Measurement of Multipoint Acceleration in the Bladder Wall: A Study of Voiding in Awake Minipigs

Soebadi M1, Weydts T2, Brancato L2, Puers R2, De Ridder D3

Research Type

Basic Science / Translational

Abstract Category

Research Methods / Techniques

Abstract 380
E-Poster 2
Scientific Open Discussion ePoster Session 18
Thursday 5th September 2019
13:35 - 13:40 (ePoster Station 9)
Exhibition Hall
Biomechanics Animal Study New Devices Urodynamics Techniques Physiology
1.Universitas Airlangga, 2.ESAT MICAS KU Leuven, 3.KU Leuven
Presenter
M

Mohammad Ayodhia Soebadi

Links

Poster

Abstract

Hypothesis / aims of study
Spontaneous bladder wall activity plays an important role in the pathogenesis of detrusor overactivity. There are limited methods for long term observation of these autonomous micromotions in vivo. Motion sensing by accelerometers has been used for quantification and classification of activity in organs and organisms. In this preliminary study, we aim to develop and test the feasibility of a combined pressure and motion implantable sensor for the bladder wall in an awake animal model.
Study design, materials and methods
In collaboration with the micro-electronic engineering department, we developed an implant with four accelerometers (Bosch BMA280) and a submucosal pressure sensor (MS5637) as shown in Figure 1. The microsensors were attached on a flexible circuit board and encapsulated with parylene and biocompatible silicone material (Nusil MED-6017). A larger central island was necessary for control circuitry. Connections between sensors were specially designed to accommodate large changes in bladder volume. After approval from the Animal Ethics Committee, we implanted the device in two Gottingen minipigs. The sensor islands were implanted on the bladder apex, posterior wall, as well as right and left lateral sides. Data were read out via a wired connection tunneled to a flank exit wound. After 1 week of recovery we started measurements during consecutive voiding cystometries. A 3-way air-charged urethral catheter was inserted. Room temperature saline was continually infused at 50 ml/min until voiding was observed. Catheter pressure was recorded using T-doc air-charged catheters on a urodynamics examination system (Laborie Aquarius TT). 

The acceleration signal consists of high-frequency oscillatory bursts of linear acceleration and a baseline value. This baseline is determined by the orientation of a particular axis relative to gravity. The two signal components were separated at a cut-off frequency of 0.15 Hz, with low-pass filtering for baseline and high-pass filtering for linear acceleration. Change in baseline value (∆a) was calculated by subtraction of the start value from the end value. Total linear acceleration (TLA) from three axes of the same sensor was calculated by root mean square. Start of voiding was adapted from definitions of voiding phase 1 described by Andersson et al. as shown in Figure 2. We compared accelerometer measurements to adjacent 10-second premicturition periods. Values are mean +/- SD unless otherwise specified.
Results
We performed measurements on 19 voiding cycles with filling volume of 720 +/- 310 ml. In each measurement session, we observed 3 to 5 consecutive voiding events. Submucosal pressure differed from catheter pressure by -10.1 +/- 27.1 mbar and correlation between both measurement methods was 0.29 (p<0.0001). Pressure curves were markedly different after the first voiding peak. Correlation of pressure during the premicturition period until the first voiding peak was 0.52 (p<0.0001). 

Largest magnitude of ∆a was observed in the z-axis of the sensor implanted in the bladder posterior wall compared to apical and lateral locations. Value of ∆a is higher during voiding compared to preceding premicturition periods (0.61 +/- 0.2 v 0.038 +/- 0.086 g). Linear acceleration activity occurred in bursts interspersed with periods of low activity. TLA at start of voiding was higher than the preceding period (0.068 +/- 0.021 v 0.049 +/- 0.027 g). Interval between maximum TLA correlated with interval between peaks of voiding pressure recorded by the submucosal sensor (r=0.760, p<0.001).
Interpretation of results
Submucosal pressure traces was more consistent on repeated voiding compared to catheter traces. In some cases, catheter sensitivity was decreased in subsequent micturitions.  
Accelerometer measurements mark the start of voiding by increased TLA. Baseline accelerometer value during voiding reflects change in bladder wall orientation and volume. This also indicates quite clearly the emptying of the bladder at the end of the cycle.
Concluding message
This is the first report of acceleration data recorded in vivo from an awake voiding animal model from multiple sites in the bladder. We observed an increase in acceleration activity at the start of voiding and change in baseline acceleration during voiding. Analysis of the entire voiding cycle, integrating input of all four sensors will further establish the potential use of accelerometers in the study of bladder motion. This implantable device is the first step towards identifying autonomous bladder micromotions in situ.
Figure 1 Acceleration measurement device, sensors are placed on three satellite arms and one on the central island.
Figure 2
References
  1. Andersson, K.-E., Soler, R., & Füllhase, C. (2011). Rodent models for urodynamic investigation. Neurourology and Urodynamics, 30(5), 636–646. https://doi.org/10.1002/nau.21108
Disclosures
Funding The research described in this article was performed within the ERC advanced grant agreement, µThalys, n° 340931. The first author received funding from the Indonesian Endowment for Education (LPDP). Clinical Trial No Subjects Animal Species Minipig Ethics Committee Animal Ethics Committee KU Leuven