Obstructive Sleep Apnea Syndrome Disrupts Glymphatic-Related Physiological Brain Pulsations

Background: Obstructive sleep apnea (OSA) affects over one billion people and increases neurodegenerative risk. Brain vasomotor, respiratory, and cardiac pulsations are thought to drive glymphatic clearance during sleep, yet OSA's effect on these pulsations remains poorly understood. Methods: We studied 20 healthy controls (HC; 39.7{+/-}8.0 y) and 12 patients with OSA (PWOSA; 53.0{+/-}11.0 y) using a four wavelength (690-980 nm) functional near-infrared spectroscopy (fNIRS) measuring oxygenated, deoxygenated and total hemoglobin, water and cerebrospinal fluid (HbO, HbR, HbT, H2O, CSF). Polar devices provided heart rate variability (HRV). Spectral power, coherence and phase transfer entropy analysis was performed for very low frequency (VLF), respiratory, and cardiac bands from 30 min sleep segments and event-based whole-night analysis assessed autonomic responses. Results: OSA patients exhibited lower fNIRS spectral entropy for HbO, HbT, H2O & CSF (p<0.05), with increased VLF and respiratory band power across all concentrations (HbO, HbR, HbT, H2O & CSF, p<0.05). Signal coherence was reduced in respiratory and cardiac bands. Phase transfer entropy revealed disrupted directional coupling toward HbR (cardiac) and CSF-to-HbO (respiratory). HRV showed parallel VLF amplification (p <0.05), elevated heart rate during event-free and respiratory-event periods (p<0.001) and reduced Root Mean Square of Successive Differences (RMSSD, 32.5 vs 43.0 ms, p<0.001). Hypoxic burden correlated with cardiac band power of HbO, HbT and CSF (r>0.73). Conclusions: OSA reorganizes cortical pulsatile dynamics - reducing complexity, amplifying low frequency power and disrupting directed coupling. This state may compromise sleep-related glymphatic clearance. fNIRS-based spectral analysis offers a promising bedside tool for monitoring brain pulsatility.