusor and organ bath tube. The compliance and maximum volume of bladder ,bladder leak point pressure were examined by filling cystometry.ResultsThe bladders of BOO animal model demonstrated typical post-obstruction alterations after partial ligation of the bladder neck. The maximum volume increased significantly in DI group (10.8±3.0) ml, DS group (10.3±1.9)ml and BOO12W group (9.5±2.3)ml as compared with that in sham-operation group (2.1±0.3)ml (P<0.01). The bladder leak point pressures were significantly greater in DI group(39.4±7.1)cmH2O , DS group(35.9±6.2)cmH2O and BOO12W group(48.6±9.5)cmH2O as compared with that in sham-operation group(16.2±2.1)cmH2O, (P<0.01).The bladder compliance were significantly higher in DI group(0. 27±0.08)ml/cmH2O, DS group(0. 29±0. 05)ml/cmH2O and BOO12W group(0.21±0. 05)ml/cmH2O as compared with that in sham-operation group(0.13±0. 03)ml/cmH2O, P<0.05.The detrusor contractile force of DI group was significantly lower than that in the sham-operation group(P<0.05)and DS group (P<0.01). the contractile force in DS group was higher than that in the sham-operation group (P>0.05) . No definite contraction wave was detected in the detrusor muscle of BOO12W group. (amplitude<0.05g)Conclusions(1) BOO animal model established by partial ligation of the bladder neck of adultrats with a horizontal strength of 0.1Kg is simple and can give high survival rate and good stability, suitable for the studies of bladder outlet obstruction.(2) There are two different types of the detrusor contraction after BOO: DI group with impaired contraction and conversely DS group were higher. The contractility of detrusor muscle will be damaged and even irreversible contractile function incapacitation will occur if the obstruction was not removed. The effect of bladder stability to bladder compliance is inconspicuous and there is close correlation between bladder compliance and bladder capacity.(3) Increased bladder leak point pressure and high pressure of bladder may be the main cause of impaired kidney after BOO and bladder function should be evaluated by using bladder compliance and bladder leak point pressure together.