Breathing and buoyancy

[firstdive2005]

Am an engineer and this way makes me understand better
Hi Solly! While I respect the analytical mind, I hope your just trying to figure out the dynamic behind the science of breathing at pressures. After you have tried this and I think most have, dumb down and just dive. If you dont 'just dive', it will take too long to have fun.


or am I missing something?
An understatement, I realize the context, what you are missing is time underwater. Please, I really am not trying to make light of your analyzing the 'art of breathing compressed gas', but truly Solly the results you seek are in the experience after you practice. It's a cool ride once you master it, as others has stated. I wish you well. kev

It only gets better.

 

[TSandM]

Thansin, you have it exactly right. THIS thread from Rick Murchison goes into more detail. (Don't pay attention to the people who are giving you grief for thinking about this -- they just aren't people who like to analyze everything. I understand you.)

Changing the volume you cycle around is the breath control that we use for fine tuning buoyancy during a dive -- to go up and over a small obstacle, for example, or to initiate a descent. But it's a tool that needs to be used carefully, because overuse can result in ineffective ventilation, CO2 headaches, and increased gas consumption. When I first started running line, my gas usage climbed a lot -- until a friend told me that he noticed I was using my breath for neutral buoyancy while putting ties in, and recommended adjusting my wing or suit instead. Once I did that, my consumption dropped quite a bit.

So yes, your analysis is correct, and it is a tool to be used but not overused.

 

[gypsyjim]

My dad was an engineer, and I am more of an artist. Dad and I spoke very different languages at times.
But whether he was using his slide rule, or I my less scientific methods, many times the answer was the same when we were done. Just different minds, working different ways.

 

[HenrikBP]

Let's say the lungs fill from 0 to 10.
You could set the neutral buoyancy at 8 and then keep:
- A symetric breathing cycle ranging from 6 to 10.
-<snip>
Alternatively, you could set the neutral buoyancy at 2, and reverse the full and empty times, or set it at 5 and keep a symetric breathing cycle from 0-10, 2-8 or whatever.

That's how I think of using my lungs for the fine buoyancy control TSandM mentions.

If I pay attention I will notice if for instance I'm breathing around your "higher" lung fill point (8 in your example). That makes me realize I need a bit more positive buoyancy to stay neutral at that depth, and my higher "lung fill" accomplishes that.

If I then want to descend, I shift my breathing to cycle around a lower "lung fill" which in turn makes me a bit less buoyant and I will descend.

Not boring at all

Henrik

 

[elan]

- You shouldn't stop breathing.

I do not think you should not stop breathing. What's the reasoning of that ?

 

[ScubaSteve]

I do not think you should not stop breathing. What's the reasoning of that ?

Perhaps rewording this question will help but are you asking why one should not hold their breath underwater?

 

[elan]

depth will affect your analysis, when you breath near the surface the volume of your lungs are large as there is not a lot of pressure around hence your analysis about breathing and buoyancy is correct, however once you get deeper, your lung volume change with breathing will not have that effect over your buoyancy.
That is why when diving shallow you can dispense with your BCD inflating/deflating action and just use your lung volume to control your depth, however once you get to below 15m (in my case) I have to use the BCD to control my buoyancy.

You lung volume does not change over depth. If you have to use BCD to control your buoyancy I think you are doing something wrong. Depending on the amount of gas you have you do have to add end remove air from you bcd if you do great changes in depth (those you cannot compensate with your lungs) as air compresses or expands in the BCD. This will only be true if you have any air in BC. And the deeper you go the less BC operating you need to do per feet of the water column as the pressure does not change as quick as on the surface.

 

[elan]

On the other hand your lung max volume at surface is not the same max volume at 10m, as pressure increases the volume will tend to decrease, or am I missing something?

Yes you are missing the point that the pressure in your lungs will be equal to the pressure in the water column as your regulator will be adjusting the pressure of the gas.

So if you are on the way down not breathing the volume will be reducing , but once you take another breath the volume will return to the initial. So the volume of your lungs is the same at the surface and say at 100'

 

[elan]

Perhaps rewording this question will help but are you asking why one should not hold their breath underwater?

Nope, I'm asking exactly what I have asked Holding the breath implies not breathing but the opposite is not true. I can be non-breathing and keep my airway open. Though it's just a wording I have found that it does make difference when maintaining good buoyancy.

I used to breath continuously underwater after misinterpreting "do not hold your breath phrase" when I started diving and my air consumption went though the roof. I do not breath continuously on the surface as a matter of fact. When I switched to my normal breathing my consumption fell as much as 2 times and it became much easier for me to be stable underwater.

 

[ScubaSteve]

Well, if you understood "do not hold your breath" to mean "eliminate the split second pause while the body switches from inhale to exhale to inhale", then I understand but wonder what the Instructor said when you questioned this. However, that is an extremely dangerous way to dive which, for most people (not you though I suppose), would lead to hyperventilating and possibly a build up of CO2 in the system. The pause between inhale and exhale when done as normal process for breathing, is in my layman's terms, the body's split second reconfiguration from Inhale to Exhale. It is not holding your breath. What you imply is that there is no need to inhale or exhale at all as long as you keep an airway open. Keeping an airway open but not breathing is, IMO, BOTH not breathing AND holding your breath even though it will, in theory allow for the air in your lungs to compress and/or expand according to your position in the water column and the associated pressure.

Breathe Normally says it all.

Nope, I'm asking exactly what I have asked Holding the breath implies not breathing but the opposite is not true. I can be non-breathing and keep my airway open. Though it's just a wording I have found that it does make difference when maintaining good buoyancy.

I used to breath continuously underwater after misinterpreting "do not hold your breath phrase" when I started diving and my air consumption went though the roof. I do not breath continuously on the surface as a matter of fact. When I switched to my normal breathing my consumption fell as much as 2 times and it became much easier for me to be stable underwater.