Journal of Applied Physiology, Vol 48, Issue 2 337-346, Copyright © 1980 by American Physiological Society
Ventilatory responses to intravenous and airway CO2 administration in anesthetized dogs
W. E. Fordyce and F. S. Grodins
The ventilatory responses to steady-state venous CO2 loading (iv CO2) and
CO2 inhalation have been observed in chloralose-urethan-anesthetized dogs.
Intravenous CO2 was administered by increasing the CO2 fraction of gas
ventilating a membrane gas exchanger in an arteriovenous bypass; blood flow
rate was fixed at 30 ml/min. During the study, we identified a
time-dependent hyperventilation in all 14 experimentally treated dogs and
in 4 additional sham-treated dogs. When we tested 8 of these animals with a
protocol having small progressive increments in iv CO2 loading rate, we
observed a response approaching isocapnia during iv CO2 and a large
hypocapnia when we returned to control conditions. The use of a randomized
protocol in 6 animals demonstrated the necessity of accounting for this
systematic base-line shift, because before doing so the response depended
more on the passage of time than on the nature of the CO2 load. After this
analytical adjustment was made, there was no significant difference between
the respiratory controller gains (delta nu E/delta Paco2) for inhaled and
iv CO2.
