Hemodynamic Oscillations in Mild TBI During Postural Change: An fNIRS Pilot Study

We demonstrate that low-frequency oscillations (LFOs) in cerebral hemodynamics, measured by frequency-domain functional near-infrared spectroscopy (FD-fNIRS), reflect altered cerebral hemodynamic oscillations in mild traumatic brain injury (mTBI). In a pilot study of two mTBI and 13 healthy subjects undergoing head-of-bed positional changes, we analyzed total hemoglobin concentration (THC), oxyhemoglobin (HbO), and deoxyhemoglobin (Hb) dynamics using spectral and time-frequency analyses. mTBI measurements exhibited significantly larger postural changes in THC (ΔTHC = 9.49 µM) compared to controls (ΔTHC = 1.03 µM). LFO power was consistently elevated in mTBI across all slow bands (0.01-0.2 Hz), particularly in the Slow-5 band (0.01-0.027 Hz), suggesting dysregulated cerebral vasomotion. Continuous wavelet transform (CWT) confirmed persistent LFO amplification during and after postural transitions. These findings indicate that THC-based LFO measures may serve as early, non-invasive biomarkers of cerebral autoregulatory impairment in mTBI.