Never hold your breath, except...

[Tool Belt]

I hold my breath often when I am taking a macro shot. I don't know the math, but if you are at 60 or 80 feet, the pressure differential over a foot or two really isn't that great, IMHO.

 

[kimbalabala]

I'll sometimes hold my breath when I'm doing video, especially if I am trying to get a close up shot.

Me too - but I really try to make it so that I'm holding AFTER I exhale so I don't inadvertently begin to ascend and/or break that rule in the dangerous way.

 

[Akimbo]

Remember though, it's not the air in your lungs that keeps you from needing to breathe, it's the level of carbon dioxide. So, breathing out that co2 might actually help you to stay conscious longer.

It is unclear to me if CO2 level in the lungs exclusively stimulates breathing or if that is just an easily measured indicator of CO2 in the blood. In any case, the less volume in your lungs to dilute the CO2 being added by the blood across the alveoli will cause lung CO2 to rise faster than if the lung volume were greater.

Do a simple experiment yourself. Take three deep breaths and exhale about ¾ the volume before holding. That CO2-induced urge to breathe comes on much faster.

 

[Seefourdc]

Whether or not CO2 stimulates breathing is a matter of controversy. I work in the healthcare field and I can tell you there really isn't any research to back that up. It's more likely that people who are not desensitized to heightened levels of CO2 are very aware when their CO2 level rises due to all of the effects it has on your physiologically in a very short period of time, but O2 is more than likely what drives breathing. CO2 makes you acidotic as rapidly as it's level rises which has a drastic effect on how you feel which would make you want to breathe; however, patients, or freedivers for that matter who are used to high levels of CO2 are so tolerant of the acidosis effect that they can resist it/not even be aware of it as it gets dangerously high leading into CO2 toxicity.

 

[dallaskincaid]

My doctor girlfriend has been working night shifts the last 3 days so this morning is actually the first chance we had to discuss this. Her feeling is that you're probably screwed either way as the minuscule benefit you would get by breathing out the c02 wouldn't benefit you enough to matter. We didn't get a whole lot of debate in about this though because she had just worked a 12 hour shift and was begging to go to bed... haha... I forced her to stay up to discuss this with me! I hope you're all happy! haha

The things I do for Scubaboard and diving...

 

[triplecove]

It's a shame that the only reference I have ever seen to learning to keep your glottis open, is here on scubaboard.

I have heard if you have big feet you have a big........glottis

 

[Bob DBF]

It's a shame that the only reference I have ever seen to learning to keep your glottis open, is here on scubaboard.

I learned how to do that a long time ago, but the person who showed me that paticular trick probably had no idea what a glottis was and would have washed my mouth out with soap if I said it in mixed company.


Bob
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I may be old, but I’m not dead yet.

 

[Akimbo]

Whether or not CO2 stimulates breathing is a matter of controversy. I work in the healthcare field and I can tell you there really isn't any research to back that up...

There is plenty of research in the hyperbaric arena, but there is controversy as to the exact mechanism of the physiology. Don’t confuse a repeatable stimulus reflected in breathing rate and reported symptoms with a trained apniest’s ability to ignore the stimulus or observed phenomenon in a compromised patient.