The last body part to reach full saturation

[idocsteve]

If I had to guess I'd say it was the top of my head, since that's the last body part to enter the water.

But like I said that's just a guess

 

[scubapeople59]

I'm not a deco expert or a medical expert.
But my guess is less about density and more about blood flow and the physical properties of bones ability to absorb gasses.

That was my thought behind my thinking that the eyes would be the last to absorb the nitrogen. The size of the capillaries. I am not sure that bones have the capability to absorb nitrogen.

 

[fppf]

Yes, they do, there actually very porous.

 

[Dr Deco]

Hello aquapeople59 :

Longest Halftimes

As with many questions, there can be several answers. Let us take a look.

Physiological Halftimes

These would be the uptake and elimination halftimes for tissues. These are determined by blood flow to the tissue. Since all tissues are alive, they require first oxygen and nutrients and second removal of waste products. There are probably not any tissues that would respond adversely to decompression [e.g., pain] if they did not have oxygen and produce CO2. Thus, bone and teeth might take days to absorb nitrogen but it makes little difference. This can be seen from saturation decompression. Ultra long halftimes [greater than 700 minutes] are not real as far as the deleterious effects of decompression are concerned.

Halftimes and Blood Flow

The Haldane halftimes do not correspond to nitrogen exchange rates as predicted by measured blood flows to tissues. The halftimes would be between one minute and fifty minutes from the laboratory values of flows. Thus, what is required in the “black box” algorithm is called halftime but is in reality something else. What that “else” is I do not know.

Tissues

Curiously, short halftimes and DCS, e.g. in the knee, are apparent in short deep dives. They are also apparent in an hour-long dive. The same is true in saturation decompression where the 300-minute compartment is controlling. This cannot all be in the knee [or elbow or shoulder]!

Long Compartments

Those in the hundreds of minutes probably represent a formed gas phase that exchanges slowly. [This is my opinion.]

Dr Deco :doctor:

 

[ImUrPropofol]

Would it not depend on the blood:tissue solubility coefficient for each specific tissue? That is a lower solubility would take longer to equilibrate and vice versa.

 

[Dr Deco]

Hello readers:

Bones

If you were speaking about the very solid portion of a bone, yes, that would have a long halftime. The solid portion is not really capable of dissolving nitrogen, however.

The part of bones that is of interest for diving is the bone marrow. That has a large capacity for nitrogen solubility but its role in DCS is uncertain currently.


Dr Deco :doctor:

 

[CaveMD]

Bone has an exquisite blood supply, having cut through more than one or two in the OR, it bleeds second only to actual vessels. Even cortical bone has a strong blood supply(albeit less than that of the marrow cavity or cancellous bone). The ECM of bone is not all calcium/phosphate.

The areas with the poorest blood supply would be those of cartilage and other avascular connective tissues(ex ligamentous structures). Hyaline cartialge of non-articulating joints such as the chondral junctions of the ribs to the sternum have some of the lowest nutrient flow.



Just food for thought, one of the highest blood loss surgeries regularly done in most hospitals is spine fusions. These do not involve transecting of any major vessels, almost all of the blood loss is from vertebral bone ooze.

 

[Dr Deco]

Thus, the need for "bone wax."

 

[huwporter]

Those in the hundreds of minutes probably represent a formed gas phase that exchanges slowly. [This is my opinion.]

Thanks for a very interesting discussion; I don't quite understand this bit - would you be willing to expand on what you mean by 'formed gas phase'?

TIA,
Huw

 

[NiclasG]

Bones have the longest time constant. In addition you need to consider the M value for the compartment and you can calculate the relative saturation. A dive computer like Uwatec Aladin Prime/Tec will show you the saturation of most saturated compartment. When the bar graph is 100% filled then you are in decompression, the no-stop time will tell you how long this takes.

Uwatec is a bit more complex to code due to changing time constants(work) and M-values change as a function of history, but it's not difficult.

Niclas