Ученые доказали эффективность замены газа на тетрафторид углерода для предотвращения болезни декомпрессии

Could breathing carbon tetrafluoride have a place in scuba diving? Switching breathing gases shortly before ascent recently spared the lives of a number of pigs on a simulated deep dive, raising the question of whether the gas could provide a greater measure of protection from decompression sickness (DCS) for human divers. For the new animal study, led by Duke University in the USA, researchers placed 40 sedated pigs in a hyperbaric chamber simulating a one-hour dive to a depth of 61m. Half of the animals breathed heliox (helium and oxygen) throughout, while the remainder switched for the final 10 minutes to a mixture containing oxygen and carbon tetrafluoride (CF4). After both groups underwent the same ascent, more than 80% of the heliox-only animals died from DCS within the three-hour observation period. None of the animals that had switched to CF₄ died, however, and this group also showed fewer venous gas bubbles detected in or passing through the heart, as well as less impairment in walking. The switch theory The approach exploits “isobaric counterdiffusion”, through which one inert gas leaves the tissues while another enters, without any change in ambient pressure. Helium moves through the body rapidly. CF4, also called perfluoromethane, consists of much larger molecules and enters tissues more slowly. During the 10-minute switch, helium could therefore wash out faster than CF4 was able to accumulate. The animals began decompression with a smaller total burden of dissolved inert gas, leaving less available to form harmful bubbles during ascent. This makes the application unusual. Divers are generally warned that changing inert gases can in itself produce counterdiffusion problems. Here, the researchers deliberately exploited unequal gas-exchange rates to produce a beneficial net effect, in the form of a controlled “wash-out” before ascent. For now, the practical message is one of considerable caution. This was an animal experiment using sedation, a controlled chamber and a deliberately severe exposure. It did not test conscious human divers, ordinary scuba profiles, repeated diving or long-term CF4 exposure. Human trials would need to establish respiratory safety, appropriate oxygen fractions, gas density and work-of-breathing limits (CF4 being much denser than helium), equipment compatibility, decompression procedures and reliable delivery systems. The obstacles CF₄ is not an approved recreational breathing gas, and the study does not justify experimental gas switches or any change to established decompression procedures. The researchers themselves expect any early use of CF4 to be specialised, with study co-author Richard Moon pointing out that the expense of using the gas would probably restrict the technique to commercial, military or scientific diving. High-purity CF4 currently costs about the same as scarce spot-market helium, but a certified human breathing mixture could cost far more after testing, transport, mixing and environmental controls. Carbon tetrafluoride is principally an industrial speciality gas, used in making semiconductors and solar cells, as a refrigerant and for cleaning production equipment. It also occurs as an unwanted by-product of aluminium smelting. It has exceptional chemical stability, being colourless, non-flammable and relatively inert, but is also an extremely persistent greenhouse gas, with an atmospheric lifetime measured in tens of thousands of years and a warming effect thousands of times greater than an equal mass of CO2. The experiment is nevertheless considered to provide compelling proof of concept in an animal model that DCS risk might be reduced by deliberately managing the inert gas that occupies the tissues immediately before ascent. The study was published on 10 August in Proceedings Of The National Academy Of Sciences. Also on Divernet: DCI: Why do some divers get ‘hit’, and others don’t?