DCS and Thermal Protection Choices

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Mario S Caner

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Esteemed Medical Geniuses,
I have a question regarding a report I read about regarding a contradiction on DCS and Thermal Protection Choices:

Following a tragic plan crash on the US east coast and the activities the Navy salvage divers were involved in, there were reports regarding something that has put some doubt in my mind. After analizing data from hundreds of dives, they discovered that divers using wetsuit's were less suseptible to DCS than the divers using Drysuit's or Heated Suit's. This was attributed to a theory regarding circulatory qualities and the fact that when skin is cold, it pulls more blood toward the inner body as a protective measure. Can anyone comment on whether this is feasible? Cold has always been on the list of things that lead to increased DCS suseptibility... have we been wrong all this time? Is it quite the opposite? This reminds me of another question: What's the final verdict, are eggs good for us or bad?
 
Hi Mario,

My general understanding is that the "optimum" scenario is really to be cold on the bottom (slowing perfusion and hence uptake of inert gases) and warm during decompression (to speed offgassing). Ofcourse the opposite is almost always true in my frigid Canadian waters, we're warm at first and get cold by the end of the dive - the worst possible scenario.

Were the divers using surface decompression (divers do some in-water deco, race to the surface and run like stink for the chamber to complete the deco in relative comfort). In that case then perhaps we could consider the divers "warm" during the final part of their decompression, perhaps then wet suit divers could have an advantage?

I wonder whether the wetsuit divers, being less tolerant of cold, were also being used preferentially on the shorter/shallower dives, leading to a correlation problem.

Just a couple of thoughts,

Dan Reinders
 
Dear Mario:

The TWA recovery and DCS is discussed in Leffler CT, White JC (1997). Recompression treatments during the recovery of TWA Flight 800. Undersea Hyperb Med. Winter; 24 (4): 301-8.

Yes, blood flow can be modified by temperature. The effects of temperature on the circulation to the arms and legs can be contradictory. When one is moderately cold, the body will shunt the blood from the periphery to the body’s core in order to conserve heat. If one is very cold, shivering begins and blood flow return to the arms and legs. Obviously, it depends on where you are in this scenario as to whether the blood flow is to or away from the limbs.

:bolt:When blood is shunted away from the limbs at depth, there is less nitrogen gas uptake and decompression should be safer since loads are reduced if one decompresses while they are warm. If they are cold, the situation is just a mirror on uptake and elimination. If you are warm, however, it is necessary that the perfusion be good in all tissues, since you can not necessarily open up all of the capillaries in arms and legs and expect good perfusion if there is not an increase in the heart rate.

One problem with cold water is the divers will often move more to generate body heat. This will have the effect of increasing the circulation while on the bottom and increasing the nitrogen loads.
This might well be the reason that cold is listed as a risk factor for DCS. :cold:

:fire: Divers who are warm because of the thermal protection suits will experience good blood flow to the extremities while under water, and thus gas loading will be high. If the divers are cool during decompression, the arm and leg perfusion might be reduced and elimination of nitrogen retarded. Since these are very specific effects, it is difficult to tell what actually occurred without a detailed analysis of the dive. In laboratory studies, all of these conditions would be control, but this is not the case in the external environment.

Dr Deco

 
Very Interesting, Thank you for the information Dr Deco, I will be incorporating some of this into my classes. :D
 
This was discussed at the last diving medicine conference I attended. It was noted that the divers with heated suits circulating warm water had more DCS than would be predicted for their profiles. Running them cooler decreased the DCS to closer to a normal rate. (Remember, these are in Navy divers, with very well documented bottom times and depths and workloads, with chambers and medical officers on hand the minute they get out of the water))
The doc discussing it said it showed that being very warm was somewhat risky. (Some of the suit temperatures were 90 degrees F and higher. Apparently the diver could choose his temp.)
He was speculating that post-dive hot tub dips may be somewhat risky, but it wasn't convincing enough to keep him out of the hot tub at the resort.
The Navy is semi-convinced that high temps are bad, but there hasn't been enough research or data generated to say anything more then that. So, stay comfortable, but not Hot-tub warm, and don't push the profile.
Remember, get wet in comfort. and safely.

John Reinertson
 
Sometimes it gets mighty chilly out on the dive boats, almost in a ritualistic fashion I open up my wetsuit and dump hot water into it from the shower's just before I have a bowl of hot soup. If I continue this practice, do you think it would be necessary to dive in a more concervative manner? (Just to give you an idea, on a San Clemente trip while most divers do 3-4 dives in a 7 hour period, I get 5 sometimes even the sixth dive in).

Or, does it not have as big an impact on surface intervals as my paranoia tells me it has? In other words while attemting to increase my comfort level on the boat, am I increasing my chances of getting bent?
 
Mario:

It would be my guess that trying to stay warm during the surface interval would be a good idea with respect to reducing the risk of DCS. :fire: Cold reduces the blood flow and would not promote offgassing :cold:

I would add that staying active is also a good idea. By this, I mean continue to move the arms and legs and try to get the heart rate up to increase blood flow.

One should not perform strenuous exercises in post dive periods, however (jogging in place, jumping jacks, etc.). :nono: These activities, while increasing the blood flow, also promote the formation of micronuclei in an individual who is already supersaturated with nitrogen.

Dr. Deco


[sp]For those interested, here is the next scheduled Decompression Physiology course.http://wrigley.usc.edu/hyperbaric/advdeco.htm

 
Dr Deco,

I was recently reading about bubble formation (in beverages) and your statement concerning exercise (such as jumping jacks) raised a question.

I know that your statement is primarily relating to changes in circulation during the surface interval brought on by exercise.

An unrelated component of bubble formation (in beverages) is shaking. Such as shaking a carbonated beverage and increasing bubble formation.

Would "shaking" a person, such as from a bumpy boat ride, during a surface interval increase the rate of bubble formation and increase risk of DCS?

"Once they form at tiny defects on the surface, they rapidly grow as the carbon dioxide (or nitrogen in the case of Guiness) flows into the bubbles, and is released into the atmosphere, thereby slowly de-carbonating the glass of beer until it is flat. A shock will cause enhanced formation of bubbles at the "nucleation" sites. And it is the combination of the effect of a shock and a rough surface that causes the effervescent fizzing in your mouth that enhances the flavor."-http://www.bubbleology.com/WhyBubbleology.html#Beverage

(Don't forget: they say there is no such thing as a stupid question.) :D
 
Dear Allen:

Actually, the jumping jacks and other forms of vigorous exercise DO RELATE to bubble formation. It is not a problem with blood flow, since that is favorably increased by the muscle activity. Blood flow (= perfusion) increases do promote with faster washout of dissolved (and gaseous) nitrogen.

The problem with the vigorous activity is that many processes are brought into play that can promote the changeover and/or growth of micronuclei into full-fledged decompression gas bubbles. Every time a person’s muscles contract, several things happen on the sub cellular level. For one, there is a movement, or streaming, of fluid on the outside of the muscle cells. This can cause the formation of vortices (little eddies or whirlpools) whose internal pressure is lower than the surrounding fluid. It is believed that it is these same eddies that form in liquids (such as beer) when it is poured. Naturally, some air in the form of bubbles is entrained during the pouring, but everyone is well aware that rapid emptying of the bottle into the glass with a lot of fluid motion is a big promoter of gas bubble formation in beer, soda pop, or any carbonated beverage. :mean:

In addition, we have low-pressure regions form in fluids when they pass through constrictions. Exactly where these regions are in tissue is not clear, but most likely they exist in some form. The formation of bubbles when a fluid passes through a constriction is most commonly observed when a person crimps a hose while water is flowing. That fluttering feeling and sound that one hears is the formation of bubbles from micronuclei. The bubbles are filled with water vapor and any dissolved air in the water and soon redissolve, but the observation is very distinct. Anybody who has ever held a garden hose knows it, although not necessarily by the name of Reynolds cavitation.

While one can cause bubble formation in a bottle of carbonated beverage by hitting the bottom of the container, this is the result of a shock wave. That is, a wave of high and low pressure traveling through the liquid. It is in the low-pressure region that micronuclei grow to become bubbles. This cannot occur in animals however except under unusual circumstances. One of these is a concussion to the brain. Here the head moves rapidly and the brain hits the skull. Cavitation bubbles are thought to play some role in the pathophysiology (= physiology of injury) of concussion. :bonk:

This cannot result from a bumpy ride on a boat. And, it definitely was not a stupid or silly question.....

Dr Deco

[sp]For those with a special interest in these matters, here is the next scheduled Decompression Physiology course.http://wrigley.usc.edu/hyperbaric/advdeco.htm


 
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