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Great point Rick, you should see me on ascents, Nudibranch move faster! The agencies teach a 60ft/min ascent rate, computer's prefer differing ascent rates between 30-40ft/min, I personally never let my computer's ascent rate indicator's get into even the yellow. Moderation and caution is the key. Remember you can get hit whether it's deserved or not... you're better off on the side of conservatism though...

Mario :D
 
Cool post rick :)
Yes nitrogen is relatively unreactive physiologically i.e. at normal temperatures and pressures. However we arnt talking about normal pressures here. Indeed nitrogen can form bubbles in a divers capillaries or/and veins due to high pressures and as you probably already know, thses bubbles physically puch on nerves in their body. Also acording to L.Martin M.D. author of Scuba Diving Explained -
(http://www.mtsinai.org/pulmonary/books/scuba/sectiong.htm )

"bubbles can also cause some chemical reactions in the blood which are harmful to the body"

I find it intresting. If anyone at all has any sites on nitrogen interaction (at the chemical and molecular level) i would be gratefull.

 
Infact why isnt trimix more widely available for recreational divers? Is it because it would encourage some divers to go deeper? I know that there are also problems with trimix but if used at the current recrational depths wouldt it be safer than risking DCS everytime we dive?
 
Trimix is expensive, a pain in the tail to mix and test, and requires extensive training for safe use.
Rick
 
Hello LoCz and readers:

Christmas season has not allowed for much time for posting by me on the Forum.

The question of nitrogen and blood was examined on an earlier posting (you may need to open the posts for several months). There is not any good indication that this occurs to any deleterious effect.

The reply by Rick indicates the complications of gas bubble formation and nitrogen uptake and elimination. Unfortunately, I do not have the necessary time to cover this at this moment – but I will be back with an answer!

HAPPY HOLIDAYS !!!

Dr. Deco

More on this topic was posted on 12-28-2000 in this thread....
:idea:

[Edited by Dr Deco on 12-28-2000 at 11:51 AM]
 
LoCz,
Trimix is a whole nother bag of worms, you won't even be accepted into an entry level trimix course without a couple of hundred dives under your belt...

Trimix has a much greater margin of error due to it's complexity, and doesn't have anything to do with not getting you bent... you can still take a DCS hit on Trimix.

Mario :D
 
Dear LoCz:

You have asked some big questions here when it concerns the activities of nitrogen in the body. While it does not react under conditions encountered in the body, it does present problems for the diver. Nitrogen, as is true of all gases, is soluble in the fluids of the body.

We cannot breathe pure oxygen because of its toxicity at pressure. Additionally, the muscles of the chest are not strong enough to expand the chest cavity against the pressure, so it is necessary to have assistance with breathing underwater. Hence, we are required to breathe a pressurized gas. This is either nitrogen or helium, both are soluble, and they come out of solution when the pressure is reduced.

The question is what are the necessary conditions for the formation of gas bubbles. Surprising as it may seem, bubbles do not easily form in liquids. This is true whether you are depressurizing a carbonated beverage or you have a liquid near the boiling point. It is necessary for the liquid to tear such that a void can form. This is not easy to do in a liquid, and there is a resistance for this to occur. Consequently, bubble formation should be a rare event. Unfortunately, small micronuclei (= microbubbles) exist in all liquids and serve as “seeds” for the growth of decompression bubbles (or bubbles in a boiling liquid). It is a fact of nature that liquids that move contain micronuclei. The fluids in our bodies move, and, we too have nuclei.

The question for SCUBA and decompression is how many nuclei are there in a given volume of tissue, how easily do they form, and how long do they last? In general, they form and resolve to produce a steady-state concentration. Dive tables are derived (in theory) to work successful for the individual that produces the most nuclei on their worst day. However, as you might guess, you will never find the worst diver on their worst day (except when the DM gives you that unexpected dive-buddy). Any decompression system could fail at some time or another. Sometimes you are not playing your “A-game” when you dive and may encounter a case of DCS. :boom:

Here at NASA, we are looking into the origin of some of the variablities among individuals. This is because we actually can design decompression schedules (for depress during EVA) on an individual basis. As you might suspect, we have only so many astronauts (as compared to millions of SCUBA divers) and the depressurization scenarios are limited (as contrasted with virtually thousands of profiles between the surface and 130 feet.
 
Thanks Doc. I find this very intresting indeed. Do you know if there are any scientifc papers on the internet on this subject. When you say "nuclei" what are you refering to...cellular nuclei? I have been studying molecular biology for the last 4 years. What i am trying to say is that i would like some more info in the molecular aspect of bubble formation, for example how/why certain tissues (at the cellular level) absorb hardly any nitrogen and why others absorb copiuos amounts. I want to get into the nitty gritty of it all :)
 
LoCz:

[sp]As regards gas exchange, bubble formation, and so forth, I am not aware of any sites on the Internet; others may have some and, I hope will post these on SSN. If you search through some of the postings in this ”Ask Dr. Deco” column, you will find some other material. Please note that you must go way back since the INDEX for the "Dr. Deco" Forums now covers TWO pages.) Much of what I present here is condensed from the scientific literature and placed into a more readable form (at least, I hope it is readable) for recreational divers. :rolleyes:

NUCLEI

When I speak of “nuclei,” , in the case of barophysiology, I am referring to gas bubble micronuclei. These are:
  • formed by movement of fluids (creating low pressure regions) when the body moves;
  • smaller than a red blood cell (0.1 – 2 microns);
  • stabilized for a few hours by large molecules adsorbed on the bubble surface; and
  • grow by the inward diffusion of dissolved nitrogen during the ascent (and surface interval) portion of the dive.
Gas bubble formation at the molecular level is not understood well at all. This is because the internal pressure caused by the surface tension of water is enormous (hundreds of atmospheres of pressure!) when the microbubble is only a few millimicrons in size (one ten thousandth of a red cell diameter). There is no way a bubble of that size could grow under conditions encountered in diving. Therefore scientists have postulated that help is needed for bubbles to form. This help is in the form of low pressure regions in the fluids that help the water “tear” or separate to form “holes.” The low pressures are cause by fluid motion (vortices, for example), and the whole process is termed “stress-assisted nucleation.” Micronuclei (microbubbles) can then be created and be stabilized (for a few hours, anyway) by biomacromolecules. These are the “nuclei” of which I speak.

It is important to remember that not all tissues will produce decompression problem, even when bubbles are present. Thus bubbles in the abdominal fat do not appear to result in DCS (although the fat itself distinguishes one as a “couch potato” which may decrease one’s social standing).


GAS EXCHANGE

Why some tissues absorb more dissolved nitrogen than others do depends on several factors. We could list these as:
  • the perfusion (= blood flow) to the tissue; and
  • the solubility of gas in that tissue.
The perfusion is determined by (1.) the density (number/ tissue volume) of blood capillaries in the tissue (brain > muscle > tendon >> bone) and (2.) the actual flow of blood (determined in part by the heart rate) through each capillary. Additionally, the capillaries can open and close so that, for example, active muscle will have more open capillaries than resting muscle.

The solubility of inert gas will vary from tissue to tissue. A tissue such as bone is mostly minerals and collagen and does not dissolve any gas at all. As the proportion of water in a tissue increases, more nitrogen can dissolve. Thus, much more nitrogen in dissolved by muscle than in bone. Furthermore, as the fraction of lipid (= fats and oils) increases, the nitrogen solubility increases. Thus one will find more nitrogen per volume in adipose (= fat) tissue than in aqueous (= watery) tissue such as muscle.

[sp]This whole business is not easy to follow. :confused: It cannot really be condensed in so short a form. I am considering taking my weekend class Decompression Physiology “on the road” and will let the readers know when and where these will be held. (We cover a considerable range of material; the syllabus for the class is 143 pages.) The material is more understandable with illustrations and longer explanations. Thus anyone with a true, constant, and abiding passion to know the details will have them readily available.
:idea:
Stay tuned!

_________________
[sp]Dr Deco

[Edited by Dr Deco on 12-29-2000 at 11:54 AM]
 

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