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Re: Rearing up on hind legs (was Re: Parrish's neck work ...)



Whales swim at different depths, so that the pressures of blood and
every other part of the animal increase with depth.
Wouldn't this show as an increase in, among other things, what we're
speaking of as 'blood pressure'?

Wouldn't increased pressure at depths be similar to the affect of
changing diameter of the blood vessels? For that wouldn't pressure
changes change the size of blood vessels all by itself?  

Indeed, since whales rise and fall in the ocean depths at speeds
necessary for feeding (bubble netting krill or teh surmise killing of
giant squids at depths by sperm whales) and breathing, they could even
experience this "radical *changes* in blood pressure to avoid either
passing out from lack of oxygen or suffering an aneurysm from too much
pressure" that you infer that sauropods suffer from.

Yes? No?


"Augustus T. White" wrote:
> I've been waiting for Dr. Teuton or someone else who knows whereof they speak
> to say something, but we seem to have lost everyone with a medical or
> physiology background.  Hence these admittedly ill-informed remarks.
> 
> The problem is not mass and is not gravity per se.  The problem is the blood
> pressure necessary to keep a reasonably constant flow of oxygen to the brain 
> in
> particular and to the cranium in general.  The pressure the heart needs to
> generate to achieve this feat is a function of (a) the difference in height
> between the head and heart and (b) frictional factors which are largely
> determined by (i) the distance between heart and head (regardless of
> orientation) and (ii) the diameter of the vessels through which the blood
> travels.
> 
> With these factors in mind, you will note that whales have nothing to do with,
> and nothing resembling, the sauropod problem.  By comparison with a sauropod, 
> a
> whale is, for all practical purposes, spherical.  That is, there is normally
> little difference in the elevation of heart and head, the distances involved
> are significantly smaller in relation to mass and, because the body is 
> compact,
> there is little constraint on the diameter of the vessels in between.
> 
> Not only is the sauropod neck potentially at a very different elevation from
> the heart, it supports a head at the very end of a thin, extended, and rather
> crowded neck structure.  Thus the blood pressure problem is acute.  Worse, the
> sauropod had, perhaps, a very large vertical range of motion.  Thus, the
> problem is not only blood pressure, but radical *changes* in blood pressure to
> avoid either passing out from lack of oxygen or suffering an aneurysm from too
> much pressure.
> 
> Obviously these problems got solved somehow -- maybe in part by restricting 
> the
> height to which the head could be raised.  The point is that this not at all a
> trivial problem and may have significant consequences for our concept of
> sauropod behavior and physiology.

>   --Toby White (itinerant curmudgeon)

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