Are rhythmic bladder contractions affected by fill rate and bladder work in neurogenic bladders

Rhythmic bladder contractions (RBCs) are routinely observed in neurogenic bladders (NB) during urodynamic studies (UDS), often below the standard clinical threshold. These rhythmic bladder contractions may contribute to bladder hypertrophy despite low measured pressures, highlighting the need for objective quantification of this intrinsic activity.

This study aimed to validate Fast Fourier Transform (FFT) analysis for precisely characterizing RBCs in NB patients, assessing its relationship to visual inspection and its stability across varying bladder filling rates and motion artifact.

We retrospectively analyzed 115 UDS from 70 NB patients (0.5-18 years). Python-based FFT was applied to detrusor pressure data to derive the Highest Amplitude Frequency (HAF). The HAF was compared for reproducibility between same-day studies performed at identical and different filling rates. We used Bayes Factor (BF) analysis for robust statistical evaluation, Bland Altman analysis and Receiver Operating Characteristic (ROC) analysis to determine the lowest discernible amplitude measured on FFT.

The HAF was the most reproducible measure (r = 0.85)and highly consistent across same-day UDS, irrespective of changes in filling rate (moderate evidence, BF). This key finding suggests the underlying RBC mechanism is filling rate independent. HAF closely aligned with the visually measured frequency (mean difference ≅ 5 %), validating the FFT method. ROC analysis determined the optimal amplitude cutoff for visually confirming a contraction was overall 1.06, and 1.53 when motion artifact was significant, demonstrating FFT's efficacy in penetrating noise.

FFT analysis is a reliable, objective, and reproducible method for quantifying bladder rhythmic activity, yielding an HAF that is stable regardless of filling rate or movement. The HAF is introduced as a robust, reproducible urodynamic parameter to objectively monitor neurogenic bladders.