Effects of hyperbaric oxygen on neurologic outcome for cerebral ischemia in rats

To evaluate the effect of hyperbaric oxygen (HBO) therapy on neurologic outcome (assessed by the quantal bioassay approach) following acute focal cerebral ischemia in rats.

Two separate experimental trials were conducted. Trial 1, a nonblinded experiment, used 38 rats. Trial 2, a blinded experiment, used 59 rats. Focal cerebral ischemia was induced with a surgically placed intraluminal occlusion of the left middle cerebral artery; subsequent removal allowed reperfusion. Arterial occlusion times were varied from 5 to 90 minutes in trial 1, and from 3 to 45 minutes in trial 2. The control groups were maintained at ambient pressure for the duration of each trial. The trial 1 treatment group received a single 30-minute HBO treatment at 2.0 atmospheres absolute (ATA) on the initial day of ischemia. The trial 2 treatment group received 30-minute HBO treatments at 2.0 ATA daily for 4 consecutive days. The animals underwent daily 5-point neurologic examinations. A computerized quantal bioassay was used to determine the ET50--the occlusion time required to cause a neurologic abnormality in half of the animals. The control and treatment ET50 values were compared in each trial using a 2-tailed t-test. An increased ET50 for the treatment vs the control group implied a beneficial effect of HBO; a decrease, the opposite. The study had a power of 80% to detect a difference of 11.4 minutes in the ET50 for a 2-sided alpha = 0.05.

For trial 1: the HBO ET50 was 18.1 +/- 21.9 minutes and the control ET50 was 22.8 +/- 25.0 minutes (p > 0.2). For trial 2: the HBO ET50 was 9.49 +/- 17.4 minutes and the control ET50 was 14.9 +/- 14.2 minutes (p < 0.2).

HBO therapy showed no apparent benefit in a rat model as a treatment modality for acute cerebral ischemia with reperfusion.