Is there a strategic time to consume mask reserve?

[robertonator]

My understanding of SWB is that as the diver ascends toward the surface and atmospheric pressure decreases, or as the diver exhales immediately after surfacing, the diver is subject to low pressure of oxygen in the blood, and is at highest risk of blackout or samba.
Assuming that is a fairly accurate summation of the applicable theories, is there any point during an ascent more beneficial than another to clear the expanding air in your mask?
While I assume that with all of the other factors the is a fairly negligible discrepancy, it occurred to me that there may be a depth at which oxygen pressure proves more crucial to consciousness, than at others. For instance, perhaps an instant before your initial purge of air at the surface?
Any insight?

 

[Mullins]

Well if you don't clear it periodically, it just bubbles out and you lose it.

 

[rddk]

I dunno if it's my idea placebo effect but i feel some difference if i try or not to re inalhe the air, i mean i feel better when i rebreat it. DO you have the same feelings?

 

[Bill]

There is at least one deep diver that believes your moving in the wrong direction and if you fully exhale at 20 meters, the lungs will not be able to pull enough O2 from the blood to reduce it's saturation below the point where you are able to remain conscious. How long does it take for the first inhale to hit the brain and how fast does desaturation occur? Looks like it could work, on paper.

 

[trux]

There is at least one deep diver that believes your moving in the wrong direction and if you fully exhale at 20 meters, the lungs will not be able to pull enough O2 from the blood to reduce it's saturation below the point where you are able to remain conscious.

In fact Eric's habit to exhale at 20m has not this purpose. It won't prevent the ascent desaturation effect. Its purpose is trigerring stronger diving/survival response by de-facto switching to an FRC dive. Eric then also helps the saturation artificially with a diaphragmatic pressure. However, I would not advise this technique to any beginner. At Eric, his long experience with FRC diving certainly plays a role.

 

[Rik]

Robert, you are describing two different causes of black-out.

The first type, the ascent black-out, is related to a decrease in partial oxygen pressure during the ascent of the dive, which is caused by too much oxygen consumption at depth.

The second type describes a hypoxic black-out at the surface which is related to a drop in blood pressure after forcible exhalation. This can happen both in open water as in the swimming pool and is thus independent from deep diving.

It is true that the amount of air that can be re-used from the mask is marginal. If we assume a content of 40 ml for the shera mask, you would be able to re-use 120 ml air at best after a 30 meter dive. And this is only true if we assume you would equalize your mask correctly, and you would be able to inhale all the air that you have used for equalization during the whole dive. You can't wait until a certain depth, because the volume of the air in the mask is continuously increased, although you might predict the most benefit in the last 10 meter where you might be able to successfully retrieve 40 ml of air.

If the actual volume of inhaling air from the mask is so low, why do freedivers feel they benefit from it? Afterall, it does seem to relieve air hunger at the end of the dive. The act of inhaling the air from the mask might work more on a psychological level. Being able to breath might cause relaxation and therefore decreased oxygen consumption.

What are the disadvantages of re-using air from your mask? It adds to task loading. Especially during the last strokes of your dive, you should try to concentrate on surfacing and a calm recovery breath. The act of re-using the air in the mask might break this concentration, and therefore would be disadvantageous.

Another disadvantage is dependency. If you would be able to actually retrieve some air from the mask that might make a difference, you would be in trouble if you would need this air, and would be unable to do so.

I am not in favor re-using air from the mask, but if you really want to use this technique, you might want to slightly inhale through your nose during the last 10 meters for best result.

 

[efattah]

Re-inhaling air from the mask can be very beneficial. You can re-inhale it continuously during the ascent. In particular the bits you re-inhale in the last 15m can 'clear up' your vision if heading towards a blackout. I think if the mask is high enough volume this air can actually prevent a blackout. Way back in 1998 I had the idea of using a higher volume mask on purpose, just for that reason.

If you use the re-inhale method, just be very careful-- you don't use your diaphragm to inhale the air. You must 'pack' the air through your nose. Use only your mouth muscles. Once you have sucked/packed the air into your mouth, then use you mouth to push the air into your lungs. Don't use your diaphragm, because that will confuse you body into thinking it is time to breathe and your heart rate could go up and other 'breathing' systems might kick in.

 

[rxcnc2]

I hear and read all the time different opinions about re-breathing the air in the mask. What I know is that spearfishers do it often, but then they don't dive very deep. It does make a difference if you are trying to re-inhale air when you are lungs are expanding to their normal volume, or when they have undergone blood shift and cannot take the same amount of air that you started with.

What I also know is that a lot of deep freedivers do not use the mask anyway, or if they do then it's one of those minimum-volume highly-deformable masks which does not even need to be equalized anymore below say 30-40m. Not much volume, and less O2 than you started with.

The cases in between are subjective enough that I think the conclusion is: do what feels best for you. And conclusion number 2: if you are counting on the air in the mask to avoid a blackout, then you are either a very experienced diver or you are gambling too much.

 

[Don Paul]

I hear and read all the time different opinions about re-breathing the air in the mask. What I know is that spearfishers do it often, but then they don't dive very deep. It does make a difference if you are trying to re-inhale air when you are lungs are expanding to their normal volume, or when they have undergone blood shift and cannot take the same amount of air that you started with. Quote rxcnc2.

I have been doing this for 30 years, but I don't dive deeper then 105fsw while
spearfishing. I mainly do it to avoid bubbles escaping and sometimes scarring my prey. I have recycled the air in my mask (inhale- refill- inhale) when I was pushing too deep too long a few times. Perhaps this is a mental crutch and is actually dangerous? Old habits die hard. My holds while hunting average 2:00 to 2:30 min max. What do you guys think ?
Thanks, Don Paul

 

[robertonator]

Don,
I think that the type of repetitive recycling of the air that you're describing would trigger your heart rate to jump, as your body may feel that it isn't in apnea any more.

Personally, I like to let the volume increase the whole way up and about 3m from the surface suck it back in, about 1m from the surface start a slow exhale. If anything, it distracts me from any mental complications I might encounter upon surfacing.

You guys had some good feedback, I appreciate it.

 

[blueface]

If you use the re-inhale method, just be very careful-- you don't use your diaphragm to inhale the air. You must 'pack' the air through your nose. Use only your mouth muscles. Once you have sucked/packed the air into your mouth, then use you mouth to push the air into your lungs. Don't use your diaphragm, because that will confuse you body into thinking it is time to breathe and your heart rate could go up and other 'breathing' systems might kick in.
__________________
Eric Fattah
Canada

Eric, Is there a way that you can practice this dry? I'm sitting here trying to shut my epiglotis and take in air through my nose. I still feel my diaphragm moving (I think) and I am pretty sure I use my diaphragm when diving. I don't want my hr to go up.

 

[efattah]

Practice packing your lungs through your nose. Inhale to the max (dry), now start packing-- through your nose. Your lungs should fill and fill until they feel extremely full (much fuller than before). Keep your mouth closed during the packing process.

 

[blueface]

Thanks Eric.