How Expertise Changes Cortical Sources of EEG Rhythms and Functional Connectivity in Divers Under Simulated Deep-Sea Conditions.

Although the recent years have witnessed a growing interest in functional connectivity (FC) through brain sources, the FC in extreme situations has not been completely elucidated. This paper is aimed at investigating whether the expertise acquired during the deep-sea diving is reflected in FC in a group of professional divers (PDs) compared to a group of new divers (NDs), and how it could affect the concentration and stress levels. The sources of brain frequency rhythms, derived by the electroencephalography acquisition in a hyperbaric chamber, were extracted in different frequency bands and the corresponding FC was estimated in order to compare the two groups. The results highlighted a significant decrease of the alpha source in PDs during air breathing and a significant increase of the upper beta source over central areas at the beginning of post-oxygen air, as well as an increase of beta FC between fronto-temporal regions in the last minutes of oxygen breathing and in the early minutes of post-oxygen air. This provides evidence in support of the hypothesis that experience and expertise differences would modulate brain networks. These experiments provided the unique opportunity of investigating the impact of the neurophysiological activity in simulated critical scenarios in view of the investigation in real sea-water experiments.

Bluetooth Communication Interface for EEG Signal Recording in Hyperbaric Chambers.

Recording biological signals inside a hyperbaric chamber poses technical challenges (the steel walls enclosing it greatly attenuate or completely block the signals as in a Faraday cage), practical (lengthy cables creating eddy currents), and safety (sparks hazard from power supply to the electronic apparatus inside the chamber) which can be overcome with new wireless technologies. In this technical report we present the design and implementation of a Bluetooth system for electroencephalographic (EEG) recording inside a hyperbaric chamber and describe the feasibility of EEG signal transmission outside the chamber. Differently from older systems, this technology allows the online recording of amplified signals, without interference from eddy currents. In an application of this technology, we measured EEG activity in professional divers under three experimental conditions in a hyperbaric chamber to determine how oxygen, assumed at a constant hyperbaric pressure of 2.8 ATA , affects the bioelectrical activity. The EEG spectral power estimated by fast Fourier transform and the cortical sources of the EEG rhythms estimated by low-resolution brain electromagnetic analysis were analyzed in three different EEG acquisitions: breathing air at sea level; breathing oxygen at a simulated depth of 18 msw, and breathing air at sea level after decompression.

Tracking EEG changes during the exposure to hyperbaric oxygen.

OBJECTIVE: The aim was to investigate and define possible alterations in cerebral activity during prolonged hyperbaric oxygen exposure and decompression as compared to baseline activity. METHODS: Thirty-two channel electroencephalography (EEG) was recorded with a Bluetooth EEG system in 11 subjects. A 20-min EEG recording was carried out under three different conditions: breathing air inside a hyperbaric chamber at sea level; breathing oxygen at a simulated depth of 18 msw; breathing air at sea level after decompression. Relative EEG power was estimated in frequency ranges. RESULTS: During oxygen breathing, brain activity showed an early fast delta decrease in the posterior regions, with a synchronous and significant increase in alpha in the same regions. After decompression, the delta relative power decrease was uniformly distributed over the cerebral cortex until minute 8, and the alpha relative power was maximal in the posterior regions during the first 2 min. CONCLUSIONS: These results may be relevant for establishing a reference point in future studies on oxygen-sensitive subjects who reported problems during oxygen diving. SIGNIFICANCE: Significant changes in EEG relative power suggest that it may be possible to define and recognize landmarks of oxygen-induced brain activity, which would be useful in the medical treatment of subjects reporting "oxygen-toxicity diving-related problems".

EEG patterns associated with nitrogen narcosis (breathing air at 9 ATA).

INTRODUCTION: The narcotic effect of nitrogen impairs diver performance and limits dive profiles, especially for deep dives using compressed air. It would be helpful to establish measurable correlates of nitrogen narcosis. METHODS: The authors observed the electroencephalogram (EEG) of 10 subjects, ages 22-27 yr, who breathed air during a 3-min compression to a simulated depth of 80 msw (9 ATA). The EEG from a 19-electrode cap was recorded for 20 min while the subject reclined on a cot with eyes closed, first at 1 ATA before the dive and again at 9 ATA. Signals were analyzed using Fast Fourier Transform and brain mapping for frequency domains 0-4 Hz, 4-7 Hz, 7-12 Hz, and 12-15 Hz. Student's paired t-test and correlation tests were used to compare results for the two conditions. RESULTS: Two EEG patterns were observed. The first was an increase in delta and theta activity in all cortical regions that appeared in the first 2 min at depth and was related to exposure time. The second was an increase in delta and theta activity and shifting of alpha activity to the frontal regions at minute 6 of breathing air at 9 ATA and was related to the narcotic effects of nitrogen. DISCUSSION: If confirmed by studies with larger case series, this EEG pattern could be used to identify nitrogen narcosis for various gas mixtures and prevent the dangerous impact of nitrogen on diver performance.