Cold, Circulation and Nitrogen

[MarkH]

I was wondering: I dive in reasonably cold water. At the start of the dive, the extremities (hands, feet, other things I won't mention) are nice and warm. I go deeper and nitrogen starts to build up. I am still warm. I decide I've been down long enough and start to acsend. Since I've been down for awhile, I'm starting to feel cold. My body shuts down the blood supply to my extremities to keep my core warm. There is still excess nitrogen in these tissues that now has no blood supply to carry it to the lungs to off-gas. As I near the surface, what happens to this nitrogen? This is a theoretical situation. I am usually warm throughout my dives, but I always hear local divers saying that their hands were cold near the end of their dive. Why don't they have the bends?

 

[Diver0001]

I was wondering: I dive in reasonably cold water. At the start of the dive, the extremities (hands, feet, other things I won't mention) are nice and warm. I go deeper and nitrogen starts to build up. I am still warm. I decide I've been down long enough and start to acsend. Since I've been down for awhile, I'm starting to feel cold. My body shuts down the blood supply to my extremities to keep my core warm. There is still excess nitrogen in these tissues that now has no blood supply to carry it to the lungs to off-gas. As I near the surface, what happens to this nitrogen? This is a theoretical situation. I am usually warm throughout my dives, but I always hear local divers saying that their hands were cold near the end of their dive. Why don't they have the bends?

Excellent observation and not theoretical. What you're describing is a known DCS risk factor. When it's cold you need to leave a bigger margin for the NDL's and do longer slower ascents, especially close to the surface. Too much off-gassing can't hurt, too little can.

R..

 

[The Iceni]

Hi Swankenstein,

Being as pedantic as I can! - You ask about "the bends". Strictly this is DCI affecting the limb girdles and the back (joint, and possibly CNS DCI) causing the sufferer to curl up into the fetal position to ease the pain. Hence the name bends, originally given to caisson workers with DCI.

Although the skin and peripheral tissues cannot therefore cause the traditional "bends", like all living tissue they can suffer from DCI. However a so-called "skin bend" is not recognised as a major problem.

This is not the place to go into great detail but soft tissues (such as fat and connective tissue) simply expand to accomodate any bubbles growing within. Problems arise when the affected tissue is enclosed in a fixed volume and has nowhere in which to expand (such as the brain and spinal cord) or the bubbles block the blood supply to such vital organs.

The resulting increase in pressure causes direct physical damage and reduces the blood supply which itself causes further damage.

A skin "bend" typically results in a very itchy rash caused by localised damage to the integrity of the skin!

 

[Diver0001]

Hi Swankenstein,

Being as pedantic as I can! - You ask about "the bends". Strictly this is DCI affecting the limb girdles and the back (joint, and possibly CNS DCI) causing the sufferer to curl up into the fetal position to ease the pain. Hence the name bends, originally given to caisson workers with DCI.

Although the skin and peripheral tissues cannot therefore cause the traditional "bends", like all living tissue they can suffer from DCI. However a so-called "skin bend" is not recognised as a major problem.

This is not the place to go into great detail but soft tissues (such as fat and connective tissue) simply expand to accomodate any bubbles growing within. Problems arise when the affected tissue is enclosed in a fixed volume and has nowhere in which to expand (such as the brain and spinal cord) or the bubbles block the blood supply to such vital organs.

The resulting increase in pressure causes direct physical damage and reduces the blood supply which itself causes further damage.

A skin "bend" typically results in a very itchy rash caused by localised damage to the integrity of the skin!

This is totally off topic but I noticed your name is Paul Thomas. Are you *the* Paul Thomas who had a pretty close call resulting from a PFO a couple of years ago?

R..

 

[ArcticDiver]

A skin "bend" typically results in a very itchy rash caused by localised damage to the integrity of the skin!

From a field exam viewpoint just what would the S&S be that would differentiate this condition?

 

[BigJetDriver]

From a field exam viewpoint just what would the S&S be that would differentiate this condition?

From personal observation, the surface of the skin looks like really exagerrated "goose bumps" that are easily felt as raised bumps with the finger-tips. If a little pressure is put on the finger-tips as you run them across the surface, a "crackling" noise is heard. Hence, another name for them: "the crackles", or another, "popcorn skin". Later there are red spots where the bumps were, and the skin itches.

BJD :anakinpod

 

[dbulmer]

Diver0001,
Yes I believe it is the same chap.

 

[MarkH]

From personal observation, the surface of the skin looks like really exagerrated "goose bumps" that are easily felt as raised bumps with the finger-tips. If a little pressure is put on the finger-tips as you run them across the surface, a "crackling" noise is heard. Hence, another name for them: "the crackles", or another, "popcorn skin". Later there are red spots where the bumps were, and the skin itches.

BJD :anakinpod

Thanks everyone for your replies, and by the way, the above comment is one of the creepiest things I've ever heard.

 

[ArcticDiver]

Thanks BJD.

 

[Dr Deco]

Dear Scuba Board Readers:

Cold Water

Cold water certainly will reduce the blood flow and retard gas uptake in the extremities. However, if the diver attempts to keep warm by increasing activity, this will lead to an increase in blood flow, and an increase in gas loads. When the diver returns to the surface, s/he will settle down and rest, and the extremities will stay cold. Blood will slow and so will elimination of nitrogen. This can lead to DCS.

The “Bends”

In reply to Dr Thomas’s note, I have heard another explanation for the origin of the term “the bends.” It deals with pain in the joints suffered by the caisson workers in about 1870 and a fashion craze known as the Grecian Bend. In the days of skirts with large bustles, it was popular to walk with a stooped posture, known as the Grecian Bend. caisson works afflicted with joint pain walked sometimes with an affected gait and were kidded by their coworkers as walking the Bend. The name appears to have stuck long after the walk has gone out of fashion.

Dr Deco :doctor: