Bent at Devils?

[bleeb]

Sweat can also be a significant fluid loss in hot, humid places (like Florida in the summertime). Intravascular volume can be lost and repleted VERY rapidly -- in the order of minutes. Anybody who has consumed a soft drink while driving knows this

Or coffee.

Would it be possible for you to maybe quantify "VERY rapidly" a bit more numerically? From various sports, I've heard the figure frequently quoted that the average digestive system can absorb about 1 L/hour, presumably into intravascular space, to give an idea of how much exactly a person can actually usefully drink. I've been given to understand that water absorption is mainly through the stomach wall, with 10-20% through the small intestine, although maybe this doesn't have much impact on hydration. Also, 1 L/hour of sweat might not be too unusual with moderate exertion under warm, humid conditions. Any idea how accurate this all is? Which of the three spaces does sweat get mainly pulled from?

As a more general comment speaking to the original thread, I've assumed that by the time you feel thirsty, you're already at least mildly dehydrated. By the time you feel it, you've already lost 1.5%-2% of you body mass in water, which for most of us means something like 3 lbs/1.5 L/6 cups @ 8 oz each, and as Lynne said, getting this all the way back into the cells takes quite a while. Maybe the same concept of 'compartments' in decompression models may have some limited application to the diffusion of water through the body, as well.

 

[rjack321]

lynne, what's the thought behind diluting the gatorade?

I'm not Lynne

But...
Many sports drinks are hypertonic so water leaves the body to dilute them (by osmosis). In time, as the solutes pass the stomach and small intestine wall, the water can migrate back into the body as well. Some of the newer fomulations are getting more and more dilute so this isn't quite as much of an issue as it was with the sugary Gatorade of yester-year.

Diluted drinks or plain water will attempt to diffuse osmotically into the bloodstream immediately.

 

[TSandM]

I've never seen a maximum absorbable volume for the GI tract, but it is possible to rehydrate cholera patients orally, and their fluid losses are enormous, so the absorption capacity is very high and I'm sure it exceeds 1L per hour. I would be VERY surprised if one can lose 1L/h of sweat, even in high heat stress conditions, as that would be a 24 kg weight loss over 24 hours. But it may be possible.

One may reasonably think of sweat as being drawn from the intravascular space, because, although the cells which are creating sweat are making it from their own intracellular contents, they are very few, and the volume is repleted from the intravascular compartment. The case where you really have to worry about intracellular volume depletion is when you have had big fluid losses which haven't been replaced, and fluids have had to shift from the cells into the bloodstream. Patients with severe vomiting and diarrhea would be an example (which can certainly happen to people in MX to cave dive, although one would think they wouldn't be cave diving at that point).

Richard nailed the explanation for diluting the Gatorade.

 

[stairman]

Randy,
Where have you been? Hunting season has been over for along time now.

Hey Chad you know me, Im a warm weather diver. Hit Ginnie Saturday to open up my season. Ill see you around fer sure.