Development of a Non-Invasive External Compression Protocol to Quantify Dynamic Elasticity in an Isolated Working Pig Bladder

Balthazar A1, Cullingsworth Z1, Speich J E1, Klausner A1

Research Type

Pure and Applied Science / Translational

Abstract Category

Anatomy / Biomechanics

Abstract 544
Open Discussion ePosters
Scientific Open Discussion Session 28
Friday 31st August 2018
12:45 - 12:50 (ePoster Station 6)
Exhibition Hall
Overactive Bladder Biomechanics Animal Study Basic Science
1. Virginia Commonwealth University
Presenter
A

Andrea Balthazar

Links

Poster

Abstract

Hypothesis / aims of study
During urodynamic studies, we previously demonstrated that filling and passive emptying of the bladder results in a reduction of intravesical pressure, a material behavior termed strain softening. However, unlike a latex balloon in which strain softening is not fully reversible, active voiding restores the pressure back to baseline. We termed this reversible strain softening “dynamic elasticity”[1]. Because passive emptying of the bladder requires catheter placement to facilitate bladder drainage, it is an invasive technique. We hypothesize that strain softening can be produced in a completely non-invasive manner through the use of a bladder external compression protocol. Therefore, the aim of this study was to determine if strain softening produced by passive emptying is equivalent to strain softening produced by repeated external compressions in a working perfused isolated pig bladder. In doing so, we aim to take an essential step toward the development of a novel, non-invasive technique (repeat external bladder compressions) to reduce intravesical pressure and possibly urinary urgency.
Study design, materials and methods
Adult male and female porcine bladders were procured from local abattoirs immediately after slaughter. Using a previously designed ex vivo functional porcine model, the bladder was perfused with Krebs-Henseleit buffer at a flow rate of 4 ml/min [2]. The bladder was maintained at physiological temperature (37-42°C) using a heat lamp and a humidifier throughout the experiment. Each bladder was filled to 250 ml then allowed to reach equilibrium pressure over 5 minutes (P1f). Study 1 – passive emptying phase: The bladder was then filled from 250 ml to 500 ml in order to find the peak pressure (Pref) and the equilibrium pressure after 5 minutes. Next, the bladder was passively emptied via syringe aspiration to a volume of 250 ml and intravesical pressure was recorded (P2f). Active voiding of the remaining volume was induced with a potassium enriched solution, KPSS, to reset any strain softening that had occurred (Fig. 1A). Study 2 –compression phase: The bladder was filled to 250 ml and intravesical pressure was recorded (P1c). Then the bladder was allowed to reach equilibrium. The bladder was then isovolumetrically compressed using external compression to reach the intravesical pressure recorded at a volume of 500 ml (Pref) during Study 1 of the protocol. This external pressure was held for 15 seconds and released for 15 seconds to allow the bladder to rest between compressions. This cyclic loading was repeated 5 times. Afterwards, the bladder was given 5 minutes to reach equilibrium pressure (P2c) (Fig. 1B). The pressures after each 5-minute wait period were recorded, particularly the pressures after equilibration at 250 ml during Study 1 (P1f), the highest pressure reached at 500 ml during Study 1 (Pref) and the pressure after equilibration at 250 ml following syringe aspiration (P2f). P1f and P2f pressures were compared to P1c and P2c, which were the corresponding pressures, measured during Study 2 while compressing to Pref obtained during Study 1.
Results
Six bladders were studied (n = 6). Strain softening was demonstrated during the filling and passive empting phases (Fig. 1A) as well as during isovolumetrical compression with an external pressure source (Fig. 1B). Intravesical pressure decreased in 4 of the 6 bladders following the compression and was on average 2 cm-H20 lower after compression, which was indicative strain softening.
Interpretation of results
Although to a lesser degree, the bladders in study 2 undergoing application of compression external pressure showed a similar decrease in intravesical pressure as those in study 1 undergoing passive voiding. This suggests strain softening occurs in the bladders undergoing isovolumetric compression.
Concluding message
This study revealed that the methods employed to increase the pressure within the bladder, one through filling and the other through isovolumetrical compression, results in measureable strain softening. Further studies are warranted including an in vivo porcine model to further refine and characterize the properties and reversibility of strain softening, dynamic elasticity. Repeated external bladder compression as a potential means to induce strain softening and lower intravesical pressure is a novel, non-invasive technique. This method may represent a potential clinical application to reduce intravesical pressure and possibly prolong the filling phase.
Figure 1
References
  1. Colhoun AF, Klausner AP, Nagle AS, Carroll AW, Barbee RW, Ratz PH, et al. A pilot study to measure dynamic elasticity of the bladder during urodynamics. Neurourol Urodyn. 2017;36(4):1086-90.
  2. Potential Vascular Mechanisms in an Ex Vivo Functional Pig Bladder Model (Anele et al, accepted Neurology & Urodynamics).
Disclosures
Funding No funding or grant Clinical Trial No Subjects Animal Species Pig Ethics Committee IACUC approved protocol
28/03/2024 03:37:20