"Marrioni"-style ascent questions

[BigTuna]

A DAN-Europe paper by Marrioni et al (https://www.daneurope.org/eng/whatascent2.pdf [thanks for the reference, Charlie]) reports results of an experiment aimed at reducing DCS rates by planning ascents so as to manage bubbling in neurological spinal tissue. A motivation for the experiment is the observation that about 2/3 of DCS cases seem to involve the spinal cord, which has a tissue half time of 12.5 min. The experiment involved a series of dives to about 80 feet. The context is non-technical, recreational diving on air.

The main finding of the paper is that introduction of a deep stop to ascents significantly reduced bubbles and gas tensions in tissues that have half times of 5 and 10 minutes.

I'd like to hypothesize what I'll call a "Marrioni"-style ascent profile consistent with the best profiles reported in the paper: 30 fpm ascent rate, 5 min deep stop, and 5 min safety stop. The total ascent time needs to be comparable to that of neurological tissue, or about 12 minutes.

Some questions for the deco experts out there:

ABOUT THE PROFILE...
- What's your opinion about the profile I've hypothesized?
- How would you design an optimal Marrioni-style ascent for recreational dives, and when might you use it?

ABOUT THE DEEP STOP...
- How deep should the deep stop be? Marroni doesn't specify this, having selected a specific depth for a specific dive depth. A good choice would seem to be 1/2 the dive's maximum depth. This would seem to put it somewhat above the depth at which off-gassing starts.
- Presumably, deep stops would add most value for dives to depths where the fast tissues are taxed significantly, which would be dives below 60 to 80 feet, or thereabouts. Is this a reasonable presumption?
- How long should a deep stop be? It would seem that less time is needed the less the fast tissues are taxed.

 

[Dr Deco]

Hello BigTuna:

Deep Stops

There has been considerable discussion over the past decade about slow ascents and deep stops. As often occurs in science, one person will intimate the discovery of this and another group who claims that history proves otherwise will counter this. For example, the RGBM incorporates microbubble control and advocates deep stops. The DAN contingent claims that JS Haldane originally advocated these.

In a sense, it makes little difference, since two scientists can independently discover something, and the credit is accorded to both. A small battle ensues.

Currently DAN is interested in deep stops and neurological DCS. There is an apparent preponderance of neurological DCS over joint-pain DCS. Personally, I believe the problem lies with a gross under reporting of joint pain DCS or “the bends” by recreational divers. Many recreational divers simply do not recognize the mild pains of DCS. It is very difficult for active divers in the field to know whether the problem arises from excessive movement or gas loads. Laboratory subjects are monitored and queried at regular intervals to determine true DCS pain, however mild it might be.

Models

The question of slow ascents and deep stops is connected with the transformation of tissue micronuclei into decompression bubbles. The answer is not to be found in analysis of tissue gas loads. Mathematical models do not currently provide the total answer since these are dependent upon nuclei size/number distribution and surface tension. Both quantities are not known.

Nuclei Generation

There are two competing camps out there at the moment:
- One considers that tissue micronuclei are present in the body in a roughly steady state distribution.
- The other [espoused by me and familiar to readers of SCUBA BOARD ] is nuclei are generated by musculoskeletal activity and are greatly influenced in their number by diving practice. Thus boarding the boat with heavy gear or excessive activity on board will result in nuclei generation and/or growth and possible lead to DCS problems.

Marroni Study

Without question, you want to eliminate dissolved nitrogen during the ascent. The reduction in the number total tissue bubbles – and a high Laplace pressure from a tiny bubble – will foster the elimination through capillaries and prevent trapping of gaseous nitrogen in tissues. Upon reaching the surface, even strenuous activity would nit produce lasting nuclei if there was no super saturation at all.

The study addressed the formation of bubbles by the addition of stops. The implication is that the Doppler bubbles were related to the number of bubbles in spinal cord tissue. This may or may not be true, but it is not proven so. [Actually one study showed that bubbles do not correlate with short deep dives; these are most associated with spinal cord DCS. REFERENCE below]

Certainly, deep stops reduced Doppler bubbles (mostly from fat and muscle tissue) and this would bode well for joint-pain DCS.

Bottom Line

I would perform both the deep stops and refrain from straining and lifting topside.

Dr Deco :doctor:

References :book3:

Bayne CG, Hunt WS, Johanson DC, Flynn ET, Weathersby PK. Doppler bubble detection and decompression sickness: a prospective clinical trial. Undersea Biomed Res. 1985 Sep;12(3):327-32.

Decompression sickness in human beings exposed to high ambient pressure is thought to follow from gas bubble formation and growth in the body during return to low pressure. Detection of Doppler-shifted ultrasonic reflections in major blood vessels has been promoted as a noninvasive and sensitive indicator of the imminence of decompression sickness. We have conducted a double-blind, prospective clinical trial of Doppler ultrasonic bubble detection in simulated
diving using 83 men, of whom 8 were stricken and treated for the clinical disease. Diagnosis based only on the Doppler signals had no correlation with clinical diagnosis. Bubble scores were only slightly higher in the stricken group. The Doppler technique does not appear to be of diagnostic value in the absence of other clinical information.

 

[homo maris]

Dr. Deco:

Thanks for the very informative explanation. Your position on micronulei is consistent with what I have read in Exercise Fizzy-ology and Exercise and decompression sickness: a matter of intensity and timing.

However, I also read that aerobic exercise before diving (at least 24hr) seems to have a beneficial effect according to "Aerobic exercise before diving reduces venous gas bubble formation in humans", "Exercise and nitric oxide prevent bubble formation: a novel approach to the prevention of decompression sickness?" and "NOS inhibition increases bubble formation and reduces survival in sedentary but not exercised rats".

I would like to hear your opinion about these findings as i am not a doctor but you are.

So far, my layperson's research has lead me to draw the following diagram on my slate for NDL dives. I use it to explain to my buddy what the plan is and also to let them know that I will dive the plan (e.g. stop 5 min at 1/2 max. depth) .

What do you think about it? What would you add to make it better?

DIVE PLAN
DESCEND to max depth ___
RELAX
ASCENT 10m/33ft per Minute
STOP 5 Min @ 1/2 max. depth w/ mild swimming
STOP 5 Minutes @ 5m/15ft w/ mild swimming
SLOW ASCENT to surface for 30 seconds
DO NOT EXERCISE

Thanks,
JL

 

[Kendall Raine]

It's hardly appropriate to offer DAN credit for doing more than coming around some 30 years late to acceptance of the efficacy of deep stops in reducing Doppler scores. Brian Hills, who recently passed away, made this the subject of his doctoral thesis in the mid-60's. His paper used observations of pearl divers in the Torres Straight who seemed generally uneffected by profiles well off the Haldanean chart. They used deep stops. They also never heard of DAN. David Yount and Bruce Weinke produced useful models to compute deco profiles employing deep stops well over a decade ago.