I don't understand: breathing deeply and using breathing for buoyancy control seem to contradict each other

[leadduck]

(...)
The only difference is that your CO2 rises faster during the breath hold because the CO2 is now flowing into a smaller air volume. In other words, you exhaled good CO2-poor air, thus only wasted some air.
(...)

Inhale-pause-exhale also takes more effort on your breathing muscles (most time under tension, rarely relaxed), producing more CO2 again. Shouldn't the pause state better be relaxed, not fully inhaled, neither fully exhaled to the residual volume?

( The Process of Breathing | Anatomy and Physiology II )


I think divers are afraid of involuntary ascents, and staying permanently inhaled gives you a little extra safety margin to stop the ascent by a quick exhale. That may be the bigger reason why they do this.
Of course there are better ways to solve this problem and you have to think about it and do it (minimize lead weight for example, don't inhale too deeply in shallow waters, and so on).

 

[NothingClever]

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[CG43]

Inhale-pause-exhale also takes more effort on your breathing muscles (most time under tension, rarely relaxed), producing more CO2 again. Shouldn't the pause state better be relaxed, not fully inhaled, neither fully exhaled to the residual vol

Very good : This is exactly the point where it gets a bit complicated and interesting.
Physically, deep breathing is the most effective, but the mind and anatomy of humans do not necessarily agree with that.
When you relax on land, the gravitational forces and the elastic forces from the chest, lungs, and abdomen work towards exhalation. Therefore, we exhale when we relax.
The older ones might still remember the Thomson breathing method. The rescuer presses the arms of the unconscious person against his chest and then pulls the arms of the unconscious person upwards and to the side. In this way, breathing occurs because different positions of the body cause differences in lung capacity. When I practice breathing exercises on land, I lie on my back and support the inhalation or exhalation state by the corresponding position of my arms. Exhalation is done with the arms loosely to the side of the body or on the chest, and inhalation is done with the arms stretched upwards and back. If one can also manage to keep the breathing muscles of the chest and stomach/diaphragm relaxed, one can even enjoy holding breath with a moderately deep inhalation on land.
In the water, the weight forces are compensated by buoyancy; there may even be more buoyancy at the chest. The depth of the regulator in relation to the lung/diaphragm and even their differed depth now plays a role in what lung volume is established with relaxed respiratory muscles.
The diver can hold the weight-compensated arms in a position that fits his lung capacity.

And what about the mind?
There are basically different opinions on this. Some say that a person holds their breath out of fear because one is not allowed to breathe underwater.
Others think that being surrounded by a water activates old memories and reflexes, for example, from the state before birth when breathing was not necessary.
For me, diving is always the freedom of not having to breathe as long as the evil CO2 doesn't push .
In the end, it is good to experiment and train oneself.
Then one can relax and leave the regulation to their trained regulators who can do it much better than consciousness and its philosophies.
And it will certainly not be the case that one squeezes out the last bit of air during exhalation or fills the lungs to the maximum during inhalation.

 

[LFMarm]

Deep slow breathing is the right way when in closed circuit.

For open circuit, you should find neutral buoyancy after your natural exhale (lungs are not completely empty because it’s quite uncomfortable to go to minimum volume), then breath in normally and trying to have a slightly longer interval between breaths than what you do on the surface. This way it’s very easy to find neutral buoyancy and typically helps you be efficient with gas consumption while not developing CO2.

This is quite well explained here:

 

[stretchthepenn]

Inhale-pause-exhale also takes more effort on your breathing muscles (most time under tension, rarely relaxed), producing more CO2 again. Shouldn't the pause state better be relaxed, not fully inhaled, neither fully exhaled to the residual volume?

Mostly what @CG43 wrote. When I dive, I usually use a Superman pose, so it's more comfortable to keep a mostly-full lung than to exhale and ride on a semi-empty lung. Were I to keep my hands at my buckle, the opposite would likely be true.

 

[EdMcNeill09]

Let's consider how to reconcile the requirements of rinsing the lung well and not having much buoyancy.


After exhalation, there is always a volume left in the lungs and airways that is diluted by CO2-poor air during inhalation. Let's assume that after inhalation, the concentration of CO2 should only be 50% of the exhaled air.
Diver1 has a minimum residual volume of 1.5 L and a maximum lung capacity of 6 L.
Diver2 has a residual volume of 2 L and a maximum lung volume of 8 L.
If Diver1 now exhales to a volume of 2 L, he must inhale 2 L (for 50% CO2), his total volume will be 4 L.
If he exhale only to 3 L he must inhale 3 L up to 6 L what is his max lung capazity .
Diver2 may exhale to 2,5 liter , inhale 2,5 L to 5 L . When he exhale to 3 L and inhale 3 L ,
he don't reach his full lung capazity of 8 L .
For good lung ventilation and little buoyancy, it is important to exhale well.

A german instructor is promoting a breathing system that he calls "Diving without Lead."
I only know this system from a second hand and I apply it when I am too light at a shallow depth (e.g. deco) . It is : Inhale, exhale, rest, inhale , exhale , rest....................
Here, the diver has exhaled for the longest time, which significantly reduces their average buoyancy.
In order to dive with pleasure exhaled, some practice is required.
For example, I dive in the pool with exhaled distance and inhaled distance,
holding breath while exhaled and inhaled.

I'm not sure I really understand your concern. The urge to breathe is due to a build up of C02. So whenever we have the urge to breathe we know we have some C02 to get rid of.

the way I approach this is to say our air needs underwater are the same as our air needs above water. Breathe naturally and normally. You don't need to take huge breathes unless you feel a need to.

 

[Watterlogged]

Being 60 years old, and living most of them on a farm and 21 of them rubbing elbows with scuba divers i have come to learn that farmers and divers are mostly brilliant, i am the anomaly. I'm both and not particularly clever at any of the sciences of either. But man i like a cold beer after a long day of diving and that is enough !

 

[Watterlogged]

Mostly what @CG43 wrote. When I dive, I usually use a Superman pose, so it's more comfortable to keep a mostly-full lung than to exhale and ride on a semi-empty lung. Were I to keep my hands at my buckle, the opposite would likely be true.

Have you ever heard of the falling man picture ? It was taken during the 9/11 "events". The Superman pose was struck during a fall from 100s and 100s of ft. possibly from as many as 1000 ft. I always think of that gent when i hear Superman and i hope i always will. All men should aspire to be so fearless in the face of IMMENENT DOOM ! RIP Falling Man ! Scuba related if we are talking about altitudes n stuff right !?

 

[CG43]

the way I approach this is to say our air needs underwater are the same as our air needs above water. Breathe naturally and normally. You don't need to take huge breathes unless you feel a need to.

There are important differences between breathing on land (1 bar) and underwater (e.g. 5 bar).
Let's look for the influence of pPO2 on tolerated pPCO2.
The following is translated from German: Karl's Kreislauftauchgeräte Seite

The Influence of Oxygen Partial Pressure on Breath Holding Time

Unfortunately, some diving books still state that breath holding time is independent of oxygen partial pressure. However, this is not the case when it comes to increased ppO2!For example, if one breathes pure oxygen at the surface instead of air, one will notice a significant increase in the possible breath holding time. This effect is due to a shift in the threshold of the body's ppCO2 sensors that regulate breathing.

Divers whose normal breath-holding time (after breathing air) is 3 minutes will be surprised to notice that they can hold their breath for about 6 minutes after breathing pure oxygen beforehand (this test was conducted at the surface).
A graphic: 'Blood-ppO2 & -ppCO2 during apnea after oxygen breathing' will be added later.

If our respiratory control system, which is adapted to 1 bar, regulates higher pPCO2 values at higher ambient pressures, the question is what can be done about it.
Since the respiratory stimulus threshold is raised, we can only keep the starting value (lowest pPCO2) of a respiratory cycle low in order to keep the average pPCO2 as low as possible. The only way to do this is to exhale deeply in order to get rid of as much CO2 as possible. Then inhale deeply to dilute the remaining amount as much as possible.
Unfortunately, I cannot cite any scientific sources that describe this topic qualitatively or, even better, quantitatively.
In my experience, the importance of deep breathing begins at around 30 m and is no longer negligible at 50 m.

​

 

[dmaziuk]

The importance of deep breathing begins at home: it is fairly well established by now that slow deep abdominal breathing promotes relaxation and reduces stress. In diving, relaxation is generally believed to improve buoyancy control and gas mileage. QED.