Isobaric counterdiffusion of carbon tetrafluoride breathing gas to prevent severe decompression sickness.

Decompression sickness (DCS) risk limits human undersea operations through tissue inert gas supersaturation and pathological bubble formation. Switching the inert breathing gas prior to decompression to a gas with lower diffusivity could allow faster and safer decompression. This principle was tested in 20 kg swine after a helium-oxygen (He/O2) dive using carbon tetrafluoride. Sedated swine breathed He/O2 79/21 at a pressure equivalent of 200 feet of seawater (714 kPa) in a hyperbaric chamber for 50 min until randomized to continuing He/O2 or switching to carbon tetrafluoride and oxygen (CF4/O2 79/21) for 10 min before decompression. The CF4/O2 group had reduced DCS with lower mortality, hypoxemia, pulmonary edema, venous gas emboli, gait disturbance, rash, and central nervous system hemorrhage. CF4/O2 has the potential to expand human exploration through enabling deeper dives, longer dives, and rapid decompression while maintaining safety.