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Re: Lung ventilation rates



The following is a bit long winded, but might be of interest to the
discussion of breathing rates.


The recent discussion of elevated oxygen and dinosaur breathing is my field
of research.  Although CO2 is the driving force in breathing, the rhythm of
breathing lies elsewhere, like a pacemaker that is adjusted by CO2 levels.
I have done limited elevated O2 work with reptiles and more extensive work
with mammals altered so as to breath in the manner biomechanically similar
to dinosaurs.  My first surprise was that elevated O2 has almost no effect
on breathing rates in mammals (I have not tested birds  ... yet).  That is,
they are CO2 driven accoding to their metabolic needs and activity levels.
However, when I presented alligators with elevated O2, it dramatically
alters the breathing frequency.  This is a situation which strengthens, not
weakens, JR's case for ectothermy.  By the way, the problem is not one of
maximum performance which almost always has some component of anaerobic
metabolism, but high end sub-maximal performance where metabolic needs must
be met by aerobic means ... such as climbing a hill or extended migrating.

A second point.  Elevated O2 is quite controversial.  Berner and later
Landis have shown elevated O2 from atmospheres trapped in amber.  This has,
as Norm King pointed out, been very controversial.  Gary Landis has
examined every criticism and tested it in the lab. The nitrogen in the
PRIMARY amber bubbles is original (as shown by isotope ratios), and it is
assumed (but not proven) that oxygen is also from original atmospheric
sources.  On the negative side, there is no known way that plants can
produce O2 in these levels due to biochemical competion in the
photosynthetic process that creates atmospheric oxygen.  This is very
difficult to resolve.  However, there are still biological indicators that
are most simply (Occam's razor) explained by elevated O2.  This has been
part of the recent paper by Gans et al on paleozoic oxygen and its effects
on life.

Point three.  In analyzing breathing mechanics of dinosaurs, the problem of
ventilation becomes very real.  There is no question that the volume of O2
supplied to the animals per minute makes or effective absorption and
transport by heart, lungs, and blood.  However, if the ventilation is
mechanically poor, this becomes the bottleneck.  In modern animals
cardiovascular, cell waste, or cells' abilities to use O2 are normally the
limiting factors for aerobic activity.  My own experiments testing this
question have converted me from a proponent of endothermy to one of slower
metabolism.  Some ecthotherms are really quite aerobic.   For what it is
worth, when I first began doing this work in 1992, I could not get
calculations of O2 needs versus O2 delivery (breathing) to match known
walking speeds for dinosaurs (from leg length and socket angles plus
trackway evidence), let alone have these beasts climb a modest hill.  When
I was presented with the idea of 30-35% oxygen as a possibility, I found
somewhat better agreement. (Remember, an animal cannot absorb nor transport
oxygen that has never been made available through breathing.)
Unfortunately, this still required an efficiency in O2 extraction that is
simply not seen in modern animals.  However, when re-examining thoracic
structure, I realized that there is a mechanical possibility of a variation
- (totally unproven with only circumstantial evidence for support - at
least for now) that, gives a fairly normal animal with normal efficiencies
in its physiological systems.  My experiments consistently support the 30+
O2% scenario as a separate line of evidence.

Hopefully, this line of research will continue to bear fruit.  To be fair,
not everyone agrees with my analysis and their objections are always very
carefully considered in the design of future experiments.  (a tip of the
hat to Greg Paul).  However, I must say that everything John Ruben has said
falls exactly in line with my own research including full scale model tests
of air flow rates for various tracheal diameters.

I hope is as interesting to you as it is to me.

Rich

------------------------------------------------------------------------------
Richard Hengst
Biol. Sciences
Purdue Univ. / North Central
Westville, IN  46391
phone   219/785-5251
fax     219  785-5355
email   rhengst@purduenc.edu