diving reflex

maarten fornerod (seismo@dds.nl)
Tue, 26 Sep 1995 05:57:57 +0100 (MET)

According to Jim Moore the human dive reflex is no evidence for an
aquatic lifestyle of our ancestors, because:

1) it is also found in rabbits, sheep and dogs
2) it can be triggered by cold stimulation of the face, without wetting.

For the first point I would like to see references. The dive reflex is
characterized by 1) breath-holding, 2) slowing of the heartrate and 3)
decreasing the blood supply to the extremities and 4) gradual rise in
mean arterial blood pressure [1]. Such a defense against
asphyxia can be found in many different vertebrates, for example, fishes
taken out of the water (don't know about breath-holding here), newborn kittens
and human baby's with birth anoxia [2]. So in order to know whether an
anti-asphyxia-reflex is a dive-reflex or something else, it's important
to know what exactly triggers it. The only thing I could find on a
"diving reflex" in terrestial mammals were anti-asphyxia-reflexes
(slowing of heart-rate) in dogs by stimulation of the larynx of with
water or electrical pulses [3] and in rabbits by nasal stimulation with
cigarette smoke and other irritants [4]. These are more anti-choke and
anti-poisening reflexes. The fact that the human "diving reflex" is triggered
by cold water touching the face (or, indeed, an ice-bag) in combination with
voluntary or involuntary arrest of breathing, suggests that this is indeed
especially aimed at preventing asphyxia underwater.

As for the strength of the human diving reflex compared to that of other
[;)] aquatic species: the slowing of the heartrate of the diving seal is
80-85% [ref in 5], that of human beings in rest 15-30% [6], and in exercise
up to 40% [7].

[1] Gooden, BA (1994). Integr. Physiol. Behav. Sci. 29:6.
[2] Gooden, BA (?). Grrr I lost this reference! Integr. Physiol. Behav. Sci.
Scholander, PF (1966). Scientific American 20(6):92.
[3] Angell-James, JE (1978). J. Physiol. (London) 274:349.
[4] McRichie and White (1974). Austr. J. Exp. Med. Sci 52:127.
[5] Lancet of Jan. 1975, p.12.
[6] Hurwitz, BE (1986). Physiol. Behav. 36:287.
[7] Bergman, SA (1972). J.Appl.Physiol. 33:27.

Maarten (maarten.fornerod@stjude.org)

Disclaimer: first draft.

"Thus, the scenario of our possible amphibian past is based on a great
deal of probability..."
-Bjorn Kurten.