Breathing

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It is absolutely true that breathing is commanded by CO2. Exactly for this reason a proper breathing technique can improve the situation significantly. If you leave the CO2 to command your breathing, you easily go in Dyspnea: this is an anomalous breathing mode, where a lot of CO2 is accumulated in your body, stimulating breathing. But the "natural way" of reacting to such a stimulus is to speed up the breathing rate, not to increase the volume of each respiration. The result is a very fast, very shallow breathing, which is highly inefficient in removing the CO2. So a vicious circle is established, the more CO2 you have, the faster is the breathing.
The correct way of breathing for not retenting CO2 is the way which is taught for CC rebreathers, particularly those operating with a single hose (as the old ARO pure-oxygen rebreathers which were widely employed, here in Italy, in the seventies and eighties).
With such rebreathers you are obliged to breath very slowly, always depleting your lungs almost entirely, very, very slowly, and filling them up almost completely, again very slowly. An inspiratory pause of 5-10s further improves the efficiency of CO2 elimination, as when the lungs are fully extended the exchange surface is maximum, so CO2 is expelled better form the blood.
Learning this way of breathing takes months. In fact, in the seventies, a scuba diving course was 6-9 months long, during which the ARO was employed routinely, mostly in the swimming pool, whilst OC air was employed only in the last lessons and in the sea.
All this was entirely incompatible with the PADI method, based on a very quick and superficial OW training, followed by a large number of other "speciality" courses.
Teaching breathing control, in this approach, is not only too slow and too difficult, it is also quite dangerous: in particular the inspiratory pause, or the simple fact of reaching full inhalation, increases significantly the chance that a student emerges quickly without exhaling, causing severe lung damage and gas embolism.
Better to tell him to just "breath normally", and leave that he gets a bad headache due to CO2 retention for not being able to eliminate it efficiently with proper breathing control, than risking much worst physical damage due to a quick uncontrolled ascent without expiration...
But why would CO2 build up in a healthy fit diver diving on open circuit if it wasn’t happening on land considering there using higher ppO2. I’m really having trouble understanding this
 
But why would CO2 build up in a healthy fit diver diving on open circuit if it wasn’t happening on land considering there using higher ppO2. I’m really having trouble understanding this
The higher concentration of O2 is not helpful. as a normal person's hemoglobin is nearly 100% saturated when breathing room air, 21%. There is some additional dead space in scuba equipment, more important with exertion, higher CO2 production, and shallower breathing.
 
The higher concentration of O2 is not helpful. as a normal person's hemoglobin is nearly 100% saturated when breathing room air, 21%. There is some additional dead space in scuba equipment, more important with exertion, higher CO2 production, and shallower breathing.
where is the dead space in open circuit scuba for co2 to build up? why would a persons blood oxygen be lower in the water if they are breathing the same as on land. how does getting in the water change a persons blood oxygen? this is what i can't understand
 
Small extra dead space inside the regulator, dead space in respiratory system is unchanged. It has nothing to do with O2, blood content is essentially unchanged. Stimulus for breathing is CO2, may be increased with shallow breaths.
 
Small extra dead space inside the regulator, dead space in respiratory system is unchanged. It has nothing to do with O2, blood content is essentially unchanged. Stimulus for breathing is CO2, may be increased with shallow breaths.
So blood oxygen stays the same
 
I think the most important skill for a new diver is buoyancy (which has been mentioned a few times in this thread already. If you don't have your buoyancy right you will be using your legs (and arms :( ) more to stay in the right place. This uses energy and so you will need to breathe more - just like you breathe more on a brisk walk versus a slow walk.

Additionally, as breathing itself changes your buoyancy, you keep making adjustments.

Do a buoyancy course and concentrate on your buoyancy and your air consumption will improve.

Also, how warm are you? The colder you are, the more energy you will use and again you will need to breathe more.
 
...Also, how warm are you? The colder you are, the more energy you will use and again you will need to breathe more.

My relative warmth, or lack thereof, is a major determinate of my RMV, ranking right in there with the other major variable, exertion. As I have gotten older, I tolerate cold less well than I used to. I tend to dress more warmly than many of my fellow divers. This includes the SI. A good boat coat is one of the best investments I have made in my diving.
 
My relative warmth, or lack thereof, is a major determinate of my RMV, ranking right in there with the other major variable, exertion. As I have gotten older, I tolerate cold less well than I used to. I tend to dress more warmly than many of my fellow divers. This includes the SI. A good boat coat is one of the best investments I have made in my diving.
Me, too. I find I'm wearing my drysuit for a longer and longer period each year. I wore it yesterday and the water was 21-22ºC (but it was cool in the air). Last Saturday I warm my semidry but was cold after 2 hours.

Additionally, as your buoyancy gets better and you are using less energy, you are also generating less heat so you get colder.

In fact, it becomes a vicious cycle. The better you get your buoyancy, etc, the longer your dives become. The longer the dives, the less warm you become and so you start to use more air again.
 
@Jason72 Following your RMV is a good way to see how the variables affect your gas consumption
Average Gas Consumption

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