Why is inhaling while ascending safe, if breathing holding will cause lung over expansion?

[Nitrox_DiverNY]

So the reason we say never hold your breath on scuba is because it's the easy way to prevent an issue.
Physiologically there is a HUGE difference between "holding your breath" and "not actively breathing". That difference is whether or not the epiglottis is open or closed.
When you take a breath in and are asked to "hold your breath", if you pay attention to your throat you can actually feel when you stop inhaling when the epiglottis closes. The reason this matters is that the epiglottis can hold back a higher pressure than the lungs can withstand. I.e. the lungs are the weak link in the chain and if you are "holding your breath" with the epiglottis closed the lungs will burst before the epiglottis lets go.
When you are actively inhaling or exhaling, the epiglottis is open and as long as it is open it is highly unlikely for you to be able to suffer a lung over expansion injury. I suppose it is possible but you would have to do something pretty egregious so it is highly implausible. The same applies to when you "pause breathing", so long as the epiglottis is open, there won't be a differential pressure between your lungs and your open air cavities *sinus, mouth, nose, etc. that can equalize with ambient pressure*.

thank you that was very informative and helpful!

I just took a deep breath then stopped inhaling to feel the epiglottis close and I think I can feel it close. Its very cool you can actually feel if its opened or close and control it, I guess its one of those things you never think about that's on auto pilot.

Maybe to some extent it takes a little practice to keeping the epiglottis open correctly, but I assume that comes with time and experience diving

 

[Rollin Bonz]

thanks, and very interesting. so regardless if your lungs are full of air, the pressure will force the excess air out as long as your airway is open

@tbone1004 did a superb job of explaining it. The easiest way to ensure your away is open is to keep breathing (i.e. don't hold your breath). You don't HAVE to be actively breathing to maintain that open airway, but it's the easiest way to know for sure, and it's something you can actively "do" rather than "relax" your airway, which is hard to know if you're doing.

 

[tbone1004]

thank you that was very informative and helpful!

I just took a deep breath then stopped inhaling to feel the epiglottis close and I think I can feel it close. Its very cool you can actually feel if its opened or close and control it, I guess its one of those things you never think about that's on auto pilot.

Maybe to some extent it takes a little practice to keeping the epiglottis open correctly, but I assume that comes with time and experience diving

I'm also a professional wind musician so I've always paid attention to breathing but you can definitely feel it when it closes because your diaphragm won't really let you create a vacuum in your lungs and it feels weird. You can push against the epiglottis and build pressure from your diaphragm and then open it. With time you can mess around with it and really get a feel for what your body is doing.
As instructors though, the reason we ask for small bubbles whenever the regulator is out of your mouth is because it's the only way we know that you don't have it closed. There is a bit of fear mongering that happens from most instructors who don't fully understand the physiology behind it and from the ones that do, they often don't have the time or interest from the students in why so it is undoubtedly easier to just say "never hold your breath, exhale small stream of bubbles whenever the regulator is out of your mouth".

In terms of diving though, the key is really to just keep a natural breathing pace. We talk about the "scuba breath" and breathing from the bottom of your lungs which is important to prevent a buildup of CO2, but that doesn't mean that the rate of breathing both in terms of volume and respirations per minute should be anything you think about. If you're just casually diving you should be breathing similarly to walking down the street and if you're hovering over a coral head then it's the same as sitting on the couch reading Scubaboard. Volume is not big, frequency is quite low. If you pay attention to your breathing you will find your natural pace of breathing and habits that make you feel comfortable.
Part of that comfort is how your breathing affects your buoyancy. I like to be slightly negative on an empty breath so my breathing pattern is a fairly rapid inhale, pause, slow exhale for about half of my breath, then a rapid exhale to purge everything out and then rapid inhale again. This keeps my position in the water quite stable and on a normal sized breath if I'm pausing at the end of the inhale I don't rise in the water column. A slightly bigger breath and I'll go up but normal is stable. Exhale is going down hence the rapid second half of exhale and immediate inhale again. This actually follows what I do playing instruments so it's a natural breathing pattern for my body but some of my buddies who are athletes have completely different breathing patterns so it's all unique to what your body is comfortable doing.

 

[Nitrox_DiverNY]

I'm also a professional wind musician so I've always paid attention to breathing but you can definitely feel it when it closes because your diaphragm won't really let you create a vacuum in your lungs and it feels weird. You can push against the epiglottis and build pressure from your diaphragm and then open it. With time you can mess around with it and really get a feel for what your body is doing.
As instructors though, the reason we ask for small bubbles whenever the regulator is out of your mouth is because it's the only way we know that you don't have it closed. There is a bit of fear mongering that happens from most instructors who don't fully understand the physiology behind it and from the ones that do, they often don't have the time or interest from the students in why so it is undoubtedly easier to just say "never hold your breath, exhale small stream of bubbles whenever the regulator is out of your mouth".

In terms of diving though, the key is really to just keep a natural breathing pace. We talk about the "scuba breath" and breathing from the bottom of your lungs which is important to prevent a buildup of CO2, but that doesn't mean that the rate of breathing both in terms of volume and respirations per minute should be anything you think about. If you're just casually diving you should be breathing similarly to walking down the street and if you're hovering over a coral head then it's the same as sitting on the couch reading Scubaboard. Volume is not big, frequency is quite low. If you pay attention to your breathing you will find your natural pace of breathing and habits that make you feel comfortable.
Part of that comfort is how your breathing affects your buoyancy. I like to be slightly negative on an empty breath so my breathing pattern is a fairly rapid inhale, pause, slow exhale for about half of my breath, then a rapid exhale to purge everything out and then rapid inhale again. This keeps my position in the water quite stable and on a normal sized breath if I'm pausing at the end of the inhale I don't rise in the water column. A slightly bigger breath and I'll go up but normal is stable. Exhale is going down hence the rapid second half of exhale and immediate inhale again. This actually follows what I do playing instruments so it's a natural breathing pattern for my body but some of my buddies who are athletes have completely different breathing patterns so it's all unique to what your body is comfortable doing.

really great stuff! I am very appreciative of your thorough explanations, this was very helpful!

 

[rick00001967]

hi all I had a question about inhalation while ascending,

If ascending at a safe conservative rate say 10-20fpm why does the act of inhalation of breathing gas no pose a risk of lung over expansion injury?

It is the slow ascent that basically rules out a LOP injury, or is it because your airway is open even if you are rising in the water column while breathing in?

Is it safe to breath in while ascending (given a safe ascent rate below 30fpm) or will this cause any issues?



I hope my question made sense, as a relatively new diver if anyone could offer any more clarity of this question that would be great!. Thanks and safe diving to all!

 

[rick00001967]

You should always feel comfortable asking any questions here. But in all seriousness, if this issue was not clearly explained by your instr i would be questioning what else was not taught properly.

 

[Rollin Bonz]

You should always feel comfortable asking any questions here. But in all seriousness, if this issue was not clearly explained by your instr i would be questioning what else was not taught properly.

OP doesn't sound like he rides the short bus to school. It's a complex "why?" question to what was probably presented to him as, at worst "it's just the way you do it" and at best "to prevent a lung injury from gas expansion" in his OW class. Curiosity should be commended. If you received a more complex anatomical and physiological answer in your OW class, I assure you, you are in the minority.

PS. Lighten up...

 

[tursiops]

OP doesn't sound like he rides the short bus to school. It's a complex "why?" question to what was probably presented to him as, at worst "it's just the way you do it" and at best "to prevent a lung injury from gas expansion" in his OW class. Curiosity should be commended. If you received a more complex anatomical and physiological answer in your OW class, I assure you, you are in the minority.

PS. Lighten up...

I sort of agree with you, but mostly I do want to take very seriously any questions (or inadequate explanations) of why one doesn't hold their breath, especially while ascending. This is perhaps the number one safety issue for a diver, so I question the "lighten up."

 

[Rollin Bonz]

I sort of agree with you, but mostly I do want to take very seriously any questions (or inadequate explanations) of why one doesn't hold their breath, especially while ascending. This is perhaps the number one safety issue for a diver, so I question the "lighten up."

I don't think OP was asking why you don't hold your breath while ascending, he was asking why actively inhaling isn't the same as or as bad as holding your breath...

Was that not the question?

If I mis-interpreted the question and it WAS simply why you don't hold your breath while ascending I would agree with you, but I'm pretty sure it wasn't.

Edit: Yeah, it's actually the title of the post now that I re-examine it..

 

[Blackcrusader]

is having a brief pause after inhalation considered to be breath holding in this situation? or should it inhale in and then right back out ?

This is how I sometimes dive. If going slowly and not moving then there is no need to have more frequent breaths. I inhale but never fill my tidal volume, and I also have a very tiny bubble trail as I always have gas being exhaled. It is not something I did as a new diver. I played wind instruments for many years Euphonium and Trombone. So you learn about using your exhale to play music and also to control how long you could hold a note. I think that has also helped me.