Has there been any research in reducing nitrogen time?

[hhsuey]

After a dive, we all well know that there is a recovery time before the next dive, calculated by tables or our dive computers. Also, we shouldn't fly within certain hours after a dive.

Aside from the algorithms that are behind these calculations, has anyone found any research into whether there are other variables that may affect the durations of these recovery times? For instance, how would exercising and sleeping after a dive affect recovery time? Would there be any benefit in visiting an oxygen bar after diving? Do dramatic differences in heart rate and blood pressure in Olympic athletes affect nitrogen elimination? Etc...

I am a beginner diver but I am curious about the science and health issues related to decompression sickness, partially because I don't remember seeing too much of it discussed in my open water course and Padi guidebook. I recall the back of the padi dive planner saying that not much was known about the health effects of multi day diving, yet this is exactly what I would hope to do on vacations and liveaboards.

 

[altaskier]

A great resource on dive medicine is Divers Alert Network or DAN, and here are a few web pages of interest:
https://www.diversalertnetwork.org/medical/articles/Are_Tissue_Halftimes_Real
https://www.diversalertnetwork.org/medical/articles/Juggling_Physical_Exercise_and_Diving

Breathing oxygen helps with removing nitrogen, and in fact it is also the standard treatment for divers who may be at risk for decompression illness (DCI). Nitrogen offloading is mainly a diffusion-across-membranes process so my understanding is that blood flow rate is not a big factor so the offloading rate is not helped by exercise. But again, turn to DAN!

The main things to say are these:
1. If you dive within table and/or computer limits, and make very slow ascents, you have a very low risk of ever experiencing DCI. The statistics suggest once per 3000 dives:
https://www.diversalertnetwork.org/...ence_in_a_Select_Group_of_Recreational_Divers
2. You can further reduce your risk by getting Nitrox certified (air with typically 32% oxygen instead of the usual 21%) for dives of similar-to-air depth and duration. Nitrox costs a few dollars more per tank fill, and you have to then limit your depths to avoid oxygen toxicity; all of this is covered in Nitrox training.
3. People on liveaboards will often do 5 dives per day, and have a blast doing it!
4. Getting DAN insurance is nevertheless a great idea. Plans start at $30/year, whereas a medical evacuation and decompression chamber ride can easily cost more than $10K.

 

[hhsuey]

Thanks for the links. Those were really interesting.

The general thought seems to be that there can be many factors contributing to a half time of dissolved nitrogen in the blood, and more factors that affect the formation of nitrogen bubbles. Unfortunately, no interventions were mentioned that could definitively shorten or lengthen the total recovery time needed. For example, exercise may help blood flow, transporting nitrogen to the lungs for offgasing, but exercise also increases joint loading, which is associated with bubble formation, directly contributing to DCS.

 

[Mr Carcharodon]

Michael Powell did a study that showed that post dive exercise increased bubble scores. Increased blood flow should speed up the time constants of the tissues getting the blood and that seems to be what happens. Bubble scores however do not equal DCS at least below a critical threshold. So exercise likely would be OK below a threshold, but where that is unknown. The problem is that DCS is relatively rare so it is hard to do a study with a reasonable number of subjects and discern the difference between two small numbers.

Oxygen is helpful both because you are not breathing nitrogen and because it changes the pressure gradient on the venous side of circulation. That happens because oxygen is converted to carbon dioxide which is much more soluble than nitrogen (40x?). Again there are not a lot of studies but as rule of thumb it is thought to double the rate of decompression. Rubicon and Journal of Applied Physiology are good places to look for information.

 

[DevonDiver]

I know some technical divers who approximate a 1hour reduction in no-fly time for every extra 10 minutes spent breathing 100% on the final stop. Never seen any research to support that, but it sounds a plausible approach. I've never [needed to] try it myself.

 

[SailNaked]

the reason you will only find theories on this subject is that there is no way yet to measure the amount of nitrogen loading in the body, so we have no real idea about one person to the next. all of our information is based on experimentation and so far we do not have a large enough sampling of Olympic athletes that dive to know if they are better or not at off loading nitrogen. unfortunately, we are still assuming we understand the process and the fact that we use a computer to calculate a guess is a little amusing to me.

 

[Lorenzoid]

As pointed out, there have been studies about the effects of exercise, both pre and post-dive, but from what I've read there is nothing conclusive enough or significant enough that it makes sense for divers to modify their exercise habits. I mean, most of us have the intuitive sense that doing strenuous cardiovascular exercise just before or just after a dive is probably not normal.

 

[nimoh]

Michael Powell did a study that showed that post dive exercise increased bubble scores. Increased blood flow should speed up the time constants of the tissues getting the blood and that seems to be what happens. Bubble scores however do not equal DCS at least below a critical threshold. So exercise likely would be OK below a threshold, but where that is unknown. The problem is that DCS is relatively rare so it is hard to do a study with a reasonable number of subjects and discern the difference between two small numbers.

Oxygen is helpful both because you are not breathing nitrogen and because it changes the pressure gradient on the venous side of circulation. That happens because oxygen is converted to carbon dioxide which is much more soluble than nitrogen (40x?). Again there are not a lot of studies but as rule of thumb it is thought to double the rate of decompression. Rubicon and Journal of Applied Physiology are good places to look for information.

I will add that there is a great book on the subject by Mark Powell (not the same person) called Deco For Divers. In it, he breaks down decompression theory so that those (like me) that are new to it, can better understand it.

 

[dreamdive]

As pointed out, there have been studies about the effects of exercise, both pre and post-dive, but from what I've read there is nothing conclusive enough or significant enough that it makes sense for divers to modify their exercise habits. I mean, most of us have the intuitive sense that doing strenuous cardiovascular exercise just before or just after a dive is probably not normal.

Actually there have been quite a few studies involving pre- intra- and post-excercise and diving. Not specifically to N2 loading, but DCS incidence. There is very good evidence that pre-dive exercise and intra-dive exercise (during your deco) will reduce the risk of DCS via differing pathways. There is one recent study that actually showed a reduction of DCS risk post-dive, but the majority of studies contradict it (would not recommend it).

Another way to reduce N2 loading (if that is all that you are interested in rather than reduction of DCS from N2 loading) is adding helium. Helium is much more soluble than N2 and thus many dive computers will give you a Helium "penalty" for that. Helium is also very expensive and we use it for deep dives only.

Your hydration status may also play a role in reduction of DCS. Although a lot of people support pre-dive hydration, what research seems to indicate is that POST-dive hydration to be more important. This is often overlooked and post-dive a lot of recreational divers head to the bar for some alcohol (which may dehydrate you further) than rehydrating first.

Your thermal status is another one: A large Navy study showed that divers who were cold during descent and bottom time but were warm during ascent and deco, had the best DCS outcome. The idea being that you have less gas loading during the bottom time and due to inreased perfusion on ascend, get more favorable off-gassing.

Regards,

Claudia R

 

[Lorenzoid]

Actually there have been quite a few studies involving pre- intra- and post-excercise and diving. Not specifically to N2 loading, but DCS incidence. There is very good evidence that pre-dive exercise and intra-dive exercise (during your deco) will reduce the risk of DCS via differing pathways. There is one recent study that actually showed a reduction of DCS risk post-dive, but the majority of studies contradict it (would not recommend it).

I didn't want to confuse the OP, who refers to himself as a beginner diver. From what I understand about the studies (which I admittedly haven't read but only know through second-hand interpretation), they've found a correlation but don't conclude with specificity exactly how much exercise and exactly how long before or after a dive would be beneficial. They've found some parameters that seemed to be beneficial, but is it safe to say we all should adopt it for all our dives no matter the profile or other factors? If I understand correctly, depending on the timing of the exercise relative to the dive and level of intensity, it's believed that exercise could reduce or increase the likelihood of DCS. What I distilled from all of this is that the exact parameters are just not well enough established that most of us should be mucking about with exercise in conjunction with our dives, as we could inadvertently do something detrimental to ourselves. Until the dive community, certification agencies, DAN, etc., come to some kind of consensus, I think adopting some kind of exercise pattern in conjunction with our dives is not a good idea for most of us. That's all I was trying to say to the OP. I'm sure you're more knowledgeable of the literature than I am.