(D-132) Abdominal Compressions During Ultrasound Urodynamics Used to Quantify Elevated Provoked Bladder Compliance in a Subgroup of Older Women

Urodynamics (UDS) testing is used to assess bladder function during filling and voiding. During UDS, bladder “filling compliance” is calculated as the ratio of the change in volume to the change in pressure throughout artificial bladder filling. In bladders with low filling compliance there is concern for retrograde urine flow causing upper urinary tract damage.  However, because filling pressures in healthy bladders are relatively small, filling compliance is not an ideal metric to identify bladders that are too compliant. The effect of too much compliance on bladder filling biomechanics is not well known, but a bladder that is too floppy may not be able to maintain an efficient shape. A recent comparative-fill UDS study showed that the bladder exhibits dynamic elasticity that may be acutely regulated through a balance of competing active contractile and passive strain mechanisms.1 Acute regulation of dynamic elasticity and/or chronic age-related changes in the bladder wall could contribute to a floppy bladder, and metrics to quantify elevated bladder compliance are necessary. Compression exercises have been shown to acutely alter bladder compliance in an isolated porcine bladder model,2 therefore compression may be a suitable method to strain the bladder for in vivo compliance measurements. 

The first objective of the present study was to use ultrasound during UDS to quantify isovolumetric compliance in response to abdominal bladder compressions. The second objective was to correlate this novel “provoked compliance” metric with participant characteristics, including age, body mass index (BMI), and traditional UDS filling compliance.

Women indicated for UDS were recruited for a prospective IRB-approved study. During UDS, each participant’s bladder was filled to ~50% of estimated capacity using the UDS catheter and then filling was paused. An abdominal ultrasound probe was used to compress the bladder five times to ~50% of its anterior-posterior diameter. Each compression was held for ~5 seconds and then released, and there was ~5 seconds between compressions. A video of the transverse abdominal ultrasound bladder image was recorded throughout the compression protocol, and an ultrasound image was captured before the first compression and during each of the five bladder compressions. A screenshot of each image was loaded into Image J, where the bladder wall was traced and bladder circularity was quantified for the traced shape using the circularity function (Fig 1AB). Vesical pressure (Pves) values were recorded from the UDS data corresponding to the ultrasound images taken before the first compression and during the five compressions. For each compression, the changes in circularity and pressure were calculated compared to the values prior to the first compression. Provoked compliance was calculated as the ratio of the change in circularity to the change in pressure due to compression (Δcircularity)/(Δpressure) for each compression, and the average of these five provoked compliance values was calculated for each participant. Filling compliance was also calculated, and age and BMI data were collected. 

Results: Data from 45 women were analyzed for groups ≤50 and >50 years of age. Provoked compliance values for women >50 spanned over a broader range (Fig 1C, above horizontal line). 10/33 (30%) of women >50 years of age, but 0/12 (0%) of women < 50 years exhibited provoked compliance greater than 0.0275 cm-H2O-1 (Fig 1C), indicating a significant association of age with provoked compliance (Fisher’s exact, p< 0.05). No correlation between provoked compliance and either BMI or filling compliance was identified. 

Discussion: The results of the present study suggest that bladder provoked compliance may increase with age in a subgroup of women. Additional studies are needed to identify whether there is any relationship between elevated provoked compliance values and specific types of bladder dysfunction and whether the mechanism for altered compliance is a change in dynamic elasticity regulation or some other change in the bladder wall.

A novel method to quantify provoked compliance in response to bladder compression was developed by combining abdominal compressions and ultrasound imaging with clinical UDS.  Future studies are needed to identify whether non-invasive compression and imaging techniques can provide useful clinical biomechanical metrics without the need for invasive UDS catheters.

Funding: NIH R01DK101719, NSF REU 1852116, VCU School of Medicine Summer Research Fellowship 

Disclosure: Drs. Klausner & Speich have ownership interest in Vesi Corporation, a startup company that may benefit from the results of this study.

1. Cullingsworth ZE, Klausner AP, Li R, Nagle AS, Carroll AW, Roseman JT, 2nd, Speich JE. Comparative-fill urodynamics in individuals with and without detrusor overactivity supports a conceptual model for dynamic elasticity regulation. Neurourol Urodyn. 2020;39(2):707-14.

2. Balthazar A, Cullingsworth ZE, Nandanan N, Anele U, Swavely NR, Speich JE, Klausner AP. An external compress-release protocol induces dynamic elasticity in the porcine bladder: A novel technique for the treatment of overactive bladder? Neurourol Urodyn. 2019;38(5):1222-8.