"Diving" reflex... was Re: First Family and AAT

J. Moore (j#d#.moore@canrem.com)
Sun, 1 Oct 95 17:33:00 -0500

Jt> In article <44afv4$4bk@news.global1.net>, pnich@globalone.net (Phil
Jt> Nicholls) writes:

Jt> >The so-called "diving reflex" is now known to occur in all mammals
Jt> >that can be trained to dive, most noticably dogs. If they can
Jt> >control the panic, they get a diver's reflex.

Jt> I hate to sound like JDM, but what are your references for this?
Jt> Regards, John Thurber

Asking for references for a statement is hardly a heinous crime...
well, unless you're asking an AAT proponent, it seems. ;-)

Here are a few more refs on this subject:

(Lin 1982) pg. 271:
"However, universality of the "diving" responses is well recognized
in that these responses exist in all vertebrates studied so far,
differing only in intensity and tempo."

(Elsner and Gooden 1983) pg. 20:
"Bradycardia during diving, breath-holding and asphyxia has been
observed in many vertebrate species, including man. Among those
studied are rabbit (Bauer, 1938), sloth (Irving, Scholander &
Grinnell, 1942b), snake (Johansen, 1959; Murdaugh & Jackson,
1962), dog (Elsner *et al.*, 1966a), pig (Irving, Peyton & Monson,
1956), armadillo (Scholander, Irving, Peyton & Grinnell, 1943),
echidna (Augee *et al.*, 1971) and lizards (Wood & Johansen,
1974). Terrestrial mammals generally do not respond as
immediately nor as markedly as the aquatic species."

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My note:
Note that at least several of these references substantially predate
the statement of Hardy's recently quoted here by Maarten Fornerod
(Maarten gave no reference for this statement, but it would appear
to be from Hardy's 1977 article in *Zenith*). As quoted by
Maarten, Hardy claims that the diving reflex is "only found
among mammals and birds that dive under water". Hardy first wrote
about the AAT in 1960, and even then there had been evidence for
some 22 years that this statement of his wasn't true. If this
statement was actually from his 1977 article, then the evidence
was even greater, as can be seen from just the refs mentioned in
the above-quoted Elsner and Gooden cite. This clearly indicates
that Hardy's knowledge of this reflex was, shall we say, somewhat
out of date. Some 20-30 years out of date, in fact.

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These following remarks point out some of the marked differences
in response between diving animals and humans, differences which
never seem to be mentioned by AATers:

(Lin 1982) pg. 272:
"Many previous reports indicated that there is a slow development
of bradycardia response in humans. Undoubtedly, these reports
refer not to the onset but to the slow attainment of the maximum
bradycardia response. It should be noted that diving mammals
arrive at maximum bradycardia much faster."

(Lin 1982) pg. 277:
"In contrast to diving species, hypertension is a consistent
finding in man during BH."

(Bove and Davis 1990) pg. 66:
"Unlike in diving animals, arterial blood pressure seems to
increase while cardiac output decreases only slightly during
breath-hold diving in humans."

(Bove and Davis 1990) pg. 66:
"One of the most intriguing findings with regard to diving
medicine is the occurrence of cardiac arrhythmias during
breath-hold diving. This is in contrast to diving animals who
display a marked bradycardia but never show any cardiac arrhythmias
during diving. In humans, it is common to find various types of
arrhythmias even during simply breath-holding."

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My note:
If this response in humans is derived from an aquatic past, rather
than being an evolutionary holdover -- as seems more likely, since
it's seen in other terrestrial mammals -- it is hard to understand
why we would differ so markedly from diving animals in such an
critically important, and potentionally life-threatening, way.

************************************************************************

Refs:

1982 "Breath-hold Diving in Terrestrial Mammals"
by Yu-Chong Lin (Department of Physiology, John A. Burns School of
Medicine, University of Hawaii, Honolulu, Hawaii). In *Exercise
and Sport Sciences Review*, vol. 10, pp. 270-307.

1983 *Diving and Asphyxia: A comparative study of animals and man*
by Robert Elsner (Professor of Marine Science, University of
Alaska) and Brett Gooden (Adelaide, South Australia. Formerly
Lecturer in Physiology, University of Nottingham).
Cambridge University Press: Cambridge.

1990 *Diving Medicine*, Second Edition.
by Alfred A. Bove, M.D. (Chief, Section of Cardiology, Temple
University Hospital, Philadelphia, Pennsylvania) and
Jefferson C. Davis, M.D. (Hyperbaric Medicine, P.A., San Antonio,
Texas). W.B. Saunders Company: Philadelphia, London, Toronto,
Montreal, Sydney, Tokyo.

Jim Moore (j#d#.moore@canrem.com)

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