ICS 2018: Spectral Analysis of Urodynamic Data Can Pick Up Low Amplitude Phasic Bladder and Rectal Contractions in Neurogenic Bladder Patients

Philadelphia, PA (UroToday.com) Recent work by Colhoun et al. has identified low amplitude rhythmic contractions (LARC) in patients with overactive bladder in muscle specimens, as well as in bladder pressure studies using Fast Fourier transform (FFT) analysis.  FFT is a form of signal analysis which is capable of taking data that has a cyclic nature and identifying hidden frequencies or periodicity in the data. 

Dr. Israel Franco and his team hypothesized that in many of our neurogenic patients we would be able to find rhythmic patterns using FFT on the raw urodynamic data that is readily available to the urodynamics that would match the low amplitude contractions that were seen on the urodynamic studies.

 The study was designed as a pilot study to evaluate the hypothesis that LARC has commonly seen in neurogenic patients urodynamic studies could be identified with FFT based spectral analysis and these would coincide with each other. There were 39 urodynamic studies available for review from 21 patients.  Some patients had 2 studies on the same day, while 7 patients had pre and post botulinum A injection studies, others had studies after starting new therapy or an increase in medication doses. Urodynamic curves were compared to the results from the FFT analysis. Results were recorded if there were LARC visible on the abdominal, and detrusor channels and the frequency of the 3 highest peaks for each channel were recorded.  The slope of the ApEn was compared to the urodynamic curve and confirmation was made whether the entropy rose or declined with increasing bladder volume. 

There were 39 Urodynamic studies analyzed from 21 patients (9 male and 12 female) with a mean age of 10.8 (sd=5.1). Spectral density graphs were produced for each urodynamic study and the peaks for each urodynamic parameter were plotted and the first 3 highest peaks if the present were recorded and tabulated for the Abdominal and Detrusor curves.  Invariable a spike was noted in the range of 1 cycle/min or a period of 60 secs in both the abdominal and Detrusor spectral analysis.  In 35 of 39 plots, phasic detrusor contractions were identified in the second spectral band (median 2.7 cycles/min).  In 1 of the 4 who did not have a spectral peak, this patient had an underactive bladder, while the other 3 had received botulinum toxin A injections 2- 3 months earlier.  17 of 39 studies had a drop in approximate entropy and 3 of the 4 without phasic detrusor contractions showed no decrease in the ApEn. The patient with underactive bladder did not have a decrease in ApEn nor did he have phasic contractions.  Of the seven patients that underwent Botulinum toxin, A injections 6/7 had no decrease in entropy and the one that did had had an injection more than 6 months earlier.   A normality test was run on the data and the data was determined to not follow a normal distribution.

Standardization of urodynamics by utilizing objective criteria is a critical need in urology and especially when medications are being assessed for efficacy.  One common problem in pediatric patients with neurogenic detrusor overactivity (NDO) is that in many cases low-level phasic contractions are ignored as not being significant.  It is critical in this NDO population that these contractions be eliminated since continued contractions can be detrimental to the patients over the long-term.  Utilizing FFT analysis of the pressure curves allows for identification of signals that may indicate bladder overactivity and in some cases, we have seen spectral evidence of contractions that were not apparent but were ameliorated after Botulinum toxin A  injections.  There was ApEn decreased in almost all patients after Botulinum toxin A  injections indicating that there may be a beneficial effect by Botulinum toxin A  in eliminating LARC in NDO bladders.  As the ApEn decreases there was an increase in order which is associated with an increase in the phasic contractions amplitude on the urodynamic tracings.  Increasing ApEn would lead to chaotic contractions and thereby not lead to phasic contractions. Their findings diverge minimally from the work by Colhoun et al.,  they observed a frequency was an average of 2.7 cycles/min which has a period of 22 sec between contractions, while they observed a frequency of 2.34 cycles/min or a  period of  25 sec between contractions.  Whether these differences are significant or just differences in technique it is reassuring that the numbers are relatively close together indicating that the technique is reproducible.

They concluded that the use of FFT based spectral analysis can produce results that give important data that can substantiate the effects of medical treatment in this pilot study.  Additionally, their data matches the results noted by Calhoun et al in their series of patients with detrusor overactivity due to overactive bladder.  This indicates that there is a similarity and a regularity to the overactive detrusor contractions seen in both OAB and NDO patients.  Further work needs to be done to further improve the predictive power of this technique.

Presented by: Israel Franco, FAAP, FACS, MD, Professor of Clinical Urology; Director of Yale-New Haven Children’s Bladder and Continence Program; Director of Yale Medicine Pediatric Bladder & Continence Program

Co-Authors: Zaveri H P2, Collett-Gardere T F3, Murphy K3, Hittelman A1 
1.  Yale University School of Medicine, 2. Yale University, 3. Yale New Haven Hospital

Written by: Bilal Farhan, MD; Clinical Instructor, Female Pelvic Medicine and Reconstructive Surgery, University of California, Irvine Medical Center, Twitter: @Bilalfarhan79 at the 2018 ICS International Continence Society Meeting - August 28 - 31, 2018 – Philadelphia, PA USA