Electrocorticographic characteristics of rats exposed to hyperbaric nitrox
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Published on: March 31, 2016
Chenglong Li1, Shuo Yan1, Rihui Shen1
1Naval Medical Center of the People's Liberation Army (PLA), Naval Medical University, Shanghai, China.
Background:
This study aimed to characterize and compare the dynamic changes in cortical electrophysiological activity during hyperbaric nitrox exposure and subsequent hyperbaric heliox exposure in rats receiving continuous electrocorticographic (ECoG) recording.
Methods:
Male rats were randomly assigned to the 3% O2-N2, 16% O2-N2, and 100% O2 groups (n=8 per group). Rats in the 3% O2-N2 and 16% O2-N2 groups were exposed to their respective gas mixtures at 700 kPa for 60 min, whereas those in the 100% O2 group were exposed to pure oxygen at 200 kPa for 60 min. Following hyperbaric nitrox exposure, the 16% O2-N2 mixture was replaced with a 16% O2-84% He mixture at the same pressure for additional 60 min. ECoG was continuously recorded, and power spectral density (PSD), absolute power in the δ, θ, α, β, and γ bands, delta-theta/alpha-beta ratio (DTABR), median frequency (MF), sample entropy (SampEn), and Higuchi fractal dimension (HFD) were calculated and compared among groups.
Results:
Rats in the 3% O2-N2 and 16% O2-N2 groups exhibited increased slow-wave activity and a shift in spectral power toward lower frequencies, accompanied by increased δ-, θ-, α-, and β-band power, decreased γ-band power, increased DTABR, and reduced MF, SampEn, and HFD as compared to the baseline levels. Changes in several ECoG parameters emerged earlier in the 3% O2-N2 group than in the 16% O2-N2 group. Compared with the 100% O2 group, rats in the 3% O2-N2 and 16% O2-N2 groups generally exhibited lower MF, SampEn, and HFD, whereas ECoG parameters in the 100% O2 group showed relatively minor changes as compared to the baseline levels. Following substitution with hyperbaric heliox, DTABR tended to decrease, whereas MF, SampEn, and HFD tended to increase, suggesting a trend toward baseline ECoG characteristics.
Conclusions:
Hyperbaric nitrox exposure was associated with a shift in ECoG activity toward lower frequencies, reduced signal complexity, and greater regularity in rats. Following substitution with hyperbaric heliox, these ECoG characteristics showed trends toward baseline levels. These findings characterize cortical electrophysiological alterations associated with hyperbaric nitrox exposure and may provide a basis for future investigations into the electrophysiological characteristics of nitrogen narcosis.
