Between July 15-17, the Office of Naval Research (ONR) and the Naval Sea Systems Command (NAVSEA) hosted an undersea medicine progress review meeting in Durham, North Carolina. The presentations focused primarily on topics of interest for the Navy, but most of the research also benefits recreational and technical divers. One topic I found particularly interesting concerns the combined effect of increased carbon dioxide levels (CO₂) in breathing gas and the breathing resistance that breathing apparatuses impose on divers.

If breathing is unimpeded, slightly increased levels of CO₂ pose no problem. However, the more CO₂ that is inhaled, the less CO₂ can be added, and a larger breathing volume per unit of time will be required to wash out the same amount of CO₂. This increase of breathing volumes occurs automatically, successfully washing out the metabolic CO₂ and maintaining a nearly normal level of CO₂ in arterial blood (even during exercise when the internal metabolic production of CO₂ is increased).

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