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RMV Spinoff from Accident & Incident Discussion - Northernone - aka Cameron Donaldson

Discussion in 'Marine Science and Physiology' started by johndiver999, Mar 20, 2019.

  1. Dan_T

    Dan_T Great White

    # of Dives: 500 - 999
    Location: Texas
    Then I get headache after the dive :D At least I did. So, I do no more skip breathing after that.

    My RMV now is 0.4 CFM (it was 0.8 at the beginning, 14 years ago) at normal recreational dive down to 100’ depth. With AL80 my dive is limited by NDL, not by how much air left in the tank. So, I'm not trying to go below 0.4 by skip breathing. Just breathe normally & learn to relax during the dive. Getting the neutrally buoyant at the bottom is my first goal after entry.
  2. rsingler

    rsingler Scuba Instructor, Tinkerer in Brass ScubaBoard Sponsor

    # of Dives: 500 - 999
    Location: Napa, California
    It DOES work. Sort of.
    You can artificially lower your measured RMV, and your tank use, by allowing CO2 to accumulate. CO2 is much more diffusible than oxygen. So it can accumulate in the alveoli and be breathed off in higher concentrations if you skip breathe. But you are NOT decreasing your metabolic requirement. There's enough oxygen to breath-hold and survive because of pressure at depth (more O2 molecules). But the CO2 accumulates as acid, due to trained suppression of the urge to breathe.

    One is trading self-congratulation for a long dive and a low SAC on one's computer log, for a headache, acidosis and decreased reserve in an emergency. Doing that for the pretty fish in the shallows with a short fill is understandable, if imprudent. Doing it out of habit, at depth, with higher gas density, is an invitation to a disaster.

    I get enough headaches at work.
  3. markmud

    markmud Self Reliant Diver ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: South Lebanon, Ohio
    Hi rsingler,

    I have read the training manuals, listened to the instructors, and understood the carbon dioxide thing in general. I have read the threads on Scubaboard.

    I require repetition for learning and the repetition needs to be explained in different terms.

    And then, someone says something short, simple, and profound that takes me full circle. It locks-in permanently. You may have just done that for me with your quoted text.

    I have never had gas consumption issues, per se. Experience has helped. An al80 on a tropical dive was enough. Now it is more than enough. I just relax and breathe normally.

    Now I think I can explain this concept to someone else (in layman's terms).

    The rubber meets the road:
    So an al80 is not big enough for you? Don't use radical breathing techniques, get a bigger tank (assuming proper buoyancy and trim, of course)!

    Sam Miller III and rsingler like this.
  4. rsingler

    rsingler Scuba Instructor, Tinkerer in Brass ScubaBoard Sponsor

    # of Dives: 500 - 999
    Location: Napa, California
    One last thought, for those that are saying to themselves, "He just said skip breathing actually works! I can extend my tank time!"

    CO2, by itself, is narcotic. If you recognize that you have become narc'ed during a dive, then you were already narc'ed well before that. Why would you deliberately impair yourself on top of what will happen with deep air? You cannot train yourself out of CO2 narcosis. Ask me about my buddy's patient in a coma in the Recovery Room whose pO2 was just fine on supplemental oxygen. He was breathing, but it just didn't look right. He had no reason to be in a coma. He woke up when we started bagging him, without doing anything else but lower his pCO2. His blood gas during the resuscitation showed a pCO2 around 100 (normal 40).

    As the airline industry has taught us, mishaps are the result of a small series of holes in the Swiss cheese that just happened to line up that day. Blocking any single one of those holes would have prevented the accident. And you're going to ADD a hole for ten more minutes of dive time?
  5. lermontov

    lermontov Manta Ray

    # of Dives: 500 - 999
    Location: christchurch
    I had a raised eyebrow moment once - I was doing a wreck penetration with a guy and suggested taking an extra al80 ( 3 in total) he said he wouldn't need it to which I thought was a bit cavalier. After the dive I was gobsmacked at how little he used - turns out he held the world record for longest time under water on a single tank
  6. lermontov

    lermontov Manta Ray

    # of Dives: 500 - 999
    Location: christchurch
    im applying for a doctorate thanks to scuba board
  7. RayfromTX

    RayfromTX Student Of Gas Mixology Staff Member ScubaBoard Sponsor

    # of Dives: 100 - 199
    Location: Hill Country of Central TX
    I'd like to thank Cameron for instigating this thread and Pedro Burrito for moving it here where we can discuss it and to our anesthesiologist moderators for not putting us to sleep while explaining it.

    We are often told do this don't do that and not why and why not. It is easy to discard instructions like "just breathe normally and don't skip breathe and you can't conserve air by focusing on breathing less." It is easy to convince ourselves that we know how to make that work and maybe it's just oversimplified like "never hold your breath".

    The explanations by Rsingler and Compressor make it very clear the why's and why nots and also what we actually can do to use the least gas possible. I appreciate the respectful tone that we have seen here and the moderator in charge that has kept it that way when required.

    I will end by suggesting that when we disagree, that we will be much more successful if we avoid telling another member that they are wrong. We can share our knowledge without beginning the statement with. "That is wrong or you are wrong about that." In that way, we may show them the respect that will encourage them to be a part of the conversation instead of making them an adversary. If Cameron taught me anything, it's that we are all in this together and we should all be learning and that happens best without a club.

    Let's go dive and test this new knowledge.
    Hoyden, lv2dive, markmud and 4 others like this.
  8. BRT

    BRT Orca

    I firmly believe CO2 is narcotic. If I raise my exertion without raising my breathing I can get a really unsettled, unhappy feeling at 70' or less. Two FULL exhales and DEEP inhales makes it go away. In my mind this has to be a CO2 narc. When I dive with my fisherman friend I can't ever quite keep up and I just breathe as hard as I can. When my air is low I go up. I try to get bigger tanks for this. He uses much less air than I do under those circumstances. I have done 4 tourist dives with him in Cozumel. Under those circumstances I come up with quite a bit more air than he does.
  9. Jay_Antipodean

    Jay_Antipodean Need to dive more!

    # of Dives: 50 - 99
    Location: Melbourne, OZ.
    I recall reading a while back that the occasional full/lung emptying exhale was good. I have a feeling that comment was found in a rebreather discussion. Is that helpful/good for the OC diver @rsingler @Compressor ?
    markmud likes this.
  10. johndiver999

    johndiver999 Manta Ray

    # of Dives: 500 - 999
    Location: Gainesville FL
    I think skip breathing is a very unwise thing to do unless you are trying to survive an emergency. Perhaps you are deep and run very low on air... you could come up pretty fast at maybe 60 feet per minute rate for 30 or 45 seconds and if you skip breath, you can really save some air. Once you get shallower, you can resume a more comfortable rate and consume your air more slowly. This would be a valid situation to engage in skip breathing from my perspective..

    I can see commending people for being calm and relaxed on a dive and moving smoothly and gracefully. People seem to view the concomitant decrease in air consumption as also commendable, but in reality, equating a low air consumption rate to being "skillful" or "good" is not something I think is smart. It sends the wrong message.

    Who cares how much air you use - as long as you have enough.

    People who are loaded up with Co2 have very little or no reserve capability for exertion should an emergency happen. They are diving in a weakened state. If they have to make a dash to their buddy to secure emergency air or discontinue breathing for a minute or so, they are going to find it much more difficult than someone who has not been doing this.

    In addition, at depth, if you do get behind in respiration demands, the increased density makes it much harder to catch your breath,

    I'm not mentioning the narcotic effects of building acid in your blood because others have already talked about it. I've gotten some pretty terrible CO2 headaches by being stupid. Skip breathing should be discouraged.

    Perhaps I'm being redundant, but moving efficiently and smoothly and gracefully and remaining calm underwater are all desirable skills to acquire, but trying to short circuit the whole "process" and just trying to use less air and viewing it as a surrogate for diving skills is very shortsighted and probably dangerous. I'm honestly unsure why this perspective seems to be somewhat rare.
    markmud and RayfromTX like this.

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