Audio-visual triggers may lead to or exacerbate sensations of urgency in certain individuals with overactive bladder (OAB) [1].  Functional near-infrared spectroscopy (fNIRS) of the brain can be used to quantify neuroexcitation in response to bladder filling [2].  The aim of this preliminary study was to determine whether fNIRS is a feasible tool for non-invasively identifying objective changes in neuroexcitation in response to audio-visual triggers of urinary urgency.

Individuals with OAB and healthy participants with minimal urgency were recruited based on ICIq-OAB survey scores (question 5a ≥2 or ≤1, respectively).  Participants completed an accelerated oral hydration study while brain fNIRS data were collected using an Artinis Brite24 headcap and while real-time participant-reported bladder sensation was recorded on a 0% to 100% scale using a tablet-based sensation meter [3]. A 1.5-minute control period at 50% sensation was compared to a subsequent 3-minute period during which participants watched and listened to a video containing scenes and sounds of expected triggers of urinary urgency (restrooms, running water, fountains, rain, waterfalls and swimming). fNIRS oxygenated hemoglobin (O2Hb) data were obtained with a receiver located just above the right ear, corresponding to known cortical areas of bladder neuroexcitation [2].  Data were filtered by a 0.1Hz low-pass filter, analyzed to quantify relative changes in neuroexcitation and correlated with changes in participant-reported sensation.

Data from individuals with relatively flat O2Hb signals during the control period were available for two healthy participants and three participants with OAB. Overall, 4/5 participants (80%) demonstrated an increase in O2Hb during the trigger video. This includes 2/3 participants with OAB and 2/2 healthy participants. An example is presented in Figure 1 for an OAB participant with a relatively flat O2Hb control period (Figure 1A) and an increase in O2Hb during the fountain portion of the trigger video (Figure 1B) that also corresponded with an increase in reported sensation (Figure 1B, red line).  Figure 2 shows a cortical mesh plot of O2Hb from another participant with OAB.  In the region of interest (black rectangle), the color change from blue (Figure 2A) to green (Figure 2B) illustrates an increase in neuroexcitation from the start of the control period to the first peak during the trigger video.

The results from this pilot fNIRS study revealed that some individuals with OAB may experience an increase in both neuroexcitation and perceived bladder sensation when they are exposed to audio-visual urgency triggers.

This preliminary study suggests that fNIRS may be feasible for the objective quantification of neuroexcitation changes evoked by audio-visual triggers of urgency.  Additional studies are necessary to determine whether non-invasive fNIRS can be used to identify patients with brain-associated OAB.

O'Connell KA, Singer J, Rajan S. Stimulus-associated urinary urges in overactive bladder syndrome. Neurourol Urodyn. 2018;37(1):284-290, DOI:10.1002/nau.23290.
Macnab AJ, Stothers L, Speich JE, Klausner AP. Evaluation of cortical neuroexcitation in urinary urgency using simultaneous near infrared spectroscopy of the brain and bladder with quantification of sensation. Paper presented at: SPIE Optics and Optoelectronics 2019; Prague, Czech Republic.
Nagle AS, Speich JE, De Wachter SG, Ghamarian PP, Le DM, Colhoun AF, Ratz PH, Barbee RW, Klausner AP. Non-invasive characterization of real-time bladder sensation using accelerated hydration and a novel sensation meter: An initial experience. Neurourology and Urodynamics. 2017;36(5):1417-1426.