breathing out

[welshmikey]

i have read and been taught conflicting pieces of information:

as it stands this is what i think is correct for breath holding:
1) dont breath out on decent (unless you need to go deeper for short period)
2) dont breath out on the bottom

however on the accent do i breath out or not and if so how forcefully?

while scooba diving i was taught that while freediving you should breath out very hard on the accent to prevent lung damage however an article i read said that you musn't breath out on accent (no link sorry)

 

[matrixed82]

I was told to breath out on the ascent 2m below the surface. If I remember correctly this will reduce the chance of injury by not stretching the lungs as much and reduces the risk of blackout because the O2 partial pressure doesn't drop as much. Is this correct or am I missing something?
I just breath out passively, no need to waste energy on a forcefull exhale.

 

[cdavis]

Well, you have hit an area in which there is difference of opinion. Some freedivers believe it is safer not to exhale until they hit the surface and others belive it is better to exhale early. Some spearos will exhale through their snorkel in the last meter or so in order to clear the snorkel and be ready to inhale as soon as the snorkel clears the surface. Other divers exhale passively in the last 20 feet or so(snorkel out), believing that this reduces the risk of BO. I favor the latter, but there are other opinions.

Connor

 

[Søren]

nono...
only scubadivers are in risk of damaging their lungs if they don't breathe out during ascent.
here is why:
on the bottom the air entering your mouth and lungs is very compressed compared to the same air at the surface.
if a scubadiver were to hold his breath at 50 m and then ascend to the surface his lungs would probably explode because the air trapped in the airways would expand. That is one of the resons why scubadivers must stop every once in a while on ascend.
On the other hand freedivers only bring "one full lung" (two really) filled with air that "fits" in the lung on the surface and thus don't have the same problem ascending.
Nevertheless one might consider that freedivers press more air into the lungs than they normally contain (packing?) and thus may experience, on ascend, that their lungs expand and may feel the urge to breathe out before reaching the surface.

 

[welshmikey]

being a biologist i shouldnt really be asking this but since im doing marine biology and few marien animals have lungs you can let me off

during gaseous transfer you use up oxygen and give out co2, now heres teh question are they taken in and given out in equal ratios and is one mole of co2 teh same as oen mole of o2? because if not in theory wouldn't your lungs expand by teh end of the dive? or am i talking garbage :duh

 

[immerlustig]

hi,

maybe a bit late for a reply but here's my take on some statements:

1) dont breath out on decent (unless you need to go deeper for short period)

don't exhale on descent because if you exhale on descent you will get 'heavier', which means you will get down easier, but at the same time your lungs will get compressed earlier therefore you are much more likely to get lung squeeze at shallower depth. you won't go deeper when you exhale.

2) dont breath out on the bottom

don't exhale on the bottom, as the same applies as menioned above. plus you now have to work a lot harder on the ascent as you are now 'heavier'. you basically lose twice.

however on the accent do i breath out or not and if so how forcefully?

don't exhale on ascent. what many freedivers do, though (what connor and matrix mentioned), is to exhale gently on the last 1 or 2 meters, just below the surface. the main advantage being that you can inhale straight away when you break the surface.

on the bottom the air entering your mouth and lungs is very compressed compared to the same air at the surface.
if a scubadiver were to hold his breath at 50 m and then ascend to the surface his lungs would probably explode because the air trapped in the airways would expand. That is one of the resons why scubadivers must stop every once in a while on ascend.

that's not correct. the reason why scuba divers ascend slowly or stop is to offgas nitrogen that has saturated the tissues. this is necessary to avoid DCS (decompression sickness). if you inhale fully from a scuba tank in just 1 or 2 meters depth and then ascend without exhaling, your lungs will probably rupture already.

Nevertheless one might consider that freedivers press more air into the lungs than they normally contain (packing?) and thus may experience, on ascend, that their lungs expand and may feel the urge to breathe out before reaching the surface.

after packing your lungs will re-expand to roughly the same volume as before. there is a real danger of blacking out. the possibility of a lung over expansion injury is being debated but so far it is deemed very unlikely.

is one mole of co2 teh same as oen mole of o2?

it has been observed that co2 molecules occupy less space than o2 molecules, so eventually the longer you hold your breath the less volume you have in your lungs. some freedivers claim that they notice a drop in buoyancy at the end of a breath-hold dive.

cheers,

roland

 

[Tom Burnham]

"it has been observed that co2 molecules occupy less space than o2 molecules, so eventually the longer you hold your breath the less volume you have in your lungs. some freedivers claim that they notice a drop in buoyancy at the end of a breath-hold dive."

Fools rush in - but assuming they're ideal gases (deviations will not be very great at the pressures we're dealing with) a given number of CO2 molecules should occupy the same volume as the same number of O2 molecules at the same pressure (Avogadro's law). However, I think CO2 is likely more soluble in water-based fluids than O2 so that may explain the loss of buoyancy mentioned by Roland.

Regards
Tom

 

[DeepThought]

If I remember correct 1 mole of gas @ STP= 22liter~ regardless of type. CO2 is about 30 times more soluble in water than O2 yet it has a lower diffusion rate. Another reason for volume differences could be respiratory quotient of less than 1 (depending on diet and metabolism).