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.
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 ones 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.
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]
