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Re: Unidirectional [...] Science
Damn, I did not even see this one until now (Monday). Sorry about that.
Unusually hasty comments below...
--- On Sun, 1/17/10, David Marjanovic <email@example.com> wrote:
> > free-diver knows, skeletal movements are not
> constrained by the
> > pressures encountered while diving (up to 19000
> kg/m2, in personal
> > experience).
> Try moving your ribs under such pressure. That, you see, is
> the point.
Ribs move fine...
> _Of course_ you can move your arms around! The pressure on
> each side is the same, so drag is all you need to worry
> about! That doesn't tell you anything about ribcage
> expansion against the water pressure! <headshake>
Ribcage "expands", and diaphragm moves, in fact involuntary breathing motions
are big sign of air hunger...
> It is important to understand that
> in mammals, the lungs
> > must be actively expanded by muscle power alone,
> and contraction
> > occurs by relaxation (i.e., deflation is the
> relaxed state).
> Wrong and wrong, respectively.
> - You don't exclusively use the diaphragm system, you
> additionally expand the chest for inhaling. Have you never
> noticed!?! In fact, when I just sit, i can keep up using
> _only_ the ribcage for about half a minute.
You are having an illusion. If your diaphragm is disabled, you will die w/out
mechanical ventilation. It is mostly air moving into your lungs via muscular
action moving your ribcage. Granted, you can probably move small amounts by
going from very "bad" posture to "good" at zero pressure differential, but
these small amounts are likely not fresh, and stale air will build up in any
> - Both expansion and contraction can be powered in mammals.
Of course. So what? The point is, expansion requires moving a single large
piston against any pressure on the abdomen, an area much larger than the
piston. Disadvantage, mammals...
> During strenuous activity you do both. When I just sit here,
> I can exhale more deeply than normal by contracting the
> belly or even the ribcage (or of course both); t
ccurs by elastic recoil alone.
No. That is gravity working on muscles and organs BELOW your rib cage. Try it
on your back. Notice where your "rebound" goes. Flexing of the ribs is not
occurring, and your lungs are not attached to your ribs anyway. Unlike (some)
air sacs of birds.
> > In birds, [...] the relaxed state is _between_
> full deflation and
> > full inflation.
> In me, too. I just don't deflate (or inflate) fully when I
> don't need to.
Wrong. The relaxed state in humans is deflated. No, not absolute total
deflation. Bird lungs NEVER deflate OR inflate. The relaxed air sac state is
(apparently) INFLATED, or nearer to that state than deflation. Still, not 100%
sure my cites are reliable, but find nothing contra yet...
> > In other words, the elasticity of the skeleton
> itself can play a role
> > in inspiration under pressure.
> (Not the skeleton, but the muscles, and maybe various
> ligaments. If you count the ligaments as part of the
The ribs themselves flex in birds, and air sacs are interlaced w/ the ribs.
Humans cannot use the ribs minus diaphragm to inflate their lungs.
> > When the ribs are in a neutral
> > position relative to ambient pressure, (further)
> expiration can be
> > actively caused by 'contraction' of the sternum
> and ribs. When the
> > driving muscles are relaxed, skeletal elasticity
> can return the ribs
> > to neutral position, which in itself creates
> some inspiration, even
> > in the extreme case where external pressure
> cannot be overcome by the
> > muscles driving the skeleton.
> And what makes you think this recoil is necessarily
> stronger than the pressure exerted by 2 m of water?
It isn't, necessarily. But what makes you think otherwise? Were sauropod ribs
and associated parts spaghetti? 2m sets the bar fairly low, I think. What the
hell, elephants can breathe at very nearly that depth, as can exceptional
humans (6'), briefly. (DON'T TRY IT. VERY DANGEROUS. YOU COULD EASILY DIE!)
> > Further, it is not possible to aerate "dea
al" lungs by
> > small steps. You either can fill your lungs
> adequately w/ one breath,
> > or you can't. The same is apparently NOT true of
> the uni-directional
> > system, the lungs of which do not deflate, and
> can be aerated by
> > small, sequential additions of air.
> The lungs proper don't deflate much in a unidirectional
> system, but the air sacs that ventilate the lungs do. And
> very drastically so.
Good to know! This likely answers the question "Could sauropods alter their
buoyancy". Thanks for your help! :D
Theoretically, air sac deflation does not reduce air flow, assuming the ability
to alter volume still exists, and cycle frequency can be increased.
As previously mentioned, the avian has mechanical advantage relative to mammals
in that regard. As to what pressure causes inability to alter air sac volume in
various avians, that is unknown. As in zero data. It stands to reason, from the
mechanical perspective, that it is higher than in equivalent mammals, desktop
breathing anecdotes aside. The points stand, as mechanical possibilities. This
is all it takes to falsify the original falsification.
> > These additions can be accomplished in part by
> manipulation of the
> > legs,
> Only in turtles, where the ribcage and the belly cannot
> expand and the lungs are ventilated by modified leg
And penguins, and ostriches, ...
> I don't seem to ever breathe by diaphragm action alone.
> Perhaps the diaphragm cannot ventilate the cranialmost parts
> of the lungs.
Bad posture explains this perception :).
> I just tried; I can keep it up for perhaps a
> minute while sitting, but not longer.
Sigh. You cannot aerate your lungs minus the diaphragm and abdominal muscles.
You will do all this, but steadfastly refuse to crawl around in a swamp, or
pick leaves w/ model sauropod jaws. Sigh again.
> More drastically, when I sit, I can breathe by using
> _neither_ the diaphragm mechanism _nor_ the ribcage, but by
> straightening up and letting myself fall back into the usual
> enough that I can't quite keep it up for more than about
> half a minute.
Another illusion, I think. If your diaphragm is paralyzed, perhaps it will be
helpful in that your attention will be diverted from imminent death. In any
case, my points regarding the potential mechanical advantages of the avian
> > In hindsight, I now see that ridiculous
> > neck in itself as prime evidence of avian-style
> It has long been argued that breathing through the neck of
> *Mamenchisaurus* is only possible with an air sac system,
> the one already indicated by the pneumatic vertebrae.
Good point. Perhaps the same could apply to elasmosaurids someday, even in the
absence of 'airy' bones...
> > Long post, chop likely, will post repair for
> those that care...
> Strangely, that didn't happen.
That is weird.