SAC Rates - The Good, The Bad, The Average

[CuNanoTube]

Mine in a 7mm last summer was something like 16l/min. It is interesting since my father is a marathon runner with a resting heart rate of 50 and his worked out to be 18l/min though he was in a dry suit so that could make a difference (though I was freezing most dives so my HR was higher). I am looking forward to this season since I am now in better shape and diving a dry suit.

 

[Colo Hippie]

One other thought I had - How does Nitrox affect a persons SAC rate. I would think that it would lower it based on the fact that the O2 percentage is higher, which means your body is benefiting from higher O2 concentrations for the same volume of air.

 

[lowviz]

...//...Lowviz - I like that, and now my wife will love you for me making her breath a tank while sitting and watching tv . ...//...

Just don't let her meet mine, -I'm in enough trouble already...

One other thought I had - How does Nitrox affect a persons SAC rate. ...//....

Almost not at all. The short answer is that eliminating CO2 buildup determines respiration rate.

 

[waterpirate]

The resulting sac rate from athletes is never what you would expect. They have trained to process vast amounts of 02 to be effecient. Proccessing vast amounts of 02 while on scuba indicates your body is very efficient, and your sac is very high.
Eric

 

[scubadada]

Even though I had an idea earlier and occasionally calculated my SAC, I have only followed it more closely for the last 150 dives since I started using an Oceanic VT 3 which calculates SAC when downloaded to Oceanlog. My SAC is remarkably constant, with a predictable influence by exertion and temperature. I find it most useful for gas and scenario planning. How much gas do I need for a dive, can I ascend from 130 ft with a 19 cu ft pony with double my usual gas consumption?

For the last 150 dives, my average SAC was 0.37 but varied from a low of 0.29 on an effortless drift in warm water in Boynton Beach to a high of 0.63 in moderate current diving in a wetsuit in 47 degree water in Cape Ann. In general, I can count on a SAC in the mid 0.3s and use that in my planning, it's good to know.

 

[RTee]

One other thought I had - How does Nitrox affect a persons SAC rate. I would think that it would lower it based on the fact that the O2 percentage is higher, which means your body is benefiting from higher O2 concentrations for the same volume of air.[/QUOTE

Regrettably not so. We breathe gas by volume and not by PPO2. That's why we need to adjust the proper mix for the depth we are planning to dive to remin within acceptable and safe PPO2. If you breath 100 O2 it will just mean that you will exhale a greater amount of O2 as you would breathing air (21) as the body will just take what it requires and expel the rest:

 

[Rhone Man]

How does Nitrox affect a persons SAC rate.

Almost not at all. The short answer is that eliminating CO2 buildup determines respiration rate.

That is the textbook answer, but I tend to find my SAC tends to be lower when I used Nitrox. I also find that I get fewer CO2 headaches (I am a chronic skip breather), so read into that what you will.

 

[lowviz]

That is the textbook answer, but I tend to find my SAC tends to be lower when I used Nitrox. I also find that I get fewer CO2 headaches (I am a chronic skip breather), so read into that what you will.

My coldwater SAC hovers around 0.75 Nitrox (usually 28) has no effect on me.

 

[scubadada]

I almost always dive nitrox, I wouldn't know if there is a difference in my SAC between air and nitrox. The answer is not so intuitively obvious to me. I would appreciate a physiologic explanation if someone has one.

Thanks in advance, Craig

 

[Tigerman]

I almost always dive nitrox, I wouldn't know if there is a difference in my SAC between air and nitrox. The answer is not so intuitively obvious to me. I would appreciate a physiologic explanation if someone has one.

Thanks in advance, Craig

When we breathe we breathe in air (EAN21). When you breathe out, theres still most of the oxygen left in that air. We are simply unable to utilize the ammount of oxygen present in air and even less so the oxygen in richer mixes.
We do however fill our lungs when we breathe and as we cant absorb more oxygen from nitrox than we do for air, we have to breathe at the same rate wether we have air or EAN in the tank.
Also, what trigger us to breathe is not lack of O2, but the need to expell the CO2 that build up.