Breath out on accent?

[cp1204]

I've seen many photos in gallery (usualy named as "<name here> accent"), where accending guy/gal blow air out making lots of bubbles flow out of mask. :duh
Are they are doing it just for fun? I thought, that risk of getting BO is increased if you breath out before surfacing. Have i missed something?

 

[Cornholio]

As you descend, the air space inside the mask is ‘squashed’ by the water pressure. This is called mask squeeze. In order to counteract this, it is necessary to exhale through the nose.

Whilst ascending, the decreasing water pressure causes air to expand and escape under the mask’s skirt. Some of this expanding air can be reclaimed by nasal inhalation, although there is debate as to how useful this is.

Because a freediver needs to fill the ‘dead space’ inside the mask with air, some people dive with fluid-filled goggles or special contact lenses. More commonly, low volume masks are used as these have reduced air spaces compared to ‘ordinary’ masks.

 

[cjorca]

Definately expanding air from the mask, but some freedivers exhale during the last few ft of their ascent so they may inhale immediatly upon breaking the surface.
It was also thought exhaling in the last several ft of ascent would also reduce the " reverse gradient "
Upon ascent, due to the reduction in pressure, there was a higher concentration of oxygen in your blood that in your lungs, therefor there was a movement of oxygen from you blood into you lungs upon ascent, especially in the last 33 ft, althought there is actually no studies that prove or disprove this theory, that I know of.
Hope this helps, :girlie

 

[cp1204]

Whilst ascending, the decreasing water pressure causes air to expand and escape under the mask’s skirt. Some of this expanding air can be reclaimed by nasal inhalation, although there is debate as to how useful this is.

I was talking about real 'bubble showers' - that was definetly not expanding air from under mask. Expanding air comes out slowly as you accent.

Some of this expanding air can be reclaimed by nasal inhalation, although there is debate as to how useful this is.

I inhale expanding air every time on accent. What's wrong with this?
cjorca:
What is that 'reverse gradient' thing?

 

[cp1204]

Like this image
Or this shot

 

[SEDATE]

as for me , really good thread,
my idea about this image/shot is must be out of control, if you suffer more than you resist, you leave all air have in, when you leave a pinch of air , you change the pressure in your lung and you say welcome to Samba/BO, keep the breath all the time, i know that, i do that

 

[Adrian]

Many of the pro's exhale the last couple of meters on the way up, so that the first thing you do is inhale and get oxygen to the brain faster, instead of exhaling and then inhaling. That's the theory behind this. Normally since we are ascending quickly we are only talking about one or two seconds before hitting the surface, but if one is on the edge, it might make the difference between blacking out or not.

There's nothing wrong about breathing in the expanding air of the mask on ascent, it has enough 02 to be useful.

Adrian

 

[cp1204]

Hm. Then everybody shoud decide for himself, risk BO by exhaling before surfacing or risk of blacking out because you simply ran out of O2. rofl
I usualy avoid that problem by surfacing just before my limit, when I have some spare O2 just in case and I use expanding air from mask.
I have Technisub Idea, and it has comparably high volume (It just LOOKS like it's low-volume ).
Hope I'll switch to Minima soon, and then there won't be such "last resort" on accent.

 

[immerlustig]

also:
freedivers who pack a lot for deep dives get rid of air before surfacing as re-axpanding air on the surface would increase the bo-risk when surfacing. that bubble shower you see on the pix is most likely coming from releasing packed air.
...and it looks cool on fotos

cheers,

roland

 

[cjorca]

I believe its called Reverse Pressure Gradient (or something like that) "Upon ascent, due to the reduction in pressure, there was a higher concentration of oxygen in your blood that in your lungs, therefor there was a movement of oxygen from you blood into you lungs upon ascent, especially in the last 33 ft" althought there is actually no studies that prove or disprove this theory, that I know of."
There is an explaination of it in the IANTD Master freediver manual - if your interested.

When we were competing, we always exhaled the last few ft so we were able to immedialtly inhale upon surfacing. I personally don't think that doing this in the last couple of ft will enduce SWB. If done deeper, possibly.
safe dives to all

 

[cjorca]

Some of the theories and teachings in the IANTD Freediving manuals are out dated or disproved, so be open minded when reading them.

 

[cdavis]

There are some very interesting things coming out of physiological studies. One of the theories of SWB has to do with rapidly expanding lungs pushing on veins and arteries, displacing blood flow to the brain causing a reduction in blood preasure This raises the chance of a BO for a diver already low on O2 . Exhaling in the last 30 feet or so reduces or eliminates that chance. Technical types can probably give a better description, but the above is the general idea. Whatever the mechanism, Performance Diving teaches exhale on ascent. Their experiance is that it minimizes chances of a BO.

On the question of "reverse preasure gradient" effect, there was a study described in these forums maybe six months ago that found some evidence of the effect, didn't sound like proof, just an indication. I did not get a chance to read the full study.

Connor

 

[efattah]

There are some very interesting things coming out of physiological studies. One of the theories of SWB has to do with rapidly expanding lungs pushing on veins and arteries, displacing blood flow to the brain causing a reduction in blood preasure.

Connor

This is one advantage of FRC diving; you don't get that huge increase in pressure in the chest which would normally stop blood flow. Further, you don't need to exhale in the end of the dive, instead you just inhale upon surfacing.

During extreme FRC dives, I have been on the ascent, feeling hypoxic, and thinking 'for sure I'm going to black out from this one.' However, in each case I miraculously recover without a BO. During these dives I was judging my state of hypoxia compared to inhale dives. On an inhale dive if I feel very hypoxic at 25m it usually means a BO @ the surface. On FRC dives even feeling very hypoxic at 25m usually means a clean recovery.

Sebastian Murat has another additional explanation. Apparently in human lungs, the bronchii collapse before the alveoli, sealing off the trachea from the rest of the lungs. This would imply that you have a 'fresh air' supply in the trachea which is not undergoing gas exchange during the dive. Only in the end of the ascent (perhaps at 15m), as the bronchii uncollapse, the air in the trachea can flow into the lungs and give you fresh oxygen, possibly preventing a BO.

On an inhale dive, the same effect happens, except that the bronchii would collapse around 40m. So, on an inhale dive you get this sudden infusion of fresh air at 40m, which is too deep to help you in the case of a SWB.

Ideally this fresh air supply would be injected right at the end of the dive...

 

[cp1204]

So be it! Breathing out on accent.
I understood that FRC dives are *in general* shorter and less deep than usual ones. Then what are the advantages, besides lower risk of BO?

 

[efattah]

So be it! Breathing out on accent.
I understood that FRC dives are *in general* shorter and less deep than usual ones. Then what are the advantages, besides lower risk of BO?

I guess it varies from person to person. For me, although the total dive time on my FRC dives is less than my inhale dives, the total bottom time is about the same.

For example, on a 40m recreational FRC dive my safe bottom time is about 20 seconds, vs. about 25 seconds on an inhale dive. However, after such a dive I recover in about 4 minutes for FRC; however I need at least 7 minutes to recover from an inhale dive to that depth, and for an inhale dive I'd really need to take a 10 minute interval for DCS safety, and even then I could only do about 5 dives before the risk of DCS is extreme.

So, given the similar bottom time and shorter recovery time on my FRC dives, my total bottom is much more than for inhale diving. The shorter recovery times are VERY important for cold winter diving when I can't spend long in the water; during cold water diving I want to spend as little time as possible 'waiting' in between dives to recover.

Also, I don't get narcosis on FRC dives, and the descent is far more enjoyable due to the fact that I sink the whole way down. Also I don't have to do the stressful packing procedure, which also eliminates the risk of a surface BO from packing.

Summary:
FRC
- No narcosis
- No DCS; dive as soon as you are ready to go down, no 'waiting' for nitrogen offloading
- Enjoyable descent sinking the whole way down
- Similar bottom time
- Way faster recovery time
- Greater total bottom time for a given amount of time in the water
- Faster onset of dive reflex (due to quick blood shift)
- No stressful packing or packing BO's
- Reduced negative effects in last 15m of ascent
- Makes me feel more like a seal

 

[cebaztian]

So be it! Breathing out on accent.
I understood that FRC dives are *in general* shorter and less deep than usual ones. Then what are the advantages, besides lower risk of BO?

http://www.fridykning.se/freediving/features/muratarticle1.html

Sebastian
Sweden