Introduction & Objective :
Dynamic elasticity, or reversible strain softening, is a material property of bladders that is identified using comparative-fill urodynamic studies (UDS), and may play a role in the bladder’s ability to accommodate variable fill rates and volumes. The aim of this study was to test the hypothesis that individuals with acute dynamic elasticity can better accommodate the faster filling of UDS compared to individuals without dynamic elasticity.
Individuals with and without urgency based on ICIq-OAB survey question 5a (≥3 and =0, respectively) were enrolled in this prospective study and completed 3-day void diaries. Vesical pressure (Pves) data were collected during a repeat fill-and-empty UDS protocol at a rate of 10% of cystometric capacity per minute. Dynamic elasticity was quantified by comparing three fills (1-3). Fill 1 (before strain softening) was used as a baseline after an active void. Fill 2 (after strain softening) was used to show the degree of dynamic elasticity lost due to strain softening and occurred following passive emptying via syringe aspiration. . Fill 3 (after active voiding) was used to show how much dynamic elasticity was recovered due to the active voiding. For each fill, the average Pves was calculated. Individuals that showed decrease in Pves from Fill 1 to Fill 2) and increase in Pves from Fill 2 to Fill 3) were defined as having dynamic elasticity.
In this study, 5/12 (41.7%) participants with OAB and 6/7 (85.7%) participants without OAB exhibited dynamic elasticity. The maximum UDS volume (650±64 ml) in 9/12 (75.0%) individuals with dynamic elasticity exceeded the maximum 3-day voided volume (519±56 ml). This compares with only 1/7 (14.3%) individuals without dynamic elasticity. There was a significant association (Fisher’s exact test, p<0.05) between the presence of observed dynamic elasticity and the ability of the bladder to accommodate a larger volume during UDS.
Dynamic elasticity is a biomechanical property of the bladder that can be calculated using a repeat-fill UDS protocol, and individuals with OAB experience lower rates of dynamic elasticity compared to controls. These OAB individuals were unable to accommodate larger volumes during UDS compared to maximum voided volumes recorded on 3-day void diaries. Identification of reduced dynamic elasticity may help explain why individuals with OAB cannot adapt to faster filling and larger volumes, and quantification of dynamic elasticity could lead to improved subtyping of OAB and more targeted therapies.