Do Dive computer get you bent more than tables?

[Lost Yooper]

Originally posted by blacknet
Hello,

Uhm anymore? Exactly how many times have you been bent anyway? oh and btw prison doesn't count (Just kidding)

Ed

Personally, I consider sub DCS as being "bent". I was getting "bent" (very tired, sluggish, etc.) on every deeper dive I ever did on air and using a computer for deco. All of this was brought to an end when I was introduced to the benefits of helium, deep stops, and slow final ascents by Irvine, JJ, and others. Prior to this, I was going the TDI route where such topics were either taboo or outright ignored. All it took was an open mind to unconventional thought and recognition that some agencies have less-than-admirable interests in mind (IMO, of course ).

Take care.

Mike

 

[Dr Deco]

Dear Aquamore:

There seem to be several questions here. I have not heard any reports that diving with several ascents and descents can cause DCS problems. Most likely, the gas phase is already formed and growing from nuclei. Thus, bubbles are not FORMED from this up and down type of diving (it is not really “adiabatic compression”).

Because the algorithms account for the gas uptake and elimination in these rise-and-fall dives, there is (apparently) adequate tracking of the gas loads. One must keep in mind that this has never been adequately tested in laboratory trials. When gas loads are relatively small (as in recreational diving), the risk of DCS is quite low. Problems are difficult to see. However, when thousands of divers are using a decompression algorithm, one might expect something to appear that would indicate a problem. Since DCS is multifactorial (= has many different variables associated with it), it is sometimes difficult to see the pattern.

I suspect that confusion arises when some divers have different exercise levels on the days before the dive, hydration levels, genetic history (that seems to influence something), exercise levels following the dive itself, maximum oxygen uptake (= level of physical fitness), ascent rates, and gas uptake and elimination rates during the dive.

Some of this is indeterminacy removed in depressurization to altitude but it is difficult to explain everything now – and maybe we never will.

The decompression physiology class discusses all of this, but there is not a solid answer when thousands of divers and involved in thousands of different profiles.

Dr Deco :doctor:

Advanced Decompression Phsiology, June 22-23, 2002
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[Aquamore]

This is from The BSAC recommendations:
-------------><8
"Repeated multiple ascents should be avoided as they may result in decompression illness. Particular care should be taken when carrying out the various ascent training drills, for which specific advice is available.
"Sawtooth" dive profiles which involve repeatedly ascending and re-descending over an uneven bottom should be avoided, but the practice of returning to the surface from maximum depth in stages is encouraged.

It is also good practice to achieve maximum depth as early in the dive as possible and to avoid re-descending once any ascent has commenced.
-------------><8

It makes sense to me as it takes gases under pressure (in this case nitrogen) a long time to saturate the slow tissues but longer to disapate. In the case of saw tooth dive profiles the gases under pressure which are trying to come out of the tissues on ascent never equalise with their ambient pressure before they are 'Pumped up' again by the next descent. Bear in mind they are already above ambient pressure so the saturation of the slow tissues like bone, cartlidge etc. is accellerated beyond what the tables and computer algorythm are designed to calculate.

On another subject, how's NASA? I love the space Industry and I intend to visit Kennedy Space Centre next time I am in the area. I was Operations Supervisor (like Ops Chief) for ESA for 6 years, at their European Space Operations Centre in Darmstadt Germany. We had several Joint Missions with NASA, not the least of which was Cassini Huygens, SOHO, Olympus, and Uylsees.

As for the Deco course you sent the URL for.... it looks extremely interesting but sadly I will be on the wrong side of the Atlantic to be able to attend

I much appreciate your reply and keep up the good work for us lesser beings here on the boards

Aquamore

 

[devjr]

Aquamore, even if there is some minor pumping and storing of nitrogen across the boundaries of slow tissues, what practical effect would it have? The deco computers are already extremely conservative in non deco, deco and repetitive dives. The Genesis Resource allows only 20 minutes at 100 feet compared to the Navy tables maximum of 25 minutes. Taking into account the descent times, the actual bottom times are even less. Isn't this programmed conservatism of the computers an inherent recognition of the variables alluded to by Dr Deco and an attempt to protect the lowest common denominator?

Adiabatic compression? Where is the volume component of the cycle? There is no change in volume that I can see. How then could it be called compression? Are you saying that the body is storing up teeny bubbles during surface intervals and reconstituting and enlarging these on subsequent dives and that the computers are "unaware" of this?


Does any of this have a point?

 

[Dr Deco]

Dear Readers:

This question of rapid descents and ascents has never been checked in laboratory studies to my knowledge. To look into this question, I must appeal to historical data from industry. Caisson operators locked the workers in an out of the pressure environment through the man locks that had inside operators. These individuals were subjected to repeat pressurization and depressurization changes over the course of the day. They did not get “the bends” even though the prevailing thought at the time was that pressure changes forced blood into the trunk from the arms and legs. They thought it surprising that lock operators appeared “immune” since they made the greatest number of pressure excursions per day.

As long as one is in the safe zone (within the table recommendations), the degree of gas phase formation in the body is generally small. If one should perform a dive that makes a major deviation from this, then there is a definite chance that a large volume of free gas phase could form in the diver’s tissues and cause problems during repetitive dives.

It is possible that this could even occur during dives with “undeserved hits.”


Dr Deco

 

[Aquamore]

Thanks for your reply and over the past few weeks I have been trying to locate some conclusive proof based upon research that these rapid changes in pressure (Saw tooth dive profile) and I have concluded the following:

Most SCUBA organisations/associations/federations/institutes agree that Saw-tooth Dive profiles are a bad thing and can bring on the onset of type 2 decompression sicknes quicker
Apart from The BS-AC Safe diving practices I quoted in a previous posting here is further information recognising the subject fro you to consider:
The Reduced Gradient Bubble Model (RGBM) based on crushing Nuclei is the best analysis to show how 'Saw tooth dive profiles', (yo-yo diving), increases the risk of type 2 DCS whilst diving on tables or computer (see link)
http://www.homepages.hetnet.nl/~deep_ocean/index.html?science04.html

NO yo-yo dive profiles is clearly stated in the link below.
http://www.echonet.co.uk/phoenix/proplan.htm

and as a generalisation quote from the link below which looks at both tables and computers
-----------------------><8
They cannot calculate the actual nitrogen load of an individual and do not take into account predisposing environmental factors. In the 1997 DAN data, 93.7% of the divers experiencing DCI were diving within the limits of the computer or table that they were using. This clearly demonstrates that nitrogen buildup is only part of the picture in the risk of DCI. Fast ascent rates, square profile dives, saw-tooth dive profiles and progressively deeper dives during a day all increase the risk of DCI considerably. Also, we know that cold water, exertion in currents and dehydration are just some of the factors that increase the susceptibility to DCI.
-----------------------><8
http://www.divenewzealand.com/54dci.html

It's not enough for me but until proved otherwise I will 'tow the party line'.

Hi Devjr

You asked 'does any of what you you posted have a point'? Well, you will have to answer that yourself!

The change in volume occurs each ascent and descent, (remember Boyles Law), the second compression cycle takes place in the same way radio waves are propagated i.e. the collapsing EM field (in the case of diving the gases trying to disapate on ascent) never quite equalise totally before the next field is set up (this compresses the gas in the tissues again but now ata different rate) This EM field pushes the first one outwards and so the radio wave is radiated (or in the case of divinging the short rapid descent compresses the already compressed gas further).

(((((((EM1 (EM2 (EM3) EM2) EM1)))))))

With regards to your computer and the tables....... if they were so good they would come with a 100% guarantee that you will not get DCS if you use them correctly.

Have you ever seen this guarantee come with a set of tables or a computer? I haven't!

I don't think I said anywhere that the body was storing up micro bubbles during SI! I believe that was your suggestion?

If you want to learn more, check out these links with an open mind like I did.

Regards
Aquamore

 

[devjr]

I read the three links. The following disclaimer by "pro planner" caught my attention:

>>>No 'yo-yo' dive profiles. Recent research indicates that these exaggerated profiles may lead to type 2 DCI even
when the diver is inside the no stop times on the tables<<<<

Should have read: "On advice of counsel, in view of certain claims made in a theoretical paper on the mechanics of bubble formation, we are advising against doing dives which involve going up and down, or down and up where applicable".(G)

Seriously, I do recommend the statements from New Zealand, in particular advising against the practice of following a shallow dive with a deep dive, rather should be the opposite. I learned that from some Mexican divers who had never seen a deco table much less a computer. The safety stop is also good in that it provides a buffer for the divers who may be susceptible due to physical variations.

 

[Aquamore]

I think we are in total agreement about that.

Thanks for the Legalese version of the statement, it was more than amusing, it was also frightening as I see that sort of jargon on a daily basis.

Safe Diving

Aquamore

 

[Dr Deco]

Dear Aquamore:

[1.] I have heard that yo-you dives are not good, but I have never seen any evidence for or against this practice. The comments here underlie the concept that the common assessment of risk based on depth and time at depth does not apply as well to this type of diving.

One possibility for the problem might be the manner in which the dives are done. That means that the divers are descending and then ascending with a considerable amount of physical activity. This will naturally cause an increase in blood flow and gas loading. Since table and computers are designed for moderate activity, the ground rules change in this situation. I am not certain, therefore, that the problem (if there is one) can necessarily be traced to nuclei formation.

[2.] The situation of compression and expansion that you are describing (with the electrical engineering analogy) is referred to as “rectified diffusion” although the time scale for this process is considerable faster than for the yo-you dive. In the world of barophysiology, all things are possible. I am still looking for some good data on this type of diving, however.

Dr Deco
:doctor:

 

[devjr]

You fella's are over my head. Rectified diffusion? Aquamore, I don't understand the EM analogy. An electromagnetic field doesn't "collapse", the wave simply propagates into space. Are you perhaps talking about a collapsing current in an electro-magnetic coil or similar ?