Re: world with less air pressure - survivable?
- From: mn_mn <alexwilliamrussell@xxxxxxxxx>
- Date: Tue, 25 Nov 2008 23:23:41 -0800 (PST)
From interesting article below it appears some birds can survive andeven fly at very low air pressures, so maybe if air pressure drops
even down to .35 atm birds could survive and become dominant animals
(maybe in future becoming dinosaurs again) even if they could no
longer fly.
I wonder if lower air pressure would end flying, at least for bugs.
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How Can a Bird Fly Over Mt. Everest? or How to Get Oxygen Out of the
Air When There Is Hardly Any There.
Craig Black, PhD. RRT, University of Toledo Community and Technical
College, Toledo, OH 43606.
Bar-headed Geese (Anser indicus) have flown over the Himalayas for
thousands of years during their annual migration between their
wintering grounds in India and their breeding grounds in China and
Mongolia. Although many birds migrate over the Himalayas, most fly
through passes at altitudes below 20,000 feet. Bar-headed Geese
preferentially fly over the highest peaks and have been observed
flying at over 30,000 feet. Barometric pressure at this altitude is
approximately 250mmHg and the PO_{2} of dry air is only 52mmHg. If
this air is inspired and humidified at the birds body temperature of
41°C, then PIO_{2} becomes 41.6mmHg, only 28% of that found at sea
level. For the Bar-headed Goose, the O_{2} requirement for flight is
approximately equivalent to that for a person running at maximum speed
or about 12-15 times greater than basal metabolism. Normally mammals
do not live above about 18,000 feet, although humans have climbed to
nearly 30,000 feet without supplemental O_{2}. At this altitude, the
extreme hypoxia limits their activity to no more than slow walking.
1. The lungs of all birds have a totally different design from that of
the mammalian lung, one which allows pure inspired air to come to
within only a few microns of the air-blood exchange surface. This
allows the A-a gradient to be reduced to only 1-2mmHg. Mammals can
reduce the A-a gradient to no less than about 30mmHg. 2. The
hemoglobin of Bar-headed geese has higher than normal hemoglobin-O_{2}
affinity, which shifts the Hb-O_{2} curve to the left, thereby
increasing O_{2} saturation levels under hypoxic conditions. 3. The
bird lung structure allows for more complete removal of CO_{2} from
the blood. Flying birds may therefore have a relative alkalosis which
also shifts the Hb-O_{2} dissociation curve to the left, further
increasing O_{2} saturation levels under hypoxic conditions. 4. There
is some evidence suggesting that Bar-headed geese are capable of
increasing capillary density in muscle tissue. This decreases the
diffusion distance for O_{2} from capillaries to cells, allowing the
same amount of O_{2} to diffuse at a smaller partial pressure
gradient. 5. Bar-headed geese can increase cerebral blood flow during
hypoxia, allowing for increased O_{2} delivery to the brain.
The Himalayan Mountain range is a relatively "new" geological feature,
created by the collision of two massive continental plates. Biologists
suggest that Bar-headed geese actually pre-date the creation of the
Himalayas[.]
.
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