Autopsy diagnosis of decompression illness in rats by quantifying pulmonary emphysema

Objectives. In medico-legal autopsy related to decompression illness (DCI) in divers, it is important to differentiate between postmortem decompression and antemortem decompression; however, definitive criteria for autopsy diagnosis of DCI remain to be established. We aimed to clarify autopsy findings that would aid the diagnosis of DCI. Methods. A total of 27 Wistar and 33 Zucker fatty male rats were categorized into 3 groups: antemortem decompression group (group AD), postmortem decompression group (group PD), and controls. The AD and PD rats were subjected to antemortem compression (both groups) followed by antemortem and postmortem decompression, respectively, in a hyperbaric chamber. Control rats were kept at atmospheric pressure. Intravascular bubbles and histopathological findings in the 3 groups were compared, and pulmonary emphysema was quantified using ImageJ software. Results. Intravascular bubbles were observed in both AD and PD groups. In group AD, prolonged hyperbaric exposure increased mortality, intravascular bubbles, and pulmonary emphysema, with Zucker fatty rats showing more marked changes than Wistar rats. Further, intravascular bubbles and pulmonary emphysema in the dead rats were quantitatively greater than those in the rats that survived decompression. Moreover, in Zucker fatty rats, pulmonary emphysema was quantitatively significantly greater in group PD than that in the dead rats of group AD. Conclusion. Our results indicate that the quantitative evaluation of pulmonary emphysema can potentially distinguish postmortem decompression from antemortem decompression. This technique may be useful in autopsy diagnosis of divingrelated deaths, including DCI.