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Some basic questions?
- Thread starter cchen
- Start date
Thread Status: Hello
, There was no answer in this thread for more than 90 days.
It can take a long time to get an up-to-date response or contact with relevant users.
It can take a long time to get an up-to-date response or contact with relevant users.
Yes, surfacing too quickly can be risky. Do a search on this forum for Shallow Water Blackout (SWB). Exhaling as you are surfacing is recommended (again see SWB), also it prepares you to take a fresh breath when you hit the surface. Depending on visibility it can be tricky to know when to start exhaling, but this is why you practice with a buddy.
It's also really good to be predictable for you buddies. One of the signs of a blackout under water is an unexpected exhalation. For example if your swimming along under water and blow a big bubble for no apparent reason, an attentive buddy might swoop down, clamp your mouth shut and rocket you to the surface.
Sorry Jenny, I completely disagree.
If you exhale you also risk becoming negatively buoyant (you'll sink) and you'll have to kick harder once your body is already hypoxic (lacking oxygen) adding to the risk of black out.
Hold your breath the whole time you're under.
Don't muck around coming up if you need to breathe.
Remember you're only breathing air from the surface, it's not pressurised like scuba so it's safe to come up quickly.
The best way to not have a shallow water black out is not to stay down too long, stay relaxed and don't use too much energy. You don't need to push your limits diving recreationally.
If you exhale you also risk becoming negatively buoyant (you'll sink) and you'll have to kick harder once your body is already hypoxic (lacking oxygen) adding to the risk of black out.
Hold your breath the whole time you're under.
Don't muck around coming up if you need to breathe.
Remember you're only breathing air from the surface, it's not pressurised like scuba so it's safe to come up quickly.
The best way to not have a shallow water black out is not to stay down too long, stay relaxed and don't use too much energy. You don't need to push your limits diving recreationally.
I reckon timing an exhale for the last couple of metres is about optimal, Kathryn. I only just finish exhaling as I hit the surface, which is about right - no need to kick. But then, I risk doing a bit of damage if I'm packing heaps and hitting the surface still fully inflated...
Hmm, but you're talking to a beginner, who probably isn't packing or diving to huge depths and is unlikely time it quite right, potentially putting themself at risk.
Remember to take your snorkel out of your mouth for your dive if you plan to exhale...
Remember to take your snorkel out of your mouth for your dive if you plan to exhale...
I still recommend the practice of not exhaling until reaching the surface. If you are blacking out because you are holding breath extra two seconds before hitting the surface, that's what I call pushing the limit. Also, why would hitting surface fully inflated after packing cause damage? Weren't the lungs inflated the same amount when you packed prior to diving down?
Haha. Why not use crap finning technique? I mean, if you're blacking out just because your technique is a bit sub-optimal then that's what I call pushing the limit....
The question of exactly when to exhale is a pretty trivial one I think. At the surface vs 2m down is much of a muchness. I certainly wouldn't be starting to exhale much deeper than 5m though.
Ah. Thanks on the interesting point on faster lung expansion. Should show you how much I know about packing 
. For some reason I was reading your 2m below surface as 2s before the service. Blame that on lack of sleep 
but visiting one month old niece is worth the pain.
Since I usually do shore entry dive, I use the 2s to "look both ways" on the surface traffic usually at about 3m. Those surf paddlers are everywhere! I can take on buttheads from ocean swimmers just fine, but not against surfboards.
. For some reason I was reading your 2m below surface as 2s before the service. Blame that on lack of sleep but visiting one month old niece is worth the pain.Since I usually do shore entry dive, I use the 2s to "look both ways" on the surface traffic usually at about 3m. Those surf paddlers are everywhere! I can take on buttheads from ocean swimmers just fine, but not against surfboards.
Well, 2s is about the same as 2m anyway. 2m often represents even less than the 2s, so no problem there. Do not forget, though, that Dave Mullins is an elite competitive freediver, so 2m or 2s less or more can decide whether he breaks a new WR or not, or whether he wins a competition or not.
The exhaling on ascent is a controversial topic. Both ways have advantages and disadvantages, or associated risks, so we will probably always see defendants on both sides.
It is clear that with packing you can suffer a barotrauma at surfacing if you do not exhale. Although the volume of air is lightly reduced due to O2 consumption, the lungs volume may be reduced quite a bit more due to the bloodshift, so on surfacing the intrapulmonary pressure may be higher than at the start, which may already be critical.
On the other hand, strangely both camps often speak of exhaling in association of the "vacuum" effect on the ascent and SWB. Opponents of the exhaling tell that the exhaling accelerates the depressurizing, hence increasing the risk of SWB. And some of the defendants of exhaling think that exhaling prevents the SWB (just like JennyWren above). In fact the "vacuum effect" (which is a wrong term anyway) has nothing to do with the expansion or volume of the lungs, but just and only with the change of PaO2 in lungs during the ascent, which you will not influence by exhaling anyway.
In fact the exhaling will have relatively little impact on the depressurizing effect of SWB. First of all the PaO2 in lungs is principally given by the ambient pressure (the depth), and the additional pressure of fully inflated ribcage is completely negligible in comparison. And then, at the final phase of the breath-hold, the blood is already pretty much acidic, hence due to the shift of Bohr saturation curve, the hemoglobin binds only very little oxygen from lungs. The brain rather drains more O2 from blood, thanks to the quickly raising level of CO2. It means that at this moment the volume of O2 available in lungs is already less important and will not greatly increase the possibility of SWB.
Otherwise most of the other arguments pro and contra exhaling are valid. For those diving without good safety, and not packing, keeping the air in lungs may be safer. For competitive and heavily packing freedivers, the exhaling may be necessary for avoiding a barotrauma.
And then, we have also extreme freedivers like Eric Fattah who exhales at 20-30m to trigger a stronger survival reflex, but I do not think it would be wise to try for anyone without perfect and redundant safety in place, and without great experience with FRC diving.
The exhaling on ascent is a controversial topic. Both ways have advantages and disadvantages, or associated risks, so we will probably always see defendants on both sides.
It is clear that with packing you can suffer a barotrauma at surfacing if you do not exhale. Although the volume of air is lightly reduced due to O2 consumption, the lungs volume may be reduced quite a bit more due to the bloodshift, so on surfacing the intrapulmonary pressure may be higher than at the start, which may already be critical.
On the other hand, strangely both camps often speak of exhaling in association of the "vacuum" effect on the ascent and SWB. Opponents of the exhaling tell that the exhaling accelerates the depressurizing, hence increasing the risk of SWB. And some of the defendants of exhaling think that exhaling prevents the SWB (just like JennyWren above). In fact the "vacuum effect" (which is a wrong term anyway) has nothing to do with the expansion or volume of the lungs, but just and only with the change of PaO2 in lungs during the ascent, which you will not influence by exhaling anyway.
In fact the exhaling will have relatively little impact on the depressurizing effect of SWB. First of all the PaO2 in lungs is principally given by the ambient pressure (the depth), and the additional pressure of fully inflated ribcage is completely negligible in comparison. And then, at the final phase of the breath-hold, the blood is already pretty much acidic, hence due to the shift of Bohr saturation curve, the hemoglobin binds only very little oxygen from lungs. The brain rather drains more O2 from blood, thanks to the quickly raising level of CO2. It means that at this moment the volume of O2 available in lungs is already less important and will not greatly increase the possibility of SWB.
Otherwise most of the other arguments pro and contra exhaling are valid. For those diving without good safety, and not packing, keeping the air in lungs may be safer. For competitive and heavily packing freedivers, the exhaling may be necessary for avoiding a barotrauma.
And then, we have also extreme freedivers like Eric Fattah who exhales at 20-30m to trigger a stronger survival reflex, but I do not think it would be wise to try for anyone without perfect and redundant safety in place, and without great experience with FRC diving.
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"In fact the "vacuum effect" (which is a wrong term anyway) has nothing to do with the expansion or volume of the lungs, but just and only with the change of PaO2 in lungs during the ascent, which you will not influence by exhaling anyway."
I'm confused. Since the Bohr effect reduces the blood's affinity for O2 wouldn't the blood 'give back' O2 as the PO2 lessens ? Surely reducing lung volume by 75% would have an effect.
I'm confused. Since the Bohr effect reduces the blood's affinity for O2 wouldn't the blood 'give back' O2 as the PO2 lessens ? Surely reducing lung volume by 75% would have an effect.
No, the blood won't give back any O2 to lungs. First of all, the increasing blood acidity slows down the binding, but the O2 diffusion wont'be reversed. That's a common misinterpretation of the depressurizing effect at SWB, but it is not correct.
And then, the lung volume has no influence on the pressure inside the lungs when underwater. The pressure will be always equal (*) to the ambient pressure of the water column, regardless if you have empty or full lungs. I repeat same pressure, and hence the same PaO2 both with empty or full lungs. It is not the expansion of the lung volume that causes the drop of the pressure. It is exactly the other way - the decreasing pressure causes the expapnsion of the lungs. And if you exhale or not, the change of the pressure will be identical. The lung volume does not really matter.
(*) well, to be exact there may be a minor difference between intrapulmonary pressure and the ambient pressure at packing freedivers, shortly after the immersion, and then at negative depths (where bloodshift already needs to compensate the difference). But the difference will be very small and negligible in comparison to the changes of the water pressure.
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Doesn't always work either. I had some close calls with kite boarders, those things fast and have no noise signature. Better to have some kind of a float or boat anchored on a surface.
As for original topic - I was routinely exhaling before breaching the surface until at some point I became too laxed about my technique and started exhaling a little earlier, and earlier and my dives were closer and closer to my comfort limits. At one point I remember staying down very long, then realy dashing for suface and, in anticipation of surfacing, with clouded over counsciousness, exhaling fully. Only to find out that surface is horribly far, about 5m or so. Surface just kept on coming closer but wasn't there yet. I was scared at that point, really freaked out, I didn't have strength for that extra work, it was all maxed-out even before I exhaled. It is hard to say wether I was risking BO at that point, probably not. But although it happened some 25 years ago I don't think anybody will ever convince me it is safe or good, or worth trying. Ascent from deep dives with poor visibility (very dark at the bottom) can make it hard to judge where the surface is. Amount of light will be changing quickly for our dilated pupils and may trick diver into thinking that surface is only 2m, while it could be much more. Diving in the same spot and thinking one has figured it out never helped me, clouds or sun, plankton, surface wind - everything changes the appearance of the surface. But the main danger I think is impaired decision-making and urge to get that gulp of fresh air.
When we are teaching beginners we are always teaching students to hold their breath until they reach the surface and to do appropriate recovery breathing at that point. I think that this is a strait forward approach for beginners, limiting confusion and the probability of any negative outcome from a given dive. Also we teach our students the need to dive smart and adopt a reasonable progression rate as they increase their diving ability. This way we are limiting the potential for the diver to experience Blackouts in the early stages of their diving career.
Completive freediving is something in and of its self and top end competitive athletes like Mr Mullins have developed approaches that work well in their situations. As people progress in their diving it can be useful to experiment with alternative approaches and more advanced techniques, but when you are just starting out it is better to keep this aspect of your diving simple and focus on other aspects such as improving fining technique or whatever you need to make your diving more effective.
Completive freediving is something in and of its self and top end competitive athletes like Mr Mullins have developed approaches that work well in their situations. As people progress in their diving it can be useful to experiment with alternative approaches and more advanced techniques, but when you are just starting out it is better to keep this aspect of your diving simple and focus on other aspects such as improving fining technique or whatever you need to make your diving more effective.