New Research a Potential Safety Aid for Divers Exposed to High-Pressure Oxygen
A newly published study from researchers at the University of South Florida has demonstrated that ketogenic supplements can significantly delay the onset of CNS oxygen toxicity, and reduce the severity of the associated convulsions.
The ketogenic diet – or 'Keto diet' – is the low-carb, high-fat diet popularised in much of the world's media as a weight-loss programme. The diet forces the body to burn fat as fuel, rather than carbohydrates which, when consumed in excess, are stored in the body as fat.
Central Nervous System (CNS) oxygen toxicity is caused by the inhalation of oxygen beyond a certain partial pressure of the gas. In simple terms, breathing oxygen at depth can cause a diver to experience convulsions similar to an epileptic seizure, depending on the percentage of oxygen in the tanks from which they are breathing, and the depth to which they are diving.
High partial pressures of oxygen are also used in Hyperbaric Oxygen Therapy (HBOT) treatment for a variety of illnesses and injuries, including diabetic wounds and burn victims. The same limits apply in the chamber at the surface, however, it is much easier to manage a convulsion in such an environment rather than underwater, where the results are far more serious and usually result in fatality through drowning.
During a recreational Enriched Air Nitrox course, divers are taught to prevent the possibility of CNS oxygen toxicity by not exceeding the depth at which the percentage of oxygen in their tank reaches a partial pressure (ppO2) of 1.4ata (atmospheres). This equates to a maximum operating depth (MOD) of approximately 33m for a standard recreational nitrox mixture containing 32% oxygen. (By way of comparison, pure oxygen reaches the 1.4ata limit at just 4m of depth).
What is less well known is that there is a delay – 'latency' – between a person breathing oxygen at high partial pressures and the onset of convulsions caused by CNS oxygen toxicity. As the onset of convulsions is almost impossible to predict for an individual diver, to maintain safe and conservative dive practices the limits are fixed to the mixture's MOD, and the specifics of any kind of delay are not taught.
Previous research has already shown that a ketogenic diet inhibits and reduces the severity of seizures in patients suffering from epilepsy. The problem is that the ketogenic diet – as demonstrated by legions of fad dieters – is difficult to maintain. There is a raft of undesirable side effects, and questions remain as to its safety in terms of a person's health. Ketogenic supplements, on the other hand, raise the level of ketones in the body without having to resort to an extreme change in diet.
During the recent study, rats were given ketogenic supplements containing a mixture of ketone ester (KE) and medium-chain triglyceride (MCT) oil and placed in a small hyperbaric chamber, which was filled with pure oxygen and subsequently pressurized. As soon as the symptoms of oxygen toxicity were observed, the chamber was flushed with air to reverse the effects. The time between reaching high pressure and onset of CNS oxygen toxicity was measured and compared with test subjects that had not been fed the supplements. Not only were the supplements shown to reduce the severity of the convulsions, but also increased the latency by over 200 per cent.
How that translates into humans 'is hard to predict, since a rat's metabolism is about seven times faster than human's,' according to Dr Csilla Ari, lead author of the paper, 'but we are planning to transition to test these products in humans, hopefully soon.'
Ketone supplements are already commercially available on the market. MCT can be extracted from coconut oil and is present in diet and sports-nutritional products, but they do not all have the same effect. 'We are working on developing an optimized compound for all the specific applications we study,' said Dr Ari. 'During our research, we found that different ketone supplements work best for specific applications. The ones that worked best for [delaying the onset of CNS oxygen toxicity] are not available yet,' she said, 'but we are working with Office of Naval Research and private industry to bring them to market for human consumption within the next year.'
From a scuba diving perspective, the practical application of ketogenic supplements as CNS oxygen toxicity inhibitors may prove beneficial to technical divers, particularly those involved in commercial and military diving. 'With the emerging new technologies,' said Dr Ari, herself an experienced NAUI Divemaster, 'the increased availability to mixed-gas technical or rebreather diving means more and more people are getting potentially exposed to the dangers of oxygen toxicity seizures.'
Clearly, the addition of ketogenic supplements is not a free pass to violate the industry-standard limits for oxygen exposure. However, fatalities have occurred as a result of technical divers, for example, switching to a cylinder containing the wrong percentage of oxygen during the dive – a result of incorrect filling, gas analysis or labelling of the cylinder. Ketogenic supplements will not completely eliminate the possibility of convulsions brought on by CNS oxygen toxicity, but may delay the onset long enough for a diver to realise their mistake and switch to a more appropriate mixture.
'I have been diving all over the world, in sometimes challenging conditions,' said Dr Ari, 'so it is essential for me to give extra attention to dive safety. These results especially excite me, because I am very passionate about showing people the wonders of the underwater world and if I can contribute to making our visits to this magical world safer, that just helps.'