Skeletal response of rats to repeated short-term hyperbaric helium-oxygen exposures.

Young male rats were exposed to repeated heliox dives and analyzed for skeletal alterations. Animals were exposed 1, 3, 5, or 7 times to either 1 ATA He-O2 for 12.5 h, or to 5 ATA He-O2 for 4 h and a 8.5 h decompression, or to 5 ATA He-O2 for 4 h and a 1.5 h decompression. In a separate study, 30 rats were exposed 6 times to 5 ATA He-O2 and explosively decompressed. Animals were sacrificed 20 d after the last dive. There were no significant changes in femur wet weight, density, ash weight, length, or mineral content. Plasma calcium, phosphorus, and alkaline phosphatase remained normal. Eighteen of 30 animals survived the six explosive decompressions; however, there were no significant changes in bone. These results indicate that the number and rate of decompressions used in this study have no lasting effect on bone growth and mineral composition in the rat.