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CARBON DIOXIDE TENSION. 865
mixture after passing the blood through it will also decide if the tension of the
Carbon dioxide in the blood is greater or less than in the gas mixture; and by a
sufficiently great number of determinations, especially when the quantity of car-
bon dioxide of the gas mixture corresponds as closely as possible, in the beginning,
to the probable tension of this gas in the blood, we may learn the tension of the
carbon dioxide in the blood. As above mentioned the oxygen tension can be
determined by the same method.
According to this method the carbon-dioxide tension of the arterial
blood is on an average 2.8 per cent of an atmosphere, 1
corresponding to
a pressure of 20 mm. mercury (Strassburg). In the blood from the
pulmonary aveoli NlJSSBAUM found a carbon-dioxide tension of 3.81
per cent of an atmosphere, corresponding to a pressure of 27 mm. mer-
cury. Strassburg, who experimented in non-tracheotomized dogs
in which the ventilation of the lungs was less active and therefore the
carbon dioxide was removed from the blood with less readiness, found
in the venous blood of the heart, a carbon-dioxide tension of 5.4 per
cent of an atmosphere, corresponding to a partial pressure of 38.3 mm.
mercury.
Another method, which was first used by Pfluger and his pupils
Wolffberg and Nussbaum, depends upon excluding a part of the lungs
be means of the lung catheter
The principle of this method is as follows: By the introduction of a catheter,
of a special construction, into a branch of a bronchus the corresponding lobe of
the lung may be hermetically sealed, while in the other lobes of the same lung,
and in the other lung, the ventilation remains unchanged, so that no accumulation
of carbon dioxide takes place in the blood. When the cutting off lasts so long that
a complete equalization between the gases of the blood and the retained air of
the lungs is assumed, a sample of this air of the lungs is removed by means of
the catheter and analyzed.
When a complete exchange between the gases of the inclosed part of
the lungs and the gases of the circulating venous blood has taken place,
the tension of the gases in this part of the lungs can be considered as a
measure for the gas tension in the venous blood, if we admit that the
gas exchange is due only to physical forces. In their experiments
Wolffberg and Nussbaum found only 3.6 per cent CO2 in the air taken
out with the catheter. Nussbaum also determined the carbon-dioxide
tension in the blood from the right heart in a case simultaneous with
the catheterization of the lungs. He found almost identical results,
namely, a carbon-dioxide tensioD of 3.84 per cent and 3.81 per cent
of an atmosphere, which also shows that complete equalization between
the gases of the blood and lungs in the inclosed parts of the lungs had taken
1
Here and in the following discussion we mean by atmospheric pressure the pressure
in the lungs after subtracting the aqueous vapor tension (about 50 mm.), namely,
760 — 50 = 710 mm. mercury pressure.
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