Hyperventilation question

[TSandM]

It's extremely difficult to hyperventilate enough to get the hypocalcemia tetany while on scuba -- the equipment just about won't permit it. Cerebral vasoconstriction is important in head injuries, because of loss of autoregulation, but isn't relevant in the normal brain. Similarly, the shifted oxyhemoglobin dissociation curve isn't going to make much difference to someone whose oxygenation and blood counts are normal.

 

[windapp]

I think this is more of a free diving question, rather than a scuba question. There are thoughts that excessive hyperventilation prior to a free dive could lower your CO2 sufficiently that you could black out do to oxygen starvation before your body delivers that super urgent need to breath which is triggered by high levels of CO2. This is not a problem in Scuba as you are never breath-hold diving.

 

[boulderjohn]

This should be very helpful to you: http://www.diversalertnetwork.org/files/UHMS_DAN 2006 Breath-hold Workshop Proceedings.pdf

Here is part of a discussion on hyperventilation:

DR. LINDHOLM: No. I have not studied hypercapnic or hypoxic ventilatory drive in those subjects.
A comment on the other two things. Three to four deep breaths before breath-hold diving has long
been generally recommended and is usually not considered as hyperventilation. As you point out, you
get most of the benefit from the increased oxygen stores in the lungs from a couple of deep breaths.
So the increase after that is, I guess, minor, but it is probably quite a bit anyway. It seems to be, why
should they otherwise do it?
DR. FEINER: I think the competitive breath-hold divers' improvement in venous oxygen saturation is
probably very, very significant and they are probably benefiting from that because they are going to
extreme levels. Whereas most breath-hold divers in pools actually are not getting low enough to
really extract from hemoglobin. So there are differences between safety and benefit at the extreme
level. I would agree that there is probably significant benefit for hyperventilation for the extreme
diver.
DR. LINDHOLM: A normal person that holds his breath usually breaks with over 90% saturation if
they do not hyperventilate extensively, so they are nowhere near any hypoxia.​

As I read it, it says that the safety issues related to hyperventilation and free diving are very different if you are talking about nobodies like me or people who are doing really serious free diving. A little hyperventilation for the average free diver is not a risk. Beyond that.....

 

[greengreg]

You're right, it is more of a free diving question.

And thanks for the article, lots of good information in it.

 

[greengreg]

Hi, I have a couple more questions. 1. Is there a difference, physiologically, between hyperventilating on land vs. when standing in, say, neck-deep water? 2. How about hyperventilating when standing vs. lying down?

 

[dumpsterDiver]

This should be very helpful to you: http://www.diversalertnetwork.org/files/UHMS_DAN 2006 Breath-hold Workshop Proceedings.pdf


A little hyperventilation for the average free diver is not a risk. Beyond that.....

I think that all the real training agencies would not agree with you on that. They are VERY much opposed to hyperventilation for all freedivers.

 

[boulderjohn]

I think that all the real training agencies would not agree with you on that. They are VERY much opposed to hyperventilation for all freedivers.

I don't know what you mean by "real agencies" not agreeing with ME.

This was a discussion among experts on the topic that was sponsored by DAN. DAN is not an agency. It was not my opinion--I was summarizing their consensus decision. I don't have a personal opinion on this issue.

 

[TSandM]

1. Is there a difference, physiologically, between hyperventilating on land vs. when standing in, say, neck-deep water? 2. How about hyperventilating when standing vs. lying down?

As I wrote before, the pCO2 will be directly related to the alveolar minute ventilation. Obviously, the work of breathing when standing in neck-deep water will be higher than the work of breathing when standing on land, but if the individual can manage the same minute ventilation, the pCO2 will be the same. The person standing in water may fatigue faster at the same minute ventilation than the person standing on land. Similarly, standing or lying supine are probably the same; lying prone will increase the work of breathing.

Position is more relevant to oxygen and ventilation/perfusion relationships, which usually won't show up any significant changes in ppO2 unless the lungs are diseased to begin with.

 

[greengreg]

Thank you, TSandM.

 

[Davidccs]

Huh.... And here I thought hyperventilation caused a build up of co2... I think I've even heard doctors say that.
Glad I stumbled into this discussion.

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