Holding your breath while ascending

claymore · Mar 12, 2009

I know that this subject has been done before and I understand and believe in the always breath when you are ascending rule but I have a question on the physics and physiology that are involved when you move an unsealed vessel with a gas inside (your lungs) from an area of higher pressure to an area of lower pressure.

WouldnÃÕ the gas flow out of opening of the vessel to equalize the pressure inside?

I know that if you ascend and there is not a way for the air to escape from your lungs they will explode.

If when you are ascending you do not close your airway wouldnÃÕ any increase in air volume flow out through the airway and out of your mouth?

I am basing this on the fact that when most people take a breath and hold it they are not closing the airway off they are just keeping their diaphragm pulled down thus creating a larger volume of air in the lungs and keeping it there until the diaphragm is released. In this scenario the lungs are not sealed and should allow any increase in volume in the lungs to escape out through the mouth.

rstofer · Mar 12, 2009

claymore:
I know that this subject has been done before and I understand and believe in the always breath when you are ascending rule but I have a question on the physics and physiology that are involved when you move an unsealed vessel with a gas inside (your lungs) from an area of higher pressure to an area of lower pressure.

Clearly, there are moments during the breathing cycle when air is neither coming in or going out. That doesn't mean the airway is closed. This breathing pattern will naturally occur during ascent. It's not like there is a recommendation to 'pant' during ascent.

WouldnÃÕ the gas flow out of opening of the vessel to equalize the pressure inside?

Yes and it would occur naturally.

I know that if you ascend and there is not a way for the air to escape from your lungs they will explode.

If when you are ascending you do not close your airway wouldnÃÕ any increase in air volume flow out through the airway and out of your mouth?

Yes.

I am basing this on the fact that when most people take a breath and hold it they are not closing the airway off they are just keeping their diaphragm pulled down thus creating a larger volume of air in the lungs and keeping it there until the diaphragm is released. In this scenario the lungs are not sealed and should allow any increase in volume in the lungs to escape out through the mouth.

I don't understand your point. We are taught not to hold our breath. Nobody every said that breathing had to become panting to ensure that air was always in motion.

Richard

String · Mar 12, 2009

When holding your breath you are closing your airway so by definition that becomes a sealed system.

eponym · Mar 12, 2009

Claymore:

Yes, if you leave the airway open your lungs can vent. In training we like to see bubbles because otherwise we can't tell whether or not a student has the airway open.

You can also hum through loosely-closed lips, which produces a small bubble stream.

-Bryan

captain · Mar 12, 2009

The open air way is the basis for the CESA being possible.

Teamcasa · Mar 12, 2009

Most people can hold their breath and keep their mouth open.

I do know the lungs are pretty fragile and it does not take that much pressure to cause serious injury so why risk it?
Breathe normally during your nice and slow assent, your lungs will thank you.

bleeb · Mar 12, 2009

claymore:
I am basing this on the fact that when most people take a breath and hold it they are not closing the airway off they are just keeping their diaphragm pulled down thus creating a larger volume of air in the lungs and keeping it there until the diaphragm is released. In this scenario the lungs are not sealed and should allow any increase in volume in the lungs to escape out through the mouth.

Actually, I believe the exact opposite is true the vast majority of the time, especially since it's the 'normal' reflex. People can be trained out of it, but changing a reflex is difficult. Like swallowing, the human body's standard reaction is to close the epiglottis. That's why there's so much talk in courses about techniques like humming, which are expressly intended to override the natural reflex.

tomboyy · Mar 12, 2009

I think what the OPs asking(just for the sake of asking as i don't think he wants to know if he can hold his breath) is if your ascending wouldn't the increased volume make you let it escape or in other words you would feel the pressure and exhale or you'd have to actually try to hold it in.

If this is not what he's asking.... nevermind

TSandM · Mar 12, 2009

It would seem intuitive that increased pressure inside the lungs would make you want to exhale, but in practice, that's not what happens. A closed glottis can withstand a lot of pressure, and clearly enough to cause problems.

It is quite possible to hold a given volume in the lungs with the glottis open, and in that case, expanding gas would escape spontaneously.

siikik · Mar 12, 2009

Teamcasa:
Most people can hold their breath and keep their mouth open.

I do know the lungs are pretty fragile and it does not take that much pressure to cause serious injury so why risk it?
Breathe normally during your nice and slow assent, your lungs will thank you.

I'm going back a few years... but if memory serves, the alveoli in your lungs (where gas exchange takes place) are only capable of withstanding 2psi over ambient before they give way. You can do the math and figure out how far up the water column you need to go before you reach this... but it isn't far... especially at shallow depths.

...just in case your instructor didn't mention how easy it was to get one of the pulmonary maladies.

Ken

Holding your breath while ascending

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claymore

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