Human = beaver diving response (Re: diving hominids?
- From: Marc Verhaegen <m_verhaegen@xxxxxxxxx>
- Date: Mon, 17 Sep 2007 01:39:31 +0200
If there's much debate about homo swimming in water perhaps some physiology
is worth considering. For example the diving reflex is well established in
humans. When the face is immersed in water the heart rate drops
(bradycardia) and peripheral blood circulation is clamped down to increase
blood levels in the thorax.
This is so in most mammals (startling reaction).
The difference with marine mammals is that they know how long & deep they're
probably going to dive, eg, they'll reduce heart rate more for patrolling or
surveying dives than for simple feeding dives (cf.voluntary breath ontrol in
humans as opposed to other primates etc.).
In the diving response of trained humans, bradycardia (heart slow down) is
about that of muskrats & beavers, above that of swine & certainly dogs etc.,
but below that of dolphins etc., see, eg, work of Erika Schagatay.
Very interesting in humans is the effect of facial wetting.
I googled "Erika Schagatay trigeminus":
The human diving response - effects of temperature and training
E.Schagatay 1996
Thesis
The aim was to elucidate the cardio-vascular response associated with
breath-hold diving, especially the effects of temperature in its elicitation
and the effects of different types of training on the human diving response
(DR) & breath-holding time (BHT), and to evaluate the human DR in a
mammalian perspective. A model for simulated diving by apnea & facial
immersion in cold water was developed. Cardio-vascular parameters were
registred using non-invasive techniques. The bradycardia response to
breath-holding & chilling of the forehead was found to be more pronounced
than that obtained when other facial areas of the same size were chilled,
indicating that the ophthalmic branch of the trigeminus nerve (N.V) is the
main sensory area for initiating bradycardia in humans. It was found that
both water temperature & ambient air temperature had significant, but
opposite, effects on the magnitude of bradycardia developed at apneic face
immersion, and the results indicate that diving bradycardia is negatively
correlated to water temperature within a range that is determined by the
ambient air temperature. Furthermore, it was found that there is an increase
in BHT over 5 dives when diving is repeated with short intervals, due to a
delay of the the physiological breaking point (PBP) up to dive 3, while to
an increased tolerance by the subject up to dive 5. It was conclude that an
increased diving response is not the cause of the prolonged BHT seen in
repeated diving, as has been suggested. A positive correlation between
individual BHT & maximum bradycardia at repeated diving was found. There was
also a positive correlation between mean bradycardia, skin capillary blood
flow reduction & BHT on the group level, with the trained divers showing the
most pronounced DR & the longest BHT. In trained divers the increase in
diving bradycardia seen during apnea with face immersion compared to during
apnea in air was accompanied by an increase in diving time, which was not
seen in untrained subjects. Physical training leading to increase in maximal
oxygen uptake does not increase the time before the PBP or the diving
bradycardia. However, the tolerance to IBM appears to be enhanced after
physical training, which prolongs the BHT. Apnea training leads to a delay
of the PBP & an increased diving bradycardia & BHT, and may be an essential
factor in dive training. It was concluded that a pronounced DR is not only
genetically determined but appears as a result of training, and disappears
as a result of aging. Taken together, data suggest that the human DR may
have an 02 conserving effect in trained divers. The mean DR of trained human
divers is in the range of that of the beaver, a semi-aquatic mammal, while
that of untrained humans is in the range of the pig, a terrestrial species.
It is hypothesized, based on the results concerning temperature dependence
of the trigemi- nus cold-response in adults, that this response may be
involved in the events leading to sudden infant death syndrome.
In most humans the facial immersion reduces
heart rates by about 20%. Quite interestingly this depression of heart rate
is gradually increased when one does a significant amount of diving and
starts to look a bit more like the diving reflex of seals. I suspect most
mammals exhibit a diving reflex to some degree but in man it is markedly
enhanced with repetitive stimulation (diving). The reflex suggests that
humans developed some responses to immersion in water early in their
evolution.
Yes.
Tigers are much more aquatic than, eg, lions, see recent discussion at AAT.
-- Marc Verhaegen
http://allserv.rug.ac.be/~mvaneech/outthere.htm
http://groups.yahoo.com/group/AAT
.
- References:
- Re: running H, non-diving P (Re: Ealine Morgan
- From: Rich Travsky
- diving hominids?
- From: Cj
- Re: diving hominids?
- From: Rich Travsky
- Re: running H, non-diving P (Re: Ealine Morgan
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