For quite a while I have had this sneaking suspicion that the mammalian dive reflex in humans is more/equally attributable to a reaction
against colder temperature than the actual water. I just found out that that suspicion is justified: The reflex only works when water
temeprature is under 21C. The face is much more suspeptible/sensitive to temperature changes then the rest of the body and so it seems
triggers the reaction as a means of preparing the body for cold, and not exclusively for diving.
A long time ago I posted saying that "colder water would 'theoretically' permit you to hold your breath logner" and got shot down a little for being too 'theoretical', it seems that that idea was on the right track after all: If you are diving in tropical waters you will not stay down as long as in temperate waters if the fact is that a reflex only works under 21C. When I posted that I should have specified water which was 'cool' but not
cold and therefore leading to shivers which would increase/maintain normal heart rate.
It could be that the reaction of the dive reflext and against the cold is one and the same, but I wander how it is differnt from other mammals, whether theirs is the same double reaction or is more specific.
There is an experiment I thought of to test this:
1. Blowing cold air in the subjects face and seeing wether this triggers the reflex.
If any of you guys are keen would you perform this experiment on yourselves? If yes, run it as so:
-Do a hold without cold air exposure and test for how long you hold your breath. Take a break. Then do another after exposing your face
to air con, or maybe the freezer for a minute or so and then doing the a hold again. Repeat this as many times as you want logging your time.
Can't find wether this has been done or not, but I a have a feeling this could have an interesting result.
(Please don't take this too seriously, although I have a feeling I may be onto something)