Frontiers of Decompression Research

Presented by Peter Buzzacott, summarised by Mark Powell

At DEMA this year Peter Buzzacott, Director of Injury Monitoring and Prevention at DAN, gave a fascinating talk on the Frontiers of Decompression Research. The talk did not give any magic bullets that could be immediately used to reduce diver’s decompression risk but it did give a great overview of some of the latest aspects of decompression research. These are the topics that add to our overall understanding of decompression sickness and are the research areas that may lead to breakthroughs in the future.

The talk focused on 4 broad areas; endothelial research, the influence of food, preconditioning and genetics.

Endothelial Research:

The endothelium is the lining of the blood vessels and the endothelial dysfunction hypothesis considers that gas bubbles may not be the underlying cause of decompression sickness. Instead, it suggests that damage to the endothelium may be the underlying cause of decompression sickness [1]. This is a controversial topic and studies were presented that seemed to both support and contradict the hypothesis. A study in military divers seemed to contradict the hypothesis [2] while a study in recreational divers seemed to support it [3]. The key point here is that there is still much to learn if we still cannot definitively state what the underlying cause of decompression sickness actually is.

When endothelial cells are damaged, for example when bubbles hit the walls of a blood vessel, then fragments of these cells enter the circulation. These are known as “microparticles”. A fascinating study was presented that appeared to show that microparticles from a mouse that had been decompressed could be transfused into a second mouse who then developed decompression sickness, even though the second mouse had not been under pressure [4].

The influence of food:

A really interesting and potentially productive area of research is the influence of food on decompression sickness. A number of studies have shown that there is a link between decompression and food. The study that has caught many people’s attention is one that resulted in reduced endothelial dysfunction after consumption of dark chocolate [5]. This is probably due to the antioxidants contained in the dark chocolate which may reduce the effect of free radicals in the body. This seems too good to be true, right? Before we all go out and starting eating handfuls of dark chocolate before every dive, it should be pointed out that the study was relatively small and only covered one dive profile. It is possible that dark chocolate could potentially make things worse for some dive profiles so more research is needed in this area. Also, while chocolate might be beneficial for our endothelium, it made no difference to the number of bubbles detected and we do not yet know how it effects risk of DCS.

Similar research has also looked into the benefits of a chemical found in horse chestnuts for reducing decompression sickness. Research in rats has shown that Escin, which is an anti-inflammatory found in horse chestnuts, gave a significant reduction in the risk of decompression sickness [6].

Figure 1: A) Both DCS and death were reduced after consuming Escin, B) onset of DCS was delayed, and C) survival was longer [6]

Now some warnings on this; raw horse chestnut is poisonous so don’t go out and start snacking on horse chestnuts. Secondly, the study was done on rats so we have no idea what a suitable dose of the supplement in humans would be.

However, it does seem possible that in a few years we may be able to design snacks that could reduce the risk of decompression sickness and it might be a common sight to see divers eating dark chocolate and horse chestnut snack bars on dive boats. In the meantime, a healthy diet with lots of fruit and vegetables will contain lots of antioxidants and is the best bet for now.

Preconditioning:

Diet is one way of preconditioning the body but there are a number of others. In the same way that athletes prepare for the Olympics by training at altitude, there may be ways that we can precondition our bodies to reduce the risk of decompression sickness [7]. Pre-dive exercise has been shown to significantly reduce the risk of DCS. It is believed that the exercise produces the chemical nitric oxide (NO) which possibly eliminates micronuclei and/or reduces endothelial dysfunction.

Other recent studies have show that heat stress, pre-dive hydration and pre-dive oxygen breathing can also reduce DCS risk. More recent studies have shown that 30 mins of whole body vibration before a dive had a significant effect on DCS risk with 60% less bubbles being produced [8]. A pre-dive sauna also produced significant results with 73% less bubbles being produced [8].

Figure 2: Peter Buzzacott laying on a vibrating mat before making a provocative dive and having bubbles measured afterwards

Genetics:

The final area covered was the impact of genetics on DCS. A study was presented that showed within 3 generations it was possible to breed rats with a significantly increased resistance to DCS [9]. While it may not be feasible to focus on breeding DCS resistant divers, the fact that there is a genetic component means that if we can identify the key genes, it may be possible to screen divers that have an increased risk of DCS or who are more likely resistant.

Figure 3: After one generation, females went from 33% no-DCS to 67% no-DCS, then a generation later the males caught up [9]

Unfortunately, I can’t give you any new techniques or supplements to reduce your risk of DCS but after reviewing the latest research, I don’t think it will be too long before we will start to see the next breakthrough in reducing decompression risk.

In the meantime, a healthy diet with lots of fruit and vegetables, a sensible exercise programme and proper pre-dive hydration combined with following sensible dive profiles are still the best tools we have for reducing our decompression risk.

References

1. Madden LA, Laden G. Gas bubbles may not be the underlying cause of decompression illness – The at depth endothelial dysfunction hypothesis. Medical hypotheses. 2009 4//;72(4):389-92.
2. Lambrechts K, Pontier J, Mazur A, Buzzacott P, Morin J, Wang Q, et al. Effect of decompression-induced bubble formation on highly trained divers microvascular function. Physiological Reports. 2013;1(6):1-10.
3. Lambrechts K, Pontier J, Balestra C, Mazur A, Wang Q, Buzzacott P, et al. Effect of a single, open sea, air scuba dive on human micro- and macrovascular function. European Journal of Applied Physiology. 2013;113:2637-45.
4. Yang M, Kosterin P, Salzberg BM, Milovanova TN, Bhopale VM, Thom SR. Microparticles generated by decompression stress cause central nervous system injury manifested as neurohypophysial terminal action potential broadening. Journal of applied physiology (Bethesda, Md : 1985). 2013 Nov;115(10):1481-6
5. Theunissen S, Schumacker J, Guerrero F, Tillmans F, Boutros A, Lambrechts K, et al. Dark chocolate reduces endothelial dysfunction after successive breath-hold dives in cool water. European Journal of Applied Physiololgy. 2013;113(12):2967-75.
6. Zhang K, Jiang Z, Ning X, Yu X, Xu J, Buzzacott P, et al. Endothelia-Targeting Protection by Escin in Decompression Sickness Rats. Scientific reports. 2017 Jan 23;7:41288.
7. Gempp E, Blatteau JE. Preconditioning methods and mechanisms for preventing the risk of decompression sickness in scuba divers: a review. Research in sports medicine (Print). 2010 Jul;18(3):205-18.
8. Germonpre P, Balestra C. Preconditioning to Reduce Decompression Stress in Scuba Divers. Aerospace medicine and human performance. 2017 Feb 01;88(2):114-20.
9. Lautridou J, Buzzacott P, Belhomme M, Dugrenot E, Lafere P, Balestra C, et al. Evidence of Heritable Determinants of Decompression Sickness in Rats. Med Sci Sports Exerc. 2017 Jul 20.