Journal of Applied Physiology, Vol 48, Issue 6 1077-1082, Copyright © 1980 by American Physiological Society
End-tidal CO2 response to low levels of inspired CO2 in awake beagle dogs
P. Reischl, D. M. Stavert, S. M. Lewis, L. C. Murdock and B. J. O'Loughlin
The steady-state end-tidal CO2 tension (PCO2) was examined during control
and 1% CO2 inhalation periods in awake beagle dogs with an intact airway
breathing through a low dead-space respiratory mask. A total of eight
experiments were performed in four dogs, comprising 31 control observations
and 23 CO2 inhalation observations. The 1% inhaled CO2 produced a
significant increase in the steady-state end-tidal PCO2 comparable to the
expected 1 Torr predicted from conventional CO2 control of ventilation. We
conclude that 1% inhaled CO2 results in a hypercapnia. Any protocol that is
to resolve the question of whether mechanisms are acting during low levels
of inhaled CO2 such that ventilation increases without any change in
arterial PCO2 must have sufficient resolving power to discriminate changes
in gas tension in magnitude predicted from conventional (i.e., arterial
PCO2) control of ventilation.
