Effects of hyperbaric oxygen on heart, brain, and lung functions in rat

Electrocardiogram (ECG), electrocorticogram (ECoG), and respiratory rate (RR) were monitored in awake, unrestrained rats during continuous exposure to 1, 3, and 5 ATA O2 until death. The RR showed a consistent pattern at 1 and 3 ATA O2, while no pattern at 5 ATA O2 was observed. A characteristic pattern in heart rate (HR) was demonstrated at 3 ATA O2. At 5 ATA O2 a continuous reduction in HR occurred, while at 1 ATA O2 no significant change was found. The ECG at 3 ATA O2 showed various arrhythmias prior to convulsions, which were severely intensified concurrently with and following convulsions and respiratory distress. The ECG arrhythmias at 1 ATA O2 occurred after the first day of exposure and were intensified during respiratory distress and increased RR. The ECG arrhythmias at 5 ATA O2 usually occurred following the appearance of the first paroxysmal cortical electrical discharges (FED), and were extremely intensified following the onset of the first generalized clinical convulsions. Increased slow-wave activity in ECoG preceded the onset of the FED at 3 and 5 ATA O2. During days 2 and 3 at 1 ATA O2 the ECoG mostly contained slow and low-amplitude waves. The different levels of oxygen in this study often showed different effects on a particular physiological parameter. It is concluded that alterations in ECG, ECoG, HR, and RR at some pressures signal the appearance of severe pathophysiological changes during prolonged hyperbaric oxygen exposure in rats, and that the relations of these effects are not uniform at all oxygen pressures.