Anna Nagle

A pilot study to measure dynamic elasticity of the bladder during urodynamics

Previous studies using isolated strips of human detrusor muscle identified adjustable preload tension, a novel mechanism that acutely regulates detrusor wall tension. The purpose of this investigation was to develop a method to identify a correlate measure of adjustable preload tension during urodynamics.

Modeling the influence of acute changes in bladder elasticity on pressure and wall tension during filling

Tension-sensitive nerves in the bladder wall are responsible for providing bladder sensation. Bladder wall tension, and therefore nerve output, is a function of bladder pressure, volume, geometry and material properties. The elastic modulus of the bladder is acutely adjustable, and this material property is responsible for adjustable preload tension exhibited in human and rabbit detrusor muscle strips and dynamic elasticity revealed during comparative-fill urodynamics in humans. A finite deformation model of the bladder was previously used to predict filling pressure and wall tension using uniaxial tension test data and the results showed that wall tension can increase significantly during filling with relatively little pressure change. In the present study, published uniaxial rabbit detrusor data were used to quantify regulated changes in the elastic modulus, and the finite deformation model was expanded to illustrate the potential effects of elasticity changes on pressure and wall tension during filling. The model demonstrates a shift between relatively flat pressure-volume filling curves, which is consistent with a recent human urodynamics study, and also predicts that dynamic elasticity would produce significant changes in wall tension during filling. The model results support the conclusion that acute regulation of bladder elasticity could contribute to significant changes in wall tension for a given volume that could lead to urgency, and that a single urodynamic fill may be insufficient to characterize bladder biomechanics. The model illustrates the potential value of quantifying wall tension in addition to pressure during urodynamics.

Quantification of bladder wall biomechanics during urodynamics: A methodologic investigation using ultrasound

Overactive bladder is often characterized by biomechanical changes in the bladder wall, but there is no established method to measure these changes in vivo. The goal of this study was to develop a novel method to determine detrusor wall biomechanical parameters during urodynamics through the incorporation of transabdominal ultrasound imaging. Individuals with overactive bladder (OAB) underwent ultrasound imaging during filling. The fill rate was 10% of the cystometric capacity per minute as determined by an initial fill. Transabdominal ultrasound images were captured in the midsagittal and transverse planes at 1min intervals. Using image data and Pves, detrusor wall tension, stress, and compliance were calculated. From each cross-sectional image, luminal and wall areas along with inner perimeters were measured. In the sagittal and transverse planes, wall tension was calculated as Pves∗luminal area, wall stress as tension/wall area, and strain as the change in perimeter normalized to the perimeter at 10% capacity. Elastic modulus was calculated as stress/strain in the medial-lateral and cranial-caudal directions. Patient-reported fullness sensation was continuously recorded. Data from five individuals with OAB showed that detrusor wall tension, volume, and strain had the highest correlations to continuous bladder sensation of all quantities measured. This study demonstrates how detrusor wall tension, stress, strain, and elastic modulus can be quantified by adding ultrasound imaging to standard urodynamics. This technique may be useful in diagnosing and better understanding the biomechanics involved in OAB and other bladder disorders.

MP79-10 EFFECTS OF TRAINING AND MECHANICAL FORCE OF ULTRASOUND ON BLADDER FILLING: REPEATABILITY OF ORAL HYDRATION STUDIES IN HEALTHY ADULTS

Currently, ICS-defined verbal sensory thresholds are the only standardized, objective measures of real time bladder sensation in the micturition filling phase. A noninvasive protocol was previously developed using 3D ultrasound along with a sensation meter to better characterize real time bladder sensation and its correlation with bladder volume/shape/rhythm. This study validates the protocol by measuring the effects of participant training and ultrasound probe pressure on bladder sensation in our oral hydration protocol.

Automated quantification of low amplitude rhythmic contractions (LARC) during real-world urodynamics identifies a potential detrusor overactivity subgroup

Objectives Detrusor overactivity (DO) is characterized by non-voiding detrusor smooth muscle contractions during the bladder filling phase and often contributes to overactive bladder. In some patients DO is observed as isolated or sporadic contractions, while in others DO is manifested as low amplitude rhythmic contractions (LARC). The aim of this study was to develop an objective method to quantify LARC frequencies and amplitudes in urodynamic studies (UDS) and identify a subgroup DO of patients with LARC. Methods An automated Fast Fourier Transform (FFT) algorithm was developed to analyze a 205-second region of interest of retrospectively collected “real-world” UDS ending 30 seconds before voiding. The algorithm was designed to identify the three largest rhythmic amplitude peaks in vesical pressure (Pves) in the 1.75–6 cycle/minute frequency range. These peak Pves amplitudes were analyzed to determine whether they were 1) significant (above baseline Pves activity) and 2) independent (distinct from any in abdominal pressure (Pabd) rhythm). Results 95 UDS met criteria for inclusion and were analyzed with the FFT algorithm. During a blinded visual analysis, a neurourologist/urodynamicist identified 52/95 (55%) patients as having DO. The FFT algorithm identified significant and independent (S&I) LARC in 14/52 (27%) patients with DO and 0/43 patients (0%) without DO, resulting in 100% specificity and a significant association (Fischer’s exact test, p<0.0001). The average slowest S&I LARC frequency in this DO subgroup was 3.20±0.34 cycles/min with an amplitude of 8.40±1.30 cm-H2O. This algorithm can analyze individual UDS in under 5 seconds, allowing real-time interpretation. Conclusions An FFT algorithm can be applied to “real-world” UDS to automatically characterize the frequency and amplitude of underlying LARC. This algorithm identified a potential subgroup of DO patients with LARC.

Comparison of 2D and 3D ultrasound methods to measure serial bladder volumes during filling: Steps toward development of non-invasive ultrasound urodynamics

OBJECTIVES Non-invasive methods to objectively characterize overactive bladder (OAB) and other forms of voiding dysfunction using real-time ultrasound are currently under development but require accurate and precise serial measurements of bladder volumes during filling. This study’s objective was to determine the most accurate and precise ultrasound-based method of quantifying serial bladder volumes during urodynamics (UD). METHODS Twelve female participants with OAB completed an extended UD procedure with the addition of serial bladder ultrasound images captured once per minute. Bladder volume was measured using three ultrasound methods: (1) Vspheroid: two-dimensional (2D) method calculated assuming spheroid geometry; (2) Vbih: 2D correction method obtained by multiplying Vspheroid by a previously derived correction factor of 1.375; and (3) V3D: three-dimensional (3D) method obtained by manually tracing the bladder outline in six planes automatically reconstructed into a solid rendered volume. These volumes were compared to a control (Vcontrol) obtained by adding UD infused volume and the volume of estimated urine production. RESULTS Based on linear regression analysis, both Vbih and V3D were fairly accurate estimators of Vcontrol, but V3D was more precise. Vspheroid significantly underestimated Vcontrol. CONCLUSIONS Although the Vbih and V3D methods were more accurate than the more-commonly used Vspheroid method for measuring bladder volumes during UD, the V3D method was the most precise and could best account for non-uniform bladder geometries. Therefore, the V3D method may represent the best tool required for the continued development of non-invasive methods to diagnose OAB and other forms of voiding dysfunction.

MP63-06 CATEGORIZATION OF REAL-TIME SENSATION PATTERNS DURING URODYNAMICS

each one of the significant variables (p<0.05) in the logistic regression model. To conclude, we performed a ROC curve in order to determine the predictive ability of the score in relation to the presence of OAD. RESULTS: presence of OAD was evident in 210 women (29%). In the logistic regression analysis, independent predictors of OAD were micturition urgency, UUI, nicturia, absence of SUI symptoms, presence of diabetes, reduction of vaginal trophism and vesical capacity under 150 mL. The IDC diagnosis probability increases directly as the score raises (Score 0: 4% until Score 1⁄410: 88%). Sensitivity is 71% and specificity 72%. The area under the curve of OAB score was 0.784 (p>0.001). CONCLUSIONS: OAB score is a clinical tool that shows higher diagnostic accuracy than OAB symptoms alone when predicting overactive detrusor (OAD).

MP63-07 CHARACTERIZATION OF LOW AMPLITUDE RHYTHMIC CONTRACTIONS DURING URODYNAMICS

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.

The Sensation Meter: An Unprompted Method to Characterize Patient-Reported Bladder Sensation in Real-Time

Overactive bladder (OAB) syndrome is characterized by symptoms of urgency, with or without incontinence, usually with increased voiding frequency and nocturia [1], and is prevalent throughout the world [2]. Chronic OAB symptoms are studied with validated surveys, while acute symptoms can be assessed using bladder diaries. These methods may be subject to recall bias, since diaries are typically completed after voiding. The accepted standard for clinical assessment of bladder function and sensation is a urodynamics (UD) study which involves filling the bladder with a catheter. During a UD study, three verbal sensory thresholds (VSTs) are recorded [3]. These thresholds, First Sensation, First Desire to void, and Strong Desire to void, only provide limited, episodic information about acute sensation during filling. Thus, there is a clear need for a tool to evaluate the development of real-time bladder sensation during bladder filling. The objective of this study was to develop a novel Sensation Meter, a patient interface implemented on a touchscreen device that continuously records the patient’s real-time, unprompted sensation of bladder fullness.Copyright

AB316. SPR-43 Comparison of bladder volumes between 2D and 3D ultrasound calculations and urodynamic measurements in women with overactive bladder (OAB)

Objective Various methods are currently available to non-invasively quantify bladder volume. The goal of this project was to determine the most accurate method of quantifying bladder volume using 2D and 3D ultrasound techniques during UD. Methods Nine female participants with OAB underwent an extended urodynamics procedure (Laborie Aquarius XT) while ultrasound images of the bladder were obtained using a 3D 6 MHz transabdominal probe (GE Voluson E8). The bladder was filled with saline at a rate of 10% bladder capacity (based on an initial clinical fill) per minute while ultrasound images were captured once per minute. Bladder volume was estimated from 2D cross-sectional images in the sagittal and transverse planes assuming an ellipsoid geometry [equation 1, VSpheroid = (W*H*D)], assuming a shape in between an ellipsoid and a cube [equation 1, VBih =0.72*W*H*D =1.375*VSpheroid], and from the 3D ultrasound data obtained by tracing the bladder outline in six planes with GE’s 4D View software (V3D). In equations 1 and 2, W is the width (horizontal diameter) and H is the height (vertical diameter) in the sagittal direction and D is the depth in the transverse direction (horizontal diameter). Results VSpheroid was significantly lower than infused volume (VH2O) when compared by a paired t-test. VBih and V3D tended to be slightly larger than VH2O, but not significantly. Conclusions The bladder shape cannot be assumed to be an ellipsoid in patients with OAB. Tracing the perimeter in several 3D imaging planes better accounts for the non-uniform geometry, providing a more accurate volume measurement. Volumes estimated by VBih 2 or by tracing the bladder in 3D were not significantly different from VH2O, demonstrating that these are the most accurate methods of non-invasive assessment of bladder volume. Funding Source(s) NIH R01DK101719, VCU Presidential Research Quest Fund, and VCU Dean’s Undergraduate Research Initiative