Does breathing rate affect saturation?

[alexeames]

This sounds a bit like an exam question, but here goes...

If you take two identical twins, (of identical fitness/training level etc.) they dive the exact same profile, but one uses 20% more air than the other...


Does the air guzzler get...

more N2 saturated
less N2 saturated
the same

...than his buddy?

Does air consumption have a role in this? Or is it a total red herring because inhaled and exhaled air have the same partial pressure of N2 and so the divers are both exposed to the same constant pp of nitrogen (Henry's Law and all that?

 

[Dr Deco]

Dear Alex:

The “guzzler” gets the same at the tissue level. All gas exchange occurs first between the lungs and capillaries and then the capillaries and the tissues. If the lungs always contain the same partial pressure of nitrogen in the alveoli, then the exchange at the alveoli/capillary interface is independent of the amount of nitrogen removed from the tank, i.e., the breathing rate.

The individuals might be twins, but there the similarities will end. The flow of blood, and gas uptake, is dependent on activity level in the tissues. It is possible, in a laboratory situation, to standardize workloads but not in the field in an actual dive situation. The “guzzler” might actually be working at bit harder, producing more carbon dioxide, and breathing down the air supply for this reason.

The blood flow is also a factor in off gassing. Again the activity level might be standardized in the lab but not in the field. This flow will depend on activity and this will assuredly vary. Then we have the question of tissue micronuclei. These will also vary in twins and change their decompression characteristics. These are influenced by activity and hydration level.

Dr Deco
:doctor:

 

[alexeames]

OK that means I can breathe easy now.

Thanks Dr Deco

 

[100days-a-year]

Doc,does that mean that folks with a good cardiovascular condition would on-gas/offgas slower due to decreased bloodflow?My heartbeat resting is in the 48-54 range BP 90-105/55-60.Would I ongas slower than a cardiac risk or is the perfusion across the capillary bed not affected that much?

 

[Rick Murchison]

Originally posted by 100days-a-year
Doc,does that mean that folks with a good cardiovascular condition would on-gas/offgas slower due to decreased bloodflow?My heartbeat resting is in the 48-54 range BP 90-105/55-60.Would I ongas slower than a cardiac risk or is the perfusion across the capillary bed not affected that much?

Don't confuse flow with pressure... The person in good shape moves more blood more easily through their system at lower pressure. So if there is any difference at all, the person in better shape would on/off gas a little more easily.
The fact that there is less of a drop in pressure across the whole system may mean that the lower blood pressure person is less prone to bubbling, all other things being equal - but I don't believe there are any definitive studies to support any significant difference.
Rick

 

[Dr Deco]

The effect of physical fitness in diving has been reported anecdotally for decades. Recent work by a French group gives a quantitative perspective to this factor. There was a definite trend that as the fitness of the diver increased as measured by maximum oxygen uptake, the Doppler detectable gas bubble load post dive decreased.

For divers, this means just one more reason to stay in good physical shape.:muscle:

Dr Deco :doctor:

The abstract follows:
Carturan D, Boussuges A, Burnet H, Fondarai J, Vanuxem P, Gardette B. Circulating venous bubbles in recreational diving: relationships with age, weight, maximal oxygen uptake and body fat percentage. Int J Sports Med 1999 Aug;20(6):410-4

Decompression sickness (DCS) is recognized as a multifactorial phenomenon depending on several individual factors, such as age, adiposity, and level of fitness. The detection of circulating venous bubbles is considered as a useful index for the safety of a decompression, because of the relationship between bubbles and DCS probability. The aim of this work was to study the effects of individual variables which can be assessed non invasively, on the grades of bubbles detected 60 min, after diving by means of Doppler monitoring, in a sample of 40 male recreational scuba divers. The variables investigated were: age, weight, maximal oxygen uptake (VO2max) and percentage of body fat (%BF). Bubble signals were graded according to the code of Spencer. The relationships between the bubble grades (BG) and the variables investigated were studied. This work showed that bubble production after hyperbaric exposures depends on several individual factors. Relationships with P < 0.01 were found between Bubble Grade and the variables: age: p = 0.486, P = 0.0024; weight: p = 0.463, P = 0.0039; VO2max: p = -0.481, P = 0.0027; except for %BF: p = 0.362, P = 0.0237

The effects of age, weight and VO2max are more significant than the effect of %BF. We concluded that to take into account such variables in decompression tables and diving computer programs should allow to adapt the decompression procedures to individual risk factors and reduce the DCS probability.

 

[Rick Murchison]

Dear Dr. Deco,
I'm sure it must be obvious, but I'm having trouble putting relative significance to the data... could it be that the definition of little "p" big "P" is contained in the "code of Spencer?" Or am I missing something easy here?
Thanks,
Rick

 

[Dr Deco]

Whoops!

I did not explain the terms in the abstract. The large P represents probability and says that, in this case, there is a better than 99% probability that the data is not random. The small p represents the degree (strength) of the correlation. Here we see that there is a fairly good correlation of low Spencer bubble grade (few bubbles) with [1] high maximum oxygen uptake (during a treadmill test) [2] young age, and [3] low body weight.

Dr Deco :doctor:

 

[Rick Murchison]

Originally posted by Dr Deco
Whoops!

I did not explain the terms in the abstract. The large P represents probability and says that, in this case, there is a better than 99% probability that the data is not random. The small p represents the degree (strength) of the correlation. Here we see that there is a fairly good correlation of low Spencer bubble grade (few bubbles) with [1] high maximum oxygen uptake (during a treadmill test) [2] young age, and [3] low body weight.

Dr Deco :doctor:

So, the big P is an expression of the probability that the data is random - lower numbers implying more accurate data, while the little p is an expression of correlation - with the BF% being not so big a factor, we can conclude that young little active guys (not necessarily skinny, just small) are less susceptable than old big inactive guys (not necessarily fat, just big). Sounds like maybe the gymnist has a distinct advantage over the tackle.
That about it?
Thanks,
Rick

 

[dlarbale]

Interesting!...

So coming back to the original question and Dr Deco's answer I can safely say that the instructor that gave me advise to breath heavily on a 40min deco stop after a dive in order to offgas more quickly was speaking bull?

The instructor also stated that Narcosis doesn't just disapear when you ascend slightly and that on the deco stop 1st one at 12m's) we'd still feel a bit fuzzy until the N2 had been 'flushed out' - another reason given for breathing heavily!

The facts please!!

Later - Dave.