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

[tursiops]

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..

My response was to the greater issue of breath-holding, not the specific issue of the OP.

 

[Rollin Bonz]

My response was to the greater issue of breath-holding, not the specific issue of the OP.

?

Your response was to my response... My response was to

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.

Not sure where the greater issue of breath holding entered the discussion but I think we both agree on all major points being discussed here... I think...

 

[Nitrox_DiverNY]

My question was to understand why the act of inhalation of breathing gas during ascent did not risk the same LOP issues that breathing holding would on ascent. This was answered quite well by some of the helpful folks here.

This may have seemed like a stupid question to the more experienced here, but to me it seemed like if your breathing in and rising in the water column this in theory sounds like a LOP risk, but it must not be because divers inhale and breath whiling ascending all the time. Now I see that the open airway allows the execess pressure to be vented before it can cause LOP, unless your rate of ascent is crazy fast.

Yes I do wish I had made different choices when it came to instructors for diving, I got caught in the "puppy mill" and did not really understand it at that time. I see now that when it comes to diving instructor choice is critical, and I think some of these courses leave out so much important info.

and no I did not ride the short bus to school lol

 

[Nitrox_DiverNY]

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.

thanks for sharing, its amazing how much endurance wind instruments take. I played the trumpet in high school, but the killer was trying bag pipes I have never been so dizzy in my life trying to learn but I just didn't stick with it

 

[Rollin Bonz]

My question was to understand why the act of inhalation of breathing gas during ascent did not risk the same LOP issues that breathing holding would on ascent. This was answered quite well by some of the helpful folks here.

This may have seemed like a stupid question to the more experienced here, but to me it seemed like if your breathing in and rising in the water column this in theory sounds like a LOP risk, but it must not be because divers inhale and breath whiling ascending all the time. Now I see that the open airway allows the execess pressure to be vented before it can cause LOP, unless your rate of ascent is crazy fast.

Yes I do wish I had made different choices when it came to instructors for diving, I got caught in the "puppy mill" and did not really understand it at that time. I see now that when it comes to diving instructor choice is critical, and I think some of these courses leave out so much important info.

and no I did not ride the short bus to school lol

A lot of us got our open water under the same, or WORSE circumstances. I know my OW instructor wasn't the best. Mediocre AT best. Don't sweat it. I could tell you DIDN'T ride the short bus based on your post, that's why I pointed it out. How great, or not so great your OW instructor was is of little importance. What's important is where you go from here. Seeking knowledge on your own is an important ONGOING step. Never be afraid to ask if you don't know.

 

[doctormike]

Just to clarify one point - the thing that seals the airway when you hold your breath, valsalva, cough, go into laryngospasm, etc... is the glottis (the vocal cords), not the epiglottis.

The epiglottis is a flap of cartilage above the vocal cords. You have no fine direct control of any motion of the epiglottis, although in some patients (particularly infants or people with neuromuscular weakness) it can passively flop into the airway causing minor obstruction. From an evolutionary and developmental point of view, it exists to help avoid aspiration of swallowed food, liquids or saliva into the airway, though the vocal cords. The epiglottis does move with swallowing, along with the muscles of the throat.

While the epiglottis does shield the airway, it doesn't make an airtight seal. Rare infants with a severe version of a condition called laryngomalacia can actually have enough obstruction on inhalation to require surgery to help them with weight gain (we trim the epiglottis or release it's suspensory ligaments). But if you are ascending, no matter what is happening with your epiglottis it couldn't trap air and cause a lung expansion injury. That would be caused by keeping the vocal cords closed.

From an evolutionary point of view, the vocal cords are to protect the airway from aspiration, speech is just a side benefit...

 

[Nitrox_DiverNY]

Just to clarify one point - the thing that seals the airway when you hold your breath, valsalva, cough, go into laryngospasm, etc... is the glottis (the vocal cords), not the epiglottis.

The epiglottis is a flap of cartilage above the vocal cords. You have no fine direct control of any motion of the epiglottis, although in some patients (particularly infants or people with neuromuscular weakness) it can passively flop into the airway causing minor obstruction. From an evolutionary and developmental point of view, it exists to help avoid aspiration of swallowed food, liquids or saliva into the airway, though the vocal cords. The epiglottis does move with swallowing, along with the muscles of the throat.

While the epiglottis does shield the airway, it doesn't make an airtight seal. Rare infants with a severe version of a condition called laryngomalacia can actually have enough obstruction on inhalation to require surgery to help them with weight gain (we trim the epiglottis or release it's suspensory ligaments). But if you are ascending, no matter what is happening with your epiglottis it couldn't trap air and cause a lung expansion injury. That would be caused by keeping the vocal cords closed.

From an evolutionary point of view, the vocal cords are to protect the airway from aspiration, speech is just a side benefit...

doctormike, thank you for such a detailed explanation! very interesting stuff

If I were to inhale now or breath out and purposely hold my breath I can feel something closing in my throat, you are saying that feeling is actually the vocal cords closing and not the epiglottis?

 

[johndiver999]

I have held my breath on ascent while scuba diving a few times (I was super stressed one time and another time I must have thought I was freediving). Anyway, I think if you are healthy and not completely panicked, you will begin to feel a fullness in your lungs and (unless you try otherwise) you will just naturally exhale. Definitely not something to replicate or test, but if you remain reasonably relaxed you should probably be OK. As long as the air way is open, even a little, excess pressure should be vented before it can build up.

Also remember, the expansion rate is not that great until you get really shallow, I just always exhale for the last 3-5 feet, I think.

I found this video, it shows a diver getting an injury. Very interesting I thought. Freediving and breathing compressed air can be dangerous if you forget why your lungs are burning, I guess.

 

[doctormike]

doctormike, thank you for such a detailed explanation! very interesting stuff

If I were to inhale now or breath out and purposely hold my breath I can feel something closing in my throat, you are saying that feeling is actually the vocal cords closing and not the epiglottis?

Exactly.

I actually have a really fun lecture that I give called "The History of Aspiration" talking about how the airway evolved to keep out everything that isn't supposed to be in the lungs. A non-trivial evolutionary challenge for the 4 classes of air breathing vertebrates. I'm working on getting the video of this talk on line, happy to post it once I get it up and running.

It's not every talk that covers both pediatric airway surgery AND how humpback whales do bubble net fishing...!

 

[boulderjohn]

I just want to address the implication that if the instructor did not explain this in the normal flow of the course, the instructor must suck.

The OW course strongly emphasizes that divers should never hold their breath and should continuously breathe. The is what divers need to know. They do not need to know WHY inhaling does not create the same problem as holding the breath. If they are curious and ask exactly the way it was asked in the thread, the instructor should be able to explain it, but that does not mean it should be part of routine instruction.

In instructional design, the goal is to make sure students absolutely know the essential learning points and are pretty darn good on items on the next lower level of need. Once you get down to the items that would be classified as "nice to know," you have to question why you are teaching it. Interference Theory teaches us that time spent learning the things we don't need to know interferes with our ability to learn the things we do need to know.

For example, new OW students need to know about pressure changes upon descent, and that is a standard part of OW instruction. Students are not, however, typically required to know that it is called Boyle's Law, because they don't need to know that.

Another good example is modern first aid instruction. I taught first aid more than 50 years ago, and the standard first aid class was far, far more complete than the standard first aid course today. That is because the people designing standard first aid courses determined that they were teaching too much, and students were not performing first aid when it was needed because they could not remember everything. They therefore dropped the stuff that was less critical in the hope people would remember the critical stuff and use that knowledge when needed.