Detrusor overactivity contributes to overactive bladder in some patients and is diagnosed by visual identification of non-voiding contractions in pressure data from a urodynamics (UD) study. These non-voiding contractions can be isolated, sporadic or periodic. The aims of the present study were 1) to implement a novel automated algorithm to objectively quantify low amplitude rhythmic contractions (LARC) during UD filling, 2) compare LARC frequencies and amplitudes at low and high volumes to quantify any changes that occur during filling and 3) determine whether participants with LARC at both low and high volumes correlated with a subgroup of patients with detrusor overactivity.

UD pressure data from 95 adult patients were retrospectively analyzed by an automated Fast Fourier Transform (FFT) analysis algorithm. Three 205-second regions of interest (ROIs) were analyzed at low bladder volumes (beginning 0, 30 and 60 sec after the start of filling) and at high volumes (ending 0, 30 and 60 sec prior to the start of voiding) to identify three frequencies in the 1.75-6 cycles/minute range associated with the largest rhythmic amplitude peaks in vesical pressure (Pves) as shown in the example in Figures 1 and 2. Peak Pves amplitudes were analyzed to determine whether any significant rhythmic activity was present in Pves (Was there a peak in Pves?), and if that activity was independent of any rhythmic activity in the abdominal pressure (Pabd) (Was Pabd relatively flat compared to Pves?). Rhythmic frequencies and amplitudes were quantified for each patient in which significant and independent LARC were identified. The automated algorithm can analyze an individual UD study in less than 5 seconds, allowing for potential real-time data interpretation in the UD clinic.

A neurourologist/urodynamicist identified 52 out of 95 patients as having detrusor overacitvity based on a blinded analysis on the UD pressure data. The group identified with detrusor overactivity included 26 women and 26 men with an average age of 53±2 years, and included 28  individuals with neurogenic detrusor overactivity.  The group of 43 participants without DO included 29 women and 14 men with an average age of 51±2 years.

The algorithm identified significant and independent LARC at both high and low volumes in 11 participants.  All 11 of these participants were in the group identified with detrusor overactivity, resulting in a significant association (Fischer’s exact test, p=0.0008) and a specificity of 100%. This group included 7 women and 4 men with an average age of 55±6 years, and included five individuals with neurogenic detrusor overactivity. 

For  the group of 11 participants identified with LARC at both low and high volumes, the slowest significant and independent LARC frequencies were not different at the low and high volumes (2.3±0.2 cycles/min and 2.6±0.4 cycles/min, respectively, n=11, p>0.05). However, the LARC amplitudes at the slowest frequencies nearly doubled, increasing from an average of 6.7±1.1 cm-H2O to an average of 12.0±2.5 cm-H2O (n=11, p<0.05) as the bladder volume increased.

The algorithm identified a subset of patients with detrusor overactivity (11 out of 52 = 21%) that exhibited quantifiable LARC throughout filling and developed greater LARC amplitudes at larger bladder volumes.

This automated algorithm demonstrated that LARC amplitude, but not frequency, increased with increasing volume in a subset of individuals with detrusor overactivity. The algorithm can be implemented to provide physicians with real-time quantification of any LARC during a UD study and will permit quantitative characterization of the development of LARC throughout the bladder filling phase. Furthermore, the algorithm could potentially be used to produce quantitative metrics to determine whether the degree of LARC (based on amplitude change from low to high volume) correlates with overactive bladder severity or response to treatment.