Evaluation of cerebral gas retention and oedema formation in decompressed rats by using a simple gravimetric method

Abstract

Objective: The objective of the study is twofold: first, to develop a specific gravity method for distinguishing between bubbles and oedema following decompression, and, second, to evaluate the extent to which the change in specific gravity is due to retained gas in cerebral tissue. Methods: A brombenzene/kerosene gradient column was used to measure changes in brain specific gravity at 100 and 300 kPa, respectively. This study was performed on 23 rats. Non-exposed rats constituted the control group A (n = 6). The exposed animals were divided into two groups according to the number of bubbles they developed upon decompression; group B (bubble grade 0-2, n = 9) and group C (bubble grade 3-5, n = 8). Results: Cerebral gas retention was determined by increasing the pressure on the gradient column from 100 to 300 kPa. Median specific gravity of the brain at 300 kPa bar was significantly higher compared to 100 kPa for the decompressed groups B (p = 0.018) and C (p = 0.012), thus implying gas retention. The cerebral gas volume was significantly higher for rats with a high bubble score compared to rats with a low bubble score (p = 0.043). However, the major contribution to the change in specific gravity was due to oedema formation. Conclusion: The brombenzene/kerosene gradient column was found to be a sensitive method for distinguishing between gas retention and oedema formation in decompressed animals. There was a higher gas retention in rats with a high bubble score compared to rats with a low bubble score. The major contribution to the change in specific gravity in decompressed animals is due to oedema formation.

• Density
• Diving
• Gas Bubbles
• Specific Gravity