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Myth – Hydration is the most important factor in avoiding DCS
By Mark Powell
The maintenance of a good state of hydration is generally considered to be very important for overall health and dehydration can have significant implications on health and exercise performance. Dehydration has long been considered by many divers to be one of the most significant, or even THE MOST significant, factor in DCS risk other than following correct dive profiles.
The idea that hydration is the most important factor in avoiding DCS has been repeated so often that it is taken as an undisputed fact. Many diving manuals repeat this misconception and there are countless articles online which make the same point.
As we have already seen in this series, just because something is repeated over and over again, does not mean it is a fact and widely believed rules are sometimes found to be based on no evidence at all.
Historically there has been very little research on this point, as it was taken to be self-evidently true by many, although rejected by others. There were only a very small number of studies investigating the topic although in recent years this gap has been slowly been addressed as researchers have tried to prove or disprove the idea.
If we look at the scientific evidence for the impact of hydration on DCS risk we can find one paper from 2007 which showed that diving causes dehydration [1]. Another showed that prehydration resulted in a reduction in bubbling post dive [2] and a third showed a reduction in DCS risk [3] although there were some queries about this study. None of these were conclusive and the reduction in bubbling and DCS risk was not huge. This seemed to imply that the benefits of hydration have been overstated at best and does not have anywhere near the impact that was believed. This is especially true when compared to the impact of other forms of preconditioning such as vibration or sauna or when compared with other factors such as temperature which provided a much bigger change in DCS risk.
However, some more recent papers seem to show that hydration does indeed have an impact on DCS risk although less than many other factors such as temperature and exercise [4].
At the same time that the benefits of hydration were being questioned, the risks of over overhydration were starting to be considered.
In particular, excessive overhydration (hyperhydration) can increase the risk of immersion pulmonary edema. However, in some circles this has been misinterpreted as meaning that a normal level of hydration is bad as it increases the risk of this condition.
MYTH – Hydration increases the risk of IPO/IPE
Immersion pulmonary odema/edema (IPO/IPE) occurs when fluid leaks into the alveoli in the lungs. This results in sudden shortness of breath, cough and sometimes blood-tinged, frothy sputum.
IPO was once considered rare, but is now more widely recognized. While the actual numbers of cases are unknown, it is most likely underdiagnosed. This might be because:
- It is difficult to detect in fatalities.
- It can be mistaken for drowning.
- Mild cases of IPE can resolve spontaneously.
Factors contributing to IPO may include:
- Hydrostatic pressure gradient
- Cold-induced vasoconstriction
- Exertion
- Hydrostatic gradient between mouth and alveoli
- Inspiratory resistance caused by the regulator
- Increased gas density at depth
- Excessive pre-dive hydration
- Hypertension
Many of these factors may be present in adventurous or technical diving. Divers Alert Network (DAN) recommends that you abort the dive as quickly and safely as possible if you experience:
- Sudden shortness of breath.
- Persistent cough.
Upon surfacing breathe 100 percent oxygen and postpone further diving until you can consult a physician.
Although mild cases of IPO can resolve without further treatment once a diver has exited the water, respiratory distress while diving can be extremely dangerous. IPO becomes an even greater concern when you face an extended decompression obligation. Here you must balance the risks of:
- IPE symptoms worsening if you remain under water.
- Suffering DCS if you shorten or skip decompression stops.
You will notice that in the description above, one of the factors contributing to IPO is listed as “Excessive pre-dive hydration”. As mentioned earlier this has, in some circles, been misinterpreted as meaning that hydration is bad as it increases the risk of IPO.
When considering hydration levels, it is important to remember that there are three relative states. Which in layman’s terms we describe as dehydration, proper hydration and excessive overhydration. I have avoided the more scientific terms hypohydration, euhydration and hyperhydration in order to make this explanation more accessible to the non-scientist.
As proof that this myth exists, I have included below an extract from a genuine email I received from one of my students;
“I genuinely believed (I don’t know where I got this from) that if you drink anything before a dive, you’re putting yourself at risk of getting IPO. I didn’t realise the shear amount you actually had to drink to increase that risk. So on occasion I’ve had a tea between dives and then jumped in for a second dive and in the back of my mind be thinking ‘I hope I don’t start coughing uncontrollably now and give myself IPO because of that tea’”
One of the most commonly referenced articles on IPO, and an article that the student above had definitely read, contains the following quote [6] “I am particularly concerned that many divers overhydrate with fluids before a dive, in the belief that it will protect them against decompression illness. The evidence that it protects is not convincing. In contrast there is unequivocal evidence that excessive hydration increases the risk of IPO in both divers and swimmers. Overhydration has an additive effect on the increase in alveolar capillary pressure resulting from immersion. So I strongly advise divers not to overhydrate before diving.”
As you can see this does not state that an extra cup of tea will cause IPO but you can see how a myth could grow from this. It is easy to take the statement “I strongly advise divers not to overhydrate before diving.” and misremember it as “I strongly advise divers not to hydrate before diving.” This advice does not distinguish or give any advice on where is the line between hydration and overhydration? Is that extra cup of tea enough to tip us over the line into overhydration?
To answer the question about the difference between hydration and excessive hydration it worth looking at the article described as ‘unequivocal evidence’ in [5]. This refers to a study carried out on military swimmers.[6] An extract of the study is shown below; “Thirty young men on a military fitness training programme were engaged in a swimming time trial over 2.4 km in the open sea. The sea was calm and the measured water temperature 23°. They swam in the supine position wearing only a bathing suit and using fins. Because of the high heat load expected, the swimmers had been instructed to drink large quantities of water before the swim, to avoid becoming dehydrated. They each drank about five litres of water during the two hours preceding the exercise.”
Five litres (8.8 pints) is a huge volume of water to drink in a two-hour period. For someone who was already well hydrated it could easily put them into a position of hyperhydration. Although it might not be a problem for someone who started out in a dehydrated state. The key point is that there is a big difference between proper hydration and excessive overhydration (hyperhydration). A large glass of water, a 1 litr bottle of water or even a large mug of tea is not excessive overhydration.
Conclusion – Myth or not?
Hydration does indeed seem to be a factor in DCS risk and it seems clear that being properly hydrated is a good thing for health in general and also for diving. Hydration is not be the most important factor in reducing DCS risk but anything that reduces DCS risk at all is a positive thing. Excessive overhydration can increase the risk of IPO but excessive overhydration is not the same as being properly hydrated.
Being properly hydrates gives some advantages in reducing DCS risk and likely does not create undue IPO risk. As in so many areas of life there is a balance. Do not dive while you are excessively dehydrated and do not dive while you are excessively overhydrated. Stick to the Goldilocks zone – not underhydrated, not over hydrated but just right.
How to hydrate
The other conclusion we can draw from this discussion is that educators, scientists, researchers, speakers and writers need to be careful about the impression we create. An article or conference presentation may contain perfectly truthful information but that can be misinterpreted and be seen as promoting a very different conclusion to the one intended. This is exactly how myths develop.
Thank you to Neal Pollock who reviewed several early drafts of this article to ensure that my attempts to explain these concepts in non-scientific language did not lose any of the scientific validity. Any errors or misunderstandings are still down to me.
References
[1] Williams ST, Prior FG, Bryson P. Hematocrit change in tropical scuba divers. Wilderness Environ Med. 2007;18(1):48-53.
[2] Gempp E, Blatteau JE, Pontier J-M, Balestra C, Louge P. Preventive effect of pre-dive hydration on bubble formation in divers. Br. J. Sports Med. 2009;43:224–228.
[3] Fahlman A, Dromsky DM. Dehydration effects on the risk of severe decompression sickness in a swine model. Aviat Space Environ. Med. 2006;77:102–106.
[4] Wang Q, Guerrero F, Theron M. Pre-hydration strongly reduces decompression sickness occurrence after a simulated dive in the rat. Diving Hyperb Med. 2020;50(3):288-291.
[5] https://www.bsac.com/news-and-blog/the-hidden-killer-immersion-pulmonary-oedema-ipo/
[6] Weiler-Ravell D, Shupak A, Goldenberg I, Halpern P, Shoshani O, Hirschhorn G, et al. Pulmonary oedema and haemoptysis induced by strenuous swimming. BMJ. 1995;311:361.
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Excerpts from Jeff Goodman’s Book Action Camera Underwater Video Basics, Part 2 of 6: Underwater Lights & Lighting
Having spent your money on a camera, you may be a little reluctant to spend any more on a lighting system. But believe me, it is worth the investment. Even a small, simple light is going to make a world of difference to your images.
Remember the basic rule with lights, as with everything else, is that you get what you pay for. A small plastic-cased light of low lumen count will cost far less than a large aluminium-cased light of high lumens. A more expensive light should give you more power options, allowing you to choose output strength. This is usually controlled with power button presses: one for full, a second for half power, and a third for quarter power. This gives great flexibility in your lighting when close to a subject, allowing you to balance the power of the light with the camera exposure and ambient light. Lower power output options will also extend battery life. Higher-end devices should also give a wider spread of good, even light without any hot spots. Read the manufacturer’s specifications carefully, and also have a look for advice online from people who have already bought the light you are looking at.
I have talked with many divers who feel that the more powerful the light, the better their video will be. For me, this is not the case. Over-lighting can produce horrible results, especially when you are quite close to the subject. However, powerful lights can be an advantage when lighting large areas from a distance. On the face of it, lighting looks extremely easy. Just put the light on and shoot away. If only it were that simple. Adding artificial light is crucial to getting great underwater video but, at the same time, if done badly, it can totally ruin all your efforts. I would say that no lighting at all is far better than bad lighting.
Early lights were always fitted with a tungsten filament, which was red in colour output. Now most lights use LEDs, which are blue-biased, matching daylight. Surely this new trend is an improvement? Well, yes, it is. One of the first colours to disappear (get absorbed by the water) is red, so it does make sense to put some of that red back into a scene, as with tungsten lights. But a video light will only influence colour as far as its beam travels. So if you add red light onto a fish that is near to you, it may well look good, but the background water or reef will take on a very strange and artificial colour hue. On the other hand, a daylight-balanced light, such as a modern LED one, adds all the colours of the spectrum to the scene. So the subject simply becomes brighter, where the colours are rebalanced, thus closely matching the ambient and distant water colour.
Different camera operators have their own favourite type of light for particular applications. For general filming, my favourite is one of coated metal construction for durability and small in size for manoeuvrability — approximately 15 x 5 cm (6 x 2″) tubular. It has a maximum output of 2,500–3,000 lumens, with a dimming option for half power, a wide beam angle of 120 degrees with no hot spots, and a colour temperature of 6,500K. The following image of a turtle was taken using a single hand-held video light. There is more on lighting in the ‘theory’ chapter.
Lighting
My aim when using artificial illumination is to only raise the exposure level to that of the ambient light and no further. I am not actually lighting a subject; I am simply putting back some colour, balancing the video light with the ambient. Obviously, this only applies to daytime videoing, as at night your light source dominates, dictating exposure. Be careful not to over-light. In my opinion, this is the most common mistake any camera person can make — having a video light that is too bright and/or too close to the subject.
In the second image of pouting, the video light level matches the ambient light level. Areas not touched by my light still look natural. The fish on the right are gently enhanced with added colour, but overall exposure is unaffected — they remain in balance with the background. The light has simply replaced some of the lost colour and detail.
Remember that your video light, depending on its power output, will only have effect up to a certain distance. This is usually a maximum of about 2–3 m (6–10 ft) in daylight and 5–6 m (16–20 ft) at night time. If it reaches further than that, then it is likely too powerful for you to have next to your camera and should be turned down (if that is possible), or held further away by a willing assistant.
The above photos of a sea urchin on a reef are examples of a light that is too close to the subject and then at the correct distance. The resulting ‘hot spot’ in the over-lit image effectively ruins the shot.
NEXT WEEK:
Part 3 of 6 – Buoyancy
Action Camera Underwater Video Basics by Jeff Goodman is available now from DIVEDUP Publications:
https://www.divedup.com/shop/action-camera-underwater-video-basics-the-essential-guide-to-making-underwater-films/
About Jeff Goodman
Jeff is a multiple award-winning freelance TV cameraman/filmmaker and author. Having made both terrestrial and marine films, it is the world’s oceans and their conservation that hold his passion, with over 10,000 dives in his career. Having filmed for international television companies around the world and as author of two books on underwater filming, Jeff is Author/Programme Specialist for the Underwater Action Camera course for the RAID training agency.
Jeff has experienced the rapid advances in technology for diving as well as camera equipment, and has also experienced much of our planet’s marine life. He has witnessed, first-hand, many of the changes that have occurred to the wildlife and environment during that time.
Jeff runs bespoke underwater video and editing workshops for the complete beginner up to the budding professional.
It’s time to catch up with 12-year-old Mia DaPonte, New England’s youngest ever female PADI Master Scuba Diver, in her latest blog for Scubaverse!
It’s still a little too cold to get in the water here in New England. I wish I had a drysuit! To get my ocean fix, I asked my mom to take me and my friends to the Biomes Marine Biology Center.
What is Biomes? It’s a rescue center near my house that’s home to all kinds of ocean animals—and they’re all local! It’s truly awesome to experience. There are so many cool creatures there, like skates, sharks, stingrays, horseshoe crabs, tropical fish, lobsters, seahorses, octopuses, and even some reptiles that were given up by their owners.
Darwin the turtle is always fun to watch. He’s huge and has his own home, but he also gets to wander around the place on his own when he feels like it!
They have lots of touch tanks. I got to touch sharks, turtles, and even hold a horseshoe crab! (There’s a little lip on the side of their shell where you can hold them—but don’t do this without permission! Their gills always need to stay in the water.) I also touched stingrays! They felt slimy but rough at the same time.
One of my favorite things to do is see the octopus and watch it play with the toys in its tank. I always check to see if any seahorses are pregnant and look for the babies when they’re born. The babies are kept in their own tank at first to stay safe, and then moved when they’re big enough.
We got lucky this time—there was a baby skate in a mermaid’s purse that was ready to hatch any day! It was in a special tank with a light. When you press the button, the light turns on so you can see the baby skate moving around inside the purse!
As our visit was ending, the owner, Mark, sat down with us and told us how he started Biomes. When he was 14 years old, he began rescuing sea animals. His love for the ocean started when he was young—just like mine! As he got older, he started a traveling business, bringing animals to classrooms and doing shows. Eventually, he turned it into something bigger, and now Biomes is a huge center full of rescued animals.
He told us that most of the fish and animals are rescued from fishing boats or the cold waters of New England—places where tropical fish wouldn’t survive the winter. They try to rescue babies whenever they can, so they have a better chance of adapting. Darwin the turtle actually hatched in Mark’s hand!
My mom gets a pass to Biomes every year because I love going there so much. There are always new animals to see and feedings to watch. One time, I even got to feed the octopus!
If you ever come to Rhode Island, you have to check out Biomes!
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