CO2 Breathing Prior to Simulated Diving Increases Decompression Sickness Risk in a Mouse Model: The Microbiota Trail Is Not Forgotten.

Abstract

Decompression sickness (DCS) with neurological disorders is the leading cause of major diving accidents treated in hyperbaric chambers. Exposure to high levels of CO₂ during diving is a safety concern for occupational groups at risk of DCS. However, the effects of prior exposure to CO₂ have never been evaluated. The purpose of this study was to evaluate the effect of CO₂ breathing prior to a provocative dive on the occurrence of DCS in mice. Fifty mice were exposed to a maximum CO₂ concentration of 70 hPa, i.e., 7% at atmospheric pressure, for one hour at atmospheric pressure. Another 50 mice breathing air under similar conditions served as controls. In the AIR group (control), 22 out of 50 mice showed post-dive symptoms compared to 44 out of 50 in the CO₂ group (p < 0.001). We found that CO₂ breathing is associated with a decrease in body temperature in mice and that CO₂ exposure dramatically increases the incidence of DCS (p < 0.001). More unexpectedly, it appears that the lower temperature of the animals even before exposure to the accident-prone protocol leads to an unfavorable prognosis (p = 0.046). This study also suggests that the composition of the microbiota may influence thermogenesis and thus accidentology. Depending on prior exposure, some of the bacterial genera identified in this work could be perceived as beneficial or pathogenic.