Head high, hard breathing?

[jeffreyd]

I was doing my pool sessions for OW on 4-2,4-3. During the pool session we were told to watch the instructor ESA. Well as I was watching him (kneeling on the bottom of the 14' pool) and when I looked up it became difficult to breathe. When I looked horizontal again it went back to normal.

I know it is because the water pressure on the regulator is less than the water pressure on my lungs. (its a sherwood brute) I didn't think 6" would make such a difference in the reg.

Thanks.

 

[spectrum]

Could you have been constricting your airway by hyperextending your neck?

Could your posture have caused your BC to restrict your chest?

I have not noticed a difference from being in a vertical posture.

Other than that your physics is right on.

Keep in mind I'm only 2 pool sessions ahead of you.

Pete

 

[jeffreyd]

Could you have been constricting your airway by hyperextending your neck?
Just did the same thing here on the couch and no difference
Could your posture have caused your BC to restrict your chest?
BC fully deflated

I have not noticed a difference from being in a vertical posture.
I was vertical, but imagine kneeling on the bottom and staring straight above you.
Other than that your physics is right on.

Keep in mind I'm only 2 pool sessions ahead of you.
congrats
Pete

Jeff

 

[Mako Mark]

when you change body position you change the dynamics of the bouyancy of the air you breate.

while body position has no effect on breathing resistance on land, under water wai has the tendency to rise.

this means when you are vertical, the air wants to rise and the exit to you airway is at the top, so it is easy to exhale, the bouyancy of the air helps the exhalation.

If you invert and stand on your head, you actually have to force the air from your lungs downwards a foot and a half from the (bottom of the ) lungs out of the mouth or nose. Therefore it is very difficult to exhale and divers that are head down generally become 30% more bouyant than when they are head up.. You see this manifest in new divers that attempt a head first descent and fail.

The same is so when you lie on your back. The natural bouyancy of you breath makes it want to escape and most divers become negative when they lie on their back.

If you really want to see the effect of the mechanics of breath bouyancy, try a rebreather.....

 

[RICHinNC]

And it just could be a charachteristic of the reg you had. My primary is fine until I go totally vertical head down. Then it can be a strain to suck air. All I have to do is level out and its fine again.

My lds even told me that was what would happen even before I bought the thing.

 

[DA Aquamaster]

The relative positions of the center of the diaphragm and the mouthpiece account for much of the difference. When looking up, or worse, straight up, a seconds tage of conventional design will have the the diaphragm at the highest point in the reg and if the center of the diaphragm is above the mouthpiece, additional inhaltion effort (cracking effort) will be required to overcome the reduced water pressure acting on the diaphragm.

Conversely, if you are looking downward with a conventional second stage design, the center of the diaphragm will be lower than the mouthpiece and more water pressure will be assisting the diver in opening the valve so inhaltion effort will be reduced. In the same situation the diaphragm is also substnatially lower than the upper edge of the exhaust valve so in some cases, if the cracking effort of the valve is too light, air in the second stage leaking out the elevated exhaust valve will cause the pressure in the second stage to decrease enough to open the poppet and start a slight freeflow.

So beathing resistance will change with the angle of the second stage. With a second stage with a diver adjustable cracking effort, you can change the cracking effort to accomodate the change in position. With a non-adjustable second stage, the cracking effort will need to be adjusted as a compromise so that it is high enough to prevent a freeflow when face down and yet as light as possible to minimize cracking effort in normal swimming and face up positions.

This is where regs like the Scubapro D300, D350, D400 and the Dacor Quantum shine as their exhaust valves are co-axially mounted in the center of the diaphragm so the maximum height difference is never more than about .5 inches. The D300/350/400 has a further advantage in that the angle of the diaphragm changes the worst case postion to positions not normally experienced by divers. So the lack of a diver adjustable cracking effort is not missed as the reg breathes the same regardless of position.

 

[Hank49]

What DA Aquamaster said. When you look up the air inside the second stage wants to go up so it's pushing up on the diaphram making in harder to suck it in to depress the lever and open the valve. Looking down is the opposite. The air puts no pressure on the diaphram.