Never exhale under the dive

[Jasoncassanova]

for experienced freedivers, what does this mean?

 

[sross]

Hi Jasoncassanova,

Here are the basic principles of gas physiology:

1. Oxygen flows from places where it is at high pressure to places where it can be at low pressure

2. Oxygen actually has a presure in water, just like it does in air

3. Usually, you breathe in air with a high concentration of oxygen, and its pressure is higher in the air in your lungs than it is in your bloodstream, so oxyen flows from the air in your lungs into your bloodstream

4. When you keep the same amount of air in your lungs, total gas pressure stays the same in your bloodstream and in your lungs

5. As you swim your body consumes oxygen, lowering the pressure of the oxygen (technically speaking the 'oxygen partial pressure')

6. This means that oxygen keeps on going into your bloodstream throughout the dive (unless you stay down so long that your bloodstream and lungs completely run out of oxygen)

Now, here's what's bad about exhaling during a freedive:

7. If you breathe out air during a freedive, when you ascend you won't have enough air to re-expand your lungs to their original volume

8. Lungs, ribs & diaphragm are elastic, and create a negative pressure (suction) effect when outside pressure decreases and they don't have enough air inside to passively expand them

9. This negative pressure drives the oxygen partial pressure in the lungs lower than that of the bloodstream, which means that oxygen flow actually reverses direction and oxygen travels out of the bloodstream into the lungs!

10. This can lead to disaster, since your brain doesn’t have a sensor to tell it what the level of oxygen in your bloodstream is. So what you know about your ability level & time limits, and the ‘out-of-breath’ sense you get from carbon dioxide levels, don’t apply anymore.

11. Oxygen level can plummet if you are both consuming it and it is leaving your bloodstream, and it dramatically increases the chances of a Shallow Water Blackout (SWB) SWB tends to happen fast often without warning or little sensation, but with lowered lung pressure they can happen really fast, with the diver having no time to react

12. Here’s a secondary bad effect of exhaling: since there isn’t as much air in the lungs, the diver can be very negatively buoyant, especially if they passed out without being able to pop their weightbelt, and the diver can start sinking really fast, making it much harder for buddies to get to him or her & get them to the surface

 

[Jasoncassanova]

Hi Jasoncassanova,

Here are the basic principles of gas physiology:

1. Oxygen flows from places where it is at high pressure to places where it can be at low pressure

2. Oxygen actually has a presure in water, just like it does in air

3. Usually, you breathe in air with a high concentration of oxygen, and its pressure is higher in the air in your lungs than it is in your bloodstream, so oxyen flows from the air in your lungs into your bloodstream

4. When you keep the same amount of air in your lungs, total gas pressure stays the same in your bloodstream and in your lungs

5. As you swim your body consumes oxygen, lowering the pressure of the oxygen (technically speaking the 'oxygen partial pressure')

6. This means that oxygen keeps on going into your bloodstream throughout the dive (unless you stay down so long that your bloodstream and lungs completely run out of oxygen)

Now, here's what's bad about exhaling during a freedive:

7. If you breathe out air during a freedive, when you ascend you won't have enough air to re-expand your lungs to their original volume

8. Lungs, ribs & diaphragm are elastic, and create a negative pressure (suction) effect when outside pressure decreases and they don't have enough air inside to passively expand them

9. This negative pressure drives the oxygen partial pressure in the lungs lower than that of the bloodstream, which means that oxygen flow actually reverses direction and oxygen travels out of the bloodstream into the lungs!

10. This can lead to disaster, since your brain doesnÃÕ have a sensor to tell it what the level of oxygen in your bloodstream is. So what you know about your ability level & time limits, and the ÁÐut-of-breath sense you get from carbon dioxide levels, donÃÕ apply anymore.

11. Oxygen level can plummet if you are both consuming it and it is leaving your bloodstream, and it dramatically increases the chances of a Shallow Water Blackout (SWB) SWB tends to happen fast often without warning or little sensation, but with lowered lung pressure they can happen really fast, with the diver having no time to react

12. HereÃÔ a secondary bad effect of exhaling: since there isnÃÕ as much air in the lungs, the diver can be very negatively buoyant, especially if they passed out without being able to pop their weightbelt, and the diver can start sinking really fast, making it much harder for buddies to get to him or her & get them to the surface

thanks this is very helpful

 

[jwc3]

I guess a better way to say this is "never exhale during the dive."

 

[BigVin]

good info

 

[mtamborra]

wow this is interesting. I learned in my diving (scuba) courses to always be blowing out bubbles so they don't expand inside you as you ascend and cause issues with your lungs if you hold your breathe....so when I snorkeled alot in Cozumel and swam down to the bottom to take pics of something, usually around 20 ft, I would blow out the air very slowly. Should I have been holding my breathe that whole time?

I did

 

[jhayes75]

wow this is interesting. I learned in my diving (scuba) courses to always be blowing out bubbles so they don't expand inside you as you ascend and cause issues with your lungs if you hold your breathe....so when I snorkeled alot in Cozumel and swam down to the bottom to take pics of something, usually around 20 ft, I would blow out the air very slowly. Should I have been holding my breathe that whole time?

I did

Just so there is not any confusion, he is referring to free diving only, make sure you are exhaling while in scuba.

 

[imwright1985]

wow this is interesting. I learned in my diving (scuba) courses to always be blowing out bubbles so they don't expand inside you as you ascend and cause issues with your lungs if you hold your breathe....so when I snorkeled alot in Cozumel and swam down to the bottom to take pics of something, usually around 20 ft, I would blow out the air very slowly. Should I have been holding my breathe that whole time?

I did

You should have been but 20 ft your risk is a bit less. on scuba if you drop around 30 ft and hold your breath after taking a breath at 30 ft when you surface you have double the amount of air in your lungs as you should have so lungs go pop. with snorkling/freediving you take your breath at the surface pressure so whatever you can fit in your lungs wont grow past what it was at surface. That means that you can hold your breath until the oxygen in your lungs has been consumbed below a safe point then you have problems. if you let breath out you are potentially wasting Oxygen your body can use to help you through the dive

 

[fdog]

I found this quite... interesting.

First of all, I cannot exhale below a depth of 80'. I know - I've tried. This is because of the compression of the lungs due to pressure at depth. Freedivers are familiar with this, and use a technique nicknamed "grouper calling" to pump air out of the lungs so they can continue to clear their ears and mask, because they cannot exhale to do so.

I also found this odd because the residual volume of the lungs is the volume that you cannot exhale beyond. In order to have the lungs at a negative pressure, you would have to have less than this volume in the lungs.

Even a complete exhalation at any depth would not empty the lungs below the residual volume; the air that remains will expand on return to the surface. This would then place the lungs in the range of normal breathing cycles (the vital capacity), and although it may only be a partial breath, would not be negative pressure.

About the only reason for this caution is that the lungs are the "oxygen tank" for a freediver. There is very little oxygen storage capacity in the bloodstream (~2%), and exhaling will reduce the available oxygen. It's an oversimplification, but exhaling half the lung's contents would reduce breath hold time by approximately half as well.


All the best, James

 

[Akimbo]

Exhaling 3-6' below the surface is a technique taught in many freediving courses. At that point you have a lot of momentum toward the surface and most of your buoyancy has returned that was lost to suit and lung compression. The objective is to inhale immediately after breaking the surface instead of after the second or so it takes to exhale first.

Of course, you must also have the snorkel out of your mouth, which is another technique and discussion. However, it should not be done until you have enough experience to consistently judge your proximity to the surface.

Exhaling deeper is a really bad idea for all the reasons mentioned plus you don’t want to loose buoyancy. Freedivers go to length to choose low volume masks because keeping air in their lungs matters! Remember, exhaling one Liter if air is a buoyancy loss of 1 Kg/2.2 Lbs at the surface.