Average VO2?

Smudgegs

Hi All,

Just a quick straw poll really, what do you guys get as an average VO2?
I dive a Semi dry and seem to hover between 0.5 and 0.75 on "normal" cold water dives (Scotland in the winter!) in the 10-30metre range. Mostly seem to be around the 0.5 though...
Is this normal? Is it unusually low?

Just nosey really!

Smudge

curt

A VO2 of 0.5 lpm seems low to me, but we're all different.

Personally, my average over a few hundred "normal" cold water (3 to 5 degrees C) dives comes to 0.85 lpm.

As always, YMMV...

__________________
Curt Harpold
US Representative
Rebreathers Australia
http://rebreathers.com.au/

AD_ward9

0.5 is very low. Suggests artificially slow breathing (RMV and FO2 are strongly linked). Rest rates are not far off that (0.3 l/min).

For divers doing a dive after stepping off a hard dive boat with no rush, O2 metabolism is usually 0.8 to 1.0 l/min, and generally approaches that for most dives after 15 to 20 minutes no matter how they start off.

Heaving overweight rebreathers to the beach managed to surpass 4.0 l/min.

Doing a gentle surface swim after a walk of a few minutes with gear was 1.2 l/min, in a recent experiment we did.

Incidentally, it is possible to keep up 4.0 for 3 hours. It is equivalent to running a marathon in 3hrs 15mins. Just try keeping up with the wrong people, using the wrong fins, plus a bit of current.

High WOB will also put up the metabolic rate quite nicely on a Rebreather.

Alex

Smudgegs

Interesting... I just re-checked the upload from my last dive and using 40% Eanx through the 50% nozzle (7.3lpm) my loop FO2 shows between 35 and 38%, mostly hovering around 36 - 37%
I was aware as soon as I started using PPO2 monitors that I didn't seem to burn much O2 but I am surprised just how little!

On OC I'm normally pretty good on gas (14 lpm is probably normalish) and afaik I'm breathing normally, I'm certainly not skip breathing or breathing shallowly or any of that nonsense! Maybe helps that I'm short (5'5") and fairly lightly built, and moderately fit?

That said I'm pretty relaxed in the water and if 0.3 is a normal "resting" consumption then 0.5 sounds about right to ofset the extra work keeping warm/gently finning etc?

edited to add: Yes I know I'm even lower on those numbers but the calculations are ongoing ok!

Freef

Most people are looking at a vO2 of 1 as a basis for their calculations for CMF type Rebreather's. Then they can fine tune the flow rate over a number of dives. I believe I sent you the s/s for calculating the vO2 from cylinder fO2 and pO2? You must also consider the following:

If you change depth frequently the addition of loop gas by the ADV will cause a higher loop fO2 and this will appear to give you a lower vO2.

If you are using an oxygauge it is worth checking that it is reading the loop fO2 correctly by exposing it to a known fO2 from a cylinder mixed to the loop fO2 you think you are getting.

It is also worth checking the flow rate is correct using a flow meter rather then the Drager go/no go gauge. A higher flow rate than you are assuming will add more O2 to the loop than you think you are getting.

Is your ADV firing if you breath in hard and the OPV opening if you exhale all the way? If it constantly does this then the loop is getting more O2 added than you would see in the calculations.

It is also worth checking that you are at a fairly constant depth for a while before taking your pO2 readings. About 2/3 of the way down this post:

http://www.rebreatherworld.com/semi-...tml#post121359

shows how pO2 [and consequently vO2] can appear to be changed by the behaviour of the diver.

Using 40% through the 60% jet will magnify all the changes in vO2, so it may be worth doing a few dives in that configuration to see how your vO2 looks.

An SAC of 14 L/min equates to a vO2 of 2.94 L/min of O2 [if diving on air] , but you must remember that you cannot equate this figure with your vO2 as you will be losing most of the O2 you inhale, and breathing is triggered by CO2, not low O2.

__________________
David.

Currently owner of two differently sized ankles.

escott

I run a VO2 of 0.8 when just getting from pt. A to pt. B. , but then I rarely work too hard. Its supposed to be fun right? Freef is right, make sure you get enough readings to take into account all the variables though.

Scott

Smudgegs

Ok, I'll answer within the text as it's a little easier (for me at least!)

Thanks for the input. It's a fascinating thing this diving lark

bletso

My flow is set to 0,9 lpm. Except in very warm water, I never adjust it. Most slug dives I never add at all over a period of 30 mins or more. Except when excersizing it stays the same.

In very warm water I can drop it to 0,7. I seldom ever see 30C water.

It is dry suit 6-8 C WT.

VO2 is a function of your body's ability to convert O2 and carbon to energy. It is somewhat counter-intuitive. The higher your basal VO2 the more physically fit, (efficiency of metabolism) you are. (At least that is what I have been led to believe.)

Dale

Smudgegs

So what we're saying is that an unfit person will use less O2 for a given exercise rate than a fitter person?
I can see how a fitter person could consume more O2 at high work rates as their body is more efficient at processing gas etc, however I would expect, in conjunction with that, the fitter person to consume less O2 at rest as they are using it more efficiently? Or am I waaaay off the mark here!? (never did biology at school!)

Edited to add - After a quick web search I have found lots of info on how Max Vo2 will increase with improved physical fitness, I have however failed to find anything concrete about the effect of fitness on resting VO2.

I guess your information is correct Dale, and I mean no disrespect, I'm just curious to see if we can pin down any solid information that explains or shows the correlation between resting VO2 and fitness?

Any sports physiologists on the forums?!?

AD_ward9

Three different things are getting mixed up in the discussion here.

1. Basal Metabolic Rate. if two people are the same sex, weight, height and age then their basal rates are the same, regardless of fitness. However an unfit person generally has a higher basal metabolic rate than a fit person because he is fat: i.e. he weighs more.

There are lots of papers on VO2 at rest. The science is in the Harris-Benedict Equation which approximates the Basal Metabolic Rate as follows:
For men: BMR (REE in calories) = 66 + 13.75(weight in kilos) + 5.0(height in cm) - 6.76(age in years)
For women: BMR (REE) = 655 + 9.56(weight) + 1.85(height) - 4.68(age)

Conversion of calories or watts to VO2 is more or less a constant multipler. One calory is 0.86 watts, and watts to litres of O2 is something like 680W equates to a VO2 of 2.0 (based on a RQ 0.8, and 1.6l/min of CO2 is 680W or so: I will have to look it up, but something in that order - it is the about the same energy as in one milli-litre of alcohol for those with New Year coming up ).

So unfit fat people burn more energy than fit thin people of the same age. However, old people's metabolism does slow down and they are probably less fit as they get older. BMR also decreases with the loss of lean body mass, so unfit slim people have low metabolism. Increased muscle mass can increase BMR, but really fit people such as gymnasts and ballet dancers are involved in mostly aerobic exercise which does not put on mass, and in that case there is no difference in BMR with the couch slob the same weight. If you regard muscle men as fit, then those who report fit people as having a higher BMR are right too.

Basal rates are really low: 0.2 to 0.3 l/min of O2 typically.

2. Metabolic Equivalent (Working rate to basal rates)
Again this is led by weight. A heavy person will burn considerably more calories to perform the same work task than a light person. It has the same sort of variables as for Basal Rate, but less emphasise on age. Lots of muscle mass (which is not at all the same thing as being fit), will increase the maximum VO2, but excess muscle affects their VO2 for doing a specific piece of work much the same way as excess fat: it takes energy to move the unused muscle just like moving unused fat.

The Metabolic Equivalent factor can cause a 20:1 increase in metabolism to basal rate if someone is working really hard (e.g. over 4 litre per min of O2).

3. VO2 in diving. Now we have established that there is no macho in having a high or low basal metabolism and assume the diver is swimming at a happy rate (or in other words everyone is producing a work output which puts them into the same comfort zone, so the same VO2 in diving terms), we can get onto the diving point below.

The VO2 of 0.5 l/min mentioned at the start of this thread reflects a bad diving habit, which divers get away with on Open Circuit, but is hazardous with rebreathers. That is, artificially slow breathing. A good rebreather diver breathes usually like a train when he goes back to Open Circuit.

VO2 and RMV are linked very strongly. A good skip breather can lower his RMV by breathing very deep and slow, to manage an hour dive to 40msw on a single 10litre tank, at the cost of tolerance of high blood CO2 levels. This is a very bad thing on a rebreather, because hypercapnia reduces the CNS clock considerably, and as the WOB of many rebreathers is higher than for a good O.C. reg when the scrubber is used, this is a recipe for serious problems.

A good rebreather diver has a higher VO2 than a good O.C. diver. My post gave the normal ranges, and exceptional ranges. Glad to see most other comments are in the normal 0.8 to 1.0 l/min range.

We have done a fair bit on BMRs with divers, because we use the VO2 in accident studies to work out when the O2 supply to the rebreather stopped, and customers need reassurance that the size of the O2 cylinder is big enough etc.

Alex