Deborah Lightner

Principles of urodynamics pressure measurement and its implication to female continence function

Urodynamic pressure measurements using catheters have been widely used among clinicians. More often objective interpretation of urodynamic pressure measurements requires fundamental understanding of pressure measurement techniques due to many measurement artifacts. In this study we developed a simplified compound thick-walled cylinder model to investigate the mechanical nature of urodynamic pressure measurement as well as pressure transmission. Efficacy of collagen implantation was also explored. Lamés formulation was used to find analytical solutions. Pressure transmission can be related to catheter caliber and the compressibility of the urethral tissue (poisson ratio) in a simple mathematical form. The theoretical pressure transmission ratio will be 133% with the additional incompressibility assumption, reflecting the passive structural transmission of intraabdominal pressure increase. The relationship between the pressure measurement error and the catheter caliber was found to be linear (r2 = 0.94 +/- 0.04) and two or more pressure measurements need to be used to find the uninstrumented pressure. It was predicted that collagen implantation treatment might improve the pressure transmission ratio maximally by 33%.

MP63-08 CAN URODYNAMIC PARAMETERS PREDICT SLING REVISION FOR VOIDING DYSFUNCTION IN WOMEN UNDERGOING SYNTHETIC MIDURETHRAL SLING PLACEMENT?

INTRODUCTION AND OBJECTIVES: Human detrusor smooth muscle (DSM) can exhibit low amplitude rhythmic contractions (LARC) which may contribute to overactive bladder (OAB) in some patients. The aim of this study was to develop an objective method to identify LARC during urodynamics (UD), categorize patients with significant LARC, and potentially begin to characterize a LARC-mediated OAB/detrusor overactivity subtype. METHODS: An algorithm was developed to analyze UD filling data in low volume (1st 410 seconds) and high volume (final 410s) regions. Fast Fourier Transform (FFT) analysis identified the frequency (F) in the 1-6 cycle/min range associated with the maximum amplitude of the vesical pressure (Pves) in each region (Fig 1). A patient-specific range of interest corresponding to F 0.5 cycles/min was determined. Pves and Pabd amplitudes were analyzed separately to identify both significant (higher than average) and independent (distinct from Pabd) Pves signals. To be significant, Pves amplitude must be > 1.35 standard deviations (SD) above average Pves amplitude. To be independent, the Pabd amplitude must be < 1.35 SD above the average Pabd amplitude. SD of 1.35 was chosen using an iterative process in 0.05 SD increments to identify the maximum number of significant and independent signals. RESULTS: This algorithm was used to retrospectively analyze 43 consecutive UD studies which included 25 (14 neurogenic, 11 idiopathic) with detrusor overactivity (58%). The average age of the entire group was 55 2 years and included 14 men and 29 women. FFT analysis identified a significant and independent Pves signal in 12/43 patients (28%) of which 8/12 (67%, 5 neurogenic, 3 idiopathic) had detrusor overactivity. The average age of patients with significant and independent signals was 54 5 years and included 6 men and 6 women. CONCLUSIONS: Analysis of LARC during UD testing identified a subset of patients with a significant and independent slow wave frequency in Pves. Further refinements of this technique may help identify subsets of individuals with LARC-mediated OAB/detrusor overactivity.