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

## TL;DR

Breathing CO2 before simulated diving increases decompression sickness risk in mice, possibly due to lower body temperature and microbiota changes.

## Contribution

This study is the first to show that prior CO2 exposure increases DCS risk and links it to body temperature and microbiota.

## Key findings

- CO2 breathing before diving nearly doubled DCS incidence in mice compared to air-breathing controls.
- CO2 exposure caused a significant drop in body temperature, which correlated with increased DCS risk.
- Microbiota composition may influence thermogenesis and susceptibility to decompression accidents.

## 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.