Deep stops and ascents...

[The Chairman]

I fully agree with Lamont on this. Great description.

 

[HilaryRN71]

For typical recreational profiles, it doesnt make a snit of a difference whether you do deep stops or not - no matter how fashionable they may be. I find it a bit funny when I see loads of earnest - and well-meaning divers - doing a deep stop after a 24m doddle along the reef or whatever.

IMO, deep stops in a recreational context make sense when there is a valid risk of the free gas phase posing problems: 3 or more dives (especially 2 or more deep dives) in a day, reverse profiles, yo-yo dives or such. Otherwise, a normal slow ascent followed by a safety stop works well enough.



Vandit

I think there are a couple of scenarios one might consider before making a blanket statement. For one thing, YOU, as an observer of ME doing a deep stop (half max depth for 1.5-2 minutes) at 24 m/ 78 fsw, have no idea what is behind my rationale. Thus snickering seems a bit uncalled for. Maybe I'm considering doing deep training and think it's a good idea to practice this on EVERY dive. Maybe I just lost a friend to DCS and this is my first dive back in the water and I'm being extra safe. Maybe it's my 18th day of a dive vacation and I just want the extra off-gas time. The point is...you don't know. And if it's well-intentioned and a safe practice and it makes me FEEL better...then what's the problem? Once upon a time, you were a new diver also, and trying out different techniques and styles. Example...when I got my drysuit..I was TERRIFIED of free ascents and safety stops. I had this vision of me looking like a puffer fish rocketing to the surface. So I did EVERY ascent from a shallower depth as a free ascent just so I could do it if (and when, as it turns out) it was a necessity. If I had only gone to 24 feet, I still did a safety stop just for the practice.

When I finished OW and even AOW, deep stops had not yet come into fashion. Also, as I suspect is the case with most PADI open water and even AOW students, I had not been taught enough about the physiological aspects of bubbles formation to even understand alot about the purpose of a safety stop, other than "Stop at 15 feet for 3 minutes." While I am not a currently a trimix or technical diver, nor would I claim to be a plethora of decompression knowledge, continued dive education and training , both topside and below the water, has furthered my understanding of Boyle's law. And I don't believe that a deep stop after a depth of 78 feet would be of no benefit. I think it's actually a safe practice. The ata pressure difference between 78 fsw and 80 fsw is really pretty minimal. It slows ascents overall, gives a diver confidence and experience while hanging in blue water, and does give them an extra couple of minutes to off-gas.

 

[Charlie99]

Your #1, by your description, was probably just post-dive fatigue since a nap took care of it and there were no other reported symptoms.

Look at the analogy of sunburn and just general weather exposure. Both are stresses on the body. There is a continuum in effects from nothing at all, up through mild sunburn / mild symptoms and fatigue from too much wind and cold, up through full blown medical emergencies. Decompression also stresses the body. In most cases it is a mild stress (even though in a high percentage of repetitive dives DANs doppler testing shows that there is significant venous bubbling) and not classified as DCS. It isn't difficult or unreasonble to expect that there would also be a continuum from zero effects all the way up through severe DCS.

I have had a few dives where I felt more fatigued than normal afterwards. One, for example, was where severe surge repeatedly took me from 60' to 70' depth and back every few seconds for most of the dive. No real symptoms other than feeling a bit tired.

I also believe that this subclinical fatigue is tied in with the "less tired after nitrox" effect that many divers report. I initially noticed a slight effect like that, but then started doing deep stops and I no longer noticed a difference beween nitrox and air.

Fatigue is subjective and hard to quantify, so it is difficult (but not impossible) to do scientific testing and measurement of fatigue, so all we have to go on at this time are anectdotal reports of many divers. It is, however, independently reported by enough divers that I strongly believe it is accurate.

-------------------------

Before GUE existed, and long before NAUI started promoting deep stops, Richard Pyle, a fish nerd at Bishop Museum in Hawaii, noticed that he felt good after some deep dives, but not so good after others. He correlated it back to whether or not he had captured fish. This puzzled him until he realized that when he caught fish, he would stop for a while around 100' depth and use a hypodermic needle to bleed off some gas from the swim bladders of the fish captured at depth. His findings resulted in "Pyle Stops".

 

[Jeepster]

I do a deep stop of one to two minutes if the dive exceeds 100 ft for more than 5 minutes, especially square profile dives. In addition, when I am on a dive that meets this criteria, I spend a good five minutes or more on my safety stop.

 

[lowwall]

Could you explain please? My understanding and experience doesn't support this statement. After I explain, please educate me.

Fatigue, to me, merely indicates that a person is fatigued, i.e. tired. So when I get to the end of my workout at the gym, I'm fatigued/tired. If, like I'm doing now, I'm doing unaccustomed exercise(working out at 5700' instead of my accustomed 435') I'm unusually fatigued/tired.

So, if I'm just fatigued/tired with no other clinical symptoms how is this an indicator of anything else other than I need to rest and nourish myself? One of the tenets of strength training is to work until the muscles won't respond any more(total fatigue) then rest and nourish so the body can build new and stronger muscle.

I do a 1000+ calorie rowing machine workout several times a week, and I'm never as tired afterwards as I was following two easy warm water dives with a conventional straight ascent with 3 minute safety stop. My wife and I would basically slog our way through lunch and them immediately take a 2 hour nap. This didn't make sense to me as recreational diving should not be so physically fatiguing, we just don't work that hard (unless you are fighting a monster current and burning through your gas in 20 minutes).

The fact that (for my wife and I at least) more time spent at shallower depths reliably resulted in much less fatigue confirmed that the fatigue we were feeling was not just the result of exertion.

So the question remains - what is causing this fatigue? The hypothesis of deep stop proponents is this is actually a sign of sub-clinical DCS. In other words, we are hurting ourselves with straight ascents, just not badly enough enough to require medical attention.

The author has a theory that "may" be true. But while there is some evidence for this among commercial divers there is a paucity of similar evidence among recreational divers. Or, at least that I've been able to find.

Commercial divers are far more frequently studied for various reasons. One of the most important is they tend to have much greater exposure times, so any problems will show up more readily. But your body doesn't know who is paying for a dive, anything a shallow water commercial diver is subject too, we are subject too as well.

Next, you aren't looking very hard. First check the bibliography for the cited article, it's available in full here: http://www.scuba-doc.com/LTE.htm. Note titles like "Central nervous system lesions and cervical disc herniations in amateur divers", "Ocular fundus lesions in sports divers using safe diving practices", "A histopathologic and immunocytochemical study of the spinal cord in amateur and professional divers."

Then a quick Google and Google Scholar search reveals plenty of titles like:

Magnetic Resonance Signal Abnormalities and Neuropsychological Deficits in Elderly Compressed-Air Divers

Cohort study of multiple brain lesions in sport divers: role of a patent foramen ovale

Negative neurofunctional effects of frequency, depth and environment in recreational scuba diving: the Geneva "memory dive" study

Expiratory flow limitation in compressed air divers and oxygen divers

 

[DandyDon]

So the question remains - what is causing this fatigue?

Simple Cowboy answer: I always thought that with N2 existing in the body fluides that usually contain O2, we are Oxygen deprived - leading to exhaustion.

 

[TSandM]

No, Dandy Don. Oxygen is almost completely transported on hemoglobin molecules in the blood. Nitrogen does not compete for those binding sites. Having excess dissolved nitrogen (or bubbles) does not mean reduced oxygen availability to tissues.

 

[H2Andy]

maybe it has to do with the energy that it takes for the body to get rid of
nitrogen when it comes out of solution too fast (but not so fast to cause
symptoms)?

 

[The Chairman]

It's definitely harder to eliminate it Andy, but I think it's a combination of the narcotic effects of nitrogen and the pressure the micro nuclei are putting on the neural pathways. Other than than, elimination of nitrogen is entirely passive.

 

[Fastmarc]

maybe it has to do with the energy that it takes for the body to get rid of
nitrogen when it comes out of solution too fast (but not so fast to cause
symptoms)?

Hmm...
All that I have read so far doesn't suggest that this tranfer is assisted by the body. It is more an action due to the laws of physics.