BREATH-HOLD DIVING Workshop Proceedings - Divers Alert Network

writing continues normally. It is necessary to do that in order to convince them that they have had
hypoxia. They see what they were writing.
Do you have this denial thing? You are focusing on blackout. Do you have people denying that they
have been hypoxic?
MR. KRACK: Oh, absolutely. And it is interesting because we will have people that have blacked
out. You take care of them. Take their mask off. Then they come around, they look at you, what are
you doing? You just blacked out. No, I did not. I am fine. I remember the whole dive. No, you did
not. And they are flabbergasted.
Well, how did your mask get on your forehead? Why are you sitting on the pool deck right now. It is
the X factor, right? Aliens come down, take you to the mother ship for 15 s, bring you back, and you
have no recollection except your mask is suddenly on your forehead.
When I was working in Cayman, I used to give people the experience of blackout. I would put them
on a Draeger rebreather, then turn the oxygen supply off and have them report any symptoms. They
were to raise a hand, respond to a question, and come off the circuit. More often than not, we had to
take them off the circuit.
Blackout can either be very quick or sneak up on you. When you are competitive, it is your job to go
for it. But most of the time people do not even know they have had an issue.
MS. CRUICKSHANK: We videotaped all the courses, so when they are truly in denial, we can put
the video in and show them what they looked like.
MR. STEPANEK: It is a little bit different from the dive itself, because you have the drive to breathe
from a high level of CO 2 . So you are aware that you are running low on oxygen because it is
uncomfortable because of the CO 2 .
DR. LUNDGREN: I just want to suggest perhaps a clear distinction between vertigo resulting from a
broken eardrum, which you pointed to, which is known as caloric vertigo, and the effect of cold water
entering the middle ear versus alternobaric vertigo. And the reason we should make that distinction is
that people should not think that if they have not broken an eardrum, there is no risk of vertigo.
Because alternobaric vertigo, as I mentioned yesterday, but I want to underscore it so there is no
confusion about it, the mechanism there is the effect of changing pressure in the middle ear, where the
change of pressure in the middle ears is unequal on the two sides, right and left. And it is particularly
likely to happen during ascent.
MR. KRACK: It is our mistake for just kind of lumping it into one thing, being a pressure and
temperature differential. Thank you.
DR. SMITH: The hook breathing is really fascinating to me. I guess the anesthesiologist would
appreciate it as a CPAP [continuous positive airway pressure] because that is basically what you are
doing.
I guess my question would be, have you had people do the hook breathing and still pass out on the
surface, and if so, I would think it would be a very low percentage.
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