Difference between MB levels and Gradient Factors

[L13]

Or at least you would, if you knew the old risk.

There is a lot of risk data available in the the research to date that can be used to evaluate algorithms. See @scubadada 's post for one attempt at that.

Which IIRC is mentioned in the DSAT report and possibly may be mentioned in Tauchmedizin but I don't read German. If anyone knows what it is for various flavours of RGBM or PZ+, I never heard them tell teh rest of us. Ditto for various GF settings on top of ZH-L16.

As it is, IRL this is mostly the matter of trust. You trust ZH-L16+GF85: good on yah.

Interesting that you think research and data are less important than trust.

I don't "trust" either one. I know neither one of them is ideal.

Better to understand them and evaluate their relationship to the body of data available and then use (not trust) one. Understand the multi-tissue super saturation models. Understand the bubble models (which also use multi-tissue super saturations). ZH-L16+GFs makes that easier by not being proprietary.

In conjunction with the proprietary obscurity, ADT+MB recommends deep stops which are contra-indicated by the data. It's other enhancements likely are good, but difficult to evaluate. But research, not trust, indicates that it is sub-optimal because of it's deep stop recommendations.

He trusts ADT+MB: good for him.

You are likely right about that. From his bluster, it appears that his position is all trust and brand loyalty.

 

[scubadada]

Hi @L13

I did not mention microbubble (MB) adjustment or profile dependent intermediate stop (PDIS) in my post #148 on human factors. The MB setting has 10 options from 0 (none) to 9 (highest). If you have a setting above 0 and skip the stops, the algorithm simply decreases the MB setting to as low as 0 without penalty. I understand the theory but know nothing about the details of the MB setting. The PDIS is shallower than the customary recreational dive deep stop at a depth where the leading compartment is just off gassing with a low gradient. I don't know that a benefit has been demonstrated.

So, @ChrisDee stated that he found SurfGF and GF overly complicated. You dive with the G2 and modify its underlying algorithm with the choice of MB level, PDIS, HR monitoring, breathing monitoring, and skin temperature monitoring. If I was to dive a G2, I would be tempted to dive it with the native algorithm, without alteration, as I understand it is moderate or middle of the road in the spectrum form conservative to liberal.

 

[scubadada]

The broken link from the G2 manual was previously given by @ChrisDee
SCUBAPRO - Heart Rate Monitoring & Diving
This is a primer in HR and exercise, including diving, but gives no insight into how HR is used to alter the Scubapro deco algorithm.

From the manual "If Galileo detects a sufficient increase in workload, no-stop times can suddenly shorten and decompression stops can quickly grow."

 

[Wibble]

Struggling to square this circle:

1. Diving is relaxing; deco is relaxing; the more relaxed you are, the less gas you use
2. Heart rate monitoring

Shirley #2 isn't necessary?!?

Would expect heart rate monitoring to be important for triathlon/whatever. But not diving.

 

[Belzelbub]

Struggling to square this circle:

1. Diving is relaxing; deco is relaxing; the more relaxed you are, the less gas you use
2. Heart rate monitoring

Shirley #2 isn't necessary?!?

Would expect heart rate monitoring to be important for triathlon/whatever. But not diving.

Depends a lot on the type of dive. Most of my dives involve some type of “work.” I just checked a few dives where I wore my Garmin to see where my heart rate was. It was definitely below my exercise heart rate, but certainly above my resting heart rate. Still, though, I don’t believe it makes enough difference to necessitate altering the algorithm to compensate. If it were, I’d expect we’d see more DCs starting to use it.

 

[boulderjohn]

Would expect heart rate monitoring to be important for triathlon/whatever. But not diving.

Heart rate in itself is not usually a major indicator of anything. Mine used to be fairly steady in the low 40's, and I had to work to get it to 60, which is lower than most people's starting rate. Many people start well over 80, I have to be working very hard to get to that rate.

The important factor is perfusion--the flow of blood through the tissues. Differences really only become an issue on longer dives, particularly decompression dives. If a diver is actively swimming during the deepest part of the dive, then the perfusion will increase and the rate of on-gassing will increase as a result. If the diver then goes through an extended period of calm during decompression, the perfusion will decrease and the rate of off-gassing will decrease. This effect will be impacted by temperature differences as well.

As a result, many decompression divers will not hang motionless during the last deco stops but will instead participate in some form of mild exercise to increase perfusion.

The NEDU study had all participants equally active throughout to minimize that difference.

This is less likely to have much of an effect on a shorter NDL dive.

So there is a theoretical effect, but I know of no study that has measured it, at least to the degree that it could become part of an algorithm. That is why I have repeatedly asked for the research behind this factor int he G2 algorithm--to my knowledge, there isn't any.

 

[Belzelbub]

Heart rate in itself is not usually a major indicator of anything. Mine used to be fairly steady in the low 40's, and I had to work to get it to 60, which is lower than most people's starting rate. Many people start well over 80, I have to be working very hard to get to that rate.

Sounds like bradycardia. An instructor/friend of mine has this. His resting heartrate is often in the low 40’s. He mentioned it only caused him an issue/annoyance when he was in the army. Before the head Dr. would sign off on his physical results, he would often be called back, then the doc would just see him, realize he was fairly fit and sign off.

The important factor is perfusion--the flow of blood through the tissues. Differences really only become an issue on longer dives, particularly decompression dives. If a diver is actively swimming during the deepest part of the dive, then the perfusion will increase and the rate of on-gassing will increase as a result. If the diver then goes through an extended period of calm during decompression, the perfusion will decrease and the rate of off-gassing will decrease. This effect will be impacted by temperature differences as well.

Thanks for this explanation. I was wondering how bradycardia could affect off-gassing or on-gassing. This explanation makes sense, and is definitely something I’ll keep in mind (though I don’t have bradycardia, resting HR in low 60s) when I’m at a stop after a dive with mild deco, or at least close to the NDL.

 

[Wibble]

Mild exercise whilst at decompression is unlikely to have any affect on heart rate. For example slow swimming around a shot line/SMB; you cannot swim far from the marker line/trapeze unless you tow it around. More exercise means more oxygen metabolism, more CO2 production thus more gas consumption and scrubber use (for CCR).

In any case the decompression algorithms— Bulhmann— don’t factor in exercise therefore there is no benefit.

If the proprietary algorithm is adjusted for exercise then there needs to be a LOT more research into the affects including double blind trials and searching for "limits" where bends occur.

I am damned if I’d take part in that research as some diving lab rat. Bulhmann works and has been confirmed over millions of dives. If it means I do too much deco then I’m fine with that as I know I don’t get bent.

Doing less decompression just so a company can sell tech-rich products and proprietary algorithms is not something I am remotely interested in.

 

[JMarc]

In any case the decompression algorithms— Bulhmann— don’t factor in exercise therefore there is no benefit.

That's a strange affirmation.

 

[Wibble]

Kind of back to basics. There's a normal distribution of "bends" following a decompression dive.

Bulhmann + gradient factors is a way of moving the point on the normal distribution curve such that it's very unlikely that someone would be bent if following the algorithm AND are a normal fitness diver (e.g. no PFO).

Example lifted from Wikipedia.

Bulhmann would put the arrow such that most people aren't bent.

Playing with heart rates, and other proprietary factors, would attempt to shorten the decompression time, which is fine if the measurements and algorithm works. Otherwise what's the point of fiddling with the decompression time?