Deep dive breath rate?

[tbone1004]

So for OC, what breathing pattern eliminates CO2 most efficiently with the smallest amount of gas consumed?

I think it will be something like this: from the resting position at the low end of TV, exhale deeply to expire the ERV full of CO2, then inhale to the upper end of TV, then exhale very slowly to the low end of TV, then rest there.

not a doctor, so don't know the official answer. I do know that I breathe to whatever feels comfortable on inhale, and then when I exhale, I try to push just a bit more out so it doesn't build

 

[northernone]

@northernone taking big breaths in doesn't do anything for hypercapnia, it's about fully exhaling and on CCR's the instructors should be talking about breathing patterns and the "cough" that you are supposed to do to push the last of the volume out of your lungs. Doesn't usually matter on OC, but every once in a while you'll catch yourself taking a "big breath" to clear anything out, but it doesn't have to be every breath.

Here is an article which speaks of the relationship between tidal volume and effective CO2 elimination:

Mechanical Ventilation- Increase the Rate or the Tidal Volume? - Critical Care Practitioner

Here's another addressing the same issue when taking "smaller" breaths:

Ultra-protective tidal volume: how low should we go?

With increased gas density co2 becomes an even bigger issue and the physiological deadspace to tidal volume ratio is a factor in ventilation.

In short: breath size is a significant factor contributing to hypercapnia.

I can only refer to the research and repeat what I've been taught. My own experience shows it is significant but thats anecdotal evidence.

I hope some of our resident experts will hazard a reply in clarification or correction. Particularly if I'm barking up the wrong tree in my understanding.

Cameron

 

[tbone1004]

@northernone difference in reducing tidal volume when on a ventilator and consciously getting rid of the ERV though yes?

 

[northernone]

@northernone difference in reducing tidal volume when on a ventilator and consciously getting rid of the ERV though yes?

To be sure we are talking about the same thing:

You're suggesting diving with around .5l TV should be normal?

Quick math suggests your 8bpm and .5-.55 SAC would be 1.7l per breath.

When I'm deep I take bigger breaths using a portion of my (sitting on couch at home) ERV and IRV. As for rough math on a moving target, maybe 4-5x "normal" volume. So yes, big breaths with a slower rate.

I don't know how to reduce ERV safely without increasing the TV. Otherwise it's shallow fast breathing and that gets bad really fast.

Are we on the same topic?

 

[tbone1004]

@northernone yes, however normal TV is .5, and normal ERV is 1.2, so the 1.7l is about right I guess, that's convenient.

What I don't think matters is going into the IRV, which you would have to do with 3.5 ish bpm that you said in your first post. What is your SAC rate when your breathing is 3-4bpm?

 

[rabe]

I use the pattern deep breath-pause-exhale and repeat.
I've never check the rhythm though, but it is something I'm interested in to check...
Usually it's a natural cycle of breathing I'm doing, but I've notice that when i'm focusing on something (take a picture, fix my gear, or something else), I tend to have a longer pause between the inhaling/exhaling part...

 

[northernone]

@northernone yes, however normal TV is .5, and normal ERV is 1.2, so the 1.7l is about right I guess, that's convenient.

What I don't think matters is going into the IRV, which you would have to do with 3.5 ish bpm that you said in your first post. What is your SAC rate when your breathing is 3-4bpm?

The (my?) theory is breathing into IRV helps reduce the co2 mix in RV. In gas blending terms I'm the bottle filled with 1.5l RV gas containing 4-5% CO2. I want this mix as lean as possible, so I'd rather top it up with 3l from a SCUBA instead of 1.7l.

Denser the gas, the slower I breath. Overall I'm around .35 if I'm calm, a little lower on deco but not much. Don't know purely at depth, I use my average depth to calculate SAC.

-------
I'm somewhat derailing the thread, I am interested in the dive communities experience. I don't want to sidetrack into "slower is better" entirely.

 

[TONY CHANEY]

Okay, if I may. You really can’t bring a patient on a vent with Assist control mode for a more matter of fact any mode on a vent into a scuba diving question. Two totally different worlds. Not only are you forcing the breath into the patient (positive pressure ventilation) but also have additional dead space from the vent circuit as well as the ET tube. The ventilation of patients is Mainly based on only two things: height and gender. You might ask why not weight. Because we have to go with IBW (ideal body weight) because once you reach adulthood your lungs do not grow larger with every pound you put on (talking about obesity). Every patient is breathing at one ata, unless they are in the hyperbaric chamber. We seldom even think about gas density unless we are using helium (and that getting to deep for this discussion). Now what the article does not tell you is that when changing vent settings of the rate or tidal volume we have to look at not only the ABG (arterial blood gas) but also the patient’s PIP (peak inspiratory pressure). If the patient’s PIP is about 36cmH2O or higher then increasing their TV could result in blowing their lungs and now we are putting in chest tubes.
Now a snorkel has a lot more dead space than a reg. A reg is in your mouth and the exhaust is a couple of inches away (a little longer for us Poseidon reg. users). So if we are talking about regs. We have to factor in the critical opening pressure or just how hard you have to suck in in order to get the valve to open and give you a breath. If too hard then you will have an increased WOB (work of breathing). This can cause a lot of problems and stress as well as possible Co2 retention. This is where you hear terms like over breathing the reg, air starve, etc. Like I said before, the rebreather is so temperamental in it’s breathing depending on your position in the water column and loop volume.
Other areas we have not even touch on is the physical condition of the dive, kit awareness, number of dives, dive conditions, water temp, comfort level, age, etc. In other words, and I don’t mean this in a judging manner, if you are out of shape, use your kit or rent a couple of times a year, have a cheap reg. then your SAC rate will be high. Some of the ones that posted on here have well over 500 + dives, have a vast amount of additional training, own our kits and dive them almost once a week, have quality gear, try to stay fit, very comfortably in the aquatic environment, etc.
So once, again too many variables.
OBTW, don’t knock yourself if you are under a 100 dives, your SAC rate will improve over time.

 

[leadduck]

Okay, if I may. You really can’t bring a patient on a vent with Assist control mode for a more matter of fact any mode on a vent into a scuba diving question. Two totally different worlds. Not only are you forcing the breath into the patient (positive pressure ventilation) but also have additional dead space from the vent circuit as well as the ET tube.

Do you know a good mathematical model for ventilation that allows simulating the effect of a scuba diver's breathing pattern on the efficiency of CO2 elimination? Then we could simulate different patterns and see if the difference is significant.

 

[Patoux01]

on CCR's the instructors should be talking about breathing patterns and the "cough" that you are supposed to do to push the last of the volume out of your lungs.

I don't use a ccr, so I'm not sure what "cough" you're talking about, but as far as I could find, a "cough" at the end of a breath is typical of airway compression, which is not quite desired, from what I have understood. And it was also presented as being due to dense gas.




Sorry I'm off-topic, but I have to say I never really counted! Nor do I have long videos available at the moment, and when I am taking videos I usually skip quite some breaths.