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Teamcasa
November 3rd, 2009, 03:07 PM
This issue was brought up in another thread but I think it needs to be posted here as well.


(edited) Shallow hyperventilation is sort of like panting. When someone starts to get nervous (even if they don't realize it) or maybe starts working harder than planned, it can be a common breathing pattern.

The problem with shallow hyperventilation is that you are now not exhaling fully. So what's happening is that the CO2 your body is producing, which would normally have been expelled when you exhale, is slowly building up.

As you were (hopefully) taught in your basic class physics discussion, CO2 is the stimulus to breathe. The more CO2 we have, the more urgent that need feels like.

When you shallow hyperventilate and the CO2 builds up, you start to feel like you can't catch your breath. You may take a breath off the reg and it doesn't satisfy the feeling of air starvation. But it has nothing to do with you not getting enough air IN. It has to do with you not getting enough CO2 OUT.

So if you find yourself in this situation, the thing to do is . . . EXHALE. As big as your can. Take a breath. Exhale BIG again. Take a breath. Exhale BIG again. Generally two, three, or four BIG exhales will blow off enough CO2 that the not-getting-enough-air feeling will go away.

And once you get rid of that need-more-air feeling, you can decide whether or not to continue the dive. To me, this is all part of the walk-away lesson from your experience. Thanks for sharing.

- Ken

Also from that thread:


Ken - Sounds similar to what happened to me the first time I was 85 ft. I started experiencing tunnel vision and felt my reg was not giving me enough air. I looked at the other divers around me to see if they looked the same as how I felt, they did not. I looked at my SPG which told me I had more than enough air so I took deep inhales and exhales until the tunnel vision went away. I felt comfortable enough to continue the dive after the tunnel vision went away. My first and last time I ever had that experience.


FWIW, there's research to suggest that CO2 retention exacerbates the effects of narcosis. At the very least, it interferes with adequate oxygenation of...the brain. Ken's recommended technique to slowly inhale and exhale fully can effectively head off these problems before they become a real issue. This is definitely something that should be taught to students before the deep dive of the AOW specialty.

lowviz
November 3rd, 2009, 03:11 PM
Newbie OW training headaches are another good sign that you are breathing incorrectly.

Cave Diver
November 3rd, 2009, 03:15 PM
CO2 is thought to be a contributor to "Darc Narc." This is a type of narcosis that gives you a feeling of dread, doom, overall malaise. I've experienced this feeling during an exit in a cave that I'd dove many times.

Unrecognized and untreated I can see how it could easily build up and lead to feelings of claustrophobia and panic.

As others stated, long, full exhales are key to getting breathing under control and dispelling the effects of it.

I've also had a headache that I attributed to CO2 buildup. As someone that used to get migraines, I have to say the CO2 headache ranks as one of the worst I've had and there was no relief from it until it wore off.

Bubbletrubble
November 3rd, 2009, 03:18 PM
This review article (http://www.thetritons.com/Library/CO2 and Diving.pdf) written by Dr. Johnny Brian, Jr., (Associate Professor, Univ. of Iowa) might be of some interest to people. It's entitled "Carbon Dioxide, Narcosis and Diving." Enjoy.

CamG
November 3rd, 2009, 09:35 PM
Greetings Teamcasa and this is a great thread that would be very useful on the new divers forum as well. The breathing control and or regaining control is priceless. It is right on the money the big exhales allows the built up C02 to escape this is a practice that I have had to implement twice thus far in my time diving. Once at 120' and 137'. The post dive break down was very valuable, over stressed due to junk fins and slightly over weighted. Both were easy to correct but allowed for C02 to build up. Both times I closed my eyes and gained breathing control by using the big exhale method. I find it easier to relax when I breath long in and long out even a little past the all out phase.
This would be a really great addition to the new diver forum because it goes hand and hand to getting the point of normal breathing patterns under water nailed down.
Good material and that is what makes Scuba Board awesome!
CamG Keep diving....keep training....keep learning!

TSandM
November 4th, 2009, 01:12 AM
There are a lot of different things that contribute to CO2 retention. Excessive exertion at depth can definitely do it -- I've come out of Ginnie Springs several times sick as a dog from overworking. A poorly adjusted regulator can do it -- a friend bought a new reg, and dove it, and couldn't figure out why she always felt as though she couldn't breathe, and ended the dive with a headache. Turned out the cracking pressure on her second stage was three times what it should have been.

Diving the wrong mix contributes, too -- gas density at depth begins to play a significant role in alveolar ventilation. I'm not sure whether I like helium as much as I do because of nitrogen narcosis, or because it reduces CO2, but the difference, even at 130 feet, is night and day.

B.L. Justice
November 4th, 2009, 02:08 AM
This is a great thread. I have had that OOA feeling at depth a couple of times. I have overcome it by slowing down and trying to focus on a simple task. Until reading these entries, I didn't realize that CO2 had that big an effect.

I wonder if doing some deep breathing to purge CO2 before dropping down would help to reduce the build up? Anyone have any thoughts on this?

TSandM
November 4th, 2009, 02:21 AM
No -- deep breathing before diving would lower your CO2 for a minute or so, perhaps, but certainly within five minutes, you'd be equilibrated again.

ROMO DIVER
November 4th, 2009, 03:05 AM
I am a little confused here (it might be excessive CO2 levels) but I would like to know where the idea that hyperventilation causes an increase in CO2 levels comes from. Every medical book I have ever read states that hyperventilation actually decreases levels. Even Dr. Brian's excellent article states this and nowhere mentions that CO2 levels are increased by hyperventilation. While CO2 buildup can initiate hyperventilation it is not the other way around. If I am missing something please edumacate me.

Scott L
November 4th, 2009, 03:26 AM
Diving the wrong mix contributes, too -- gas density at depth begins to play a significant role in alveolar ventilation. I'm not sure whether I like helium as much as I do because of nitrogen narcosis, or because it reduces CO2, but the difference, even at 130 feet, is night and day.

This is were I break ranks with the High Springs boys. In recreation dives under 130ft while not using using HE I am maximizing FO to a PPO of 1.60 as I feel a heck of lot better at the end of the dive as a consequence. Team concept is not broken down completely as my dive partners are also using the same mix as I fill their cylinders after dive sites are selected and dive planning is complete...Often time when hunting with gusto gas is the limiting factor on such dives which results in less nitrogen loading and consequently greater conservatisim. Please don't tell on me...:)

fisheater
November 4th, 2009, 03:58 AM
I am a little confused here (it might be excessive CO2 levels) but I would like to know where the idea that hyperventilation causes an increase in CO2 levels comes from. Every medical book I have ever read states that hyperventilation actually decreases levels. Even Dr. Brian's excellent article states this and nowhere mentions that CO2 levels are increased by hyperventilation. While CO2 buildup can initiate hyperventilation it is not the other way around. If I am missing something please edumacate me.


The problem is that, in common usage, the term hyperventilation appears to mean two, opposite things. True hyperventilation involves very deep exhales, ridding the body of CO2. The term also can be used to refer to rapid, shallow breathing, which fails to rid the body of excess CO2

Hence, you could say that "to stop hyperventilation, you should hyperventilate."

B.L. Justice
November 4th, 2009, 04:03 AM
I am a little confused here (it might be excessive CO2 levels) but I would like to know where the idea that hyperventilation causes an increase in CO2 levels comes from. Every medical book I have ever read states that hyperventilation actually decreases levels. Even Dr. Brian's excellent article states this and nowhere mentions that CO2 levels are increased by hyperventilation. While CO2 buildup can initiate hyperventilation it is not the other way around. If I am missing something please edumacate me.

I think it has to do with rapid, shallow breathing. Ken's post makes a lot of sense. The trigger for hyperventilation is a build up in CO2 but it is also stress or cold related. The first time this happened to me, I was at the surface and had plenty of fresh air. It was my first OW training dive, from a boat and my instructor had failed to mention that the water was in the 50s. I think they call it the mammalian diver response. Rapid pulse and sudden gasping for air. A feeling of being oxygen starved and wanting to climb on top of the first person I saw. Took a little bit to settle down - no thanks to my instructor who was oblivious to it all.

Could be wrong but it made sense to me.

Scott L
November 4th, 2009, 04:08 AM
I am a little confused here (it might be excessive CO2 levels) but I would like to know where the idea that hyperventilation causes an increase in CO2 levels comes from. Every medical book I have ever read states that hyperventilation actually decreases levels. Even Dr. Brian's excellent article states this and nowhere mentions that CO2 levels are increased by hyperventilation. While CO2 buildup can initiate hyperventilation it is not the other way around. If I am missing something please edumacate me.

Hopefully TSandM will chime back in to correct any misinformation received from me but the term hyperventilation is used to describe breathing at a rate faster than your normal breathing pattern. It also occurs when you breathe more, i.e. breathing that is deeper and more rapid than normal breathing. So, a term such as hyper shallow breathing is probaly a more accurate way to describe CO2 inducing breathing patterns. TSandM, please help me! :)

lowviz
November 4th, 2009, 09:16 AM
Valhalla, time to drag out Walter's old post again. Your answer is in the next to last paragraph, but the whole post is worth a re-read. (Wish I wrote it...)



The first step in panic is feeling a lack of confidence in one's abilities.

An ability to swim fairly well is the first step toward confidence in the water. The next step is learning skin diving skills. A combination of swimming ability and mastering skin diving skills eliminates a feeling of being overly dependent on SCUBA equipment.

Skills left out of most classes (because some agencies don't include them in their standards) such as doff & don (removing all equipment on the pool bottom, swimming to the surface then returned to put it all back on) and bail out (stepping into the water while holding one's gear and putting it on during descent) also build self confidence and help to eliminate that first step toward panic.

The second step in panic is when something goes wrong. We can train and practice and maintain our equipment, but we can never eliminate problems arising. When things go wrong, a diver will either have confidence in their ability to handle the problem or they won't. If they do have confidence, they'll solve the problem and move on.

If they lack confidence, they will become scared and as a result start to hypoventilate. Hypoventilation is rapid shallow breathing. It is often, incorrectly, called uncontrolled hyperventilation. These are the next two steps in panic. Hypoventilation causes a buildup of CO2 in the lungs. This is because shallow breathing does not purge the lungs of CO2 on exhalation. As CO2 builds, the urge to breathe becomes even stronger. Hypoventilation increases, making the feeling of not being able to breathe even worse. This is what makes some divers think they are over breathing their regulator. Once hypoventilation starts, full panic is often seconds away. Once the diver is panicked, he will often take inappropriate and usually dangerous actions such as bolting to the surface.

An understanding of this cycle can allow a diver to break it and prevent panic. Most agencies teach divers, Stop, think, act. Some teach it as, Stop, breathe, think, act. This is wonderful, but it doesn't explain why and while the concept is a good one, a better understanding of the panic cycle is essential to breaking it. If a diver feels himself starting to hypoventilate, he needs to know this is an important step that can lead to his (and his buddy's) death if he doesn't take immediate action by slowing his breathing. Slow deep breaths are a life saver.

TSandM
November 4th, 2009, 11:00 AM
Yes, the term hyperventilation, as literally construed, means OVERventilating the lungs, and drives your CO2 down. Symptoms can include tingling around the mouth and cramps in the hands and feet. We treat this in the ER in a very high-tech manner -- we make somebody breathe into a paper bag until their CO2 normalizes!

Hyperventilation, as commonly used in scuba parlance, refers to a shallow, panting, rapid respiratory pattern that DOESN'T effectively ventilate the alveoli deep in the lungs, where gas exchange actually takes place. Thus the CO2 climbs.

Bubbletrubble
November 4th, 2009, 11:10 AM
Physiologically speaking, hyperventilation is usually defined as increased pulmonary ventilation due to an increased respiration rate, an increased tidal volume, or both. We have to be careful about how we use terminology here so that no one gets confused.

Shallow "hyperventilation" (rapid, shallow breathing) will invariably lead to inadequate ventilation...or hypoventilation. This increases CO2 retention within the body, as reflected by elevated PCO2 in blood (both arterial and venous).

True hyperventilation results in an actual decrease in CO2 levels within the body.

As Dr. Brian points out in his article, during exercise, metabolic CO2 production increases and to compensate for this, under normal circumstances, the body will increase minute ventilation (volume of gas breathed per minute). Here's an important point. Brian later writes:
"Under normobaric and hyperbaric conditions, the single factor that limits the ability to increase ventilation is the rate at which gas can be exhaled from the lungs."This is where the density of the gas comes into play. Helium mixes have a lower density than nitrox mixes or regular air and therefore, at depth, the gas can be exhaled more easily. This allows an increase in ventilation to compensate for the increased metabolic CO2 production.

This is the benefit of helium mixes to which TSandM was referring. Not only is there less inert nitrogen in a helium mix (for the purposes of nitrogen loading) but the mix is also less dense than nitrox or regular air so it is beneficial in protecting against CO2 retention. Also, helium has less of a narcotic effect than nitrogen and oxygen. So I guess that's 3 good reasons to be breathing helium-containing trimix on deep dives.

Clear?

[Edited later: I see that TSandM was posting at the same time. I think the info in our posts is complementary so I'll leave the post as is.]

Scott L
November 4th, 2009, 11:17 AM
Yes, the term hyperventilation, as literally construed, means OVERventilating the lungs, and drives your CO2 down. Symptoms can include tingling around the mouth and cramps in the hands and feet. We treat this in the ER in a very high-tech manner -- we make somebody breathe into a paper bag until their CO2 normalizes!

Hyperventilation, as commonly used in scuba parlance, refers to a shallow, panting, rapid respiratory pattern that DOESN'T effectively ventilate the alveoli deep in the lungs, where gas exchange actually takes place. Thus the CO2 climbs.

So what is your term of choice to describe the event? - scuba nomenclature withstanding. In the meatime, hypoventilation is looking pretty good to this layperson.

"Medical Dictionary

Main Entry: hy·po·ven·ti·la·tion
Pronunciation: -"vent-&l-'A-sh&n
Function: noun
: deficientventilation of the lungs that results in reduction in the oxygen content or increase in the carbon dioxide content of the blood or both —hy·po·ven·ti·lat·ed /-'vent-&l-"At-&d/ adjective "

Bubbletrubble
November 4th, 2009, 11:31 AM
So what is your term of choice to describe the event, scuba nomenclature withstanding? In the meatime, hypoventalation is looking pretty good to this layperson.

This may be one of those cases in which, to be absolutely clear, the phrase "hyperventilation" should not be used.

"Rapid shallow breathing" says nothing about tidal volume or true alveolar ventilation. On account of this, it's more accurate than the term "hyperventilation" in describing what we're talking about in this thread. Perhaps that's the phrase we should be using in our scuba discussions.

"Hypoventilation" would probably work...but it is ambiguous in the sense that it could mean a decreased breathing rate, a decreased tidal volume, or both. In my mind, ventilation refers to moving gas in/out of the respiratory tract.

Scott L
November 4th, 2009, 11:43 AM
This may be one of those cases in which, to be absolutely clear, the phrase "hyperventilation" should not be used.

"Rapid shallow breathing" says nothing about tidal volume or true alveolar ventilation. On account of this, it's more accurate than the term "hyperventilation" in describing what we're talking about in this thread. Perhaps that's the phrase we should be using in our scuba discussions.

"Hypoventilation" would probably work...but it is ambiguous in the sense that it could mean a decreased breathing rate, a decreased tidal volume, or both. In my mind, ventilation refers to moving gas in/out of the respiratory tract.

Gotta agree with you. Hey, can you type slower? I do not like to be beaten time wise as my posts lose their relevance after your thoughtfull responses. The forum is lucky to have you! :)

Teamcasa
November 4th, 2009, 01:27 PM
There are a lot of different things that contribute to CO2 retention. Excessive exertion at depth can definitely do it.

I would also add that not adjusting your regulator from pre-dive to dive can also lead to problems. I was at 90+ feet on a dive and began to get the tunnel vision. I did the deep exhale followed by the slow deep inhale routine a few times and the tunneling went away. Only then did I realize my regulator's adjustment was set full on pre-dive.

Bubbletrubble
November 4th, 2009, 01:28 PM
Gotta agree with you. Hey, can you type slower? I do not like to be beaten time wise as my posts lose their relevance after your thoughtfull responses. The forum is lucky to have you! :)
Thanks for the kind words. I'll try to type slower next time... :D

Bubbletrubble
November 4th, 2009, 01:45 PM
I would also add that not adjusting your regulator from pre-dive to dive can also lead to problems. I was at 90+ feet on a dive and began to get the tunnel vision. I did the deep exhale followed by the slow deep inhale routine a few times and the tunneling went away. Only then did I realize my regulator's adjustment was set full on pre-dive.
The pre-dive/dive switch on most regs is called a Venturi switch. It changes the position of a vane inside the reg to either help along the flow of air once flow has been established (ON/"dive" setting) or not (OFF/"pre-dive" setting). Some regs have another user-adjustable knob that changes the cracking pressure of the reg. Cracking pressure refers to how much pressure needs to be exerted on the demand valve in order to start the flow of air.

I think when most people talk about their regs being out of adjustment and breathing "hard" at depth it's the cracking pressure that they're complaining about. Without a user-adjustable knob on the reg, the adjustment is made by changing the position of the lever height (provided that the first stage is delivering the correct i.p.). This fix generally entails "turning a screw" where the hose attaches to the second stage. If you don't know how to do this, then I'd recommend taking the reg to your favorite trustworthy reg technician.

It's also worth noting that properly adjusted second stages will bubble air if you place them inverted (with mouthpiece up) below the surface of the water. The bubbling should stop if you turn the reg over (with diaphragm on top/mouthpiece down). The key here is how many inches of water the actual diaphragm is below the surface of the water. With most regs, the distance between diaphragm and mouthpiece is about 2 inches. Since the cracking pressure for most regs should be set in a range from 1 - 1.4 inches of water, air should begin to flow before the inverted mouthpiece is submerged. Octo regs are often tuned to have higher cracking pressures (1.2 - 1.6 inches of water) to prevent freeflow issues. Most people will find a reg uncomfortable to breath when the cracking pressure reaches 2.0+ inches of water.

Placing the Venturi switch to ON/"dive" should deliver more gas at depth once the gas has started to flow. This is probably a good thing, since, as we all know, our breathing gas becomes more dense at greater ambient pressure. Nevertheless, my gut tells me that a correctly adjusted second stage with Venturi switch set to OFF/"pre-dive" should still provide enough gas at depth so that CO2 retention is not an issue. Perhaps someone with more experience fiddling with regs will weigh in on the matter.

This being said, users should ensure both the cracking pressure and Venturi switch are set properly on their regs. (Good compromise?) :D

ROMO DIVER
November 4th, 2009, 02:38 PM
I appreciate the clarification. I had a feeling that hypoventilation would be a little more accurate term but I wanted to hear some other thoughts on the matter. I was not trying to nitpick but I think that proper terminology is important. I know that I teach my students that they should never hyperventilate due to the fact that it causes artificially low levels of CO2 and can lead to problems such as shallow water blackouts if apnea diving.

Scott L
November 4th, 2009, 03:55 PM
I would also add that not adjusting your regulator from pre-dive to dive can also lead to problems. I was at 90+ feet on a dive and began to get the tunnel vision. I did the deep exhale followed by the slow deep inhale routine a few times and the tunneling went away. Only then did I realize my regulator's adjustment was set full on pre-dive.

My first significant CO2 problem dive occured when I joined new dive buddies long ago who all used long free-diving fins. Regular paddle fins are no match. :shakehead: I still use the same pair which I acquired the next day (1999). Jet Fins for all other applications. :)

JonKranhouse
November 4th, 2009, 10:17 PM
As already said, your ability to flush CO2 is reduced at depth.

At 100-feet, you've lost 50% of your sea-level ventilation capacity. So getting shallow may be important, since slow and deep breathing is only 50% effective if you stay deep.

This chart is from an excellent presentation given by Dick Vann, Ph.D. of DAN at Duke in early 2008. You can view the video version of his PowerPoint online for free at DAN's website.

It seems like this 50% loss at just 100-feet, and the proper terminology, is something that training agencies should make more clear to freshly minted dive instructors.

http://www.rlk.biz/ScubaImages/MAX-ventilation-only-half-at-100-feet.jpg


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