We previously reported that urodynamic parameters change with repetitive filling in children with neurogenic lower urinary tract dysfunction (LUTD) (1). In this study, we aimed to search if three times repeated filling cystometries and pressure-flow studies in the same session would change the urodynamics parameters in children with non-neurogenic LUTD.

Ethical approval was obtained from the local ethical committee (2021/01-07). All consecutive children who underwent their first filling cystometry and pressure-flow study with three repeated studies in the same session between June 2017 and December 2018 were included in the study. Urodynamic reports and charts were evaluated retrospectively, and parameters were compared among all same session three times repeated urodynamic studies. Children with neurogenic LUTD, high-grade vesicoureteral reflux (VUR) and prior bladder surgeries including vesicostomy were excluded from the study. All urodynamic studies were performed when the urine culture was sterile. Every study was performed in the supine position with a fluid-charged transurethral 6Fr urodynamic catheter. Estimated bladder capacity for age was calculated with the formula, (age x30) +30, and the filling rate was taken as 10% of the expected bladder capacity according to age per minute. The filling was performed with 0.9% saline at body temperature. Bladder volume at first sensation during bladder filling (FSBF), detrusor pressure at the first sensation, maximum cystometric capacity (MCC), maximum detrusor pressure during filling (pDetmax), detrusor overactivity (DO), compliance, maximum detrusor pressure during maximum urinary flow (pDetQmax) and detrusor sphincter dyssynergia (DSD) were calculated and evaluated according to definitions of the International Children Continence Society (ICCS) standardization report (2).

40 children were included in the study. 27 (67.5%) were girls and 13 (32.5%) were boys. The median age was 9 (3.4-17) years. Indications were LUTD with low grade VUR in 19 (47.5%), LUTD refractory to conservative management in 13 (32.5%), urinary tract infection with LUTD in 6 (15%) and secondary enuresis in 2 (5%). LUTD included dysfunctional voiding and overactive bladder. FSBF, MCC, detrusor pressure at the first sensation of bladder filling (FSBF), pDetmax, presence of DO, compliance, maximum urine flow (Qmax), detrusor pressure at the maximum urine flow (PdetQmax), residual urine, and presence of DSD were compared (Table 1,2). Only FSBF (ml) , pDetmax (cm/H2O) and compliance (cmH2O/ml) were found comparable between the first and second filling where significantly changing with the third filling (respectively, p:<0.001, p: 0.027 p:0.007) (Table 1) . However, detrusor pressure at FSBF, presence of DO, MCC (Table 1), Qmax, pDetQmax, residual urine, and presence of DSD (Table 2) were comparable in all three repeated tests.

Urodynamic study is the gold standard method for evaluating lower urinary tract functions in children. Especially in children, anxiety and communication problems are serious problems during urodynamic examinations and can cause skeptical results. Therefore, the standardization report of ICCS recommends at least 2 cycles as expert opinion for more reliable results in children (2). We previously reported that detrusor pressures significantly decrease in repeated fillings in children with myelodysplasia (1). However, we emphasized that the interpreters should compare urodynamic findings with clinical signs and consider the worst worrisome results for proactive management. Similarly, in this study, we observed that pDetmax during filling tends to decrease significantly particularly in the third filling, as detected in our previous study on children with neurogenic LUTD. Interestingly, in this study, we also found that bladder volume at FSBF increases where MCC does not change with repeated fillings. It seems that there is an adaptive afferent process for first sensation filling since there is no change with detrusor pressure at first sensation. However, a significant decrease at pDetmax with stable MCC with the third test may point to the viscoelastic property of detrusor muscle demonstrated in animal studies (3) and therefore, detrusor pressures measured with more than twice filling might be regarded deceptive. On the other side, notably, detrusor overactivity would not be affected with repeated fillings. Moreover, Qmax and pdetQmax are very comparable in three times repeated pressure-flow studies. We believe that parameters of pressure-flow studies such as Q max, pDetQmax, residual urine, and presence of DSD are very constant.

In children with non-neurogenic LUTD, three times repeated filling urodynamics and pressure-flow studies including PDet at FSBF, MCC, pDetmax, presence of DO, Qmax, pDetQmax, residual urine, and presence of DSD reveal comparable results but the significant increase at bladder volume at FSBF, the significant decrease at pDetmax at filling and the significant increase in compliance may be expected particularly at the third filling test.

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Bauer SB, Nijman RJ, Drzewiecki BA, Sillen U, Hoebeke P. International Children's Continence Society standardization report on urodynamic studies of the lower urinary tract in children. J Neurourology urodynamics. 2015;34(7):640-7.
Speich JE, Almasri AM, Bhatia H, Klausner AP, Ratz PH. Adaptation of the length-active tension relationship in rabbit detrusor. American journal of physiology Renal physiology. 2009;297(4):F1119-28.