ATPL HPL

[KeroseneKeen]

A little stuck on hyperventilation.
If Breathing is controlled by CO2 levels and as stated in my books, a rise in CO2 levels triggers breathing. Then when hyperventilationg and expiring more CO2 than u should, this would lower the bodys CO2 level and thus should not trigger the breathing therefore returning the breathing rate to normal. So it should be a self fixing problem. But its not. Please explain

[Manflex55]

KK,

OK, I'll try to make it simple.

A number of the chemical reactions in the human body which sustain the processes of life are dependent on there being adequate levels of CO2. In the breathing process, what U need is a BALANCE between the levels of O2 & CO2 (not a rise in CO2). If an imbalance occurs, then all the functions of breathing become disturbed.

Most people whose body, mind or spirit is out of balance will hyperventilate or overbreathe with lots of short chest breaths that leave them DEPLETED of CO2 => O2 level too high => imbalance, which tends to increase (& become dangerous !) if U don't do anything about it.

What U want to do to solve the problem is REDUCE the loss of CO2 (by regulating your breathing) or INCREASE your CO2 level (by breathing in a bag for example).

MF

[Fortress]

>DEPLETED of CO2 => O2 level too high => imbalance, which tends to increase (& become dangerous !)

With respect, this isn't strictly true. If the level of CO2 in the blood decreases (as it does with hyperventilation), there is no concommitant rise in O2 levels. Although it is true that the levels are imbalanced.
The drive to breathe is determined wholly by blood pH and is why some drugs can alter our depth and rhythm of ventilation. As CO2 levels rise, the blood becomes more acid (lower pH) and respiratory drive is enhanced. Of course, vice versa is true also.
The normal rhythmic respiratory effort can and is 'modified' by psychogenic factors - and this is why hyperventilation can occur (eg. in anxiogenic situations) even if blood chemistry is normal. Depletion of O2 in the blood does not drive respiration. For this reason, it is very dangerous to hyperventilate in order to drive out CO2 before a deep dive under water. It is possible to 'run out' of O2 before levels of CO2 (pH remember) have risen enough to trigger respiratory effort. In this case, you'd pass out and drown before even realising you NEEDED to breathe. The blood pH effect can be felt as that dizziness after hyperventilating; the blood chemistry is altering the excitability of nerves in the brain and the tingling is this effect at the periphery.

The reason that hyperventilating is not particularly dangerous is that system is self-regulating. Hyperventilate enough and the change in blood chemistry will cause you to pass out. The unconcious person would then make very shallow, slow breaths (or sometimes not at all) for what can seem like ages whilst the pH returns to normality (CO2 rises to normal levels).

Of course, to the pilot hyperventilation can be dangerous if they were to pass-out whilst in the air!.

Hope this helps!

Paul
BSc(hons) Physiology & Pharmacology
PhD Neurophysiology

[Fortress]

>What U want to do to solve the problem is REDUCE the loss of CO2 (by regulating your breathing) or INCREASE your CO2 level (by breathing in a bag for example).

Sorry, what I should have also said is that this bag treatment has no basis in physiology. If anything, breathing a gas with a higher partial pressure of CO2 (from the bag) will only stimulate a stronger respiratory effort. The first option is spot on. If there's no physiological reason to hyperventilate - the reason is psychological. So.. just calm down!