390
KJELL JOHANSEN
interval. Concurrently, the CO, tension increases from about 7 to 30 mm
Hg inside the mouth, with most of the increase taking place early in the
breath interval. The gas exchange ratio drops from about 0.85 just after
a breath to 0.20 just before the next breath. Hence, CO, is eliminated
to a large extent by aquatic gas exchange through the skin or vestigial
gills. The low 0, tension corresponding to about 65% 0, saturation in
arterial blood results from the shunting of blood from the mouth organ
back to the systemic veins before arterial distribution. Blood from the
jugular vein draining the mouth organ and the anterior systemic veins
showed higher 0, tensions corresponding to about 90% 0, saturation.
This difference in saturation is caused by the additional admixture of
systemic venous blood from the posterior end before the blood
tributed from the heart to the arteries (Fig. 1).
50
40
30
I
E
E
-
0"
QV
20
10
0 2 salurat1on percent
10 30 50 70
4
20 4060 80 90 95
100
5
6
7 8 9 1 0 12 I 5 2 0
Gas exchange ratno
- Coeliac a r t e r y
- Juqulor vein
Gas in rnoulh
is dis8
-
i
\
I
Fig. 13. Nomogram summarizing changes in gas tensions in blood and inside
the mouth during an interval between air breaths in Electrophortrs. From Johansen
and Lenfant (1970).