Oxygen pre-breathing decreases dysbaric diseases in UW sheep undergoing hyperbaric exposure

Prolonged exposure of humans and animals to increased pressure as in a disabled submarine (DISSUB) can saturate the body's tissues with dissolved N2 as compressed air is breathed. Decompression-induced bubble formation in the long bone marrow cavity may lead to a bone compartment syndrome resulting in bone ischemia and necrosis. We tested oxygen pre-breathing prior to decompression in sheep to assess the effect upon dysbaric osteonecrosis (DON) induction in a DISSUB simulation experiment. A total of sixteen adult female sheep were used throughout the experiment. Four sheep were used as controls without oxygen pre-breathing. All sheep (99 +/- 14 kg SD) underwent dry chamber air exposure at 60 fsw (2.79 atm abs) (.2827 MPa) for 24 h followed by oxygen (88-92%) pre-breathing (15-min, 1-h, and 2-h and air for control) before "dropout" decompression at 30 fsw/min (0.91 atm/min). 99mTc-methylene diphosphonate (MDP) bone scans of the distal (radii and tibiae) long bones were used to detect "hot spots" of remodeling suggestive of DON lesions. Alizarin complexone fluorochrome was injected to visualize sites of metabolic activity indicating DON repair of both the proximal and distal long bones (radii, tibiae, femora, and humeri). Our findings showed that the amount of alizarin complexone deposition and bone scan uptake was greater in sheep with shorter oxygen pre-breathing times than those undergoing longer pre-breathing dives (p = 0.0056 and p = 0.001, for one and two hour pre-breathes respectively). Proximal limb bones (femur, humerus) displayed less alizarin complexone deposition than the distal radius and tibia (p < 0.0001).