Deeper 2nd dive - why not?

[*Floater*]

Always make repetitives dives to shallower than previous dive. This might be allow you offgas nitrogen on progressively shallower dives and prevent you from carry progressively larger amount if residual nitrogen on deeper repetitives dives.

For a contrary take on the issue have a look at George Irvine's deco articles at http://www.wkpp.org/decompression.htm

His opinion is that you have to be very careful about your ascent on the second dive but:

Otherwise, repetitive diving is a good thing, and you should do your shallower dive first and then your deeper one. The stupidity taught in that regard is beyond the pale.

 

[DandyDon]

Well, I think a waterproof and pressure capable version of the clothespin thingy my physician put over my thumb at my last physical a few weks ago to read my blood O2 content (it shined a red light through my thumb - near IR inferred property technology - something we've been using in the petroleum refining and chemical process industries in certain applications for over 10 years now) could show promise for scuba applications, as well as spinoffs from it for other gases - but trying to infer individual blood chemistry from analysis of open circuit regulator exhaust gas is something I'd see as fraught with way more hurdles from the basic concept.

Sounds cool - let me know when you have a dependable model ready to sell?

 

[WarmWaterDiver]

I'm not a physician / medical person - but the fact that such exist today for above water use is encouraging. Maybe someone like Doc Vikingo could bridge the gap between the above water current medical world and the underwater world of the future for applicability?

Or maybe TS&M? She's a member of the medical community if I remember correctly.

As soon as my new country doc used it and we started chatting about it, it was fairly obvious to me where the technology had sprung from. I've ALWAYS had much better experiences with personal physicians in rural areas than in urban ones - much more willing to discuss stuff with me!

 

[Saturation]

I know you are not "supposed" to go deeper on 2nd - but why not? If the issue is nitrogen loading, then why can't a deeper 2nd dive be off-gassed - just like the first deep dive? Especially with a dive computer that keeps a running total of your nitrogen uptake?

The reason I ask - a friend of mine went deeper on 2nd - and her computer showed no problems with any of her dive profile - but suffered a significant DCS hit. Trying to think of reasons...

Thanks!

Based on the description of the gas loads, its an unexpected hit, she should be checked for a PFO and, if she chooses to dive again, to take specific cautions against inert gas loads.

 

[BeachBumatHeart]

the clothespin thingy my physician put over my thumb at my last physical a few weks ago to read my blood O2 content (it shined a red light through my thumb

That's a pulse oximeter. It measures the amount of oxygen in your bloodstream. It can also be fooled...for example, if your hemoglobin is carrying carbon monoxide, the pulse ox will read it as oxygen. (when in fact the CO is replacing the needed O2 in the blood)

When arterial blood gases are drawn to determine respiratory/metabolic acidosis/alkalosis, the values taken into consideration are pH, bicarbonate and carbon dioxide.

This still has nothing to do with nitrogen loading during a dive.

disclaimer: I'm not a doctor!

 

[Notso_Ken]

That's a pulse oximeter. It measures the amount of oxygen in your bloodstream. It can also be fooled...for example, if your hemoglobin is carrying carbon monoxide, the pulse ox will read it as oxygen. (when in fact the CO is replacing the needed O2 in the blood)

When arterial blood gases are drawn to determine respiratory/metabolic acidosis/alkalosis, the values taken into consideration are pH, bicarbonate and carbon dioxide.

This still has nothing to do with nitrogen loading during a dive.

disclaimer: I'm not a doctor!

I'm not a doctor either, but Bio-chem is what this involves, so I can address it.

BeachBum has it right, it is looking at the color involved. Higher Oxygen cause brighter reds in the hemoglobin. Unfortunately as Beachbum points out, so does CO.

However, N2 does not cause any color change in the blood whether of the hemoglobin or anything else in the blood.

So, no there is currently nothing that can help out here. Now, maybe they could give a clip-in for use on deep dives to track oxygen loading to help avoid oxygen toxicity . . . .


Ken

 

[WarmWaterDiver]

Thanks Notso Ken - we'll keep waiting for technology to progress - if you think there's something where analysis of the exhaled gases can infer blood chemistry of the diver too, set us off that direction!

 

[ArcticDiver]

OK so there seems to be some differing opinions on shallow/deep dive sequence. Using the following scenario are there any increased hazards by doing the shallow dive first?

Diver has made no dives in the last month. Diver is using a familiar and well understood dive computer. First dive is shallow to 40' with most time spent at max depth. Slow ascent with 5 minute safety stop. All times and depths within accepted no decompression limits.

Surface Interval is calculated using the electronic table(dive computer) to allow time for a 20 minute 100 foot dive without exceeeding no decompression limits. This is the second dive of the day.

Diver makes the deep dive and does not exceed NDL. Makes a slow ascent and the diver's usual 5 minute safety stop.

No more dives in that day. No heavy exercise. No bag drags or cylinder shuffles.

My take is that off gasing will occur during the ensuing surface interval.

The diver is in a postion that they cannot go back to a manual table and must stick with the electronic table until they are free of the surface interval obligation. Other than that I haven't found anything in research that would seem to make this dive sequence any more hazardous than doing the dives in a deep first sequence.

Am I missing something?

 

[diverDano]

I'm no expert, but common sense tells me that when you make a reverse profile dive, once you surpass the previous dive depth, you will no longer off gas, but will retain the remaining nitrogen left in the tissues. Thus while keeping that nitrogen content and adding to it with continuing depth, tables are not setup to accomidate all this nitrogen. With a normal profile dive, you will be off gassing the whole dive until the loaded tissues reach an equality with the pressure experienced at the current depth.

 

[ArcticDiver]

I'm no expert, but common sense tells me that when you make a reverse profile dive, once you surpass the previous dive depth, you will no longer off gas, but will retain the remaining nitrogen left in the tissues. Thus while keeping that nitrogen content and adding to it with continuing depth, tables are not setup to accomidate all this nitrogen.

No matter the dive planning tool used certainly whenever the diver goes to the same depth, or deeper than on a previous dive the diver will no longer off gas, but will accumulate more dissolved gases. Your understanding and mine regarding manual tables are the same. The one's we commonly use are limited representations of a complete algorithm. Therefore they cannot accomodate the necessary calculations to safely accomplish a deeper second dive.

With a dive computer not only can more accurate measurements take place a complete algorithm can be used. So, the computer can calculate a surface interval that will take into account retained gases. Thus, the total dissolved gas load at the end of the second dive will not exceed that considered safe.

With a normal profile dive, you will be off gassing the whole dive until the loaded tissues reach an equality with the pressure experienced at the current depth.

Well, my understanding is that this is not exactly accurate. There is still that portion remaining in the slower tissues from the first dive and from that portion of the second dive where pressure differentials duplicate those of the first dive.


Me, I'm not a decompression expert either. I'm just a guy with a decent amount of education who knows how to do research. Then to apply that science to the art we call diving. In that respect I haven't found any research, including the guinea pigs, that duplicated the conditions in this scenario, which is a comon one.