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Diving physiology bio-chem: respiration, apnea

Divers should not hyperventilate causing alkalosis in blood, due to susceptibility to sudden black-out from lack of oxygen (with no chemoreceptor warning).
Rather they should be neutral pH, during dive the accumulation of carbon dioxide produces acidosis in the blood (even if there is abundant oxygen) which in MDR (mammalian divers reflex) is a safer mode, high CO2 triggers air hunger (oxygen conservation) and diaphragmatic contractions pump O2 & CO2 around efficiently.


REFINING THE BREATH by DOUG KELLER 2007

And then there are times when we anticipate physical stress and begin to breathe harder, using the chest muscles. The problem is that this situation of persistent mental and emotional stress has become more the rule of daily life than the exception. The body is on constant alert via the sympathetic nervous system, but the physical exertion — and the need for accelerated breathing — never comes. As a result, we’ve both pumped in more oxygen and pumped out carbon dioxide in this process of hyperventilation, and a vital chemical balance in the body has been seriously upset.

Here begins the vicious cycle that is so familiar to hyperventilators. The harder we breathe, the more oxygen-starved we feel, and we can’t ‘catch’ our breath. This is not for lack of oxygen, but because so much carbon dioxide has been forced out in the process of overbreathing. The presence of carbon dioxide in our blood allows the hemoglobins to transport oxygen to the body’s tissues. If too much carbon dioxide is ‘blown off’ by hyperventilation, the blood becomes alkaline, and the hemoglobin can’t release the oxygen molecules, which are chemically ‘stuck’ to it. The blood is carrying around plenty of oxygen: the problem is that the body can’t get any of it!
Carbon dioxide also provides the chemical message in the blood that leads us to take our next breath. At the end of the exhalation, there is a natural, restful pause before we breathe in again. During that pause, carbon dioxide builds up in the blood at the same time that oxygen is being released into the tissues. When it reaches a certain level, the respiratory center of the brain sends a signal through the phrenic nerve to the diaphragm to take another breath.

In the normal course of breathing, the entire process of respiration is driven by carbon dioxide, from the first neurochemical impulse that initiates the inhalation, to the chemical balancing act in the blood that delivers oxygen to the body. All of this happens without our having to think about or consciously direct the process, and the whole process works astoundingly well, with carbon dioxide playing a central role from beginning to end.

That, of course, describes the natural process of the breath, in which the conscious mind, with its slurry of desire, emotion and expectation, is not factored in. But what happens when we overbreathe? Usually an excess of carbon dioxide in the blood tells us to take another breath in, and the process is quite relaxed. But when carbon dioxide drops below a certain level (due to anticipatory fast hard breathing), the message from the body — which is now not receiving the oxygen it needs — is that we are suffocating! And so the breath is driven by the body’s panic, and we breathe harder, making the situation worse instead of better. A subtle chemical imbalance soon becomes a full-blown panic attack. The age-old cure for panic attacks — to breathe into a paper bag — has a very good biochemical basis: it’s meant to increase the levels of carbon dioxide by re-breathing the same air, until the proper balance is restored.

When it comes to stressful breathing patterns, or patterns of ‘overbreathing, certainly the vicious cycle of the biochemistry of hyperventilation plays the part of gasoline thrown on the fire. Mental anticipation and anxiety, however, is the match that lights the fire.
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So relax, and just glow a little. ;)

h/t kelp princess @ Deeper Blue