Neuroexcitation Patterns using fNIRS during Natural Filling in Women with Overactive Bladder

Objectives: Functional near infrared spectroscopy (fNIRS) is a non-invasive technique used to quantify prefrontal cortex oxyhemoglobin (O₂Hb) concentration. Cortical fNIRS measures changes in neuroexcitation based on the chromophores of oxy and deoxy hemoglobin to a cortical depth of 1.5 cm. The objective was to compare prefrontal cortical O₂Hb during natural filling in female participants with and without overactive bladder (OAB).

Methods: Female participants with OAB were compared to controls without urinary urgency. Participants underwent continuous recording of prefrontal cortical O₂Hb using fNIRS during validated oral hydration protocol. Simultaneously recordings of real-time sensation (0-100%) and “first desire” to void were completed. A period of “elevated urgency” was defined as the time from first desire to 100% sensation. Optodes of the 24-channel headcap were position on the forehead to maximize prefrontal cortex (figure 1). Channels were sub-analyzed by cortical regions: right (9), left (9), and middle (6). Signal data analysis included low pass filtering and mono-exponential curve fitting. Due to variation in bladder filling time, the time for each low and high sensation phase was determined, and fNIRS data was interpolated to this reference time to standardize reporting.

Results: A total of 19 female participants completed the study, including with 9 OAB and 10 without. The OAB group was older and had a higher BMI. Participants were mostly White (74%) with 21% Black and 5% Asian. Mean fill time (51.3± 23.2 minutes) and mean daily fluid intake (57.1± 22.9 ounces) were not significantly different between groups. O₂Hb rate of change during the elevated urgency time period was significantly different between groups in all cortical regions (OAB 57.0± 22.2% vs controls 89.6± 11.5%, p= < 0.001). Change in O₂Hb from 0 to 100% sensation was significantly lower in all prefrontal cortical regions in the OAB group (OAB -0.02±0.86 vs control 1.32± 0.35, p< 0.001) and 16/24 individual channels (figure 2).

Conclusions: This study demonstrates that fNIRS cortical excitation during a period of elevated urgency is consistently lower in women with OAB as compared to controls. With additional research, fNIRS has the potential to detect unique neuroexcitation patters in OAB. More importantly, although limited, this data supports the hypothesis that the prefrontal cortex plays an inhibitory role in voiding function and that there may be a lack of inhibitory control in women with OAB.