Changes in the permeability of the blood-brain barrier under hyperbaric conditions.

Hyperbaric oxygen therapy (HBO) has been used in the treatment of cerebral edema with variable results. Two different actions of HBO, one decreasing and the other increasing cerebral edema, have been postulated. We examined the permeability of the blood-brain barrier (BBB) in rats and cats. Animals of each species were treated for 90 min/d with 100% oxygen at a pressure of 2.5 atm for 5 consecutive days. Following treatment, cadmium-free ferritin was injected intravenously. Sections of the brain were prepared for electron microscopic evaluation of the capillaries and their neighboring structures. Perivascular edematous zones were observed. Ferritin particles penetrated through the capillary endothelium and into the pericapillary structures. Hyperbaric oxygenation appears to increase the permeability of cerebral vessel walls in normal animals. Further work on this phenomenon may provide a more rational basis for the treatment of cerebral edema with HBO.