Enhanced air...does it help fatigue?

[MaxBottomtime]

How do you account for the divers who don't feel any different?

 

[agilis]

How do you account for the divers who don't feel any different?

For one thing, they may be using nitrox to extend their bottom time instead of using more conservative air calculations while breathing nitrox and keeping a healthy distance from even those limits applicable to air. In addition, everyone's physiological reactions are different, and dives can be as infinitely variable as divers.

In any case, I'm not attempting to establish any kind of generalizable principle and consequently don't have to account for other people's experience. I'm only noting what I've experienced, acknowledging that it is my subjective impression, based on a consistent positive effect.

 

[MaxBottomtime]

---------- Post added December 13th, 2015 at 10:16 PM ----------

 

[DevonDiver]

Perhaps I'm missing something, but if the same person dives the same profile on enriched vs air they will have absorbed less nitrogen. Depending upon their specific physiology and thus susceptibility to DCS stress they could feel less fatigued.

This is true, of course; for a given dive of X depth and Y time, the diver absorbs less nitrogen using nitrox compared to air.

If the dive parameters were different, i.e. a given dive of X depth, but time was NDL-5 min, then the nitrogen absorption would be equal.

That, however, only covers one issue - the amount of nitrogen absorbed. On-gassing isn't the problem. Off-gassing is the problem.

Simplistically, decompression stress is a product of 3 factors;

1. The amount of nitrogen absorbed (volume on-gassing).
2. The amount of nitrogen released (volume off-gassing).
3. The efficiency of nitrogen release (bubble formation).

It is wrong to consider nitrox use and decompression stress only in relation to #1, but ignore #2 and #3.

The amount of nitrogen released (#2) is primarily effected by the time taken to ascend to the surface. On no-stop (NDL) dives, our tables or computers keep us within saturation parameters that allow sufficient nitrogen to be released providing a maximum ascent speed limit is not broken. That is, sufficient nitrogen release to prevent Decompression Sickness (DCS)...i.e. ambulances, hospitals, calls to DAN and chamber rides... That is all.

Historically, the calculations used by our decompression tools were formulated to reduce incidence of decompression sickness, not decompression stress.

The calculations were refined over time against a statistical sample of dives, of which X didn't result in DCS and Y did result in DCS. Once 'Y' was within reasonably acceptable statistical parameters, they were deemed 'safe'. Only more recently did doppler ultrasound and 'bubble scoring' (counting bubble frequency and size inside test divers) become a refinement to these calculations. this led to more conservative dives and also to strategies like deep stops.

In the light of this, let's consider factor #3.... the 'efficiency' of nitrogen release. Think back on how we are taught to ascend from dives.

Most of us are taught to ascend directly to the surface at a single speed no faster than 18m/60ft (PADI) or 9m/30ft (the rest) per min. We are recommended to complete a single 'safety' stop at 5m/15ft for 3min.... simplistic, but it helps provide a cushion against decompression sickness.

If we stay within those parameters and don't end up in a recompression chamber it is satisfactory. If do end up in a chamber, assuming no other causal factors, then it is deemed 'non-blameworthy' or 'unattributed' DCS.

The incidence of divers suffering post-dive lethargy, malaise, fatigue, sleepiness and reduced vitality is totally ignored.

However, not everyone teaches so simplistically. Some agencies/instructors provide more training and, consequently, deem their students more capable of achieving more complex and refined ascent strategies. They specify varying ascent speeds at different phases of the ascent, multiple 'safety' stops..... even the use of optimal ascent gasses.

For instance; ANDI teaches multiple 'safety' stops at 9m/30ft (1 min), 6m/20ft (2 min) and 3m/10ft (2 min). Ascent speeds are 9m per min until 9m, then 3m per min thereafter. For advanced recreational (i.e. 'deep') divers, they also teach the use of 50% nitrox as an ascent gas for safety and 'conservatism'.

Example:



These refinements go well beyond simply 'avoiding DCS'. They can be considered from two perspectives. Firstly, they provide a much wider safety margin against clinical DCS incidence. Secondly, and important for this discussion, they dramatically reduce microbubble incidence; lowering decompression stress. The result: divers aren't unnaturally fatigued post-dive!

So... back to the original issue... the benefits of nitrox.

Nitrox is beneficial for TWO reasons. We are generally only taught one of them.

We know that using nitrox reduces nitrogen absorption compared to air. This can be used to allow either longer no-stop (NDL) dives or to achieve a more conservative dive (less nitrogen absorption) given identical depth/time parameters.

What we aren't generally educated about (at least, until technical diving levels) is that nitrox also maximizes the efficiency of our off-gassing. It 'accelerates' our decompression. It helps remove nitrogen from our bodies at a faster rate. There's no magical barrier between recreational 'nitrox' and technical 'deco gasses'. Simply put, the higher the % O2, the more we accelerate the process of expelling nitrogen from our bodies. Nitrox 32% is higher than Nitrox 21% (air).

Here is a simplistic table showing off-gassing efficiency ratios:



We can see that the ratios for 'recreational nitrox' mixes compared to air:

EANx32 is 16% more efficient in off-gassing nitrogen.
EANx36 is 21% more efficient in off-gassing nitrogen.
EANx40 is 26% more efficient in off-gassing nitrogen.

Just because we don't 'gas switch' onto a different 'deco gas' doesn't mean that the nitrox we breathed throughout the dive is less efficient in accelerating off-gassing.

So.... we can see that for a given ascent and safety stop, nitrox will also remove more nitrogen than air does.

Using nitrox isn't just about absorbing less nitrogen for a given time/depth; it is also about releasing more nitrogen for a given ascent time/speed.

Combined with slower ascent speeds and increased time/frequency of ascent stops, this plays a major role in eradicating nitrogen microbubbles from the body. It lowers decompression stress - reducing (or preventing) the symptoms of post-dive fatigue, sleepiness and lethargy

Back to my initial point.... considering all three factors effecting decompression stress; nitrox use can provide a significant benefit in all three aspects.

Of course, you'd only notice that benefit if you'd otherwise subject yourself to decompression stress. If you don't, then you won't.

 

[KenGordon]

Diving involves quite a lot of getting up early, moving heavy objects about and sitting or standing while supporting heavy objects. These activities are probably going to increase tiredness compared to getting up late and leaving the heavy objects alone.

I spent a week on a liveaboard a couple of weeks ago. By day three I was going to bed at 8pm and feeling quite tired. I was doing three one hour ish dives with 3 hour surface intervals each day, getting up at 5.30 or 6am.

My buddy was diving 29 to 32% and we never really pushed NDL limits on a Suunto for that. I was diving a rebreather so I was almost always diving a richer mix, and especially during the later shallow portions of the dive was on the equivalent of about 50%, more on stops. My deco stress at surfacing was as low as you could imagine. I was still properly tired.

Earlier in the year I was on a boat where we got to the site, knitted up and then binned the diving due to bad gas. I was just as tired that evening as the previous one.

So I claim that diving at all or high ppo2 makes no significant difference given all the other factors.

Going diving for a day is a busy day of activity with a nice restful bit in the middle when in the water.

Consider also that a very high ppo2 will eventually lead to complications which are not well understood. Perhaps some of that 'stress' might lead to tiredness. Obviously I have no evidence what so ever for that and literally just made it up, it is pure speculation, just like the claims for the benefit of a high ppo2 for tiredness.

I don't mind being tired at the end of the day. It reminds me I have done something that day.

 

[Storker]

I don't mind being tired at the end of the day. It reminds me I have done something that day.

I do other outdoor-related stuff in addition to diving. I'm not a stranger to getting up early and spending a day doing physical stuff. If I get up at five o'clock in the morning, drive for one to two hours, then hike - with a backpack - in conditions that in a typical tourist guide book would be characterized as "strenuous" for some 8-10 hours before driving for one to two hours to get back home, I'm "tired". In a good way. The way I feel after a day of diving - unless I take a lot more care to avoid decompression stress than you learn in OW class - is not the same nice type of tiredness. Call it fatigue, call it lethargy, call it sleepiness, but it's not the same "good" tiredness I feel after a day of physical activity.

As I said earlier in the thread, clinical studies have shown that the amount and duration of microbubbles in the blood stream of asymptomatic divers vary dramatically between individuals. It's no surprise that different people have different physiological reactions to non-DCS decompression stress and thus respond differently to the use of nitrox.

 

[DevonDiver]

How do you account for the divers who don't feel any different?

 

[DevonDiver]

Diving involves quite a lot of getting up early, moving heavy objects about and sitting or standing while supporting heavy objects. These activities are probably going to increase tiredness compared to getting up late and leaving the heavy objects alone.

For some of us that is a normal daily routine.

....and yet, we notice a difference.

... and we don't suffer our lives like zombies either...

Talk to most dive Pros and they'll express a preference for nitrox.

Talk to tech-level pros and they'll regale you with examples on how they manage decompression stress...

 

[KenGordon]

Talk to most dive Pros and they'll express a preference for nitrox.

Talk to tech-level pros and they'll regale you with examples on how they manage decompression stress...

And is that because the don't want to be bent or because of some mysterious unproven benefit of less fatigue?

 

[Storker]

View attachment 221124

You forgot individual variability between divers

clinical studies have shown that the amount and duration of microbubbles in the blood stream of asymptomatic divers vary dramatically between individuals.

I attended a presentation of one such study. The scientists had a number of subjects undergo a 2-hour chamber dive to 18m, followed by decompression according to the Norwegian Navy table (slightly more conservative than the US Navy table; the deco schedule was 5min/6m, 25min/3m). After this, they monitored microbubbles in the subjects' blood stream by ultrasound imaging. The bubble scores were all over the place, from a score¹ of 0 right out of the chamber, to a score of 3+ for more than two hours post-dive.

¹ A semi-quantitative scale that goes from 0 (no bubbles) to 4.