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860 RESPIRATION AND OXIDATION.
In 100 cc. blood Oxygen taken up
Oxygen
Chemically ,9
x
ypn , ?
er cen
,^ Dissolved in
tension in mm. combined dissolved chemically
1QQ laama
v^uatuu iii ii.»u.
oxygen in plasma combined i^ac^xa
10 6.0 0.020 30.0 0.030
20 12.9 0.041 64.7 0.061
30 16.3 0.061 81.6 0.091
40 18.1 0.081 90.4 0.121
50 19.1 0.101 95.4 0.152
60 19.5 0.121 97.6 0.182
70 19.8 0.141 98.8 0.212
80 19.9 0.162 99.5 0.243
90 19.95 0.182 99.8 0.273
150 20.00 0.303 100.0 0.455
From the above table we see that even, with an oxygen tension which
amounts to only one-half of the oxygen pressure in the air, the haemoglobin
is saturated in greatest part with oxygen. The dissociation is hence at
70-80 mm. pressure only slightly more than with a pressure of 150 mm.
and indeed even with as low a pressure as 40-30 mm., still 90-80 per cent
of the entire quantity of oxygen taken up chemically at 150 mm. is com-
bined with the haemoglobin.
Frcm these and other observations it follows that the oxygen partial
pressure may sink to one-half of that existing in the atmospheric air
without markedly influencing the oxygen content of the blood. This
also coincides with the experience of Frankel and Geppert x
on the
action of low air pressures upon the oxygen content of the blood of dogs.
With an air pressure of 410 mm. Hg, they found that the oxygen content
of arterial blood was normal. With an air pressure of 378-3G5 mm.
it was slightly diminished, and only on reducing the pressure to 300
mm. was a noticeable decrease observed. A. Loewy 2
found that
the lowest oxygen pressure of the alveolar air wherein the exchange
of material can go on normally both qualitatively and quantitatively,
is equal to 30 mm. Hg.
In regard to the above-mentioned action of low air pressure it must
be remarked that the alveolar oxygen tension is regulated by changes
in the respiration, so that with great diminution in the quantity of oxygen
of the inspired air, the alveolar air contains the same quantity of oxygen
as with a higher oxygen partial pressure of the inspired air (Loewy).
For example, Loewy found the same quantity of oxygen, namely, 6.1
per cent, in the alveolar air with 16 and with 10.5 per cent oxygen in
the inspired air, because the respiration in the latter case was 8.5 liters
per minute against only 4.9 liters in the first case.
It may be concluded from the large quantity of oxygen or oxyhaemo-
1
Ueber die Wirkungen der verdiinnten Luft auf den Organismus, Berlin, 1883.
1 A. Loewy, Untersuch. iiber die Respiration und Zirculation, etc., Berlin, 1895;
also Centralbl. f. Physiol., 13, 449, and Arch. f. (Anat. u.) Physiol., 1900.
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