Background: Worldwide >2.3 billion individuals are affected by bladder disease. The current evaluative test is invasive, associated with complications and often declined. Non-invasive evaluation of bladder hemodynamics using continuouswave near-infrared spectroscopy (NIRS) is an established technique. Recently, fNIRS was shown to detect activity in the brain regions previously identified by fMRI to relate to bladder sensation and control of voiding. We now report a system for simultaneous wireless fNIRS measurements of bladder and brain. Method: Two dual-wavelength (760/850 nm) fNIRS systems were used in parallel. A 23-channel array (35 mm interoptode distance) housed in a neoprene cap was positioned over the bilateral frontal cortex, and a 4-channel grid of 4 emitters and 1 detector taped to the skin over the bladder. Natural bladder filling to capacity and spontaneous voiding were monitored in two volunteer subjects. Proprietary software (Oxysoft v3.2.56) linked the devices, and generated video and graphical displays of changes in oxygenated, de-oxygenated, and total hemoglobin from raw optical data recorded at 50 Hz. Results: Simultaneous brain and bladder data were captured in both subjects. Localized brain activity was evident on video as topographical colorimetric changes indicative of increases in oxyhemoglobin concentration in areas previously linked via fMRI to bladder sensation and function; signal intensity varied in relation to phases of voiding. In the bladder detrusor muscle oxyhemoglobin increased prior to permission to void; changes during uroflow differed between the symptomatic and asymptomatic subjects. Conclusion: Simultaneous wireless fNIRS of brain and bladder is feasible, and offers new physiological dimensions for evaluating bladder control and function.
Background: A requisite for fNIRS studies of cortical blood flow is that sufficient photons are transmitted transcutaneously for the fluctuations in cerebral hemoglobin oxygenation that occur during neuronal activation to be detected. Transmission is determined by the specifications of the fNIRS device, but also influenced by the characteristics of the skin. Epidermal pigments can attenuate photon transmission; the literature states that in dark skinned subjects some NIRS devices may not achieve sufficient photon migration to monitor cortical blood flow. Hence, as fNIRS use is spreading, we describe a simple head tilt maneuver where positional redistribution of cerebral blood volume will confirm if photon transmission is sufficient. Methods: A repetitive head tilt maneuver (bending forward from a seated position, hold for 30 seconds, returning to original position X 5) performed by a pigmented (African) subject and a non-pigmented (Caucasian) subject. A 23- channel portable fNIRS system with dual wavelength (750 and 860 nm) emitters and photodiode detectors was worn over the anterior cortex, and changes in oxy, deoxy and total hemoglobin concentration measured at 50 Hz. Results: Data from both subjects were compared and found to have a comparable pattern of change in oxyhemoglobin concentration and temporal response to the effects of head tilt; clear arterial pulsations and minimal noise were also evident. Conclusion: We suggest the head tilt maneuver described as a feasible test to confirm the adequacy of transcutaneous photon transmission where fNIRS studies are to be performed in subjects with pigmented skin to detect hemodynamic change in the cortex.
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