Low SAC rate and hypothermia

[blackvans1234]

I don't think I agree with SAC rate and temperature regulation.
IF you weren't getting enough oxygen your respiratory rate would increase despite efforts to breathe deeply

Muscle contraction generates extra heat, and just cellular metabolism (being alive) generates heat, not respiratory rate.


Water just makes us colder


-I took human anatomy and physiology I and II a year ago, I should be in the ballpark

 

[Thalassamania]

I don't think I agree with SAC rate and temperature regulation.
IF you weren't getting enough oxygen your respiratory rate would increase despite efforts to breathe deeply

Muscle contraction generates extra heat, and just cellular metabolism (being alive) generates heat, not respiratory rate.


Water just makes us colder


-I took human anatomy and physiology I and II a year ago, I should be in the ballpark

Then correct me if I am wrong: Being immersed in cold water will not cause you to burn more calories, thus will have no effect (well, there is a second order metabolic inefficiency at less than normal body temperature) UNTIL you start to shiver. The action of shivering will burn more calories, thus require more "fuel" and more oxygen. The oxygen has to come from somewhere, it comes off the hemoglobin and then is replaced at the lungs. At the same time you produce, stoichiometrically, more CO2, which makes you into mild acidosis and thus raises your respiration rate.

 

[dumpsterDiver]

I defintely know that my air consumption rate will increase when I get cold. I also know for a fact that being very inactive, generates very little heat and causes less air to be consumed.

If you are a small person, then generally you will have more air in the tank than you need to keep up with a buddy. One way to be warmer is to increase your activity underwater, kicking harder with the legs will generate heat and will increase metabolism and (obviously) increase your air consumption. If you have lots of extra air, maybe a little more kicking underwater will help you some.

A more practical solution...if you must dive in a wetsuit and you suffer from cold, I would recommend that you get a wetsuit with the most efficeint design... no zippers and attached hood. If you look at the wet suits freedivers wear, this type of suit is warmest (for a given thickness and type of rubber). 2 piece suit, jacket with attached hood, famer john pants. no zippers and smooth rubber interior to decrease water flow all work together.

A well fitted freedive suit of 7mm will keep even a small person warm for a long time in below 70 degree water.

 

[PhuketPaul]

I agree with the majority of posts before:

Being small causes you to get cold, as others have mentioned as you get larger your volume (mass) increases more rapidly than your surface area - mass generates heat, and it's lost through surface area, also fat is a good insulator and prevents heat loss.

Your low SAC rate shows you are diving efficiently, without too much effort - increase the effort and the muscles generate heat.

Your low SAC rate is not related to a lack of Oxygen, your body generates CO2 as your muscles work and this will cause you to breathe more anyway, as we dive we are exposed to a higher partial pressure of Oxygen, and even we very slow breathing will always have a good O2 gradient in the lungs.

If you get cold, you will shiver, your muscles generate more heat, burn more O2, thus creating more CO2 and causing you to breathe more

So, don't worry about your SAC rate being low (what most divers strive for) but look at staying warm in other ways such as thicker, or more efficient wetsuit, Hood gloves etc

 

[ajduplessis]

Although there might be a correlation between SAC and thermal tolerance, I don't accept the oxygen-as-fuel hypothesis. I will speculate that with a low SAC you are not exerting much effort, and therefore not generating much internal heat

On a more practical note, I found that wearing a hood, even in the tropics, dramatically reduced my tendency toward hypothermia.

I have to agree with everything here....

 

[SeaHorse81]

I really appreciate everyone's time and thoughts on this. To address a couple of points that were made:

I don't get headaches, so that's a good thing.

Taking along something warm to drink could only help. I actually thought about that for the Saturday course, but would have had to borrow a thermos and didn't because I'd been told the quarry was nearly ten degrees warmer than it actually turned out to be. I don't think warm fluids would be enough to solve the problem, but might buy me a bit more time.

The wear-more-neoprene options would help, but are probably not practical. Muscling into and out of the 7 mil I have, not to mention moving around in it, is a pretty good workout and is by far the most strenuous thing I do on most dives. It's a custom suit, so it's pretty unforgiving. Wearing more neoprene would also mean wearing more weight, thus making out-of-water operations even more difficult than they already are.

I have actually begun cautious investigations into dry suits since reading the replies on this thread, because I'd like to have a local dive season that's more than six weeks long and the neoprene option just isn't getting me far enough. It's tough (and expensive) when the only way to get a really enjoyable dive is to get on a plane and go way south.

I do appreciate the thoughts on SAC vs. hypothermia, because I'd never heard the two related before and was really curious what others might think.

 

[knotical]

Another stop-gap measure you might want to try before you go dry: Periodically tense your muscles, especially large muscles like the legs, to expend more energy / generate more internal heat. Your SAC might suffer, but you might suffer less.

 

[spectrum]

SeaHorse81

There are some tips here that may help

Going dry seems like the most direct route to so comfort. However, if budget say's "stay wet" a full 7mm with 2X on the core will help and should not require "muscling" with the correct fit and technique.

Stay warm,
Pete

 

[SeaHorse81]

Pete, your link looks great! I'm on top of a lot of it already from what I could see from a quick skim (time doesn't permit more today), but it looks like there are some good new ideas in there to consider as well. Thanks so much! I hope to give it a good read tomorrow, as I've got a 13-hour schedule today.

 

[dumpsterDiver]

Pete, your link looks great! I'm on top of a lot of it already from what I could see from a quick skim (time doesn't permit more today), but it looks like there are some good new ideas in there to consider as well. Thanks so much! I hope to give it a good read tomorrow, as I've got a 13-hour schedule today.

You don't need MORE wetsuit, you need a BETTER wetsuit! Does your have zippers and a separate hood and a nylon lining on the inside? All these things reduce the thermal protection...