I've heard- and used to repeat- the mantra that you need to be really-really hydrated to avoid all kinds of problems, including DCS. But when I mentioned this in a DAN study last year, the doctor told me that hydration was pretty low on the list of causes- to the point of being not important. Depth, Time, Temperature are the important ones. I think it is probably important not to be dehyrated, but overhydration isn't good.

Here's an article that says '8 glasses of water a day' is bunk.

http://www.reuters.com/article/newsOne/idUSN0236679720080402

Oh, I'm going to do another DAN study this week- anyone have any questions about DCS I should ask?

That Dr. is full of it. Dehydration causes blood viscosity to increase. In short: body loses water; blood gets thick, therefore reducing its ability to offgas efficiently.

Dehydration is quite different than what most people talk about when 'make sure you're hydrated before you dive to avoid DCS'.

A useful rule of thumb for avoiding dehydration in hot or humid environments or during strenuous activity involves monitoring the frequency and character of urination. If one develops a full bladder at least every 3-5 hours and the urine is only lightly colored or colorless, chances are that dehydration is not occurring; if urine is deeply colored, or urination occurs only after many hours or not at all, water intake may not be adequate to maintain proper hydration.

Dehydration is quite different than what most people talk about when 'make sure you're hydrated before you dive to avoid DCS'.

Completely agree. But for the Dr. to say that hydration was pretty low on the list of causes of DCS, "to the point of being not important" is ridiculous.

The study we're doing this time involves exercise. All the recent data has been done with 'divers' being dry and just sitting in the chamber. The new study they are doing involves riding an exercise bike in and out of water seeing if activity has a difference.

Heard today that a 200 pound man's body has approximately 120 pounds of water in it. One gallon of water weighs 8 pounds. Check this out...

http://www.npr.org/templates/story/story.php?storyId=89323934

The study we're doing this time involves exercise. All the recent data has been done with 'divers' being dry and just sitting in the chamber. The new study they are doing involves riding an exercise bike in and out of water seeing if activity has a difference.

I would be quite interested in the results of this study, although the chamber is not an exact duplication of diving.

As far as the hydration thing, there is so much anecdotal eveidence from people who got bent while underhydrated that drinking a lot of fluid is still a great idea whether proven scientifically or not.

Just got back from the pre-study.

They are investigating a few theories on this- one is if you absorb more N2 while underwater (I don't think so, but I just play a scientist on the internet), the other is that exercise might have a higher or lower uptake of gas (the speed of blood through your system triples while exercising), and the third is about temperature, so the temperature is set to body-neutral (when exercising find a temperature where you're putting out as much heat as the water takes away).

They can't really narrow any of those down in this study since the sample size is small, but they are going to correlate it to the 'dry/at rest' studies to see if there's a significant difference.

The dive starts tomorrow 6am. :crazy:

Finished the study, none of us got bent. It was an hour at 60' exercising on a stationary bike, 8 hour surface interval, then 4 hours at 8000'.

They did doppler and heart ultrasound tests every 15 minutes during the flight. This time, I didn't have any bubbling, but the other two in the test did. No one got DCS (bubbling is normal after a dive). My bodyfat was down to 17%, which helps in that. My heart rate and blood pressure were lousy- time for more exercise instead of just eating right.

I spent the time on the 'plane' questioning the dive physiologist. Lots of good information. I'm paraphrasing answers, so take it with a grain of salt, like anything else on the internet. For example: in-water recompression. A definite 'depends' (time to chamber, type of hit, temp of water, etc.). There are real protocols for in-water recompression (the navy manual has one, but it is called 'missed deco'), and DAN did a conference last year that addressed it.

I asked about safety-stopping/deco-ing on pure O2 instead of air for hangs. Answer: if it is a short stop, it doesn't hurt, but you get no benefit because the tissue that needs it doesn't get enough circulation. Minimum of 5, preferably 10 minutes doing a hang on O2 for added safety.

I asked about breathing O2 on the surface versus O2 at 15' on a hang. O2 on the surface is good, but far more effective under water. By the time you are on the surface, you might already have DCS issues that might have been resolved if you hung on O2.

On carrying O2 versus having it off the boat. *Hang off the boat*. Only exception would be planned O2 deco and a danger of not coming up at the boat, with other safety stuff added in.

I did not ask specifically about hydration, but it was never mentioned in any of the discussions of these other topics (leading me to think again it isn't high on the list).

The DAN studies are pretty cool- you get a little cash for doing it, and you get a year of DAN premium insurance- but the real benefit for me is the wealth of information I get from the chamber techs and doctors. These studies are done in Durham, NC at Duke. If you're in the area, check out http://dan.org and look for the studies section.