Electroencephalographic changes during hyperbaric oxygen therapy in patients with chronic disorders of consciousness

Prolonged disorders of consciousness (PDOC) impose a substantial socioeconomic burden, and objective electrophysiological markers that can accompany hyperbaric oxygen therapy (HBOT) remain lacking.

This retrospective self-controlled study analyzed serial quantitative electroencephalographic (qEEG) changes during HBOT, with consciousness assessed by the Coma Recovery Scale-Revised (CRS-R), in patients with PDOC. Resting-state qEEG measures-power spectral density (PSD), permutation entropy (PE), and Lempel-Ziv complexity (LZC)-were obtained before HBOT (T1, baseline), during the first HBOT session (T2), and during the twentieth session (T3). CRS-R scores were assessed before and after the treatment course. Forty PDOC patients were stratified by baseline CRS-R into a higher-level group (CRS-R ≥ 8, n = 14) and a lower-level group (CRS-R < 8, n = 26).

PE and LZC increased progressively and significantly from T1 to T3 in every brain region in both groups (all FDR-corrected p < 0.05); for example, frontal PE rose from 0.37 ± 0.01 to 0.66 ± 0.03 in the CRS-R ≥ 8 group and from 0.37 ± 0.03 to 0.62 ± 0.05 in the CRS-R < 8 group, with corresponding frontal LZC increases (0.14 ± 0.01 to 0.30 ± 0.03, and 0.15 ± 0.02 to 0.28 ± 0.04, respectively). PSD was otherwise stable, with a significant change confined to the occipital theta band in the CRS-R < 8 group (F = 6.047, FDR-corrected p = 0.022; T1 vs. T3, p = 0.028). Mean CRS-R improved over the course from 6.3 ± 2.8 to 8.7 ± 3.6 (p < 0.001; CRS-R < 8: 4.5 ± 1.4 to 6.7 ± 1.8; CRS-R ≥ 8: 9.6 ± 2.4 to 12.4 ± 3.2). The increases in EEG entropy and complexity occurred in parallel with the improvement in consciousness, but no formal correlation between qEEG and CRS-R changes was performed.

These findings provide adjunctive electrophysiological measures for consciousness assessment and objective information accompanying HBOT as an adjuvant treatment for PDOC; causal or predictive inference awaits controlled studies.