(Poster 18) Bladder and Brain near Infrared Spectroscopy Comparative Motion Analysis

Objectives: Near infrared spectroscopy (NIRS) is a non-invasive method to study oxyhemoglobin (O2Hb) concentration in the bladder with placement over the abdominal wall (measuring the anterior bladder wall). Motion artifacts can significantly disrupt NIRS signals, but can be overcome with utilization of accelerometers or IMU (inertia motion units). The location of the IMU can vary by device and manufacturer, and prior analysis has shown body motion rarely occurs without concurrent head motion. This study aimed to evaluate differences in headcap mounted IMU verses anterior bladder wall mounted IMU NIRS signal during a validated natural filling protocol.

Methods: Normal participants of both biologic sexes without voiding dysfunction completed a validated natural filing protocol with continuous recording of bladder O2Hb using a 3-channel NIRS device with both headcap and abdominal mounted IMU. Real time bladder sensation (0-100% fullness) was recorded using a Sensation Meter throughout bladder filling. NIRS signals were processed first by dividing fills into regions of low and high sensation of bladder filling at point of “first desire,” based on prior methods. NIRS signals during high sensation were compared using either motion segmentation from the abdominal IMU or headcap IMU using Pearson correlation.

Results: Ten participants (male n=5/ female n=5) completed the study with adequate data for paired analysis. The Pearson correlation between NIRS headcap-IMU and NIRS abdominal-IMU was greater than 0.75 in 8/10 samples (Table 1). Two samples had lower correlations (0.51-0.55) with notable phase shifts but with very similar visual NIRS patterns. NIRS signals obtained with both the abdominal and headcap devices demonstrated similar O2Hb patterns as a function of filling (Figure 1).

Conclusions: This study supports the use of headcap-IMU measurements as a reliable proxy for abdominal-IMU NIRS data during natural bladder filling. The observed highly correlated NIRS signals demonstrate the relative accuracy of NIRS in capturing bladder hemodynamics measurements during filling protocols. Furthermore, this study helps control for inherent variability in NIRS analytics through objective characterization of physical motion.
Legend: Figure 1. Selected representative samples of oxyhemoglobin concentration comparisons using headcap-IMU (red) vs abdominal- IMU (blue). Visually, the bladder and head tracings are similar even with lower R values, highlighting the correlative methods.