Journal of Applied Physiology, Vol 38, Issue 4 598-602, Copyright © 1975 by American Physiological Society
Effect of chronic hypobaria on isolated tracheal preparation
J. F. Souhrada and D. W. Dickey
Isolated tracheal preparation (ITP) has been studied from rabbits adapted
to 24 days simulated hypobaria (PB = 395 mmHg), corresponding to an
elevation of 17,000ft (5,000m). During this daily hypobaric exposure, the
growth of these animals was continuous and final hematocrit reached 70%.
After 24 days of hypobaric exposure, the sensitivity of ITP was tested to
acute hypercapnia and acute anoxia. Acute hypercapnia was induced by
aerating a muscle chamber with a gas mixture of 85% oxygen and 15% carbon
dioxide. During that time, the PCO2 of the experimental solution increased
from 24 to 66 mmHg with a corresponding change of pH from 7.39 to 7.10. ITP
from rabbits exposed to chronic hypoxia reveals a greater sensitivity to
acute hypercapnia as measured by active tension (AT max) and rate of
tension development (dT/dt). Acute anoxia was induced by aerating a muscle
chamber with a gas mixture of 95% nitrogen and 5% carbon dioxide. During 20
min of these conditions, the Po2 decreased from 520 to 25 mmHg. Although
the contractility diminished at approximately equal rates in both groups in
response to acute anoxia, preparation from animals exposed to hypobaria
showed statistically a significantly greater ability to recover from the
anoxic state.
