Purpose: We evaluated the natural evolution of detrusor voiding contractility in boys who underwent posterior urethral valve ablation using pressure flow analysis, which is a mathematical computerized analysis of pressure flow studies.
Materials and methods: Among 30 boys with posterior urethral valves who were being prospectively followed, even if asymptomatic on serial pressure flow studies, 11 were included in our study. These 11 patients had had at least 2 evaluations performed between ages 5 and 15 years, a minimum interval of 4 years between the first and last examination, and all pressure flow studies records available for mathematical analysis of voiding contractility. The first examination had been done at ages 5 to 10 years (average 7 +/- 2.04) and the last one at ages 9 to 15 (12.5 +/- 2.5), including 6 evaluated after puberty. All but 1 patient underwent valve endoscopic resection as a newborn and none received urinary diversion. Voiding symptoms, post-void residual, cystometric bladder capacity and bladder instability were considered. Voiding phase maximal detrusor pressure and flow rate were evaluated and detrusor contractility was calculated by the pressure flow analysis parameters of contraction velocity, detrusor contractile power expressed as watt factor and Schafer's nomogram. Contraction velocity and contractile power factor were considered low if below 2 standard deviations of previously determined normal values. True hypocontractility was diagnosed when at least 2 pressure flow analysis parameters were low.
Results: True hypocontractility was detected in 3 of the 11 boys at the first examination and in 8 at the last pressure flow analysis. The remaining 8 and 3 cases of first and last examinations, respectively, were considered to have normal contractility even if 4 of the 8 and 1 of the 3 had 1 low pressure flow analysis parameter (covert hypocontractility). Detrusor contractility worsened in 6 patients, hypocontractility was detected at the first pressure flow analysis in 2, hypocontractility changed to normal in 1 and pressure flow analysis remained normal in 2. Of the 6 boys followed through puberty 5 had hypocontractility, including 3 with cystometric bladder capacity greater than 700 ml., high post-void residual and strained voiding. Of the 11 patients 8 had detrusor instability, including 7 with urge symptoms, at first evaluation which was not found at last examination.
Conclusions: Pressure flow analysis extensively used in men has been confirmed as a useful tool to assess voiding contractility in children. The majority of boys with posterior urethral valves have progressive impairment of detrusor contractility at voiding many years after relief of obstruction. The pattern of hypocontractility, which is detected early on pressure flow analysis, follows a prolonged phase of instability in many cases and leads to an over distended bladder in most patients followed after puberty. Questions arise if this evolution may be prevented by early (pharmacological or rehabilitative) treatment and if it is partially determined by extensive use of drugs acting against unstable detrusor contractions.