Uncontrolled Orthostatic Hypotension and Multi-channel Cerebral Hemodynamic Changes in a Young Male Participant: A...

We aimed to determine the changes in mean arterial pressure (MAP) due to uncontrolled orthostatic hypotension and the oxygenated hemoglobin(O₂Hb), deoxygenated hemoglobin (HHb), and total hemoglobin (THb) changes in a young male participant. The participant (23 y.o. male, no medication) stood in a quiet room before the main experiment. Changes in O₂Hb, HHb, and THb levels were detected using NIRS optodes comprising 12 light sources and 12 detectors, providing 24-channel simultaneous recording. A 30-mm inter-optode distance was set for measuring cortical tissue hemodynamics. The Cz position of the international 10-20 system was used to ensure consistent optode placement. The regions of interest were the right (R-) and left (L-) prefrontal cortex (PFC), supplementary motor area (SMA), and sensorimotor cortex (SMC). We also measured MAP and skin blood flow (SBF) from the forehead and hemodynamic changes in the left vastus lateralis (VL) muscle. The participant stood for 600 s, including baseline measurements. The MAP decreased rapidly at approximately 500 s. A decrease was noted in the O₂Hb and THb of the SMA from 420 s and L- and R-PFC from 450 s, but was more pronounced after 500 s. The HHb signal showed a change opposite to that of O₂Hb and THb. The SBF decreased momentarily at approximately 500 s but increased immediately after and did not recover until the end of the measurement at 540 s. The O₂Hb and THb of the VL increased from 500 to 540 s. NIRS may detect uncontrolled orthostatic hypotension before a decrease in the MAP.