Lungs underwater

[rsingler]

...studies performed with ultrasonic metering for analyzing microbubbles did show clearly that the harder the work load, the more Nitrogen is absorbed, as the hearth pumps more blood, and more air is vented for discharging the additional CO2 produced, etc.

Concur 100%

A style of ventilation as I described reduces the venting workload, which is a significant fraction of the total workload when deep diving and not making other mechanical actions, in what I call a "contemplative" diving.

Let's just say I'm a bit skeptical. I would guess that work of breathing as a component of a total workload significant enough to increase nitrogen absorption is pretty insignificant, especially in "contemplative" diving. Counting on less N2 absorption based on how you breathe is...imaginative. I think regulator exhalation valve design might be a more measurable contribution, but again, except at greath depth/gas density, other factors would be more significant. But I'm open to solid data...

 

[Angelo Farina]

Let's just say I'm a bit skeptical. I would guess that work of breathing as a component of a total workload significant enough to increase nitrogen absorption is pretty insignificant, especially in "contemplative" diving. Counting on less N2 absorption based on how you breathe is...imaginative. I think regulator exhalation valve design might be a more measurable contribution, but again, except at greath depth/gas density, other factors would be more significant. But I'm open to solid data...

I am not saying that with proper ventilation, as I described, you get LESS Nitrogen. Read it the other way around:
using improper ventilation (short breaths and high rate) you exert an anomalous effort, which CAN result in additional Nitrogen absorption, particularly if you loose control and waste a lot of energy on your pulmonary workload.
But in the end the effect is the same: learning to breath properly is safer, both in term of releasing CO2 and not getting anomalous Nitrogen absorption.
Allowing our students to "breath as you want, just never stop venting" is not a proper approach, in my opinion.
There is another factor, related to brains-body interaction.
Underwater we are in an adverse, foreign environment, hence it is better if we keep full rational control of everything, instead of relying on automatic reflexes which, in our species, are not well adapted to it.
This means:
1) Control of your emotions
2) Control of your body (asset, attitude, movements, behaviour)
3) Control of your breathing
4) Control of your reflexes
All these types of control are interrelated, and improving one of them has positive effects onto all the other forms of control. Often teaching control of breathing is the key for controlling unwanted reflexes, such as the glottis closing when water hits the receptors around the nose, or the gig reflex when water flows inside the nose while evacuating the mask, etc.
This also means that a diver controlling his breathing is also a diver which avoids unwanted body movements, better controls his kicking to be effective and elegant, and controls his brains, reducing oxygen consumption and CO2 production (the brains, alone, can account up to 1/4 of total body's energetic consumption, hence O2 demand and CO2 production).
This means that you should not only take into account the (relatively small) amount of workload required by proper (very relaxed) ventilation, but also the (much larger) amount of workload that a diver in full control of his body and his brains is saving, thanks to such a deep control on everything.

 

[EireDiver606]

I'll grant the "can", but please explain the "should".

I can't think of situations where holding your breath is more desirable than slowly exhaling. Even more important, you want to train the way you want to act in an emergency. If you don't breath hold during normal diving, you are much less likely to do so when stressed or task loaded.

hold your breath for 10 secs as you ascend over a rock, exhale as you ascend and then you've cleared the obstacle. You "should" only because you're using gas if you inflate your wing and the deflate. Use your lungs people, the bc isnt an elevator...

 

[EireDiver606]

Of course this can be dangerous, if the diver goes up without exhaling, hence it is a practice which is usually adopted only by skilled technical or military divers.

Please explain what you said earlier? Are you saying that only experienced technical divers and military divers do this?? Of course not. I started after OW

minimized air consumption

There is no special breathing technique will minimise gas consumption folks, just go diving...

 

[lowwall]

hold your breath for 10 secs as you ascend over a rock, exhale as you ascend and then you've cleared the obstacle. You "should" only because you're using gas if you inflate your wing and the deflate. Use your lungs people, the bc isnt an elevator...

This is extremely bad advice. Do this with a full breath and, if the rock is big enough or you are shallow enough, you will damage your lungs.

Nobody said anything about using your BC buttons. The proper way to do this is inhale to initiate the rise and then, as you are exhaling, use your fins to maintain forward progress.

 

[lowwall]

There is no special breathing technique will minimise gas consumption folks, just go diving...

Sure there is. The only question is whether you call it "special". Your consumption rate is simply the number of breaths you take per minute x the volume of each breath. If you want to decrease consumption, one of those has to decrease. Decreasing the volume of your breaths is a bad idea, it leads to increased CO2 levels and if shallow enough, decreased O2 levels. So the only option left is to decrease the number of breaths per minute. The one advantage to breathing compressed air is you have enough O2 molecules per breath to safely slow down your breathing rate at the same work level compared to your surface rate. But it's not an intuitive thing to most people. Many divers gradually adopt a slower breathing rate over the course of dozens or hundreds of dives. But many don't. There's no reason to doom people to poor consumption rates by keeping this information from them. It's something you can work on if you are aware of it.

 

[Angelo Farina]

Please explain what you said earlier? Are you saying that only experienced technical divers and military divers do this?? Of course not. I started after OW

Sorry for my bad syntax, I am not English mothertongue.
I was meaning that only military or professional divers are routinely trained to breath with an inspiratory pause, while recreational divers are routinely trained to never make a pause.
After training, everyone finds his optimal way of breathing, and often after some experience, and perhaps some reading, many recreational divers also start using the inspiratory pause.
American diving schools as Naui, Padi, etc. deprecate this, while for example here in Italy I was trained since the beginning of my first course to breath like a Navy Seal. This because at that time (in the seventies) diving schools were not using OC air, we were using CC oxygen rebreathers (Aro Cressi), in their original pendular version (single hose).
With these rebreathers it was absolutely mandatory to always employ the full lung volume, with a very slow speed, and with a long inspiratory pause. If not, the risk of hypercapnia was very large...
After 6 months of training with rebreathers, we were finally getting air tanks (and no BCD), and we were trained to breath exactly the same way as with the rebreather....

 

[Bigbella]

I was meaning that only military or professional divers are routinely trained to breath with an inspiratory pause, while recreational divers are routinely trained to never make a pause.
After training, everyone finds his optimal way of breathing, and often after some experience, and perhaps some reading, many recreational divers also start using the inspiratory pause.

My first scuba training was through the YMCA, in the mid-seventies; and our instructor was a scary old navy dude who looked like Ernest Borgnine, who was involved with demolition in WWII. He also mentioned how he had been trained to use that "inspiratory pause," and gave us a similar rationale for its use -- then eventually discouraged us from using it, much as you had your students.

Its second appearance was with a colleague who had taken an industrial course in full-face mask use in the early 1980s. They were using positive pressure masks and were basically practicing some form of skip-breathing, both to relax, focus, and to perhaps minimize air consumption, which is inherently higher with those slightly free-flowing masks. They also trained for instances of bradycardia, where that breathing pause then exhalation supposedly came into play.

In an emergency situation with a FFM, it may be necessary to remove and replace it with a conventional "split" mask and an alternate air source. The issue, though, is with that sudden influx of potentially cold water to the face (typically 10˚ C and below), triggering sudden bradycardia, which could prevent any further inhalation from a second stage, due to the mammalian diving reflex. That sudden stimulation of the trigeminal and vagus cranial nerves, could lead to immediate apnea, and the possibility of drowning. The notion, I suppose, was that that forced exhalation, and that habitual "inspiratory pause" would make it simpler for a later inhalation.

Thankfully, I have never had to put that to the test . . .

 

[Angelo Farina]

I know very well the mammalian reflex, causing the glottis to close. Keeping it under full control was a requisite to be checked during the exam for becoming a 3-stars Cmas instructor. The exam was in Arona, Lago Maggiore, very cold and muddy water. Visibility 5 meters, depth 30 m, and the examiner suddenly did strip away my mask, for checking that I could control the reflex and continue breathing.
I can confirm what you say: being in inspiratory pause, I had to exhale before inspiring, which opened the glottis, so I had no problem.
But, as instictive reaction, I also stripped away the mask of the examiner. He was not in inspiratory pause, he had just expired, so his lungs were almost empty. The reflex locked his glottis, so he could not breath. He had to go up some meters, until the air inside his lungs expanded enough to expire, and luckily this allowed him to unlock his glottis and to exhale.
In the meanwhile I was searching for my mask, which he had dropped. Found it, evacuated it properly and then I started searching for him. After the prescribed one minute search, I resurfaced slowly and with the recommended safety stop. Once on boat, I found him very, very angry, saying that I had attempted to kill him. The examiners discussed my actions for a while, and I was sure to be rejected. Instead in the end I was judged positively and got my certification...

 

[rsingler]

What's sauce for the goose, is sauce for the gander, I guess.
Still...if an uppity student did that to me, I think we'd have a serious talk about his taking away his safety net.
And unless it was the very last dive of the course, I think he'd have to finish with another instructor. I wouldn't fail him, but I don't think I really want someone presumptuous enough to test me in the middle of class. Still, bad on the instructor for not being able to control his reflex, lol!
Sorry, Angelo!