Diving reflex, part 2

maarten fornerod (seismo@dds.nl)
Wed, 27 Sep 1995 07:10:39 +0100 (MET)

Found two papers on diving reflexes in terrestial animals, looks like Jim
Moore is right in his claim:

1. Tchobroutsy, C. et al. (1969). The diving reflex in Rabbit, Sheep and
Newborn Lamb and its Afferent pathways. Respiration Physiology 8:

Head immersion (with free access to air) in water of different temperatures
(6-40 C) caused breath arrest and slowing of heart-rate in rabbits (no
numbers given). Newborn lambs reacted with breath arrest and a slowing of
the heartrate of 59%. Adult sheep reacted variable, usually with partial
breath arrest and a mean drop in heartrate of 38%.

2. Grogaard J. et al. (1985). Effect of alcohol on apnea reflexes in
young lambs. Journal of Applied Physiology p420-425.

This paper distinguishes between the laryngeal chemoreflex (LCR), an
anti-asphyxia reflex that is triggered when water is placed on the
laryngeal area, and the trigeminal diving reflex (TDR), the true diving
response, that is elicited by stimulation of the face. Placing an
ice-cold towel against the lamb's snout resulted in a mean drop in
heart-rate of 24%.

Question is: how wide-spread is this terrestial diving reflex (maybe
better: anti-drowning reflex), and does it occur in our closest relatives?
Anyway, it doesn't seem that the diving reflex argument is a particularly
strong one :(

Yet :)

Speaking of anti-AAT arguments: why would it be that most diving animals
exhale reflexly on submergion, whereas man inspires? [Anderson HT (1963).
Factors determining the circulatory adjustments in diving. I. Immersion.
Acta Physiologica Scandinavia 58: 173-185].

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