Seizures Caused by Exposure to Hyperbaric Oxygen in Rats Can Be Predicted by Early Changes in Electrodermal Activity

Figure 1. (A) Subdermal needle electrodes after removal from animal, postmortem. The length of the tip distal to the 90° bend ranged from 1 to 3 mm. (B) Subdermal needles implanted in the back of a euthanatized animal prior to removal.

Figure 2. The animal exposure chamber inside the hyperbaric chamber. The main hyperbaric chamber houses the animal exposure chamber, which contains the animal cage (c1) and wire cage lid (c2). The main chamber is compressed using air only while the animal exposure chamber is ventilated with either air at 1 ATA (control) or 100% O2 at 1 or 5 ATA (hyperoxia). In this experiment, the front edge of the lid to the animal exposure chamber is demarcated by the horizontal white dashed line; one of six buckles used to seal the cover of the animal exposure chamber is seen here. A preset pressure relief valve (5) prevents over-pressurization of the animal exposure chamber during the experiment. Other important items seen here include the animal’s jacket and tether (1) that passes up through an opening in the wire cage lid (c2) and connects to the moveable tether assembly (2) mounted on the cage lid (c2). The two, needle electrode leads pass upwards through the tether cable to the tether assembly (2), exit through the roof the animal exposure chamber (3), and plug into the internal electrical connector panel behind the animal exposure chamber (4). The welded window port (6) is barely visible in this…

Figure 3. A video image captured at the beginning of an experiment showing the rat’s jacket and tether (1) and the tether assembly (2) mounted on the inverted wire cage lid (c2). The metal triangular-shaped side panel was removed, which normally reinforces the depression that supports an animal’s water bottle and replaced with a plexiglass panel (P) so the animal inside the cage (c1) could be viewed using the video camera.

Figure 4. Samples of normalized skin conductance responses (SCRs) of human and rat.

Figure 5. The same animal as in Figure 8 but with the x-axis compressed in time to show continuously measured raw EDA and its derived TVSymp activity before, during, and after seizure. Top: Raw EDA and time-varying spectral analysis of EDA (TVSymp, non-dimensional units) for a rat undergoing exposure to 5 ATA of HBO2. Bottom: Profile of the dive.

Figure 6. Exploring and walking (A-C) in a tethered rat did not affect measured EDA (D). The black dots (D) indicate when the video images were sampled in A–C.

Figure 7. Kaplan–Meier survival curve adapted for reporting the range of latency times prior to onset of seizures while breathing 5 ATA O2. Each vertical step indicates the latency time to seizure in a rat after reaching 5 ATA O2. Refer to text for definitions of a, b, and c.

Figure 8. (top to bottom). Animal behavior, EDA, and cortical EEG activity in a rat before (1 ATA air and O2) and during exposure to HBO2 (5 ATA O2). The times demarcated by the vertical green lines in EDA and EEG traces mark the time of the accompanying video image.

Figure 9. Ensemble of normalized power spectral densities of EDA signals for N = 10 rats.

Figure 10. TVSymp elevation before seizure observed in a sample rat.

Figure 11. Top: Boxplot for the maximum value of TVSymp at the Start (chamber pressurized) and Before seizure for the entire population. N = 10, * represents significance difference to Start of HBO2 (p = 0.005). Bottom: Boxplot of the time-lapse from the peak of TVSymp to the occurrence of the seizure.