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#1 Rule In Scuba, Don't Hold Your.....

Discussion in 'Basic Scuba Discussions' started by rob.mwpropane, Sep 7, 2017.

  1. Schwob

    Schwob Solo Diver

    # of Dives: 100 - 199
    Location: Illinois - ("Schwob", formerly "Schwaeble")
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    :wink:Sincere apology, but for a millisecond my gutter control circuitry failed and I could not avoid this thought: "Good thing nobody's mind is in the gutter for longer than a millisecond..."
     
  2. MikkelBC

    MikkelBC Instructor, Scuba

    # of Dives: 200 - 499
    Location: Denmark
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    I apologize if I came across as patronizing. I was responding to the post you made where you suggested that you would train one way during the course but prefer to use another procedure "in a real situation".

    In a real situation, your handling of it will come down to what you have programmed into your 'muscle memory' by repetitive training. Knowing something consciously is often not enough - it needs to be a reflex in order to work in a stressful situation. This is true even for very experienced divers.
     
  3. FinnMom

    FinnMom Divemaster Staff Member

    # of Dives: 500 - 999
    Location: Finland
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    Preferable to actually holding your breath is to simply breath in very, very deeply and then exhale as incredibly slowly as possible. It's best not to "stopper" your brath like you do before trying to swim a long distance underwater.
    Two items for thought
    1) We are creatures of habit. It's a good habit to not ever really hold your breath on scuba in order that hopefully you will be less likely do it without realizing it. It is for example easy to unconciously hold your breath when trying to take a photo/video, and then drift upwards w/o realizing it as you attention is absorbed with your activity. Esp at very shallow depths (exactly where the good light for photos/videos is) it's good to be careful. The pressure at 5m is 50% greater than at the surface; that's a huge change in a very short distance.
    2) Learn more about how incredibly tiny and fragile the air sacs in your lungs are. This helps a great deal in understanding how easily some measureof damage could be done.

    So no, it's not a law carved in stone, but it is a good habit.
     
    RainPilot likes this.
  4. dmaziuk

    dmaziuk Loggerhead Turtle

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    It should vent some CO2. I don't believe it will vent enough CO2 to help with the urge to breathe though. As far as the ability to extract more O2 from what you have in your lungs, I think it's irrelevant really: it's the CO2 that's gonna make your CESA miserable. Unless you're freediver trained to ignore the urge.
     
  5. TMHeimer

    TMHeimer Divemaster

    # of Dives: 500 - 999
    Location: Murphy Cove, NS ,CANADA (Eastern Shore-Atlantic)
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    1,550
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    Doesn't answer my "more O2 to tissues"? question, but what you say makes sense.
     
  6. boulderjohn

    boulderjohn Technical Instructor Staff Member

    # of Dives: 1,000 - 2,499
    Location: Boulder, CO
    22,102
    12,580
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    Think it through.

    Part I: What's going on with the air in the lungs
    Just to make up some numbers, let's say that at sea level your lungs have 1 million molecules of oxygen in them with each normal breath. If you are at 20 meters/66 feet of seawater, that same volume of lungs will have 3 million molecules of oxygen. As you ascend and exhale, you will still have more molecules of oxygen in your lungs than you would breathing normally at the surface until maybe the very end, assuming you maintain a normal lung volume throughout the ascent.

    Part II: What's going on with blood and body
    Your blood circulates throughout the body, passing regularly through the lungs where it comes into contact with the air through the thin walls of the alveoli. As it goes through the body, it carries oxygen, chiefly through the hemoglobin. The blood volume remains the same throughout the experience. The amount of hemoglobin remains the same. The ability of the hemoglobin to carry remains the same. In normal breathing on the surface, we only use a fraction of the oxygen we inhale--the rest is exhaled. We therefore have more than we need. When we are diving, each lungful contains even more oxygen than we need, and most of it is just exhaled. During a CESA, the blood continues to pass through the excess oxygen in the alveoli, just as it did before the CESA.

    Part III: What about oxygen already in the tissues?
    Our sadly departed diving physician, Lynne Flaherty (TSandM) used to explain that the body has enough oxygen in its tissues to sustain consciousness for 1 to 1.5 minutes, even with no additional oxygen coming from the blood.

    Part IV: Why do I have that panicky urge to breathe--doesn't that mean I need oxygen badly?

    Nope. Although the body does have a signal when it needs oxygen, it is barely perceptible, and most people have never even experienced it. That panicky urge to breathe is created by the buildup of carbon dioxide, which is in turn caused by our failure to exhale rather than our failure to inhale.
     
    Last edited: Sep 13, 2017
  7. dmaziuk

    dmaziuk Loggerhead Turtle

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    Yeah, I got distracted. I was thinking more that the gas exchange keeps going, but CO2 isn't getting out. I.e. you can utilize more O2 than the couple of percent we usually do. But not because of the pressure or "expanding air". For that, the answer is what @boulderjohn says in part 2: your hemoglobin won't carry more O2 just because PPO2 in your lungs goes up.

    Back when I was an athlete I too was told about one minute of oxygen in the tissues. At the previously safe ascent speed, it would mean you could safely CESA from your quoted 60' without any air in your lungs at all. I'm sure a trained freediver could do it without going faster than 60 feet per minute...
     
  8. TMHeimer

    TMHeimer Divemaster

    # of Dives: 500 - 999
    Location: Murphy Cove, NS ,CANADA (Eastern Shore-Atlantic)
    9,351
    1,550
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    OK, think I get it. In simple terms you're both saying that there is plenty of oxygen in the blood (and thus tissues) regardless of what's in the lungs--to do a reasonably normal safe speed CESA, even from 60' or more. Expanding air in the lungs doesn't change that, correct? So am I correct in that exhaling slowly amounts to the same thing as sitting in a chair at home holding your breath (other than as you say dmaziuk, that some CO2 is escaping, which may slightly reduce your urge to breathe)?
     
  9. rob.mwpropane

    rob.mwpropane Angel Fish

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    No worries. Actually, after my car ride over practicing, I would do it exactly how I did it in class. Just needed to learn how to "aaaahhh" with expelling too much too fast.
     
  10. boulderjohn

    boulderjohn Technical Instructor Staff Member

    # of Dives: 1,000 - 2,499
    Location: Boulder, CO
    22,102
    12,580
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    As I said seveal times before, it is easier when you are ascending than it is when going horizontal. There are other ways to do it than saying "aaahhh." Some people prepfer to do a zzzzzzz sound to limit air escaping. My students generally preferred what I called the "King Tut" technique--making a "tut tut tut tut tut" sequence as you go.
     

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